within: NR DOM. pn os - ‘ ee pin
ont ie eae ~ ay tema TY -

Uniform Mud (Unifite)
Deposition

in the Hellenic ‘Trench,
Eastern Mediterranean

~.. CHRISTIAN BLANPIED

DANIEL JEAN STANLEY

61g Nee

“cacao

er ae

setae

SERIES PUBLICATIONS OF THE SMITHSONIAN INSTITUTION

Emphasis upon publication as a means of ‘“‘diffusing knowledge’’ was expressed
by the first Secretary of the Smithsonian. In his formal plan for the Institution, Joseph
Henry outlined a program that included the following statement: ‘“‘It is proposed to
publish a series of reports, giving an account of the new discoveries in science, and
of the changes made from year to year in all branches of knowledge.”’ This theme
of basic research has been adhered to through the years by thousands of titles issued
in series publications under the Smithsonian imprint, commencing with Smithsonian
Contributions to Knowledge in 1848 and continuing with the following active series:

Smithsonian Contributions to Anthropology
Smithsonian Contributions to Astrophysics
Smithsonian Contributions to Botany
Smithsonian Contributions to the Earth Sciences
Smithsonian Contributions to the Marine Sciences
Smithsonian Contributions to Paleobiology
Smithsonian Contributions to Zoology
Smithsonian Studies in Air and Space
Smithsonian Studies in History and Technology
In these series, the Institution publishes small papers and full-scale monographs
that report the research and collections of its various museums and bureaux or of
professional colleagues in the world of science and scholarship. The publications are

distributed by mailing lists to libraries, universities, and similar institutions throughout
the world.

Papers or monographs submitted for series publication are received by the
Smithsonian Institution Press, subject to its own review for format and style, only
through departments of the various Smithsonian museums or bureaux, where the
manuscripts are given substantive review. Press requirements for manuscript and art
preparation are outlined on the insidd Back tober fei

S. Dillon Ripley
a Secretary
Smithsonian Institution

ated We eaee OS)

ree)

CATT hte Abie it bed

SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES © NUMBER

Uniform Mud (Unifite) Deposition
in tae inlelienne IWineewely
Eastern Mediterranean

Christian Blanpied
and

Daniel Jean Stanley

ISSUED
DEC 21 i981

SMITHSONIAN PUBLICATIONS

SMITHSONIAN INSTITUTION PRESS
City of Washington
1981

ABSTRACT

Christian Blanpied and Daniel Jean Stanley. Uniform Mud (Unifite) Dep-
osition in the Hellenic Trench, Eastern Mediterranean. Smithsonian Contribu-
tions to the Marine Sciences, number 13, 40 pages, 15 figures, 2 tables, 1981.—
Unifites are nearly structureless, often thick, layers of clayey silt and silty clay
that appear compositionally homogeneous and generally show a subtle fining-
upward trend. Formed by uniform and faintly laminated muds, unifites are
deposited from rapidly emplaced single gravity-flow events. Along the Hellenic
Arc, unifites are restricted to small trench basins and interpreted as an end-
member gravity-emplaced facies. Unifites are not truly homogeneous and the
petrological distinctions observed are closely related with the trench basin
depositional site relative to steep margins bounding the trench plain. The
faintly laminated portions of unifites contain a higher silt content; the uniform
mud portions are slightly better sorted and display an upward increase of
planktonic tests. The sand fraction is dominated by clastic aggregates eroded
from older margin sediments; unifites also comprise a large silt-size nannofossil
content (including reworked forms).

The increased uniformity basinward of unifites records deposition from
turbidity current-related flows of diminished concentration that spread over
large areas of a flat trench floor. Faint laminae may be related to phases of
flocculation and depositional sorting of the sediment load during transport,
and to the hydraulic jump affecting a flow upon its arrival on a near-flat
basin floor. The slower-moving tail releases the uppermost nonlaminated,
graded unifite mud term. The thickness of Hellenic unifites is a function of
entrapment of moderate amounts of material in small trench plains. The
homogenization process essential for unifite deposition involves relief bypass,
1.e., the preferential entrapment of coarser or denser fractions 1n slope depres-
sions, while finer or less dense particles are transported further downslope
across irregular seafloor features. Unifite deposition records the interplay of:
(1) complexity of dispersal paths and accessibility of sediment to the trench
basin, (2) redepositional processes, grain-support mechanisms and gravity-
induced flow characteristics, (3) type of material transported, (4) extent of
textural segregation and compositional sorting during flow, (5) slope relief
bypassing process, and (6) selective entrapment of essentially fine-grained
particles in the more distal trench catchment basins. Mediterranean unifites
can serve to interpret uniform mud facies on both active and passive margins
and in the rock record.

OFFICIAL PUBLICATION DATE is handstamped in a limited number of initial copies and is recorded
in the Institution’s annual report, Smithsonian Year. SERIES COVER DESIGN: Seascape along the
Atlantic coast of eastern North America.

Library of Congress Cataloging in Publication Data

Blanpied, Christian.

Uniform mud (unifite) desposition in the Hellenic trench, eastern Mediterranean.
(Smithsonian contributions to the marine sciences ; no. 13)

Bibliography: p.

Supt. of Docs. no.: SI 1.41:13

1. Marine sediments—Helenic Trough. I. Stanley, Daniel J. II. Title. III. Series.
GC389.B57 551.46'083/384 81-607825 AACR2

Contents

Tiratten@ GLUT G1O Teepe ewe nsw gmicte iy ne Meo WN Ne katie

PNG ANOWAC CLCTINCINGS NEP a ery cen ee tyr or Mewar ws eS cad

Methodology and Abbreviations .....

Geological Framework of the Study Ares Fe Re ye Wee lane?
CS cineral BO WSemnvatlOms iyo S ee a. Ga oes aaclin's pe gon yes ees s

Regional and Environment-related Variations

Contrasting Uniform and Faintly Laminated Mud Sea uianees
Sir SIZE MATA SIS: aay ery re ee ec ae gnc eee Moda ele ale et
(COMMDOSICOD +5 dasrvace Wat older Wa ear teen ee onc rer

Vertical Petrological Changes .......

Contrasting Margin Flat and Basin even Sequences eta ee

Emvironmental Control 9-7...

IDISCUSSIOM. | 3 5 de Sia hack Seely areca Wickens ca ane nec trernt lcs Rie aes
Evidence for Gravitative Origin of Fine-grained Mud Types .

Classification of Fine-grained Turbidite Mud Sequences ...........

Petrologic Variations Related to Flow Fluctuations ..........
ihnplications of Study and!@onclusions .-)-).........-........--
SHUTMTODBIAY *-o da'g ie 9 tole URE ete I DO ec ee

Witter uiem Orie Gamma eer Are win tee CRE a ee ee

lll

fi i! iy t a ee
Fs f , i is lp _
eo tT ai :
, f ’ a rant, i ase un
ee
nh
i
Cae
“
\
i
ae *
{
canis,
}
\ }
,
7
7 \ a
f oe Saieit

Uniform Mud (Unifite) Deposition
Mme ime llicmic drench.
Eastern Mediterranean

Christian Blanpred
and Daniel Jean Stanley

Introduction

The increased interest in the depositional origin
of fine-grained marine sediments has resulted in
the recognition of diverse mud types. Several
classifications have called attention to a struc-
tureless mud facies reported in some modern
deep-sea environments and in the marine rock
record (summaries in Piper, 1978, and Stow and
Shanmugam, 1980). The premise of this study is
that the Mediterranean region, with its well-ex-
posed mudstone formations in the surrounding
mountain chains and its thick, mud-rich post-
Miocene unconsolidated sequences in the various
isolated basins (Stanley, 1977a), should be a par-
ticularly suitable sector in which to define the
nature, distribution, and origin of such appar-
ently homogeneous lutites. Insofar as the modern
Mediterranean Sea is concerned, studies focusing
on fine-grained sediment transport have been
undertaken in several basin settings. Sedimento-
logical research has advanced during the past
fifteen years largely as a result of combined coring
and subbottom profiling surveys in diverse topo-
graphic settings where unconsolidated deposits of

Christian Blanpied, Compagnie Francaise des Petroles, Department
d Exploration, Paris, France. Daniel Jean Stanley, Dwision of
Sedimentology, National Museum of Natural History, Smithsonian
Institution, Washington, D.C. 20560.

suspension and gravity-emplaced origin have ac-
cumulated.

Sedimentological studies of ponded (cf. Hersey,
1965) Mediterranean mud facies have been un-
dertaken in deep depressions, such as the western
Alboran Sea (Stanley, Gehin, and Bartolini,
1970), portions of the Algéro-Balearic Basin Plain
(Rupke and Stanley, 1974), Tyrrhenian Basin
Plain (Ryan, Workum, and Hersey, 1965); Cor-
sican Trough (Stanley, Rehault, and Stucken-
rath, 1980); deep troughs in the Strait of Sicily
(Maldonado and Stanley, 1976; Blanpied et al.,
1979), and some small basins in the Adriatic Sea
(van Straaten, 1967), and on the Mediterranean
Ridge (Kastens and Cita, in press). In the Hel-
lenic Arc region of the eastern Mediterranean
investigations of fine-grained sedimentation have
been made by Hersey (1965), Ryan et al. (1973),
Vittori (1978), and Maldonado, Kelling, and An-
astasakis (1981).

Detailed mapping of Quaternary unconsoli-
dated sediment in different depositional environ-
ments of the Hellenic Trench reveals that clayey
silt and silty clay, rather than sand, almost in-
variably dominate the depositional cover of this
structurally and morphologically complex region.
Seven fine-grained sediment types, or lutites, have
been identified by Stanley and Maldonado (1981)

2 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

in a suite of 24 cores collected in eight distinct
depositional settings west and south of the Pelo-
ponnesus (Figure 1). Four of these mud types
(slump, debris flow, turbiditic and hemipelagic)
have received considerable attention in earlier
studies of both modern and ancient deep marine
sediments. A fifth type includes very well-lami-
nated mud facies that accumulated throughout
much of the Hellenic area (see Stanley and Mal-
donado, 1981, fig. 3b, c); this facies formed pri-
marily during periods of marked water mass strat-
ification, such as at time of sapropel formation,
which affected most of the eastern Mediterra-
nean. The present study focuses specifically on
the other two, apparently related, fine-grained
facies that are concentrated primarily in Hellenic
Trench basins proper. These types are apparently
structureless uniform mud and faintly laminated
mud.

Several possible mechanisms have been pro-
posed for the emplacement of these two lutite
types in the study area. Earlier studies indicated
that homogeneous muds may have been depos-
ited in part by fine pelagic suspension-related
processes (Ryan, et al., 1973:268) or, alternately,
by “giant” dense mud flows (Stanley and Knight,
1979). More recent detailed analysis of the uni-
form and faintly laminated muds, however, sug-
gest that these two lutite types most likely repre-
“single-event” gravitative deposits. The
mechanisms involve the settling of material from

sent

slow moving and low concentration flows, which
are related to turbidity currents that are prefer-
entially ponded in small trench basins (Stanley
and Maldonado, 1981, fig. 11).

The term “unifite’”’ (Stanley, 1980) is applied
to the nearly structureless, often thick, layers of
clayey silt and silty clay that are formed by
uniform and faintly laminated mud facies de-
scribed in this study. Such deposits generally
appear, but are not truly, compositionally ho-

"The term “unifite” was formally introduced by D. J.
Stanley in October 1980 at the Conference on “Sedimentary
Basins of Mediterranean Margins” sponsored by the Consig-
lio Nazionale delle Ricerche at the University of Urbino,
Italy

mogeneous, show various subtle fining-upward
trends, and are deposited by gravity flow trans-
port events. The formulation of a depositional
model for uniform muds requires a refined de-
scription of the petrologic attributes of these fine-
grained, structureless deposits. Particular atten-
tion is paid here to selected uniform mud sections
from seven piston cores collected in three Hellenic
Trench basins during cruises of the R/V Trident
(1975) and the R/V Marsili (1976).

ACKNOWLEDGMENTS.—Our sincere apprecia-
tion is expressed to Mr. H. Sheng, Smithsonian
Institution, who assisted with all aspects of the
petrologic and laboratory analyses. Radiocarbon
dates were generously provided by Dr. R. Stuck-
enrath, Smithsonian Institution Radiation Biol-
ogy Laboratory, and selected bottom photo-
graphs from the 1978 Hellenic Trench Rave cruise
in the Kithera-Antikithera Trench were furnished
by Messrs. J. Jarry and R. Person, Centre Na-
tional pour l’Exploitation des Oceans, France.
Drs. S. Culver, U. S. National Museum of Natu-
ral History, G. Glagon, University of Paris VI,
and C. C. Smith, U. S. Geological Survey, Wash-
ington, kindly identified selected collections of
benthic foraminifera, planktonic foraminifera,
and coccoliths, respectively.

Discussions during the early phases of the Hel-
lenic Trench study with R. J. Knight, Petro-
Canada Limited, and A. Maldonado, University
of Barcelona, proved most useful. The paper was
reviewed by Dr. R. W. Embley, National Ocean
Survey, National Oceanic and Atmospheric Ad-
ministration, Washington, D.C., Mr. P. H. Feld-
hausen, NUS Corporation, Rockville, Maryland,
and Dr. H. D. Palmer, Interstate Electronics Cor-
poration, Arlington, Virginia. The study, part of
the continuing Mediterranean Basin (MEDIBA)
Project, was supported by a fellowship to C.
Blanpied from the French Ministry of Foreign
Affairs, Paris, and by Smithsonian Scholarly
Studies grant number 1233S101.

Methodology and Abbreviations

The seven western Hellenic Trench cores con-
taining uniform mud (1975 cruise R/V Trdent,

NUMBER 13

20°

O Slope, steep smooth

BSlope, broken high relief

oO ce)
21° m7 235 24

ORK (DEPTH IN FATHOMS

P LOSES KK KKK

Y FRELRRERKKK HY
OS
LOD
SOC

SORE KKY 38°

SS SI
2S ee
KKK

COQ RRL
Qe SRK Q
e,

36°

% Canyon, depression @ Trench basin, apron

% Perched basin, proximal
%# Perched basin, distal

OTrench basin, flat margin
@ Trench basin, plain
34°

Figure 1.—Western Hellenic Trench margin showing the location of R/V Tindent (TR 34-36)
and R/V Marsili (MA 10, 20, 22, 23) cores and the physiographic environments in which they
were recovered (circled numbers = cores containing unifites; uncircled core numbers do not
have obvious unifites; ZB = Zakinthos-Strofadhes Basin, MB = Matapan Deep; KB = Kithera-

Antikithera Basin).

4 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

or TR, cores 34, 35, 36; 1976 cruise R/V Marsilz,
or MA, cores 10, 20, 22, 23) range in length from
565 to about 1000 cm. For comparison purposes,
other cores collected in this region were also
examined. Complementary data concerning these
and other cores cited in this paper, including core
position, depth, and lithological information is
provided elsewhere (Stanley, Knight, and Stuck-
enrath, 1978; Vittori, 1978; Stanley and Maldon-
ado, 1981; Feldhausen et al., 1981). For the pe-
trologic analyses, more than 250 samples were
collected from uniform and faintly laminated
mud layers at intervals ranging from about 5 to
25 cm. These samples were selected primarily on
the basis of x-radiography of split cores, which is
the most certain method to recognize both uni-
form and faintly laminated mud types.

