Full text of "Oceanus"
Volume 36, Number 4, Winter 1993/94
25 Years of
Ocean Drilling
Geological Time Scale
25 Years of Ocean Drilling
Period or epoch and its length
Beginning
(years ago)
Development of life on the earth
CENOZOIC ERA
Quaternary
Period
Holocene Epoch
70 thousand years
10
thousand
Humans hunt and tame animals, develop
agriculture, use metals, coal, oil, gas, wind
and water power, and other resources
Modern humans develop and mammoths,
woolly rhinos, and other animals flourish but
die out near end of epoch
Sea life, birds, and many mammals similar to
modern ones spread around the world,
humanlike creatures appear
Apes in Asia and Africa, other animals include bats,
monkeys, whales, primitive bears and raccoons;
flowering plants and trees resemble modem ones
First primitive apes, development of camels, cats,
dogs, elephants, horses, rhinoceroses, and rodents;
huge rhinoceroslike animals disappear near end of
period
Plentiful birds, amphibians, small reptiles, and
fish joined by primitive bats, camels, cats,
horses, monkeys rhinoceroses, and whales
Flowering plants plentiful; invertebrates, fish,
amphibians, reptiles, and mammals common
First flowering plants; horned and armored
dinosaurs common; plentiful invertebrates,
fish, and amphibians; dinosaurs disappear at
end of period
Dinosaurs at maximum size; first birds, shelled
squid; mammals are small and primitive
First turtles, crocodiles, dinosaurs, and
mammals; fish resemble modern kinds
First seed plants (cone-bearing trees) K
First reptiles, giant insects Jive in forests where
coal later forms; plentiful fish, amphibians,
scale trees, ferns, and giant rushes
Many coral reefs and abundant crustaceans,
fish, and amphibians; trilobites nearly gone
m
Swampy forests, the first amphibians and
insects, and many fish, including sharks,
armored fish, and lungfish
Spore-bearing land plants appear
y^fek, ^^d
Tiny graptolites in branching colonies join the
common trilobites, mollusks, and corals
Trilobites, some mollusks, and jawless fish
•PSvi
Bacteria about 3.5 bitlicW^ears ago; coral,
jellyfish, and worms in th^ sea 1.1 billion years
*Ni **\
ago v\ i
Pleistocene Epoch
2 million years
2
million
Tertiary Period
Pliocene Epoch
3 million years
5
million
Miocene Epoch
19 million years
24
million
Oligocene Epoch
14 million years
38
million
Eocene Epoch
77 million years
55
million
Paleocene Epoch
8 million years
63
million
MESOZOIC ERA
Cretaceous Period
75 million years
138
million
Jurassic Period
67 million years
205
million
Triassic Period
35 million years
240
million
PALEOZOIC ERA
Permian Period
50 million years
290
million
Carboniferous
Period
Pennsylvanian Period
40 million years
330
million
Mississippian Period
30 million years
360
million
Devonian Period
50 million years
410
million
Silurian Period
25 million years
435
million
Ordovician Period
65 million years
500
million
Cambrian Period
70 million years
570
million
Precambrian Time
Almost 4 billion years (?)
4.5
billion (?)
Source: The World Book Encyclopedia (1992)
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25 Years of Ocean Drilling
An Introduction
Page 10
Page 62
o
The Times, They Are A-Changing by Bruce Mai fait 6
An Abridged History of Deep Ocean Drilling
by Arthur E. Maxwell 8
OOP at Sea:
Work Aboard JOIDES Resolution by Vicky Culkn 13
Life Aboard JOIDES Resolution by Suzanne O'Connell ..17
Map & List of Drilling Sites ! 22
DSDP and ODP Statistics 24
Glossary 26
Country Reports
Australia by Ian Met calf e 28
Canada by John Malpas 29
European Science Foundation by G. Bernard Munsch ....30
France by Yves Lancelot 31
Germany by Helmut Beiersdorf 32
Great Britain by Robert B. Kidd and James C. Briden 33
Japan by Noriyuki Nasu and Kazuo Kobayashi 34
Russia by Nikita A. Bogdanov 36
United States by Ralph Moberly
37
Page 49
Ocean Drilling Science
Introduction by Thomas E. Pyle and Ellen S. Kappel 39
Paleoceanography
Paleoceanography from a Single Hole to the Ocean Basins
by Larry A. Mayer 40
Details That Make the Difference
by Nick Shackleton and Simon Crowhurst 45
Early History of the Oceans by Hugh C. Jenkyns 49
The Central Mystery of the Quaternary Ice Age
by Wolfgang Berger, Torsten Bickert, Eystein Jansen,
Gerald Wefer, and Memorie Yasuda 53
From the Greenhouse to the Icehouse by James C. Zachos ....57
Challenge of High-Latitude Deep Sea Drilling
by Jorn Tliiede 62
Copyright © 1994 by the Woods Hole Oceanographic Institution. Oceanus
(ISSN 0029-8182) is published in March, June, September, and December by the
Woods Hole Oceanographic Institution, 9 Maury Lane, Woods Hole,
MA 02543. Second-class postage paid at Falmouth, Massachusetts and
additional mailing offices. POSTMASTER: Send address change to Oceanus
Subscriber Service Center, P.O. Box 6419, Syracuse, NY 13217.
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Headings and Readings
Lithosphere
Oceanic Crust and Mantle Structure
In/ Catherine Mevel and Mnthilde Cannat 66
Oceanic Crust Composition and Structure
In/ Peter S. Mei/er and Kathryn M. Gillis 70
Exploring Large Subsea Igneous Provinces
In/ Millard F. Coffin and Olav Eldholm 75
DSDP/ODP Downhole Measurements in Hole 504B
In/ Phillipe A. Pezard 79
Tectonics
Studying Crustal Fluid Flow with ODP
Borehole Observatories by Earl Davis and Keir Becker ....82
Fluid Composition in Subduction Zones
by Miriam Kastner and Jonathan B. Martin 87
Scientific Ocean Drilling and Continental Margins
by James A. Austin, Jr 91
When Plates Collide — Convergent-Margin Geology
by Asahiko Taira 95
From the Superchron to the Microchron
by Yves Gallet and Jean-Pierre Valet 99
Sedimentary Processes
Terrigenous Sediments in the Pelagic Realm
by David K. Rea 103
Turbidite Sedimentation
by William R. Nonnark and David J.W. Piper 107
Shallow Carbonates Drilled by DSDP and ODP
by Andre Droxler Ill
Sea Level
Drilling for Sea-Level History on the New Jersey Transect
by Gregory Mountain and Kenneth Miller 116
Drilling Technology & Spinoffs
Spinoffs for Oil Exploration by Neville F. Exon 120
Technology Developments in Scientific Ocean Drilling
by Barry W. Harding 125
Borehole Measurements Beneath the Seafloor
by Paul F. Worthington 129
Book Reviews 135
Polar Day Nine; The Woman Scientist Meeting the
Challenges for a Successful Career; and Saving the Oceans
Page 15
Magrru
Page 81
On the Covers: Watercolors of drilling operations by Jack Crompton
Page 87
Oceanus
Winter 1993/94
Vicky Cullen
Editor
Lisa Clark
Assistant Editor
Justine Gardner-Smith
Editorial & Marketing Assistant
T.W. Casalegno
Publishing Consultant
Oceanus Magazine
Woods Hole Oceanographic Institution
Woods Hole, Massachusetts 02543
508-457-2000, ext. 2252
The views expressed in Oceanus are
those of the authors and do not
necessarily reflect those of Oceanus
Magazine or its publisher, the Woods
Hole Oceanographic Institution.
This issue of Oceanus magazine is
the last in its current format. Begin-
ning with the Spring 1994 issue, the
magazine will focus on research at the
Woods Hole Oceanographic Institu-
tion rather than "international
perspectives on our ocean
environment."
Paid subscriptions will be
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magazine in its revised format, the
tabloid newsletter Woods Hole
Currents, and Ocean Explorer, a lively
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Oceanus and its logo are ® Registered
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Oceanographic Institution.
All Rights Reserved.
Oceanus
International Perspectives on Our Ocean Environment
Volume 36, Number 4, Winter 1993/94 ISSN 0029-8182
1930
Published by the
Woods Hole Oceanographic Institution
Guy W. Nichols, Chairman of the Board of Trustees
James M. Clark, President of the Corporation
Charles A. Dana, III, President of the Associates
Robert B. Gagosian, Director of the Institution
Editorial Advisory Board
Sallie W. Chisholm
Professor, Department of Civil and Environmental Engineering,
Massachusetts Institute of Technology
John W. Farrington
Associate Director and Dean of Graduate Studies,
Woods Hole Oceanographic Institution
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Secretary, Intergovernmental Oceanographic Commission
Margaret Leinen
Vice Provost for Marine Programs and
Dean, Graduate School of Oceanography,
University of Rhode Island
James Luyten
Senior Scientist and Chairman, Department of Physical
Oceanography, Woods Hole Oceanographic Institution
W. Stanley Wilson
Assistatit Administrator, National Ocean Service,
National Oceanic and Atmospheric Administration
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25 Years of Ocean Drilling
An Introduction
This section provides a general look at
the accomplishment of 25 years of
ocean drilling, a bit of history, a broad
description and a personal account of
drilling work at sea, a map of drill sites,
a glossary, and brief comments from
participating countries. A geological time
scale is located on the inside front cover
for easy reference.
The Times, They Are
A-Changing
25 Years of Ocean Drilling
Bruce Malfait
Tlie scientific
return on the
ocean drilling
investment is
abundantly
obvious in the
articles of
this volume.
hange has been constant in the long and successful history
of the ocean drilling programs supported by the US
National Science Foundation and its international part-
ners. During its 25-year history, ocean drilling has con-
tinually encountered new problems, new politics, and new
programs. Each has been addressed through the scientific community's
determination and commitment to preserving its capability to sample
oceanic sediments and crustal layers. The scientific return on this past
investment is abundantly obvious in the articles of this volume— and the
potential returns from future investments promise to be equally rewarding.
The current Ocean Drilling Program (ODP) is the successor to the
Deep Sea Drilling Project (DSDP), a global reconnaissance of the ocean
basins. Although begun in 1968 as a US initiative, the program's remark-
able success led to growing international participation and interest. In
1974, five nations (France, the Federal Republic of Germany, Japan, the
United Kingdom, and the Soviet Union) accepted a formal commitment
to cooperatively plan and conduct the project, as well as to financially
support the operations. This International Phase of Ocean Drilling
(IPOD) continued until 1983. Although Glomar Challenger had reached
the limits of her capabilities, DSDP's remarkable scientific success, the
new questions it had generated, and the international cooperation and
focusing of research efforts it had spawned demanded an increased
capability for drilling.
Within 18 months of Challenger's retirement, the Ocean Drilling
Program (ODP) was organized, international participation was coordi-
nated, and a new drill ship (JOIDES Resolution) was contracted and
outfitted. It sailed for its first cruise in early 1985. This remarkable
accomplishment reflects the enormous dedication of the Joint Oceano-
graphic Institutions Inc. (prime contractor for ODP), Texas A&M Univer-
sity (science and ship operator), Lamont-Doherty Earth Observatory
(logging operator) and the international science community to organize
and plan the new program. With ODP, two new partners, Canada (later
joined by Australia) and the European Science Foundation Consortium
(representing 12 European countries), joined the list of nations providing
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
scientific expertise and resources in addressing geologic and oceano-
graphic problems on a global scale.
JOIDES Resolution has now operated in all oceans. It has drilled
above the Arctic Circle and within sight of the antarctic continent. More
than 1,200 scientists from 25 nations have sailed on the vessel. Larger
scientific parties have allowed for increased student participation and
training aboard ship. The state-of-the-art laboratories support rapid yet
complete initial sample analyses that provide immediate scientific results
that guide subsequent shore-based studies. Nearly 1,000 additional
scientists have used these data and requested samples from the program's
core and data archives for continuing study. The geochemical and geophysi-
cal logging capability (studies of the drill hole and its surroundings with a
variety of instruments) is unsurpassed in either academia or industry, and
has provided remarkable new data for earth studies.
What is the Future of Ocean Drilling?
The Ocean Drilling Program as presently structured will end within 10
years— however, our need to drill and sample ocean sediment and crust
will continue. The ocean drilling community has begun to identify its
future priorities and to forge direct links with a number of major new
international initiatives that require ocean drilling. Expansion of the
Global Seismic Network (for monitoring earthquakes) into the oceans is
being closely coordinated with OOP. Recent drilling in the Arctic has
supported implementation of the Nansen Arctic Drilling Program. ODP
is recognized as a major contributor to the US Global Change Research
Program because of its emphasis on climate and ocean history. ODP and
the continental drilling communities are increasing their cooperation as
they begin to face similar problems in drilling high-temperature environ-
ments and developing new logging and experiment programs.
The success of one drill ship has, of course, generated the need for
additional platforms to expand the options available for addressing the
scientific questions of the future. Japan has begun to plan construction of
a next-generation drill ship [humorously] referred to in the ocean drilling
community as Godzilla Mam. The new vessel would provide sampling
capability for deep crustal and sedimentary holes, and allow deep
drilling with a riser system (use of a second pipe surrounding the main
drill string to circulate drilling fluids and prevent any oil or gas deposits
encountered from "blowing out" the drillhole). In Europe a smaller drill
ship is under discussion to focus on shallow drilling for sedimentary
studies and experiments deployed in drill holes. The ability to drill in
shallow water from jack-up platforms to address global sea-level history
will be an important requirement in future ocean drilling. And, of course,
JOIDES Resolution will be a highly capable ship into the next century.
Identifying the priority research questions to be addressed, justifying
the proper mix of platforms to be used, and formulation of a new
operational plan with increased international participation will be critical
activities for the US and international communities in the coming years.
Marshalling the necessary resources to support the next generation of
ocean drilling will be an equally important task. •
Bruce Mnlfait is the
Program Director for
the Ocean Drilling
Program at the
National Science
Foundation, a position
he has held since 1987 .
Malfait received his
Ph.D. in marine
geology at Oregon
State University. He
joined the National
Science Foundation in
1974 as an Assistant
Program Director in
the International
Decade of
Oceanography
Program. In 1980 he
became an Associate
Program Director in
the Submarine Geology
and Geophysics
Program.
Oceanus
Winter 1993 /94
7
In April
CUSS I
drilled the
first deep sea
hole in 3,800
meters of
water off
Guadalupe
Island,
Mexico.
An Abridged
History of Deep
Ocean Drilling
Arthur E. Maxwell
his issue of Oceanus concerns 25 years of ocean drilling for
scientific purposes. However, the decade preceding these
25 years represents one of the most exciting and controver-
sial periods of earth-science research. The full impact of the
success of scientific ocean drilling would be incomplete
without a brief recapitulation of this tumultuous period.
The Mohole
As near as can be reconstructed, the history of deep ocean drilling began
in 1957, when Walter Munk (Scripps Institution of Oceanography) and
Harry Hess (Princeton University) suggested that a combination of
increased capability to drill deeply into the earth and continuing devel-
opment of offshore drilling techniques would allow oceanographers to
sample the material beneath the boundary of Earth's crust and mantle.
This boundary, which lies about 10 kilometers below the ocean surface
and some 30 to 40 kilometers beneath the top of the continental crust, is
called the Mohorovicic discontinuity, after the Croatian geologist who
first discovered it. More commonly, it is referred to as the Moho.
Later that year, several members of an informal group known as the
American Miscellaneous Society refined the idea at a breakfast meeting
at Walter Munk's La Jolla home. The unconventional American Miscella-
neous Society, or AMSOC, was born in the Office of Naval Research in
1952, when a number of scientists formed a loose affiliation to look at the
lighter side of heavier problems. Contrary to its normal modus operandi,
AMSOC took seriously the initiative to drill to the Moho. An AMSOC
committee was formed, and chaired by Gordon Lill of the Office of
Naval Research. Next, AMSOC submitted a proposal for a feasibility
study to the National Science Foundation (NSF), only to be turned down,
not because of the proposal's merit, but for lack of a formal organiza-
tional structure. Not to be disenfranchised, the AMSOC committee
reestablished itself as an official National Academy of Sciences/National
Research Council committee and resubmitted the proposal — this time
successfully. Thus, the AMSOC Mohole project was born.
8
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Willard Bascom (a specialist in
ocean engineering on the National
Academy staff) became major-
domo of the project and immedi-
ately set off to prove feasibility. His
tack was to utilize a barge, CUSS I,
originally owned by Continental,
Union, Shell, and Superior oil
companies and recently acquired
by the newly established Global
Marine Exploration company.
CUSS I's main assets were a
drilling rig plus four large out-
board motors for positioning the
barge in deep water. In April 1961,
CUSS I drilled the first deep sea
hole in 3,800 meters of water off Guadalupe Island, Mexico. The hole
penetrated about 200 meters of sediment with ages up to 25 million
years, and beneath that recovered 14 meters of basalt. This represented the
first verification that layer "2" under the ocean floor was basalt, and proved
the concept of deep sea drilling. It was indeed a momentous occasion.
Following this heady success, AMSOC recommended proceeding to
the next goal — the Moho. However, this recommendation carried with it
a seed of dissent that later grew to proportions nearly fatal to ocean
drilling. The dissent centered on the question of whether there should be
a single ship designed to drill all the way to Moho, or whether the Moho
ship should be preceded by a vessel designed primarily for coring
sediment and developing the prerequisite skills for deep ocean drilling.
With a scientific community nearly equally divided on these two strate-
gies, trouble was inevitable. Nonetheless, the extent of the subsequent
conflagration was anticipated by none.
In spite of its initial successes, other factors caused AMSOC to lose
its favored lead-role position in the Moho project by late 1961, and the
AMSOC group was relegated to advisory capacity, forcing NSF to seek a
new prime contractor. The project's lucrative financial and prestige
factors brought a large industry response, including some unlikely
partners. There were five leading contenders: a partnership of Socony
Mobil Oil, Texas Instruments, General Motors, and Standard Oil of
California; another of Global Marine Exploration, Shell Oil, and Aerojet-
General; plus the individual companies Brown and Root; Zapata Off-
Shore; and General Electric. Competition was intense, with members of
the California, Colorado, and Texas congressional delegations actively
supporting their constituents. After thorough and repeated reviews,
including considerable wrangling at high government levels, NSF
selected Brown and Root to be the prime contractor. Because Brown and
Root had not ranked highly in early evaluations of bids, protests were
loud and many. Much attention was drawn to the fact that Brown and
Root was located in the Texas congressional district of Albert Thomas,
who at the time was chairman of NSF's appropriations committee. Texas
was also the home state of then Vice President Lyndon B. Johnson. What
should have been a routine governmental contract negotiation had
suddenly become a cause celebre.
In August 1968,
Glomar Challenger
began the first of
DSDP's epic 96 legs.
From 1968 until 1983,
tlie ship traveled over
600,000 kilometers,
covering the world's
oceans and collecting
more than 97 kilome-
ters of core. The
scientific results from
these cruises can only
be described as notJihig
sJiort of revolutionary.
Oceanus
Winter 1993/94
Roger Revelle, right,
and Bill Ricdcl (both of
Scripps Institution of
Ocea } i ograpln/ ) a boa rd
CUSS I examine basalt
recovered during
Moliole drilling in
1962. The rock came
from the first deep sea
hole drilled, off
Guadalupe Island,
Mexico.
Simultaneous with the unfolding contractual controversies, the
scientific community was engaged in what might be considered open
warfare over the one-ship/two-ship issue. Ironically, the primary
proponents for each strategy were both located at Princeton, namely,
Harry Hess (professor), who opted for proceeding directly to Moho, and
Hollis Hedberg (part-time professor and vice president for exploration at
Gulf Oil Corporation) for the intermediate sediment coring approach.
The issue was hotly debated in journals and at scientific meetings, each
side essentially accusing the other of scientific chicanery. It was not
science at its most glorious moment. In the end, NSF decided there
would be a single ship that would drill sediments as its first phase. This
decision satisfied few. Brown and Root, as prime contractor, proceeded
with a single-ship design utilizing the relatively new semisubmersible
technology. The initial cost estimate was $47 million, more than double
AMSOC's original estimate. This proved to be a harbinger of more
escalations. In 1965, a San Diego shipyard was selected to build the
Brown and Root design at a cost of $30 million; by this time the esti-
mated overall cost of the project was $127 million. This factor-of-six
escalation over initial AMSOC estimates caused alarm in both the
scientific community and Congress, so much so that Congress passed a law
in 1966 forbidding NSF to proceed. Project Mohole was officially dead.
JOIDES, DSDP, and IPOD
After such intense and divisive activity, the speed of reconciliation was
surprising. Even before Mohole's official demise, the four major oceano-
graphic laboratories, Scripps, Woods Hole Oceanographic Institution
(WHOI), University of Miami Institute of Marine Sciences, and Lamont
Geological Observatory of Columbia University, under the respective
leadership of Roger Revelle, Paul Fye, F.G. Walton Smith, and Maurice
Ewing, united to form Joint Oceanographic Institutions for Deep Earth
Sampling (JOIDES). In 1965, Lamont proposed that JOIDES use the drill
ship Caldrill off Florida. Anxious for unity, NSF supported this JOIDES
effort. Its success led NSF to
encourage JOIDES to
continue. In 1966, Scripps
was designated as the
operating member of
JOIDES and was given a
$12.6 million NSF contract
to establish the Deep Sea
Drilling Project (DSDP).
In August 1968, Glomar
Challenger, operated by
Global Marine Exploration,
began the first of DSDP's
epic 96 legs. From 1968 until
1983, Glomar Challenger
traveled over 600,000
kilometers, covering the
world's oceans and collect-
ing over 97 kilometers of
10
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
core. The scientific results from these cruises far exceeded expectations;
they can only be described as nothing short of revolutionary. During this
period, major advances were also made in deep sea drilling technology.
In the mid-1970s, DSDP changed its character and name when non-US
participants joined JOIDES in providing scientific guidance and support
for the program. These countries included: the USSR, the Federal Repub-
lic of Germany, Japan, the United Kingdom, and France. With the
inclusion of official international participation, DSDP became known as
the International Phase of Ocean Drilling or IPOD.
Ocean Margin Drilling
Shortly after IPOD's inception in 1976, the US
members of JOIDES, which by now numbered nine,
incorporated to form Joint Oceanographic Institu-
tions Incorporated (JOI). In 1993, the JOI members
are: Scripps Institution of Oceanography, Lamont-
Doherty Earth Observatory (LDEO), University of
Hawaii's School of Ocean and Earth Science and
Technology, University of Miami's Rosenstiel School of
Marine and Atmospheric Science, Oregon State
University's College of Oceanography, University of
Rhode Island's Graduate School of Oceanography,
Texas A&M University's College of Geosciences and
Maritime Studies, University of Texas's Institute for
Geophysics, University of Washington's College of
Ocean and Fishery Sciences, and Woods Hole
Oceanographic Institution.
This was a first step in restructuring the manage-
ment of ocean drilling. JOI assumed the legal role of
management. Actual planning still involved all
participants through a JOIDES executive committee. The executive
committee, in turn, established a planning committee and a series of
panels to provide scientific and technical advice. As the IPOD phase of
ocean drilling was approaching its planned 1979 conclusion, a long-
range plan was deemed essential. Consequently, the JOIDES executive
committee convened the first of several meetings on the future of scien-
tific ocean drilling (FUSOD) in Woods Hole in 1977. The meeting, noting
the past great scientific successes of the program, recommended that a
different vessel, Glomar Explorer, constructed in the early 1970s for a
failed attempt to raise a Soviet submarine that sank in the Pacific, be
engaged to provide the increased capability required by science. The
Woods Hole meeting, combined with another in Houston (HUSOD), led
to the formation of the Ocean Margin Drilling program (OMD) in 1980.
OMD had significantly different aspects. First, there were to be a limited
number of deep holes requiring riser or cased drillholes. This scenario
carried OMD beyond the bounds of existing technology. Second, OMD
was to be supported half by NSF and half by 10 petroleum companies:
Atlantic-Richfield, Cities Service, Conoco, Exxon, Mobil, Pennzoil,
Phillips, Standard of California, Sunmark Exploration, and Union.
Following industry practice, as part of the planning, a synthesis was
initiated of all data in the regions of interest. However, before this was
The author, center,
along with Jim Dean,
foreground, and Dick
Von Herzen, Co-Chief
Scientist, removing a
core aboard Glomar
Challenger OH DSDP
Leg 3 in 1968.
Oceanus
Winter 1993 J94
11
Between 1987
and 1993, ODP
has sloivly
transformed
from a US
program with
international
support to a
truly
international
program.
completed, an apparent decision-making mismatch between government
and industry — not the scientific caliber of the proposed program-
caused industry to terminate its support in late 1981. At that time Glomar
Explorer was dropped from further consideration as a drill ship. Surviv-
ing remnants of OMD are its atlases of regional data syntheses. Within a
year OMD was born and dead, without drilling a single hole. Conse-
quently, IPOD was extended to 1983. (As a footnote, OMD had been
curiously silent about international participation.)
Ocean Drilling Program
Because OMD appeared not to include all IPOD participants, JOI re-
solved to plan a long-range, international program. An international
Conference On Scientific Ocean Drilling (COSOD) was held in 1981 at
the University of Texas. In 1983, Texas A&M University proposed a plan
to use SEDCO/BP 471, which was larger, newer, and offered much
greater capability than Glomar Challenger. The new program, known as
the Ocean Drilling Program (ODP), with JOI as the prime contractor and
Texas A&M as the science operator, was approved by all participants.
SEDCO/BP 471, known to the scientific community as JOIDES Resolution,
was outfitted with a seven-story scientific laboratory. Its first ODP cruise
began in January 1985. Subsequently, in 1987, some 340 scientists from 20
countries participated in COSOD II, hosted by the European Science
Foundation in Strasbourg, France. This meeting was convened to rede-
fine the scientific objectives of ODP through 1993 and beyond.
Between 1987 and 1993, ODP has slowly transformed from a US
program with international support to a truly international program. In
addition to the US, participants at the present time include: Canada-
Australia, France, Germany, Japan, the United Kingdom, and the Euro-
pean Science Foundation (representing Sweden, Finland, Norway,
Iceland, Denmark, Belgium, the Netherlands, Spain, Switzerland, Italy,
Greece, and Turkey). Many ODP activities are based outside the US. This
internationalization has led to a significant strengthening of the program,
and the next decade of ocean drilling is currently being planned.
The Deep Sea Drilling Legacy
The legacy left so far by the DSDP, IPOD, and ODP drilling programs, in
addition to the manifold scientific and technical contributions, are some
182 volumes of reports requiring 9 linear meters of shelf space. Further,
about 182 kilometers of core recovered from the drilling are available to
scientists in repositories located at Scripps, L-DEO, and Texas A&M.
Data from site surveys and down-hole logging associated with the
drilling programs are housed in repositories at L-DEO. These data represent
an incalculable future resource available to scientists worldwide. •
As a founder of the American Miscellaneous Society, since 1957 Art Maxwell has
cajoled many on the virtues of ocean drilling programs. But noting he has served
time at the Scripps Institution of Oceanography, the Office of Naval Research,
the Woods Hole Oceanographic Institution, and The University of Texas at
Austin, he anticipates time off for good behavior. He is currently Director of the
Institute for Geophysics at the University of Texas at Austin.
12
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Tlic "JOIDES" in the ship's name stands for Joint Oceanograpliic Institutions
for Deep Earth Sampling. The name reflects the international commitment
from the program's 20 member countries. The "Resolution" honors an earlier
ship, HMS Resolution, commanded more than 200 years ago by Capt. James
Cook. Cook's intrepid explorations into the Pacific and Antarctic regions
highlighted England's second great Age of Discoven/.
Work Aboard JOIDES Resolution
Vicky Cullen
The drillship JOIDES Resolution is outfitted with the most
modern laboratory, drilling, and navigation equipment.
The ship is 143 meters long and 21 meters wide, and its derrick
rises 61.5 meters above the water line. A computer-controlled system
regulates 12 powerful thrusters in addition to the main propulsion system
to stabilize the ship over a specific drill hole located in water as deep as
8,235 meters. The drilling system can handle 9,150 meters of drill pipe,
enough for drilling in all but the deepest parts of the world ocean.
In the most common drilling sequence, the four-coned tung-
sten-carbide roller bit that will cut into the seafloor is attached to
the drill pipe along with its stabilizing weights. This assembly is
lowered from the drill floor to the "moonpool," a seven-meter-
diameter hole in the bottom of the ship, where it passes through a
funnel-shaped guide horn into the water. The seven-member drill-
floor crew employs various mechanical and hydraulic devices to
extend the drill string down toward the seafloor. Twenty-eight and a
At left, JOIDES
Resolution works in
choppy seas. Below, top
to bottom, drill-floor
crew members make up
drill pipe, the hard-rock
guide base is ready for
descent to the seafloor,
and drillers remove
hard rock from the
core barrel.
Oceanus
Winter 1993/94
13
•*• HjKaAslE
.. ly&y
Above: Please see inside
back cover for caption.
Below: An ODP
technician carries a 30-
ineter core from the
drill floor to the cutting
rack, where it will be
cut into 1.5-meter
sections (bottom
photo).
half meter lengths of pipe weighing
874 kilograms are moved from
their racks, lifted by the
drawworks at the base of the
drilling tower, threaded onto the
drill string, and then lowered. In
5,500 meters of water, it takes 12
hours for the drill bit to reach the
seafloor. Just before its arrival, an
electric motor begins to rotate the
drill string to drive the core bit into
the sediment. Surface seawater is
pumped down the drill pipe to
remove cuttings and cool the bit.
The drill string is decoupled from
the surface motion of the ship by a
heave compensator, a huge shock
absorber built into the derrick so
that cores can be cut and lifted
smoothly.
An inner core barrel just above the bit at the bottom of the drill string
is retrieved by a wire cable that travels down the center of the drill pipe.
When the bit has advanced by an interval that matches the length of the
inner core barrel (9.5 meters), the core barrel is pulled up through the
drill string and delivered to the laboratory. Another core barrel is then
lowered to receive the next core. It takes an hour and 40 minutes for a
core barrel to make the round trip in 5,500 meters of water.
Drilling technique and equipment vary as different types of material
are cored. When the target is soft sediment that would be considerably
altered by the rotation of the drill bit, water pressure is used to drive the
hydraulic piston corer developed by DSDP through the bit and into the
sediment. When alternately hard and soft materials are encountered, a
rotating extended core barrel pushes ahead of the bit in soft sediment
and then retracts within the drill string when the core bit is needed to cut
through harder material.
An important recent advance in technology now allows
drilling in bare rock. Previously, at least 50 to 100 meters of soft
sediment were required to stabilize the bottom of the drill
string before hard rock could be drilled. With the new tech-
nique, a guide base filled with cement stabilizes the drill string,
and specially designed drilling motors drive the bit without
rotating the entire string. This process reduces damaging
vibration and drill-string fatigue that would otherwise occur in
coring young rock that has no sediment cover.
Each scientific cruise (called an ODP leg) lasts about two
months. A normal shipboard party includes approximately 24
scientists, half from the US and two each from the other ODP
partners. The scientific party typically includes the following:
• paleontologists who provide age determinations for cored
sediment, and rock and environmental descriptions for the time
of deposition based on the fossils found in the cores,
• sediment geologists who describe cores and provide compo-
14
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
sitional, environmental, and tectonic interpretations,
• petrologists who describe and classify the rocks recovered,
• magnetics specialists who study the magnetic reversals Earth has
experienced as they are recorded in seafloor sediments and basement
rock,
• geophysicists who consider the physical properties, such as density
and heat flow, of the sediments and rocks and also interpret the
general geologic setting of the site, and
• geochemists who study fluctuations of organic and inorganic material in
the cores and monitor recovered samples for the presence of hydrocarbons.
An OOP technical support staff is responsible for collecting, record-
ing, and preserving core materials and archiving routine scientific data.
They also operate the shipboard computer system and maintain and
repair laboratory and other equipment.
OOP shipboard operations run 24 hours a day with members of the
scientific party standing 12-hour watches so that someone from each
scientific discipline is always available. A well-established routine is
initiated, night or day, when a core arrives in the laboratory in its plastic
tube or "liner." It begins with measuring the length of the core, cutting it
into sections for study and storage, coding the top and bottom of the core
with colored caps, and clearly marking the liner with the core's original
location on the seafloor.
The paleontology staff on duty immediately begins to examine
fossils found at the bottom of the core to determine the age of the oldest
material sampled. A chemist checks for gas pockets, bubbles, or frothing
within the liner, indications of hydrocarbon presence. If these
are found, drilling at the site is reevaluated and perhaps
terminated. For safety reasons, every effort is made to avoid
drilling into hydrocarbon accumulations that might erupt
through the drillstring.
The core is then taken to the Physical Properties Laboratory
where the Gamma Ray Attentuation and Porosity Evaluator
(known as "the GRAPE") measures density by determining the
amount of radiation able to pass through the core. Other
physical measurements include determination of the strength of
the cored material and of thermal conductivity for studies of
the earth's heat flow.
When the whole-core analyses are completed, the core is split
lengthwise, and the halves are moved to separate tables. One half
becomes the working section and the other is preserved as the
archive section. Small samples of the working half are removed
according to the cruise sampling plan and the dictates of direct
observation. The archive section is photographed and a geologist
writes a rigorously detailed description of it before it is boxed for
long-term storage under refrigeration.
As initial analyses of each core are completed, the data are
entered into the computer for display on terminals throughout the
laboratory complex. Scientists working anywhere on the ship can
track the arrival of new samples and become immediately involved
in their analysis if appropriate.
Depending on the hardness of the sediments or rocks being
cored and the depth of drilling, cores are delivered from the drill
Top to bottom,
technicians measure a
core's deusiti/, porositi/,
and velocity
characteristics with the
Multi-Sensor Track
Si/stem, split cores
lengthwise, use the
cryogenic
magnetometer to record
magnetic reversals in a
core, and emploi/ the
ship's extensive
computer network.
Oceanus
Winter 1993194
15
Half of each core is
preserved intact as the
archive section, and the
other half is extensively
sampled and described.
Thin sections (top
photo, below) allow
study of the finest core
detail. Tim/ flags in the
bottom photo mark
sampling locations.
floor to the laboratories at intervals
ranging from 20 minutes to five or
six hours. Each one follows the
routine described above before core
samples are taken to specialized
laboratories for intensive study.
In the Paleomagnetics Labora-
tory, a state-of-the-art magnetom-
eter reads the record of Earth's
magnetic field changes, informa-
tion that helps determine the ages
of rocks cored and at what latitude
they were originally formed.
Paleontologists retreive
microfossils from sediment
samples with sieves, chemicals,
filters, and centrifuges, in some cases recovering millions of tiny skel-
etons from a sample smaller than your thumb. Light microscopes are
used to identify and examine fossil species at magnifications up to 2,000
times. This analysis provides information on the age of the sediment and
climatic conditions at the time of its deposition. The climate and water
conditions preferred by certain species can be inferred from the prefer-
ences of their living relatives. Then the conditions of ancient ocean
represented by a section of core can be determined by identifying the
proportions of similar fossil species found there. As shell forms common
to certain periods of earth history become known, the fossils can be used
to determine the age of the sediments in which they are found.
The finest details of rock and consolidated sediments are studied
with thin sections of these materials cut with diamond saws and pol-
ished to a high gloss for study under special microscopes. Two of the
four shipboard petrological microscopes can photograph the minerals,
and each of the microscopes can be connected to a video camera so that
scientists can view the thin section on a screen. Petrologists also study
and classify mineral structures with an x-ray diffractometer, which
identifies minerals by characteristic scattering patterns of x-rays
passing through cored samples.
The Chemistry Laboratory is equipped for detailed analy-
ses of the elements contained in sediments and rocks and in the
water they contain. Determination of elemental variations
along a core helps to reveal the history of the ocean recorded as
the sediments were deposited over millions of years.
Once all core has been recovered from a particular drill site,
the resulting borehole usually becomes a geochemical and
geophysical laboratory itself. Characteristics of the layers of
sediment and rock penetrated by the drill bit are determined
with sophisticated instruments specially designed for this
downhole work, which is called "logging." A discussion of
downhole measurements begins on page 129. •
16
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Two Months Before the Derrick:
Life Aboard JOIDES Resolution
Suzanne O'Connell
Why would anyone go to sea for two months? Leave the
comforts of home and work, friends and family — especially
family — for 64 days of exploring arctic ocean paleoclimate,
sleeping on a bunk bed in a small, windowless room, sharing your life
with people you barely know? Leaving children is especially hard-
some people just won't do it. Still, there is no shortage of people willing
to be part of a 28-person OOP scientific party. Some, despite the hard-
ships, are almost regulars. On the Arctic Gateways Leg, one participant
left his wife of three weeks, another an eleven-week-old baby. About half
of the scientists had sailed before; for me and several others, it was the
fifth cruise.
So why do it? Professionally the answer is easy: It's a chance to be
part of the university of the seas. You have the opportunity to work with
an international team of scientists, exploring critical questions about
Earth's history. Everything is arranged to allow you to focus
completely on your work, rather like an extended scientific
retreat. If you're lucky, not only will you come away with
answers and exciting new science questions, but also with new
colleagues, people you will work closely with for the rest of
your professional life.
But it is also a gamble, a sort of scientific lottery. Even
though years of preparation are involved to ensure that the best
sites are selected, there are always surprises. While surprises
may enhance the science, they also can mean your particular
interests go unfulfilled.
My most recent gamble ran from July 28 to September 24, 1993, as
sedimentologist for Arctic Gateways, OOP Leg 151. From Saint John's,
Newfoundland, we sailed past Iceland to the high northern latitudes.
Though JOIDES Resolution has an ice-strengthened hull, a Finnish icebreaker
accompanied us to scout for ice, protect us from ice flows, and, in the event
of an emergency, rescue us.
Although the list of cruise objectives was extensive, I was particu-
larly interested in investigating the relationship between the opening of
many small arctic basins and our planet's major cooling during the last
50 million years. These small, drowned seas link the present-day Arctic
Ocean with the North Atlantic, allowing cold Arctic Water to become
part of North Atlantic Deep Water, and to have a major climatic influ-
ence as it flows south. Our goal was to use the cores retrieved from these
basins to help us understand the initial cooling and the intense high-
northern-latitude glacial and interglacial cycles that began roughly 3
million years ago and intensified 750,000 years ago. The entire shipboard
Top: Finnish icebreaker
Fennica holds back ice
flow as JOIDES
Resolution crew
member performs hull
maintenance. Bottom:
Scientists and ship and
operations personnel
gather around "color-
ful" mid-Eocene cores
at Site 913.
Photos in this section courtesy of Suzanne
O'Connell except as indicated
Oceanus
Winter 1993/94
17
A marine technician
prepares X-ray
diffraction samples for
mineralogy studies.
Graduate students take
a break in their 12-hour
shift to practice
juggling.
party was there to address these questions, and each day's work brought us
closer to the answers.
Everyone worked a 12-hour shift; mine was noon to midnight.
Around 11:30 a.m., I'd hear the shower (shared with the adjacent room)
turn on. When it stopped, I'd roll out of my top bunk, and, by way of
desk and chair, make my way to the floor. Outside my door, the rumpled
dirty clothes I'd left the night before would be cleaned and folded. A
quick shower, dress, and I was off to the "lab stack," where there are
seven tiers of science work spaces. I'd first stop by the x-ray lab where
Wendy Autio, a marine specialist from Minnesota and also my room-
mate, had fresh coffee and a croissant waiting (the lab is also known as
"Wendy's Hard Rock Cafe"). Of course, I could have gone to the galley,
but the coffee there was terrible, too terrible even for a Java junkie like
me. Coffee and croissant in hand, I'd climb the stairs to the core lab. At
the watch change it was usually bustling, with eight sedimentologists,
four physical properties specialists, two paleomagnetists, two to four
core samplers, and many technicians, as well as the odd "tourists"-
people like geochemists, loggers, and co-chief scientists based elsewhere
in the lab stack but passing through to see the cores and to hear the old
watch briefing the new.
As the lab cleared after the watch change, we four sedimentologists
would parcel out jobs. I'd usually start with smear slides, samples that fit
on the head of a toothpick, the primary instrument for determining the
type of sediment in a core. After swirling sediment and water on a glass
slide, drying the sample on a hot plate, and covering it with
optical cement or Canada balsam, I'd examine it under a
microscope to estimate its sand, silt, and clay content, and then
the composition percentage of such elements as quartz, feld-
spar, mica, glauconite, and various microfossils such as fora-
minifera, nannofossils, diatoms, and radiolaria. As I sat at my
microscope, University of Miami physical properties specialist
Julie Hood worked at a nearby computer. At this time of the
day, she was often yelling the names of night-shift co-workers,
lamenting data entries or calculations that made no sense to
her. (By the end of the cruise, Julie's laments became a good-humored
joke that we all shared and loved.)
At 2 p.m., I took my two-hour turn at the sampling table, where the
drill began with carefully recording the core location of each sample into
the database. Then we sealed the sediment samples in plastic bags for
shore-based studies, work that would go on for one to two years to
answer questions that could be only loosely addressed during the cruise.
My sampling partner, Jim Briskow, a British downhole logging specialist,
was also a good juggler. My son is enamored of juggling, and I've always
wanted to learn to juggle. So, during the weeks of the cruise, I slowly
worked my way up to sometimes getting nine continuous passes of the
three balls. Of course, other people wanted to learn too — Jerry McManus, a
sedimentologist from Lamont-Doherty Earth Observatory, and David
Williamson, a French paleomagnetist, both became very good. Annyk
Myhre, the Norwegian co-chief scientist, was adept at juggling with two
balls in one hand — she recommended that anyone who wanted to sail as a
future co-chief scientist practice the two-handed juggle!
18
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
At 4 p.m. I became a sedimentologist again, trading places at the
sampling table with Thomas Wolfe from Germany to begin describing
cores. Depending upon the complexity of the core, this could take from
30 minutes to several hours. Generally, the most varied cores, requiring
the most description, were retrieved at the start of the hole, where
recovery is fastest. If cores arrived on deck every half hour and it took
two hours to describe a core, there was bound to be a problem. However,
coring went more slowly as the sediment became stiffer with depth, and
several days were usually devoted to downhole logging once coring was
completed, so we could catch up. We never had cores from the previous
site still waiting to be described when the next site's cores began to
arrive, though sometimes it was close.