All samples were treated in the same way. The
sand fraction (>63 wm) was recovered by sieving,
while the silt-clay separation was made using the
Andreasen pipette method. Determinations of the
complete size distribution of the silt and clay
(<2 pm) fractions were completed with a Coulter
Counter Model ‘TA-II with two apertures (140
and 30 pm). The distribution (volumetric per-
cent) of the entire silt and clay fraction was
determined with the 140 micrometer aperture;
selected samples from each core were processed
using the 30 micrometer aperture to better define
the fine silt and clay size distribution.

In those samples (approximately 150) where
sufficient sand size material was available, the
composition of 150 to 500 sand grains was iden-
tified using a petrographic microscope. Eighteen
mineralogic components are recognized, and
these are grouped into four major categories: (1)
terrigenous (light minerals, heavy
mica); (2) biogenic (planktonic foraminifera, shell

minerals,

fragments, benthic foraminifera, spicules, pyri-
tized planktonic foraminifera, pteropods, pyri-
tized benthic tests, ostracodes, juvenile forms of
pelecypods, radiolarians and diatoms); (3) oxi-
dized or reduced aggregates (red, black and plate-
shaped); and (4) clastic aggregates consisting of
cemented silt-sized particles.

The silt size fraction (2 to 63 pm) of all 250

samples was examined. This fraction includes 13
mineralogical components identified by high-
power petrographic microscope and SEM, and
these are grouped into five major categories: (1)
terrigenous (quartz, feldspar); (2) biogenic (fora-
minifera, coccoliths, spicules, carbonate shell
fragments); (3) volcanic products (palagonite, sid-
eromelane, chlorite and heavy minerals, includ-
ing microlite); (4) authigenic (recrystallized cal-
cite and dolomite); and (5) clastic aggregates.
The proportions of these silt-size groups are de-
termined semiquantitatively by using a relative
abundance scale, from 1 (trace amounts) to 5
(abundant).

The composition of the clay size fraction (<2
f4m) was determined by x-ray diffraction, SEM,
and chemical probe analyses. Forty-four samples
were selected from cores MA-10 and MA-20, and
twenty additional samples were obtained from
the other five uniform mud-bearing cores. In
addition, about 105 samples were selected from
the other 17 cores shown in Figure | to determine
the clay mineral composition of silt size.

Calcium carbonate content was determined for
all mud samples using the standard ascarite ab-
sorption technique. These data were supple-
mented by thirty radiocarbon dates obtained
from the seven uniform mud-bearing cores and
two dates from slope core TR-37 (Table 1); nine
of these were previously published in Stanley,
Knight, and Stuckenrath (1978). Also utilized in
this study were high-resolution 3.5 kHz records
collected near the core sites during the 1975
Trident and 1976 Marsili cruises, and a suite of
about 300 bottom photographs collected in 1978
in the Kithera Trench by the French Centre
National pour |’Exploitation des Oceans.

Abbreviations used in this study are as follows:
FL = faintly laminated mud, KB = Kithera-
Antikithera Trench system, MA = Marsili cruise,
MB = Matapan Deep Trench system, S = sap-
ropel, TR = 77dent cruise, U = uniform mud, ZB
= Zakinthos-Strofadhes Trench system.

Geological Framework of the Study Area

The study area southwest of the Peloponnesus
and west of Crete (Figure 1) occupies a seismically

NUMBER 13

TasBLe 1.—List of 30 radiocarbon dates obtained for seven
western Hellenic Trench basin cores containing unifites, and
two dates for core TR-37 collected on the steep Zakinthos
slope (B.P. = years before present)

Gp Sample Radiocarbon

eee depth date
(cm) (B.P.)

MA-10 50— 63 12,775#155

261-275 15,170+130

495-507 15,0304#125

MA-20 16— 30 12,090+ 90

151-166 11,880+110

272-287 13,000+ 120

392-407 12,450+ 95

589-604 14,045+110

942-957 14,840+105

MA-22 89-106 11,260+160

171-185 10,215+130

239-254 19,290+325

357-388 19,4604325

686-698 25,300+370

MA-23 25— 40 UPS HIS 2295

110-130 28,060+610

250-264 29,100+550

415-440 29,700+730

495-507 26,860+460

TR-34 130-144 14,500+120

187-200 17,810+175

389=353 28,730+650

667-679 25,240+350

TWR=3}5) 135-150 OM M5225 7/5

220-235 16,510+150

290-310 18,600+140

470-490 19,710+210

TR-36 240-260 16,510+130

450-465 16,910+155

530-550 20,100+220

TR-37 50— 65 17,380+160
240-255 >43,000

active region in the western part of the Hellenic
Arc. Overall, this sector occupies a tectonically
complex, largely compressive setting, believed to
have experienced subduction and considerable
vertical and lateral offset. The roles of plate col-
lision and transform fault motion are discussed
by Comninakis and Papazachos (1972), Mc-
Kenzie (1972), Makris (1976), Biju-Duval, Le-
touzey, and Montadert (1979), Mascle and Le

Quellec (1979), Le Pichon and Angelier (1979),
and many others. The structural and _ strati-
graphic configurations of this investigated region
have been detailed by means of several closely
spaced, high-resolution seismic surveys, the results
of which are summarized by Got, Stanley, and
Sorel (1977), Vittori (1978), and Le Quellec
(1979). These studies reveal a structurally de-
formed unconsolidated sediment series of highly
variable thickness. This series, dated as probable
Phocene and Quaternary age, lies above indur-
ated strata locally comprising deposits of Creta-
ceous (Ryan, et al., 1973), Miocene, including
probable Messinian evaporites, and Pliocene age
(Ariane, 1979; Le Pichon, 1980).

Three distinct and well-individualized trench-
basin systems, clearly apparent on morphological
charts (Carter et al., 1972), result from this geo-
logically recent tectonic activity. The three sepa-
rate trench slope and basin systems are delineated
largely by NW-SE and WSW-ENE tectonic
trends, involving some extension (Got, Stanley,
and Sorel, 1977), as well as compression. From
NW to SE the western Hellenic Trench basin
plains lie at depths of about 4150 m, 5000 m and
4615 m, and are named, respectively, the Zakin-
thos-Strofadhes system (ZB), the Matapan Deep
system (MB), and the Kithera-Antikithera system
(KB). Bathymetric and seismic profiles show that
the trench basins proper are not simple U-shaped,
elongated troughs. The trenches proper, as dis-
played in cross-sections of the Matapan Deep,
include small depressions broken by ridges that
subdivide, and thus limit, the size of the near-flat
basin plains (Vittori, 1978:121; Le Quellec, 1979:
60). The surface area of the flat trench basins
proper ranges from little more than 100 (ZB) to
about 250 km? in the case of the Kithera-Antik-
ithera Basin.

The extremely complex morphology between,
and within, each of the trench-slope and basin
systems complicates the dispersal pattern of sedi-
ments transported from the Peloponnesus land
mass and contiguous margin to the distal basin
plains (Stanley, 1977b:435). Moreover, morpho-
logic features of high relief which, include ridges

SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES
Margin Flat Basin Plain

oy ee aT tar SUMQ Ee oy

TRO

oe, he ie its acon

ban aE he ae F ‘ j ‘ ;
phe M RATNER OR aaah ‘4

ham in cme an een te. re an ee NE

‘hn ee “ a‘

sal yaaa i

EDEN y ate toi

os

np i, I

WT ee ALY Late % vA Bi

NERA hae tin Ny

{ ¢ % Ean |
‘ » Meat Sf \
man can ;

f Ua : ‘ 8 MG

ot a
' NES
bahia:

| Hi aa
ma23 | TN
1 Ihe vee
ae ay 7
ae aa le : ill Me ‘
| a | t ed ua
| i |
My |
HAE
MA - 20
MA- 10 sepeesswytioereyat, Yaoi tng TRE z <

Ficure 2.—High-resolution 3.5 kHz subbottom profiles of the seafloor at core recovery sites
(scale = 50 m). Core pairs, from top to bottom (from NW to SE), are: TR-34 and TR-35 in the
Zakinthos-Strofadhes Basin (ZB), respectively 4060 and 4140 m; MA-22 and MA-23 in the
Matapan Deep (MB), respectively 4090 and 4120 m; and MA-10 and MA-20 in the Kithera-
Antikithera Basin (KB), respectively 4300 and 4510 m. Profiles in the left column show trench
margin flat sectors near the base of steep slopes; profiles in the right column illustrate trench
basin plain subbottom configuration.

NUMBER 13

and submarine prolongations of the Peloponne-
sus, effectively separate trench basins and pre-
clude gravitative transport from one basin to
another (Stanley, 1974:248; Vittori, 1978:193).
Sediments transported into the trench basin sys-
tems within the study area are derived primarily
from the adjacent Peloponnesus landmass and its
narrow shelf and slope margin (Emelyanov, 1972:
364; Feldhausen and Stanley, 1980:M27-M29;
Vittori et al., 1981) and also, to a certain extent,
from the Aegean Sea (Stanley and Perissoratis,
1977) and the Mediterranean Ridge, which
bounds the trench basins to the west and south.
Dispersal is also influenced by the water mass
circulation patterns in the eastern Ionian Sea
(Venkatarathnam and Ryan, 1971; Lacombe and
Tchernia, 1972:33-34; Miller, 1972). From seis-
mic evidence, there appears to be a general
increase in the accumulation rate of Pliocene and
Quaternary sediments from the NW toward the
SE: the thicknness of the ponded unconsolidated
strata is locally in excess of 500 m in the ZB basin,
over 1000m in the MB basin, and ranges from
about 700 to 1200 m in the KB basin. Considering
the thickness of this Plio-Quaternary cover, min-
imal averaged long-term rates of sedimentation
since the end of the Miocene (Messinian) range
from about 10 to 20 cm per 1000 years. Higher
rates are recorded toward the SE. Seismic profiles
published by Vittori (1978) and others indicate
that these trench basin deposits, including Qua-
ternary strata are, in almost all cases, deformed,
thus recording syndepositional tectonic activity.
The two trench basin environments in which
unifites are recovered are (1) the margin flat
(trench plain near the base of steep basin slopes)
and (2) the basin plain (near-flat plains away
from steep margins). The configuration of the
upper 30 to 70 m of sediment in these two envi-
ronments is illustrated on 3.5 kHz profiles ob-
tained on the Trident 1975 and Marsili 1976 tra-
verses (Stanley, 1977b). Selected seismic lines
from each of the three basins, showing near-hor-
izontal acoustic reflectors near the sites of cores
studied herein, are illustrated in Figure 2. Profiles
obtained across the margin flat (close to cores

TR-34, MA-23, MA-10) and the basin plain (near
cores TR-35, MA-22, MA-20) reveal strong re-
flectors, probably sandy horizons. This assump-
tion is confirmed by drilling at Jozdes Leg 13 sites
127 and 128 (Ryan et al., 1973:243), which re-
covered sand layers. Thick (10-15 m) transparent
acoustic layers are interpreted as largely mud
strata. This is confirmed by the piston cores,
particularly in the case of the 10-m long core
MA-20 (Figure 2). Close-grid seismic traverses
show the lateral continuity and extensive areal
coverage of both hard and transparent acoustic
layers across the basins and their discontinuity on
slopes, thus demonstrating the ponding phenom-
enon as defined by Hersey (1965) and others.

General Observations

Three criteria enable us to identify unifites
composed of unzform muds (U), or faintly laminated
muds (FL), or both. The most obvious criteria
used to recognize these two lithofacies are pri-
mary bedform stratification and/or bioturbation
structures (or their absence) as revealed in x-
radiographs (Figure 3), supplemented by color
and texture observed in split cores. The strati-
graphic position of a unifite can be defined with
respect to previously identified diagnostic key
horizons such as sapropels, oxidized layers, and/
or ash tephra (Stanley, Knight, and Stuckenrath,
1978). Particularly valuable in this respect is the
upper sapropel (S;) dated at about 8000 years
before present throughout most of the eastern
Mediterranean (Stanley, 1978). Determination of
the relative stratigraphic position of the unifites
examined in this study is facilitated by the avail-
ability of numerous radiocarbon dated core sam-
ples (Figure 4, Table 1). Most of these dates,
however, prove too old as a result of high propor-
tions of reworked carbonate material incorpo-
rated in unifites (page 17).

Only x-radiographic analyses can satisfactorily
reveal the absence of any bedform structures,
which are characteristic of the uniform mud facies
(Figure 3c), and the presence of vague or diffuse
stratification that characterizes faintly laminated

260

7

700

290

Ls Li ee

290 i

300

73

a0 a0)

Figure 3.—X-radiograph prints of the three fine-grained types discussed in text (core width
~ 6 cm; numbers are depths in cm below core top): A, Well-developed fine-grained mud
turbidite showing laminated and graded mud terms (core TR-34, 260-290 cm; see Figure 4).
B, Faintly laminated mud overlain by uniform mud defining an FL+U sequence (core MA-23
(unifites), 280-310 cm; see Figure 7). c, Uniform mud showing absence of bedform structures
(core MA-20 (unifite), 770-800 cm; see Figure 6).

NUMBER 13

KITHERA-
ANTIKITHERA
BASIN

11315|
Wy 12775
28060
a=
=
©
Z
lw
—!
lw
2
O eco 15170
O
29700
26860 15030

8m — Upper Units (Undifferentiated)
—> "XC Date ( years B.P.)
— Sapropel
9
4 — Uniform Mud
} Uniform Mud Sequence
Bl — Faintly Laminated Mud =Unifite
10m

Ficure 4.—Simplified lithofacies logs of the seven cores containing unifites detailed in this
study, showing their stratigraphic position relative to the upper sapropel (Si) layer. (Numbers
on left of logs are radiocarbon age determinations (Table 1), dotted lines correlate stratigraphic
sections, age of the S; sapropel is ca 8000 years B.p., T and arrow in TR-34 core log denote a
classic mud turbidite. Core positions are shown in Figures 1 and 2.)

10 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

mud facies (Figure 3B). In some cases uniform
mud overlies the faintly laminated mud facies
(Figure 3B), while in others uniform mud overlies
well-laminated turbidite sands and silts (Figure
3a). The petrology of unifites in the various cores,
regardless of stratigraphic position, is quite simi-
lar. In split cores, the uniform and faintly lami-
nated sections are generally pale olive to grayish
olive (LOY 4/2 to LOY 6/2), and in few cases (TR-
35 at about 450 cm from the core top), are dusky
yellow, or 5Y 6/4 to 8/4. These mud types,
essentially poorly sorted silt and clay mixtures,
have a sticky-plastic consistency, trace sand frac-
tions (generally <1%), and an absence of macro-
fauna and bioturbation structures. These aspects
of unifites result in the textureless and relatively
homogeneous deposit observed in split cores.
Typical unifite characteristics include: (1) high
clay fraction content (<2 zm, ranging from 35 to
60%) mixed with silt, (2) very low sand fraction,
which usually consists of a mixture of both terri-
genous and bioclastic (largely planktonic) com-
ponents, (3) marked thickness (usually >1 m and
to as much as 10 m in piston cores, and possibly
even thicker in acoustically transparent layers
from 3.5 kHz records), (4) continuity of such
layers across large areas of the trench basin floors,
as revealed by high-resolution subbottom profiles,
(5) spatial restriction of the associated structure-
less and faintly laminated mud facies in trench
basins, both on the plains proper and flat basinal
sectors near sloping, usually steep margins, and
(6) radiocarbon dates showing a consistently nar-
row range of time interval within any one mud
stratum, regardless of the thickness of the unifite
layer. Together, these observations and the close
association of uniform muds with classic mud
turbidites (Stanley and Maldonado, 1981) tend
to indicate that unifites were deposited rapidly.