After Thomas finished sampling, we'd all walk down the stairs to
"The Portuguese Restaurant" (so named because the cooks are Portu-
guese). The menu, listed on a large white board, changed with every
meal but always included cheese, bread
(baked fresh daily), desserts, salads, and fruit.
Garry Brass, a geochemist from the University
of Miami, and Julie Hood usually joined us for
dinner. The tables were meant for five, but
since they were round, we sometimes man-
aged eight. More than any other cruise I've
been on, dinner on Leg 151 was a wonderful
time to relax and tell jokes and stories.
Back in the core lab for the seven-to-
midnight stretch brought a chance to really
delve into the cores. Each new, unique core
records a bit of earth's history, something that
may never have been seen before or may
never be seen again. I encountered a beauti-
fully preserved Ordovician Rugosa coral
dropstone in a core that couldn't be more than
3 million years old, thin beds of bright blue
JOIDES Resolution
Fo'c'sle Deck (forward)
Library, hospital, and
living quarters
Deck 1: Hold
Refrigerated core storage
and freezer
Deck 2: Lower Tween
Refrigerated core storage,
cold storage, and second-
look lab
Deck 3: Upper 'Tween
Electronics shop and
photography lab
Deck 4: Main
Computers, computer-user
room, science lounge, and
offices
Deck 5: Fo'c'sle
Paleontology lab,
microscope lab, chemistry
lab, thin-section lab, and
X-ray lab
Deck 6: Bridge
Core handling, sampling,
and description, physical
properties lab, and
paleomagnetics lab
Deck 7: Lab House Top
Downhole measurements
lab
Poop Deck (aft)
Underway geophysics lab
Oceanus
Winter 1993/94
19
A micropaleontologist
studies tiny fossils in a
core sample to
determine the age and
origin of a particular
core stratum.
Styrofoam cylinders
replace core samples as
they are removed.
and purple clays, and black minerals that faded as I tried to describe
them. Each core's information was put into a graphic database for
publication in the Initial Results volume at the end of the cruise.
Shortly before midnight the lab would fill again as members of the
midnight-to-noon shift appeared for the between-shift exchange of
information. Occasionally, there was a midnight meeting of the entire
scientific party to discuss the site just completed and to plan for the next
sites, but midnight was usually decision time: dinner? the gym? the library?
a movie? reports? and certainly, e-mail (electronic mail). I'd usually have
something to eat, and then check my e-mail. Leg 151 was my first experi-
ence with shipboard e-mail. There had always been radio phone patches,
but static on the line, having to say "over" each time you finished talking,
and knowing any number of people both on and off the ship were listening
made it less than ideal for all but the most minimal communication. On my
first cruise, Leg 74, it didn't make much difference since there was no one I
was particularly interested in calling. This leg was different as I had left a
husband and child at home. Three-year olds do wonderful things, and dads
describe them so well!
Even on the best e-mail days, reading and responding
rarely took more than an hour at the computer. With caloric
intake high and life sedentary, I generally went to the gym at
least every other day, but usually not until 2:30 or 3:00, when I
could have the place to myself.
Many nights we spent some time writing reports on the
work we'd been doing. Although few of us, if any, found
writing easy, it certainly helped to solidify ideas, and because
so much of the work was collaborative, the camaraderie made it a more
pleasant experience. The four of us whose first language was English
tended to do most of the writing, but everyone contributed to the
discussions.
Scientists often work in isolation as they generate initial data sets,
and then seek out other scientists with similar interests to discuss
interpretations or obtain additional information. One of the real joys of
working aboard JOIDES Resolution (or its predecessor, Glomar Challenger)
is the sharing of information with people in your own and other fields. It
must be one of the best places in the world to experience how different
areas of science complement one another. For example, we sedimentolo-
gists could tell that material had been ice rafted, but we didn't know
when. The paleontologists and paleomagnetists could identify the time
for us. When we found unusual layers of sediment, we gave samples to
the chemists and a day or so later they could provide its composition.
Another advantage of the ocean drilling program is the special
opportunities it provides to women. I first heard about Glomar Challenger
as an undergraduate at Oberlin College. Helen Forman, a radiolarian
micropaleontologist and the wife of the former geology department
chair, had been on several cruises. I don't think I ever met her, but I do
remember that the male faculty spoke about her participation in the
program with awe in 1972 and 1973, when the program was still young.
It sounded wonderful to me, a personal and scientific adventure story,
and at least one other Oberlin female student was also impressed: Kathy
O'Neal was a seagoing curator aboard Glomar Challenger for several
years, and her initial inspiration came from the same stories.
20
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Twenty years later, here I am, having completed
my fifth cruise and with my own credits for people-
all women to my knowledge — who had their first
introduction to this program through me: Audrey
Meyer, former manager of science operations and
current US Science Advisory Committee (JOI/USSAC)
Chair; Gretchen Hampt, former seagoing curator and
chemistry technician, and now graduate student at the
University of California, Santa Cruz, soon to sail on
Leg 154; and Sara Harris, a USSAC fellow and gradu-
ate student at Oregon State University, also scheduled
to sail on Leg 154.
There are still no women among those who run the ship, do the
drilling , or prepare the food, and as in the rest of the field, women are a
minority in the science party; still, the program does offer women a
wonderful way to begin and build a scientific career.
Participation in a cruise doesn't end with the docking of the ship. At
the October 1993 Geological Society of America meeting in Boston,
Massachusetts, I presented a paper entitled "Arctic Gateways — High
Latitude Paleoenvironmental Change: Preliminary Results from ODP
Leg 151." The post-cruise work will continue for many years as my
colleagues and I build on the work begun during Leg 151 and share the
ocean drilling experience with other scientists. •
Vicky Cullen is manager of publications, graphic services, and public information
as well as Editor of Oceanus for the Woods Hole Oceanographic Institution. She
also does occasional publication work for other oceanographic organizations and
agencies; this description was written for a brochure on the Ocean Drilling
Program published in 1987 by Joint Oceanographic Institutions Inc.
Suzanne O'Connell grew up on an Ordovician carbonate continental shelf in
western Massachusetts and went further west to college. Throughout the last two
decades she has made repeated but unsuccessful attempts to leave college
academics, and during this time accrued enough degrees to become a college
professor. Currently at Wesleyan University, she tries to instill information about
the blue part of our planet in both suspecting and unsuspecting students. On her
most recent ODP leg she learned to juggle — somewhat.
Some 80,000 meters of
ODP cores are
archived at Texas
A&M University,
Lamont-Doherty Earth
Observatory of
Columbia University,
and Scripps Institu-
tion of Oceanography
at tlie University of
California, San Diego.
Markey builds world-class research winch systems,
CTD, Hydrographic, Trawl, and
Traction Winch Systems
Manual and Automatic Controls
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Oceanus
Winter 1993/94
21
P. o £
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Ol O\
Deep Sea Drilling Project
Leg Area
Sites (#Holes)
Core Recov'd
Leg Area
Sites (#Holes) Core Recov'd
1968
1975 (International Phase of Ocean Drilling Begins)
1 Gulf of Mexico
1-7(11)
181.40m
41 South Atlantic
366-370 (7)
1,673.00 m
2 North Atlantic
8-12(12)
216.20 m
42 Med., Aeg., Black Seas 371 -381 (17)
1,944.00 m
3 South Atlantic
13-22(17)
761.10m
43 North Atlantic
382-387 (6)
955.90 m
1969
44 North Atlantic
388-394 (15)
577.10 m
4 Central Atlantic
23-31 (16)
393.00 m
45 North Atlantic
395-396 (3)
327.00 m
5 North Pacific
32-43(14)
868.00 m
1976
6 North Pacific
44-60 (35)
684.70 m
46 North Atlantic
396A-396B (2)
63.64 m
7 Central Pacific
61-67 (15)
934.00 m
47 North Atlantic
397-398 (7)
1,813.10m
8 Central Pacific
68-75 (15)
1,208.43 m
48 North Atlantic
399-406 (10)
1,229.00 m
9 Central Pacific
76-84(17)
1,540.10m
49 North Atlantic
407-414(11)
881.00m
1970
50 North Atlantic
415-416 (5)
356.40 m
10 Gulf of Mexico
85-97 (14)
732.00 m
51 North Atlantic
417-,417A-D(5)
460.80 m
11 North Atlantic
98-108 (15)
636.70 m
1977
Reentry Trials
109-110
52 North Atlantic
417D-418A(3)
336.00 m
12 North Atlantic
111-119(13)
839.50 m
53 North Atlantic
418A-418B (2)
404.00 m
13 Mediterranean
120-134 (28)
640.53 m
54 Central Pacific
419-429 (18)
459.20 m
14 Central Atlantic
135-144 (17)
406.10m
55 North Pacific
430-433(11)
406.60 m
15 Caribbean
146-154 (16)
1,227.00m
56 North Pacific
434-437 (7)
497.00 m
1971
57 North Pacific
438-441 (10)
1,415.50m
16 Central Pacific
155-163(12)
1,268.50 m
58 Philippine Sea
442-446 (9)
1,591.10m
17 Central Pacific
164-171 (10)
905.00 m
1978
18 North Pacific
172-182(15)
1,215.06m
59 Philippine Sea
447-451 (7)
1,160.40 m
19 Bering Sea
183-193 (16)
1,062.30 m
60 North Pacific
452-461 (17)
833.20 m
20 North Pacific
194-202 (13)
163.50m
61 Central Pacific
462 (2)
726.00 m
21 Tasman & Coral
Seas203-210 (14)
1,384.30m
62 North Pacific
463-466 (5)
635.00 m
1972
63 Gulf of California
467-473(11)
1,522.20 m
22 Indian Ocean
211-218(11)
1,379.70 m
64 Gulf of California
474-481 (14)
1,632.70 m
23 Arabian Sea
219-230(17)
1,427.00 m
1979
24 Indian Ocean
231-238(11)
1,994.40 m
65 Gulf of California
482-485 (15)
750.00 m
25 Indian Ocean
239-249 (13)
790.10 m
66 Central Pacific
486-493 (14)
1,838.50 m
26 Indian Ocean
250-258 (13)
1,179.10m
67 Central Pacific
494-500 (15)
1,192.49m
27 Indian Ocean
259-263 (5)
960.30 m
68 Central Pacific
502-503 (8)
860.78
28 Ross Sea
264-274 (16)
1,406.30 m
69 Central Pacific
504-505, 501 (7)
455.61 m
1973
70 Central Pacific
506-510, 504B (33)478.84 m
29 Tasman Sea
275-284 (16)
1,181.93m
1980
30 South Pacific
285-289 (9)
1,162.00 m
71 South Atlantic
511-514(6)
822.80 m
31 Philippine Sea
290-302 (17)
1,233.80 m
72 South Atlantic
515-518(12)
1,543.95 m
32 North Pacific
303-313 (13)
737.20 m
73 South Atlantic
519-524 (13)
1,049.40 m
33 North Pacific
314-318 (8)
887.10m
74 South Atlantic
525-529(11)
1,830.70 m
34 South Pacific
319-321 (6)
231.00m
75 South Atlantic
530-532 (8)
1,443.49 m
1974
76 North Atlantic
533-534 (4)
982.10m
35 Antarctic Ocean
322-325 (4)
192.00 m
77 Gulf of Mexico
535-540 (8)
1,077.70 m
36 South Atlantic
326-331 (10)
576.90 m
1981
37 North Atlantic
332-335 (9)
415.30 m
78 North Atlantic
541-543,
38 Norwegian Sea
336-352 (18)
1,802.00 m
395A,B (8)
841.00m
39 Atlantic
353-359(11)
1,060.10 m
79 North Atlantic
544.547 (9)
1,088.50 m
40 South Atlantic
360-365 (7)
1,502.00 m
80 North Atlantic
548-551 (8)
1,480.00 m
24
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
81 North Atlantic
82 North Atlantic
83 Central Pacific
1982
84 Central Pacific
85 Central Pacific
86 North Pacific
87 North Pacific
88 North Pacific
552-555 (8)
1,180.30m
89
556-564(10)
757.00 m
90
504BU)
107.00 m
19!
91
565-570(11)
1,042.50 m
92
571-575 (17)
2,073.60 m
93
576-581 (11)
954.50 m
94
582-584 (14)
1,176.00m
95
581 (3)
44.60 m
96
89 Central Pacific 585-586, 462A(7) 872.20 m
90 Coral & Tasman Seas587-594 (18) 3,707.00m
Central Pacific
Central Pacific
North Atlantic
North Atlantic
North Atlantic
96 Gulf of Mexico
Totals
595-596(6) 110.10m
597-602, 504B (20) 296.68 m
603-605(7) 1,678.20m
606-611(22) 3,395.00m
612-613,603(5) 967.08m
614-624(20) 1,670.80m
635 (1,112) 97,053.91 m
Ocean Drilling Program
Sites (Holes) Core Recov'd
Leg Area
1985
100 Gulf of Mexico 625(3)
101 Bahamas 626-636(19)
102 Western Atlantic 418 (0)
103 Galicia Bank 637-641 (14)
104 Norwegian Sea 642-644 (8)
105 Labrador Sea /Baffin 645-647 (11)
106 Mid- Atlantic Ridge 648-649 (12)
1 07 Tyrrhenian Sea 650-656 (11)
1986
108 Northwest Africa 657-668(27)
109 Mid-Atlantic Ridge 395,648,
669-670 (5)
110 Lesser Antilles 671-676(10)
111 Panama Basin. 504,677-678
112 Peru Margin 679-688(27)
113 WeddellSea 689-697(22)
1987
114 South Atlantic
115 Mascarene Plateau
116 Bengal Fan
117 Oman Margin
118 SW Indian Ridge
119 PrydzBay
1988
120 S Kerguelen
121 Broken Ridge
122 Exmouth Plateau
123 Argo Abyssal Plain
124 SE Asia Basins
125E Luzon Strait
1989
125 Bon /Mar
126 Bon Mar II
127 Japan Sea I
698-704 (12)
705-716 (22)
717-719 (10)
720-731 (25)
732-735 (20)
736-746 (22)
747-751 (12)
752-758(17)
759-764 (15)
765-766 (5)
767-771 (13)
772-777 (15)
778-786 (15)
787-793 (19)
794-797 (10)
281.40m
1,429.00 m
Om
593.90 m
1,695.00m
1,884.40m
12.00 m
1,908.00m
3,842.50 m
12.00 m
1,897.70 m
(5) 428.00m
2665.60 m
1,944.00 m
2,297.00 m
3,075.00 m
991.60m
4673.00 m
447.00 m
2,102.00 m
1,082.00m
1,824.00 m
2,445.80 m
1,080.20 m
2,122.00 m
156.00 m
1,019.00m
2,127.70 m
1,655.00 m
Leg
Area
Sites (Holes) Core Recov'd
794, 798-799 (9) 1,548.00m
800-802 (5) 469.00 m
128 Japan Sea II
129 Old Pacific Crust
1990
130 Ontong Java Plateau 803-807 (16)
131 Nankai Trough 808(7)
132 West/Central Pacific808-810 (11)
133 N/E Australia 811-826(36)
134 Vanuatu 827-833 (16)
135 Lau Basin 834-841 (18)
1991
136 OSN-1 842-843 (6)
137 Hole504B 504(1)
138 E Equatorial Pacific 844-854(42)
139 Sedimented Ridges 855-858 (23)
140 Hole504B 504(1)
141 Chile Triple Junction 859-863(13)
1992
142 East Pacific Rise 864 (3)
143 Atolls & Guyots -I 865-870(12)
144 Atolls & Guyots -II
145 N Pacific Transect
146 Cascadia
147 Hess Deep 894-895 (13)
1993
148 Hole504B 504,896(2)
149 Iberian Abyssal Plain 897-901 (10)
1 50 New Jersey Sea Level 902-906 (11)
151 Atl. Arctic Gateways 907-913 (18)
152 E Greenland Margin 914-919 (13)
Totals 306 (758)
4,821.61 m
735.99 m
164.69 m
5,505.00 m
2,044.20 m
1,248.90 m
66.00 m
8.80 m
5.536.80 m
932.90 m
47.70 m
1,018.80m
0.50m
1,075.70m
801, 871-880 (21)1,087.70 m
881-887(25) 4,321.70m
857, 888-893 (20) 1,190.30 m
122.80m
81.43m
1.531.81 m
4,034.50 m
3,004.60 m
1,256.80m
87,547.03 m
Drilling sites planned for 1994 include the Mid-Atlantic
Rise near the Kane Transform, the Ceara Rise, the
Amazon Fan, the North Barbados Ridge, and the TAG
(Transatlantic Geophysical Profile) site in the Atlantic.
Oceanus
Winter 1993/94
25
Permian - 265 million years ago TriaSSlC - 222 million years ago Jurassic - 171 million years ago
Glossary
accretionary complex (accretionary prism) —
sediment assembly scraped from a subducting
crustal plate and added to its overriding plate
basalt — medium gray to black igneous rock that
constitutes the uppermost 2 to 3 kilometers of
oceanic crust
bioclastic rock — a biochemical sedimentary rock
consisting of fragmented remains of organisms, for
example, limestone composed of shell fragments
calcareous — containing calcium carbonate; used with a
rock name, it general]/ implies that as much as 50
percent of the rock is calcium carbonate
chert — (syn: flint) dense, extremely hard sedimentary
rock consisting mainly of interlocking quartz grains
clastic — descriptive term for sediment or rock composed
primarily of pre-existing rocks or minerals
conjugate margins — continental margins that
originated on opposite sides of a spreading center,
such as the margins of eastern South American and
western Africa
continental margin — area from the shoreline to the
abyssal ocean floor, including the continental shelf,
slope, and rise
decollement — a detachment structure associated with
folding and overthrusting characterized by indepen-
dent patterns of deformation in the rocks above and
below the boundary
deltaic — describing the sedimentary deposit of gravel,
sand, silt, or clay formed where a river enters a body
of water
detachment fault — special category of low-angle
normal fault due to the downhill sliding of rocks
from an uplifted region
diagenesis (adj: diagentic) — sum of the physical,
chemical, and biological changes in sediment after
its deposition
diapir — a general term to describe any body that has been
able to flow and to intrude the surrounding rock
dike — a thin, plateJike pluton that intrudes preexisting
structures
dropstone — a piece of rock that is transported from its
place of origin by ice (such as an iceberg) and
deposited on the seafloor, usually as a result of the
ice melting
fault — rock fracturing that displaces the sides of the
fracture relative to one another
fault block — unit of Earth's crust bounded completely
or partly by faults
gabbro — a group of granular, dark-colored igneous rocks
composed largely of plagioclase and clinopyroxene
hot spot — heat source from deep within Earth's mantle,
surface manifestation of a rising plume of hot
mantle, such as the Hawaiian Islands
hydrology — study of the occurrence, distribution,
movement and properties of water
ice rafting — transport of rock and other materials by
floating ice
igneous rock — a rock formed by the crystallization of
magma
IPOD — International Phase of Ocean Drilling
JOIDES — Joint Oceanographic Institutions for Deep
Earth Sampling
log — a spatially continuous record of the physical and
chemical properties of the formations penetrated by a
borehole
metamorphism — structural and mineralogical changes
in solid rock caused by physical and chemical
conditions that differ from those under which the
rocks initially formed
Nansen Arctic Drilling Program (NAD) — An
internatinal research effort designed to understand,
through future arctic drilling, environmental change
in the arctic and the history of its geolocial evolution
(member nations include Canada, France, Germany,
Japan, The Netherlands, Norway, Sweden, United
Kingdom, US, and Russia)
offset drilling — siting holes where tectonic processes
have exposed rocks of deep origin on the seafloor
26
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
CretaceOUS - 100 million years ago CenOZOic - Present
Left: Continental positions in
geologic time frames. Below:
Schematic drawing o/JOIDES
Resolution relocating a previ-
ously drilled hole. Sound bounc-
ing between the ship's hydro-
phones and sonar beacons near the
reentry cone, along with powerful
thrust ers, aid pinpoint navigation.
oolite — a sedimentary rock, usually a limestone
composed mainly of small round calcareous particles
that resemble fish eggs
ophiolite — sequence of igneous rock of oceanic crustal
origin that has been pushed up onto a continent by
plate collision
passive margin — continental margin in the interior of a
lithospheric plate where continental and oceanic
crusts are fused together (at active margins, oceanic
crust is subducted beneath continental crust as
plates collide)
pluton — general term for an intrusive rock body
reentry cone — guide horn placed in a drillhole to aid
entry of the drill string at a later time
sediment — solid material that has settled out of liquid
suspension that has been transported by wind,
water, or ice; loose sediment such as sand, mud, and
till may become consolidated to form coherent
sedimentary rock
serpentine — a mineral formed by the hydrothermal
alteration of olivine. The resulting rock,
serpentinite, is generally considered to have been
derived from oceanic crust altered in the presence of
water
Southern Ocean — all the water around Antarctica
subaerial — formed, existing, or taking place on the land
surface (contrast with subaqueous)
subduction zone — area of crustal plate collision where
one crustal block descends beneath another, marked
by a deep ocean trench caused by the bend in the
submerging plate
tuff — rock composed of volcanic-ash fragments cemented
or consolidated by the pressure of overlying material
turbidite — sediment deposited by a turbidity current, a
water flow caused by an excessive load of suspended
sediment. Such currents flow downslope at very high
speeeds and spread horizontally, gradually dropping
their sedimentary load as the current slackens and
the water comes to rest
Maximum
water depth
8,200 meters
(27,000 feet)
Television camera
Reentry cone
Oceanus
Winter 1993/94
27
ODP Member Reports
The member reports, written from a variety of viewpoints, collectively provide some idea of the
history of various nations' participation in ocean drilling, tell who some of the key players have been
and how individual members structure their participation in drilling activities, offer ideas for the
future of drilling, and, in one case, note with regret they will no longer be able to participate.
Australia
Ian Metcalfe
Australian geoscientists' involvement in
ocean drilling began with planning and
field work for early 1970s DSDP work in
Australasian waters and subsequent shore-
based studies on the resulting cores. Although
the Consortium for Ocean Geosciences of
Australian Universities (COGS) was created in
1974 to promote Australian participation in the
International Phase of Ocean Drilling, funding
constraints prevented the country's formal
presence in the drilling programs until 1988,
when Australia and Canada joined ODP
together as a consortium member. In the
meantime, however, COGS maintained ties
with the ocean drilling community and helped
to develop drill site proposals for the
Australasian region.
The benefits Australia currently enjoys
from ODP participation are in large part due to
those geologists who provided many years
worth of energy and impetus for membership
in ODP, notably Roye Rutland, Peter Davies,
and David Falvey (all of Bureau of Mineral
Resources— BMR) and Keith Crook (ANU),
along with many others, and also to the
foresight of the Australian Research Council,
which declared ODP membership to be a
national research priority in 1988.
Following Australia and Canada joining
ODP as a consortium member, the Minister for
Resources appointed an Australian ODP
Council, formed by representatives of the four
major funding agencies, and the Australian
ODP Secretariat was established at the Univer-
sity of Tasmania. Since 1992, the Secretariat has
been housed at the University of New England
in the Department of Geology and Geophysics.
Australian involvement in ODP has been
particularly strong in legs drilled in the Indian
Ocean (especially off the Northwest Shelf), and
a number of Australian scientists were invited
contributors to the American Geophysical
Union's Indian Ocean Review. One of the major
discoveries from the Northwest Shelf drilling
was the recovery of Triassic sediments and the
identification of previously unknown potential
hydrocarbon resources (see "Spinoffs for Oil
Exploration," page 120). Another highlight of
Australia's ODP involvement was the excep-
tionally successful Leg 133 BMR-instigated
program off the Great Barrier Reef .
To date, 26 Australian scientists have
participated in ODP legs. Many of them have
been eager, young scientists and graduate
students in the course of establishing their
careers. Besides the obvious benefits of work-
ing shoulder-to-shoulder with international
experts for two months, these participants
report that the ODP experience has dramati-
cally broadened their scientific horizons,
brought them into new research projects,
extended their international contacts, and,
importantly, developed confidence in their
own abilities as research scientists. In addition,
numerous shore-based scientists are working
on ODP samples in Australian laboratories,
and ODP benefits many Australian geologists
indirectly via exposure to new concepts and
ideas through seminars, conferences, papers
and teaching. •
Ian Metcalfe is the Science Coordinator for the
Australian ODP Secretariat.
28
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Canada
John Malpas
Canada became a member of the Ocean
Drilling Program in 1985, giving Canadian
scientists the chance to participate directly in
an international research venture and access
core samples and research results of truly
global significance. Becoming one of the first
five partners in the program was a result of
considerable effort by several members of the
Canadian earth science community, including
the late William Hutchinson and the late Michael
J. Keen. Working with the Geological Survey of
Canada sector, together with the National
Science and Engineering Research Council and
the federal Department of Fisheries and Oceans,
they established a funding base for national
participation.
However, despite significant Canadian
participation in planning, as well as shipboard
and shore-based research, the federal govern-
ment has found it difficult to provide a funding
level sufficient to maintain Canada's participa-
tion as an independent member. This, in part,
resulted in the 1988 formation of a consortium
with Australia, in which the two partners have
since worked closely and successfully. Al-
though Canada is a geographically large
maritime nation, its scientific base is relatively
small and widely scattered. Nevertheless, since
1985, more than 84 Canadian scientists and
technicians have been involved in the Ocean
Drilling Program. Some have developed
drilling proposals of national and international
interest, including those resulting in Leg 105 to
the Labrador Sea and Baffin Bay, and Leg 139 to
the Middle Valley area of the Juan de Fuca Ridge.
In Canada, ODP has a two-tiered adminis-
trative structure: The Canadian Scientific
Committee (CSC) oversees the program's
scientific aspects, and comprises scientists
acting as consortium representatives on JOIDES
panels; the Canadian Council implements the
overall policy that governs ODP in Canada,
and looks after the administrative and financial
aspects of Canadian participation in the
program. The Canadian Secretariat coordinates
the program in Canada and acts as the day-to-
day CSC operating arm. CSC and Canadian
Council members are selected from the indus-
try, government, and university communities,
providing the best possible cross section of the
geoscientific community.
The program has had a significant impact
on Canadian marine geosciences, with a
number of national successes. There have also
been a wide variety of spinoffs; for example,
drilling the Juan de Fuca Ridge required
successful implementation of the first major
marine environmental impact study, which
was undertaken by the Geological Survey of
Canada. The scientific community, having
gained access to some of the most inaccessible
areas on the globe, as well as more parochial
targets, has undoubtedly benefited from
consortium membership. While we acknowl-
edge that there will be a continuing struggle to
ensure that Canadian marine geoscientists can
fully participate in this global program, we
look forward to a second ten years as ODP
members.
When not on an airplane to the sunny climates of
Cyprus. New Zealand, or Australia (anywhere away
from the foggy Rock!), John Malpas is the Director of
the Canadian Secretariat for the Ocean Drilling
Program and Chairman of the Canadian Council. He
is also the Dean of Graduate Studies at Memorial
University of Newfoundland. Malpas has been
involved with the Ocean Drilling Program from its
infancy, and with the program 's predecessor. DSDP.
His research focuses on ophiolites and the origin of
oceanic crust.
Oceanus
Winter 1993/94
29
European Science Foundation
G. Bernard Munsch
The idea of establishing an Ocean Drilling
Program (OOP) consortium of European
countries first came from the US National Science
Foundation in March 1983 to the European
Science Foundation. The idea was rightly
perceived as potentially beneficial for all
parties concerned: the countries who could not
afford individual ODP membership them-
selves, the Ocean Drilling Program, and the
European Science Foundation (ESF).
The first step was to assess interest level
among scientists in these countries. Not
surprisingly, interest appeared to be quite
high. Though many scientists in these coun-
tries had participated in the pre-international
phase of the Deep-Sea Drilling Project, there
were very few involved during the Interna-
tional Phase of Ocean Drilling, although some
had kept themselves informed about drilling
activities. This discovery cleared the way for
the ESF to proceed.
The main difficulty, as usual, lay in the
next step: converting interest into funding. The
problem was that the ESF, despite its name,
has no resources of its own and can only
operate using funds obtained from its member
organizations and sometimes other entities
(such as ministries and companies); hence the
need to convince a sufficient number of these
to provide funds. No wonder it took nearly
three years of countless meetings and all sorts
of other steps — and sometimes dramatic
developments that nearly resulted in abandon-
ment— before the nascent consortium eventu-
ally managed to obtain the full requested
membership fee from its 25 constituent organiza-
tions in 12 countries: Belgium, Denmark, Fin-
land, Greece, Iceland, Italy, Netherlands, Nor-
way, Spain, Sweden, Switzerland, and Turkey.
The next significant challenge was to build
up a suitable management structure for a
consortium that was first of its kind in the
Ocean Drilling Program — and get it to work.
Legal and financial matters were easiest to
settle, with the ESF speaking and acting on
behalf of the entire group vis-a-vis the interna-
tional community. A more difficult task was to
divide fairly among the various members,
whose contributions ranged from 2 percent to
20 percent of the consortium's membership fee,
the various ODP benefits, such as representa-
tion on JOIDES panels (one seat on each panel
for the consortium as a whole), numbers of
shipboard participants and co-chief scientists,
and quotas for ODP publications. In addition,
the consortium needed a mechanism to make
fair decisions that took due account of financial
contributions while preserving minorities'
rights. To this end, two committees were set
up, one for management and one for science,
each with one representative per country.
Decisions were to be reached by consensus,
and by vote only if a consensus was impossible
(to date, a vote has never been necessary).
Complicated though it may seem, this
machinery has not only worked (with minor
adjustments) since June 1986, it has even
inspired others. Above all, this system has
enabled the ESF consortium to act as a full
G. Bernard Munsch holds a Ph.D. in theoretical
chemistry from the University of Strasbourg (the
most continental place in France), and knew next to
nothing about earth sciences and even less about
the ocean when he joined the staff of the European
Science Foundation in 1983. Having thus a naive
and totally unprejudiced mind made him the obvious
choice to be the officer-in-charge of ODP affairs, a
duty he carried out for close to six years.
30
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
ODP partner while strengthening its cohesion,
despite the inevitable conflicts of interest. In
this respect, this structure may be judged to
have successfully stood the test of time, the
best proof of which may be the recent ESF
renewal of ODP membership.
France
Yves Lancelot
The French earth and ocean science commu-
nity has long been an active, demanding,
passionate participant in the ocean drilling
programs (perhaps too demanding for some
members of the JOIDES community).
Along with those of several other non-US
countries, French scientists were involved in
the early phases of DSDP in the late 1960s and
early 1970s when the concept of "global tecton-
ics" was just emerging. At that time, France had
just launched a major effort to organize modern
ocean research on a large scale with the creation
of a specialized agency, the Centre National por
1'Exploitation des Oceans (CNEXO), which later
became the Institut Franqais de Recherche pour
1'Exploitation de la Mer (IFREMER) .
The "golden sixties" gave us modern ships,
a fresh supply of young brains, and enough
money to engage in global international ventures. In
France, as in many countries, marine geosciences
were abruptly placed at the forefront of earth
sciences by DSDP's early success and the fierce
debates provoked by some of its astounding
discoveries, such as the evolution of the Atlantic
and the desiccation of the Mediterranean. Neverthe-
less, it took the vision of some key individuals at
CNEXO (notably Jacques Debyser and Xavier Le
Pichon) and the enthusiasm of shipboard partici-
pants returning from early Gloinar Gwllmgei- cruises
to persuade our government to enter the JOIDES
community when IPOD began in 1975.
From then on it was "natural" (I was
tempted to say "routine") for the following
years to send French scientists off to the
drillship every two months, to regularly hear
about great achievements, leg after leg, and to
successfully maneuver proposals into the
system, helping to promote a strong French
ocean drilling community of several hundred
scientists. Funding was assured for this well-
organized community for several years, based
on the program's outstanding scientific
achievements and the active participation of
French scientists. The financial commitment,
today exceeding $6 million (US) per year
including salaries, was very significant within
the national earth science research budget, but
French participation regularly passed all
evaluations with flying colors. During the last
two or three years, however, ugly clouds of
reduced funding began looming over the
horizon and some scientists realized that long-
term participation could be in real danger. We
had to prepare for the future by consolidating
our position in the French earth science com-
munity, which was growing rapidly outside
the drilling community, if we were to justify
further participation in the program.
We identified two ways to improve our
position. The first was to secure better ODP
interaction with other major research programs
in order to demonstrate that drilling is indeed
a key element in earth sciences. (Although this
effort continues, it is still not completely
achieved today.) This meant increasing com-
munity support by bringing new disciplines
and "new blood" into the program. Step by
step, new communities are indeed coming
closer to the drilling program, particularly
since the evolution of drilling is opening new
research possibilities. High-resolution sedi-
ment studies are bringing part of the "global
change" community into ODP, and the "offset
drilling" strategy (drilling in mid-ocean ridge
fracture zones for closer access to Earth's
mantle), along with emphasis on drilling deep
into the ocean crust, has helped to develop the
international effort to coordinate and expand
ridge-crest research. The spectacular develop-
ment of in situ downhole observations, mea-
surements, and experiments now attracts more
geophysicists and geochemists than ever
before. All this, of course, is in addition to the
program's traditional geodynamics aspects.
Another way to secure the French
Oceanus
Winter 1993/94
31
community's long-term participation in the
program was to develop a strategy for remov-
ing the "routine" coloration that any long-
lasting program acquires over the years. It has
become clear to many of us that the future will
necessarily demand some decentralization of
the program, and that a better adaptation of
the tools to the tasks becomes critical if we are
to face the increasing demands of the commu-
nity. Very deep drilling will some day require
a large riser-equipped platform that may have
to stay on one drill site for many months.
Paleoceanography and global change ap-
proaches should rely on the rapid recovery of
numerous well-preserved and relatively short
sediment sections from all over the world
ocean. In situ downhole experiments also need
more ship time. This prompted France to
propose, during the 1987 COSOD II conference
in Strasbourg, that the program become multi-
platform after 1998.
France, like all of its "neighbors," must
face the organizational and political challenge
of building a truly European scientific "com-
munity," sharing facilities as well as man-
power. DSDP and OOP have demonstrated
how powerful the sharing of a major facility
such as a drilling vessel can be in bringing a
large community together. The need for a
multi-platform program may become a major
opportunity for developing an efficient part-
nership, both within Europe and between
Europe and the rest of the world. We are
convinced that the development of a European
state-of-the-art vessel specially equipped for
high-resolution coring and downhole experi-
mentation could best assure our long-term
commitment to the international drilling
program of the future. Hi
1 (_J
Yves Lancelot spent some of his early years of
research at Lamont-Doherty Geological Observa-
tory, before becoming DSDP's Chief Scientist at
Scripps Institution of Oceanography. After being one
of the most French of the American scientists, he
was perceived by his French colleagues as one of
the most American of the French scientists and
decided to simply become one of the most Euro-
pean of the European scientists. Much to his and
many others' surprise, he has finally settled down in
Marseille, as head of the CNRS's Laboratoire de
Geologie du Quaternaire, specializing in paleoclima-
tology and paleoceanography.
Germany
Helmut Beiersdorf
he Federal Republic of Germany was one
of several countries that responded to the
1972 US invitation to help plan a new program
based on early DSDP accomplishments. When
the International Phase of Ocean Drilling
(IPOD) was initiated in 1975, 20 German
scientists had already been members of Glonmr
Challenger scientific parties.
During the early 1970s, Eugen Seibold and
Hans Closs were among those most instrumen-
tal in organizing German participation in
ocean drilling. Seibold was at that time Chair-
man of the Senate Commission for Oceanogra-
phy of the Deutsche Forschungsgemeinschaft
(DFG, the German equivalent to the US
National Science Foundation), while Closs was
Head of the Department of Geophysics of the
Bundesanstalt fiir Bodenforschung at
Hannover, FRG (now Bundesanstalt fiir
Geowissenschaften und Rohstoffe, BGR, the
Federal Institute for Geosciences and Natural
Resources). Friedrich Wilckens of the Federal
Ministry for Research and Technology (BMFT)
and Franz Goerlich of DFG also contributed
significantly to forming and maintaining a
"critical mass" of German DSDP scientists.
Although most of the scientists initially
approached by DFG and BMFT were enthusi-
astic about the possibility of working with the
world's best drilling researchers, others were
concerned about the limited number of Ger-
man marine geoscientists, fearing that this
resource would quickly become exhausted if
each DSDP leg required a German scientist to
go to sea and then concentrate for a year or two
on the resulting data and samples. On the
other hand, it was expected that the number of
seagoing scientists would increase with time as
a consequence of guaranteed participation in
32
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
each Gloinar Omllenger cruise and the increas-
ing number of German research cruises that
would be dedicated to surveying drilling
targets. In fact, the number of German scientists
involved in ocean drilling has more than tripled
since the country became an IPOD member.
Germany's IPOD science plan, finalized on
February 13, 1973, called for DFG and BMFT to
share OOP membership costs, and for DFG to
be responsible for scientific activities related to
IPOD. This arrangement continues today, with
BGR coordinating the German scientific
contribution and providing administrative
assistance to DFG. There is close cooperation
between the ODP community and the German
continental drilling program.
The German geoscientific community
submitted 49 ODP-related proposals to the
DSDP/ODP Schwerpunktprogram (Priority
Program) for the period from July 1993 to June
1994, and the Priority Program review board
recommended 45 of them for funding. In both
1992 and 1993, approximately 3.75 million
deutsche marks were allocated to the Priority
Program for research, as well as for travel to
ODP cruises and meetings, maintaining the
German ODP office at BGR, and distributing
such information as ODP Proceedings, German
ODP circulars, panel meeting reports, etc. In
addition, along with host institutions, BGR
organizes an annual German ODP colloquium,
and several million deutsche marks are allo-
cated annually to support surveys of potential
ODP drill sites by the German long-range
research vessels Meteor, Polarstern, and Sonne.
Since Germany became a member of IPOD,
166 German scientists have participated in
drilling cruises, and some 150 scientists
currently involved in research based on the
drilling program assure continued German
support of the Ocean Drilling Program into the
next century.
A refugee from East Germany in 1960, Helmut
Beiersdorf went to Goettingen (West Germany) to
study geology. Following completion of his doctorate
at the University of Goettingen, he joined the
Bundesanstalt fur Geowissenschaften und Rohstoffe
(BGR) at Hannover, specializing in the exploration of
seabed mineral resources. This took him on many
research cruises in all oceans, including a Glomar
Challenger cruise. He is Head of Basic Geology and
Marine Geology at BGR. coordinates the ODP
Priority Program, and represents the German Ocean
Drilling Program community on the JOIDES Execu-
tive Committee.
Great Britain
Robert B. Kidd and James C. Briden
Britain was one of the founding members of
the International Phase of Ocean Drilling
(IPOD) which began in 1975, but British
scientists had, in fact, participated in earlier
phases of the Deep Sea Drilling Project aboard
D/V Glonmr Clinllenger. Individual British
marine geophysicists were particularly active
in the planning and execution of drilling legs
that extended theories of seafloor spreading
and established the early evolution of the
North Atlantic and the breakup of the southern
continents to form the Indian Ocean.
UK sedimentologists and stratigraphers
were heavily involved in the development of
paleoceanography as a subdiscipline based on
studies of oceanic sedimentary sequences.
Their special interests included drilling on the
Pacific seamounts, and in the Mediterranean
Sea, the Indian Ocean, and around Antarctica.
During the IPOD phase, the British com-
munity was particularly interested in studies of
continental margin evolution. Participating
scientists called for greater emphasis on
logging and downhole instrumentation in the
overall drilling effort, a continuing theme that
has subsequently paid great dividends in the
development of scientific ocean drilling.
Toward the end of DSDP, UK scientists
were very active in paleoceanographic studies
that became possible with the advent of
hydraulic piston coring. This technique extended
undisturbed high-resolution stratigraphy from
levels of conventional surface core sampling (10
to 30 meters) to depths of hundreds of meters.
This work included studies of North Atlantic
climate and water-mass circulation and of
sediment distribution on submarine fans.
As members of JOIDES, British scientists
recognized that pressing issues in geoscience,
such as the linkages between ocean history and
Oceanus
Winter 1993/94
33
global climate change, the evolution of conti-
nental margins, and the effects that fluids and
gases emanating from the ocean floor have on
the ocean's geochemistry, required a platform
with increased capability. Our community was
therefore frustrated when, as DSDP was
succeeded by the Ocean Drilling Program
(OOP) utilizing JOIDES Resolution, funding
difficulties caused a brief hiatus in British
participation from 1984 to 1986.
Happily Britain did become a full OOP
partner in 1986. Since then the British scientific
community has been extremely active in the
program, with particular interest in the Indian
Ocean and Southern Ocean campaigns, and in
the Pacific OOP program. The first two have
generated major synthesis studies, drawing
together the results of both DSDP and ODP
drilling in these areas. British scientists have
chaired a number of the JOIDES advisory
panels in recent years, and UK proponents
have figured prominently in preparation for
the current Atlantic and Mediterranean
programs.
One feature of British ODP participation
has been the widening of the disciplinary
science base within its ODP community to
include microbiologists, more geochemists,
downhole logging specialists, and develop-
ment engineers, as well as geologists whose
primary interests had been in land-based
geological studies far removed from marine
geology. Recognizing this widening of interest
and increased importance of ODP to British
science, the Natural Environment Research
Council was the first of the non-US funding
agencies to sign the Memorandum of Under-
standing ensuring continuation of the JOIDES
partnership through 1998. Britain will host the
first JOIDES Office to be located in a non-US
partner country when coordination of the
JOIDES advisory structure rotates from the
University of Washington, Seattle, to the
University of Wales, Cardiff, for two years
beginning October 1994.
Rob Kidd grew up in the West Wales seaport of
Milford Haven, where his family, made up of
generations of seafaring Navy- and trawler-men,
encouraged him to get an education and not go to
sea. After a research career spanning over 30
cruises, he still blames his intoxication with marine
geology on a first post-graduate expedition in the
Mediterranean Sea in 1969 that gave him the
mistaken impression that research cruises could all
be 10 days long! His primary interests are in deep
marine sedimentary processes. He holds the Chair
of Marine Geology at the University of Wales, Cardiff
and represents the UK on the JOIDES Planning
Committee. He was Head of ODP Science Opera-
tions at Texas A&M University for the program's first
two years (1984 to 1986).
James C. Briden is Director of Earth Sciences for the
Natural Environment Research Council in UK, having
casually thrown away tenure as Professor of
Geophysics at the University of Leeds. Previously a
landlubbing paleomagnetist who wallowed in the
Paleozoic, the Precambrian, and in directional
statistics, he was lured into love with marine geo-
science through representing UK on the JOIDES
executive committee, of which he is chair-elect. He is a
Murchison Medallist of the Geological Society of London,
and a Frequent Flyer on most of the world's airlines.
Japan
Noriyuki Nasu and Kazuo Kobayashi
Tapan was first invited to become an interna-
| tional member of DSDP by a letter from
William Nierenberg, Director of the Scripps
Institution of Oceanography and chairman of
the JOIDES Executive Committee, to Noriyuki
Nasu, Director of the Ocean Research Institute,
University of Tokyo. Japanese earth scientists
knew and appreciated the Deep Sea Drilling
Project and were enthusiastic about member-
ship. Nasu secured official and budgetary
support from the Japanese Government and
the Ministry of Education, Science and Culture
(Monbusho) eventually became the sponsor.
Japan joined IPOD at its start in 1975 and has
continued as a member through DSDP and
ODP to the present.
34
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
The Japanese Ocean Drilling Committee,
organized within the Ocean Research Institute,
consists of eminent scientists from across Japan,
both geographically and administratively. The
committee has the authority to decide how
Japan will participate in various international
and domestic ocean drilling activities. Nasu
was Japan's representative to the JOIDES
Executive Committee until April 1, 1984, when
he retired from the University of Tokyo. He
was succeeded by Kazuo Kobayashi, who
served until his retirement in early 1993.
Asahiko Taira, whose contribution to this
volume appears on page 95 is the current
international OOP coordinator for Japan.
A total of 57 Japanese scientists actively
participated in 52 IPOD legs (Legs 44A to 96),
and 91 scientists in 45 OOP legs (Legs 106 to
151). There were six Japanese co-chief scientists
in IPOD and seven in ODP. Japanese research-
ers have especially contributed to drilling
activities in the Japan Trench, the Nankai
Trough, and the Shikoku, West Philippine, and
Japan Sea back-arc basins. They have also had
special interest in the deepest ocean-crust
drilling in the east equatorial Pacific and in
such environmental cruises as the Indian
Ocean monsoon leg.
A number of Japanese geophysicists and
engineers have contributed to comprehensive
downhole experiments, including seismic and
electromagnetic measurements, in the Yamato
Basin (southeastern Japan Sea) working aboard
JOIDES Resolution and support vessels such as
Tansei-Mnru, provided by the Japanese team.
Japan has contributed many drilling-site
survey cruises using R/V Hakiino-Mnni and
other vessels, particularly in the northwestern
Pacific Ocean around Japanese islands. Ocean
drilling work in these areas has contributed
significantly to understanding subduction
processes and back-arc-basin tectonics.
The Japan Marine Science and Technology
Center (JAMSTEC) is now promoting a plan for
a new ocean drilling vessel with financial and
administrative support from Japan's Science
and Technology Agency. Using marine-riser
technology, the new ship aims to overcome the
present difficulty in achieving deeper penetra-
tion caused by both possible danger of hydro-
carbon blowout and hole instability. The initial
target for riser length is 2,000 meters; with
continuous effort, we will try to reach 4,000
meters. The length of the drill pipe will be
10,000 meters. We hope that this new drilling
facility will provide world geoscientists with the
opportunity for further scientific exploration of
the vast ocean floor, and eventually for a sound
understanding of our living Planet Earth.
Noriyuki Nasu is Professor of the University of the Air
and Professor Emeritus of the University of Tokyo,
where he served as Director of the Ocean Research
Institute from 1968 to 1972 and 1980 to 1984. He
served for many years on various ocean drilling
committees. Nasu's research interest is marine
geology, and he served as a co-chief scientist of Leg
57, which explored the Japan Trench.
Kazuo Kobayashi is now Science Advisor for the
Japan Marine Science and Technology Center and
Professor Emeritus of the University of Tokyo, where
he was a Professor of the Ocean Research Institute
from 1967 until early this year. He has been a
member of the JOIDES Active Margins Panel, the
Planning Committee, and, in the immediate past, the
Executive Committee. His research interests range
from paleomagnetism to tectonic processes in the
subduction zones. He served as a co-chief scientist
for Leg 58, drilling in the Shikoku and northern
Philippine Sea back-arc basins.
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Oceanus
Winter 1993/94
35
Russia
Nikita A. Bogdanov
In the second half of the 1960s, after
geophysical investigations had proved the
structural differences between continental and
oceanic crusts, both Russian and American
scientists decided to drill deep holes to better
understand the Conrad and Mohorovicic (Moho)
discontinuities (boundaries between the upper
and lower continental crust and between the
crust and mantle, respectively). Thus competition
that began between the former Soviet Union and
the US with the atomic bomb and continued
during the initial steps toward conquering space
extended into earth sciences as well.
In 1967 the Former Soviet Union began
drilling a super deep hole on the Kola Penin-
sula, with the primary objective to reach the
Moho boundary. In the US, deep sea drilling
started in 1968. This tough confrontation
(characteristic of the cold-war epoch) did not,
however, affect scientific cooperation: Close
contacts developed between Russian and
American scientists from the earliest phases of
deep sea drilling. As far back as 1971, Russian
scientists A. P. Lisitsyn and V.A. Krasheninni-
kov participated in the US Deep Sea Drilling
Project, and in 1974 the USSR Academy of
Sciences became the first foreign partner in this
successful project.
From the very beginning of DSDP, Russian
scientists have been especially interested in the
drilling programs' data on deep sedimentation
and the stratigraphy of upper Mesozoic and
Cenozoic sediments. Though systematic ocean
drilling supported the plate-tectonic concept of
Earth's evolution and every new cruise
brought new geophysical and geological data
confirming it, in our country, where this
concept was not readily accepted, scientists
focused on the drilling results that were
inconsistent with plate tectonics. However,
most of the small group of Russian scientists
who participated in Glomar Challenger cruises
from 1974 to 1981 returned home as ardent
defenders of this concept. As new data on
seafloor geology was gradually assimilated,
more and more supporters of modern plate
tectonics appeared in our country, and by the
mid 1980s the majority of USSR marine geolo-
gists supported plate-tectonic theory.
Despite being slow to accept lithospheric
plate motion, Russian geologists were among
the world leaders of ocean drilling, especially
in the first stage, from 1968 to 1980. Their
interest in oceanic crust was sparked by the
abundance of ophiolite rocks found on the vast
former Soviet Union territory. (Ophiolites are
segments of oceanic crust found on land — now
known to be pushed into the continents by
plate collisions). The age of these ophiolites
ranges from late Cretaceous at the Pacific
Ocean coast to late Precambrian in Altai, Central
Asia. Dredging the ocean floor helped confirm
the identities of ophiolitic sections, but Russian
marine geologists and geophysicists who
participated in the Deep Sea Drilling Project did
not fully accept this view until 1981, when a dike
complex was penetrated in Hole 504B. Today,
nobody doubts the similarity of oceanic crust and
continental ophiolites, though they may differ in
chemical composition. It is a pity that continental
geologists' ideas about the advantages of offset
drilling over super deep drilling for studying
crustal magmatic rocks was given no priority by
the ODP Planning Committee. Offset drilling of
holes 250 to 300 meters deep would reveal
details about the small-scale transitions be-
tween crustal layers that cannot be obtained
from deeply drilled holes (1,500 meters or so).
Russian scientists participated continu-
ously in deep sea drilling from 1974 to 1981,
when their participation was interrupted
because of the political climate at the height of
the cold war. In 1991 with great support from
Joint Oceanographic Institutions Inc. and the
US National Science Foundation, Russian
scientists returned, only to retreat the follow-
ing year for economic reasons. Despite a less-
than-encouraging economic situation for
scientific investigation in our country, our
scientists remain optimistic — and the optimism
brings rewards: The past year and a half of our
participation in ODP has been the most fruit-
ful. We collected much data on lithology,
36
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
stratigraphy, and other Pacific geology fields,
mainly pertaining to this region's Cenozoic
history. Unfortunately, since no deep sea
drilling has yet been done in seas adjacent to
Russia or the Arctic, our scientists can so far
only correlate Pacific drilling results with those
from distant Kamchatka and the Aleutian
Islands. Using material they collected while on
cruises and data obtained from studying ODP
core samples and the Initial Reports and Scien-
tific Results volumes, Russian scientists have
published 16 separate books and several
hundred scientific articles. The largest recent
review of ocean drilling results was a catalog
of all deep sea drilling cores from the Pacific
and the Atlantic in geological and geophysical
atlases for these oceans.
Russian scientists have maintained close
contacts with NSF, even during the periods
when they were unable to participate in Gloiuar
Challenger or JOIDES Resolution cruises. We
have always felt like full partners of ODP, as
we have been kept apprised of drilling results
and ODP activity by Texas A&M University.
Unfortunately, economic complications dictate
that our partnership and publication flow will
cease this year. Nevertheless, Russian scientists
consider it fortunate that with the help of
American scientists and other ODP partners
they have had 20 years of deep sea drilling
involvement.
Nikita A. Bogdanov has been chairman of the
Russian Committee on the Deep Sea Drilling Project
(DSDP) and then the Ocean Drilling Program (ODP)
since 1980. He is Director of the Institute of the
Lithosphere. a member of the Russian Academy of
Sciences, and a Moscow State University professor.
United States
Ralph Moberly
In his keynote address at the 1976 International
Geological Congress in Sydney, Philip H.
Abelson, a geophysicist who was then presi-
dent of the Carnegie Institution, listed deep sea
drilling with Apollo as programs whose
geological samples form the basis for revolu-
tionary advances in science. Great depth and
range of new knowledge is chronicled in
hundreds of articles published by ocean
drilling scientists, and numerous review
papers, including those in this issue of Ocennus,
summarize that knowledge.
This review from the US perspective
provides not another detailed account of the
discoveries, but rather mentions something of
the development of late 20th-century science,
with examples both from the science itself and
the participants.
Future historians and philosophers of
science will find ocean drilling abrim with
significant patterns — changing science para-
digms, the international aspects of science, the
interplay of technological and scientific ad-
vances, and the funding and direction of science.
The predominance of American scientists and
institutions in the early years of ocean drilling,
and indeed the very concept and fruition of
ocean drilling itself, were but two facets of the
overall position of American science after World
War II. Thus science historians will find an
immense American contribution to the many
successes — and occasional failures — of drilling.
Several of the earliest DSDP legs confirmed
that an American theory, seafloor spreading,
was an acceptable explanation of a mainly non-
American concept, continental drift. The ages
of samples overlying identified magnetic
anomalies aided the quantification of seafloor
spreading into the more-inclusive paradigm of
plate tectonics.
Early DSDP co-chief scientists became
American Princes of Serendip, accidentally
discovering evidence that did not fit with
existing models of earth processes, that instead
brought new insights. To take only one ex-
ample, finding records of igneous activity in
oceanic settings other than on the ridge crest,
above subduction zones, or as traces of hot
spots in time led to fruitful theories about the
origin of back-arc basins, and about mid-plate
volcanism from giant mantle plumes.
Oceanus
Winter 1993/94
37
Piston cores and early ocean-drilling cores
gave birth to a new earth science discipline,
paleoceanography. In response to requests by
marine scientists, American DSDP engineers
developed the hydraulic piston corer, which
allowed recovery of long sections from many
oceans and many latitudes, and the new
paleoceanographic focus in the earth sciences
grew to maturity. Paleoceanography is con-
cerned with evidence from microfossils, isotopes,
sediments, and hiatuses that reveal, for instance,
how the changing distribution of seaways
affected ocean circulation and Earth's climate.
Ocean drilling has provided a generation
of American scientists some perspective into
the often complex and changing relationship
between those who pursue science and those
who fund the pursuit. The demise of the
Mohole project in 1966 showed that mandated
programs might literally live or die with the
life and death of a congressional leader (see
"An Abridged History of Deep Ocean Drilling,"
page 8). Years later, the demise of Ocean Margin
Drilling showed how difficult it is in the US for a
government agency to design a plan for science
and operations and then impose it on industry
and on individual scientists in academic institu-
tions. Yet industry, government agency, and
academic partnerships are the norm for most of
our international ocean drilling partners. A
succession of science plans and budgets has
demonstrated that the US and its partners can
stretch their own operating modes to accommo-
date others' modes. After some initial weak-
ness, Joint Oceanographic Institutions Inc.,
born of the US part of Joint Oceanographic
Institutions for Deep Earth Sampling (JOIDES)
but later to subsume its parent, showed that
complex international programs can be man-
aged successfully.
Science devours new ideas. New hypoth-
eses lead to proposals for new drilling legs that
will help test theories. The demand for new
postulates and better information on which to
plan drilling constitutes a demand for the
cross-fertilization of ideas. At first, the JOIDES
advisory panels and the shipboard scientific
parties were composed mainly of scientists
from the US Oceanographic community and
those with ties to early ocean drilling advocates
such as the American Miscellaneous Society and
the Long Cores Committee. Later, a broader
sector of US academic, federal, and industrial
earth scientists became involved, with occasional
non-US participation. Formation of the Interna-
tional Program of Ocean Drilling and such
international advisory workshops as COSOD
(Conference on Scientific Ocean Drilling), ended
the American predominance in drilling advice
and leg cruise participation. Today, ocean
drilling is closely attuned to such international
efforts as Nansen Arctic Drilling, Global Sedi-
mentary Geology, Federation of Digital Seismic
Networks, and InterRidge, the international
ridge-crest research effort. I know of no one
deeply concerned with drilling who has not
applauded the internationalization of what was
once a closely restricted American venture. •
Ralph Moberly's first Oceanographic cruises were
on a US Navy Agor in the North Atlantic in 1952
and 1953. He had been on the Pacific earlier, and
knew it would be warmer. Most of his professional
life has been at the University of Hawaii, in
teaching, in marine geology, and in the frustrating
lower levels of science administration. Participa-
tion on several legs of ocean drilling, on the
Planning Committee of JOIDES, and in the past 25
years' of cabals in dark rooms and at bars gave
him the viewpoint for this article.
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38
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Ocean Drilling Science
For 25 years the Deep Sea Drilling Project and the Ocean Drilling Program have
been the international test-bed of fundamental earth science hypotheses. From the
dynamics of plate tectonics to the composition of ocean crust to the history of ocean
circulation, these scientific drilling programs have provided vital information — actual
samples from the seafloor — to confirm the ideas that have guided our current under-
standing of the earth. Equally important but generally unknown are the many times
when samples of the seafloor provided by drilling have shown that a seismic reflector
was misidentified or that the timing of a proposed sequence of events was wrong,
disproving hypotheses that scientists had formed based on data collected by other
methods. On the following pages, scientists describe some of ocean drilling's research
accomplishments — this volume doesn't provide space for many, many more that are
detailed in the scientific literature and official drilling program reports.
Because sampling in the third dimension, beneath the seafloor, is so obviously a
requirement of earth science and because the long-term continuity of drilling pro-
grams has made them a "given," we are in danger of taking ocean drilling for granted.
If we don't take ocean drilling for granted, its next phase is likely to be more experi-
mental. We envision a program with more than one drillship. One large and very
capable ship would likely stay in one place for long periods of time, drilling the very
deep holes needed to sample the lower crust and thick sedimentary sequences. The
other ship or ships would be engaged in a variety of tasks, some like today's, but with
more emphasis on installing geophysical and geochemical sensors and observatories
on and below the seafloor.
This experimental ocean drilling program will provide the tools for and be more
integrated with other earth science programs. It will drill the necessary seafloor holes
and help greatly to install the seafloor observatories required by InterRIDGE (Interna-
tional program of mid-ocean Ridge Interdisciplinary Global Experiments), the seis-
mometers required by the Ocean Seismic Network, and the drillhole reentry cone
"corks," flowmeters, and other downhole sensors required by geochemists and
hydrologists. The program will provide opportunities for a variety of between-hole
measurements that will broaden our scale of understanding beyond the drill's several-
inch-diameter probe. With the ability to drill deeper and through very thick sedi-
ments, ocean drilling will be able to join with continental drilling to profile the conti-
nental margins as part of scientific drilling programs that are not labeled by the
presence or lack of water overlying the objectives.
— Thomas E. Pyle and Ellen S. Kappel
Pyle and Kappel are Director and Associate Director,
respectively, of the Ocean Drilling Program. They are based at
Joint Oceanographic Institutions Inc. in Washington, DC.
PALEOCEAN-
OGRAPHY
Changes in
climate or
ocean
circulation
will result in
changes in the
types of
sediment that
accumulate on
the seafloor.
Paleoceanography
from a Single Hole
to the Ocean Basins
Through Seismics and Logging
Larry A. Mayer
40
cientific ocean drilling has revolutionized our understanding
of Earth and ocean history. The remarkable results gleaned
from ocean drilling cores have allowed us to begin to piece
together detailed records of the changes in ocean conditions
and climate over the past 40 million years. While we are
constantly improving the temporal resolution at which we can see these
changes (see "Details That Make the Difference," page 45), we are often
frustrated by the limited spatial resolution of our drill holes. Ocean
drilling is expensive and time-consuming; we are often faced with trying
to interpret the climatic and oceanographic history of the ocean basins
from a relatively small number of widely spaced drill holes. To address
this frustration we have called upon remote geophysical techniques
originally developed for oil exploration, including seismic profiling and
downhole logging to attempt to extend the paleoceanographic results of
a single borehole over large areas of the ocean basins.
Seismic Profiling
Seismic profiling is a geophysical technique that allows us to remotely
image subsurface features both on land and at sea. In order to produce a
seismic profile, we generate seismic (elastic, for example, sound) waves
using a variety of sources such as explosives, compressed air, and steam.
When the seismic wave traveling through the earth encounters a rapid
change in the properties of the rocks, some of its energy is returned
(reflected) back to the surface while the remaining energy continues on,
encountering deeper layers. The returned energy is received by a series
of microphonelike devices (geophones on land, hydrophones at sea),
then recorded and displayed both on paper and computers. Seismic
profiling is, in essence, a scaled-up version of the medical ultrasound
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
technique that provides images of a fetus in ntero. For marine work, the
seismic energy source is typically the release of compressed air through a
device known as an airgun, and the receiver is a long (often several
kilometers) array of hydrophones, both of which are towed by the
survey vessel at speeds up to 10 knots. Successive echoes are aligned on
a recorder and the resulting image, the seismic profile, is a continuous
record of subsurface structure that looks very much like a geological
profile; the individual horizons on the seismic profile are referred to as
seismic reflectors.
Historically, seismic profiling has been used in oil exploration to
delineate subsurface geometric relationships (faults and folds in the
rocks) that may trap oil and gas. In the paleoceanographic application of
seismic profiling we are not primarily concerned with the geometry of
the layers; rather, we seek to associate a particular seismic reflector (or
group of reflectors) with a particular paleoclimatic or paleoceanographic
event. Our basic premise is that changes in climate or ocean circulation
will result in changes in the types of sediment that accumulate on the
seafloor — changes that are large enough to cause seismic reflection. For
example, during times of intensified wind circulation (perhaps during
glacial periods), the productivity of ocean waters may change, causing
different planktonic organisms to dominate the surface waters. As the
type of plankton changes, so does the accumulating sediment below
because it is primarily composed of planktonic skeletons. As sediment
composition varies in response to climatic and oceanographic factors, a
series of layers is deposited whose different properties may give rise to
seismic reflections. If we can relate a particular seismic reflector to a
given oceanographic or climatic event (as determined from the study of
drilled cores), we have a means for continuously tracing the event's
spatial distribution.
Sounds Good, But...
While the prospect of tracing oceanographic events by seismic profiling
sounds reasonable, the reality is often not so simple. When we examine
the sediment cores, we find property changes for the most part on scales
of centimeters to tens of centime-
ters. Unfortunately, the seismic
profiling equipment used for deep
sea work generates waves on the
order of meters long that can only
resolve layers of the same dimen-
sion. Also, we measure the varia-
tions in sediment properties in the
drill hole as a function of depth
below the seafloor, but our seismic
records are measured as a function
of the amount of time it takes the
seismic wave to travel to the
subsurface horizon and back
(seismic travel time). If we are
going to relate seismic reflections
to changes found in drillhole cores,
A marine seismic
profiling si/stem. The
research vessel tows the
seismic source (red and
white nirgmi) and
receiving system
(hydrophone array).
Seismic waves travel
thmugJi the water
column into the
seafloor and are
reflected from layers
tliat have relatively
rapid changes in
pin/steal properties. The
echoes are aligned on a
recorder and displayed.
The position of the
seismic reflectors is
measured as a function
of the time it takes the
seismic wave to travel
from the source to the
reflector and back
(seismic travel time).
Oceanus
Winter 1993/94
41
Deep sea
reflectors
appear to be
linked to
continental-
margin
reflectors that
are associated
with major
changes in
global sea
level.
we must find a way to convert seismic travel time into depth below
the seafloor.
Downhole Logging and Seismic Modeling
We can address both of the problems described above using our basic
knowledge of sound-wave propagation to produce a model of the
seismic wave's interaction with the earth. Once generated, a seismic
wave will happily travel along at a speed that is a function of the physi-
cal properties of the material in which it is traveling. Nothing much will
happen to the wave (except that it will gradually lose energy as it gets
farther away from the point where it was generated — this is called
attenuation) until it encounters a rapid change in material properties.
The property that determines the seismic wave's behavior is known as
the "acoustic impedance" or hardness, which is, in turn, a function of the
speed of sound in the material and the saturated bulk density (or weight
per unit volume) of the material. When there is a change in acoustic
impedance, some energy is reflected and some energy continues on; the
amount reflected depends on the abruptness and magnitude of change.
With this knowledge and a little computer wizardry we can model
how a seismic wave that is several meters long will interact with imped-
ance changes that are on the order of centimeters. First we must know
what the acoustic impedance changes are. We can directly measure both
sound speed and bulk density in the laboratory on cores recovered from
the drill hole (and we often do), but this is both time-consuming and
inaccurate because samples measured in the lab do not necessarily have
the same properties as the in situ material. Instead, we use the technique
of downhole logging, which involves lowering specially designed
instruments into the borehole after coring. A wide range of instruments
are available that can make in situ measurements of the properties of the
rock surrounding the borehole, including sound speed and bulk density
(see "Borehole Measurements Beneath the Seafloor," page 129 and
"DSDP/ODP Downhole Measurements in Hole 504B," page 79). Logging
thus provides a nearly continuous record of the changes in sound speed
and bulk density down the length of hole, from which we can easily
calculate changes in acoustic impedance. The sound-speed log has
another benefit. As mentioned before, to figure out where to look for the
changes that cause seismic reflectors, we must first convert seismic travel
time, the amount of time it took for a seismic wave to travel to the
reflector and back, into sub-bottom depth. This can be done if we know
how fast the seismic wave travels through the earth; the depth will be
this measured travel time multiplied by the speed divided by two.
Before we run our model we also must determine exactly what the
seismic wave looks like. We do this by hanging a hydrophone far below
our ship, firing the seismic source, and actually measuring the shape of
the outgoing seismic wave. With a measurement of the downhole
variations in acoustic impedance (from logging) and our measurement of
the seismic wave's shape, we now have all the information we need to
model the interaction of the relatively long seismic wave with the fine-
scale changes in acoustic impedance.
The modeling begins with calculation of a parameter called the
"reflection coefficient," which is the rate of acoustic impedance change.
42
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Acoustic Impedance „ ,. .
Velocity Bulk Density (grams per square centimeter, HeTlection
(meters per second) (grams per cubic centimeter) per second) Coefficient
1400 1600 1800 2000 1 1.25 1.50 1.75 2 1.5 1.9 2.3 2.7 3.1 3.5 -1 -0.6 -0.2 0.2 0.6
0
Seismic Synthetic
Wave Seismogram
1 -20 o 20
Jayne Doucette/WHOI
Then, following millions of multiplications and additions (clearly a job
for a computer), we mathematically move the seismic wave through the
impedance changes. The product of this process (known as convolution)
is a "synthetic seismogram" that, if we have done everything properly,
should represent the fine-scale changes of impedance as filtered, or
smeared out, by the long seismic wave. The synthetic seismogram
should also look something like the actual reflection profile.
Equatorial Pacific Reflectors and
Paleoceanographic Change
Over the past few years we have applied this modeling approach to
several drilling legs in the central, western, and eastern Pacific Ocean. In
our first study, in the deep central equatorial Pacific (DSDP Leg 85), we
identified a number of regionally traceable seismic reflectors ranging in
age from 3 to 22 million years old. By using synthetic seismograms we
showed that most of these reflectors were impedance changes caused by
dissolution of the calcareous component of the sediment as it accumu-
lated on the seafloor. This dissolution was in response to major changes
in deep ocean chemistry and circulation that appear to be linked to
climatic and tectonic events (for example, the closing of the Isthmus of
Panama about 3 million years ago, or the isolation of the Mediterranean Sea
about 6 million years ago). Most intriguingly, these same deep sea reflectors
appear to be linked to continental-margin reflectors that are associated with
major changes in global sea level, indicating a clear connection between
margin and deep sea and continental margin processes.
Having established the ability to use the seismic record to investigate
the deep sea's response to regional and perhaps global oceanographic
and climatic events, we then turned to other areas of the Pacific. On OOP
Leg 130 we found reflectors in the western equatorial Pacific represent-
ing some of the same events we identified in the central Pacific. Here,
however, the reflectors were not caused by dissolution, but instead
Seismic modeling.
These data are from
OOP Site 844 in the
eastern equatorial
Pacific. Downhole
logging is used to make
detailed measurements
of the speed of sound
and the bulk density of
the rocks surrounding
the borehole. These are
combined to calculate
acoustic impedance (or
hardness) and the
reflection coefficient.
The reflection coeffi-
cients are mathemati-
cally combined with a
replica of the seismic
wave produced by the
airgun to produce a
synthetic seismogram.
Oceanus
Winter 1993/94
43
appeared to be related to changes in the sediment's physical properties
resulting from increased bottom-current activity (increased currents
carry away fine material and change the material's bulk density). On
OOP Leg 138 in the eastern equatorial Pacific, we again found several of
the same reflectors, but here some of the reflectors were caused by
changes in bulk density due to massive outpourings of siliceous organ-
isms (diatoms, which represent high productivity) rather than dissolu-
tion or increased currents.
In combining seismic profiling, downhole logging, and seismic
modeling, we are extending the experimental results of discrete
drillholes far beyond the borehole. What we are seeing in the seismic
record is the ocean's response to regional and sometimes global events.
While these reflectors are found in widely diverse regions of the oceans, the
processes responsible for creating them differ from region to region. By
determining the mechanism of reflector formation in each region we can
begin to map, over large areas (and through geologic time), the distribution
of these processes. In this manner, we can piece together a global picture
of the ocean's response to tectonic and climatic change, and further
understand the fundamental workings of the earth-ocean system. •
Larry Mayer has always had a tough time making choices — as a graduate
student at Scripps Institution of Oceanography he couldn't decide between
geophysics and paleoceanography so he ended up with two advisors and tried to
do both (paleogeophysics???). He continues this fence-walking today, and as a
result cannot be considered an expert in either field. He survives by only talking
about geophysics with paleoceanographers and only talking about paleoceanog-
raphy with geophysicists. He is presently the Natural Sciences & Engineering
Research Council Chair in Ocean Mapping at the University of New Brunswick in
Canada where his research deals with sonar imaging and remote classification of
the seafloor. He continues to have strong a interest in the paleoceanography of
the equatorial Pacific, particularly in the midst of a Canadian winter.
In view of the changing focus of Oceanus,
consider the following.
If you are interested in continuing to receive a publication
addressing interdisciplinary oceanography topics, think about
Oceanography magazine, published quarterly by The Oceanography
Society (TOS).
Oceanography exists to promote and chronicle all aspects of
ocean science and its applications. It publishes brief articles, critical
essays, and concise reviews that deal with topics of broad interest to
the ocean science community. Oceanography is an exciting
profession, TOS is its professional society, and Oceanograpliy is its
principal means of communicating.
OCEANOGRAPHY
TOS membership includes a subscription to Oceanography magazine. For further details or for a sample
copy, contact the Society at 1 124 Wivenhoe Way, Virginia Beach, VA 23454; (804)496-8958; fax
(804)496-8960; Oceanography. Society/Omnet.
44
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Details That Make
the Difference
Nick Shackleton and Simon Crowhurst
n studying the oceans, as in studying astronomy, improvements
in data resolution can be crucial to identifying the natural
processes at work. However, in the early years of ocean drilling,
techniques were more profligate even than the Hubble space
telescope in their loss of high-resolution data. Only recently have
improved sediment-recovery techniques realized their full potential for
revealing information about geologically rapid processes recorded in
deep sea sediments.
During the first 15 years of ocean drilling, most sites really were only
"drilled," but the past decade has brought increasing use of two other
techniques: downhole logging and hydraulic piston coring. Logging,
passing sensors down through the hole to examine surrounding sediments,
allows us to learn more about the core sections and is particularly valuable
where sediment recovery is poor. In the upper 200 meters (usually soft,
unconsolidated sediments), drilling too often
brings back homogenized slurries that have lost
all but the largest-scale information about the
sediment. However, advanced piston coring,
which drives the core barrel through the sedi-
ment by hydraulic pressure, yields almost perfect
recovery of soft, unlithified sediments that would
be severely disturbed by rotary drilling. This
technique's potential was first demonstrated
during DSDP's Leg 64 in 1970, when the proto-
type hydraulic piston corer, brought aboard
Glomar Challenger halfway through the cruise,
performed spectacularly well in recovering
laminated sediments in perfect condition at Site
480 in the Gulf of California. No trace of the laminations had been visible in
equivalent material recovered by rotary coring at nearby Site 479. More
recently, similar laminated sediment was recovered from the open ocean at
several of the sites cored during Leg 138 (see photo above), forcing us to
reject the notion that laminated sediments invariably imply deposition in
an anoxic water mass, such as the Gulf of California. Alan Kemp (Uni-
versity of Southampton) and Jack Baldauf (Texas A&M University) have
shown that the laminations at the Leg 138 sites were created by mats of
Laminated diatom ooze
was recovered from
Site 851.
Oceanus
Winter 1993/94
45
1.7
1.6
1.5
1
| 1.5
§ 1.4
.u
J5
3 1.3
I
I
O
1.4
1.3
1.2
A hole
the diatom Thalassiothrix that episodically blanketed the seafloor during
intervals of very high surface productivity, and suppressed bioturbation.
The main thrust of recent paleoceanographic research based on
ocean drilling is investigation of the whole Neogene period (the past 20
million years) with the same degree of detail previously available only for
the late Quaternary (a fraction of the past one million years). The conven-
tional view of earth history holds that high-frequency environmental
variability was confined to the Quaternary, with its characteristic ice-age
cycles, and that variability observed in outcrops
of older rocks was only of local significance. We
are now learning that this was a false picture.
OOP Leg 138, with author Shackleton in the
scientific party, provides just one example of a
drilling leg largely or entirely devoted to high-
resolution paleoceanography. It was, however,
enormously successful in a number of ways,
and the rest of this article focuses on it as a case
study in high-resolution paleoceanography.
Composite
_L
J_
1.5
1.4
1.3
1.5
1.4
1.3
5 10 15 20
Composite Depth (meters)
25
Data from several holes
drilled at one site were
combined to fill in gaps
between cores to
provide a more
complete picture
(composite at bottom)
of the site's
geological history.
Filling in the Blanks:
Gaps in Sediment Cores
Gaps in the sequence of sediments recovered at
many earlier drilling sites were disappointing.
These gaps occur between successive cores as
the drill string is driven further into the sedi-
ment. However, if several holes are drilled
within a few tens of meters of each other, it
should be possible to fill one hole's gaps using
sediment from an adjacent hole, provided that
the gaps in the second hole are vertically offset
from those in the first. All too often, this has not
been successfully achieved. The co-chief scientists on Leg 138, Larry Mayer
(University of New Brunswick) and Nick Pisias (Oregon State University),
made it their prime objective to recover a complete section at each site.
Substantial innovation was required to speed up ship-board analysis
procedures, to be certain that we did not pull pipe and sail away until the
sedimentary section had indeed been fully recovered. As each 9.5-meter
core was recovered, high-resolution GRAPE (Gamma Ray Attenuation
Porosity Evaluator) density, magnetic susceptibility, and color-reflectance
scans were obtained. (GRAPE density and magnetic susceptibility data are
routinely collected, but the digital color scanner was a new device devel-
oped by Alan Mix (Oregon State University) and used for the first time on
Leg 138.) These data, from each of the holes drilled at a site, were compared
to ensure that we had successfully covered every core-to-core gap with
material from another hole. That this was a feasible objective in itself
indicates the pervasiveness of high-frequency lithological variability: We
never recovered sediment so monotonous that we could not recognize and
correlate details.
Sedimentary variations may reflect the impacts of many types of
environmental variability. For example, there is evidence in the high-
resolution data from a late Pliocene section of Site 846 for variability in
46
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
several different components of the climate system: local surface-water
productivity, global ice volume, seafloor dissolution of carbonate, and the
influx of wind-blown dust from adjacent continents. It is also evident
that, although there are similarities between the various records, they are
certainly not identical. For example, we can see major oxygen-isotope
cycles (reflecting global ice volume) spaced at about 2-meter intervals
between 80 and 90 meters in the figure below; we know from work here
and elsewhere that these reflect glacial cycles controlled by changes in
the obliquity of Earth's rotational axis that occur with a regular period of
41,000 years. At the same time, the GRAPE density record shows shorter
cycles about 1 -meter thick (very clear at about 85 meters) that reflect changes
in surface productivity, which controls the diatom concentration in the
sediment. These changes appear to be governed by climatic alternations
linked to astronomical cycles with a period of about 21,000 years. The blue-
band color reflectance shows similar cycles, probably because in this band
calcite is more reflective than biogenic silica (although both calcareous and
siliceous sediments appear white to the human eye). Magnetic susceptibility
arising from the terrigenous dust component of the sediment is higher in the
more reflective (whiter) sediment, suggesting that in the diatom-rich part of
each cycle the terrigenous material is more diluted by the increased flux of
biogenic material to the seafloor.
Subtle quasi-cyclic variations in earth-sun orbital geometry, known
as "Milankovitch cycles" (see page 53) are believed to be largely respon-
sible for Quaternary glacial variability — the "Ice Ages." We are now
learning that these orbital changes also affected climate in earlier times,
and perhaps throughout earth history. Earth's climatic and biological
response to such orbital variations appears to have changed slowly
through geological time, and as it did so, the nature of the signal left in
the sediment also changed. For example, during the last million years, the
waxing and waning of huge polar
ice sheets left a strong isotopic
signal in the chemistry of sedi-
ments over large areas of the
world's oceans. Studies of sedi-
ments recovered on Leg 138 show
that during the last 20 million
years, changes in regional biologi-
cal productivity, probably related
to wind strength, were well marked
even when the oxygen-isotope
variations were small and irregular.
Calibrating the Geological
Time Scale
Once we recognize that cyclic
signals represent the response of
climate and ocean circulation to
variations in Earth's orbital geom-
etry, we can use them to accurately so
calibrate the geological time scale.
The Milankovitch astronomical
Major cycles that
reflect global ice
volume are evident at
about 2-meter intervals
in these portions of
oxygen isotope,
GRAPE density,
magnetic susceptibil-
ity, and color reflec-
tance records from Site
846. The shorter cycles
clearly present in the
density record, and
visible to a lesser
degree in the reflec-
tance data, indicate
changes in surface
productivity.
s
en
i \
S -v
40 <=?
2 01
30 £
1
1
I
1.4 $18
SI
0) ;Q 10
•
85 90 95
Composite Depth (meters)
100
Oceanus
Winter 1993/94
47
2.4
2.5
2.6
2.7 2.8 2.9 3.0
Age (millions of years)
3.1
3.2
GRAPE density
records from Sites 849
and 851 shoiv
remarkable correlation
with orbital
calculations (red line)
for the period from 4 to
3 million \/ears ago.
cycles have been calculated for the past 10 million years by Andre Berger
and Marie-France Loutre (Institut d' Astronomic et de Geophysique G
Lemaitre, Universite Catholique de Louvain), and more approximate
calculations can be made for 100 million years into the geological past.
The figure below plots portions of GRAPE density variation data from
two sites against calculated orbital variations. We have calibrated orbital
variations for the whole of the past 6 million years (back to the latest
Miocene), and we have also made detailed correlations between all the
sites drilled, by matching GRAPE
density cycles back through more
than 10 million years. Since Fritz
Hilgen (Institute of Earth Sci-
ences, Utrecht) and his colleagues
have independently calibrated
cycles in Pliocene sediments
exposed in southern Italy with
astronomical cycles, this means
not only that the last 6 million
years of earth history are cali-
brated with a precision approach-
ing a few thousand years, but also
that each lithological cycle
observed in southern Italy can be
uniquely associated with a
particular cycle in the sediments
of the equatorial Pacific, a truly
astonishing match across time and distance.
This in turn permits exploration of climate-change mechanisms, and
the ocean's response to external forcing. Understanding these processes
is essential for developing and testing computer models of Earth's
climate system, including models intended to predict climatic response
to human activities such as carbon-dioxide production. Equally impor-
tant, a true calibration of the rates of climate change, biological evolu-
tionary change, sea-level change, and so on, are crucial to our under-
standing the geological record. The high-resolution records recovered by
ocean drilling are making enormous contributions in paleoclimatology,
paleoceanography, and many other aspects of geology- •
Nick Shackleton transmuted his early interest in the physics of sound into
paleoclimatology, and with John Imbrie and Jim Hays he published the 1976
paper "Variations in the Earth's Orbit — Pacemaker of the Ice Ages, " which is
widely regarded as having provided the first conclusive evidence that the
Milankovitch orbital variations were responsible for major climatic change in the
geological past. He is Director of the Subdepartment of Quaternary Research,
Cambridge University, UK. His recent research focuses on improving the
resolution of geological time scales and clarifying the interaction of climate-
related processes in the Neogene. He has also managed to pursue a keen
interest in collecting and playing clarinets.
Simon Crowhurst worked for a Cambridge, UK. company making industrial robots
before moving to the Godwin Laboratory four years ago to become a research
technician working with Professor Shackleton on the astronomical "tuning" of
data from ocean cores.
48
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Early History of
the Oceans
Hugh C. Jenkyns
ince ocean crust is created by seafloor spreading and de-
stroyed by subduction, the sedimentary record of ancient
oceans can only be found as far back as the Jurassic (about
170 million years ago) by drilling into the oldest parts of the
oceans themselves. Continents, however, are potentially
immortal and drilling into their margins may reveal older sedimentary
rocks. As a counterpoint to these studies, sediments and fossils exposed
on land but formed in oceans or their margins can be investigated by the
geologist. Such rocks typically occur in mountain chains formed where
continents have collided and fragments of all-but-vanished oceans have
been preserved. Clues to the history of ancient oceans can be gleaned
from studying all these different types of evidence, but the record is
tantalizingly incomplete and interpretations are often tentative.
The Triassic Tethys
In the latter part of the 19th century, European geologists realized that
certain marine sedimentary rocks and fossils found in the Himalayas and
East Indies were identical to those already known and documented from
Alpine Triassic
Outcrops
Site of Leg 112
drilling
View of the late
Triassic world,
indicating the areas
where Tethyan
sediments and fossils
are found. The shaded
area indicates the
possible extent of the
ancient Tethyan
seaway during the
latest part of the
Triassic period.
Drilling during ODP
Leg 122 off northwest
Australia found
limestones and fossils
identical with then-
Alpine counterparts.
Oceanus
Winter 1993/94
49
Site
of Leg 44
Drilling
View of the Late
Jurassic world,
indicating the
suggested geometry of
the Tethyan Ocean in
the Alpine-
Mediterranean region
and showing its
connection to the proto-
Atlantic (green-shaded
areas). Shallow-water
banks, like the present-
day Bahamas, bordered
both these oceans (tan-
shaded areas).
Although the oldest
shallow-water
limestones drilled by
DSDP/ODP in the
Blake Plateau-Bahama
complex are Cretaceous
in age, similar
environments existed
during the Jurassic.
the Alps. Most of these were
dated as Triassic in age (about 210
million years old) and were
interpreted as deposited in a peri-
equatorial seaway that girdled
half the Earth, along whose length
faunas could freely migrate. This
seaway was named "Tethys,"
after the sister and consort of
Oceanus, god of the sea, in Greek
mythology. Examination of the
assumed pattern of continents
and oceans during the Triassic
Period shows how this ancient
seaway must have stretched from
southern Europe and northern
Africa across India to lands
farther east. Just how much
farther east was revealed on ODP
Leg 122, which cored Triassic
sediments off northwest Austra-
lia. These, the oldest sediments
cored by ODP, include white limestones of shallow-water origin, rich in
sponges, mollusks and corals, that are indistinguishable from those
found in Austria, northern Italy, and Sicily. Indeed these fossils would
not be out of place in a museum in Vienna. A snapshot of the latest
Triassic world would reveal a discontinuous band of reefs and tropical
carbonate sediments running approximately east-west for thousands of
kilometers.
The Jurassic Atlantic
The story of Tethys continues with the revelation that Jurassic sediments
cored in the easternmost and westernmost Atlantic are similar to those
found in the Alpine-Mediterranean domain and locally in the
Himalayas. First cored on DSDP Leg 11, and subsequently on Legs 41,
44, 50, 76, and 79, upper Jurassic sediments (about 155 million years old)
include characteristic red nodular limestones and light-colored chalks
that could equally derive from outcrops in Austria, Spain, or Italy.