Regional and Environment-related Variations

There are distinct differences in the granulo-
metric and mineralogical characteristics of unifite
(uniform and faintly laminated) mud core sec-
tions among the geographically separated trench

basin systems. The marked regional trends char-
acterizing the Zakinthos-Strofadhes system to the
NW and the Kithera-Antikithera system to the
SE are summarized in Figure 5. With few excep-
tions, the Matapan Deep, lying between these
two basins, presents intermediate characteristics.
These NW to SE regional trends occur regardless
of stratigraphic position in a core, time of em-
placement, or type of unifite bedform (FL or U)
involved. Sediments in the KB system (SE sector
of the study area) are characterized by (1) a
somewhat coarser (siltier) grain size, (2) a slightly
poorer sorting, (3) a sand-size fraction dominated
by clastic aggregates and bioclastic fragments,
and (4) a silt fraction dominated by coccoliths,
recrystallized calcite and dolomite, volcanic prod-
ucts and attapulgite (= palygorskite). In contrast,
the finer, somewhat more clay-rich, and better
sorted sediments to the northwest (ZB system) are
characterized by sand and silt fractions domi-
nated by planktonic foraminifera and associated
pyritized tests, and biogenic fragments, together
with important proportions of terrigenous mate-
rial. Sediments in the Matapan Deep, having
accumulated in an intermediate geographic po-
sition, differ subtly from the ZB and KB trench
basins: They have a bioclastic fraction with some-
what higher proportions of pteropods and benthic
foraminifera than sediments in the other two
trench basins.

A synthesis of all mud (U and FL) sample data
recorded for the three basins suggests that factors
other than those related to geography account for
most core-to-core petrologic differences. We can
demonstrate, for example, that some petrologic
distinctions are more closely related to specific
morphologic attributes of environment than to
geography per se. Thus, considerable effort has
been made in this study to distinguish between
petrologic differences among cores collected in
the trench basin margin flat environment (1.e.,
cores MA-10, MA-23, TR-34) and cores recovered
in the basin plain environment (i.e., cores MA-20,
MA-22, TR-35, TR-36). The typical configura-
tion of these two environments is illustrated in
Figure 2. We recall that slopes bounding the

NUMBER 13

NW.

ZAKINTHOS-STROFADHES BASIN. f
a

DOMINANT CHARACTERISTICS

Clay content
Carbonate content
Better sorted mud
Sand components:
Planktonic foraminifera
& pyritized tests
Spicules
Light and heavy minerals
Silt components:
Foraminifera
Spicules
Quartz, feldspar
Clastic aggregates
Carbonate fragments

DOMINANT CHARACTERISTICS

11

KITHERA-ANTIKITHERA BASIN if

DOMINANT CHARACTERISTICS

Silt content

Sand Components:
Clastic aggregates
Ostracodes
Pelecypods (juvenile forms)

Shell fragments
Mica
Oxidized and reduced aggregates
Silt components:
Coccoliths
Dolomite, recrystallized
Calcite, recrystallized
Volcanic products
(palagonite, sideromelane,
chlorite, microliths)
Attapulgite

Sand Components
Pteropods

Radiolarians
Diatoms

Ficure 5.

Mean grain size (largest)
Median grain size (largest)

Benthic foraminifera
& pyritized tests

Synthesis of the dominant petrographic characteristics of unifites collected in the

three Hellenic Trench basins systems. This scheme emphasizes regional variations from NW to
SE, i.e., Zakinthos-Strofadhes (ZB); Matapan Deep (MB); and Kithera-Antikithera (KB)
sectors. Arrows show that characteristics that dominate in the KB system are often less
important in the ZB system, and vice versa. In some respects, the Matapan Deep cores are
intermediate, petrologically, to those of the two other trench systems; the listed sand and silt
components of Matapan Deep cores are those that predominate in this basin and serve to

distinguish it from the ZB and KB basins.

trench basin floors are generally steep (>10°) as
revealed by echograms and seismic records (cf.
Wattonit9/7/82 Le @uellec, 1979).

In general, the margin flat sediments tend to
be somewhat less well sorted, display a slightly
higher proportion of sand-sized terrigenous (es-
pecially light minerals) than biogenic compo-
nents, and contain more benthic foraminiferal
tests and silt-sized recrystallized calcite. In con-
trast, the basin plain sediments are somewhat
better sorted, and contain (in both the sand and
silt fractions) higher proportions of clastic aggre-
gates and biogenic components, particularly
planktonic tests. In addition, the silt fractions of
basin plain core sections tend to contain more

palagonite and recrystallized dolomite than the
margin flat sediment.

We can demonstrate that the above distinctions
are only in part related to regional provenance
differences but, more importantly, are related to
transport processes effective in the different dep-
ositional environments.

Contrasting Uniform and Faintly Laminated
Mud Sequences

As noted previously, unifite lithofacies are dif-
ferentiated primarily by the presence or absence
of stratification structures and by comprehensive
grain size and compositional analyses. In the

VW SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

following sections we compare petrological attri-
butes of unifite core sequences (Figure 4) formed
essentially of structureless mud (U) with those
containing faintly laminated mud and the di-

Cores MA-10 and MA-20 are designated as the
type cores for unifites composed of uniform muds.
These cores are, respectively, from the trench
margin flat and basin plain environments of the

rectly overlying structureless mud (FL+U). Kithera Trench system (Figures 1, 6). Type

MA-10 Margin Flat MA-20 Basin Plain

(%)

SAND
COMPOSITION
(%)

ATTAPULGITE
ILLITE (1) + QUARTZ (Q)
ATTAPULGITE
ILLITE (1) + QUARTZ (Q)

CARBONATE
(Y%
AGGREGATE
(%)
COMPOSITION
)
CARBONATE
Yo
AGGREGATE
(%)

CLASTIC
SAND
CLASTIC

w
a

400 50100

0 50 100

So
co
no

el

et

Zee

I

||
ot

\V

V

\I/

im/ lS

\

inl

LX 2
nee Wry

MEAN (um)

SAND COMPOSITION
EJ Pteropods Spicules
Co Planktonic Foraminifera Be Shell fragments and
Volcanic Products
BB Planktonic tests,pyritized Light Minerals
CI Benthic Foraminifera | Heavy Minerals
Bi] Benthic tests,pyritized Baie

° F idi duced
23.c| Ostracods + juvenile Pelecypod Oxidizediand tecuce
aggregates

MEAN( pm

Ficure 6.—Detailed logs of selected unifites in the Kithera-Antikithera Basin cores MA—10
(trench margin flat) and MA-20 (basin plain). Logs depict major bedform based on x-
radiography, grain size (silt content and mean), carbonate content, clastic aggregates, and other
sand-size mineralogical components; the sand-size mineralogical components (excluding clastic
aggregates) are recalculated to 100%. The abundance of silt-size attapulgite (=palygorskite)
relative to dominant quartz (Q) or illite (I) is also shown. (E2 = graded mud term; E3 =
ungraded mud term. Explanation in text.)

NUMBER 13

FL+U core sections are represented by cores MA-
23 and MA-22, respectively, from the trench mar-
gin flat and basin plain environments of the
Matapan Deep (Figures 1, 7). Detailed petrologic
sections of cores TR-34, TR-35, and TR-36 (not
shown here), recovered from the Zakinthos-Stro-
fadhes Trench system, are most similar to core
sequences MA-22 and MA-23. Simplified litho-

MA-23 Margin Flat

>
5 zZ
* ws ©)
as E =
Depth s q < =
) % 6€ Hs Q
— oO

0 Sa pe Boe Ze
20 S og AG

oO 2 Se

80 25 30 35 40 0 50100 50

; ee) 60 70
=|

SAND COMPOSITION

| Pteropods
Planktonic Foraminifera

| Planktonic tests, pyritized

Spicules

asi Shell Fragments and

Volcanic Products

ZG Light Minerals

(%)

CC] Benthic Foraminifera
Ee) Benthic tests, pyritized

CJ Heavy Minerals
m

Ih)

facies logs of these seven cores may be compared
in Figure 4.

GRAIN SIZE ANALYSIS

In both U and U+FL mud sequences the rel-
ative percent, by weight, of the sand fraction does

MA-22 Basin Plain

So
rs)
SILT
CONTENT
(%)
CARBONATE
(%)
CLASTIC
AGGREGATE
(%)
SAND
COMPOSITION
(%)

un
oO

4045 ] 55 20304050600 50100

ie

Ostracods+ juvenile Pelecypod Ea Oxia eepiand aves

Ficure 7.—Detailed logs of selected unifites in the Matapan Deep cores MA-23 (trench margin
flat) and MA-22 (basin plain). Logs depict major bedform based on x-radiography, grain-size
(silt content and mean), carbonate content, clastic aggregates, and other sand-size mineralogical
components; the sand-size mineralogical components (excluding clastic aggregates) are recal-
culated to 100%. (El = laminated mud term; E2 = graded mud term; E3 = ungraded mud
term; explanation in text.)

SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

Ihe

NUMBER 13

not exceed 0.3 percent, and in general, there is
more silt than clay (<2 pm). However, the silt
content in the U-type section displays a slightly
higher average (58%) and a narrower range (50-
65%) than in the FL+U sections (average of 56%;
range of 44—75%). The latter sequence records an
enhanced silt content in the lower faintly lami-
nated muds, and a vertical upward change from
clayey silt to fine silty clay. The mean and median
grain sizes of the uniform mud are somewhat
smaller (range respectively, x = 6.4 to 7.5 ym and
Md = 5.5 to 7.0 um) than in the FL+U sequence
(x = 7.5 to 8.0 um and Md = 6.5 to 7.5 pm). It is
noted that sediment of comparable size (fine silt)
was earlier reported in the Matapan Deep by
Pareyn (1968:66). Sorting values (cf. Folk and
Ward, 1957) indicate that the uniform mud se-
quences are slightly better sorted (3.6 to 4.6) than
FL+U sequences (3.5 to 5.3). These differences
reflect the influence of the somewhat higher silt
content in the lower, faintly laminated mud por-
tions of the FL+U sequences.

Vertical variations in silt content and mean
grain size are apparent on core logs (Figures 6,
7). Both U and FL+U sequences show an upward
decrease in grain size. This fining-upward is most
obvious in core MA-23 and coincides with a
transition from the FL to U mud type; this trend

Ficure 8.—Scanning electron micrograph components in
Hellenic Trench unifites (scales = 1 zm): a, Clastic aggregate
composed of cemented silt-sized grains (from core MA-20,
900 cm from core top, X 10K); 8, Gephyrocapsa oceanica
Kamptner (arrow 1) of Pleistocene to Recent age and Syra-
cosphaera pulchra Lohman (arrow 2) of Late Pliocene to
Recent age (from core TR-34, 500 cm from core top, X
10K); c, poorly preserved test of Discoaster (species not deter-
mined, arrow 1) with overgrowth, pre-Pleistocene in age,
and Scapholithus sp. (arrow 2) (from core MA-20, 900 cm
from core top, X 12K); p, Cyclococcolithus leptoporus (Murray
and Blackman), possibly of Pleistocene to Recent age (from
core TR-36, 610 cm from core top, X 10K); £, Rhabdosphaera
clavigera (Murray and Blackman) (arrow 1), possibly of Pleis-
tocene to Recent age, Scapholithus fossilis Deflandre (arrow
2), possibly of Cretaceous to Recent age (from core TR-35,
410 cm from core top, X 5K), and diatom (arrow 3); F,
Helicopontosphaera kamptner: (Hay and Mohler) of Miocene to
Recent age (from core TR-36, 610 cm from core top, X 7K).

is less well developed in core MA-22 in the same
basin. A less pronounced but nevertheless overall
fining-upward trend is also apparent in cores
MA-10 and MA-20 that contain only by U sec-
tions (Figure 4).

COMPOSITION

The total calcium carbonate content of U se-
quences averages 35% and ranges from 30 to 50%;
that of FL+U sequences averages 39% and ranges
from 26 to 60%. Higher carbonate contents are
recorded particularly in some faintly laminated
muds, such as those in core MA-23 (Figure 7). In
general, carbonate content tends to fluctuate
markedly but, unlike grain size, no distinct ver-
tical trend in either U or FL+U sequences is
noted.

Grain counts of the sand size fraction in all
seven cores reveal a predominance of clastic ag-
gregates formed by poorly cemented silt-size frag-
ments (Figure 8a). Aggregates constitute as much
as 90% of the sand fraction, but tend to diminish
upward in U-type sequences, as illustrated in logs
of MA-10 and MA-20 (Figure 6). In FL+U se-
quences their upward increase, from about 5 to
80%, is related to the transition from faintly
laminated to uniform mud type (see core MA-23,
Figure 7). To better evaluate fluctuations of the
sand size components, clastic aggregates were
excluded in the point-counts of the terrigenous
biogenic components (sand composition column
in Figures 6 and 7). Although there are compo-
sitional differences from core to core, the domi-
nant components almost always comprise plank-
tonic foraminifera, quartz, shell fragments and
altered volcanic products. The U sequences gen-
erally contain higher proportions of sand-sized
biogenic components and planktonic tests than
the FL+U sequences. Proportions of planktonic
foraminifera tend to be higher in faintly lami-
nated (FL) muds (MA-23, Figure 7). In both U
and FL+U sequences, there is an upward increase
of planktonic tests in the upper, somewhat finer-
grained, sections. Moreover, pyritized foramini-
feral tests abound in the FL+U sequences, often
in the laminated mud portions. They tend to

SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

NUMBER 13

increase upward, particularly in cores TR-34,
TR-35, and TR-36. This upward increase in the
three Zakinthos-Strofadhes Trench basin cores
appears related to the presence of the overlying,
well-developed sapropels (Figure 4). Pyritized
tests associated with sapropels in other regions of
the eastern Mediterranean generally signal the
development of reducing conditions, the most
recent event of this type occurring from about
9000 to 7000 years ago (Ryan et al., 1973:713;
Stanley, 1978; Thunell and Lohmann, 1979).

In the silt-size fraction, nannofossils are the
dominant component within both U and FL+U
sequences in all seven cores; their relative abun-
dance in a core sample is often proportional to
the carbonate content. Coccoliths include upper
Pleistocene to Holocene species, as well as much
older (Miocene and Pliocene) reworked forms
(Figures 8, 9). Volcanic products (palagonite, sid-
eromelane, chlorite, microlite) and recrystallized
dolomite are somewhat more abundant in the U
than in the FL+U sequences. Conversely, quartz
and feldspar are somewhat less abundant in U
sequences. In the silt fraction of both types of
sequences, recrystallized calcite is abundant,
while spicules, foraminifera and fragments of car-
bonate tests occur in lower proportions. No dis-
tinct vertical trends of silt size components are
recorded.

Illite dominates the clay mineral suite in this
region as noted by Venkatarathnam and Ryan
(1971) and Vittori (1978:131). Minerals of the

Ficure 9.—Scanning electron micrographs of components
in Hellenic Trench unifites (scales = 1 zm): a, Rod-shaped
attapulgite (arrow) (from core MA-20, 600 cm from core
top, X 10K). B, Discoaster varrabilis (Martin and Bramlette)
from late mid-Miocene to Pliocene in age (from core MA-
20, 600 cm from core top, X 9K). c, Discoaster cf. brouwern
Tan Sin Hok (4-ray form), from late Miocene to Pliocene in
age (from core TR-36, 550 cm from core top, X 8K). p,
Discoaster asymetricus Gartner from the middle Pliocene (from
core MA~20, 50 cm; X 4.5K). £, Discoaster cf. brouwert Tan
Sin Hok (6-ray form), badly overgrown and poorly pre-
served, possible late Miocene to Pliocene in age (from core
TR-34, 240 cm, X 10K). F, Discoaster perplexus Bramlette and
Riedel, possibly of late Oligocene to Pliocene age (from core
MA-20, 600 cm, X 10K).