Essentially, this discovery meant that the Tethys must have continued
westward along the proto-Atlantic into the Caribbean. Indeed the sedimen-
tary history of the early Atlantic Ocean and its margins provide an exact
analog for the evolution of the Tethys. The Blake Plateau and the Bahama
Bank complex, for example, drilled on DSDP Leg 44 and ODP Leg 101, have
their counterparts in the limestone mountains of Italy, Croatia, and Greece.
The Jurassic Pacific
Two DSDP legs, 61 and 89, were dedicated to finding the oldest crust
and sediment in the Pacific before these elusive rocks were finally found.
The early attempts were frustrated by the presence of Cretaceous basalt
that blankets much of the older Pacific Plate. (More of this anon.) Unlike
the Atlantic's Jurassic sediments, deposited when that ocean was small and
50
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
narrow, deposits of equal age in the Pacific were laid down in a super-ocean
that covered half the globe. The nature of the Pacific Jurassic was finally
revealed on Leg 129. Unlike the Atlantic, whose Jurassic sediments are
dominated by the skeletal remains of calcareous plankton, the coeval Pacific
record of 160 to 150 million years ago shows clay and siliceous microfossils
deposited in depths below which calcium carbonate could not be preserved.
Vividly red-brown in color, the silica-rich and clay-rich layers alternate,
probably in accordance with astronomically influenced climatic changes
that affected the fertility of the surface waters and hence plankton produc-
tivity over intervals of tens to hundreds of thousands of years.
The Cretaceous of the World Ocean
The Cretaceous has been cored in many places across the world ocean,
and our knowledge of the paleoceanography of this period is commensu-
rately greater than that of the Jurassic. Two aspects of Cretaceous oceanic
geology are of particular significance. The first takes us back to Leg 61,
the first scientific cruise that tried unsuccessfully to find the Jurassic of
the Pacific Ocean. What was incidentally revealed was the presence of
voluminous flows and intrusions of basalt across much of the Cretaceous
Pacific Plate, associated with such submarine volcanic edifices as sea-
mounts and plateaus. A further discovery of this leg, echoing findings of
Legs 17 and 33, was the presence of redeposited shallow-water microfos-
sils of Caribbean affinity in deep-sea sands. The episode of seamount-
building volcanism must have provided atoll-like stepping stones that
facilitated westward migration of these reef-associated faunas during the
Late Cretaceous (65 to 80 million years ago). Subsequent studies show
that this migration route was used by other shallow-water fossil groups.
Caribbean faunas penetrated as far west as the Middle East, while the
Atlantic apparently remained an insuperable barrier.
View of the Cretaceous
Pacific, indicating the
presence of volcanic
pedestals or stepping
stones across which
reef-associated faunas
could migrate west-
wards from the Carib-
bean. Numbers refer to
drilling sites where
redeposited shallow-
water faunas of
Caribbean affinity have
been found in deep-sea
sands. Arrows indicate
areas where these
faunas are known from
outcrops on land. In
tectonic terms, the
ancestral Pacific was
made up of the Pacific
and Farallon plates and
several others.
Oceanus
Winter 1993 /94
51
Location of carbon-rich
black shales from
numbered DSDP and
OOP sites restored to
their position some 90
million years ago (late
Cretaceous) and from
outcrops on land. All
shales are of identical
age, dated exactly at 93
million years ago, and
probably record a
period of elevated
plankton productivity
operating on a
global scale.
It has been suggested that the profuse volcanic activity characteristic
of the Cretaceous globe would have increased the content of atmospheric
carbon dioxide, thereby increasing global temperatures. One effect
would have been a decrease in the amount of oxygen dissolved in
marine waters, which could have helped preserve planktonic organic
matter in marine sediments by protecting it from oxidation. Is there
evidence for burial of anomalously large amounts of organic matter in
Cretaceous oceans? The answer is yes, but higher global temperatures
are but one of the mechanisms used
to explain this phenomenon.
Cretaceous carbon-rich black
shales were cored in the Atlantic
during DSDP Leg 1 as well as
during several subsequent legs in
the same ocean. As long as these
carbon-rich black shales were seen
as a uniquely Atlantic phenomenon
they could be viewed as the product
of a relatively narrow and restricted
ocean, possibly stagnant and
oxygen-depleted like the present-
day Black Sea. But during Legs 32,
33, and 62, such sediments were
cored on topographic highs in the
ancestral Pacific super-ocean.
Moreover, detailed dating of these
sediments from all oceans, and from outcrops on land, showed that they
were confined to discrete intervals of geological time, for example, about
120 and 93 million years ago. The balance has now swung to investigat-
ing anomalously high rates of plankton productivity as the proximal
cause of these black shale "events." But what caused the elevated pro-
ductivity? There are no definite answers yet, but if the ocean-atmosphere
system is in steady state, one response to the production of excessive
amounts of volcanogenic carbon dioxide could be to fix it as organic
carbon in marine sediments. That most of the world's petroleum source
rocks were formed during this period spotlights the economic impor-
tance of understanding the processes involved. •
Hugh Jenkyns did his thesis work on deep-sea Mesozoic carbonates in Sicily
from 1966 to 1969, working close to the village of Corleone. and has since seen
the area depicted in a number of well-known movies. He was almost blown up in
Palermo only once. He then went to the University of Basel in Switzerland,
followed by a two-year spell at Oxford, but continued his love affair with Italy,
particularly the less turbulent north Alpine region. The fact that the sediments
exposed there were similar to those cored in the Atlantic introduced him to the
Deep Sea Drilling Project, and he has since participated in three Pacific legs. He
taught at the universities of Cambridge and Durham before returning to Oxford in
1977, where he has remained ever since.
52
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
The Central
Mystery of the
Quaternary Ice Age
A View From the South Pacific
Wolfgang Berger, Torsten Bickert, Eystein Jansen,
Gerold Wefer, and Memorie Yasuda
e live in an ice age: current sea level is some 70 meters
below where it would be if the polar regions were
warm. However, we live in a warm interval of this ice
age — sea level is 120 meters higher than it was at the
last glacial maximum 20,000 years ago. As large
continental ice sheets wax and wane in the Northern Hemisphere, sea
level fluctuates. Water locked in the ice is depleted in heavy stable
isotopes of both hydrogen and oxygen; thus, a buildup of ice enriches the
ocean's water with oxygen- 18 relative to oxygen- 16. The enrichment (and
its cancellation during melting) can be measured as changes in oxygen
isotope ratios within the calceous shells of marine organisms (as shown by
University of Miami paleontologist-physicist Cesare Emiliani in 1955).
Certain planktonic foraminifera are well suited as recorders of
isotopic ratios. However, in addition to recording the ice budget, the
oxygen-18 to oxygen-16 ratio of their shells reflects changes of surface water
temperatures. The best places to obtain unadulterated records of ice mass,
therefore, are tropical regions that show little change in temperature from
glacial maxima to glacial minima. Such a place is the Ontong Java Plateau in
the western equatorial Pacific. The plateau is roughly the size of Texas and
rises from the surrounding abyss to 1 .6 kilometers below the water surface;
it accumulates well-preserved shells of foraminifers.
The Ice Age Record from the Ontong Java Plateau
Five cores collected on OOP Leg 130 (in 1990) at Site 806 provide an
excellent record of ice-mass fluctuations over the last two million years
(the Quaternary period). We base our interpretation of this record on the
theory of the Serbian astronomer Milutin Milankovitch (1879- 1958). He
proposed that periodic changes in the tilt of Earth's axis and in the
Five cores
collected on
ODP Leg 130
provide an
excellent record
of ice-mass
fluctuations
over the last
two million
years.
Oceanus
Winter 1993/94
53
40
Hess Rise
20C
Oc
20C
o —
Ontong Java
Plateau
Magellan
Rise
Manihiki
Rise
140°
160°
180
Location of Ontong
Java Plateau where Site
806 was drilled. The
plateau is one of the
great basaltic edifices in
the western Pacific
created by enormous
volcanic outpourings in
the Mesozoic.
eccentricity (deviation from a circle) of Earth's orbit translate into
growth and decay of ice mass through changes in summer insolation
(the amount of sunlight reaching Earth's surface) in high northern
latitudes (say, at 65°N). The formulation and step-wise confirmation of
the Milankovitch theory is one of the great scientific success stories of
our century (see Nicklas G. Pisias and John Imbrie, Oceanus, 29:4, 1987). In
essence, the theory solves the mystery of why ice ages occur in cycles. The
study of deep-sea sediments (and especially of oxygen isotopes) was of
crucial importance in this context.
There is evidence in the Site 806 oxygen-isotope
record for ice-mass control by both eccentricity and
obliquity (figure opposite). Three subdivisions regarding
climatic state are readily distinguished. The oldest third
is dominated by 41,000-year axial-tilt cycles, the young-
est third by roughly 100,000-year eccentricity-related
cycles. The central third shows the transition from one
regime to the other. The three regimes are labeled
"Milankovitch" chron, "Croll" chron, and "Laplace"
chron after the scientists who introduced the fundamen-
tal ideas underlying orbital dating. The Scot James Croll
made the first attempt at template-dating of ice ages,
while French astronomer Pierre Simon de Laplace's
calculations provided a firm base for celestial mechanics,
which allow extrapolation of orbital conditions into the
distant past. Boundaries between the chrons are set
according to the strength of the eccentricity cycle present.
For simplicity, they are put precisely at the crests of
obliquity-driven cycles 15, 30, and 45. The single most
striking feature of the Site 806 ice-mass record (beyond the cyclicity itself) is that
the nature of the cyclicity changes at the center of the Quaternary, about
900,000 years ago. We call this the "Mid-Pleistocene Revolution" (MPR).
An Orbital Template for the Ontong Java Plateau
Can simulation of the ice-record from orbital data help us understand
the nature of the mid-Pleistocene climate shift? An early attempt to
provide a match between target and template using data from the
Ontong Java Plateau (by science journalist Nigel Calder, in 1974, with
data from Nick J. Shackleton of Cambridge University and Neil D.
Opdyke of Lamont-Doherty Geological Observatory) provided a good
match back to about 600,000 years. We repeated the exercise using the
longer (and less disturbed) oxygen-isotope record of Site 806, and a more
efficient template-making model.
To generate the template we use the July insolation at 65°N, follow-
ing the arguments of Milankovitch. Also, heeding his advice that cold
winters do not necessarily have more snow than warm ones, we assume
the same potential ice-growth year after year, regardless of the seasonal
insolation distribution. The change in sea level at any time is then
provided by the difference between steady ice growth and insolation-
dependent melting. The record indicates that strong melting events
follow maximum buildup. This effect can be achieved in the model by
introducing negative feedback on ice growth in such a fashion that it
160C
54
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Mid-Pleistocene Revolution
47 ODP806B
77
Brunhes-Matuyama Boundary
Croll LaPlace
i i i
0 200 400 600 800 1,000 1,200 1,400 1,600 1,800 2,000
Age (thousands of years)
becomes important only when large ice masses are present for some
considerable time, and when insolation values are high.
The transform algorithm resulting from fitting the last 300,000 years
(figure below) is next used to "postdict" the record for the million years
preceding 300,000 years. Although some ill-fitting portions remain, the
quality of the match is remarkable.
Oxygen isotope record
of the planktonic
foraminifer
Globigerinoides
sacculifer at Site 806
(top curve). Numbers
are isotope stages.
Middle and bottom
curves are cycles
extracted by Fourier
expansion of the record,
centered on 41, ,000-year
and 100,000-year
periods, respectively.
TJie right-hand orange
line shows the mid-
Pleistocene Revolution
and the left-hand orange
line the Brunhes-
Matuyama boundary.
See text for tripartite
subdivision.
Nature of the Climate Shift
at 900,000 Years
One striking result of the template
matching is that the fit between
template and record is no longer
very good before the time of the
climate shift: The rules of response
have changed. The decisive
change 900,000 years ago is the
buildup of "surplus" ice, as is
evident from comparing template
and record. Apparently it is this
additional ice (about 15 percent of
the total active ice mass) that turns
on the mechanisms responsible for
the change in response.
The expansion of the maximum
ice mass has two opposing effects:
1) It provokes additional cooling,
thus stabilizing glacial conditions,
so that little ice is removed except
during periods of extreme summer
insolation; and 2) the expansion
increases instability by building ice
on marine shelves and thus provid-
ing the potential for inland inva-
sion of seawater below ice, when
Input
50 100 150 200 250 300 350
Age (thousands of years)
400
Tuning the transform algorithm by minimizing the
mismatch of template and target. Here the template is built
from a model using input calculated by astronomers Andre
Berger and M.F. Loutre. The target is the record of
806B-1H. The model is given by the equation
ASL = -IGR + INS" • ICE" - MEMC, which describes sea-
level change (ASL) as a function of constant ice growth
(IGR) opposed by melting, with variable insolation (INS),
ice mass (ICE), and average ice mass over the last 40,000
years (MEM). Calculations are in normalized space (0 to
1). IGR is set to 0.14, and exponents are set to 3, 2, and 2,
for a good fit to the last 300,000 years.
Oceanus
Winter 1993/94
55
Comparison of orbital
templates (based on the
fit shown in the figure
at the bottom of page
55) and isotope record
of 806B, for the time
span from 300,000 to
1,300, 000 years ago.
Note the distinct misfit
appearing before the
mid-Pleistocene climate
shift.
Brunhes-Matuyama Boundary
13
-1.5
Mid-Pleistocene Revolution
i i I I i
300 400 500
600 700 800 900 1,000
Age (thousands of years)
1,100 1,200 1,300
sea level rises. The process called "marine downdraw/' which involves
collapse of marine-based ice-sheets (for example, on the Barents Sea
shelf) is thought to be of special importance. In addition, increased
pressure at the bottom of an ice cap favors melting after maximum ice
buildup.
Increased maximum ice mass is not the only change at the Mid-
Pleistocene Revolution event. Melting tends to go further after the shift
than before it. The role of the ocean in providing heat to high latitudes
during deglacial and interglacial times may be crucial in prolonging inter-
glacials and making them more extreme. From piston cores we know that
periods of strong heat influx to the arctic realm are characterized by high
foraminifer content in Norwegian Sea sediments. Deep drilling on the
Voring Plateau has shown that the onset of strong pulses of foraminifer
accumulation coincides with the MPR event 900,000 years ago.
We do not know exactly why buildup of "surplus" ice and pulsed
northern heat delivery are coupled and why they were initiated some
900,000 years ago. Many processes must be considered in addition to those
mentioned above: changes in North Atlantic Deep Water formation (and the
possible influence of Mediterranean outflow and bottom water production
in the Barents Sea), effects on atmospheric carbon dioxide from greatly
accelerated growth of the Great Barrier Reef during interglacials of the
Milankovitch chron, uplift of mountain ranges from erosion and tectonic
forces, and volcanism. Given these complexities, it is likely that the mid-
Quaternary climate shift shall remain a mystery yet for some time. •
Among many scientific honors, Wolf Berger received the Bigelow Medal in
Oceanography from WHOI in 1979. He obtained his Ph.D. from the Scripps
Institution of Oceanography (SIO), University of California, San Diego, in 1968.
Finding that opportunities for interaction with the ocean are abundant and
pleasurable in La Jolla, he has stayed on since, except for (sometimes extended)
visits to the old country. Graduate student Memorie Yasuda helps hold the fort at
the SIO Foram Lab during such visits. Eystein Jansen studies ice-age history at
the University of Bergen, ready to clear his office should the ice advance again.
Gerold Wefer heads the marine geology group at Bremen University, of which
Torsten Bickert is a member. All the authors are indebted to Monika Segl, who is
in charge of the isotope laboratory in Bremen.
56
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
From the
Greenhouse
to the Icehouse
A Southern Ocean Perspective
of Paleogene Climate
James C. Zachos
lomar Challenger's retirement in 1983 marked the end of a
highly successful 15-year international scientific drilling
program that radically altered our understanding of the
geologic and climatic evolution of the oceans. Among the
many achievements was a new understanding of the early
Cenozoic period of climate change known as the Paleogene era, which is
further subdivided into three epochs, the Paleocene (57 to 65 million years
ago), Eocene (35 to 57 million years ago), and Oligocene (25 to 35 million
years ago). Paleontological and geochemical investigations of deep sea cores
revealed that the Paleogene was a time of dramatic earth climate transition
from warm, equable conditions of the "hothouse" or "greenhouse" mode,
to cooler, glacial-like conditions of the "icehouse mode." Although the
"greenhouse" mode prevailed during much of the Paleocene and early
Eocene, the warmest conditions
existed during the early Eocene,
some 55 million years ago.
Temperatures of the deep sea at
that time were some 10°C warmer
than the present, as were tempera-
tures of higher latitude surface
waters, which were inhabited mainly
by warm-water species of marine
plankton. The warmer conditions
found in marine environments
seemed to conform with reconstruc-
tions of climate on the continents,
where high-latitude regions were
inhabited by temperate to subtropical
species of vertebrates and plants, such
Huge tabular icebergs
float in the Southern
Ocean. This one was
photographed along the
Antarctic peninsula.
Oceanus
Winter 1993/94
57
Locations of ODP drill
sites near Antarctica.
Drilling at many of the
sites penetrated
sediments deposited
during the early
Paleogene (60 million
i/ears ago).
as alligators and palms. This episode
of early Eocene global warmth
lasted for several million years
before the onset of cooling and a 20-
to-30-million-year gradual transition
to the "icehouse" mode. By Oli-
gocene time, polar regions had
cooled substantially, although it
remained unclear whether or not ice
sheets had existed.
As the details of this global-
climate transformation emerged in
the late 1970s, it began to draw the
attention of paleoclimatologists
who wondered why Earth's
climate changed as it did. Was the
early Eocene warmer and the
Oligocene cooler because of a
decline in the concentration of
atmospheric carbon dioxide, a
greenhouse gas, or were other
factors responsible, such as rear-
rangement of oceanic passages and
currents by slowly drifting continents? These questions grew in impor-
tance, especially with concern increasing over the future climatic impact
of recent high carbon-dioxide levels. However, despite the great interest,
the questions remained unanswered, partly because many critical details
about the character of the Paleogene climate were still vague. In particu-
lar, the absence of sediment cores from the climatically sensitive high
latitudes had left a crucial gap in the paleoclimatic record. Attempts to
obtain deep sea sediments from polar regions during the initial drilling
program were limited by persistent harsh, icy weather. As a result, little was
learned about the pre-Pleistocene climate history of the high-latitude oceans.
A New Perspective From the Bottom:
Southern Ocean Paleoceanography
In 1985, with the initiation ofJOIDES Resolution and the second phase of
scientific drilling, scientists gained the capacity to drill in some of the
more remote and inhospitable reaches of the world oceans, including the
polar oceans. One immediate regional target was the Southern Ocean,
where nearly 10 kilometers of sediment were recovered at more than 25
sites during four legs of drilling (Legs 113, 114, 119, and 120). In the years
since, shore-based investigations of these cores have provided new
insight into the Paleogene climate. Some of these findings are beginning
to have profound effects on our understanding of the forces that altered
Paleogene climate, as well as on climate-change dynamics in general.
Long- and Short-Term Warming in the Eocene
One of the more unexpected findings from high-latitude drilling resulted
from high-resolution geochemical and paleontologic investigations of
cores recovered from atop Maud Rise, and later Kerguelen Plateau,
58
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
which revealed that the long-term climatic transitions were much more
complicated than previously recognized. In reconstructing the sea-
surface temperature records from the late Paleocene to the early Eocene,
geologists found that Southern Ocean sea-surface temperatures (SST)
first warmed from 4°C to 5°C, from 59 to 55 million years ago, reached a
maximum of 14°C to 16°C in the early Eocene, and then began to decline.
This was expected since the already available record of deep ocean
temperature showed a similar trend.
A completely unforeseen result was the discovery of a brief but
exceptional episode of high-latitude and deep-ocean warming midway
through the longer-term trend, near the end of the Paleocene at roughly
57 million years ago. This unprecedented "event" was marked by an
abrupt (less than 10,000 years) increase in high-latitude Southern Ocean SST
with peak values in excess of 20°C, and deep sea temperatures as high as
16°C, conditions that were sustained for only a few tens of thousands of
years. Moreover, this abrupt warm episode coincided with the demise of
many species of bottom-dwelling, deep sea organisms, as well as increases
in rainfall and chemical weathering rates on the antarctic continent.
Region
Ross Sea
Marie
Byrd
Land
Weddell
Sea
Prydz Bay
Kerguelen
Plateau
Site
DSDP
270
MSSTS-1
CIROS-1
Mt.
Petras
OOP
693
OOP
739
OOP
742
OOP
738
OOP
744
OOP
748
Latitude
77°S
78°S
77°S
76°S
71°S
67°S
67°S
63°S
62°S
58°S
Present Ice Volume
(percent)
0 50 100 150 200
20-
25-
30-
B
^35-
c
•2 40-
45-
Oi
Di
50-
55-
60 -I
Intervals sampled
Mo glacial sediments
IGlacial/Glaciomarine
Well documented
IGlacial/Glaciomarine
Deposits of Uncertain Age
Calculated -1
Temperature
(Ice-Free)
60
10
15
Disconformity
Hyaloclastite
Bottom Water Temperature (°C)
Jack Cook/WHOI Graphics
Rock debris deposited by ice sheets as "glacinl till" is very distinct, mid thus serves as the most direct
evidence of continental glaciations. This figure shows the age range and location of ice-rafted debris
recovered from sites on and around Antarctica. The red area represents deposits whose exact age is uncer-
tain. Many shallow and some deep sites show significant accumulation of ice-rafted debris throughout the
Oligocene, indicating widespread glaciation. An indirect measure of ice-volume is obtained by reconstruct-
ing changes over time in seawater's mean oxygen-isotopic composition, which is sensitive to changes in
global ice volume. Although this method provides only the lower limit on ice volume, it is currently the
only semi-quantitative means to estimate ancient ice volume. The record shows that global ice volume was
roughly 50 percent of present day volume by the earliest Oligocene.
Ocecinus
Winter 1993/94
59
Until high-
latitude
drilling began,
timing of
antarctic
glaciation was
an extremely
controversial
subject.
Discovery of this short-term event immediately prompted several
reinvestigations of other pelagic sequences from all ocean basins that
eventually proved the event was global in scale.
The Onset of Antarctic Glaciation
In addition to documenting early Eocene global warming, the Southern
Ocean investigations also provided critical evidence on the magnitude
and timing of subsequent high-latitude cooling and continental glacia-
tion. SST reconstructions showed a long-term, 8°C gradual cooling of the
Southern Ocean over the middle and late Eocene from about 54 to 36
million years ago. As observed during the late Paleocene-early Eocene
warming trend, a number of more abrupt steps were found in the
record, times when Southern Ocean temperatures appeared to decrease
rapidly in tens of thousands of years. Several short-term excursions
toward warmer conditions — reversals of the long-term cooling trend-
were also noted in the middle and late Eocene.
By the late Eocene and early Oligocene, high-latitude climate had
cooled sufficiently that conditions seemed frigid enough for continental
glaciation. However, until high-latitude drilling began, timing of antarc-
tic glaciation was an extremely controversial subject, with many geolo-
gists doubting the existence of continental ice sheets on Antarctica prior
to the middle Miocene, some 15 million years ago. This perception was
based mainly on the lack of significant physical evidence for earlier
glacial activity. As a result of Antarctic drilling, however, it became
evident that ice sheets were present on Antarctica as long ago as the
earliest Oligocene. Thick sequences of glacially deposited debris found
in Prydz Bay, together with similar deposits found earlier in McMurdo
Sound on the opposite side of the continent, indicated widespread
glacial activity, not atypical of continental ice sheets. Some of the oldest
glacial sediments, however, were deposited in the late Eocene, suggest-
ing that the very first ice sheets, albeit small, formed nearly 40 million
years ago. Thus, it appears that glacial activity was limited regionally to
portions of east Antarctica until about the earliest Oligocene (about 35
million years ago) when ice rafting became more widespread with
occurrences even in distant offshore locations, indicating a permanent
transition to full-scale continental glaciation.
Additional evidence for these continental ice sheets has come from
oxygen-isotope geochemistry. This technique is based on the observation
that the ratio of two naturally occurring isotopes of oxygen, ]-O:lhO, is
higher in ocean water than in ice sheets. The difference results from
evaporation and condensation because these processes transfer relatively
more 16O-enriched water into precipitation, including snow. During
glaciations enough of this lbO water is locked up in ice sheets to increase
the 18O:lbO ratio of water remaining in the ocean.
Because changes in the ratio of seawater lsO:lhO are imprinted in the
calcareous shells of microscopic marine organisms, past variations in
global ice volume can be reconstructed by measuring fossil shells from
sediments of different ages. Analyses of microfossils from early Oli-
gocene sediments deposited at roughly the same time as the glacial
debris in Antarctica and the Southern Ocean yielded high 18O:lbO ratios
for seawater, indicative of large ice sheets, by at least 35 million years
60
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
ago. This is tens of millions of years earlier than previously thought.
Moreover, the oxygen-isotope records indicate that the ice sheets formed
very suddenly, and briefly attained volumes close to those of present day
ice sheets, before settling into a smaller, but more stable configuration.
Rapid Transitions and Transient Climates:
Ramifications of Global Change
Not surprisingly, these recent discoveries of more rapid, and sometimes
brief, excursions in early Cenozoic climate have influenced thinking
about climatic driving forces. Can large-scale climate-forcing mecha-
nisms behave episodically? For example, can carbon-dioxide outgassing
due to volcanic activity along subducting margins or at mid-ocean ridges
increase rapidly enough to produce the kind of abrupt, episodic warm-
ing that occurred near the Paleocene/ Eocene boundary? Or does the
global climate system respond episodically to gradual forcing due to the
existence of physical thresholds in the climate continuum?
Some climatologists have suggested that even with gradual changes
in boundary conditions, the ocean /atmosphere system is capable of
shifting rapidly between two equilibrium modes, and in the process may
temporarily overshoot equilibrium with the help of physical and chemi-
cal feedbacks in the ocean /atmo-
sphere system. While there are many
potential feedbacks, the exact
source(s) of such nonlinear behavior
in the climate system remains un-
clear. Nevertheless, these past excur-
sions in global climate illustrate that
climatic processes and forcing mecha-
nisms can sometimes behave in
unexpected ways. Although the
Paleogene excursions were long by
human time scales, such feedback-
driven instability might exist at a
variety of time scales, including the
human. At the very least, the Paleo-
gene climate excursions should serve
as reminders of the climate system's
J
unpredictable nature. •
James Zachos is an Assistant Professor
of Earth Sciences at the University of
California, Santa Cruz. After obtaining his
Ph. D. in oceanography from the University
of Rhode Island in 1988. he spent four
productive years at the University of
Michigan before realizing that Ann Arbor
is very far from the ocean. His current
research interests range from early
Cenozoic paleoceanography to horse
diets.
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Oceanus
Winter 1993/94
Bipolar distribution of
ice shields during the
last glacial maximum.
The drilling programs
have collected cores in
high southern and
northern latitudes for
studies of these
conditions.
The Challenge of
High-Latitude
Deep Sea Drilling
Jorn Thiede
ontrary to all older glacial episodes in earth history, the
most recent development of cold polar climate was bipolar
because of the peculiar Cenozoic plate tectonic subdivision
of Earth's crust into relatively small ocean basins and
continents. This ultimately resulted in an isolated conti-
nent over the South Pole, and a very restricted ocean basin over the
North Pole. To learn more about these conditions, the deep sea drilling
programs have collected cores in high southern and northern latitudes.
The technique for drilling in ice-infested, high-latitude waters was first
proven in the Southern Ocean on DSDP Leg 28. Since then, several DSDP
and OOP legs have been devoted to unraveling the exciting story of
the onset of Southern Hemisphere glaciations as early as Eocene/
Oligocene times (see "From the Greenhouse to the Icehouse," page
57). In several instances the drill vessel required the assistance of
ice picket (patrol) boats. The rather dry Initial Reports published
do not reflect the reality of the harsh Southern Ocean environ-
ment— only by unearthing the "gray operational reports" can
one read the stories of picket boats being "towed" by the icy
giants and the dramatic experiences of scientists and crews
during fierce storms and near-encounters with icebergs,
either of which could force the drill ships to abandon sites.
Jayne Doucette/WHOI Graphics
62
The Arctic Challenge
Giant floating ice fields keep the surface of the Arctic Ocean
in constant motion, gyrating clockwise around a hidden
western center (the Beaufort gyre), and moving straight
across the eastern Arctic Ocean (transpolar drift) along a
strange, narrow structural feature, the Lomonosov Ridge,
between the Siberian and Canadian continental margins. It is
only here that the world ocean reaches true high latitudes and
its sediments hide the history of the most poorly known element
of the global paleoenvironment's evolution. Sea ice is most
common here, with icebergs as rare exceptions. The ice here is
young because of the high, seasonally dependent rate of melting and
freezing, and it is, therefore, not thick (generally only 3 to 5 meters). But
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
it is hard and dense, so that most platforms available to scientific deep-
sea drilling cannot penetrate it. The presence and movements of the ice
cover have prevented collection of any long, stratigraphically undis-
turbed sediment sequences or underlying basement rocks. Therefore we
know less about the Arctic Ocean's plate-tectonic and environmental
history than we know about other oceans.
While seeking ways to circumvent the technical problems of drilling
in permanently ice-infested
waters, drilling engineers
and geoscientists have
conceived a whole new
drilling program, the
Nansen Arctic Drilling
Program, which is associ-
ated with OOP but must
employ a platform different
from the vessels presently
available for scientific deep
sea drilling. Potential
platform designs range from
subsea installations and
dynamically positioned
nuclear submarines to ice-
strengthened drill ships and
semisubmersibles to power-
ful derrick-equipped
icebreakers with the potential for station keeping even against the
mighty pack ice. The necessary site surveys — detailed bathymetric data
and networks of seismic reflection profiles — are lacking in most areas,
and pose an additional intricate and expensive methodological chal-
lenge. However, the changing political arctic winds have also brought
new possibilities for using unconventional research platforms such as
formidable nuclear submarines for reaching regions hitherto closed to
the international geoscience community.
Seafloor exploration in the Arctic began with the famous Norwegian
explorer Fridtjof Nansen, who was seeking to explain why a few pieces
of equipment from the American arctic research vessel Jeannette were
found off eastern Greenland in 1884 although the ship was wrecked off
the coast of Siberia in 1881. Nansen embarked in 1893 on an arctic survey
in his newly built research vessel Fmm, specially designed to be frozen in
the arctic ice for a drift of unknown duration across the top of the world.
Though he did not reach the North Pole, Nansen proved the transpolar
drift theory, took the first bottom samples from the arctic abyss, and
learned that the arctic sea ice covered a deep sea basin rather than the
shelf area he had imagined. Many high arctic expeditions that followed
Nansen were heroic and successful, but there are also many histories of
tragic loss by expeditions unprepared for the hostile arctic environment.
In modern times, however, advanced technology has opened fascinat-
ing new opportunities for geoscience research in the Arctic. American and
Russian ice-island station crews made important progress in arctic deep-sea
geology, especially by sampling near the seafloor surface. Further progress
in determining the geological properties of the arctic deep seafloor now
This photo was taken
as JOIDES Resolution
confronted northwest
Atlantic icebergs
during OOP
Leg 105.
Occanus
Winter 1993/94
63
120C
150C
30C
0°
30C
90
Several current
systems that move the
arctic ice pack make
drill ship research in
this area a challenge.
Jayne Doucette/WHOI Graphics
requires penetration through the sediment cover into basement rock. Fossil
hydrocarbon exploration has led to the discovery of large exploitable oil
and gas accumulations whose origins are related to peculiar high con-
centrations of organic carbon in arctic and subarctic marine sediments, to
their tectonic fate after burial, and to the poorly understood Mesozoic
paleogeography of the Arctic Ocean and its surrounding shelf seas. Modern
research in paleoceanography and climatology has shown that the Arctic
Ocean and surrounding seas have experienced rapid, dramatic environmen-
tal changes — and their impact on the climate of now densely populated
North America and Europe is recognized: An ice-free Arctic could result
from future environmental changes in
response to the greenhouse effect.
Possibilities for scientific drilling in
the arctic abyss have been discussed in
the deep sea drilling community since
the mid 1970s. However, it was only
after several successful Glomar Chal-
lenger and JO1DES Resolution legs to the
iceberg-infested Southern Ocean,
Norwegian and Greenland Sea, and
Labrador Sea /Baffin Bay waters that
JO1DES Resolution undertook true arctic
drilling. Accompanied by the
hypermodern Finnish icebreaker
Fennica, the drill ship visited the north-
ernmost Norwegian and Greenland seas
as part of the North Atlantic Arctic
Gateways Program during late summer
1993. Drilling sites included Fram Strait,
1 50° the deep passage between the Arctic
Ocean and the northern extension of the
Norwegian and Greenland seas area, and
Yermak Plateau, which is thought to be a
true marginal arctic environment.
Data from the older DSDP and ODP
legs combined with more recent evi-
dence suggest a middle-to-late Miocene onset of Northern Hemisphere
glaciations, first in the form of small glaciers and intermittent sea-ice
covers. The occurrence of large proportions of ice-rafted, coarse, terrig-
enous debris increases substantially to the south of Greenland later, at
approximately 4 million years ago, while in other areas it only increases
at about 3.5 to 2.5 million years ago. Cyclical Milankovitch changes in
sediment properties (the result of variations in Earth-Sun orbital geom-
etry), a common characteristic of presently available sediment sections,
suggest a close linkage between deep ocean sedimentation and
paleoclimate. The search for the place and time of the oldest Northern
Hemisphere glaciations continues, posing a great challenge to the
scientific drilling community. It probably requires unconventional
platforms that can withstand the onslaught of the arctic ice pack.
Sediment
Sources
120C
64
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
The Bipolar Challenge
Bipolar glaciation resulting from late Mesozoic and Cenozoic cooling has
caused steep gradients in tropical-to-polar oceanic water-mass and
atmosphere properties. The ultimate glaciation in both hemispheres'
polar regions has forced terrestrial and marine biota to adapt to gener-
ally slow but sometimes catastrophically fast changes in their habitats,
both on land and in the sea. The highly specialized arctic and antarctic
marine biota have responded to
this change by developing, gradu-
ally in the Southern Ocean and
very late in Arctic Ocean popula-
tions, faunas and floras whose
characteristics coincide in many
instances, but also diverge in a
wide range of examples. Today's
Earth has reached an extreme
environmental evolution; it has no
analog in the geological past but
can only be understood through
studying long time series of
sediments from the climatically
most sensitive regions of our earth,
the high-latitude, deep sea basins
of both hemispheres. H
Jorn Thiede was Germany's first professor in paleoceanography. After studying
geology in Kiel, Vienna, and Buenos Aires and after having jobs in Denmark,
USA, Norway, and Germany, he is now working at the young GEOMAR in Kiel.
He has participated in studies of coastal upwelling systems and their geological
record and in DSDP and OOP legs in all major ocean basins, but his recent
interest is centered around polar and subpolar deep sea basins and their
paleoenvironmental record.
Sub-arctic deep sea
drill core (OOP Leg
104) sliowing alterna-
tions between glacial
(dark) and interglacial
(light) periods.
Oceanus
Winter 1993/94
65
LITHOSPHERE
Seven legs of
drilling in
Hole 504B
brought a
wealth of
data on the
structure and
composition
of the upper
oceanic
crust.
Oceanic Crust and
Mantle Structure
Catherine Mevel and Mathilde Cannat
he ocean drilling programs have provided us with a
wealth of new information about the nature of the oceanic
crust a 5- to 10-kilometer-thick layer of rock that covers
more than two-thirds of our planet. Our knowledge of the
oceanic lithosphere has traditionally been limited to indirect
observations, such as bathymetric, gravity, and magnetic maps, or
various kinds of seismic experiments made through the vast water
column. Ocean drilling allows validation of these indirect methods
through direct studies of rock samples. While it is possible to observe
and sample oceanic rocks using submersibles and dredging, only drilling
can provide long, vertically continuous sections of rock, and drill holes
for logging experiments. Long rock sections are critical to identify the
magmatic and tectonic relationships between the various rock types, and
logging experiments provide data on the rocks' physical properties,
allowing comparison with surface geophysical data, and providing ways
to fill gaps in recovered cores. Through logging we can also relate
tectonic or magmatic structures observed in the cores to their surround-
ings in the crust and sediment.
The Architecture of Oceanic Lithosphere:
Fast- Versus Slow-Spreading Ridges
A multilayered model for oceanic lithosphere emerged in the 1970s from
comparisons of oceanic seismic data with the stratigraphy of ophiolites
(sequences of rocks found on land, usually incorporated in mountain
belts, but believed to be pieces of oceanic lithosphere). The uppermost
layer, composed of sediment, is called Layer 1 . Layers 2 and 3 follow,
bounded by increases in seismic velocities that may be either sharp or
gradual. The model suggests that Layer 2 is made of fine-grained basaltic
rocks, erupted as pillow lavas or intruded as dikes (pathways for up-
ward movement of magma), and that Layer 3 is made of gabbros, coarse-
grained rocks crystallized at depth from the same basaltic magma that
feeds Layer 2. The Mohorovicic discontinuity, or Moho, defines a sharp
increase in seismic velocities that usually lies 6 to 8 kilometers below the
seafloor. In the layered model, it is interpreted as a petrological boundary
between the gabbros of Layer 3 and the residual upper-mantle peridotites.
66
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Validating the interpretation of seismic layering in terms of litholo-
gies is not easy. Drilling through the Moho would require a hole several
kilometers deep, which is still beyond the technological capability of the
drilling community. Presently the deepest hole in the oceanic crust is
located at Hole 504B, south of the Costa Rica rift, a ridge spreading at an
intermediate rate. Seven legs of drilling have extended this hole to 2,111
meters and brought a wealth of data on the structure and composition of
the upper oceanic crust. Beneath a sediment cover, the magmatic crust
consists of 571 meters of basalts that erupted on the seafloor as pillow
lavas or flows, then 200 meters of basalt breccias with crosscutting dikes
that overlie a sequence of steep, sheeted dikes at least 1,100 meters thick.
This is similar to the layered-model predictions, except that the dike/
gabbro transition has not yet been crossed, although samples cored in the
lowest part of the borehole exhibit Layer-3-type seismic velocities. In fast-
spreading environments, seismic imaging shows a thin, narrow magma lens
at the ridge axis, 1 to 3 kilometers below the seafloor. Gabbros must have
crystallized in this thin magma lens, which appears to be permanently
located at about the depth of the Layer 2 /Layer 3 transition. The lithosphere
of fast and intermediate spreading oceans is likely to be similar to the
ophiolitic and seismic layered model.
The first indications that this layered model does not adequately
describe the lithosphere composition of the slow-spreading Mid-Atlantic
Ridge came in the 1970s with a series of holes several hundreds of meters
deep, drilled near the ridge (Legs 37, 45, and 82). While most of these drill
holes produced "normal" sections of extrusive basalts occurring as pillow
lavas and flows, a few holes crossed peridotites or gabbros, either just
beneath the sediment cover or within the lava sequence. According to the
layered model, these rocks should only be found deep in the crust (Layer-3
gabbros) or below the Moho (mantle peridotites): Here, however, they were
found in the uppermost crustal levels.
These drilling results were largely ignored, because nobody quite
knew what to do with them. Then in the late 1980s and early 1990s, detailed
bathymetric and gravity maps of the Mid-Atlantic Ridge became available,
providing some explanation for the surprising results of earlier drilling legs.
Late magmatic liquid
(white) intrudes a
foliated gabbro. This
core was retrieved from
ODP Hole 735B.
Oceanus
Winter 1993/94
67
Offset
drilling sites
holes where
tectonic
processes
have exposed
rocks of deep
origin at the
seafloor.
These maps suggest that magma supply to the slow-spreading Mid-Atlantic
Ridge is variable in both time and space, causing the oceanic lithosphere to
be segmented into magma-rich and magma-poor portions. Ridge segments
receiving large volumes of magma should have a thick magmatic crust,
possibly with a permanent magma lens favoring a layered structure similar
to that of faster spreading oceans. By contrast, in ridge segments receiving
very little magma, there should be no permanent magma lens at the axis,
and spreading should be largely due to tectonic extension, causing the
uplifting of gabbros and mantle peridotites to the seafloor.
Some evidence from recent drilling at Hole 735B in the Southwest
Indian Ocean favors this interpretation, linking low magma supplies
with a highly tectonized and lithologically discontinuous lithosphere
structure. Another example is given by the mantle peridotites drilled at
Site 670 in the wall of the Mid-Atlantic Ridge axial valley, which display
evidence of high-temperature ductile deformation that is consistent with
the highly tectonized structure this new model predicts for magma-poor
oceanic lithosphere. These peridotites have interacted with seawater and
recrystallized to serpentinites; however, their texture suggests that the
recrystallization was not associated with the deformation, and it prob-
ably occurred after their emplacement.
One consequence of this new nonlayered model is that the
seismically defined Moho does not systematically correspond to the
petrological transition between magmatic crust (consisting of rocks
crystallized from magma) and residual mantle. Since residual peridotites
outcrop, the seismic discontinuity must reflect another type of boundary.
The most likely interpretation correlates the transition to the depth of
seawater penetration, as the serpentinites are much less dense than
freshwater peridotites.
Building the Lower Crust: How Do Magma
Chambers Function?
Gabbros and other coarse-grained magmatic rocks must crystallize at
some depth beneath the ridge axis, presumably in some sort of magma
reservoir. Most of our knowledge of how this chamber functions comes
from indirect assessments, such as studying the composition of the
erupted lavas or geophysical images of the crust. A major step toward
understanding magmatic processes in magma-starved, slow-spreading
ridges was taken at Hole 735B, where drilling initiated in outcropped
seafloor gabbros produced a 500-meter section with few gaps.
Detailed core studies revealed that magmatic and deformational
processes were strongly intermingled: Deformation started before the
rocks were completely cooled, and therefore the crystals were oriented in
preferential planes, creating a planar fabric called magmatic foliation.
Formation of shear zones facilitated early seawater penetration in the
deep crust and consequent reaction with rocks at high temperature.
Several low-dipping normal shear zones were encountered. These were
interpreted as resulting from the lithospheric stretching that was ulti-
mately responsible for the deep crust's exposure. A conjugate network of
fractures facilitated the seawater's penetration.
It is, however, beyond our present technological capability to reach
the lower crust by drilling through the thick, layered oceanic lithosphere
68
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
formed at fast- and intermediate-spreading rates. This technological
limitation has led the ocean drilling program to design a new approach for
drilling the lower crust and mantle: the offset drilling strategy, siting holes
where tectonic processes have exposed rocks of deep origin at the seafloor.
Offset drilling was first applied during Leg 147 (December 1992 to
January 1993) at the fast-spreading East Pacific Rise, in Hess Deep, a rift
opened in the crust by propagation of the Cocos-Nazca Ridge. Here
gabbros and peridotites outcrop in the walls and on the flanks of an
intrarift ridge. Hole 894G provided a 150-meter gabbro section of hetero-
geneous texture with coarse-grained pockets, similar to the upper part of
the gabbro sequence in ophiolite complexes. The section drilled displays
no evidence of high-temperature deformation such as in slow-spreading
ridges, but a spectacular magmatic foliation characterizes many cores. Its
magnetic inclination tends approximately north to south, parallel to the
East Pacific Rise ridge axis.
Similar steep magmatic foliation has been observed in the upper
gabbros of the Oman ophiolites, and could correspond to the roots of the
dike complex. At Site 895, several holes were drilled in mantle peridot-
ites, yielding invaluable information about the percolation of magmatic
liquids within the mantle. The residual mantle rocks were deformed at
high temperature, then subsequently impregnated by magmatic liquids.
They segregate to form small dikes that may react with the enclosing
peridotites. By analogy with ophiolites, this zone is interpreted as the
transition between the mantle and the lower crust. An important obser-
vation made at Site 895 was that three holes drilled a few hundred
meters apart produced various proportions of residual and magmatic
rocks, suggesting that
the liquids feeding
the crust are chan-
neled along preferen-
tial pathways.
A drawback to
the offset drilling
strategy is that the
mechanisms leading
to the exposure of
normally deep rocks
overprints the processes occurring at the axis. At Hess Deep, for instance,
structural observations show that the opening of the rift is responsible
for the formation of an east-to-west oriented fracture network. However,
it is possible to decipher the successive episodes, and therefore better
understand the evolution of the oceanic lithosphere. •
Catherine Mevel is a Senior Scientist working as a CNRS researcher at the
Universite Pierre et Marie Curie in Paris. Her research interest is to understand
the processes of interaction between seawater and the lower oceanic crust and
mantle.
Mathilde Cannat obtained her thesis in ophiolite studies at the Universite de
Nantes, then moved seaward to the coast of Brittany (Universite de Brest) and
mid-ocean ridges studies. She is now a CNRS researcher at the Universite
Pierre et Marie Curie. Paris.
On ODP Leg 147, core
retrieved from Hole
895C reveals black
peridot ite impregnated
with white ningnmtic
liquid.
Oceanus
Winter 1993/94
69
Drilling has
recovered
most parts of
the crust by
drilling deep
and by taking
advantage of
lower crustal
rocks exposed
on the
seafloor.
Oceanic Crust
Composition
and Structure
Peter S. Meyer and Kathryn M. Gillis
agmatic and volcanic activity that creates oceanic crust
plays an important role in controlling the fluxes of
elements and heat in the oceans, and it was the
degassing of magmas on Earth's surface that gave rise
to the oceans and atmosphere in the first place. Heat
from cooling magmas drives hydrothermal systems that underlie hot
springs and black smokers on the seafloor, initiate ore-deposit forma-
tions, and support seafloor ecosystems in the absence of light. It is also
possible that volcanic heating of the ocean leads to periodic events such
as El Ninos, warm-water currents off Peru that cause major changes in
global weather patterns every four to seven years. To further examine
these phenomena, however, we need to know more about how magma is
generated in the mantle, how it crystallizes to form oceanic crust, and
how the crust is disrupted by faults and altered by the circulation of
heated seawater.
Oceanic crust is created at mid-ocean ridges where magma is con-
tinuously supplied from the mantle below, generated by the rise of hot,
solid material from deep in the earth, followed by its partial melting at
shallow depths. Three main crustal formations result from different rates
of magma cooling and crystallization: fossil magma chambers, sheeted
dikes, and pillow lavas. Fossil magma chambers are composed of
gabbroic rocks with large crystals (1 to 10 millimeters in diameter) that
form by slow cooling of magma within the crust. The crust acts like a
Thermos bottle, insulating magma from cold seawater, and allowing
crystallization and solidification to proceed over tens of thousands of
years. Sheeted dikes are "frozen" channels where magma once flowed
up toward the seafloor. When flow in these channels ceased, magma
crystallized rapidly, perhaps within hours, to form basalts with small
crystals (most less than 1 millimeter in diameter and many too small to
see without the aid of a microscope). Pillow lavas form by the eruption
and "quenching" of magma on the seafloor — cooling is so fast that
volcanic glass forms on the rims of pillows. Slightly slower cooling
within pillows produces crystalline basalt.
70
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
The amount of magma generated and the proportion of it that erupts
varies along mid-ocean ridges, leading to significant variations in total
crustal thickness and in the relative proportions of gabbroic rocks,
sheeted dikes, and pillow lavas. High magma supply, high eruption
rates, and a thick crust are typical of rapid spreading rates at mid-ocean
ridges such as the East Pacific Rise. Low magma supply, low eruption
rates, and a thin crust are typical of mid-ocean ridges where spreading
rates are low, such as the Southwest Indian Ridge. Theoretically, high
magma-supply rates should also result in slower cooling rates and a higher
proportion of gabbroic rocks in the crust, but this remains to be proven.
To fully characterize the oceanic crust's composition and to under-
stand how its composition is influenced by magmatic and hydrothermal
processes requires a scale of sampling that can only be achieved by
drilling. DSDP and OOP have successfully recovered most parts of the
crust by drilling deep at a few sites and by taking advantage of lower
crustal rocks exposed on the seafloor. A complete section of upper crust,
including the lava and sheeted dike complex, has been sampled in a hole
about 2,200 meters deep drilled during seven legs in the eastern equato-
rial Pacific at Site 504. Leg 118 recovered 500 meters of gabbroic rocks
that formed in a magma chamber beneath the very slow-spreading
Southwest Indian Ridge. Leg 147 recovered a sequence of gabbros that
formed at the magma-rich East Pacific Rise, as well as the complex
transition zone between the crust and upper mantle, revealing the
Pillow
Lavas
Sheeted
Dikes
Upper
Gabbros
Layered
• Gabbros
Mantle
KEY
<^=i Pillow Lavas
///// Sheeted Dikes
Magma Lens
Crystal Mush
• — Shear Zone
•-- Layers in Gabbro
^^ Direction of
Mantle Flow
Schematic representation of ocean crust at a mid-ocean ridge. In an active ridge, magma rises out of the
mantle and into the overlying crust where it feeds a magmatic system comprised of a crystal mush zone (85
percent crystals and 15 percent melt) and a magma lens at the base of sheeted dikes. Magma is also chan-
neled through dikes to the seafloor. On both sides of the crystal mush zone are gabbroic cumulates, the fossil
remains of earlier magmatic systems. The gabbros are divided into upper gabbros where there is no signifi-
cant crystal layering, and layered gabbros, where crystal layering (dashed lines in the figure) is well
developed. The upper gabbros are further characterized by shear zones oriented parallel to the high-angle
normal faults. These provide channels for the migration of late, evolved melts. The sheeted dikes and pillow
lavas are composed of basaltic rocks formed, respectively, by the rapid cooling of magma near the seafloor
and the quenching of magma on the seafloor.
Oceanus
Winter 1993/94
71
Leg 139
investigated a
hydrothermal
system that
extends from
the basaltic
basement into
an overlying
sequence of
marine
sediments.
72
trapping and crystallization of rnagma within a previously melted piece
of mantle. Investigation of these and other cores has significantly
changed our view of how oceanic crust is built.
Variations in magma supply imply variations in the average degree of
melting in the mantle, which affects the composition of primary magmas
coming out of the mantle and therefore the average composition of the
oceanic crust. At one extreme, low magma-supply rates result in infrequent
intrusion of magma into the crust and "freezing" of the magma to form
dikes whose basaltic composition is nearly the same as the melt initially
generated in the mantle. With greater magma supply, more magma is
intruded into the crust, its cooling rate decreases, and it is subject to the
process of fractional crystallization prior to solidification. Just as evapora-
tion of seawater leads to removal of pure water and concentration of salt in
the water, the fractional crystallization of magma leads to the removal of
some elements in crystal form and the concentration of others in the residual
liquid. Dikes and lavas formed after fractional crystallization are signifi-
cantly different in chemical composition than the melts originally generated
in the mantle. This is because the first crystals to form in a basaltic magma,
olivine and plagioclase, are chemically very different from the initial
magma. Extensive crystallization and the addition of iron-titanium oxide
minerals to the crystallizing assemblage may lead to the generation of melts
that are very rich in silica (trondhjemite in the table opposite).
As magmas cool, crystals may accumulate on the floors, walls, and
roofs of magma chambers and form crystal mushes that initially contain
40 percent melt, but prior to solidification contain less than 15 percent
trapped melt. Melt may be expelled from a mush by such processes as
compositional convection, compaction, and deformation. Solidification
of mushes produces cumulate gabbros (troctolite and iron-titanium
oxide gabbro in the table) with compositions that are significantly
different from magma compositions (basalts). Troctolites are primitive
cumulates, assemblages of olivine and plagioclase crystals together with
a small fraction of crystallized trapped liquid, that formed during the
early stages of magma crystallization. Iron-titanium oxide gabbros, on
the other hand, are evolved cumulates that formed after extensive
crystallization of basaltic magma at mid-ocean ridges.
Crystallization models and magmatic intrusions exposed on land
suggest a simple crustal stratigraphy for the lower ocean crust, with primi-
tive gabbros at the base displaying well-developed crystal layering and
evolved gabbros toward the top characterized by the absence of layering. So
far, we have yet to observe well-developed layering in drilled sequences of
oceanic gabbros, and at Site 735 we found evolved gabbros interdigitated
with primitive olivine gabbros and troctolites. Detailed chemical mapping
of contacts between iron-titanium oxide gabbros and olivine gabbros at Site
735B indicates that evolved melts are sometimes mobilized in response to
crustal deformation, and that melt flow may be either diffused through
intergranular networks or focused along centimeter-scale channels. Depend-
ing on magma supply and cooling rates, crystal mushes may be invaded
with new magma prior to solidification, modifying the bulk composition of
the mush in addition to the composition of the invading magma.
The composition of the oceanic crust that results from magmatic
processes is the starting point for a complex history of chemical exchange
with seawater that leads to the formation of ore deposits and influences
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Composition of Common Rocks Found in Oceanic Crust
Magma Compositions
Iron-titanium r
Basalt . , , ,L Trondh emite
oxide basalt
Products of
Crystallization
Iron-titanium
Troctolite . , ,,
oxide gabbro
Silicon dioxide
48.00
49.47
70.82
44.87
42.53
Aluminum oxide
16.44
14.02
17.28
17.42
10.93
Titanium oxide
1.90
3.21
0.22
0.14
6.89
Iron oxide
10.45
12.88
1.12
7.20
20.67
Magnesium oxide
Manganese oxide
Calcium oxide
9.71
0.17
9.24
5.22
0.16
9.21
0.17
0.02
1.93
17.69
0.12
8.64
5.50
0.3
9.21
Sodium oxide
3.26
3.84
6.95
1.95
2.70
Potassium oxide
0.13
0.39
1.48
0.06
0.04
Phosphorus oxide
0.28
0.43
0.01
0.0
0.0
the composition of the world's oceans, arc volcanics, and the mantle.
When erupted on the seafloor, volcanics immediately begin to react with
the surrounding seawater. Within a hydrothermal system, seawater
flows downward through cracks, fissures, and faults and may penetrate
to depths as great as 5 or 6 kilometers. It reacts with rocks all along its
path, resulting in exchanges of elements and the chemical modification
of both seawater and crust. The extent of this exchange depends prima-
rily on temperature and the abundance of seawater passing through a
volume of rock, or, in other words, the water /rock ratio. Seawater heats
as it migrates down into the crust toward an active magma chamber, and
resulting hydration reactions enrich crustal rocks in magnesium and
sodium and depletes them of calcium. By the time seawater makes it to just
above the magma chamber, its composition has been significantly modified
and low water/rock ratios and high temperatures (about 400°C) lead to
leaching of metals from the rocks. These buoyant, hot, metal-enriched fluids
rise to the seafloor where they mix with the ambient seawater and precipi-
tate sulfides that accumulate in chimneylike structures and mounds. Leg
139 investigated the structure and composition of a hydrothermal system
that extends from the basaltic basement into an overlying sequence of
marine sediments. In fall, 1994, Leg 158 will drill into an unsedimented
deposit. Chemical exchange within the deep root-zones of hydrothermal
systems has been documented at Hole 504B where the base of a sheeted
dike complex was found to be depleted in copper and zinc.
Although it is not known whether or not seawater-derived fluids
actually enter into active magma chambers, the gabbroic core recovered
at Hole 735B demonstrates that seawater did penetrate the lower crust
very early in its history. Alteration of gabbroic rocks was initiated at
temperatures greater than 600°C and focused within zones of ductile
deformation. These zones show very little change in composition be-
cause the fluids had become strongly enriched in basaltic components by
the time they reached this depth (3 to 4 kilometers). Lower-crust hydra-
tion may not be a significant process at ridges where there is a high rate
of magma supply, simply because the crust is too hot to deform in a way
All compounds are
given in percent by
weight.
Oceanus
Winter 1993/94
73
Drilling the
oceanic crust
has proven to
\)e an essential
step in
furthering our
understanding
of global
geochemical
cycles.
that provides pathways for fluids to flow deep into it. In fact, East Pacific
Rise gabbroic rocks recovered during Leg 147 show that ductile deforma-
tion is not prevalent at this magma-rich ridge.
Modification of oceanic crust composition does not stop when a
section of crust moves away from a mid-ocean ridge and off -axis. Seawater
continues to circulate in and out of the crust until fluid pathways are sealed
by the precipitation of minerals, or until sediment accumulation prevents
penetration into the crust. As a crustal section ages and moves away from
the mid-ocean ridge, the most significant compositional change occurs in
the upper volcanic carapace, as fluid pathways deeper in the crust are
thought to become sealed by the time it leaves the ridge. Within 5 to 10
million years, the volcanics are enriched in elements such as magnesium
and potassium, and much of the basaltic iron has been oxidized. Although
isotopic age dating of carbonates shows that mineral precipitation ceases
within 20 million years, heat-flow data indicate that seawater may well
continue to circulate beyond this time frame. The chemical consequences of
such prolonged seawater circulation are not known.
Most of our knowledge of crustal aging processes comes from the
recovery of shallow oceanic crust that ranges from essentially zero age
(such as at Site 649) to as old as the Jurassic, about 160 million years ago
(Hole 801C). Core from more than 150 basement sites demonstrates that
interaction between seawater or sea water-derived fluids and rock has a
significant impact on crustal composition. Downhole compositional trends
at Hole 504B show that different elements are mobile in different parts of the
crust. Differences in chemical fluxes found in cores from Sites 417 and 418,
drilled only 500 meters apart, show that the composition of the upper-
most crust may be quite heterogeneous. Comparing cores of varying
ages from all ocean basins suggests that the rate of chemical exchange is
not simply a function of age, and that the greatest change in composition
may occur in young crust. Chemical exchange within the oceanic crust
plays an important role in world-ocean water composition by contribut-
ing to the delicate balance of sources and sinks that include the conti-
nents (through river input), the atmosphere, ocean sediments, and the
ocean itself. Drilling the oceanic crust has proven to be an essential step
in furthering our understanding of global geochemical cycles. •
Peter S. Meyer is an Associate Professor at Rhode Island College and an
Adjunct Scientist in the Department of Geology and Geophysics at the Woods
Hole Oceanographic Institution. He developed an interest in geology while writing
a career notebook in the eighth grade and visiting marble quarries in Vermont,
then became hooked while scrambling up volcanos in Central America as an
undergraduate at Dartmouth College. His current research interests include
magma chamber dynamics, crystal-melt equilibria, and the evolution of the lower
oceanic crust.
Kathryn M. Gillis is an Associate Scientist in the Department of Geology and
Geophysics at the Woods Hole Oceanographic Institution. She developed an
interest in geology during a family vacation across the US and Canada where
she encountered a thoughtful observer of the earth, her cousin Jack. Over the
years this interest became linked with her roots in eastern Canada and she
eventually developed into a marine geologist. Her research interests revolve
around the processes that shape the seafloor and the interaction between fluids
and rocks.
74
DSDP (Deep Sea Drilling Project) A OOP (Ocean Drilling Program)
Exploring Large
Subsea Igneous
Provinces
Millard F. Coffin and Olav Eldholm
olcanic eruptions, such as the 1991 eruption of Mt.
Pinatubo in the Philippines, can severely damage the local
environment. Yet such events pale in comparison to the
huge convulsions of magmatic activity during the under-
sea formation of large igneous provinces, or LIPs. Com-
pared with other large geological features, most of these provinces were
constructed very rapidly indeed.
Today LIPs (composed primarily of iron- and magnesium-rich rock)
are found both on land, as continental "flood basalts," and under the sea,
mostly as oceanic plateaus in the middle of oceans and as volcanic
passive margins along the edges of continents. In fact, the two largest
provinces, the Ontong Java and Kerguelen plateaus, now lie mostly
below sea level. The construction of these two provinces, together with
the volcanic passive margins
between Greenland and
Northwest Europe and in the
South Atlantic, not only have
profound implications for the
regional and global environ-
ment, but also partially reveal
the workings of the mantle,
that part of Earth's interior
between the outer crust and
the molten core. Cores
obtained from oceanic
plateaus and volcanic passive
margins by the Deep Sea
Drilling Project and the
Ocean Drilling Program,
together with high-quality
seismic reflection images
The onshore portion of
the North Atlantic
volcanic province on
Greenland. The offshore
portion, the volcanic
continental margin,
urns recently drilled
during Ocean Drilling
Program Leg 152.
Oceanus
Winter 1993/94
75
;'. Hawauan-Empero
. : Seamounts
• .£0.
Large
igneous provinces,
shown in fuschia,
appear in many
geologic settings
worldwide. Studies of
these huge magmatic
emplacements are
adding to our
understanding of how
Earth's interior
behaves, and how these
features may affect
conditions at Earth's
surface.
have been instrumental in allowing scientists to understand the causes
and effects of large igneous provinces.
While the theory of plate tectonics explains much of the geology we
observe on Earth's surface, it does not readily explain large igneous
provinces. These provinces are created neither by "normal" seafloor
spreading, which occurs along the mid-ocean ridge system, nor by the
subduction process, where one roughly 100-kilometer-thick lithospheric
plate slides beneath another. On a geological time scale, both processes
reflect persistent phenomena while LIP formation is transient. Although
large igneous province rocks resemble those created by seafloor spread-
ing, subtle differences suggest that they arise from deeper, hotter regions
of the mantle. Early on in the development of plate tectonic theory, these
regions were proposed to produce "hot spots" such as Hawaii, which
somehow remain anchored in the mantle while the lithospheric plates
above move horizontally. Most researchers believe that mantle hot spots
account for large igneous provinces, although the details of how such hot
spots work are poorly known.
How big are large igneous provinces? The volume of the biggest LIP,
the Ontong Java Plateau and associated provinces in the western Pacific,
would cover the contiguous US with 5 kilometers of basalt. Another
large igneous province, the Columbia River continental flood basalt in
the Pacific Northwest, encompasses only 3 percent of Ontong Java's
volume. Individual lava flows of this lesser province, however, can be
traced for over 750 kilometers. The enormous scale of these provinces is
simply hard to grasp or even compare to historic eruptions. Their rapid
emplacement is similarly difficult to comprehend. We know, for ex-
ample, that the global mid-ocean ridge system has produced between 16
and 26 cubic kilometers of basaltic crust annually over the past 150
million years. By dating rocks from the Ontong Java Plateau, we calcu-
late that the feature was constructed at a rate between 12 and 152 cubic
kilometers per year over 0.5 to 3 million years. This considerable range in
values expresses uncertainties about crustal structure and whether the
LIP was created on a spreading axis or away from it. The minimum rates
76
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
for Ontong Java and common rates for other large igneous
provinces are thus comparable to emplacement rates for
"normal" oceanic crust, but one must bear in mind that LIPs
are produced only episodically within limited regions of
Earth's surface.
LIPs are surface manifestations of localized and tran-
sient increased melt potentials or plumes below the lithos-
phere that have reached Earth's surface through a conduit
called a plume. Hence the size and construction rates of
large igneous provinces reveal to some
extent how the mantle works. In this way
analysis of LIP parameters provides "hard
facts" to the vigorous debate about such
topics as scale of mantle circulation, origin
of mantle plumes, and relations between hot
spots and volcanic margins, to name a few.
For example, if one knows the volume of
rock contained in these provinces, one can
estimate the dimensions of the hot mantle
regions where they originated. We estimate
that each large igneous province contains
between 5 and 30 percent of the mantle
plume's original volume, and use these
numbers to calculate sizes of the thermal
anomalies in the mantle that are responsible for the North Atlantic
volcanic margins and the Ontong Java and Kerguelen oceanic plateaus.
The analysis indicates that the largest plumes contain at least some
material from the lower mantle more than 670 kilometers beneath Earth's
surface, suggesting some interaction between the lower and upper
mantles.
The surfacing of a mantle plume leads to physical and chemical
changes of the local, regional, and global environment, which in turn
affect the conditions and evolution of life on Earth. The burst of subma-
rine magmatic activity roughly 122 million years ago that created the
Ontong Java Plateau coincided with increased biologic productivity,
higher sea level, and a warmer climate than at present. In contrast,
subaerial emplacement of the Kerguelen Plateau approximately 110
million years ago coincided with mass marine extinctions. Another signifi-
cant change in the global environment took place about 55 million years
ago, when many benthic plankton species and land mammals became
extinct. Ocean temperatures were the warmest of the past 70 million years,
and 55-million-year-old ash layers are found over large areas of northwest-
ern Europe. These events coincided with emplacement of the North Atlantic
volcanic margins and associated continental flood basalts. The temporal
correlations among these three examples — Ontong Java, Kerguelen, and the
North Atlantic provinces — as well as of continental flood basalt provinces,
and global environmental changes, suggests some relationship must exist.
Although the potential forcing functions and feedback mechanisms have yet
to be refined, it appears that magmatic production rates, geological setting,
and the environmental state during LIP formation are primary factors
that determine environmental impact.
Tliese core samples
from the Kerguelen
oceanic plateau were
acquired by scientists
on OOP Leg 120. Left:
subaerialty weathered
basalt; center: basalt
conglomerate with
molluskand volcanic
grain infill; middle
bottom: thin section of
basalt showing hema-
tite weathering; right
top: mud pebble
conglomerate with
volcanic sediment and
coal; riglit bottom:
wentJiered basalt.
Oceanus
Winter 1993 /94
77
1J ^
is ••
10km
Seismic reflection
profiles show a cross-
section (in seismic
wave travel time) of
Earth beneath the sea.
Dipping reflector
sequences (below the
black lines) indicate
basalt flows on the
Norwegian volcanic
passive margin (top)
and the Kergnelen
oceanic plateau
(bottom).
Scientific ocean drilling has
only begun to scratch the surface
of large igneous provinces; their
crust is up to 40 kilometers thick
with a cover of numerous basalt
flows exceeding 5 kilometers.
Most DSDP basement holes were
quite shallow, whereas ODP Leg
104 volcanic margin drilling by
JOIDES Resolution proved the
feasibility of penetrating deeply
into basement rocks. Presently, the
deepest LIP hole has penetrated
almost 1 kilometer into the igne-
ous crust, but most other holes
have only penetrated a few tens of
meters into the basalts. The drill
ship's capabilities were recently
tested with success in late 1993
when scientists aboard JOIDES
Resolution returned to drill the
North Atlantic basalt off Greenland, with the ultimate objective of
learning more about how plumes work.
The present LIP drilling data base is indeed sparse, but what we
have learned from the existing holes and associated geophysical surveys
is intriguing. Our current knowledge amply demonstrates that they
contain crucial information about the internal behavior of Earth and about
the natural causes of global change. The Ocean Drilling Program provides a
unique tool for solving such fundamental problems in geoscience. •
This is University of Texas Institute for Geophysics contribution number 1023.
The marine geoscientific career of Mike Coffin marks a return to the seafaring
tradition of his Nantucket ancestors, although his more immediate forebears
spent a few generations landlocked in Maine, New Brunswick, and France. A
research scientist at the Institute for Geophysics, The University of Texas at
Austin, he was educated at Dartmouth College and Columbia University. His
interest in LIPs developed while amassing 6 months of "frequent floater" awards
over the Kerguelen Plateau. When not studying tectonic problems, his diversions
have included performing with the Royal Ballet, helicopter and cross-country
skiing on several continents, and bareboat sailing in the Atlantic, Pacific, and
Indian oceans.
Olav Eldholm grew up in western Norway and was educated in Bergen, but
became "indoctrinated" at Lamont-Doherty Earth Observatory before returning to
Norway where he is now a professor of marine geophysics at the University of
Oslo. His Large Igneous Provinces interest was ignited as co-chief scientist
during deep ODP drilling on the Voring volcanic margin, and further stimulated by
a sabbatical visit to the University of Texas Institute for Geophysics center of
excellence. He keeps fit by climbing Norwegian glaciers and completing New
York Times crossword puzzles.
78
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
DSDP/ODP
Downhole
Measurements
in Hole 504B
Phillipe A. Pezard
he Ocean Drilling Program's continuous downhole mea-
surements have become essential to seafloor exploration.
(See "Borehole Measurements Beneath the Seafloor," page
129 for a description of downhole measurements.) They
supplement and verify information obtained from core
studies and often provide data in sections where cores are not recovered.
Over the past 10 years, these methods have steadily become more important
to research on the structure and dynamics of Earth's upper crust.
DSDP/ODP Hole 504B, by far the deepest hole yet drilled into the
oceanic basement, illustrates the importance of downhole measurements
to earth science. The work done in 504B provides the scientific commu-
nity with an excellent means for verifying models of the upper oceanic
crust's structure and evolution.
Hole 504B is located beneath 3,475 meters of eastern equatorial
Pacific water and penetrates ocean crust assembled on the southern flank
of the Costa Rica rift. Beginning with DSDP Leg 69 in 1978, eight ocean
drilling expeditions have been dedicated to drilling Hole 504B, to reach
the present depth of 2,111 meters below the seafloor. Beneath 275 meters
of sediments, including pelagic oozes and chert, 1,836 meters of basaltic
basement has been cored, with recovery often less than 20 percent. The
basaltic section comprises about 600 meters of pillow lavas and massive
lava flows extruded 5.9 million years ago on the seafloor at the rift
spreading center. Below the basalt layer lies a transition zone that leads
to a 1,200-meter-thick section of sheeted dikes, solidified conduits from
the magma chamber to the seafloor. As the gabbros (the prime objective
of the last two drilling legs) were unfortunately not reached, downhole
measurements covering the entire basement section were recorded.
The data collected from downhole measurements can generally be
classified into two main categories associated, respectively, with the struc-
ture and the dynamics of the penetrated section. That related to structure
reveals, either in terms of physical properties or lithostratigraphy,
The work done
in 504B
provides an
excellent
means for
verifying
models of the
upper oceanic
crust's
structure and
evolution.
Oceanus
Winter 1993 /94
79
Downhole
measurements recorded
during drilling on
OOP Leg 111 into
young oceanic
basement created at the
Costa Rica rift. The
electrical resistivity
profiles reveal, at the
top of the basement,
extremely porous and
permeable pillow lava
formed on tlie seafloor
and, below, nearly
nonporons and
nonpermeable sheeted
dikes of basalt formed
by lava intrusion at the
rift. The total and
fracture porosity
profiles were calculated
from the analysis of
resistivity data.
continuous data around the drillhole, gener-
ally at meter scale. From within the borehole,
dynamic parameters reveal information at
kilometer scale for mapping present or past
fluxes, as well as force fields such as those
associated with tectonic stresses.
Probably the most important finding in
Hole 504B downhole measurements is a
strong downflow of sea-bottom water into
the upper basement. This vigorous flow was
first discovered in 1979 as the hole was being
re-entered during DSDP Leg 70. Scientists
were surprised to observe a temperature
profile showing 2° to 3°C water down to 300
meters, a few tens of meters into basement,
where they expected to see water at 60°C.
This was the clue for the downflow. Row
experiments with downhole packers, combined
with geophysical measurements of electrical
resistivity, revealed the presence of a 30-meter-
thick, porous, permeable and underpressured
aquifer located under a 14-meter-thick massive
sheet flow of basalt at 300 meters. Since that
time, temperature data are routinely recorded
first whenever the hole is being re-entered for
deepening and downhole experiments.
The temperature profile taken at the beginning of Leg 111 in 1986
showed that ocean-bottom water was still flowing into the aquifer,
proving the large extent of this underpressured reservoir and, at the
same time, the similarly large extent of its basalt seal.
The seal must have originated in a massive outpouring of basalt onto
the seafloor near the ridge axis, an eruption different in many ways from
somewhat more classic modes of volcanism that lead to emplacement of
pillow lava. The pillows, characterized by low electrical resistivity (about
10 ohm-meter) appear to constitute more than 75 percent of the lava pile
at Site 504 and are, consequently, considered to be the main mode of
oceanic crust emplacement there.
Massive flows, on the other hand, have high electrical resistivity
(above 300 ohm -meter) associated with low porosity and low permeabil-
ity, so they are a limiting factor for upper crustal fluid circulation. A 5-
meter-thick massive basalt flow at 580 meters appears to have played an
even more important role in past fluid circulation near the ridge axis.
Both the texture and thin sections from the recovered core show that
nearly all of the basalts at 580 meters have been altered to some degree,
while the geochemistry of the freshest rocks is remarkably uniform
throughout the upper 1,500 meters of basement. Successive stages of
near-axis hydrothermalism have produced three depth zones character-
ized by different mineral assemblages outlining the circulation of:
• seawater and oxygenated fluids at low temperature down to 580 meters,
• more evolved fluids that imply anoxic conditions at higher tempera-
ture below that depth, and
• fluids leading to the development, at even higher temperatures, of
80
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
greenschist-facies minerals through the transition zone and into the
sheeted dikes.
While the upper section is dominated by smectite and potassium-
rich phases, pyrite abruptly appears at 580 meters. The extremely
different chemical nature of these two regions proves here again the
large lateral extent of the permeability barrier located between them.
Downhole measurements may, then, not only reveal the presence of
static structures such as basalt flows, but also help to understand their
role in the dynamic evolution of the crust.
While these observations were mostly derived from measurements
performed in the hole at meter-scale, centimeter-scale electrical images
have recently been recorded throughout the hole and are still being
analyzed. So far, this analysis has lead to a finer description of upper-
basement structures. Also, a continuous vertical seismic profile obtained
down to 2,000 meters will help to characterize the seismic nature of
basement features located below the present bottom of the hole, as well
as in the close vicinity of the borehole such as a fault at 825 meters that
was revealed in OOP Leg 111 data.
Much has been learned over the past 15 years from downhole measure-
ments in deep scientific holes such as 504B. The reliability and precision of
the recording techniques have evolved substantially, to the point that they
now constitute additional research tools specially suited to continuous
observation of crustal processes along the length of the drillhole. •
Philippe A. Pezard was initially educated in France, but soon ran away to the
Middle East and Africa where he worked as a field logging engineer. After this,
he somehow felt ready to face New York City and the Lamont-Doherty Earth
Observatory, where he obtained his Ph.D. in borehole geophysics. Now emi-
grated back home at the Institut Mediterraneen de Technologie in Marseille, his
research is focused on the analysis of borehole data and images, with a particu-
lar emphasis on electrical methods and implications for the structure and
evolution of the upper oceanic crust.
DSDP/ODP Hole
504B, near the Costa
Rica Rift. At the rift
axis, magma forces its
wai/ from the upper
mantle to the ocean
floor, creating pillow
lava and massive flows
on top of vertical
"feeder" dikes. Hole
504B was drilled in
3,475 meters of water
to a depth of 2, 111
meters below the
sea floor during several
visits of the drillships
Glomar Challenger
and JOIDES
Resolution. As the
overall core recovery is
under 20 percent,
the hole was
extensively logged.
Oceanus
Winter 1993/94
81
Water
circulating in
the igneous
crust
dominates
the heat budget
at seafloor
spreading
centers, and
rapidly
quenches
magma.
Studying Crustal
Fluid Flow With
ODP Borehole
Observatories
Earl Davis and Keir Becker
82
f you depend on a well for your water, chances are good that
you have some notion about ground water flow. The level of
water in the ground, referred to as the water table, rises and
falls (but never below the bottom of your well, you hope) with
variations in supply from season to season. Water flow is often
confined to discrete layers or fracture zones in the earth or rock (provid-
ing employment for countless diviners and a handful of geophysicists).
The geometry of these zones, and the degree to which they are connected
to one another and to other forms of porosity defines the ease with which
water can flow through the rock (and hopefully to your well). In some cases,
the combination of topography and the confinement of permeability can
produce artesian or natural upward flow (the well owner's dream).
Most people are not aware, however, that many of these principles
apply to fluid flow beneath the seafloor as well. Beneath the oceans, the
water supply is unlimited, and the concept of a "water table" must be
revised, but the sediments and rocks beneath the seafloor are porous and
variably permeable, and the general rules for "groundwater" flow are
the same. As beneath continents, water is driven through rock at rates that
are established by a combination of the permeability and pressure gradients.
Instances of topographically driven flow, the most common type on
land, are found beneath continental shelves, where water can be forced
along permeable rock strata by the "loading" imposed by the above-sea-
level water table in the adjacent continent. Elsewhere, the primary
driving forces for sub-seafloor groundwater flow are different; they result
from sedimentation and associated compaction in deep ocean basins,
tectonic thickening and compaction in subduction-zone accretionary prisms,
and thermal buoyancy at volcanically active seafloor spreading centers.
The consequences of fluid flow within the igneous and sedimentary
parts of the oceanic crust, and of fluid exchange between the crust and
the water column, are profound. Water circulating in the igneous crust
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
dominates the heat budget at seafloor spreading centers, and rapidly
quenches magma erupted and intruded at these locations. High-tempera-
ture hydrothermal fluids are extremely effective at dissolving and
transporting large quantities of sulfur and base metals from the igneous
crust to the seafloor and forming large polymetallic sulfide deposits.
Long-term circulation of lower-temperature crustal fluids is responsible
for widespread mineralogical alteration and mechanical consolidation of
the upper igneous crust. Fluid pressures generated in subduction-zone
accretionary prisms modify the mechanical behavior of the deforming
sediment section, and the resultant fluid flow is
believed to be responsible for hydrocarbon migra-
tion, the formation of methane hydrates, and major
diagenetic changes in the sediments. In all instances,
the seawater that circulates into the crust is modified
substantially before it returns to the ocean, and this
exerts a strong influence on the chemical composi-
tion of the oceans.
Observing Crustal Fluid Flow
To a limited extent, fluid flow regimes at depth can
be inferred from seafloor observations. Variations in
measured heat flow, geochemical anomalies de-
tected in sediment cores, and observations of
focused flow through the seafloor all provide
valuable information. The best information about
the physical and chemical nature of crustal fluid
flow within the sediments and rocks beneath the
seafloor, however, comes from observations that have
been made in boreholes drilled by the Deep Sea
Drilling Project (DSDP) and the Ocean Drilling
Program (ODP). Downhole temperature measure-
ments, logging, hydrologic experiments, and observa-
tions of pore-fluid chemistry and rock alteration have
provided invaluable information about flow rates and
directions, the crustal permeability structure, and the
history and long-term consequences of fluid flow.
Unfortunately, hydrologic disturbances caused by drilling are large
and relatively long lived, making accurate determinations of pressure
and temperature, and samples of pristine pore fluids, difficult to obtain.
Considerable quantities of heat are transferred conductively from the
rock to the borehole, where cold seawater is circulated continuously to
remove drilled-rock fragments. In zones of high permeability, the heat
exchange can be even greater, because the cold drilling fluid can invade a
large volume of rock. If the crustal formation is sufficiently permeable
and the borehole sufficiently deep, this can lead to a runaway situation in
which the cold, dense seawater in the hole displaces the warm, buoyant
water in the formation. Left unchecked, this downhole flow can severely
disturb the natural thermal, chemical, and hydrologic regime, thus
rendering observations in the borehole meaningless. In formations that
are naturally over pressured (artesian), up-hole flow can result. This
creates different (but equally difficult) problems.
A Circulation
Obviation Retrofit Kit
(CORK) observatory
installation assembled
for deployment at the
rig floor of JOTDES
Resolution.
Occanus
Winter 1993 /94
83
CORK
observatory
—Sensor
2 string
or
perforated —
- casing
Schematic cross section of an ODP CORK installation, and
records of pressures measured above and beneath the
seafloor. In this hole, the pressure had only begun to recover'
from the drilling disturbance. The magnitude of the initial
disturbance was equivalent to a 100-meter loss of head. The
daily tidal signal, roughly 2 meters in amplitude at the
seafloor, is highly attenuated but still present in the rock over
500 meters below the seafloor.
Formation pressure
23,500"
Time (days)
New Instrumentation for
Long-Term Borehole Observations
With the goal of accurately determining the hydro-
logic conditions in deep ocean boreholes, a new
device (dubbed the Circulation Obviation Retrofit
Kit, or CORK) has been developed through a coop-
erative project among the authors, Tom Pettigrew
(Ocean Drilling Program), Bobb Carson (Lehigh
University), and Bob Macdonald (Pacific Geoscience
Centre). This device provides a means to stop forma-
tion-fluid flow into seafloor boreholes in order to
minimize the thermal and chemical effects on the
formation from drilling-induced disturbances, and a
means to monitor the in situ thermal and hydrologi-
cal conditions and sample fluids long after holes are
drilled and drilling disturbances have dissipated. The
CORKs include:
• a hydrologic seal that is compatible with existing ODP reentry cones
and slightly modified ODP casing hangers,
• a data logger with a 2- to 3-year recording capacity,
• a downhole string of 10 thermistors,
• a pressure sensor situated below the reentry cone seal, and
• plumbing through which fluids can pass from the formation through
the seal for sampling by a submersible or a remotely operated vehicle
(ROV).
Instruments constructed most recently include orthogonal pairs of tilt
sensors for monitoring tectonic deformation. Future instruments may
incorporate other seafloor and downhole sensors, such as ion-sensitive
electrodes for detecting changes in borehole fluid composition, strain
84
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
gauges for identifying motion on faults, and accelerometers for revealing
local seismic events.
The seal comprises two parts. The outer part, deployed and recov-
ered by the drill ship, provides a seal to the standard (30-centimeter
inside diameter) casing that lines the upper part of each hole. This outer seal
also serves as a landing collar for an inner seal that is part of a slim (6-
centimeter inside diameter) pressure case containing the data logger. This
part can be recovered with the drill ship, a submersible, a wire line, or an
ROV. All seals and latches are designed to be capable of containing either
positive or negative differential pressures of up to 10 megapascals. The data
from the instrument are recovered via an electrical connection that can be
mated by submersible, ROV, or wire line. A newly developed acoustic
telemetry module, first deployed in 1993, now provides a way of communi-
cating with the observatories and recovering data with only a surface vessel.
Recent Observations and Future Installations
Four holes have been sealed and instrumented with CORKs to date. Two
were drilled in Middle Valley, a sedimented rift valley of the northern
Juan de Fuca Ridge seafloor spreading center. One of these penetrated to
a total depth of nearly 1 kilometer, through the relatively impermeable
sediments that fill the valley, and into highly permeable rocks beneath,
where 300°C hydrothermal fluids reside in a hydrothermal "reservoir."
The second CORKed hole in the valley was drilled in the middle of a
hydrothermal vent field, where fluids from the regional reservoir
discharge through the seafloor, and, in one case, through a shallow
exploratory borehole!
These holes have been visited three times since the CORKs were
installed, the first time about three weeks after installation with DSV
Alvin from the Woods Hole Oceanographic Institution, the second about
ten months later with ROV ROPOS from the Canadian Institute of Ocean
Sciences, and the third again with Alvin, just over two
years after installation. Large drilling disturbances were
seen in the records from both holes. A pressure offset
equivalent to 100 meters of head was observed at the
time the deeper hole was sealed. Virtually all of this
negative differential pressure was caused by the tendency
for the cold, dense water, unavoidably injected into the
hole during drilling, to sink into the hot formation. (A
similar suction is created when liquid is held in a soda
straw with a finger on the top.) The initial drilling distur-
bance had decayed by only 50 percent during the first three
weeks of recording. Large thermal and pressure distur-
bances were also observed in the hole drilled into the vent
field. Pressures in this borehole eventually became positive,
but only after a full year of waiting! Data from both holes
clearly demonstrate the need for long-term measurements.
A second pair of holes has been drilled into the
Cascadia accretionary prism, where over 2 kilometers of
sediments are being scraped off the subducting Juan de
Fuca plate along the west coast of North America, and
slowly compressed into rock. One hole, located off the
The "business-end"
of a borehole seal
is prepared for
deployment from the
OOP drill ship
JOIDES Resolution.
Oceanus
Winter 1993/94
85
Photograph taken from
the research submers-
ible Alvin showing an
ODP reentry cone in
Middle Valley,
Norther )i Juan de Fuca
Ridge, fitted with an
instrumented seal that
filters through the hole.