17
attapulgite (palygorskite) group, recorded in
many areas of the eastern Mediterranean (Cham-
ley and Millot, 1975), occur only in the silt frac-
tion of uniform muds in cores MA-10 and MA-
20 (Figure 9a). Attapulgite (palygorskite) is abun-
dant in these cores (the attapulgite to illite plus
quartz ratio generally exceeds unity), but no ob-
vious vertical trend is recorded (Figure 6). The
sedimentological significance of the attapulgite
distribution as a tracer of disperal is dicussed
elsewhere (Stanley, Blanpied, and Sheng, 1981).

Vertical Petrological Changes

ContTRASTING MarGIN FLAT AND BASIN PLAIN
SEQUENCES

The marked vertical changes in grain size and
compositon recorded in the U and FL+U cores
collected in the margin flat and basin plain en-
vironments bear on unifite deposition.

Although almost structureless, analysis of core
MA-23 recovered in the Matapan Deep margin
flat reveals distinct vertical bedform, grain size,
and compositional changes. These nonrandom
trends are cyclic in nature. The FL+U sequences
are about 450 cm thick (100 to 550 cm from the
core top). Size histograms (Figure 10) reveal an
overall upward size decrease involving two super-
posed fining-up cycles. The latter are revealed by
the vertical variations in silt content and mean
grain size (Figure 7). The two granulometric
“breaks” correlate well with the presence of
faintly laminated mud seen in x-radiographs at
about 550 and 300 cm from the core top. The
lower cycle is coarser (about 60% silt content),
and its upward-fining trend is more pronounced
(decrease in mean size from about 15 to 7 pm);
the upper cycle is finer (about 55% silt content),
and shows a more gradual upward diminution in
grain size (mean size decreases from 8 to 5 wm).
The vertical distribution of the modal class shows
a less marked distinction between the two cycles
(Figure 10). In this repetitively graded mud sec-
tion, we find that the lower coarser, faintly lam-
inated terms (1.e., any petrologically distinct divi-

18 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

sion of a unifite cycle) contain a somewhat higher
carbonate content with higher proportions of silt-
sized carbonate components, lower proportions of
sand-size clastic aggregates but larger amounts of
biogenic components (mainly planktonic tests),

MATAPAN DEEP

MA-23 MA-22
Margin Flat Basin Plain

U
10 % ae Be
T Trost matali Vaca Viger seh as tamale LW)
Ss ) 2 & 2S
micrometers & U

(a a
eee ge sy
(erent 1 soon ee eG i T
0.3 1 2 5 10 20 i: ao y

micrometers a.
is LTUSLELELiseare eee =
2 5 10 20 40 60

micrometers

and minor amounts of mica than the overlying
material. In contrast, the upper finer-grained uni-
form mud terms in the sequence contain higher
amounts of terrigenous components and volcanic
products in both the sand- and silt-size fractions.

KITHERA-ANTIKITHERA BASIN

MA-10 MA-20
Margin Flat Basin Plain

l
A
Ses Be

ae
in oe a U
= TS q
ee _ — Il a
SS U ———_—a a
rn ee _ U
gE ae U a
ee ee U

tm ,
saree eee ou
i Ei
(ne ee oy U
SS,
ee
ne _U Ls
ee iG FL
a om
U
E US ——
SS >. U

ee La,
os U
= ae Or ae =,
eS
—_S foo y
a ee UE ae
ae oe LW
10 % U
eI sen nee So wale
2 5 10 20 40 coal seen) gs Lim | on) ia ee Tine a Tonle) eae
micrometers 2 5 10 20 40 60

micrometers

Ficure 10.—Size distribution histograms of Matapan Deep and Kithera-Antikithera Basin
unifite core samples (sample position shown on logs in Figures 6 and 7). Data (in volumetric
percent) obtained using a Coulter Counter Model TII-A (size in um). (Shaded area depicts
primary modal class. Note expanded complete size histogram of one core MA-22 sample; dotted
portion of histogram depicts finest particle distribution as determined from a separate Coulter
Counter run. FL = faintly laminated mud; U = uniform mud.)

NUMBER 13

The FL+U sequence in core MA-22 in the
Matapan Deep basin plain is about 500 cm thick
(from 200 to 700 cm from the core top) and, like
core MA-23, shows two superposed sequences,
revealed by the vertical changes in silt content
and mean grain-size distribution. The upward
changes shown by these trends, however, are less
pronounced than in core MA-23. The major gran-
ulometric “break” within this sequence is associ-
ated with faintly laminated muds at about 450
cm from the core top (Figure 7). As in core MA-
23, the lower cycle is coarser (about 57% silt) than
the overlying portion of the cycle (about 53%).
An upward decrease in mean grain size ranges
from 10 to 6 pm. An examination of the vertical
sequence of size histograms (Figure 10) shows less
cyclicity of the primary modal class than in core
MA-23; a systematic upward size decrease, nev-
ertheless, appears in the upper 200 cm above the
faintly laminated term (Figure 7). Moreover, his-
tograms of this core (unlike those of MA-23 core
samples) display a slight bimodal size distribu-
tion: a primary mode ranging from 8 to 25 um,
and a less pronounced modal class of about 3 um.
An example of an expanded size distribution
histogram of the clay and fine silt size range (from
0.3 to 10 wm) is shown in Figure 10. In contrast
with the uniform mud term (U), the faintly lam-
inated mud segment at about 450 cm contains a
somewhat lower carbonate content, fewer sand-
sized clastic aggregates, and a higher proportion
of biogenic (more planktonic) components. The
major fluctuation in proportions of sand-sized
components (Figure 7), particularly the plank-
tonic versus the terrigenous elements, appear
closely related to grain size changes. For example,
in the lower cycle, the rapid upward decrease in
terrigenous components and volcanic products
coincides with a decrease in grain size. These
concomitant compositonal and grain size fluctu-
ations appear to correlate with tonal (densito-
metric) variations, recording differences in sedi-
ment density observed on x-radiographs; lighter
tones generally denote somewhat coarser, or den-
ser, sections.

Observed vertical and core-to-core changes in

19

the largely uniform (U) mud sequences in Kith-
era-Antikithera Basin cores MA-10 and MA-20
are different than those in the Matapan Deep
and Zakinthos-Strofadhes cores. The two MA
trench basin cores consist essentially of uniform
mud (faintly laminated sections are absent) but
nevertheless show an overall upward decrease in
silt content and mean grain size.

The margin flat MA-10 core sequence exceeds
5 m in thickness, and displays an overall upward
decrease in silt content (from about 60 to 55%),
mean grain size (from 8 to 6 wm), and modal class
size (12 to 6 fim, Figures 6 and 10). This is
accompanied by a slight upward decrease in car-
bonate content, clastic aggregates, sand-sized ter-
rigenous fraction, and concomitantly, an upward
increase in biogenic components (mainly plank-
tonic). The proportions of terrigenous and vol-
canic components of silt size, and of attapulgite
(palygorskite), also increase upward. A major tex-
tural break at 200 cm is accompanied by a
marked increase in carbonate content and sand-
sized planktonic foraminifera, and conversely, a
decrease in the terrigenous fraction and clastic
aggregates (Figure 6). Many of the compositional
variations in this U sequence correlate directly
with grain size fluctuations.

Basin plain core MA-20 recovered the thickest
section (about 1000 cm) of uniform mud in the
study area, and as in MA-10 core, displays an
overall upward decrease in both silt content (63
to 54%) and mean grain size (from about 9 to 6
pum). Unlike core MA-10, however, there is no
sharp textural break within this vertical sequence
and, unlike cores MA-22 and MA-23, no obvious
repetitive grading or cycles are noted (Figure 6).
While the lower 6 m display some minor textural
variations, the upper 4 m fine-upward gradually
and are almost uniform in texture. Grain size
histograms show an overall range of modal class
variation between 8 and 20 pm, and a bimodal
distribution in the lower 6 m comparable to that
in basin plan core MA-22. Although the vertical
textural distribution is fairly constant, there are
some marked compositional fluctuations as noted
by carbonate content, clastic aggregates, sand-

20 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

size components (particularly planktonic forami-
nifera), and attapulgite. Noteworthy are the up-
ward increase in biogenic components and de-
crease in clastic aggregates. Fluctuations of var-
lous compositional components are most closely
related to the observed subtle grain size changes.
These grain size variations, in turn, correlate with
observed tonal-density differences observed on x-
radiographs.

ENVIRONMENTAL CONTROL

The major overall difference between the mar-
gin flat and basin plain unifites in the three
trench systems examined is that the former com-
prise primarily FL+U sequences, while U se-
quences dominate basin plains proper. Moreover,
the basin plain (MA-20, MA-22, TR-35, TR-36)

core samples contain, for the most part, somewhat

higher carbonate, sand-sized planktonic forami-
nifera and clastic aggregate contents, but less
terrigenous material of sand and silt size than in
the basin margin flat (MA-10, MA-23, TR-34).
A synthesis of the petrologic characteristics
(Table 2) indicates that vertical variations are
environmentally related. There are some compo-
sitional components whose proportions are simi-
lar in both margin flat and basin plain cores.
These are identified as “constants” in Table 2:
sand-sized pteropods, shell fragments, mica and
silt-sized recrystallized dolomite, and volcanic
products prevail in the finer terms of either U or
FL+U cycles; sand-sized benthic foraminifera,
heavy minerals, oxidized and reduced aggregates
and silt-sized foraminifera, coccoliths, spicules,
carbonate fragments and volcanic products dom-
inate the coarser terms of either U or FL+U
cycles. Overall, however, there are major com-

TaBLe 2.—Comparison of dominant compositional characteristics of unifites collected on trench

margin flat and basin plain environments

i

JPaae Trench margin Trench basin
oe flat dominant Constant plain dominant
as characteristics components characteristics
Fine Terms or Cycies
Sand Radiolarians & Pterpods & shell Planktonic species &
diatoms fragments pyritized planktonic
Benthic tests, Mica tests
pyritized Shell fragments
Light & heavy Mica
| minerals
| Clastic aggregates
Silt Chlorite & quartz Palagonite & Feldspars & aggregates
Foraminifera & sideromelane Recrystallized
coccoliths Dolomite calcite
Sideromelane Dolomite
Carbonate content
Coarse TERMS OF CYCLES
Sand Planktonic species & Benthic tests Radiolarians & diatoms
tests Heavy minerals Benthic tests, pyritized
Shell fragments, Aggregates, oxidized & Light & heavy minerals
pyritized reduced Clastic aggregates
Mica
Silt Feldspars, aggregates Palagonite, sideromelane Chlorite & quartz
Recrystallized calcite Foraminifera & Foraminifera &
Dolomite coccoliths coccoliths

Carbonate content

Spicules & carbonate
fragments

Sideromelane

NUMBER 13

positional differences between margin flat and
basin plain cores as summarized in Table 2; the
coarse terms clearly differ from the fine terms of
FL+U and U cycles.

In margin flat cycles, the sand-sized compo-
nents in the coarser-grained, often faintly lami-
nated terms are generally dominated by plank-
tonic tests (foraminifera, including pyritized tests
and pteropods), bioclastic shell fragments and
mica; in contrast, the sand fraction in the finer
(often U) part of cycles is enriched by terrigenous
material, mainly light minerals, and benthic tests
(including pyritized benthic foraminifera and spi-
cules). The highest total carbonate content occurs
in the coarsest cycles. The silt fraction of the
faintly laminated terms of the FL+U cycles shows
enhanced amounts of clastic aggregates, feldspars
and recrystallized calcite. In the silt fraction of
the fine terms of the FL+U cycles, quartz and
volcanic products (chlorite, sideromelane) domi-
nate, along with important proportions of plank-
tonic foraminifera and coccolith tests.

In basin plain cycles the above listed compo-
nents of sand and silt size also occur, but in a
reversed order of importance. Table 2 depicts this
“reversal” phenomenon: Mineralogical compo-
nents that are dominant in the coarsest terms of
margin flat cycles abound in the finer terms
(largely U sequences) of basin plain cycles; com-
ponents important in the finer terms of the mar-
gin flat cycles dominate the coarser, faintly lam-
inated terms of basin plain cycles in those cases
where they occur. It is recalled that fine-grained,
U-dominated cycles prevail in the basin plain
environments.

Discussion

EVIDENCE FOR GRAVITATIVE ORIGIN OF
FINE-GRAINED Mup Types

An examination of all cores collected in the
western Hellenic Trench area (Figure 1) has re-
vealed a high proportion of classic fine-grained
turbidites in most environments, including prox-
imal settings, areas of relief, slopes, and perched
slope basins and trench plains (Vittori, 1978;
Stanley and Maldonado, 1981). In contrast, uni-

21

fites are restricted to trench basin plains (Stanley
and Knight, 1979; Stanley, 1980). In this study
we show that trench basin FL+U and U se-
quences are laterally extensive in each of the
basin plains (Figure 2). The emplacement of such
unifites is apparently rapid, a contention sup-
ported by their stratigraphic position (Figure 4),
radiocarbon-14 dates, and the common associa-
tion of unifites with classic, well-graded mud
turbidites (Stanley and Maldonado, 1981, figs. 5,
10). Moreover, statistical analyses of over 450
samples collected from all of the cores shown in
Figure | show that, regardless of sediment type,
there is a general decrease seaward in the per-
centage of the sand size material in muds. The
Hellenic sediments, for the most part mixtures of
silt and clay, thus reveal a lateral fining toward
the three distal trench basins (Vittori, 1978:177;
Feldhausen et al., 1981).

The present study also indicates that the fine-
grained lithofacies distribution is not random
within basins, but rather is specifically related to
trench margin flat and basin plain environments.
This distinct relation between environment and
mud type is exemplified by the markedly in-
creased proportion of uniform mud relative to
faintly laminated mud in basin plains proper,
away from basin slopes. We believe that such
environment-related lithofacies
most readily attributable to the influence of trans-

variations are

port processes, and evaluation of all data collected
(seismic profiles and petrology) sheds light on the
mud emplacement mechanisms involved.
Although the unifites are very fine-grained,
usually clayey silt with a fine silt mean size class,
deposition from primarily suspension-related
processes (hemipelagic “‘rain’’) is minimized. The
specific restriction of unifites to basin plains
would not occur if accumulation was largely by
suspension-related mechanisms (related to water
mass circulation). The core analysis data base
does not support a settling “rain” origin for uni-
fite emplacement. We recall that calculated min-
imum sedimentation rates for entire thick se-
quences are extremely high (in some cases
>300cm/1000 years). The sand fraction in unifite

No
ine)

mud is very low (<0.5%) and comprises mostly
clastic aggregates of reworked, indurated silts and
only low amounts of planktonic tests. Bioturba-
tion structures are not observed in x-radiographs.
Moreover, the proportion of the terrigenous sand-
size fraction, excluding clastic aggregates, fre-
quently exceeds 50%, and an important part of
the biogenic fraction of silt consists of older,
reworked coccolith tests (Figures 8, 9).

Although unifites almost always contain an
assemblage of modern and much older reworked
fauna and, in some cases, display faint laminae
(the only bedform observed in x-radiography), we
eliminate strong bottom currents as a dominant
transport process. This conclusion is supported by
the extensive regional distribution and lateral
continuity of the very thick, evenly bedded units
within each of the three morphologically isolated
deep basins (as noted in 3.5 kHz profiles), the
cyclic nature of the almost structureless mud
sequences, and poor textural sorting of sediment
recorded by size analyses. A bottom current origin
would not satisfactorily explain the overall fining-
upward trend in all sequences, even the thickest,
including the 10-m-thick unifite in core MA-20.

Our study does not lend strong support to
pelagic settling, or to erosion of the sea floor by
currents, or to combinations thereof for the origin
of uniform muds as suggested by Ryan et al.
(1973:268) and Kastens and Cita (in press). In
contrast, the data base strongly supports a turbid-
ity current-related origin for the thick unifite
sequences of both uniform and faintly laminated
muds. Numerous size analyses demonstrate that
all ponded unifites display an overall upward
graded bedding (Figures 6, 7); graded muds are
characterized by very poor sorting (Figure 10).
Lateral distality-related changes beween the base-
of-slope and the basin plain proper include a
decrease in laminated mud terms, an increase in
the proportion of graded and ungraded mud
terms, and a somewhat higher content of sand-
sized biogenic (largely planktonic) tests of rela-
tively low density. The basinward increased uni-
formity of mud bedforms and compositional char-
acteristics suggest deposition from flows moving
across, and spreading over, large areas of the flat

SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

trench floor. All vertical and lateral petrologic
changes observed within the three trench basins
examined tend to support deposition from sedi-
ment gravity flows of diminished concentration
as depicted by the transformation continuum
model presented by Stanley and Maldonado
(CISL, tines, 110).

CLASSIFICATION OF FINE-GRAINED TURBIDITE
Mupb SEQUENCES

The vertical succession of bedforms and general
fining-upward of unifites in the seven cores is
generally comparable to that of idealized fine-
grained turbidite units, Te’, defined by Rupke
and Stanley (1974:9) and others. The several mud
types recognized as a result of detailed petrologic
analyses can be related to specific mud turbidite
subdivisions defined by Piper (1978:165) and
Stow and Shanmugam (1980:38).

The most complete FL+U sequence recovered,
that in the core MA-23 (Figure 7), serves as a
reference section. The unit, from 530 and 490 cm,
corresponds to the vertically graded laminated
medium and fine silt, and also to the laminated
mud (E1), terms illustrated by Piper (1978:165)
and, more specifically, to the indistinct laminated
subdivision, 14, of Stow and Shanmugam (1980:
38). This is overlain, from 490 to about 470 cm,
by a graded mud division, coded respectively E2,
or T6, by these authors. This is topped, from 470
to 310 cm, by a mud sequence that shows only
vague grading, 1.e., the ungraded mud division,
E3 or T7. A marked change is observed at about
310 cm: Faint laminae reappear from 320 to 310
cm (El or T4); this is followed by graded mud
from 230 to 140 cm (E2 or T6), and finally by
faint, but graded, laminae at 140 to 110 cm (El
or [T4). The position of the above E terms, cor-
responding to those defined by Piper (1978), are
depicted on the logs in Figure 7.

On closer inspection, the thick, apparently un-
graded division (E3, or T7) shows subtle fluctu-
ations of grain size, 1.e., a slight upward increase
in silt content from 470 to 390 cm (= ungraded
mud), and then a slight decrease from 390 to 310
cm (= graded mud). The variations in content of

NUMBER 13

clastic aggregates and sand-sized mineralogic
components parallel,
otherwise subtle grain-size fluctuations in both
graded and ungraded muds. Thus, grain size and
mineralogy, supplementing bedform, reveal from

and actually magnify,

base to top a complex succession of terms:
El>E2—E3—E2; El—E2; and El. The three
El terms are characterized by a high carbonate
(mostly silt-size coccoliths) and low clastic aggre-
gate content, and a sand-size fraction dominated
by biogenic components. In the E2 terms, the
content of carbonate decreases, but that of clastic
aggregates is high but fluctuates, and terrigenous
components dominate the sand fraction. Proceed-
ing upward in the sequence, each successive
faintly laminated El term contains progressively
larger proportions of clastic aggregates and sand-
sized biogenic components. Thus, all three El
terms in the MA-23 sequence are interpreted as
an integral succession emplaced by a single flow
event and do not represent the base of three
separate deposits. The overall decrease of silt
content, and vertical trends of mean (Figure 7)
and modal (Figure 10) grain sizes favor this “‘sin-
gle event” interpretation. Further support for this
is provided by (1) the rapid upward increase in
sand-sized planktonic, and concomitant decrease
in terrigenous fractions within the lower, un-
graded (E3) mud section, and (2) the lack of
correlation between planktonic-terrigenous con-
tent and grain-size changes associated with the
middle laminated E1 division. The overall cyclic-
ity of this Matapan Deep margin flat FL+U
sequence, and the variations within both E2 and
E3 terms, probably record velocity and turbu-
lence fluctuations in a single flow event.

The FL+U sequence in core MA-22 in the
Matapan Deep basin plain reveals trends gener-
ally similar to core MA-23 (Figures 7, 10). There
is overall fining-upward (decrease in silt content
and mean grain size), and cyclicity is apparent,
but somewhat less marked than in core MA-23.
The vertical succession includes ungraded mud,
E3 or T7, from 710 to 550 cm; graded mud, E2
or T6, from 550 to 470 cm; faintly laminated
mud E1 or T4, from 470 to 440 cm; graded mud,

23

E2 or T6, from 440 to 220 cm; and faintly lami-
nated mud, El! or T4, from 220 to about 210 cm.
The three cycles in this core are: E3>E2;
E1—E2; El. As in core Ma-23, there are compo-
sitional and granulometric fluctuations, some-
times important, within both vaguely graded and
ungraded terms. Differences, however, include
somewhat less pronounced overall vertical grad-
ing, an upward trend in carbonate content that
does not parallel grain-size variations, and a
higher proportion of clastic aggregates through-
out the sequence.

The FL+U sequences recovered in the three
Zakinthos-Strofadhes Trench basin cores (Figure
4) display cyclicity involving vertical successions
of bedform, grain-size, and composition. This
cyclicity is similar to that noted in Matapan Deep
cores MA-22 and MA-23. Specific differences in
mineralogical components between MB and ZB
unifites are related primarily to a different prove-
nance (lateral source input from the northwest
Peloponnesus) rather than to transport mecha-
nisms. We interpret the unifite mud sequences in
cores MA-22, TR-34, TR-35, and TR-36 as grav-
itative deposits emplaced by mechanisms similar
to that of MA-23, 1.e., transport and deposition
by turbidity current-related flows of diminishing,
but fluctuating, velocities and turbulence. An
example of a classic, well-graded mud turbidite
occurs above one of the unifites (see section from
310 to 180 cm in core TR-34, marked by T and
arrow in Figure 4, and also the x-radiography
print in Figure 3a).

Cores MA-10 and MA-20 in the Kithera-An-
tikithera Basin (Figure 6) differ most obviously
from the five above-cited cores in that they com-
prise only uniform (U) mud sequences and dis-
play less obvious vertical cyclicity. The higher
proportion of sand-sized clastic aggregates, and
silt-size attapulgite and volcanic products (glass
shards, etc.) reflect local provenance and dispersal
factors rather than a different emplacement pro-
cess per se. While both cores display an overall
fining-upward trend, comparable to the Te’ tur-
bidite sequence of Rupke and Stanley (1974),
close inspection shows petrologic “breaks” within

24 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

the U sequences. In MA-10, this occurs at about
200 cm, separating a lower ungraded mud (E3 or
T7) from an upper graded mud (E2 or T6); the
break in MA-20, although less well marked, is
noted at about 400 cm, separating a lower E3 (or
T7) from an upper E2 (or T6) term. Unlike the
FL+U sequence in reference core MA-23, the
principal mineralogical changes in both MA-10
and MA-20 closely parallel major
‘‘breaks.”’ A sudden decrease in clastic aggregates
and increase in sand-size biogenic components
correlates with a decrease in grain size. The
“break” between E2 and E3 terms in MA-10 and
MA-20 unifites indicates superposition of two

textural

important successive depositional episodes. In
each case, the superposition is related to a major
turbidity current flow event. Vertical variations
of both grain size and mineralogical components
are observed within the ungraded mud, E3 or T7,
terms in these (Figure 6) as well as in cores of
other basins (Figure 7).

From this classification we propose a vertical
succession of terms that characterizes, from base
to top, an idealized complete unifite cycle: (1) a
faintly laminated, generally siltier term, which
may be graded and contain a sand-size fraction
that is largely biogenic; (2) a graded fining-up-
ward mud term with terrigenous components
dominating the sand-fraction; (3) an ungraded
mud term that, on close inspection, actually
shows slight coarsening-upward and/or may dis-
play cyclic fluctuations and that contains a sand-
size fraction dominated by terrigenous compo-
nents; and finally (4) a graded mud (fining-up-
ward) term with an enhanced biogenic fraction.
This cycle may be repeated and, in thick se-
quences, some terms may be absent. Cores MA-
10 and MA-20 comprise the thickest E2 and E3

terms examined.

PETROLOGIC VARIATIONS RELATED TO FLOW
FLUCTUATIONS

The general upward-temporal and lateral-spa-
tial fluctuations (larger scale cycles as well as
more subtle changes in bedform, grain size, and

composition) are comparable in the three Hel-
lenic basins. Insight on transport mechanisms
involved in unifite deposition is provided by the
vertical petrologic changes within each core and
lateral variations between trench margin flat and
basin plain cores. We have shown that a complete
unifite sequence includes laminated (E1), graded
(E2), and ungraded (E3) mud terms, and that
their succession varies within a core, and laterally
from core to core. Variations in mud type cyclic-
ity, associated with an overall decrease in grain
size, record internal fluctuations within a flow of
diminishing velocity and sediment concentration.
The development of faint laminae, for example,
may be related to phases of flocculation and to
the depositional sorting during flow; 1.e., a reor-
ganization of mud and silt flocs and their concen-
tration result in their settling through the bound-
ary layer at the base of a flowing turbidity cur-
rent. Formation of fine-grained laminae by in-
creased shear at the bottom boundary layer, as
invoked by Stow and Bowen (1978), seems an
appropriate explanation. We note that the faintly
laminated El terms comprise a unimodal grain-
size distribution consisting of a mode generally
larger than 20 wm (Figure 10).

We are unable to ascertain why several such
flocculation-induced laminated terms appear
within a single sequence deposited from one ma-
jor event (cf. core MA-23, Figure 7). Several
possibilities may explain the presence of succes-
sive laminated zones within a single unifite. In all
cases, the following are considered as constants:
(1) steep gradients of the walls that bound trench
basins (Le Quellec, 1979:64), (2) irregularities on
these steep slope surfaces (Figure 11) and in can-
yon thalwegs (Vittori, 1978:37-117), (3) floccu-
lation initiated within the flow on the slope as a
result of particle collision (Kranck, 1975), and (4)
hydraulic jump phenomenon that produces a
sudden reduction in velocity and density and
thickening of the flow as it reaches the flat basin
floor just beyond that base of slope (Komar,
1971). As noted in most experimentally produced
sediment gravity flows, larger or denser grains are
concentrated at the head and near the base of the

NUMBER 13

body of a rapidly downslope-moving gravity-en-
trained flow; the upper interface of the flow
incorporates ambiant seawater and is thus more
dilute (Kuenen, 1965:69). Both large and small
topographic irregularities on the slope induce
turbulence and, in consequence, a continuous
rearrangement of the sediment load and its con-

25

centration. Inasmuch as the transported load con-
sists largely of silt and clay particles, continuous
flocculation and disaggregation occur within the
flow as it moves downslope.

In the simplest case of unifite deposition on the
margin flat province, we envision a flow column
of roughly even thickness moving along a fairly

Ficure 11.—Selected bottom photographs obtained from the deep-tow Raze system in the
northern part of the Kithera-Antikithera Trench, near location of core MA-20 (1978 cruise
Raicette, depth about 4400 m, near 35°50’/N latitude and 22°13’E longitude): a, Slope swept
partially free of thin surficial sediment veneer; note current lineations and minor scour-and-fill

structures around burrows (circular structures are about 3 cm in diameter); the arrows are
oriented along the predominant downslope transport direction. B, Eroded slope surface (arrow);
note stirring of thin surficial sediment veneer by bottom compass. Compass and vane are about
30 cm long. c, Recently eroded block of mud ~1 m in length, lying near base of slope. p,
Turbid flow, triggered by deeptow compass touching the slope, displaying multilobe configu-
ration. Much larger flows of this type are believed to displace the thin sediment veneer
downslope and probably produce the current-lineated erosional bedforms illustrated in “a”.
(Photographs generously provided by the Centre National pour |’Exploitation des Océans,

Brest, France.)

SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

uID|q ulsog

(G3HDIYN3-DINIOOI9)
salov4 1VvLsid

yo| 4 UIBIDW

(G3HDIUNI-SNONIONNYSL)
SalIOV4 TVWIXO'd

NOILV1IND9014 GNV
‘NOLLVOIVOOVSIG FAIL1L3d3y
NOILVYLNSINOD “INAW3ONWadVad NIVYOD
avO1 ONY ALIDO13A G3HSINIWIG G39NGNI-JDN3TNGINL
NW MO1d 3HL JO ONINAXOIHL

YaLVM JO
IN3IWNIVYLNA

N
1x9] ul UoNeuLldxy ‘Apnjs sty} Ul paAsasqo saqyun
your], olusT[aHY 9Yyi JO suonviuva o1sojosjed jeneds pure jesodura} ayi donpoad 0} poeastjaq
diez suonenjonyy paivjai-moy asay J, ‘adojs-jo-aseq ey} puodoq uouswousyd duinf oneapAy oy)
pure sz9hv] Arepunoq WO}OG-Iv9U dy} OF paiva UONeSaISSeSIP pur ‘uone[No.0Y ‘Judas UeIUIvAI
uIeIs JO JaJJO ay) oziseydura SWIRISVIP IY], “Seqo] IAIssadons ssonpoid adoyjs zeynSos1 ue uo
wodsuva “a ‘odojs yioous Ajaanvyad e UO [eua}eUI peuless-ouy Ajasvy jo wodsuery ‘v :sayyrun
wsodap 0} Ajaytt addi ay) Jo smoy AVARIS JUSUUIpas JUa;Nquny SuNoIdap soUsyYIG—'Z] AMNOLY
}O|4 UBUD,
S31OV4 TWWIXONd
= wNIVYn D1DV13d | W3H ’
MO14 NIVW ONY 3807 N33ML98 YJAVT AYVGNNOS = ann,
YIAV] AYVONNO@ WOLLOd = “SE
x4
3ZIS SNOIWVA 40 SOTA Cao)
°
(STVYINIW LHD) LNINOdWOD SNONIONYIL =
JONIINGINL
dO1S WOYd GIGOY3 ILVOIVOOV IUSVID |B QD
> ) INJNOdWOD DINIOOIS
LNaWdO13A90 3801 AS SS am —- Ne? a exe WINODUNWAd @
G3NGNI NOILYINDD0N4 sya \ ®
AYVANNO 3807 GYVMOL ><
$9014 TIVWS JO ONITLIIS © o | ALIYVINDI IdO7S
a
° » 9 ‘
a as) Ke
a x
) ° es
08° KX? D
NOILVYLNJONOD X \ ——_
ALA HLIM 3807 @ -c-
x S oh ae
; a <n!
YaLVM JO AGS : Z
LNAWNIVYLNA CK SA
Nolivinooo14
JONGNI - JONIINANL
lao)

NUMBER

28 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

smooth slope and which, upon arrival on the
near-horizontal basin floor, is subjected to hy-
draulic jump effects (Figure 12a). As a result of
the jump, deposition of larger and denser grains
and flocs concentrated at the head and near the
base of the flow will settle out through the bottom
boundary layer as flow velocity is rapidly re-
duced; this accounts for the deposition of the
lower, faintly laminated El term. The rapid set-
tling of finer materials above the basal El term
produces both graded and ungraded muds (E2
and E3). During and following the passage of the
flow head and deposition of this first cycle, the
hydraulic jump effect above the same base-of-
slope sector continues to induce rearrangement of
grains that are entrained by the body of the
downslope-moving flow; flocculation occurs
again as a result of particle collision (cf. Kranck,
1975) due to temporary intensified turbulence.
Thus, larger flocs settle once again, resulting in
accumulation of a second cycle of laminated mud,
followed by settling of finer, or less dense, mate-
rial. ‘This repetitive deposition of laminated,
graded and ungraded muds continues as long as
there is sufficient concentration of material car-
ried by the downslope-moving flow over this sec-
tor and as long as flocculation is induced by
hydraulic jump turbulence. The final passage of
the slower-moving dilute tail is recorded by the
uppermost nonlaminated mud.