A submersible landing
grid covers the top of
the 5-meter-diameter
cone. The observatory
instrumentation
includes a pressure
sensor below the seal,
tilt sensors, a chain of
10 thermistors, and a
port through which
formation fluids can be
sampled. Holes up to 1
kilometer deep have
been fitted with these
instruments in the
Pacific Ocean; four
more are planned for
the Atlantic.
coast of Oregon, penetrates through
a shallow thrust fault within the
prism. The other was drilled off
Vancouver Island in an area where
seismic reflection profiles indicate
the presence of frozen methane
hydrate in the accreted sediments.
Observations in these holes are
helping to define the relative impor-
tance of focused and diffuse fluid-
flow pathways, and are showing that
water may be expelled in an episodic
manner. The observations will also
answer questions about the seismic
rupture potential of the deep thrust
fault that lies beneath the prism and separates the sedimentary rocks
accreted to the North American continent from the oceanic crust that slides
beneath.
In 1994, four additional CORK installations are scheduled. In the
spring, three holes will be drilled and instrumented in the Barbados
accretionary prism. These holes will penetrate directly into the primary
subduction thrust-fault zone that at this location lies at a depth that can
be reached by drilling. One will penetrate an anomalously reflective part
of the fault, where extremely high fluid pressures are believed to be
present. Later in the year, another CORK will be placed in a hole that is
to be drilled in the large TAG hydrothermal deposit. This hydrother-
mally active site is situated in the sediment-free rift valley of the Mid-
Atlantic Ridge at 26°N. Information from this hole will complement the
information gained from the Middle Valley sedimented-rift sites.
Hydrogeologic observations in deep ocean environments will never
be as simple as equivalent observations on land. The consequences of
porefluid pressures and "groundwater" flow beneath the seafloor are
great, however, and the extra effort required to understand sub-seafloor
fluid flow processes is well justified. Holes drilled by ODP provide
unique opportunities for studying the surprisingly active hydrologic
environments beneath the seafloor; the tools described here provide one
way to take advantage of these opportunities. •
Earl Davis is a senior research geophysicist at the Pacific Geoscience Centre,
Geological Survey of Canada, where he spends most of his time either studying
the signals and wrestling with the noise associated with crustal fluid flow, or
dreaming up new ways to measure them. When asked privately, he reveals that
he would rather be a diviner, but concedes that where he likes to work, even a
good diviner would be in over his head.
Keir Becker is a professor at the Rosenstiel School of Marine and Atmospheric
Science, University of Miami. His interests have been focused on the
hydrogeology of oceanic crust for much of his career: he has spent nearly two
years of his life on the drill ships of the Deep Sea Drilling Project and the Ocean
Drilling Program, conducting downhole hydrogeologic experiments like those
described here. He openly admits that he would rather be windsurfing, where his
love for water can be realized more simply, and where being in over his head is
just part of the fun.
86
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Fluid Composition
in Subduction
Zones
Miriam Kastner and Jonathan B. Martin
vidence for large-scale fluid flow and fluid expulsion at
subduction zones includes several observations:
• the porosity of the originally water-rich sediments of
accretionary complexes is rapidly reduced by tectonic forces,
• heat flow is regionally variable,
• depth profiles have characteristic temperature and pore-fluid chemical
and isotopic anomalies that can only be maintained by rapid and rather
recent fluid flow, and
• diffusive and /or channelized fluid venting is widespread.
The latter occurs along sedimentary and structural-tectonic conduits
such as unconformities, faults, and the decollement (the prominent
boundary between the overriding and underthrusting plates shown in
the figure on page 87) as well as through mud volcanoes.
These fluids sustain prolific benthic biological communities and
cause widespread carbonate deposition as cement, vein filling, crusts, or
chimneys, mostly from oxidation of microbially or thermogenically derived
methane. The fluids also play an important role in the deformational,
thermal, and chemical evolution of subduction zones, and enhance sedi-
ment diagenesis and rock metamorphism. Fluids
released from these reactions transport dissolved
components into the ocean, some of which may be
important for global geochemical budgets. At greater
depths (more than 80 kilometers), released fluids,
especially water from the subducted sediments and
altered oceanic basement and carbon dioxide from
methane oxidation and decarbonation reactions, may
expedite partial melting processes in the overlying
mantle wedge, leading to arc volcanism.
The presence of sediment-derived isotopes and trace elements,
especially cosmogenic beryllium 10 (half life 1.5 million years) in arc lavas,
provides evidence for sediment recycling in some subduction zones. Global
estimates of sediment contribution to arc lavas range from a few to 20
percent of the subducted sediments.
The total volume of the internally available fluid sources in subduc-
tion zones through steady-state processes has been estimated to be 1 to 2
An extensively
fractured sediment core
from the decollement at
Nankni, retrieved
during OOP Leg 131,
Site 808, about 960
meters below the
seafloor.
Oceanus
Winter 1993/94
87
Deep-towed side-scan
sonar image of a mud
volcano, located about
20 kilometers east of
the deformation front
at the Barbados
convergent margin.
The swath width of the
image is 1,500 meters
and the height of tlie
mud volcano (above the
surrounding
sediments) is about
50 meters.
cubic kilometers per year. These estimates, however, do not account for
the 2 to 6 order of magnitude larger than predicted fluid-flow rates
measured at numerous channelized fluid venting sites, for example, at
the Barbados, Nankai, and Cascadia accretionary complexes. This
discrepancy in fluid volumes suggests either that the channelized fluid flow
is transient in nature and /or that a major external fluid source exists.
Meteoric water (rain or snow) is the most likely external source, but how it
might be transported to the subduction zones is yet unknown.
Geochemistry of the Fluids
Detailed studies of the chemical and isotopic compositions, mostly of the
pore fluids obtained through drilling and of the channelized venting
fluids obtained with submersibles and conventional coring, indicate that
the chemical and isotopic characteristics of the expelled fluids differ
markedly from seawater, the original pore fluid (see the figures on page
88). Of particular interest are the ubiquitous fresher-than-seawater fluids
often found in accretionary complexes and associated with fluid conduits
such as faults, the decollement, or mud volcanoes. Seawater chloride
dilution of 10 to 64 percent has been recorded. Unraveling the origin of
fresher-than-seawater fluids is of great importance to understanding
subduction zone hydrogeochemistry. The only internal sources and
processes that may provide water for the formation of the low-chloride
fluids are: 1) Dehydration or breakdown of hydrous minerals, particu-
larly clay minerals, amorphous opal (opal-A), and zeolites in the accre-
tionary complex and of minerals such as talc, phengite, serpentine, and
amphiboles in the oceanic basement, 2)
Dissociation of gas hydrates (clathrates), ice-
like crystalline compounds whose expanded
ice-lattice forms cages that contain gas
molecules (mostly methane hydrate has been
recovered from several accretionary com-
plexes, and geochemical and geophysical
evidence for the presence of gas hydrateshas
been observed at most of them), and 3) Clay
membrane ion filtration: Geochemical evi-
dence for the occurrence or importance of the
latter process in clay-rich subduction zones is
yet unavailable.
These overall dilute and fresher-than
seawater fluids are often characterized by other
chemical and isotopic anomalies. They are
generally enriched in alkalinity, lithium,
sodium, silica, beryllium, boron, iodine, methane (ethane, propane), carbon
dioxide, and hydrogen sulfide; in contrast, they are depleted in potassium,
magnesium, and sulfate. Concentrations of calcium and strontium vary,
influenced by carbonate recrystallization and, at greater depths, by decar-
bonation. Strontium isotopic ratios that vary from highly radiogenic conti-
nental crustal to nonradiogenic oceanic basement values suggest communi-
cation with various deep-seated basement sources. This is also supported by
the presence of mantle-derived helium; for example, based on helium
isotopic analyses, at Nankai below the decollement, about 25 percent of the
• •
88
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
helium is mantle-derived. Helium,
like chloride, is an excellent
geochemical tracer because it is
conservative and unaffected by
chemical or biological reactions; its
isotopic composition uniquely
defines its source. Trace amounts
of magmatic methane and carbon
dioxide may be present as well. If
so, they would be masked by the
abundant microbially and thermo-
genically-derived biogenic meth-
ane and carbon dioxide.
Unusually high pH (alkaline)
and chloride-depleted (57 percent
seawater dilution) fluids that are
rich in methane, ethane, and
propane as well as in hydrogen sulfide, carbonate alkalinity, and ammo-
nia, have been recovered from the Conical Seamount, an active low-
density serpentinite mud volcano in the Mariana forearc, and in the
Chile convergent margin adjacent to the triple junction. This suggests a
rather deep (greater than or equal to 10-kilometers) source for these
fluids. The global flux of these unusual fluids is as yet unknown. The
Mariana subduction zone lacks an accretionary complex; here all the
sediment is being subducted.
Mud Volcanoes
A variety of seafloor bathymetric features known as mud volcanoes
typify sites of focused fluid venting. Their shapes range from conical, with
diameters of a few meters to about 1 kilometer, to linear ridges that are
occasionally greater than 10 kilometers long. These features are common at
subduction zones; they have been found at every convergent plate margin
surveyed at the appropriate resolution. One of the most extensively studied
mud-volcano fields occurs at the Barbados convergent margin. Here the
surface area of the mud volcanoes covers nearly 45 percent of an approxi-
mately 1,600-square-kilometer region. About 30 square kilometers of this
mud-volcano field, situated on the oceanic side of the deformation front, has
been extensively surveyed using geophysical and coring techniques.
Deep-towed side-scan sonar images of the Barbados margin show a
variety of mud volcano features. These images allow us to record tempera-
ture gradients in detail and recover cores from individual mud volcanoes.
One of the larger mud volcanoes is shown in the figure at left. In its center,
temperatures of about 20°C were measured at only I meter below the
seafloor (mbsf); the surrounding bottom water temperature is about 2°C.
The venting fluid is characterized by chloride concentrations of 211 milli-
moles, about 40 percent of seawater's value. These temperatures and
chloride concentrations reflect extraordinarily rapid, focused, vertical flow
of fluid from the mud volcano. Numerical calculations based on the tem-
perature gradients indicate flow rates of 17 meters per year. The tempera-
ture gradients and chloride dilution decrease closer to the edge of the
volcano, indicating that flow is most rapid in its center.
This cross-section of a
subduction zone with
an accretionary
complex reveals fluid
influence on processes
at various depths of the
zone. At depths of I to
5 kilometers, fluids
flow through accreted
sediments (small
arrows) either along
conduits such as faults,
stratigraphic horizons,
and mud volcanoes, or
by porous flow. At
depths of 13 to 18
kilometers, water from
the subducting slab
forms serpentinite
within the overlying
mantle wedge. It erupts
because its density is
lower than that of the
surrounding peridotite
(large arrow at green
blobs). At depths of
about 80 kilometers,
water evolves from the
slab and initiates
mantle wedge melting,
causing arc volcanism
(large arrow at red
blobs).
Oceanus
Winter 1993/94
89
Chloride (millimoles)
200 400
600
u.uu
0
n
.0
1 °-05
-
OJ
-c
o
•*-•
£
a
•§ 0.10
n
-a
n
Qi
«J
0)
o
Box
5
^0.15
-
Cores
Barbados
•4-J
CL
o
Mud
„
Volcano
Q
D Center
n in
, , o ,
• Edge
Chloride (millimoles) \
550?
Chloride concentration versus depth profiles, in pore fluids
extracted from sediments recovered with piston cores from the
Barbados mud volcano, in pore fluids extracted from
sediments recovered with drill cores in the accretionary
complexes at Barbados and Nankai, and from slope sediments
at the Peru subduct ion zone.
Saline Fluids in Subduction Zones
The residual fluids from gas hydrate formation and clay
membrane ion filtration are brines, fluids of high solute
concentrations and of high density. However, brines have
not been observed in association with the ubiquitous gas
hydrates in accretionary complexes. This is best explained
by loss of solutes through diffusion or fluid advection at
the sites of hydrate formation.
In addition to precipitation or dissolution of evapor-
ite minerals such as halite or sylvite, brines with more
than twice seawater chloride concentrations result from the
hydration of volcanogenic sediments or of oceanic base-
ment rocks to hydrous minerals such as clay minerals and
zeolites. An excellent example of a brine formation from
seawater evaporation has been observed in the Peru forearc
basins; brines from volcanic ash alteration occur in the New
Hebrides intra-arc Aoba basin and in an Izu-Bonin forearc
basin. At all the previously drilled accretionary complexes,
however, the fresher-than-seawater fluids dominate. Saline
fluids should, however, be present in accretionary com-
plexes associated with evaporites, for example in the
Mediterranean Sea. The only fluids with somewhat (less
than 15 percent) higher chloride concentrations than
seawater were observed in association with volcanogenic
sediments in the Nankai and New Hebrides accretionary
complexes. Similar to submarine hydrothermal fluids, the
elevated chloride fluids associated with volcanogenic
sediments or oceanic basement could evolve into calcium-
chloride brines. Saline fluid inclusions have been observed in mineralized
veins in metamorphic rocks of accretionary complexes. Because of the
scarcity of geochemical data on these fluid inclusions, it is premature to
speculate on their origin or quantitative importance. •
Miriam Kastner, the first woman professor at Scripps Institution of Oceanography, gradually migrated
westward from Harvard University where she received her Ph.D., through the University of Chicago at which
she spent a year as a post doctoral fellow. During her first summer as a Harvard graduate student, she
became interested in oceanography, and worked with a prominent conservative scientist on the geochemis-
try and mineralogy of sediments recovered from the flanks of the Mid- At I antic Ridge. She is interested in
natural-fluid rock processes, especially between seawater and marine sediments and oceanic basement.
Her finite "spare" time is mostly dedicated to music.
Jonathan B. Martin came to Scripps Institution of Oceanography to work on fluids after graduating with a
master's degree in geology from Duke University, where he worked on rocks. During the past year, he has
completed his Ph.D. dissertation and produced a son, Peter. He is grateful to his wife, Ellen, for her help in
both endeavors. After graduation, he will continue to work on convergent margin processes, both modern
and ancient, at the University of California, Santa Cruz, and at the US Geological Survey.
Jayne Doucette/WHOI Graphics
90
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Scientific Ocean
Drilling and
Continental Margins
Understanding the
Fundamental Transition
from Continent to Ocean
James A. Austin, Jr.
xtending from the beach to the base of the continental rise,
continental margin waters are the "ocean" most familiar to
Earth's human population. They are a popular recreational
site, and fish from these waters sustain much of the global
population. Most of the remaining hydrocarbons that fuel
modern civilization's activities are expected to be found beneath these
waters, associated with the thick sediments that line many continental
edges. Climate researchers are now concentrating on continental mar-
gins, because their sediments hold vital historical clues for helping us
unravel global temperature changes and associated sea-level fluctua-
tions. However, we still know little about the most fundamental crustal
transition on the earth's surface: that from continent to ocean. The study
of plate tectonics has rewritten Earth's geological history as a story of
continents moving across the surface of a (presumed) rigid sphere through
time, but it has not yet provided details of their interactions, the critical link
in understanding the nature of ocean-continent boundaries (OCBs). Drilling,
along with detailed geological and geophysical surveys, must fill that gap.
Ascertaining the geological history of continental margins has been a
priority of scientific ocean drilling for many years. Drilling transects
across margin pairs are now recognized as critical to properly describe
the competing models of intracontinental extension, in particular the
roles of throughgoing crustal detachment faults in margin formation and
subsidence. The Atlantic Ocean is an obvious place for ODP to attack this
important theme, because conjugate "passive" continental margins (defined
as those where continental and oceanic crusts are fused together) are better
We still know
little about
the most
fundamental
crustal
transition on
the earth's
surface: that
from continent
to ocean.
Oceonus
Winter 1993/94
91
North
Atlantic
(closed)
South
Atlantic
(closed)
A reconstruction of the
Atlantic and adjacent
seas approximately 180
million i/ears ago. A
number of conjugate
margin pairs with
widely differing
estimated ages of
formation are available
for study. The black
lines near the colored
coastlines are presumed
ocean-continent
boundaries, based upon
available geological and
geophysical data.
developed and more accessible around the Atlantic than anywhere else.
The birth of various Atlantic margin pairs has occurred at different
times: about 50 million years ago north of Iceland, 130 million years ago
between southern South America and Africa, 180 million years ago between
North America and Africa, and 110 million years ago for eastern Canada
and the Iberian Peninsula. (Even younger margin pairs, for example in the
Red Sea, may be addressed in the future.) OOP has chosen two of these
pairs as prime examples of volcanic and nonvolcanic end-members of
continental fragmentation and ocean-basin
formation: southeast Greenland-Norway (see
"Exploring Large Subsea Igneous Provinces,"
page 75) and Iberia Abyssal Plain-eastern
Canada, respectively.
The Eastern Canada-Iberia
"Nonvolcanic" Transect
The margins off the Grand Banks and Iberia
are logical drilling candidates for several
reasons. They have been intensively studied
using a variety of marine geophysical and
geological techniques, including coring,
dredging, bottom and subbottom sound
profiling, and submersible diving. As a result,
their prebreakup reconstruction is well under-
stood. Breakup-related crustal structures, the
key to these margins' early history, are buried
under just 2 to 3 kilometers of sediments, making
basement rock accessible to ocean drilling. In
addition, their locations relative to other themati-
cally important OOP study sites allow conve-
nient repeated access by JOIDES Resolution, and
return visits of the drill ship are essential for
successful margin drilling, because the research
targets are deep and technically challenging.
OOP has just commenced a systematic approach to drilling in
passive margins in the North Atlantic with Leg 149 (March to May 1993),
which included a transect across part of the Iberia Abyssal Plain (IAP)
west of Portugal. The shipboard scientific party encountered faulted
blocks composed of rocks of continental affinity separated from normal
Atlantic Ocean seafloor basaltic volcanic crust by a broad zone contain-
ing both exhumed, faulted oceanic crust and altered plutonic igneous
rock known as peridotite. The peridotite forms a ridge that extends for
more than 100 kilometers and delimits the approximate ocean-continent
boundary along this margin.
The northern Newfoundland Basin (NB) is the conjugate to the Iberia
Abyssal Plain. Available geophysical data suggest that the Newfound-
land Basin contains a zone approximately 150 kilometers wide of thinned
continental crust separating known Grand Banks continental crust from
known oceanic crust seaward of a mid-Cretaceous period (about 118
million years ago) isochron, a magnetic anomaly known as MO. This
crustal transition is much like that postulated for the Iberia Abyssal
92
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Plain. This zone constitutes one of the largest areas of enigmatic seafloor
in the North Atlantic. The Newfoundland Basin may also be character-
ized by a peridotite ridge. However, the Newfoundland Basin differs
significantly in one major way — it exhibits a well-defined geological
unconformity ("U"/Avalon, in the figure on page 94) that caps and occa-
sionally truncates underlying crust out to the interpreted ocean-continent
boundary 20 to 40 kilometers west of magnetic anomaly MO. The strong
development, relative flatness, and wide areal extent of "U" suggest that it
was eroded at or near sea level during the Iberia-Grand Banks breakup.
The first-priority issue for proposed OOP drilling in the Newfound-
land Basin is to ascertain the origin of the "U" unconformity and the nature
of underlying crust. If the wide transition zone in the Newfoundland Basin
proves to be floored by continental crust that has thinned, faulted, and
eroded in a subaerial environment, a fundamental ueiv class of crust will be
documented that must be accounted for in future models of continental
breakup. Drilling in the Newfoundland Basin will also provide the crucial
geological control for understanding the early history of this part of the
North Atlantic, particularly when used in conjunction with results from the
Iberia Abyssal Plain, the other half of the conjugate pair.
What the Future Holds
Continental margin drilling represents a long-term, multinational
commitment. Completing the volcanic and nonvolcanic transects as
presently defined will take multiple drill ship expeditions over a period
of years. This will cost tens of millions of dollars, because continental
margin holes require multiple nested metal liners to promote stability for
deep penetration. Furthermore, thick sediments present safety hazards
because of their potential to contain overpressured fluids and gases.
JOIDES Resolution or her successor will eventually need to be equipped
Illuminated from the
northwest, this shaded
relief bathymetry map
shows the positions of
Iberia, eastern Canada,
and adjacent plates at
magnetic anomaly MO
tune, approximately
118 million years ago.
This paleo-reconstruc-
tion is extraordinarily
well constrained, which
is one of the reasons
that OOP has decided
to concentrate on the
Iberia-eastern Canada
margin pair.
Data courtesy S Snuastava. Bedford
Institute ot Oceanography
Oceanus
Winter 1993/94
93
10-
Sound profiles near
OOP Site NB-4
illustrate geology
characteristics of the
Newfoundland Basin.
The recording above is
in reflection time, and
the recording at right is
of actual depth (relative
to the sea surface). The
nature of the prominent
"ll"IAvalon
unconformity, ami its
relationship to underly-
ing basement, is clear.
Basement rock may be
thinned continent, part
of North America
affected profoundly
during its separation
from Iberia. ODP plans
to drill to and sample
both the "U"/Avahn
unconformity and
basement rock.
NW
SE
with complicated and expensive blowout-prevention capabilities, similar
to those now used in the oil and gas industry. Despite these inherent
costs and the remaining engineering difficulties, ODP must meet the
margin challenge if we are ever to understand the essence of the global
jigsaw puzzle that we call home. •
This is University of Texas Institute for Geophysics Contribution #1016.
James A. Austin, Jr.. first recollects seeing the Woods Hole Oceanographic
Institution as a toddler, staring through the railing of the ferry bound for his
parents' summer home on Martha's Vineyard. About 18 years later, he was
admitted to the MIT/WHOI Joint Program in Oceanography, from which he
emerged (relatively unscathed) with his doctorate at the end of 1978. Since that
time, he has been a research scientist at the University of Texas at Austin.
However. New England still calls, that summer home on the Vineyard still exists,
and the ferries from Woods Hole still run. so with luck he will never get too far
from his oceanographic roots.
94
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
When Plates Collide
Convergent-Margin Geology
Asahiko Taira
n the modern globe, Earth's tectonic plates mostly con-
verge in deep sea trenches or collisional troughs. (See
Oceanus Winter 1992/93 for a discussion of "Island Arcs,
Deep-Sea Trenches, and Back- Arc Basins.) Ocean drilling
has provided fundamental information about colliding-
plate processes, including accretion of sediments and volcanic edifices
from underthrusting to overriding plates, emplacement of rocks that
have been altered by the forces at work in colliding-plate zones, and the
nature of continental collisions. It has opened new avenues for compara-
tive studies of modern and ancient earth processes. Recent plate-tectonic
models indicate that many areas known as "erogenic belts," where
Earth's crust has been deformed by such mountain-building phenomena
as thrusting, folding, and faulting, have evolved through convergent-
plate-margin processes such as formation of accretionary prisms, accre-
tion of various exotic terranes, and the collision of arcs and continents.
Accretionary Prisms
The seafloor-spreading concept posed the question of the fate of sedi-
ments on descending oceanic plates, and the ocean drilling program
offered an opportunity to study the nature of sediment deformation in
the deep trenches. DSDP investigations demonstrated that oceanic plate
sediments progressively adhere to the leading edge of the overriding
continental plate, forming an "accretionary prism." Drilling results also
show that sediments from the descending plate are underplated onto the
overriding plate, apparently thickening and lifting the prism. The figure
on page 96 shows seismic reflection and drilling data for the Nankai
accretionary prism, where coring penetrated the incoming sedimentary
sequence completely, transecting the frontal thrust, the decollement zone
(zone of detachment that separates accreted and underthrust sediments),
and underthrust deposits to the ocean basement. The Nankai drilling
provided basic trench stratigraphy, including small-scale structural features
that develop during initial deformation, and it allowed measurement of
Drilling results
show that
sediments from
the descending
plate are
underplated
onto the
overriding plate.
Oceanus
Winter 1993 /94
95
ODP drilling results
from the Nankai
accretionary prism,
offshore of southwest
Japan. The seismic
reflection image on the
left was correlated with
ocean-drilling data,
revealing the informa-
tion on the right,
including the presence
of accreted sediments
above and underthrust
sediments below the
overriding plate.
frontal thrust displacement and decollement zone thickness. In addition
to clarifying the geology of initial deformation, the deep coring shows a
sharp increase in porosity of mudstone across the decollement, indicat-
ing that the decollement is a zone of overpressured pore fluid.
We know from studies of erogenic belts on land that they contain
large volumes of highly disrupted and deformed clastic sediments
(mostly turbidites) with minor amounts of apparently interlayered
basalts, cherts, and tuffs. Detailed stratigraphic work in the Shimanto
belt of Japan, for example, showed an orderly sequence before disrup-
tion: oceanic basement (basalts), pelagic sediments, hemipelagic sedi-
ments with silicic tephras and muddy turbidites, and coarser grained
turbidites, basically similar to that found in the Nankai Trough. Identifi-
cation of such stratigraphy in the erogenic belts is a key to the recogni-
tion of ancient accretionary prisms.
Analysis of small-scale structures in the Nankai cores showed that
they faithfully recorded the geophysically determined direction of plate
convergence. This verification of the connection between small-scale
structural development and plate motions lends a whole new level of
credibility to studies that claim this correlation in ancient rocks.
SW Japan
Eurasia
Plate
500 meters
Nankai Trough
Philippine Sea
Plate
Jack Cook/WHOI Graphics
Depth
Facies
Porosity (percent) I
leters below
seafloor)
Association
cpocn
20 40
1 Lower Slope r
1 I ' i. r
-
Apron !
'*' «
100-
Upper Axial
1 Trench Wedge f
' V
200-
Lower Axial
<U
— ' "*0
Trench Wedge
C
'• v:
(D
«* .'
300-
Frontal Thrust
U
- sm
-
.__ 365 meters in
o
• 7;
Hole SOSC
" * "•
400-
f/\
_ " ^^
500-
Outer
Marginal
Trench Wedge
'o;
cx
: -I
Trench-to-Basin
»••
600-
Transition
"C"-
700-
Upper
Shikoku
' -f'
—
Basin
'.X'- '
800-
C
- #•.
_
a;
_ ^
u
^
900-
.9.
5
Decollement
s
^ * .
1,000-
1,100-
^^_ Zone
1945-964 meters)
Lower
Shikoku
Basin
cene
; 1
o
f-
1,200-
x^
-
Acidic Volcaniclastic
Deposits
*^
". **"
1 , jUU —
Basaltic Basement
*j -I i 1 i
96
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Older Accretionary Complex
"Head-
Scraping
Accretionary Prism
Normal Trench
Faulting
Limestone
Continental Crust
Seamount
Basalt
Blueschist
Gnderplated Seamount
Clnderplated Oceanic Crust
Exotic Terrane Accretion and Blueschist Emplacement
Recent advances in the study of erogenic belts include discovery of
many exotic geologic bodies such as fragments of oceanic plateaus or
island arcs that have traveled great distances to their present position.
Recent drilling in the Vanuatu forearc of the southwest Pacific (the
leading edge of Fiji microplate) unequivocally demonstrates the accre-
tion of sediments and mid-ocean ridge volcanic rocks as discrete thrust
sheets that form a frontal accretionary prism.
Many orogenic belts are characterized by metamorphic rocks called
blueschists that have been formed under high-pressure and low-tem-
perature conditions. The frequent mixing of such "high-grade" meta-
morphic blocks with materials of lower metamorphic grade (green-
schists) presents a perennial problem in accretionary tectonics. Recent
ocean drilling penetration of serpentine diapirs and volcanoes in the
Mariana forearc (leading edge of the Eurasian plate, in the Philippine
Sea) documents intermixed blocks of mid-ocean ridge basalt and
blueschist. The metamorphic grade indicates transport of the blueschists
from sources 13 to 18 kilometers below the serpentine volcano and
suggests accretionary processes are at work in deeper parts of the
forearc. These drilling results strongly support field observations in
many orogenic belts that accretion and underplating of seamounts and
parts of oceanic crust occur over a range of depths (see the figure above).
Summary ofseamount
and oceanic crust
accretion at and under
the lending edge of an
overriding plate. Parts
of an incoming
seamount can be
accreted at the "toe"
and also underplated to
several kilometers deep,
and a part of the
oceanic crust can be
underplated 10 to 30
kilometers beneatli
the sea floor.
Oceanus
Winter 1993/94
97
Drilling in the
Chile triple
junction
penetrated a
site previously
interpreted as
an emplaced
ophiolite and
discovered,
instead...
in situ
volcanism.
Ridge Subduction
The effect of the collision or subduction of an active spreading center has
been controversial. One can argue that oceanic highs such as spreading
ridges provide a principal mechanism of ophiolite emplacement in fore-
arc regions. It can also be inferred that forearcs record unusual thermal
events. Ocean drilling in the Chile triple junction penetrated a site
previously interpreted as an emplaced ophiolite and discovered, instead,
evidence for near-trench in situ volcanism.
Shikoku Basin basalts recovered during Nankai Trough drilling are
covered by a thick submarine pyroclastic deposit that dates to about 15
million years ago. This correlates with land geology in southwest Japan,
where there is evidence of several contemporary unusual thermal events:
near-trench igneous activity including gabbro and granitic rock intrusions, as
well as high-temperature metamorphism. The combination of ocean-drilling
results and orogemc-belt studies shows the geologic events in the forearc that are
associated with the subduction of an active spreading center.
Collision Processes
Collision of major crustal features such as continents and island arcs is
considered to be a principal cause of orogenesis that normally results in
building mountain chains and thickening the crust. Mountain-building
processes, however, are poorly understood. One approach to this prob-
lem is to study the eroded sediments that are deposited in the ocean,
such as Leg 116 drilling in the Indian Ocean's Bengal fan, which was
formed by Himalaya Mountain erosion as perhaps the largest sedimen-
tary deposit in all earth history. Detailed study of heavy mineral assem-
blages suggests a two-phase uplift of the higher Himalayas, one during
the period from 1 1 to 8 million years ago and the other less than 1 million
years ago. Compilation of DSDP and OOP data from various places in
the Indian Ocean also reveals a similar two-phase uplift pattern. The
general inference of such studies is that mountain-building processes are
episodic, and considerably swifter than previously thought.
Ocean Drilling Contributions to Continental Evolution
Accretion of various materials from one plate to the other is a part of the
global material cycle. In early earth history, igneous rocks derived from
the mantle were progressively assembled and accreted to form continen-
tal crusts. Subsequent collision of continental blocks and arcs produced
mountains and yielded new sediments. As a result, sedimentary accre-
tionary prisms became a major part of modified continental blocks. Thus
ocean drilling should continue to be important not only to marine
geoscientists but also to those who study continental geology. •
Asahiko Taira went from Japan to Texas where, to his astonishment, everything
was flat. After receiving his Ph.D. from the University of Texas at Dallas in
sedimentology, he went to Kochi University in Japan, where he encountered the
vertically dipping, highly deformed Shimanto accretionary prism. The Shimanto
belt research led him further into the study of the deep sea. Since 1985, when he
moved to the University of Tokyo, he has been in charge of Japanese OOP
operations. He was co-chief scientist for the drilling he describes in Nankai
Trough. His current research interest lies in the evolution of arcs and continents.
98
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
From the
Superchron to the
Microchron
Magnetic Stratigraphy in
Deep Sea Sediments
Yves Gallet and Jean-Pierre Valet
ed intents acquire the signature of Earth's prevailing mag-
netic field at the time of their deposition. Because the polarity
of the geomagnetic field has reversed repeatedly in the
geological past, the successive polarity changes imprinted in
sedimentary sequences provide the physical basis for mag-
netic polarity stratigraphy. This "magnetostratigraphy" can be used as a
correlation and dating method. A general outline of the magnetic polar-
ity time scale has emerged from scientific studies over the past 30 years;
the ultimate goal is to extend and date the record over even older
periods. Recent new methods in chronology considerably improve the
time resolution of marine sediment magnetic records and provide the
first opportunity to resolve fine-scale features of Earth's magnetic field.
We consider the present-day polarity field to be normal: Magnetic
lines of force are directed toward the north magnetic pole, and the north-
seeking pole of a compass needle points north. However, when the field
has the opposite polarity, the lines of force are directed south and a
compass needle points south. Until the mid 1960s, magnetic polarity time
scales were calibrated using only continental volcanic rocks younger
than 5 million years old. Study of marine sections became possible in the
mid 1960s with the development of more sensitive magnetometers that
could measure the weak magnetization of sediments. Correlation of
magnetic records from various deep-sea cores and with paleomagnetic
and radiometric studies of on-land lava flows followed and verified the
value of sedimentary sequences as records of polarity changes in Earth's
geomagnetic field. With succeeding work on much longer time series,
Recent new
methods in
chronology
considerably
improve the
time resolution
of marine
sediment
magnetic
records.
Oceanus
Winter 1993/94
99
magnetostratigraphy has become a very accurate method of dating
sedimentary sequences.
The first long (pre-Pliocene) magnetic polarity time scale was
proposed by geophysicists from the Lamont-Doherty Geological Obser-
vatory of Columbia University in 1968. Covering the last 80 million
years, the scale was constructed from profiles of marine magnetic
anomalies of the South Atlantic Ocean. A few years later, this scale was
extended to the Lower Cretaceous and late Jurassic periods, with the first
continuous sequence of reversals for the last 160 million years, using
magnetic surveys from the Pacific Ocean. In the meantime, some authors
cautioned against uncritical acceptance of sediment magnetostratigraphy
because the record may be complicated by several factors, such as post-
depositional overprinting of the signal due to chemical changes in the
sediment. The situation then greatly improved with the development of
extremely sensitive (cryogenic) magnetometers, making it possible to
measure large numbers of weakly magnetized samples.
During the 1970s, magnetostratigraphic studies from pelagic limestone
sections of land and deep sea sediments drilled during DSDP confirmed
most of the magnetic polarity intervals (or
chrons) determined from profiles of marine
magnetic anomalies. Magnetostratigraphic
results were also used to calibrate the polarity
time scale. This was achieved by cross-correlat-
ing biostratigraphic zonations deduced from
paleontological studies with the magnetic
polarity sequences observed in sedimentary
sections and revealed from the magnetic stripes
of the seafloor. This research has advanced
significantly through the work of the ocean
drilling programs. For example, coring on
DSDP Leg 73 in the South Atlantic yielded a
tight calibration between bio- and magnetic-
polarity time scales for the Paleogene. Magne-
tostratigraphic and paleontological data are
now available for most of the geological
boundaries since the late Jurassic, the age of the
oldest oceanic crust. Among these boundaries,
the Tertiary-Cretaceous time boundary, which
is important because of its signature faunal
extinctions, is particularly well documented.
The relationship to biostratigraphic zones is in
general well established, but it is not yet
possible to relate the zones to isotopic ages with
the same precision. Magnetic polarity intervals that are directly dated by
isotopic methods are rare. There are two possibilities to obtain this absolute
calibration. The first is to date one or several interstratified lava flows in
sections where a magnetostratigraphic sequence has been identified. The
second possibility is to drill the ocean floor beneath a well-defined magnetic
anomaly and determine the age of the basalt layer using isotopic dating.
After 20 years of detailed studies, the paleontological calibration of the
magnetic polarity time scale is now in good shape, though there is work to
be done to obtain detailed absolute datings.
Magnetic Reversals
Earth's magnetic field is generated in the iron-
rich outer core through a dynamo process, by
which the mechanical energy released from
fluid motions is converted to magnetic en-
ergy. The geomagnetic field is dominated by
a dipolar geometry with either a normal (north
pole of the magnetic needle pointing toward
the north geographic pole) or a reversed (north
pole pointing toward the south geographic
pole) polarity. The brief periods of a few
thousand years of switch between the two
polarity states are called reversals. Reasons for
the reversals are still unknown. However, the
magnetization of rocks as they are formed
provides records, like a tape recorder, of the
succession of the magnetic reversals through
time, ultimately yielding the definition of the
magnetic polarity time scale with more than
300 reversals over the last 1 60 million years.
100
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Oceanic ridge
Magnetostratigraphy of Site 522
Magnetic polarity Inclination Biozonation
sequence
A High-Resolution Stratigraphic Method
The frequency of reversals appears to have changed markedly since the
late Jurassic. Indeed, if the reversal sequence is observed over several
million-year periods, the character of the polarity time scale shows
successive periods of low and high frequency. The rate of reversals
gradually decreased from about 4 reversals per million years at 155
million years to zero reversals at 118 million years when a 35-million-
year-long normal period occurred, the so-called Cretaceous Long Normal
Superchron. From 83 million years onward, the mean frequency of
reversal increases more or less regularly, up to about 5 reversals per
million years for the recent period.
The Cretaceous Superchron is not unique in geomagnetic history.
Another long polarity interval has been identified during Permo-Carbon-
iferous times from land sequences. At the other extreme of the time scale
are very short intervals of a few tens of thousands of years. The mini-
mum polarity interval that can be resolved on individual marine mag-
netic profiles is about 20,000 years; it requires that high spreading-rate
profiles be available. Magnetostratigraphic records from sedimentary
sequences with high deposition rates can provide sufficient resolution to
detect shorter intervals, in the range of a few thousand years. No less
than 10 short magnetic polarity features lasting less than 30,000 years
(microchrons) have been proposed for the last 3 million years.
Microchrons observed at a single location remain speculative, while
others appear to be relatively well documented by distinct records from
various geographic locations. Among these, events known as Cobb
Mountain at about 1.1 million years and the Gilsa at about 1.7 million
Typical
magnetostratigraphi/
obtained at Site 522
from Leg 73 in the
South Atlantic. The
magnetic polarity
sequence is deduced
from clianges in
inclinations. Green
shoivs normal polarity
intervals, white
reversed poles. These
intervals, which are
easily correlated to the
magnetic oceanic
anomalies, are well
calibrated to the
geological stages.
Tlierefore, these results
provided a tiglit
calibration of the
magnetic polarity time
scale since the late
Eocene. (After Tauxe
etal.,1984.)
Oceanus
Winter 1993/94
101
One of the
current major
objectives of
research in
magneto-
stratigraphy is
to confirm the
existence of the
short magnetic
polarity events.
years could be studied in detail from Hole 60913 (Leg 94) sediments in the
North Atlantic.
One of the current major objectives of research in magnetostratigra-
phy is to confirm the existence of the short magnetic polarity events. So
far, none of the events reported during the Brunhes epoch (from 780,000
years ago to the present) appear to be sufficiently worldwide for inclu-
sion in the polarity time scale. Their existence is critical for statistical
analyses based on the distribution and frequency of reversals, which in
turn have important implications for the mechanisms that generate the
magnetic field. Short events could also be used for detailed calibration
and high-resolution stratigraphic correlations between sites.
The new technologies developed by the Ocean Drilling Program
represent a significant step toward the acquisition of very detailed
magnetic records from sediments. Several techniques (X-ray, magnetic
susceptibility, color reflectance) allow detailed between-hole correlation
and the construction of continuous composite sequences from multiple
holes drilled at the same site, such as during Leg 138 in the equatorial
Pacific. Improvements in drilling technology have significantly reduced
the physical disturbance of sediment collected in cores. Continuous
measurements of very weak magnetization intensities are now routinely
made with the horizontal pass-through cryogenic magnetometer aboard
JOIDES Resolution, and most techniques required for detailed magnetic
analyses can also be used in ship laboratories. All these factors have contrib-
uted to the acquisition of very long and detailed paleomagnetic records.
After many years of analyzing the directional changes of the field,
scientists are now trying to obtain records of geomagnetic field intensity.
Since the intensity changes are synchronous over the entire globe, their
record should provide a powerful new stratigraphic tool and new
constraints on the process. Recently, during OOP Leg 138, a detailed
record of geomagnetic field intensity was obtained by Laura Meynadier
and Jean Pierre Valet (Institut de Physique du Globe de Paris) for the last
4 million years from sediments of the equatorial Pacific. The typical
pattern of the curve and the similarity to results from other geographic
areas indicate the promise of this new approach for future studies. •
Yves Gallet completed a Ph. D. on fundamental and practical aspects of
magnetostratigraphy in the Paleomagnetism and Geodynamic Laboratory at the
Institut de Physique du Globe de Paris. His research interests include the
magnetic polarity time scale for pre-oceanic periods and changes in magnetic
reversal frequency since the Paleozoic Era.
Jean-Pierre Valet completed his Ph.D. thesis at the Centre des Faibles
Radioactivites at Gif/Yvette by trying to extract information from the magnetiza-
tion of tiny specimens of sediment, hoping that they would tell him something
about geomagnetic reversals. He is now working at the Institut de Physique du
Globe de Paris, looking at various kinds of materials, sediments and basalts, that
record geomagnetic field variations.
102
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Terrigenous
Sediments in the
Pelagic Realm
David K. Rea
he composition, mass accumulation rate, and grain size of
the terrigenous component of deep-sea sediment provide
records of both the sediment's continental source region
and of transport and depositional processes. By volume,
most terrigenous material arrives in the deep ocean through
the deposition of turbidites (see "Turbidite Sedimentation," page 107).
Here I will review the other three pertinent processes and outline how 25
years of ocean drilling has allowed marine geologists to understand the
earth history thus recorded. The three processes provide the following
kinds of sediment to the deep sea:
• ice-rafted debris, which gives direct physical evidence of glaciers at sea
level;
• aeolian (wind-borne) dust, which offers information about the climate of
the dust-source region and the intensity of the transporting winds; and
• hemipelagic muds, which record continental erosion and runoff in
their flux data.
There is no way to obtain long, relatively continuous records of these
processes other than ocean drilling. The resulting cores contain informa-
tion that spans extended time periods so that geologists may track global
change through many tens of millions of years. The hydraulic advanced
piston core (APC) technology developed by the drilling program also
permits recovery of undisturbed cores containing very high-resolution
sequences of the climate cycles of the past few hundred thousand years.
Finally, a quarter of a century of ocean drilling has resulted in nearly
global coverage; samples are available from most parts of the world's
oceans with the exception of the Arctic and the central Pacific south of
about 20°S latitude.