A somewhat more complex but more probable
unifite origin involves a flow column of uneven
thickness, characterized by partially superposed
and successive, imbricated lobes (Figure 12s).
These lobes may record the development of major
turbulence within the flow induced by large sea-
floor irregularities upslope; the lobes are thus
viewed as perturbations produced by a succession
of hydraulic jump effects along the flow path. As
each major lobe passes above the same base-of-
slope sector, it releases material; the resulting
deposit resembles that accumulated from a rapid
succession of turbid flows. Analysis of the sedi-
ment load in each individual imbricated lobe
would probably reveal that each has its own
distinct, internal grain-to-grain distribution pat-

tern. As each lobe reaches the base-of-slope and,
in turn, is affected by the hydraulic jump, a cyclic
deposit consisting of superposed El, E2, and E3
terms will accumulate. Each lobe will release
progressively finer material over the same base-
of-slope sector.

The minor variations in grain-size and com-
position within any one cycle is accounted for by
smaller-scale fluctuations of turbulence, velocity,
and load concentration. Planktonic tests and clas-
tic aggregates, on the one hand, and terrigenous
components, on the other, have different densi-
ties; inasmuch as they become segregated during
transport they are sensitive indicators of turbu-
lence-related changes in a flow. We thus interpret
cyclicity, repetition of laminated and uniform
muds, and variations in mineralogical compo-
nents on margin flats as largely the result of
hydraulic jump effects both upslope and at the
base of the slope. We conclude that the vertical
variations observed in unifite sequences illus-
trated in Figures 6 and 7 do not represent time-
separated turbid-layer flows of the type described
by Moore (1969:83). Moreover, Hellenic unifites
are petrologically unlike lithologic sections em-
placed by current flows that cross and repeatedly
rebound from basin pond walls, as illustrated by
Van Andel and Komar (1969). While not com-
pletely ruled out, we tend to discount this latter
process primarily on the basis of (1) the observed
cyclicity, (2) unusual thickness (as much as | m)
between each El term, (3) narrow range of pe-
trologic variations, (4) very poor sorting of the
mud throughout an entire sequence, and (5) the
vertical distribution pattern of planktonic tests
between the base and top of sequences.

Unifites on the trench basin proper differ mark-
edly from those on margin flat sectors near the
steep basin walls, particularly with respect to
vertical variations in grain-size and composition,
and a higher proportion of planktonic tests. This
difference records changes that occur within the
gravity-entrained flow as it moves away from the
base-of-slope toward the more distal, near-hori-
zontal trench basin plain proper (Figure 12a).
The mineralogical “reversal phenomenon” that

NUMBER 13

occurs between these two trench basin environ-
ments (Table 2) probably is most closely related
to hydraulic jump effects; 1.e., a transfer of energy
markedly enhances turbulence and grain support
characteristics within the turbidity current flow
just beyond the base-of-slope break.

The hydraulic jump effect thus induces a sharp
modification of the grain-to-grain configuration,
which accounts for a temporary disorganization
of the sediment load distribution within the flow
column. Disaggregation within flow recurs as the
turbidity current moves basinward across the
plain; an increased regularity in settling of sus-
pended grains accompanies diminished turbu-
lence-related flocculation and floc rearrange-
ment. Thus, the E2 and E3 terms that dominate
more distal sectors contain progressively finer
uniform mud terms, with lower proportions of
denser terrigenous components. The observed
subtle normal fining-up and reversed grading
highlight a cyclic pattern even in the more dis-
tally deposited fine-grained ungraded (E3) uni-
fites (core MA-20, Figure 7). This textural config-
uration attests to the still turbulent and moder-
ately concentrated character of the slower, basin-
ward moving flow. The uppermost graded mud
term of idealized complete unifites on both basin
margins and in trench plains proper records final
phase settling of the sediment load, over large
areas of the basin plain, from the tail of a flow.

Implications of Study and Conclusions

Hellenic Trench unifites have been interpreted
as the end-members of a depositional series that
are initiated in proximal, generally steep slope
settings (Stanley, 1980). A theoretical complete
transport continuum from slumps, to dense mass
flows (debris flow), to turbidity currents, and
eventually to very low concentration but still
turbid layer flows, referred to as a transformation
series, has been depicted by Stanley and Maldon-
ado (1981, fig. 11). This continuum series depo-
sitional model is based on the recovery of a diverse
suite of gravitative deposits whose distribution in
the western Hellenic Arc study area appears non-

29

random. Slumps, debris and other dense mass
flows, and coarse-grained turbidites abound on
slopes, while associations of finer deposits, includ-
ing well-developed, classic silt turbidites and un-
ifites, occur at the base-of-slope and in basin
plains.

The thickness of a depositional unit is, in large
part, a function of the volume of material trans-
ported relative to the surface area on which it
accumulates. The remarkable thickness of indi-
vidual fine-grained Hellenic Trench unifites (>10
m) detailed in this study is closely related to the
very small surface area (100 to 250 km?) of the
flat trench basins that trapped the sediment grav-
ity flows. The estimated volume of sediment car-
ried by individual flows that actually reached the
trench basin floor ranges from about 0.5 to 1.0
km?®, based on both core and seismic data. Such
volumes are moderate when compared to those
calculated for turbidites in modern ocean abyssal
plains (Normark, 1970; Heezen and Hollister,
1971:183; Pilkey, Locker, and Cleary, 1980) and
in the rock record (Scholle, 1971; Hesse, 1975;
Rupke, 1976; Mutti, 1977).

In the larger Mediterranean basins, such as the
Algero-Balearic Basin in the western Mediterra-
nean (Rupke and Stanley, 1974:11) and the Ion-
ian and Herodotus Basin plains in the eastern
Mediterranean, thin unifites comprising mixes of
modern and reworked microfossils in fact are
difficult to distinguish from thin mud turbidites
and planktonic-rich hemipelagites. The gravita-
tive deposits are more likely to display an absence
of bioturbation and contain more reworked mi-
crofossils. Mediterranean basins are extremely di-
verse in terms of shape, size, and depth (Stanley,
1977a:128) and in consequence probably contain
unifites of variable thicknesses. Unifite thickness,
frequency in cores, and rates of accumulation
depend not only on basin size and sediment flux,
but also on dispersal and degree of accessibility
of sediment to a basin plain.

The western Alboran Basin between Spain and
Morocco and the Golo Basin in the Corsican
Trough exemplify small ponds that are bounded
by smooth slopes and have relatively direct access

30 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

to substantial volumes of fluvial-derived and bio-
genic sediment transported basinward by gravity
flows. As a result, relatively important propor-
tions of thick structureless mud layers, or unifites,
are recovered (cf. Huang and Stanley, 1972:539;
Stanley, Rehault, and Stuckenrath, 1980:30). In
contrast, other isolated basins are bounded by
topographically more complex margins, and have
limited or no direct access from land or proximal
source terrains. It is noted that some of these
basins nevertheless contain thick unifites. Exam-
ples include many of the topographically isolated
Hellenic ‘Trench basins of the type discussed in
this study, as well as depressions on the Mediter-
ranean Ridge, some Tyrrhenian and Aegean Sea
basins, and narrow troughs in the Strait of Sicily.
Many of the unifites in such settings are most
probably related to earthquake tremors that trig-
ger failure, initiate progressive downslope dis-
placement, and in some manner insure sediment
entry into basins.

Fine-grained laminated and unlaminated mud
alternations usually form sequences 1 to 10 cm
thick in most ocean cores and in rock slabs studied
to date (Piper, 1978, fig. 12-6; Stow and Shan-
mugam, 1980, fig. 2). The typical ponded Hel-
lenic unifite serves as an ideal example for study
in that its thickness expands almost one hundred
times that of commonly studied, much thinner,
compacted gravitative deposits and magnifies the
fluctuations of fine-grained bedform sequences.
The vertical petrologic trends detailed in the
expanded sections of such thick, fine-grained
units are most valuable in that they record short-
term fluctuations of flow characteristics. Impor-
tant among the latter are changes in turbulence,
velocity, grain-support mechanisms, and settling
phenomena that may occur over a short time and
limited space in small ponded basins.

Petrologic difference between unifites in the
three Hellenic Trench basins examined demon-
strate that major changes in flow properties af-
fecting largely silt and clay-size loads occur rap-
idly and over a small area, i.e., within a few
kilometers. Both 3.5 kHz profile and core data
suggest that, upon entering basins, mud-carrying

turbidity current flows deposit laminated se-
quences that thin distally. Moreover, proportions
of larger, more buoyant planktonic tests, tend to
increase relative to smaller, denser terrigenous
components in a direction away from the site of
the flow entry on the basin floor: this in large
part accounts for the “reversal” petrologic phe-
nomenon illustrated in Table 2. In the case of
larger basins, we postulate that a flow of dimin-
ishing turbulence, velocity, and concentration of
the type envisioned eventually becomes a dilute,
almost stationary cloud. The end-member deposit
of such a flow would be difficult to distinguish
from hemipelagic, largely suspension-emplaced
layers: both are likely to be thin to moderately
thick, foraminifera- and coccolith-rich mud lay-
ers. The former flow deposits, however, would
likely contain somewhat more reworked micro-
fossils than hemipelagites.

Combined factors of accessibility and transport
process are largely responsible for the petrologic
variations in ponded western Hellenic Trench
unifites. We recall that these basins are separated
from each other and from the Peloponnesus and
Crete by physiographic features of marked relief,
and are bounded by steep slopes, many of which
include perched basins (Got, Stanley, and Sorel,
1977; WVittori, 1978:44; Le Quellec 1979144)
likely to trap sediment moving downslope. The
physiographic complexity, a result of geologically
recent displacement resulting from plate motion,
minimizes the paths along which sediment can be
moved directly from adjacent land and proximal
margin sectors, and from the Mediterranean
Ridge, to the trench basin plains. It is our conten-
tion that the direct land and shelf—slope—basin
plain sediment dispersal pattern, important in
some of the larger oceanic trenches (cf. Piper, von
Huene, and Duncan, 1973; Schweller and Kulm,
1978; Underwood, Bachman, and Schweller,
1980), does not prevail in the study area.

Our scheme, involving a succession of down-
slope dispersal events between shallow proximal
and deep distal settings, has been depicted by
Vittori (1978). This model involves transport
through submarine valleys that extend from shal-

NUMBER 13

low gulfs to slope depressions and perched basins,
and in some cases, further still to the trench basins
proper. Sediment is moved from proximal to
distal settings by a succession of redepositional
events; the time span between gravitative flows is
variable, but generally short. The diminished
basinward proportions of sand and compositional
homogenization of fine-grained sediments in the
distally located cores (Figure 1) are accounted for
by a barrier or dam effect, resulting from the
complex topographic setting. This complexity in-
duces preferential entrapment of coarser fractions

31

in slope-perched catchment basins (Vittori, 1978:
44; Feldhausen and Stanley, 1980; Feldhausen et
al., 1981). The major evidence that sediment has
been carried into Hellenic Trench basins via sub-
marine valleys is the presence of low-gradient
basin aprons localized along some base-of-slope
sectors (Figure 13). These aprons are actually
small fan deposits. Cores recovered from such
canyon-related aprons comprise large proportions
of well-developed mud turbidites, a few sandy
turbidites, but no thick unifites (Stanley and
Maldonado, 1981, figs. 6, 8). Moreover, some core

Ficure 13.—Hellenic sediment dispersal scheme emphasizing near-continuous downslope trans-

port from proximal margin to distal sectors. A sediment gravity flow may be channeled into a

submarine valley (SV) and carry material into perched slope basins (PB) and, eventually, onto

the trench basin apron (A) and near-flat basin plain (BP). In this manner, coarse material is

selectively entrapped in submarine valleys, perched slope basins, and depressions in the

cobblestone terrain. Line drawings of selected 3.5 kHz profiles (on the right) from the Zakinthos-

Strofadhes Trench system illustrate examples of sediment deposited in a valley (SV), perched

basin (PB), and basin plain (BP). Hellenic core surveys indicate that the acoustically transparent

layers in the basin (BP) include mud hemipelagites and enhanced proportions of mud turbidites

and unifites.

B2 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

samples from these aprons include reworked shal-
low water microfossils and volcanic materials,
and relatively important contents of terrigenous

fractions of both silt and sand size (Feldhausen
and Stanley, 1980).

Some unifites, particularly those in the Zakin-
thos-Strofadhes Trench basin, were probably em-
placed by canyon-derived turbidity currents
spreading across trench basins. Here the deposits
contain sand-size shallow water benthic species
derived from the adjacent shallow margin. How-
ever, the petrologic characters of most FL+U and
U unifite sequences we examined indicate that
other types of dispersal were probably even more
important in the introduction of fine-grained de-
posits onto basin floors. For example, the absence
of shallow marine faunas and the dominance of
clastic aggregates in the sand fraction are noted
in many unifites, particularly those in the Kith-
era-Antikithera Basin. Clastic aggregates (Figure
9a) are almost certainly reworked from older,
semi-consolidated sediments that cover slopes and
high-relief features, including those adjacent to
trench basins. The clastic aggregates (clasts of
cemented silt particles) are always associated with
reworked microfossils of Pliocene and, in some
cases, Miocene age; they sometimes occur with
pyritized planktonic tests from resedimented sap-
ropels and with disseminated silt and sand-size
volcanic particles (glass shards, palagonite, etc.)
reworked from several Quaternary ash layers,
including the Ischia Tephra (cf. Ninkovich and
Heezen, 1967).

This reworked assemblage records a mixing of
slope sediments of different age and origins as a
result of successive resedimentation events. The
failure of older sediment formations that form
slopes constitutes a primary source of material
reaching trench basins; this is recorded by direct
observation made during submarine dives (Drake
and Delauze, 1968; Pareyn, 1968) and from bot-
tom camera photographs. These reveal a thin (or
absent) unconsolidated sediment veneer on steep
gradients (Figure 11a) that is metastable and
easily set in motion (Figure 11p). Downslope-
oriented bedforms (Figure 11a, B, arrow) record

recent seafloor erosion of the slope. Large individ-
ually displaced (allochthonous) blocks observed
on high-resolution sparker profiles (Vittori, 1978:
81) and on 3.5 kHz records (Figure 14) and
smaller detached blocks of mud directly observed
on dives and in photographs (Figure 11c) provide
further evidence for the failure of silt and clay on
slopes. Graphic depiction of localized slope failure
as an important source of trench fill sediments is
also presented on the trench deposition models
illustrated by Piper, von Huene, and Duncan
(1973, fig. 7), Schweller and Kulm (1978, fig. 21)
and Underwood, Bachman, and_ Schweller,
(1980).