Ice-Rafted Debris
The geological history of glaciation has been a subject of lively debate
ever since Swiss naturalist and geologist Louis Agassiz (1807-1873)
convinced the scientific public that his idea of vast continental glaciers
was correct. Discussions of the timing of glacial onset centered first on
Sedimentary
Processes
There is no way
to obtain long,
relatively
continuous
records of these
processes other
than ocean
drilling.
Oceanus
Winter 1993/94
103
34.0
34.5
o 35.0
8
o
35.5
Ol
01
36.0
36.5
\
100 200 3001.0 1.5 2.0 2.5 3.0 3.5
Ice-Rafted Debris Oxygen Isotopic
Concentration Composition
(grains per gram) (parts per thousand)
Ice-rafted debris (IRD)
distributions and
oxi/gen-isotope values
for benthic foraminifem
from ODP Site 748 on
Kerguelen Plateau. Tlie
IRD pulse matches the
timing of the early
Oligocene rapid
increase in oxygen
isotope values, linking
this phi/sical and
chemical evidence for
the onset of antarctic
glaciation.
the Northern Hemisphere, and then the
Southern. Early in the history of DSDP, Legs 12
to the North Atlantic and 18 and 19 to the
North Pacific had among their major objectives
the determination of the timing of Northern
Hemisphere glaciation, especially the age of
glacial onset. Cores from all three of these cruises
clearly showed that ice-rafted debris became an
important component of the sediment at a rime
then estimated to be in the middle to late
Pliocene. Later, North Atlantic Legs 38 and 49
confirmed the original results of Leg 12.
The ice-rafted debris stratigraphy was
reasonably clear in these regions, but use of the
hydraulic piston corer in the late 1970s along
with improved resolution of the biostratigraphy,
oxygen-isotope stratigraphy, and magnetic-
reversal stratigraphy were needed before the timing of glacial onset could
be determined precisely. These improved stratigraphies were provided for
the North Atlantic by the scientists of Leg 81, and by the mid 1980s it
became clear that Northern Hemisphere ice rafting began in both the North
Atlantic and North Pacific almost exactly at the time of the Matuyama-
Gauss magnetic reversal, recently dated at 2.6 million years ago.
The details of high northern latitude glaciation were an important
objective of DSDP Leg 94 and ODP Legs 104, 105, 151, and 152 to the
North Atlantic and DSDP Leg 86 and ODP Leg 145 to the North Pacific.
In addition to further defining the Plio-Pleistocene glaciation 0 to 2.6
million years ago, these cruises found evidence for a latest-Miocene to
earliest-Pliocene ice advance: 4- to 6-million-year-old glacial dropstones
have been recovered from both the North Atlantic and North Pacific oceans.
The drilling history of the high southern latitudes is similar. Legs 28
and 35 recovered ice-rafted debris as old as the Oligocene with large
numbers of such grains occurring in Miocene and younger sediments. ODP
has made high southern latitudes a special target. A major objective of legs 113
to the Weddell Sea and 119 and 120 to the Kerguelen Plateau and the margin of
Antarctica was articulation of this history. As a result, scientists have been
able to link the onset of significant ice rafting with the shift in oxygen
isotopes at the Eocene /Oligocene boundary that signifies the buildup of ice
on the southern continent.
Aeolian Dust
Although some aeolian studies arose from Pacific Leg 62, the first DSDP
cruise to specifically target accumulations of aeolian dust was Leg 86 to
the Northwest Pacific. That cruise cored the area's well-known red clay
sediments and recovered one of the first whole Cenozoic records of
aeolian deposition. It showed very low dust fluxes through most of the
latest Cretaceous and Cenozoic, with an order of magnitude increase in
dust input beginning about 3 million years ago, corresponding to the drying
of Asia and the beginning Northern Hemisphere glaciation.
Dust-grain size provides a record of wind intensity. In the North
Pacific the Leg 86 data confirmed a large reduction in aeolian grain size
found to occur once before at the Paleocene/Eocene boundary, suggest-
104
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
ing that atmospheric circulation in the early Eocene was much more
sluggish than in the late Paleocene. Samples from that same cruise were
later used to demonstrate that this grain-size change was one of several
significant paleoclimatic changes that occur at the Paleocene/Eocene
boundary. Refining the aeolian history of the Northern Hemisphere was
among the objectives of North Pacific Leg 145 in 1992.
Leg 108 in 1986 investigated the late Cenozoic record of dust trans-
ported from the Sahara to the eastern North Atlantic and documented the
history of north African drying over the past several million years. Leg 117
in 1987 to the Arabian Sea demonstrated a strong monsoonal influence in
the aeolian-grainsize wind-strength record and that dust fluxes from Arabia
to the Indian Ocean increase severalfold during glacial times.
Unraveling the history of Southern Hemisphere atmospheric circula-
tion from the aeolian dust record was one among several paleoclimatic
objectives of Legs 92 to the South Pacific, 121 to the Indian Ocean, and
130 to the western Pacific. Those cruises found very low flux values of
dust to these areas for the past 60 million years, suggesting among other
things that Australia has been essentially deflated for most of the Cenozoic
(all the fine-grained dust has blown away). Grain-size
data suggest that an increase in zonal wind intensity of
the Southern Hemisphere trade winds occurred in the
early part of the late Miocene, the only significant
change found in those Neogene records. Finally, there
is little or no indication of any Southern Hemisphere
response to the late-Pliocene onset of Northern Hemi-
sphere glaciation.
Comparing the aeolian records from the two
hemispheres suggests that they may vary indepen-
dently, a concept termed "hemispherical asymme-
try." Such asymmetry should be strongest during
the 30 million years beginning in the early Oligocene
when the earth was characterized by one glaciated
pole and one warm pole. Leg 138 to the eastern
Equatorial Pacific allowed an explicit test of this idea,
using aeolian dust to construct a history of the past
locations of the Intertropical Convergence Zone, which
has been in its present latitude only for the past 4
million years. Prior to that time it lay well to the north,
consistent with the idea of the Southern Hemisphere
being more energetic than the Northern Hemisphere
before the late Pliocene.
Hemipelagic Mud
The hemipelagic muds that may extend many hundreds to a thousand
kilometers offshore are one of the last major unknowns of the several
kinds of deep sea sediment. These deposits have been hard to date, but
should provide an important payoff because they may contain records of
climate, particularly continental runoff, in their mass accumulation rate
and compositional data. Though no DSDP or OOP cruise has had this
kind of deposit and the paleoclimatic record it might contain among its
major objectives, combined terrigenous flux data from the several legs to
Grain and flux of
aeolian dust from
DSDP Site 576 in the
northwest Pacific
Ocean. Micrometer
equivalents of the
loga rithm ic ph i- 1 1 n its
of size are about
9.0O = 2 micrometers,
8A<$> - 3 micrometers;
lower phi numbers
correspond to larger
grains.
Aeolian Dust Grain Size (d>5o)
9.2 9.0
c
o
0;
175 350 525 700
Aeolian Dust Flux
(milligrams per square centimeter
per thousand years)
Oceanus
Winter 1993/94
105
the northern Indian Ocean — Legs 22 and 23, 116 and 117, and 121 — allow
the history of sediment delivery to that ocean from the rising Himalayas
to the north to be constructed. That record shows uniformly low deposi-
tion rates before 11 or 12 million years ago, and high rates of terrigenous
clastic deposition since about 9 million years ago. This is interpreted to
represent rapid uplift and erosion of the Himalayas beginning in late
Miocene time.
Leg 146 recovered advanced piston cores from a basin in the Califor-
nia borderland that is characterized by a very high deposition rate of
hemipelagic sediment. Cores from these kinds of settings will play an
increasingly important role as we turn our attention to climatic and
environmental changes on short oceanic or societal time scales. The
abrupt climatic changes found in ice cores and lake cores should also be
present in the hemipelagic sediments of the marginal basins, allowing
the development of a direct link between continental and oceanic cli-
matic regimes in the sedimentary record.
Drift deposits formed from a mixture of hemipelagic mud and
pelagic sediment are the result of contour-following deep-ocean currents
adhering to the sides of bathymetric features, often the lower continental
slope or continental rise. Their depositional history provides a record of
bottom-water formation and flow that can be obtained in no other
manner. Although drift deposits have been identified in the South
Atlantic and South Pacific, nearly all of our information on drifts is from
the North Atlantic, Legs 12, 49, 93, and 94, and 104 and 105, where such
current-controlled deposition began in the early Oligocene and increased
in rate in the Miocene. Leg 145 to the North Pacific showed that the thick
sediment deposit along the northeast side of the Emperor Seamounts,
called the Meiji Tongue, is a drift deposit similar in character and geom-
etry to those of the North Atlantic. This recent finding in the North
Pacific means that there has been bottom water flowing south out of the
Bering Sea into the North Pacific since early Oligocene time. The similar
response of the North Atlantic and Bering Sea to climate change in the
early Oligocene provides new insight into the degree of Northern
Hemisphere cooling that occurred at the same time as the onset of
glaciation in the Southern Hemisphere.
Since the early days of the ocean drilling programs, an important
objective has been to provide the means to decipher the record of terrig-
enous material in pelagic and hemipelagic sediment accumulations. The
global coring operations have resulted in information essential to our
understanding of continental climate and atmospheric and oceanic
circulation during the Cretaceous period and Cenozoic era, information
that is not present on the continents but only beneath the oceans and
which can be recovered only by ocean drilling. M
David K. Rea is one of those people who was not really convinced that in 1970 we knew more about the
back side of the moon than the deep sea, but, after a quick reality check, he entered graduate school in
oceanography and not the space program. After finishing a Ph.D. in marine geophysics and plate tectonics
at Oregon State in 1974, he moved to Ann Arbor where he immediately set up a sedimentology lab and
began studies of the paleoclimatic record of terrigenous, especially aeolian, and other sediments. He is now
Professor of Geology and Oceanography in the Department of Geological Sciences at the University of
Michigan, working on projects ranging from the climatic records preserved in the sediments of the Great
Lakes to the geological history of the North Pacific as based on the results of Leg 145.
106
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Turbidite
Sedimentation
William R. Normark and David J.W. Piper
urbidity currents are the fastest and most destructive
currents in the ocean. The most powerful of them, which
can carry hundreds of cubic kilometers of sediment as
coarse as gravel, are commonly initiated when
earthquakes or storm waves cause submarine
landsliding that dislodges sediment on the slopes of continental
margins. Hurricane storm surges can initiate turbidity currents
from otherwise peaceful atoll and oceanic-island coral reefs.
Another important turbidity-current environment lies offshore
from Earth's largest rivers, where sediment-laden river water can
generate turbidity currents through hyperpycnal flow in which
some of the suspended sediment of the river discharge flows along
the seafloor and continues downslope as a turbidity current. In
addition, the rapidly deposited deltas of these rivers are prone to
periodic failure and landsliding.
Rare, very large turbidity currents periodically deposit thick
sequences of sediment on oceanic abyssal plains, but their return
periods span many thousands of years. However, in some high-
discharge fan deltas, several turbidity currents may occur in a
single year. Turbidity currents often damage and even destroy
human structures, especially submarine telecommunications
cables. In fact, our best "observations" of turbidity current veloci-
ties are drawn from records of the time elapsed between progres-
sive down-slope cutting of a series of submarine telecommunica-
tion cables as a current flows. Velocities of 10 to 20 meters per
second are not uncommon. Our understanding of turbidite sedi-
ments comes principally from conventional marine-geologic
sampling of near-surface sediment and three-dimensional studies
of the sediment sequences using seismic-reflection profiling. Ocean
drilling allows us to verify this data by sampling the sediment sequences
revealed by seismic profiles.
The most fascinating attributes of turbidity currents, their high
speeds and their ability to transport coarse sediment into deep water, are
also those that make them difficult to study with ocean-drilling tech-
niques. Standard HPC (hydraulic piston core) coring techniques normally
Photo of turbidite layer
recovered during OOP
Leg 146, Santa Barbara
Basin, California.
Oceanus
Winter 1993/94
107
A seismic-reflection
profile from the
Amazon Fan shows
din nn el and levee
turbidite elements and
two of the proposed drill
site objectives
for Leg 155.
used to recover the upper, softer sediment cannot penetrate the thick
sand layers left by large turbidity currents. Older, deeply buried sand
deposits are easily penetrated by standard rotary drilling, but the sand
layers generally are not consolidated (unlike the interbedded mud
layers); as a consequence, the sand outside the drill string begins to flow
down the hole eventually wedging the drilling pipe in the hole and
sometimes causing pipe loss.
Channel
Levee
W
••7". > •; ^ ,~3*!^ j- V '" r^vf '• : ^ h. '-L: -V' r^-?-: » -
'., & ' . t /f* ' . '*iar.~5- - -- -_--_i^- -i_ j,-"-— -A-fJ~^ • .
*•,_*! t+f\ «^- _0ii«yyi LI -i, ^j*je
SS&Eft
>%ttW~.> .^ :„.
^,4^p^^
^;-/-i^^;^--:^.-?
5.0 sec
!»^r£r> ' AJ^t^Jr'^'-L£. "^ -TE"-^*
m ?^ftv^-.
W
Modified after R D Flood
Many ocean-drilling scientific objectives require the recovery of
continuous and uniform records of deposits for studies of biostratigra-
phy, past ocean environments, and subsurface geochemical processes.
Turbidite deposits typically represent discontinuous or episodic sedi-
mentation and the inclusion of many microfossils transported from
shallower water. In thick sediment sequences, turbidite sands commonly
comprise hydrocarbon reservoirs and thus must be avoided for safety
reasons. As a consequence, many ocean-drilling legs are deliberately
planned to avoid turbidite deposits.
Nevertheless, turbidite sediment deposits do provide important
information on ocean history. They are the most direct record of rapid
mountain-belt erosion and provide a high-resolution record of the
supply of terrigenous detritus to the ocean. Turbidite sediment derived
from volcanic seamounts or oceanic-carbonate platforms provides
evidence of the timing of tectonic and volcanic events or faulting on the
ocean floor and eruptive activity of seamounts. Predominantly muddy
turbidite sediment has been drilled successfully, with high rates of
sample recovery on several ocean-drilling legs, with the objective of
obtaining continuous stratigraphic sections for interpreting both ocean
history and tectonic history of surrounding land areas. Examples of such
sections include the Weddell Abyssal Plain (Leg 113) for the glacial
history of West Antarctica, the Lau Basin (Leg 135) for volcanic history of
adjacent islands, and the Argo Abyssal Plain (Leg 123) for the erosional
history of the adjacent continents. Leg 116 drilled the abyssal plain south
108
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
of the Bengal deep-sea fan, primarily to understand the erosional history
of the Himalayas and the character of oceanic-floor tectonism in the area.
In addition to revealing information on oceanic events and tectonic
history of the adjacent land areas, the turbidite layers also provide
information about some of the flow characteristics of the turbidity
currents themselves. Because the precise source area for turbidite-
sediment grains can commonly be determined, the Deep Sea Drilling
Program and Ocean Drilling Program cores have shown, for example,
that sediment from the Columbia River off the Pacific Northwest has
been carried by turbidity currents more than 700 kilometers south, then
moved west about 150 kilometers before being carried north into an axial
valley of a spreading ridge (Leg 5). Turbidity currents generated by large
landslides on the flanks of the Hawaiian volcanoes have traveled at least 250
kilometers seaward and moved up and over topographic barriers some 500
meters high (Leg 136).
Ocean-drilling targets selected primarily for stratigraphic or tectonic
significance also provide opportunities to determine what turbidite
sequences are typical of particular submarine environments. However,
many of the fundamental questions concerning the processes of turbidite
deposition cannot be addressed on basin floors, reached only by occa-
sional turbidity currents. Cores from deep-sea fans that are crossed by
channel /natural levee complexes offer the most continuous record of
turbidite deposition and allow us to unravel the complex interplay
between seabed morphology and turbidity-current processes.
Glomar Challenger's last cruise (Leg 96) drilled the Mississippi Fan, one
of the largest modern turbidite deposits, with the express purpose of
learning about the history and
processes of deep-water sedimenta-
tion in an area where the
paleoclimatic effects on sediment
supply were relatively well known.
The Leg 96 program confirmed
extremely rapid rates of deposition on
the mid fan (11 meters per thousand
years at a distance of nearly 500
kilometers from the river mouth) and
that large-scale landsliding also
provides major contributions to deep-
sea fan sequences. Core samples from
the major fan-valley areas further
demonstrated a marked change in
sedimentation (rate and type of
sediment) as sea level rose after the
last glacial period.
The next major program for turbidite study will be in early 1994 on
the Amazon Fan, which is even larger than the Mississippi Fan. The
Amazon Fan exhibits a complex series of meandering channels built by
basinward-flowing turbidity currents. A lobe-like deposit of sediment
builds up from turbidity currents flowing through and exiting the
channels. The channels periodically change course and build new lobes.
The Amazon Fan leg aims to further define the sediment types and ages
of deposits that have been identified by seismic-reflection profiling, and
Exposed in nortJiern
Italy, this typical
turbidite sediment
outcrop is a tens-of-
meters-thick section of
flat-lying turbidite
sand and mud beds.
The Santa Barbara
turbidite beds may look
like this in a few
million years if they are
exposed above sea level
by tectonic activity.
Oceanus
Winter 1993/94
109
The
relationship
between sea-
level change
and turbidite
deposition is
one of the major
objectives of
the forthcoming
Amazon
Fan leg.
to relate this information to controls on sediment supply for turbidity
currents, such as sea-level change and river discharge.
The thick turbidite sequences on the Mississippi and Bengal subma-
rine fans and other abyssal plains drilled by the Deep Sea Drilling
Program and the Ocean Drilling Program are in areas underlain by
oceanic crust. The closing of ocean basins through subduction means
that the ultimate fate of these turbidite sequences is to be highly frag-
mented and deformed in subduction zone accretionary wedges and
eventually to form part of collisional orogenic belts, and become welded
into the crystalline metamorphic fabric of continental crust. Indeed,
many of the accretionary wedges drilled on the ocean margin contain a
high proportion of turbidite deposits.
The stratigraphic record provided by ocean drilling has brought
better understanding of some of the external controls on the accumula-
tion of turbidite deposits. For example, turbidite deposits are more
common when sea levels are low worldwide, particularly at mid and
high latitudes, and there is a marked increase in turbidite abundance
with the onset of extensive continental glaciation in the late Tertiary
(during the last 5 million years). The detailed relationship between sea-
level change and turbidite deposition remains unclear and is one of the
major objectives of the Amazon Fan leg planned for spring 1994. •
Being reared near Ocean Lake, Wyoming, is one of the more plausible excuses
for Bill Normark's keen desire to go to sea whenever possible. He has been a
loyal fan of deep-sea turbidite fans ever since his thesis advisor at Scripps
Institution of Oceanography suggested that he choose between global marine
excursions and a career in research. When he is not actively involved in the
study of modern turbidites or doing his duty as Assistant Chief Geologist for the
US Geological Survey, he dreams about continuing his other research interests,
including the submerged parts of the Hawaiian volcanoes where humongous
submarine landslides dominate the seafloor.
David Piper was educated as a traditional land geologist at Cambridge Univer-
sity. During his Ph.D. studies, he spent a sabbatical year at Scripps Institution of
Oceanography, where he met Bill Normark, and has enjoyed working at sea ever
since. His interests are in using marine geology to understand the processes
involved in depositing rocks seen on land. He is a Research Scientist with the
Geological Survey of Canada at Bedford Institute of Oceanography.
110
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Shallow Carbonates
Drilled by DSDP
and ODP
Oceanic Benchmarks and
Dipsticks for Continental Margins
and Volcanic Aseismic Ridges
Andre W. Droxler
hallow carbonates, mostly marine and biogenic in origin,
originate within the ocean, instead of being transported there
from land as are siliciclastic sediments. Individual carbonate-
secreting fauna and flora produce shells, micro- to macro-
scopic in size, to protect themselves from predators and
adverse physical conditions. The bulk of the carbonate production,
related to benthic carbonate-secreting flora and fauna living in symbiosis
with micro-algae, is limited to the upper 100 meters of the water column
where sunlight penetrates. Furthermore, the optimum carbonate produc-
tion is restricted to relatively warm waters (subtropical and tropical
regions) within a narrow range of water depths between low-tide depth
and 20 meters. These basic parameters, in addition to the general evolu-
tion of oceanic carbonate-secreting biota, have greatly influenced the
development of thick carbonate platforms and shelves, usually character-
ized by successive phases of
growth, reduction, recovery, and
ultimate demise or "drowning."
Taken together, billions of
individual carbonate-secreting
fauna and flora produce huge
volumes of carbonates, indirectly
compensating for the sinking of
the substratum and /or the rising
of sea level and thus unconsciously
attempting to remain within the
light. In addition to being relatively
accurate indicators or "dipsticks" of
Oceanus Winter 1 993/94
Bottom of ODP Hole
6276, core 60X, from
Leg 101 in tlie Baha-
mas. From the late
Albian (about 100
million i/ears ago) these
bioturbated skeletal
dolostones unth small
benthic foraminifers
(miliolids), shell molds
(such as gastropods),
and gi/psum inclusions,
indicate they were
deposited in a shallow
subtidal lagoon in a
very shallow tidal to
supratidal evaporitic
environment (sabkas).
111
(right) Molds of coral pieces such as this (species
undetermined) were recovered from Hole 715 A
through drilling the far eastern edge of an early
Eocene (some 50 million year old) shallow carbon-
ate platform that was established briefly on a
volcanic basement.
(left) Recovered from Hole 812B on the Queensland
Plateau, this mold offaviid scleratinian coral
(presumably Platygyraj offers evidence for tropical
shallow carbonate during the middle Miocene.
112
sea-level fluctuation, shallow carbonates become also excellent benchmarks
for quantifying the magnitude and rate of vertical morion (subsidence and
uplift) characteristic of passive continental margins and intraplate volcanic
ridges in the context of plate tectonics. Finally, because of the temperature
limitation of most carbonate-secreting biota, shallow carbonates are rather
precise recorders of latitudinal plate movement (horizontal translation) and
climatic and biochemical changes.
During the past 25 years, the ocean drilling programs have recovered
numerous shallow carbonate sequences, ranging in age from the late
Triassic (230 million years ago) to the Quaternary period (the last 1 .6 million
years), along continental passive margins and aseismic volcanic ridges in
intra-oceanic basins (see map). Several OOP legs have been drilled specifi-
cally to address questions about the evolution of shallow carbonate systems.
For instance, Leg 101 in the Bahamas, the OOP maiden voyage in spring
1985, was the first drilling leg fully dedicated to a single carbonate system.
Shallow Water Carbonates on Continental Margins
Triassic Development of the Northwest Australian Continental Margin. On the
Wombat Plateau, Triassic (230 to 205 million year old) shallow carbonate
rocks, so far the oldest sediments recovered by ocean drilling, were first
deposited in association with deltaic sediments and then as shelf-lagoon
limestone/marlstone and more than 200-meter-thick coral/sponge reef.
The reef complex has some close similarities to the spectacular reefs of
the Northern Calcareous Alps in the Dolomites that developed at the
same time.
Late Jurassic/Early Cretaceous Development of the North Atlantic's
Conjugate Continental Margins. In addition to dredging and seismic
profiling, drilling on the Blake Plateau, in the Bahamas, and in the
southeastern Gulf of Mexico, has helped to constrain the early evolution
of the western North Atlantic passive margin. A Mesozoic shallow
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
carbonate shelf or "giga-bank" at some point surrounded the Gulf of
Mexico and stretched from the northern part of Cuba and the Bahamas
to the Grand Banks off Newfoundland. In the southeastern Gulf of
Mexico, the first shallow water limestones encountered by drilling are
late Jurassic (about 140 million years old). Drilling in the Bahamas and
on the edge of the Blake Plateau showed that the Mesozoic carbonate
giga-bank, though segmented by several deep reentrant basins, already
existed in the late Jurassic and early Cretaceous periods (approximately
125 million years ago). Drilled in several sites, this giga-bank is charac-
terized by limestones typically deposited along a shelf edge, on tidal
flats, and on very restricted platform interiors. The "drowning" of the
mega-bank occurred earlier in the northern part of the Blake Plateau/
Grand Banks (in Barremian rime, about 115 million years ago) than the
southern part (late Albian, about 100 million years ago). On the eastern
North Atlantic margin, another carbonate platform evolved from an Early
Jurassic (about 190 million year old) carbonate ramp to a Middle Jurassic
(some 165 million years old) platform, that is, a phase of vertical buildup
followed by a phase of mostly lateral growth. Based on drilling along the
Moroccan continental shelf, high energy oolitic shoals and scattered coral-
sponge reefs, similar to those observed on the conjugate Scotian Shelf
margin, colonized the edge of the Late Jurassic platform. The early Creta-
ceous demise of the Moroccan platform was constrained by sudden change
in the composition of limestone turbidite beds in the deep Moroccan basin.
Emperor
Seamounts
Rio Grande
chagos-Laccadiue
Mascarene Plateau Ridge rsorthwest
Australia Austra[ia
20 Winter
Isotherm
Continental
Margins
Shallow Carbonates on
Aseismic Volcanic Ridges
Coral Reefs
Jack CookWHOI Graphics
The main continental passive margins and nseismic volcanic ridges where shallow water carbonates have
been drilled in the past 25 years by DSDP and ODP are indicated. The global distribution of modern coral
reefs and the 20°C winter isotherm are also shown.
Oceanus
Winter 1993/94
113
Results from
drilling
offshore of the
Great Barrier
Reef clearly
show that the
largest modern
barrier reef on
Earth was
established
only very
recently.
Cenozoic Development of the Northeastern Australian Margin. Recent
drilling during Leg 133 on the Queensland and Marion plateaus illus-
trated a rather sudden transition from temperate bryozoan-rich shallow
water limestones (middle Eocene to late Oligocene, approximately from
40 to 25 million years old) to tropical coral and green algae-rich shallow
water limestones (early /middle Miocene, some 20 to 11 million years
old). This sharp transition is better explained by an abrupt onset of the
tropical surface water convergence off Northeast Australia than the
steady northward drift of the Australian Plate at that time. The Miocene
shallow-water carbonate systems on the Queensland and Marion pla-
teaus, drowned during the late Miocene and early Pliocene (an interval
between 10 and 3.0 million years), only partially recovered during a global
lowering of sea level 2.9 million years ago when parts of the plateaus
reentered the photic zone. Results from drilling offshore of the Great Barrier
Reef clearly show that the largest modern barrier reef on Earth was estab-
lished only very recently, possibly less than a million years ago!
Shallow-Water Carbonates on Aseismic Volcanic Ridges
Central and North Pacific Basins. Guyots (flat-topped volcanic seamounts
currently at water depths exceeding 1,000 meters) within the Mid-Pacific
Mountains, the Line and Marshall islands, and east of the Izu-
Ogasawara-Mariana Trenches, have been visited several times during
the past 25 years of ocean drilling. Recently OOP Legs 143 and 144
focused on drilling the shallow carbonate caps and the upper part of the
underlying volcanic pedestals of seven guyots. The shallow carbonate
systems found atop the guyots surprisingly more resemble carbonate
banks than the modern Pacific atolls, which are characterized by a solid
rim built of a coral-algal-reef framework surrounding a lagoon. The
interiors of the shallow Cretaceous and Eocene carbonate caps range
from shallow subtidal environments characterized by oolite shoals,
occasionally deepening into depths of perhaps 10 to 20 meters with
rudist banks, to supratidal depositional environments. Their edges consist
mainly of poorly cemented bioclastic sands, deposited along beaches and
shoals and interbedded with muddy lagoonal deposits. On their very edges,
drilling revealed only thin constructions of abundant rudists, sponges, and
some corals, implying that these organisms flourished in water depths to 30
meters below sea level; therefore, evidence is lacking for a physiographic
wave resistant reef characterized by a cemented framework at sea level.
(Rudists were bivalves that grew up to 1 .5 meters in length. During the
Cretaceous period they proliferated, then disappeared.) The irregular
patterns of subsidence and the discovery of late-stage eruptive phases in
some guyots make our theoretical models for thermal rejuvenation and
seamount subsidence less predictable. Even though sea-level fluctuations
seem to have played a role in the demise of the Pacific shallow-carbonate
systems, the preferential drowning of four of the seven Pacific guyots
during the mid-Cretaceous (Albian time, approximately 100 million years
ago), though a relatively warm time, could have been caused by changes in
ocean circulation and nutrient cycling. The Paleogene (approximately 60
million year old) shallow carbonates atop four of the seamounts along the
Emperor Chain in the North Pacific Basin are rich in skeletal debris of
bryozoans, echinoids, mollusks, and red algae with pervasive red algal
114
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
encrustations and only rare coral. This bryozoan-
algal limestone, typically deposited today
between 24°N and 30°N, contrasts with the
tropical coral-algal calcareous sediment charac-
teristic of the modern Hawaiian sub littoral
deposits, under which a hot spot is currently
located (at 19.5°N). The latitudinal difference in
sediment reinforces 7 degrees of true polar
wander for the Hawaiian hot spot estimated
from paleomagnetic data.
Nineti/east Ridge and Laccadive-Chagos-
Mascarene Plateau Ridge in the Indian Ocenn.
Shallow carbonates recovered from several
sites along the Ninetyeast Ridge evolved from
Campanian (approximately 80 million year
old) algae and coral-rich limestones at the most
northern site, Maestrichtian (about 70 million
year old) shallow carbonates farther south,
Paleocene (some 63 million year old) gastro-
pods, bivalves, and echinoderms at a more
southern site, and, finally, at the most southern
site, a middle/upper Eocene to lower Oli-
gocene (52 to 30 million year old) faunal
assemblage. This progressive decrease in age from north to south illustrates
that the ridge formed gradually as an island-seamount chain related to a hot
spot. By drilling some limestones, characterized by typical shallow reef
(right-hand photo on page 112) assemblages with small and age-diagnostic
larger benthic foraminifers (photo above), and radiogenicly dating the
volcanic basement in several sites (such as the early Eocene, about 55
million years ago, in the Maldives), the Chagos-Laccadive Ridge, along with
the Mascarene Plateau, was also found to be part of the volcanic track for a
hot spot located today under the island of Reunion. Contrary to the main
carbonate system of the Maldives Archipelago that has been thriving from
the early Eocene (55 million years ago) until today, the carbonate platform
drilled during leg 115 on the far eastern edge of the archipelago rapidly
sank below the photic zone after a very short life (a few hundred thousand
years) toward its current depth of 2,400 meters.
Study over the past 25 years of cores from the sites described, along
with many others, has brought understanding of shallow carbonate
systems that could be accomplished only through ocean drilling. •
First introduced to Jurassic carbonates in the Jura Mountains of Switzerland, his
native country, Andre Droxler pursued graduate studies at the Rosenstiel School
of Marine and Atmospheric Science of the University of Miami, studying the slope
and basin carbonate sediments offshore of the Great Bahama Bank. He has been
a Rice University faculty member for the past seven years, currently as an
Associate Professor of Geology and Geophysics. His current and past research
has lead him to conduct research in the Bahamas, in the Caribbean Sea on the
Nicaragua Rise, and along the Belize Barrier Reef, in the Maldives (Central Indian
Ocean), and on the Queensland Plateau/Great Barrier Reef (Coral Sea). In
addition to spending many months at sea on more than 10 research cruises, he
participated as sedimentologist on OOP Legs 101, 1 15, and 133, and has been
involved at different levels within the JOIDES advisory panel structure.
Bioclnstic limestones
with abundant larger
foraminifers (including
alveolinids and
nnmmnlites), small
foraminifers (miliolids),
and rfjodoliths (algal
balls) are also charac-
teristic of an early
Eocene (some 50
million year old)
shallow-carbonate
platform drilled in Hole
715 A on Leg 115.
Oceanus
Winter 1993/94
115
Studies focus
on the global
sea-level
signal locked
in the
sedimentary
record of the
coastal plain,
shelf, and
slope.
Drilling for
Sea-Level History
on the
New Jersey Transect
Gregory S. Mountain and Kenneth G. Miller
116
ediments deposited along ancient continental margins repre-
sent a significant portion of the geological record and comprise
a sensitive and lengthy record of environmental change, not
the least of which is a position change of the sea itself. Sea
level is a complex interaction of processes that operate both
locally and globally. Variations in sediment supply and adjustments to
stress placed on the underlying crust are two local processes that can
temporarily overwhelm global sea-level controls. For example, as the
crust beneath Scandinavia continues to rebound from the weight of its
last glacier, the shoreline is retreating and local sea level is falling as fast
as several meters per century. Elsewhere, tide gauges detect inexorable
shoreline flooding at the rate of tens of millimeters per century, and
though the cause is uncertain, a strong candidate is polar ice melting.
Many researchers in the academic community are striving to under-
stand the history of sea-level change on geological time scales (10,000 to
10,000,000 years) because of its profound influence on fundamental
elements of the earth system, such as: particle, chemical, and nutrient
flux into the ocean; distribution and character of near-shore ecosystems;
and air-sea-land interactions and their relationship to global climate.
Consequently, studies are focused on extracting the global sea-level
signal that is locked in the sedimentary record of the coastal plain, shelf,
and slope in key regions of the world.
The industrial community has long had an interest in understanding
what controls the character and distribution of sediment deposited in
shallow water (less than 200 meters deep), particularly as this understand-
ing helps to predict the occurrence of hydrocarbons. Peter Vail and his
colleagues at the Exxon Production Research Company published a water-
shed monograph in 1977 that described how to read the history of local sea-
level change in seismic reflection profiles collected along continental
margins. They argued that angular relationships between reflectors are the
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
key to identifying times of local sea-level change, and that when profiles are
compared around the world, common signals emerge to form a truly global
sea-level record. The work met with immediate controversy that was based,
in part, on the challenging argument that the effects of local processes
typically swamp the sedimentary record.
The Deep Sea Drilling Project entered into the conflict by conducting
three legs in search of the imprint of sea-level changes along continental
margins: Leg 80 drilled on the Irish continental slope, and Legs 93 and 95
drilled on the New Jersey slope and rise. The results of all three pro-
grams provided tantalizing support for the times of sea-level change Vail
and his associates had proposed back several tens of millions of years
into the past. Unfortunately, all drill cores encountered long stratigraphic
gaps and were located in relatively deep water (more than 1,000 meters),
where the record of sea-level change is indirect at best. The results swayed
few opinions, and the "Vail curve" remained controversial.
Beginning in 1987, Exxon again revolutionized the search for a
record of global sea level. This advance was achieved in part by im-
proved technologies, and in part by improved insight into how these
technologies can be integrated. A series of publications described the use
of outcrops, cores, wireline logs, and seismic profiles for detailing
sedimentary histories at previously unattainable spatial and temporal scales.
Ironically, a continuously cored hole is rare in the oil industry, so the
potential of this technique cannot always be achieved with commercial data.
The academic community soon realized that it had in JOIDES
Resolution a unique and valuable tool to probe continental margins for
evidence of sea-level changes. Continuously cored and logged boreholes
are routinely collected by this vessel, though to date it has not drilled in
typical continental shelf water depths. In a series of meetings between
1987 and 1991, the scientific drilling community developed the strategy
72°W
MID-ATLANTIC TRANSECT
Ew9009MCS
- - oiher MCS
Existing Drillsites
* DSDP
* Offshore Exploration
o Onshore Misc.
OOP Leg 150. 150X
Future Drillsites
2o Offshore, Onshore
Map of tJic middle-
Atlantic const, showing
the locations of geologic
samples and seismic
reflection profiles. In
1993, OOP Leg 150
(offshore) recovered
4,034 meters of cores
from Sites 902 to 906,
and Leg 150X (on-
shore) recovered 816
meters at Island Beach
and Atlantic City.
Cape May drilling is
scheduled for early
1994. The authors hope
to gain permission to
complete the New
Jersey Sea Level
Transect by drilling
most of the additional
sites on the continental
shelf, which are located
here on a grid of
multichannel seismic
data collected on a 1990
R/V Maurice Ewing
cruise.
Oceanus
Winter 1993/94
117
The ages of
many falling
sea-level
trends match
the oxygen-
is o topic
record
assumed to be
a proxy
indicator of
glacial ice
growth.
needed to address sea-level change based on transects of boreholes extend-
ing from the coastal plain to the continental slope. To build on the success of
Legs 93 and 95, we proposed a transect of the New Jersey margin. The first
two of three steps in this effort began in 1993: 1) during Leg 150, sponsored
by the Ocean Drilling Program, four boreholes on the continental slope and
one on the rise were completed; and 2) the National Science Foundation
Continental Dynamics Program along with ODP funded the drilling of two
boreholes on the onshore coastal plain. Step three requires drilling on the
continental shelf, but has been postponed until sufficient data are collected
to evaluate risks posed by the chance of encountering hydrocarbons.
Several characteristics make New Jersey an ideal margin for this
transect: We know there have been few local tectonic disturbances in this
well-studied region; its mid-latitude setting maximizes the chance for
excellent age control built on the integration of biostratigraphy and
chemical isotopic and paleomagnetic stratigraphies; and high sedimenta-
tion rates over the last 30 million years promise a record with especially
high resolution. We focus on this time interval for an important reason:
Oscillations in the marine-oxygen isotopic record detail a 30-million-year
history of glacial ice growth and decay. This geological interval repre-
sents a starting point for a detailed study of the stratigraphic response to
known changes in global sea level. Conclusions about the mixed local/
global record along the New Jersey margin will be evaluated by future
studies on other margins that focus on this same time interval in places
where local conditions such as the age of continental rifting are different,
and the global signal can be more confidently extracted.
We began our study in fall 1990 by collecting a grid of seismic reflection
profiles across the New Jersey margin. Based on these data and background
information provided by Exxon Production Research, we laid out a transect
of drill sites needed to document the age and character of discontinuities
recognized in these profiles. We anticipated that the most dramatic
discontinuities would have formed when local sea level fell rapidly and
little sediment could be retained on the shelf. By contrast, intervals of
widespread shelf deposition would indicate times of rapid sea-level rise.
We led ODP Leg 150 last summer and drilled four sites on the slope
and another site several tens of kilometers out on the continental rise. Water
depth at the slope sites ranges from 450 to 1,130 meters. We are able to trace
over a dozen reflectors to all four sites and correlate each to the rock record.
In most cases the reflectors match debris swept off the adjacent shelf; in
others they match especially well-cemented intervals that developed during
times of especially slow sediment accumulation. We conclude that the
former occurrences mark times when local sea level fell, and the latter, times
of local sea-level rise, when a wide continental shelf — not the slope — was
the primary depository for sediment washed in by rivers. Preliminary
analyses suggest that the ages of many falling sea-level trends that we found
match the oxygen-isotopic record that is assumed to be a proxy indicator of
glacial ice growth and, consequently, of global sea-level minima.
Two more holes were drilled onshore of the New Jersey shelf in 1993
to sample shallow-water (less than 200-meter) marine environments now
beneath the coastal plain. Another hole is planned for 1994. The onshore
boreholes recovered an excellent record of sedimentary environments
that are especially sensitive to sea-level changes. With this sensitivity,
however, comes a challenge: These sediments typically lack the fossils
118
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
found in deep-water sediments, and biostratigraphic control is often too
coarse to be useful for sea-level studies. Fortunately, we have recovered
numerous shell beds that can be dated with strontium isotope techniques.
As a result, we are confident that we will be able to establish time planes
that tie the continental slope record to the coastal plain record.
We have thus continued a transect begun by DSDP Legs 93 and 95.
We are completing the onshore drilling and integrating the results with
those of the five continental slope and rise boreholes. Our most challeng-
ing work awaits us:
determining that
drilling can be done
safely on the shelf,
completing this bold
effort, and integrating
these results with
existing data.
After two years of describ-
ing cores at the Woods
Hole Oceanographic
Institution as a Research
Assistant, Greg Mountain
concluded that most cores
are cylindrical and full of
mud. With that foundation
he enrolled in graduate
school in 1974 at Columbia
University's Lamont-
Doherty Earth Observa-
tory; he is still there, now
as a Research Scientist
studying the effects of sea-
level change. He has
learned that one such
effect — rarely mentioned —
is a rising tide of planning
documents, meetings, and
ancillary activities that
accompany such interdisci-
plinary efforts. When not
treading in this sea of
paperwork, Greg makes
his home in Westwood,
New Jersey, where he and
his wife are raising two
boys at 1 76 meters above
sea level.
cdp 1700
Ew9009Line 1027
cdp 1700
Ew9009 Line 1027
(Top) Multichannel seismic line 1027 down the continental slope offshore of
Neiv Jersey. The vertical scale is seconds of two-way travel time (1 second in
sediment is approximately 950 meters), and the horizontal scales are shown.
Sound generated In/ airguns towed at the sea surface reflects off surfaces of
discontinuity in the sediments beneath the seafloor; the authors are investi-
gating how sea-level changes contribute to generating these discontinuities.
(Bottom) Line drawing interpretation of line 1027 crossing ODP Leg 150
Sites 906, 902, and 904 drilled in summer 1993. Numerous reflectors were
traced across this line and throughout the grid of the seismic data. Leg 150
data allowed matching of reflectors to surfaces in the cores for age
determination: p = Pleistocene, m = Miocene, o = Oligocene,
and e = Eocene.
Ken Miller is a Professor at Rutgers, the State University of New Jersey, an
Adjunct Scientist at Lamont-Doherty Earth Observatory, and a 1982 graduate of
the MIT/WHOI Joint Program. When not teaching, going to sea, or attending
meetings, he can be located somewhere on the New Jersey Turnpike, caught in
traffic during one of his frequent commutes to Lamont-Doherty. Otherwise, Ken
can be found at the Jersey shore, keeping a diligent watch on the inexorable rise
in sea level from the deck of his house at 4 meters above sea level.
Oceanus
Winter 1993/94
119
Drilling
Technology
& Spinoff s
ODP cores
revealed when
the Tethys
Ocean lapped
a united
Gondwana
continent as a
shallow sea in
Triassic and
Jurassic times.