The episodic, but almost constant, downslope
displacement of sediments, involving failure of
slope deposits and subsequent movement via can-
yons is thus envisioned (Figure 13). Sediment
gravity flows, sometimes widespread, sometimes
localized, are able to displace admixtures of both
originally land-derived terrigenous and biogenic
fragments and also incorporate during their
downslope descent eroded clastic aggregates and
planktonic foraminifera. Similar examples of such
reworking in ancient marine examples have been
described by Scholle (1971). Successive gravita-
tive events apparently result in size-sorting effects
and, consequently, in changes downslope in the
proportions of mineralogical components. Re-
peated redeposition may explain, for example,
the downslope increase in clastic aggregates and
planktonic tests relative to the sand-size terrigen-
ous fraction (Feldhausen and Stanley, 1980). The
increased proportion of attapulgite (palygorskite)
downslope in the Kithera-Antikithera Trench is
still further evidence of gravity-induced processes
involving slope erosion (Stanley, Blanpied, and
Sheng, 1981). We do not believe, however, that
canyon transport and slope erosion models in
themselves satisfactorily account for the remark-
ably limited range of textural and compositional
variations that characterize many Hellenic unifite
sequences.

The exceptional homogenization of sediment
that must occur prior to its arrival at the base-of-
slope requires that another phenomenon be con-
sidered. We suggest that homogenization results,

NUMBER 13

33

Ficure 14.—Line drawings of selected 3.5 kHz seismic profiles from the Zakinthos-Strofadhes
Trench system that show sediment failure on steep slopes: a, Slumps with poorly defined
internal structure. B, Overlapping series of mass failure deposits. c, Failed sediment accumulat-
ing in immediately adjacent depression in cobblestone terrain (arrow). p, Slump deposits
showing undefined internal structure at base-of-slope (arrow 1); note improved definition of
bedding basinward (arrow 2), and well-stratified ponded facies in the basin plain (arrow 3).

to a considerable extent, from a slope relief by-
passing-related mechanism (Figure 15); 1.e., the
upper, less concentrated portions of thick gravi-
tative flows, initiated in canyons or on slopes,
probably spill over and carry some of the fine
sediment load onto and across topographic highs.
In this manner, coarser-grained elements would
accumulate preferentially in depressions, includ-
ing submarine valleys, lows between cobblestone
topography (Stanley, 1977b) and perched slope
basins (Vittori, 1978:193). This model emphasizes
the progressive seggregation of sand from mud
and its preferential entrapment on the slope,
whereas finer grained sediments are carried fur-
ther downslope across irregular slope relief fea-
tures toward the basin plain.

The fine-grained, largely silty clay or clayey
silt veneer resides on slopes, particularly the steep
ones, only temporarily; this sediment fails easily
(Figure 11p) and apparently can be displaced
basinward by means of successive gravitative
events. Steep slopes are thus locally devoid of

unconsolidated sediment cover as observed by
Drake and Delauze (1968) and others. Downslope
flows that displace the thin sediment veneer can
also form erosional bedforms on slopes (figure
11a, B). As they progress downslope, flows pick
up and incorporate recent planktonic foramini-
fera, coccoliths, and clay that settle through the
water column over most of the seafloor; these
hemipelagic components are eventually trans-
ported to trench basins along with the gravity-
displaced, size-sorted, fine-grained material. This
process helps explain the high proportions of older
(pre-Pleistocene) coccoliths.

Earthquake tremors affect most of the Hellenic
Arc and are particularly frequent and intense in
the study area (Comninakis and Papazachos,
1972). These are the dominant triggers that set in
motion material of mixed terrigenous and _ bio-
genic origin. The almost continuous failure of
slope sections, gravity-induced transport through
canyons and channels, and sediment gravity flows
spilling over and bypassing areas of relief result

34 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

Ficure 15.—Sedimentation model, depicting relief bypass-
ing along the Hellenic Arc margin, emphasizes textural
segregation and progressive fining and homogenization of
muds toward base-of-slope and basin plain environments: A,
Line drawing of a 3.5 kHz seismic profile in the Zakinthos-
Strofadhes Trench sector illustrating preferential sediment
entrapment in depressions in cobblestone terrain. B, Sche-
matic profile depicting a thick, turbulent sediment gravity
flow (SGF) traversing irregular topography. Arrows show
selective deposition in the depressions of coarse or denser
particles, released largely from the base of the flow; the less
dense and finer material carried in the upper, less concen-
trated portion of the flow are thus able to bypass relief. (HP
= hemipelagic “rain.”’)

in stratigraphically disrupted (repeated or incom-
plete) core sections throughout the study area
(Stanley, Knight, and Stuckenrath, 1978). Anom-
alous sequences of radiocarbon-dated core sec-
tions, (Figure 4), irregular distribution or absence
of key horizons (sapropels, oxidized layers, te-
phra), dilution of sapropels by incorporation of
terrigenous material, and the extremely high rates
of deposition in trench basins relative to slope
environments (Stanley and Maldonado, 1981)
support this active and complex provenance-dis-
persal model.

Depositional events of the type described above
have occurred during much of the Quaternary,
including the late Pleistocene to the recent.
Noted, in this respect, are the unusually thick
unifites in the Kithera-Antikithera Trench basin,
which consist of material radiocarbon-dated from
about 15,000 to 11,000 years B.p. (Figure 4), or
from late Pleistocene to early Holocene. It is
important, however, to signal the absence in both
cores MA-10 and MA-20 of the upper sapropel
(Si), a key stratigraphic layer that is widely dis-
tributed throughout the eastern Mediterranean
and which is dated about 8000 years B.p. (Stanley,
1978; Thunell and Lohmann, 1979). This absence
of the upper sapropel suggests that the two thick
unifites were deposited at their present trench
basin sites since S; time, 1.e., in the mid-Holocene
or more recently. We recognize that radiocarbon
dates are influenced by the presence of older
reworked material, and thus likely indicate the
time of earlier deposition on the slope, and not
the time of final sedimentation of the unifites in
the trench plain. It is possible that the final
gravity flow emplacement of unifites in the two
Kithera-Antikithera Trench cores is related to a
regionally widespread tsunami triggered by the
major Thera explosive event at about 3500 years
B.P., a Suggestion proposed by Kastens and Cita
(in press). The presence, however, of similar uni-
fites of older but variable ages below the upper S;
sapropel in other cores of this same trench basin
indicates that transport events of this type oc-
curred during much of the Quarternary (cf. La-
mont-Doherty Geological Observatory core RC-
184, illustrated in Stanley, 1974, fig. 8; Joides
drilling at sites 127 and 128, in Ryan et al., 1973:
243-322). There is no reason to restrict unifite
deposition to tsunami events. Earthquake tremors
in this zone of high seismicity are the most likely
cause of almost constant remobilization and ba-
sinward displacement of the underconsolidated
and unstable slope sediments.

Some thick (>1 m) single-event silt and clay-
rich shales and marls described in the geological
record (€.g., Scholle; 1971; Rice LucchitgliSis:
Rupke, 1976) may have a similar origin to the

NUMBER 13

Hellenic unifites. Paleogeographic analyses sug-
gest that most of these ancient examples accu-
mulated in small, or at least topographically re-
stricted, catchment basins. As shown in _ the
present Hellenic study, the thickness of a single
redepositional sequence does not necessarily cor-
relate directly with distance from source. Rather
than proximity, the fine-grained “distal” charac-
teristics of the Hellenic unifites we examined are
primarily the result of progressive sorting by re-
petitive downslope displacement events across
highly irregular slope surfaces, i.e., textural seg-
regation involving the relief bypass phenomenon
(Figure 15). We would also expect that in the
case of some ancient unifites, this type of textural
and compositional sorting prior to final trench
basin emplacement also resulted from flow spill-
over and selective bypassing of progressively finer
grains across topographically highly complex
slope terrains.

Unifites accumulating on an active margin,
such as those along the Hellenic Arc, often do not
represent distal facies in the geographic sense. In
contrast, however, some thick unifites have ac-
cumulated in small to moderate size basins in
locales truly distant from shelves and slopes; these
geographically distal unifite facies represent a
bypassing of morphologically less complex mar-
gins. In larger basins, a unifite may represent the
low concentration or slow moving end-member of
a gravity flow transformation continuum (_.e.,
settling from the tail of a turbidity current or
from a turbid layer flow), or may be deposited
from a near-stationary cloud.

In summary, thick unifites are closely related
to the interplay of a number of factors: (1) the
degree of accessibility to sediment flux, (2) rede-
positional processes and particularly gravity-in-
duced flow characteristics, (3) type of material
transported, (4) degree of textural segregation
and compositional sorting during flow, (5) effi-
ciency of slope relief bypassing, and (6) entrap-
ment in relatively restricted catchment basins.
We suspect that continued research on unifites

will demonstrate that this facies occurs in a di-
versity of modern ocean and ancient marine set-
tings that include both active and passive mar-

gins.

Summary

1. Unifites are nearly structureless muds, usu-
ally thick layers of clayey silt and silty clay that
appear homogeneous in composition and often
show an overall fining-upward trend; along the
Hellenic Arc, unifites are restricted to small, iso-
lated trench basins and interpreted as an end-
member facies of gravity-emplaced transport
processes.

2. Unifites are formed by uniform muds, or
faintly laminated muds, or both; uniform mud
may overlie either faintly laminated mud or clas-
sic mud turbidites, but in either case it appears
to be deposited from a single gravity-induced
flow event.

3. Rapid deposition of unifites from sediment
gravity flows is implicated by the association of
unifites with turbidites, their spatial restriction to
trench basins, their lateral continuity and con-
sistent thickness across large areas of trench ba-
sins, their marked thickness (to >10 m), their
high clay fraction (to 60%) and very low sand
fraction content (<0.3%), and a consistently small
accumulation time range as indicated’ by
radiocarbon dates.

4. This study shows that unifites are not truly
homogeneous petrologically, and that the tex-
tural and compositional distinctions observed
within a unifite appear closely related with the
geographic position of a trench basin depositional
site relative to the steep margins bounding the
trench plain, i.e., the base-of-slope margin flat
setting versus the flat, more distal basin floor
proper.

5. Unifites recovered well within basin plains
tend to comprise higher proportions of uniform
mud, are somewhat better sorted texturally, and
generally contain higher proportions of plank-
tonic tests, but somewhat fewer benthic forami-

36 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

niferal tests and terrigenous components than
unifites along trench margins.

6. In detail, unifites display an overall, albeit
subtle, fining-upward trend; the faintly lami-
nated portions of unifites contain a somewhat
higher silt content, while the uniform mud por-
tions are slightly better sorted.

7. A complete unifite sequence may display a
vertical cyclic trend formed by four terms, from
the base up: a faintly laminated, generally siltier,
fining-up term characterized by a largely biogenic
sand-size content; a graded mud term with terri-
genous components dominating the sand frac-
tion; an ungraded mud displaying textural fluc-
tuations and an important sand-size terrigenous
fraction; and an upper fining-upward term with
increased proportions of sand-size biogenic com-
ponents.

8. The sand fraction of Hellenic Trench uni-
fites is commonly dominated by clastic aggregates
eroded and reworked downslope from older mar-
gin sediments; unifites also comprise a large silt-
size nannofossil content (including an important
proportion of reworked pre-Quaternary forms),
and an upward increase of planktonic tests.

9. A petrological ‘“‘reversal” phenomenon, at-
tributable largely to the influence of transport
processes, involves a change in the proportion of
mineralogical components between the edge and
the center of a near-flat trench basin; for example,
components that are dominant in the coarsest
terms of margin flat cycles may, in contrast,
abound in the finer (largely uniform mud) terms
of basin plain cycles.

10. The increased uniformity of unifites in a
basinward direction indicates deposition from
turbidity current-related flows of diminished con-
centration that move across, and spread over,
large areas of a flat trench floor; the observed
probably

changes in flow character (turbulence, velocity,

subtle petrologic variations record
grain-support) that likely occur during a single-
transport event over a brief time and limited area
in a small ponded basin.

11. Faint laminae may be related to phases of

flocculation and depositional sorting of the sedi-

ment load during flow; a reorganization of mud
and silt flocs and changes in their concentration
may induce accelerated settling of particles
through the boundary layer at the base of a flow.

12. The faintly laminated terms in unifites are
herein related to the hydraulic jump effect that
produces a sudden rearrangement of the sediment
load at the head and in the body of a flow and
flocculation upon its arrival on the near-flat
trench basin floor; the eventual passage of the
slower moving dilute tail of the flow beyond the
base-of-slope is recorded by the uppermost non-
laminated, graded unifite mud term.

13. The mineralogical “reversal” phenomenon
that occurs between the margin flat and some-
what more distal basin plain environments is also
attributed to hydraulic jump effects, which in-
duce a transfer of energy and changes in turbu-
lence and grain support characteristics within the
flow over a short distance beyond the base-of-
slope.

14. Unifite thickness is in large part the result
of the available volume of material transported
relative to the surface area on which it accumu-
lates, 1.e., the thick Hellenic unifites do not nec-
essarily record transport of particularly large sed-
iment loads or a direct dispersal of concentrated
flows between proximal and distal environ-
ments. Rather the unifites indicate entrapment
of moderate amounts of material carried by sed-
iment gravity flows into small trench basins.

15. The homogenization process essential for
the deposition of fine-grained unifites along the
Hellenic Arc results in large part from a barrier-
dam effect, i.e., a modification of flows as they
move basinward across the highly irregular slope
topography characteristic of this region.

16. Homogenization involves both textural
and mineralogical segregation. Coarser or denser
fractions are preferentially trapped in slope de-
pressions, while finer or less dense silt and clay
particles in thick gravity flows are transported
further downslope across irregular seafloor fea-
tures (relief bypass phenomenon).

17. The failure of the thin, metastable sedi-
mentary veneer on steep slopes is most frequently

NUMBER 13

triggered by earthquake tremors that affect large
sectors of the Hellenic Arc; this episodic but
frequent downslope transport of sediment, much
of it reworked from older sedimentary strata,
deposits by successive basinward displacement of
progressively finer material that includes both
land-derived terrigenous and biogenic fragments.

18. Much of the thin silty clay veneer on pre-
sent Hellenic slopes has been emplaced by the
relief bypass process and this sediment resides
only temporarily on high gradient, seismically
unstable features; core analysis shows that during
much of the late Quaternary to the present sedi-
ments on the margin have been transported ba-
sinward through a series of repetitive displace-
ment events that produced textural and compo-
sitional sorting on the slope prior to final trench
basin accumulation.

oH

19. The petrologic attributes of unifites record
the interplay of several factors more important
than proximality or distance from source: (1)
complexity of dispersal paths and the degree of
accessibility of sediment flux to the trench basin,
(2) redepositional processes, grain-support mech-
anisms and gravity-induced flow characteristics,
(3) type of material transported, (4) extent of
textural seggregation and compositional sorting
during flow, (5) role of the slope relief bypassing
process, and (6) selective entrapment of essen-
tially fine-grained particles in relatively restricted
trench catchment basins.

20. Continuing studies in the Mediterranean
Sea indicate that unifites occur in diverse settings
on both active and passive margins and that these
modern ocean deposits can serve as examples to
interpret some uniform mud facies in the rock
record.