Spinoff s for Oil
Exploration
ODP Leg 122 off
Northwest Australia
Neville F. Exon
120
first heard of the Exmouth Plateau in 1974 when, as a geologist
at the Australian Bureau of Mineral Resources, I was transferred
to a geophysical group that was studying the plateau's geology
and petroleum prospects for the first time. This work was being
done as part of the large-scale Continental Margins Survey:
222,000 kilometers of continuous geophysical profiles recorded at 4-
kilometer intervals around Australia, from close inshore to the abyssal
plain — a survey far ahead of its time in scope and imagination. The
Exmouth Plateau is a deep-water extension of the Australian continent
northwestward under the Indian Ocean. With a total area of about
263,559 square kilometers, it is almost half the size of Texas. Much of the
plateau is in water shallower than 2,000 meters, but it is surrounded on
three sides by abyssal plains more than 4,500 meters deep.
We studied 18,000 kilometers of seismic-reflection profiles recorded
by the Bureau of Mineral Resources, Gulf Oil, and Shell Oil (which
provided cross sections through Earth's crust as deep as 15 kilometers)
and any other relevant geophysical and geological information we could
lay our hands on. The result was a positive assessment of petroleum
prospects that was published in several different forms, including in the
widely read Bulletin of the American Association of Petroleum Geologists. The
area's main attraction was huge buried fault blocks of Triassic deltaic
sediments, similar to those of the giant North Rankin gas field, east of
the plateau. We had reason to speculate that more valuable oil, rather
than gas, might be trapped in these fault blocks. A secondary attraction
was the overlying early Cretaceous Barrow delta, the reservoir of a giant
oil field at Barrow Island, southeast of the plateau. When five large lease
areas were made available, they were taken by consortia of exploration
companies, including several of the world's largest.
In 1977 to 1980, an unprecedented deep-water petroleum exploration
program commenced with detailed seismic reflection surveys, and ended
with the drilling of 11 wells on the plateau in water as deep as 1,354
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
1CW
meters. The deepest well, Phillips Saturn No. 1, was 4,000 meters deep
and was drilled in water 1,177 meters deep. At that time there was much
excitement around the world about deep-water oil potential, and huge,
dynamically positioned drill ships were being built especially for explor-
ing it. No oil fields had ever been found or exploited in the prevailing
water depths of 800 to 2,000 meters, but the consortia assured us that
new exploitation technology could be developed if large fields were
discovered. The total exploration cost was about $150 million (US), and
the result was the discovery of the
giant Scarborough Gas Field in the
Barrow delta (which is still not
developed) and whiffs of gas and
oil elsewhere.
Although the results of this
round of exploration were disap-
pointing, we still believed the
plateau had oil potential and we
set out to gather new information
for another assessment. For this we
needed a geoscience research
vessel. Fortunately the German
Bundesanstalt fur Geowissen-
schaften und Rohstoffe was
studying passive continental
margins like Australia's, and in
1979 their R/V Sonne came to the
virtually unexplored northern
Exmouth Plateau for a joint
survey. The Sonne dredging and
coring program returned tons of
rocks, including potential oil source and reservoir rocks. Since then our
own R/V Rig Seismic has carried out three more geoscience cruises over
the plateau, providing more data and a better understanding of the
plateau's origin and evolution.
In 1985, Ulrich von Rad (Bundesanstalt fur Geowissenschaften und
Rohstoffe) and I realized the vital role that deep drill holes with continu-
ous core could play in understanding the plateau's geology and the
Mesozoic Tethys Ocean's history. This ocean lapped over the region
before the plateau came into existence as a topographic feature. It was a
warm ocean, extending many thousands of kilometers east and west,
flanked by broad shelf seas where thick limestones were laid down.
Many of the limestones that extend from southeast Asia to the Pyrenees
are Tethyan rocks, and the most valuable of them host the oil of the
Middle East. We marshalled all our information and submitted a pro-
posal to the Ocean Drilling Program.
In 1988, OOP Legs 122 and 123 were drilled on and near the plateau.
Vital new information gleaned from the resulting cores revealed more
about the region's history:
• when Tethys lapped a united Gondwana continent as a shallow sea in
Triassic and Jurassic times,
• when a small part of Gondwana broke away to the north in the late
Jurassic and the Argo abyssal plain formed from upwelling basalt
i — i
ARGO ABYSSAL PLAIN
LATE JURASSIC
TRIASSIC REEFS
Bathymetnc contours tn meters
O Petroleum exploration well
O Gas well o Gas field
Oil lield
' OOP sue
Location of OOP
sites. Leg 122 Sites
759-764 were drilled
on the Exmouth
Plateau and Leg 123
Sites 765 and 766 were
in deeper water nearby.
Triassic and Jurassic
reefs grew in the Tethys
Ocean, and were
discovered for the first
time in Australia as a
result of the OOP work.
The ab\ssal plains
formed later as the
supercontinent
Gondwana broke up in
two stages, in the late
Jurassic and earl\
Cretaceous (160 and
130 million years ago).
Oceonus
Winter 1993/94
121
behind the departing fragment,
• when west Gondwana broke away and moved westward in the early
Cretaceous, leaving the basalts of the Gascoyne and Cuvier abyssal
plains behind, and
• when the plateau subsided to its present depth and moved steadily
northward with Australia in Cretaceous and Cenozoic times.
OOP was concerned about the danger of striking gas during Leg 122,
especially in the Cretaceous strata of the central plateau, because the drill
ship JOIDES Resolution (which, coincidentally, had once drilled for oil on
the plateau before it was converted to a research vessel) had been
modified to simplify deep water drilling in a way that prevented it from
controlling a gas "blowout" at the sea bed. So the exploration geologists
on the ODP Safety Panel turned their minds to the novel problem of not
finding large accumulations of gas. They decided that the safest proce-
dure would be to drill near existing exploration wells where gas had
been monitored continually and had been shown to be incapable of
blowing out. (As these wells were not cored at our levels of interest,
there was little duplication of effort.) While the ODP holes were drilled,
gas was continuously monitored by geochemists and a petroleum
geologist; any unexpected rise in core gas content would lead to that hole
being plugged with concrete and abandoned. One hole was, in fact,
terminated 50 meters above its planned depth. Abundant gas is con-
stantly being generated at depth and trapped beneath impermeable
limestones. Although the concentrations we measured could not cause a
blowout, they were high enough for gas to stream from the cores at
surface air pressure, bulging the plastic core liners and dislodging their
end caps. Geochemical studies revealed that the gas was not generated in
Strata Drilled on ODP Leg 122
Stratigraphic
Age
Absolute
Age
(million years)
Maximum
Thickness
(meters)
Sediments Deposited
Cenozoic
Cretaceous
Late Jurassic
Oto65
65 to 140
140 to 160
550
850
none
Early & Middle 160 to 205
Jurassic
Late Triassic
205 to 230
none
700
Deep water limestone, chalk, and ooze
Shallow marine mudstone and limestone
deposited as the continental margin sank
Shallow marine mudstone deposited after
continental break up and during initial
subsidence
Shallow marine limestone and coal
measures deposited in rift valleys before
continental break up
Deltaic sediment and shallow water
limestone deposited during rifting before
continental breakup
122
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Seabed -
200
CD
4—.
Qj
Qj
-Q
JP
CD
400 i
§ 600-
QJ
QQ
•
Q
800-
1,000
Cretaceous strata, but probably in
the Triassic sediments.
Like all good scientific work,
the OOP drilling had its surprises.
The greatest of these was the
coring of several hundred meters
of late Triassic limestones contain-
ing reefs very similar to those in
the Alps, above deltaic Triassic
sediments on the northernmost
part of the plateau, nearly 3,000
meters below sea level. Such
deltaic sediments provide the
main petroleum reservoirs of the
Northwest Shelf, now a major
producer of both gas and oil. Late
Triassic and early Jurassic lime-
stones were known from the
Exmouth Plateau and some other
areas on the outer Northwest
Shelf, but these were the first reefs
of this age ever found in Australia.
This was of considerable scientific
interest, but also of commercial
interest because limestones
provide more than half the world's
oil. The reasons for this are many
and complicated, but two are
significant: Certain lagoonal
sediments are rich in organic
matter that is capable of producing
oil when it is deeply buried and
thermally "cracked," and many
buried reef complexes contain
highly porous beds that are excellent
oil reservoirs. We publicized the
results in oil industry journals to
encourage exploration companies to take another look at their seismic
sections, in case potential reefs have not been seen because of the mind-set
"they don't occur in Australia."
Furthermore, we at the Bureau of Mineral Resources decided to do
what we could to help companies in their assessments. First we defined
the seismic character of the newly discovered reefs, and then we took a
new look at existing seismic profiles farther inshore. To our great plea-
sure, we discovered several very large bodies that looked like Jurassic
(not Triassic) reef complexes sitting on uplifted fault blocks, in water
depths as shallow as 1,000 meters (therefore, economically feasible to
drill). Although most of the bodies were deeply buried beneath younger
sediments, one rose above the seabed and was dredged. The rocks
recovered proved to be identical to Early Jurassic limestones from the
Alps, where they occur as mounds formed by calcareous organisms. We
also recorded new seismic profiles linking exploration wells (with their
Methane Gas in OOP Site 763
Permeable ooze and soft chalk
allow methane to escape
to the ocean
Less permeable Cretaceous
limestone, marl & chalk trap
methane moving upward
Silty Cretaceous sediments allow
methane generated at depth
to move freely upward
0 20,000 40,000 60,000 80,000
Methane in Pore Waters (parts per million)
Gas IMS routine!]/ extracted from rock core and then nnah/zed
aboard JOIDES Resolution. On the central Exmouth
Plateau, abundant gas was known to be present, and it was
monitored closely to ensure that levels did not become high
enough to cause a "blowout" at the hole. The plot shows the
variation of methane, the most abundant gas, with depth at
Site 763. Gas generated at depth migrates upward through
the strata, accumulating beneath impermeable beds. Its
chemistry shows that it formed below the Cretaceous
sequence, probabh/ in Triassic deltaic rocks.
Jayne Doucette/WHOI Graphics
Oceanus
Winter 1993/94
123
liplll
69 70 71 72 73 74 /5 76 77
illlli- •Illlil
f OCEAN OH t N Illljllll liiijill! lip IJlijllliil
2 83 84 8S 86 87 88 89 0$ 91 92
lliillflllllKMitllifllsilllfflHlllHlli
90-90 a-
Porous late Triassic
limestones, like these
from a core taken 250
meters below the seabed
at Site 764, prove that
reefs existed here in the
warm waters of the
southern Tetln/s Ocean.
Some of the pores have
formed where coral
branches have weath-
ered out. Slid i reefs are
now potential targets
for oil drilling further
inshore.
known geology) to the lower continental slope, not only of the plateau
but also farther northeast in the Canning Basin. We then dredged the
continental slope along the profiles and recovered late Triassic reef
limestones in two areas of the Canning Basin, providing hard evidence
that fossil reefs are indeed widespread.
Only time, and the economics of exploration, will tell whether oil
exists in Mesozoic reefs on the Northwest Shelf. However, OOP drilling
that was originally performed for purely scientific purposes has pre-
sented us with new, potentially valuable information for the petroleum
exploration industry, and ultimately for Australia as well. •
Neville Exon is a Senior Principal Research Scientist at the Australian Geological
Survey Organisation (AGSO. formerly the Bureau of Mineral Resources) who
started his career in regional geological mapping of onshore sedimentary basins.
After seven enjoyable years he decided to study recent marine sedimentation in
the epicontinental Baltic Sea, a modern analogue for the marine Cretaceous
sequences of the Australian Great Artesian Basin, and went off to Kiel University
in Germany to earn a Ph.D. Since then he has worked largely in studies of
offshore sedimentary basins around Australia, but did have a spell in the South
Pacific as a United Nations marine geologist based in Fiji, which led to an
ongoing interest in deep sea manganese nodules. He has thoroughly enjoyed his
association with OOP — planning, participating in, and writing up the results of the
Exmouth Plateau drilling. He publishes this article with the permission of the
Director of AGSO.
124
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Technology
Developments in
Scientific Ocean
Drilling
Barry W. Harding
ngineering technology and drilling operations advance-
ments have been preeminent since the Ocean Drilling
Program (OOP) began in 1984. Engineering and drilling
challenges identified at COSOD I (Conference on Scientific
Ocean Drilling) in 1981 and met in the first two years of
operation include carbonate reefal sequencing (Bahamas, Leg 101), high-
latitude drilling (Baffin Bay, Leg 105), ridge-crest drilling (Mid-Atlantic
Ridge, Leg 106), and accretionary prism sequencing (Barbados Transect,
Leg 110). In addition to converting an oil/gas industry drillship and
outfitting it for scientific coring, the Ocean Drilling Program's Engineer-
ing and Operations team began in 1984 to plan for the difficult and wide
range of lithologies and conditions to be encountered.
Diamond Coring System (DCS)
Planning how to best drill a hole on an unsedimented ridge crest of the
Mid-Atlantic Ridge was ODP's first major technical challenge; known
rock-drilling techniques required 50 to 100 meters of sediment for drill-
string stabilization before rock could be cored. Completely new systems
were required, and industry contracts were awarded for the design and
development of:
• a hard-rock guide-base system (including deployment on the seafloor),
• a real-time subsea TV system for reentry operations,
• positive displacement coring motors,
• a cementing system for both guidebase anchoring and hole
stabilization, and
• improved roller-cone drill bit design for basement lithologies.
While ODP's results from coring unsedimented ridge crests have not
been totally successful, they are, however, encouraging. With each
successive leg dedicated to either ridge-crest or crystalline rock drilling,
ODP has gained better understanding of the problems posed by bare
rock and fractured formations. The results from Legs 106, 109, 118, and
Planning how
to best drill a
hole on an
unsedimented
ridge crest of
the Mid-
Atlantic Ridge
was ODP's
first major
technical
challenge.
Oceanus
Winter 1993 /94
125
Major ODP Development Engineering Projects
Project
XCB: Extended core barrel system
• Incorporated first venturi vent
system (v.108)
• Added improved cutting shoes (v.121)
• Improved cutting shoe flow (v.!24E)
• Extended core-barrel flow control
system (XCB/FC)
APC: Advanced piston corer system
• Minor upgrades over DSDP
models ( v.l 01)
• General design overhaul (v.l 29)
• Modification of v.l 29 (v.l 50)
DIG: Drill-in casing system
Core bit development
roller cone, PDC, hybrid
Hard rock spud systems
(for Legs 106, 109, and 11 8)
APC core orientation system
Colmek underwater TV system
NCB: "Navidrill" core barrel
Reentry cone redesign
VIT: TV vibration isolation frame
PDCM: Positive displacement
coring motor
LFV: Lockable flapper float valve
Line cutter/crimper (Kinley)
PCS: Pressure core sampler
VPC: Vibro-corer
CSES: Conical side entry sub
HRO: Hard rock orientation system
Mini-HRB: Hard rock guide bases
CORK: Reentry cone plug and
instrument feedthrough
Commandable-retrievable beacons
Initiated Current Status
DSDP Operational for ODP since Leg 101
1 1 /85 Did not pass sea trials during Leg 108;
alterations made to later XCB versions
1/88 Successful upgrade modified to V.124E
8/88 Operational XCB through Leg 101
4/91 Prototype versions tested; results
inconclusive; further testing planned
DSDP Operational for ODP since Leg 101
4/84 Used successfully for Legs 101 to 103
1 /90 Upgraded versions used for Legs 129 to 149
I /93 Successfully introduced for Leg 150
DSDP Used several times since, with success
DSDP Continuous development and testing
3/84 Successfully used for assigned legs, then
made obsolete in favor of mini guidebases
5/84 Used and upgraded since Leg 101
6/84 Used since Leg 106
6/84 Tested until Leg 124E, then made obsolete
10/84 Continuous ODP upgrade since Leg 106
2/85 In use with upgrades since Leg 106
2/85 Developed and used for Legs 106, 109,
and 118; still operational
3/86 Developed and used since Leg 113
I 1 /86 Developed and used since Leg 1 1 3
7/87 Developed and operational
4/88 Initial design failed; under redevelopment
4/89 Developed and used since Leg 133
6/89 Overall system still unproven
8/89 Successfully deployed on four legs
10/89 Successfully developed and tested; four
installations emplaced to date
10/90 Developed and used since Leg 138
126
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Primary Heave
Compensator
Secondary Heave
Compensator
Electric
•Top Drive
Varco
Top Drive
147, together with advice from the mining drilling industry, led OOP to
develop a slimhole high-speed coring system, named the Diamond
Coring System or "DCS."
The DCS prototype (demonstrated on Leg 124E in 1989, offshore of
the Philippines) had a tubing length limited to 2,000 meters, while the
DCS currently under development will have 4,500 meters of total tubing
length. The DCS encompasses several primary subsystems: a tubing/
drill-rod string for offshore deep water slimhole drilling and coring
operations; special slimhole (less than 15
centimeters outside diameter) diamond core
bits to function in a variety of operating
environments; a modified wireline retriev-
able core barrel, modeled after a mining-style
design; an electric top drive, secondary
compensation system, mud-pump controls,
hydraulic power unit, and other ancillary
support functions; and a specially designed,
tapered stress joint, for modulating American
Petroleum Institute drill-string bending
stress at the hard-rock base.
The DCS system is expected to solve
several high-priority objectives identified in
1987 by COSOD II working groups, espe-
cially for deeper drilling in difficult litholo-
gies. In the last five years the oil and gas
industry has begun using slimhole technol-
ogy and rigs in their exploratory drilling.
Because of the technological progress amid
environmental and budget constraints in the
oil field, slimhole drilling has been pushed to
the forefront. Slimhole drilling is advanta-
geous both economically and environmen-
tally: It costs less per foot to drill as it re-
quires a smaller rig, and less area is cleared
for the drill site, which translates to less
clean-up once drilling is complete. A com-
bined industry project entitled DEA-67
(Drilling Engineering Association, study
number 67), which has 55 industry partici-
pants and nearly $2 million in funding, is
under way to study the drilling and equip-
ment-related problems of slimhole drilling.
ODP is part of the DEA-67 study.
Coring Tool Development
In the 23-plus years of ocean drilling operations, the DSDP/ODP devel-
opment engineering groups have initiated a total of 65 projects, ranging
from minor tool upgrades to entire coring system development. Cur-
rently 48 projects have been successfully completed, 10 projects are
under development, and 7 have been dropped or were unsuccessful.
o
I
DCS Platform
Suspended
in Derrick
DCS Tubing f
String T~
-API Drill Pipe
Re-entry Cone
-i/Hard Rock Base
Drill-in
Bottom Hole
Assembly
Wireline
Core Barrel
Diamond
Core Bit
The Diamond Coring
System (DCS) is a
slimhole high-speed
coring system. The
original system had a
tubing length of '2, ,000
meters. A new system
(now being developed)
will go to 4,500 meters.
Oceanus
Winter 1993/94
127
BARRY HARDING
CUBS ROOKIE MAY '92
The table on page 126 lists the higher profile coring-tool develop-
ment projects to date and their current status. During the 15 years of
DSDP, Glomnr Challenger drilled 1,092 holes at 624 sites worldwide, and
recovered 96 kilometers of core. The first 50 legs of OOP operation have
resulted in 719 holes at 293 sites, and 83.3 kilometers of recovered core.
Because the geological challenges presented at COSOD I and II and
in the OOP Long Range Plan (1990) have become increasingly difficult,
technology developments for scientific ocean drilling are critical. For
example, geological challenges presented at COSOD II include drilling
hot-spot traces and fractured oceanic crust to study plate motion through
time, and drilling crustal holes 5,000 meters below the seafloor to define
crustal compostion. The Long Range Plan purposely divided the scien-
tific goals into three phases, with Phase I requiring more near-term
technologies (such as drilling very deep sites in both igneous rocks and
unconsolidated sediments, and overall improved sample recovery) and
progressing from there.
To develop economically viable technology with low-risk methods,
the oil and gas offshore industry has initiated cost-sharing
consortia to drill and obtain hydrocarbons from deep water
tracts. ODP has always looked at ways to adapt or modify
existing technologies before initiating development of any tool
or system. In addition to numerous subcontractors and industry
consultants, ODP receives technical advice and assistance from
many companies and corporations within the oil and gas,
mining, geothermal, and scientific drilling industries, both in the
US and abroad. The ambitious scientific goals stated in the Long
Range Plan can be achieved, but only with the proper commit-
ments of funding and manpower, and the reservation of ship
time for the development process. •
Barry W. Harding has been the ODP Manager of Development Engi-
neering and Drilling Operations, based at Texas A&M University, for
eight years. As an engineer who has never been averse to taking risks,
he started a land-drilling company partnership in early 1981, after 13
years of experience in the offshore drilling industry. The diverse and challenging
work at ODP aside, he found time in 1992 to pursue his original dream —
attending a "Major League Fantasy Baseball Camp. "
128
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
Borehole
Measurements
Beneath the
Seafloor
Paul F. Worthington
I
Wireline-
a c
O ci-
hen a scientific borehole is drilled beneath the seafloor,
there is an opportunity to measure rock properties in
an environment that would otherwise have remained
totally inaccessible to us. Although physicochemical
rock properties of recovered cores have been mea-
sured routinely in shipboard
laboratories, it is desirable for i'-\
several reasons to complement
these data with measurements in
the borehole, which constitutes a
natural laboratory. First, core
recovery can be erratic, leaving
substantial sections of the bore-
hole column unsampled, especially
in hard sediments and basement
rocks, which fragment easily and
are too hard for piston-coring.
Second, core measurements are
usually made at surface conditions,
whereas borehole measurements
are necessarily made at in situ
conditions of temperature and
pressure, thereby leading to a more
realistic database of physicochemi-
cal rock properties. Third,
downhole measurements are
usually made at a scale that is
many times greater than the core
scale, and this attribute provides an
important linkage between labora-
tory studies and surface geophysi-
cal surveys.
In borehole logging, the
soude is pulled up the
Iwle nt constant speed.
1,1,1
r~r
II.
I.I.I
T7T
I . I . I . I . I . I
IT
I . I
I . I . I . I . I . I . I
J L
Probe
I
TTT
Physical Parameter
Oceanus
Winter 1993/94
129
Downhole probes
sample fluids and
measure temperature
and pressure ahead of
the drill bit: ODP has
developed a probe
capable of measuring
up to 200°C.
The Nature of Downhole Measurements
Downhole measurements used in scientific ocean drilling programs can
be grouped into three categories. The most common are wireline logs,
spatially continuous records of the physical and chemical properties of
the formations penetrated by a borehole. The wireline is a cable that extends
from a ship down to a probe or sonde in the borehole; it comprises one or
more conductors that allow real-time communication between the probe
and the surface. Logs or depth records are made as the probe is pulled up
the length of the hole at constant speed to provide continuous measure-
ments of the surrounding formation. Some tools are lowered on a me-
chanical line, or slickline, that provides no digital communication with
the surface: These are known as memory tools, and they are deployed
where cable specifications would be inadequate, for example, in very hot
holes where temperatures are greater than 400°C. Logging tools are
available for measuring a wide range of formation properties, including
electrical resistivity (laterologs and induction logs), sonic velocity,
natural radioactivity (gamma-ray log), porosity (neutron log), density,
susceptibility, magnetic field orientation and strength, and temperature.
The primary sources of tool technology have been the oil-field well-
logging service companies, which have provided and run the majority of
drilling program logging tools on a contractual basis.
The second category of downhole tools includes formation testers
and fluid samplers, which provide spatially discrete data. These tools are
designed to respond to formation-behavior-induced mechanical distur-
bance, such as an applied stress or a pressure drawdown in the wellbore.
They can be deployed on a wireline, a slickline, or as part of the drill
string. Primary objectives of such tools are the in situ measurement of
dynamic parameters such as permeability, temperature, and pressure;
determination of stress distributions; and the acquisition of pristine pore-
fluid samples.
The third type of downhole tool is a long-term sensor placed in a
drill hole to record natural data over a period of time. In this case, the
borehole is used not as a laboratory but rather as an observatory. Sensors
can be designed to record variations in local microseismic activity or in
Temperature (or Chemistry)
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130
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
fluid properties such as temperature, pressure, or chemistry. In some
cases, the long-term measurement of fluid properties requires that the
borehole observatory be sealed to prevent direct flow between the
deeper pore fluids and the sea above.
The History of Downhole Measurements
in Scientific Ocean Drilling
Although logs had been run in offshore wells in established petroleum
sedimentary provinces such as the Gulf of Mexico for many years, the
deep water sites and basement rocks encountered by the scientific
drilling programs presented new operational and technological chal-
lenges that once again made borehole measurements a pioneering
venture. The first DSDP borehole logs were run northwest of Bermuda in
September 1968. These used natural gamma-ray and neutron-porosity
tools run in the drill pipe. From this point the use of borehole logs
increased erratically, drawing eventually on most of the branches of
classical physics, but there were extended periods when no logs were
run at all. Two basic open-hole tool suites gradually emerged. These can
Data telemetry
Seafloor
Observatory
Data recorder
A downhole observa-
tory beneath the sea.
Data recorded at the
seafloor can be recov-
ered either from a
surface vessel or by
visiting the site with a
submersible or remotely
operated vehicle.
be described retrospectively as a seismic-stratigraphic tool suite (to make
resistivity, sonic, and gamma-ray measurements) and a lithology-
porosity tool suite (for density, neutron porosity, and gamma-ray
measurements). The gamma-ray log is run with all tool combinations to
facilitate reconciliation of depth scales between logging runs.
When DSDP was succeeded by ODP in 1985, the logging program
became more formalized. The standard logging suite encompassed the
seismic-stratigraphic and lithology-porosity tool sets from DSDP days,
Occanus
Winter 1993/94
131
but also took advantage of subsequent developments in tool technology
by oil-field service companies. A geochemical tool set was added to
provide the elemental concentrations of formations surrounding a
borehole. In 1988 the formation microscanner was added to the standard
suite. This is a high-spatial-resolution microresistivity tool that provides
an electrical image of the borehole wall. The formation microscanner
allows matching of cores and logs in terms of both depth and orientation.
In addition to the standard tools, several other oil-field tools have
been deployed from time
to time. These essentially
comprise in-hole seismic
tools for vertical seismic
profiling, a borehole
televiewer for obtaining
an acoustic image of the
borehole wall (analogous
to the formation
microscanner), and, more
recently, a susceptibility/
magnetometer tool for
resolving magnetic
reversals in sediments,
which are weakly magne-
tized compared to
basement rocks. All of
these are examples of
technology originally
developed for oil-field
applications. However,
several downhole tools
have been built by
scientists in the DSDP/
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Stress probing
Acoustic imaging
Electrical imaging
Acoustic waveform
Natural acoustic energy
Spectral density
Electrical resistivity
Neutron porosity
Temperature
Fluid pressure
Fluid sampling
Natural radioactivity
Geochemical
Susceptibility
Magnetization
The contributions of
downhole
measurements to
classical geological
subdisciplines.
OOP community specifi-
cally for scientific use.
They include an ultra-deep-sensing resistivity tool for hydrogeological
studies of rock porosity; a high-resolution temperature tool for heat-flow
studies; a probe tool for taking water samples and measuring tempera-
ture and pressure in sediments ahead of the drill bit; and a thermistor
string for long-term deployment in a borehole observatory.
Scientific Applications of Downhole Measurements
Downhole measurements have made a major contribution to all the
principal scientific themes of DSDP and ODP. The first key area is that of
global environmental change. Logs are especially well suited to address-
ing these problems because the solutions require a continuous depth
record so that cyclic variations in sediment composition and texture can
be evaluated in terms of paleoclimate and ocean circulation. The second
area is crustal composition and structure, which must be known in order
to understand the origin and evolution of oceanic lithosphere. For
example, the sharper spatial resolution of logs relative to surface seismic
data has led to a better understanding of the acoustic characteristics of
132
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
100 m/Ma
t
Sedimentation
rate
w
_Q
E
CL
CD
Q
350
different layers of Earth's crust. The third
area is hydrogeology, with all its implica-
tions for the global geochemical budget.
The two key parameters are porosity and
permeability. Porosity can be evaluated
from density, neutron, sonic and (in the
absence of hydrocarbons) resistivity logs.
Permeability is determined from
downhole pressure tests over an interval
of the borehole that has been isolated
using packers or seals. The fourth key
area is the global stress regime. Our
understanding of the forces that drive
tectonic plates and determine their
motions can be advanced through knowl-
edge of in situ stresses. Stress orientations
can be inferred from failures of the
borehole wall, known as "breakouts,"
which can be imaged using the borehole
televiewer or formation microscanner.
Changes in stress orientation can be
depicted with depth or mapped regionally.
Scientific borehole logging is entering
a new era. It is no longer sufficient to rely
on oil-field technology to meet ODP
logging needs. A major ODP objective is
to drill in the young brittle crust near
spreading centers. This will require high-
temperature tools that are less than 5 centimeters in diameter and rated
to 400°C. Since these specifications exceed the capabilities of commercial
logging tools, ODP will have to develop its own tools, possibly in
conjunction with other scientific programs in order to share the consider-
able engineering costs. At present, resistivity, temperature, and fluid
sampling tools are being developed for high-temperature slimhole
deployment. In this respect, scientific borehole logging is at a watershed.
The scientific community is responding to the technical challenges
positively so that the downhole measurements of the future will consti-
tute as effective a scientific legacy as their present counterparts. •
Paul F. Worthington served as Chairman of the ODP Downhole Measurements
Panel from 1987 to 1992. He is an environmental and resource evaluation
consultant, based in Ascot, Great Britain, and a visiting research professor at the
Lamont-Doherty Earth Observatory of Columbia University.
95 ka
)95Ka
0.4
0.6
Apparent porosity
0.8
Porosity logs from
ODP Site 646 in the
Labrador Sea show
cyclic properties that
can he attributed to
astronomically gov-
erned climatic varia-
tions. The spacing of
peaks is related to the
post-compaction
sedimentation rate,
which changes from 52
to 100 meters per
million \/enrs at 335
meters below the
seafloor.
Oceanus
Winter 1993/94
133
Book Reviews
Polar Day Nine
By Kyle Conner, 1993. Diamond Books;
New York, NY. 353 pp. - $5.50.
"The second Ice Age begins in nine days,"
warns the book's cover. The back cover adds,
"Dr. Cliff Lorenz knew the dangers of tamper-
ing with the environment. He had seen first-
hand the disastrous results of an experiment
with climate control."
After my wife gave me this paperback
science fiction novel for light weekend reading,
I flipped through the pages on the way to pour
a cup of coffee and happened upon this
passage: "Dive number two thousand fifty-one
is on behalf of the Department of the Interior
and the Environmental Protection Agency. The
three man crew will consist of pilot Bill Bates,
chief scientist Cliff Lorenz, and our nuts-and-
volts master mechanic Fritz Hoffmeister." It
went on to describe a dive of DSV Alvin from
R/V Atlantis II. More page flipping turned up
R/V Knorr, the drillships Glomar Challenger and
Glomar Explorer, and a discussion of deep ocean
drilling. The book had my attention!
The author (real name Ubaldo
DiBenendetto) is a Professor of Foreign Lan-
guages at Harvard University and lives south
of Boston, according to the exceedingly brief
biography in the book. He has woven together
a fascinating mix of climate modification
research, oceanography, cold-war-type compe-
tition between the US and Russia, science
advising, national decision making, internal
science competition, and the culture of ocean
science research and ocean engineering technol-
ogy. In addition, there are nearly perfect descrip-
tions of research operations at sea, believable
characters, whale stranding, a love story com-
plete with dual careers, and even a "sleeper" spy
on a Woods Hole oceanographic research vessel.
I admire the author's ability to describe the
geographic setting. One passage, for example,
where Cliff Lorenz gazes across the docks from
aboard R/V Knorr, instantly transported me back
to a view of the same scene as I departed Woods
Hole on a Knorr voyage several years ago.
I highly recommend this enjoyable book
for all readers, but especially for ocean science
fans, oceanographers, and ocean engineers.
Scientists, engineers, officers, and crew who
have sailed on Woods Hole ships or worked at
the Woods Hole Oceanographic Institution will
enjoy the challenge of identifying models for
some of the main characters. •
— John W. Farrington
Associate Director for Education
& Dean of Graduate Studies
Woods Hole Oceanographic Institution
The Woman Scientist:
Meeting the Challenges for a
Successful Career
By Clarice M. Yentsch and Carl J.
Sindermann, 1992. Plenum Press; New York,
NY. 271 pp. - $24.95.
Lately, when a student or young colleague asks
me about being a woman scientist, I don't just
tell my stories. I also recommend this book.
Yentsch and Sindermann have described with
clarity and simplicity the multiple facets of
surviving and ultimately succeeding in academia
and research science. Unlike many other books
and essays treating the woman scientist, this one
does not lead to debilitating anger about past or
continuing inequities or, alternatively, resigna-
tion. Instead we are graced with advice about
coping with the present and suggestions for
change. Mostly, I like the thoughtful analysis that
is both honest and hopeful; my women students
and young colleagues will still want to be
scientists when they finish this book!
134
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
I very much like the format of the book.
Yentsch and Sindermann present a sequence
of issues that face women as they enter and
pursue success in science. Information from
their own questionnaire and from other
publications, including helpful statistical
analyses, clarify the issues. They often then
present vignettes to illustrate their themes. As I
read, I filled the margins with exclamation
marks as I remembered my own and col-
leagues' incidents — some as recent as last week
(!) on these very same themes. A pithy action
list follows, with survival techniques and both
short- and long-term action agendas. The
authors then summarize the themes, reiterating
their key points.
I found some aspects of the book particu-
larly enlightening and intriguing. With the
book's introductory discussions, I was re-
minded of a well-known quote from Sigmund
Freud: "The great question. ..which I have not
been able to answer despite my thirty years of
research into the feminine soul is 'what does a
woman want?'" The answers are clear for
women scientists. (You will have to read the
book for them, however!) The authors deal
with some of the most personal dilemmas
women often discuss: marriage, children, the
timing of these and the "costs" they may incur.
They find that successful career women have
no single strategy, but there do appear to be
some important ancillary factors. Particularly
fascinating to me were the different daily
"menus" for time use by male and female
scientists. Their discussions give compassion-
ate insights into our perennial guilt and often
frazzled condition. The authors clearly spell
out the hazards of the research assistant,
describe the many faces of sexual harassment,
and give insider information about how to
become initiates of the "clubs" and "fraterni-
ties" found in the inner circles of science. I was
very pleased with the authors' "generational
perspective:" They clearly map both the
changes that occur over the time course of a
woman's professional career and they show
the (mostly) positive changes that have oc-
curred in the conditions for women scientists
over the last two decades or so. Again and
again the authors validated my own personal
experience and that of the many women
friends I have made in science: They were
telling "our story."
— Mary Wilcox Silver
Chair, Marine Sciences Department
University of California, Santa Cruz
The Young Associates
Let Ocean Explorer introduce a child to the
excitement and challenge of ocean science.
Recommended age group: 11 to 13.
For information about membership in the Young
Associates Program, write to E. Dorsey Milot,
Director of the Associates, Woods Hole
Oceanographic Institution, Woods Hole, MA
02543, or call (508) 457-2000, ext. 4895.
Oceanus
Winter 1993/94
135
Saving the Oceans
Joseph Maclnnis (general editor), 1992. Key
Porter Books; Toronto, Canada. 180 pp. - $50.
First let me say that this book has some of the
most spectacular pictures you will ever see of
ocean life — absolutely superb. It will make an
excellent addition to anybody's coffee table.
The text, actually a series of 11 articles
written by various authors, is a little more
variable in quality, but all are interesting (I
mention a few below). The underlying premise
of this book is the great peril that the ocean is
or will soon be facing. The beautiful photo-
graphs almost seem to be in contradiction to
this premise. None would question that parts
of the ocean, especially many coastal-zone
regions, are in trouble, but the more vast and
open ocean is really not in such jeopardy—
nevertheless, some concern is appropriate.
The story starts with the editor making a
13,000-foot dive in the Soviet Mir 1 submarine.
Some hydraulic oil has leaked from the support
ship and we are reminded about "the suffocation
and death of the great waters" (i.e., Exxon Vnldcz
and the Persian Gulf). The implication is that we
have lost touch with nature.
Hillary Hauser follows with a compelling
article ("The Meeting Place") based on his
experience as a journalist and diver. He
discusses estuaries, their use and misuse, and
coral reefs, as well as pollution from ocean
dumping, offshore oil activities, and the
impacts of global warming.
Marie Tharp writes a lovely article entitled
"Origins." A well-known cartographer, Tharp
was the co-drafter (with the late Bruce Heezen)
of the well-known physiographic chart of the
ocean that is still found in many oceanogra-
phers' offices. A smaller version covers two
pages of this book. She discusses the work she
did with Heezen that led to the discovery of
the world-encircling ocean ridge system, which
in turn was one of the cornerstones to the then-
developing concept of seafloor spreading.
"The Planet's Lifebelt" by T.R. Parsons
emphasizes the resilience of the ocean but
wonders what we are doing to it. He notes that
only 27 years after its discovery the Stellar' s
sea cow became extinct, and ponders whether
other species, such as some turtles, will suffer a
similar fate.
In "The Twilight Zone" by Sylvia Earle we
share her now-famous dives as deep as 1,250
feet in a one-person, hard-shell diving suit
(frequently called Jim for Jim Jarrett, the first
person willing to try an early version of the
suit). Earle says "there are no words to de-
scribe the blueness" of the oceans — but she
does quite well.
In "The Dynamic Abyss," Peter A. Rona
writes of his many discoveries. He does get a
little lost, however, in his explanation of the
Law of the Sea Conference and a 1982 conven-
tion for mining deep-sea nodules.
John Lythgoe, in "The Sensory World of
the Deep," writes about light and sound in the
ocean and how various organisms see and
hear, and Mike Donoghue, in "Protecting the
Oceans," describes some of the harmful effects
of pollution, such as PCB poisoning of beluga
whales in the St. Lawrence River of Canada.
He also mentions several recent treaties to
restrict or reduce pollution, and what one can
do as an individual.
After reading this pleasant and well-edited
book, I still remain somewhat skeptical about
its premise. Rather than the ocean being in
serious danger at this moment, I feel that our
recent concern and efforts toward the marine
environment have had some impact. Perhaps
it's just that a beautiful book like this makes
me see the positive.
— David A. Ross
Senior Scientist
Woods Hole Oceanographic Institution
136
DSDP (Deep Sea Drilling Project) A ODP (Ocean Drilling Program)
lfl3K
Index to Volume 36 (1993)
Number 1, Spring 1993
Coastal Science & Policy I
An Introduction — Perspectives from
a Shrinking Globe
David G. Aubrey
Competitors for Coastal Ocean Space
Edward D. Goldberg
Heavy Weather in Florida
John M.Williams and Iver W. Duedall
Tides and Their Effects
Chris Garrett and Leo R.M. Maas
Coastal Seiches
Graham S. Geise and David C. Chapman
The Coastal Ocean Processes (CoOP) Effort
Kenneth H. Brink
Sewar Infrastructure: An Orphan of Our Times
Paul F. Levy
Boston Harbor: Fallout over the Outfall
David G. Aubrey and Michael Stewart Connor
Alternatives to the Big Pipe
Susan Peterson
NOAA's Coastal Ocean Program:
Science for Solutions
Lauren Wenzel and Donald Scavia
The Oarfish, Cheryl Dybas
. The National Flood Insurance Program
Beth Millemann
A Tale of Two Lighthouses
David M. Bush and Orrin H. Pilkey
vvv
Number 2, Summer 1993
Coastal Science & Policy II
An Introduction to Coastal Science & Policy II
Vicky Cullen
Controlling the Ingredients that Flow to the Sea
Charles A. Nittrouer
Managing Coastal Wetlands
Joy B. Zedler and Abby N. Powell
Estuaries: Where the River Meets the Sea
William C. Boicourt
Nutrients and Coastal Waters
Scott W. Nixon
US Fisheries
Michael P. Sissenwine and Andrew A. Rosenberg
How Marine Animals Respond to Toxic Chemicals in
Coastal Ecosystems, Judith E. McDowell
A Local Oil Spill Revisited, John M. Teal
Monterey Bay Profiles in Depth
Judith L. Connor and Nora L. Deans
Coastal Erosion's Influencing Factors
David G. Aubrey
Ocennographic Research Vessels
Richard F. Pittenger and Robertson P. Dinsmore
Beautiful, Etliereal Larvaceans, Cheryl Dybas
Number 3, Fall 1993
Marine Protected Areas
Integrated Management of Coastal Areas and Marine
Sanctuaries
Charles N. Ehler and Daniel J. Basta
Integrated Coastal Management: The Florida Keys
Example, George Barley
Conserving Biological Diversity Through Marine
Protected Areas, Jack Sobel
Coral Reef Management in Thailand
Lynne Zeitlin Hale and Stephen Bloye Olsen
Economic Benefits of Marine Portected Areas
John Dixon
Los Marineros, Sheila Cushman
Alternative Support for Protected Areas in an Age of
Deficits, Brian O'Neill
Shoidd the Arabian (Persian) Gulf Become a Marine
Sanctuary? Francesca M. Cava,
John H. Robinson, and Sylvia A. Earle
Marine Reserves, James A. Bohnsack
Stellwagen Bank, Maureen Eldredge
New Technologies for Sanctuary Research
Bruce H. Robison
Undiscovered Diamonds for the Crown Jeiuels
Paul C. Prichard
Gigantocypris: Miniature Halloween Pumpkin
of the Deep, Cheryl Dybas
WHOI Focus: Sixty years of Publications
Kenneth O. Emery
Radioactive Dumping in the Arctic Ocean
John Lamb and Peter Gizewski
Number 4, Winter 1993/94
25 Years of Ocean Drilling
See the table of contents on pages 2 and 3
Tliese volumes and other back issues are
available. For information, call
508-457-2000, x2662
Back cover: The seven-member JOIDES
Resolution drill floor crew tises a variety of
mechanical and hydraulic devices to extend
the drill string to the seafloor. Lengths of pipe
exceeding 28 meters and weighing 874 kilos
are lifted by the drawworks at the base of the
drilling tower, threaded onto the drill string,
and lowered through the moonpool in the
bottom of the ship. In 5,500 meters of water, it
takes 12 hours for the drill bit to reach the
seafloor where drilling can begin.
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