Literature Cited

Ariane
1979. Resultats de dragages sur la bordure externe de
lV Arc Hellénique (Méditerranée Orientale). Marine
Geology, 32:291-310.
Biju-Duval, B., J. Letouzey, and L. Montadert
1979. Variety of Margins and Deep Basins in the Med-
iterranean. Jn J. S. Watkins, L. Montadert and P.
W. Dickerson, editors, Geological and Geophysical
Investigations of Continental Margins. American
Association of Petroleum Geologists Memoir, 29:293-
Silvie
C., P. F. Burollet, P. Clairefond, and M. Shimi
La Mer Pelagienne: Sédiments Actuels et Holo-

Blanpied,
1979.
cenes. Geologie Mediterranéenne, 6:61-82.
Carter, T. G., J. P. Flanagan, C. R. Jones, F. L. Marchant,
R. R. Murchison, J. H. Rebman, J. C. Sylvester, and
J. C. Whitney
1972. A New Bathymetric Chart and Physiography of
the Mediterranean Sea. Jn D. J. Stanley, editor,
The Mediterranean Sea—A Natural Sedimentation Lab-
oratory, pages 1-24. Stroudsburg, Pennsylvania:
Dowden, Hutchinson & Ross.
H., and G. Millot

Observations sur la repartition et la genese des

Chamley,

1975.

attapulgites Plio-Quaternaires de Méditerranée.
Comptes Rendus de l’Académie des Sciences (Paris), 281-
D:1215-1218.

Comninakis, P. E., and B. C. Papazachos

1972. Seismicity of the Eastern Mediterranean and
Some Tectonic Features of the Eastern Mediter-
ranean Ridge. Geological Society of America Bulletin,
83:1093-1102.

Drake, C. L., and H. Delauze

1968. Gravity Measurements near Greece from Bathy-
scaphe Archimede. Annales de l'Institut Océanogra-
phique (Paris), 46:71—78.

Emelyanovy, E. M.

1972. Principal Types of Recent Bottom Sediments in
the Mediterranean Sea: Their Mineralogy and
Geochemistry. Jn D. J. Stanley, editor, The Med-
terranean Sea—A Natural Sedimentation Laboratory,
pages 335-386. Stroudsburg, Pennsylvania: Dow-
den, Hutchinson & Ross.

Feldhausen, P. H., and D. J. Stanley
1980. Hellenic Trench Sedimentation: An Approach
Using Terrigenous Distribution. Marine Geology,
38:M21—-M30.

38

Feldhausen, P. H., D. J. Stanley, R. J. Knight, and A.
Maldonado

1981. Homogenization of Gravity-emplaced Muds and
Unifites: Models from the Hellenic Trench. In F.
C. Wezel, editor, Sedimentary Basins of Mediterranean
Margins, pages 203-226. Bologna: Italy: Consiglio
Nazionale delle Ricerche, Universita degli Studi,
Urbino.
Folk, R. L., and W. C. Ward

1957. Brazos River Basin: A Study in the Significance
of Grain Size Parameters. Journal of Sedimentary
Petrology, 27:3-26.
Got, H., D. J. Stanley, and D. Sorel

1977. Northwestern Hellenic Arc: Concurrent Sedimen-
tation and Deformation in a Compressive Setting.
Manne Geology, 24:21-36.
Heezen, B. C., and C. D. Hollister

1971. The Face of the Deep. 659 pages. New York, New
York: Oxford University Press.
Hersey, J. B.
1965. Sediment Ponding in the Deep Sea. Geological

Society of America Bulletin, 76:1251—1260.
Hesse, R.
1975. Turbiditic and Nonturbiditic Mudstone of Cre-
taceous Flysch Sections of the East Alps and Other
Basins. Sedimentology, 22:387-416.
Huang, T.-C., and D. J. Stanley
1972. Western Alboran Sea: Sediment Dispersal, Pond-
ing and Reversal of Currents. Jn D. J. Stanley,
editor, The Mediterranean Sea—A Natural Sedimenta-
tion Laboratory, pages 521-559. Stroudsburg, Penn-
sylvania: Dowden, Hutchinson & Ross.
Kastens, K. A., and M. B. Cita
In press. Tsunami-induced Sediment Transport in the
Abyssal Mediterranean Sea. Marine Geophysical Re-
search.
Komar, P. D.
1971. Hydraulic Jumps in Turbidity Currents. Geological
Society of America Bulletin, 82:1477-1488.
Kranck, K.

1975. Sediment Deposition from Flocculated Suspen-
sions. Sedimentology, 22:111-123.
Kuenen, P. H.
1965. Experiments in Connection with Turbidity Cur-

rents and Clay Suspensions. Jn W. F. Whittard
and R. D. Bradley, editors, Marine Geology and

NUMBER 13

Geophysics, pages 47-74. London: Butterworths.
[Volume 17 of the Colston Papers. |
Lacombe, H., and P. Tchernia
1972. Caracteres hydrologiques et circulation des eaux
en Mediterranée. In D. J. Stanley, editor, The
Mediterranean Sea—A Natural Sedimentation Labora-
tory, pages 25-36. Stroudsburg, Pennsylvania:
Dowden, Hutchinson & Ross.
Le Pichon, X.

1980. Importance des formations attribuées au Messi-
nien dans les fosses de subduction Helléniques:
Observations par submersible. Comptes Rendus de
V’Academie des Sciences (Paris), 290-D:5-8.

Le Pichon, X., and J. Angelier

1979. The Hellenic Arc and Trench System: A Key to
the Neotectonic Evolution of the Eastern Mediter-
ranean Sea. Tectonophysics, 60:1-42.

Le Quellec, P.

1979. La marge continentale Ionienne du Peéloponnese—Geologie
et Structure. 210 pages. Thesis, Université Pierre et
Marie Curie, Paris, France.

McKenzie, D. P.

1972. Plate Tectonics of the Mediterranean Region. Geo-
physical Journal of the Royal Astronomical Society (Lon-
don), 30: 109-189.

Makris, J.

1976. A Dynamic Model of the Hellenic Arc Deduced
from Geophysical Data. Tectonophysics, 36:339-
346.

Maldonado, A., G. Kelling, and G. Anastasakis

1981. Late Quaternary Sedimentation in a Zone of Con-
tinental Plate Convergence in the Central Hel-
lenic Trench System. Marine Geology, 41:184—211.
Maldonado, A., and D. J. Stanley

1976. Late Quaternary Sedimentation in the Strait of
Sicily. Smithsonian Contributions to the Earth Sciences,
16:1-73.
Mascle, J., and P. Le Quellec

1979. Matapan Trench
Trench Disorganization? Geology, 8:77-81.

Miller, A. R.

(Ionian Sea): Example of

1972. Speculations Concerning Bottom Circulation in
the Mediterranean. Jn D. J. Stanley, editor, The
Mediterranean Sea—A Natural Sedimentation Labora-
tory, pages 37-42. Stroudsburg, Pennsylvania:
Dowden, Hutchinson & Ross.

Moore, D. G.

1969. Reflection Profiling Studies of the California Con-
tinental Borderland: Structure and Quaternary
Turbidity Basins. Geological Society of America Special
Paper, 107: 142 pages.

Mutti, E.
1977. Distinctive Thin-bedded Turbidite Facies and Re-

lated Depositional Environments in the Eocene

39

Hecho Group (South Central Pyrenees, Spain).
Sedimentology, 24:107-131.
Ninkovich, D., and B. C. Heezen

1967. Physical and Chemical Properties of Volcanic
Glass Shards from Pozzuolana Ash, Thera Island,
and from Upper and Lower Ash Layers in Eastern
Mediterranean Deep Sea Sediments. Nature, 213:
582-584.

Normark, W. R.

1970. Growth Patterns of Deep Sea Fans. Bulletin of the
American Association of Petroleum Geologists, 54:2170-
2NOS:

Pareyn, C.

1968. Observations geologiques et sédimentologiques
dans la fosse ouest de la Mer Ionienne (Campagne
Grece 1965, Plongées GR4 et GR5). Annales de
UInstitut Oceanographique (Paris), 46:53-69.

Pilkey, O. H., S. D. Locker, and W. J. Cleary

1980. Comparison of Sand-Layer Geometry on Flat
Floors in 10 Modern Depositional Basins. Bulletin
of the American Association of Petroleum Geologists, 64:
841-867.

Piper, D.J.W.

1978. Turbidite Muds and Silts on Deep Fans and Abys-
sal Plains. Jn D. J. Stanley and G. Kelling, editors,
Sedimentation in Submarine Canyons, Fans and Trenches,
pages 163-176. Stroudsburg, Pennsylvania: Dow-
den, Hutchinson & Ross.

Piper, D.J.W., R. von Huene, and J. R. Duncan

1973. Late Quaternary Sedimentation in the Active
Eastern Aleutian Trench. Geology, 1:19-22.

Ricci Lucchi, F.

1975. Turbidite Dispersal in a Miocene Deep-Sea Plain:
The Marnoso Arenacea of the Northern Apen-
nines. Geologie en Mijnbouw, 57:559-576.

Rupke, N. A.

1976. Sedimentology of the Very Thick Calcarenite-
Marlstone Beds in a Flysch Sucession, Southwest-
ern Pyrenees. Sedimentology, 23:43-65.

Rupke, N. A., and D. J. Stanley

1974. Distinctive Properties of Turbiditic and Hemipe-
lagic Mud Layers in the Algéro-Balearic Basin,
Western Mediterranean Sea. Smithsonian Contribu-
tions to the Earth Sciences, 13:1—40.

Ryan, W.B.F., K. J. Hsu, and Shipboard Scientific Party

1973. Initral Reports of the Deep Sea Drilling Project. Volume
13, 1447 pages. Washington, D.C.: National Sci-
ence Foundation.

Ryan, W.B.F., F. Workum Jr., and J. B. Hersey

1965. Sediments on the Tyrrhenian Abyssal Plain. Geo-
logical Society of America Bulletin, 76:1261-1282.
Scholle, P. A.

1971. Sedimentology of Fine-grained Deep-Water Car-
bonate Turbidites, Monte Antola Flysch (Upper

40 SMITHSONIAN CONTRIBUTIONS TO THE MARINE SCIENCES

Cretaceous), Northern Apennines, Italy. Geological
Society of America Bulletin, 82:629-658.
Schweller, W. J., and L. D. Kulm
1978. Depositional Patterns and Channelized Sedimen-
tation in Active Eastern Pacific Trenches. Jn D. J.
Stanley and G. Kelling, editors, Sedimentation in
Submarine Canyons, Fans and Trenches, pages 311-
323. Stroudsburg, Pennsylvania: Dowden, Hutch-
inson & Ross.
Stanley, D. J.
1974. Modern Flysch Sedimentation in a Mediterranean
Island Arc Setting. Jn R. H. Dott, Jr. and R. H.
Shaver, editors, Modern and Ancient Geosyn-
clinal Sedimentation. Society of Economic Paleontolo-
gists and Mineralogists Special Publication, 19:240-
259.
1977a. Post-Miocene Depositional Patterns and Struc-
tural Displacement in the Mediterranean. Jn
A.E.M. Nairn, W. H. Kanes, and F. G. Stehli,
editors, The Ocean Basins and Margins, Volume 4A:
The Eastern Mediterranean, pages 77-150. New York,
New York: Plenum Press.
1977b. Recent Tectonic Overprint on Cobblestone Dep-
osition in the Northwestern Hellenic Arc. Jn B.
Biju-Duval and L. Montadert, editors, Structural
History of the Mediterranean Basins, pages 433-445.
Paris: Editions Technip.

1978. Ionian Sea Sapropel Distribution and Late Qua-
ternary Palaeoceanography in the Eastern Medi-
terranean. Nature, 247:149-152.

1980. Mediterranean Models: Carbonate Shelves, Slope

Bypassing, Ponding, Transformation Products
and “Unifites”. Jn W. C. Wezel, editor, Sedimentary
Basins of Mediterranean Margins, pages 47-48. Ur-
bino, Italy: Consiglio Nazionale delle Ricerche,
Universita degli Studi, Urbino.
Stanley, D. J., C. Blanpied, and H. Sheng
1981. Palygorskite as a Sediment Dispersal Tracer in the
Eastern Mediterranean. Geo-Marine Letters, 1:49-
55.
Stanley, D. J., C. E. Gehin, and C. Bartolini
1970. Flysch-type Sedimentation in the Alboran Sea,
Western Mediterranean. Nature, 228:979-983.
Stanley, D. J., and R. J. Knight
1979. Giant Mudflow Deposits in Submarine Trenches:
Hellenic Basins and Slopes in Eastern Mediterra-
nean. Bulletin of the American Association of Petroleum
Geologists, 63:532-533.
Stanley, D. J., R. J. Knight, and R. Stuckenrath
1978. High Sedimentation Rates and Variable Dispersal
Patterns in the Western Hellenic Trench. Nature,

273:110-113.

Stanley, D. J., and A. Maldonado
1981. Depositional Models for Fine-grained Sediment in
the Western Hellenic Trench, Eastern Mediterra-
nean. Sedimentology, 28:273-290.
Stanley, D. J., and C. Perissoratis
1977. Aegean Sea Ridge Barrier-and-Basin Sedimenta-
tion Patterns. Marine Geology, 24:97—-107.
Stanley, D. J., J. P. Rehault, and R. Stuckenrath
1980. Turbid-layer Bypassing Model: The Corsican
Trough, Northwestern Mediterranean. Marine Ge-
ology, 37:19-40.
Stow, D.A.V., and A. J. Bowen
1978. Origin of Lamination in Deep-Sea Fine-grained
Sedimentation. Nature, 274:324-328.
Stow, D.A.V., and G. Shanmugam
1980. Sequence of Structures in Fine-grained Turbidites:
Comparison of Recent Deep-Sea and Ancient
Flysch Sediments. Sedimentary Geology, 25:23-42.
Thunell, R. C., and G. P. Lohmann
1979. Planktonic Foraminiferal Fauna Associated with
Eastern Mediterranean Quaternary Stagnation.
Nature, 281:211-213.
Underwood, M. B., S. B. Bachman, and W. J. Schweller
1980. Sedimentary Processes and Facies Associations
within Trench and Trench-Slope Settings. Jn M.
E. Field, A. H. Bouma, and I. Colburn, editors,
Quaternary Depositional Environments on the Pacific Con-
tanental Margin, pages 211-229. Tulsa, Oklahoma:
Society of Economic Mineralogists and Paleontol-
ogists, Pacific Section.
Van Andel, T. H., and P. D. Komar
1969. Ponded Sediments of the Mid-Atlantic Ridge be-
tween 22° and 23° North Latitude. Geological So-
ciety of America Bulletin, 80:1163-1190.
van Straaten, L.M.J.U.
1967. Turbidites, Ash Layers and Shell Beds in the
Bathyal Zone of the Southeastern Adriatic Sea.
Revue de Geographie Physique et de Geologie Dynamique,
9:219-240.
Venkatarathnam, K., and W.B.F. Ryan
1971. Dispersal Patterns of Clay Minerals in the Sedi-
ments of the Eastern Mediterranean Sea. Marine
Geology, 11:261—282.
Vittori, J.
1978. Caracteres Structuro-Sédimentaires de la Couver-
ture Plio-Quaternaire au Niveau des Pentes et des
Fosses Helléniques du Péloponnese (Greéce). 194
pages. Thesis, University of Perpignan, France.
Vittori, J., H. Got, P. LeQuellec, J. Mascle, and L. Mirabile
1981. Emplacement of the Recent Sedimentary Cover
and Processes of Deposition on the Matapan
Trench Margin (Hellenic Arc). Marine Geology, 41:
113-135.

REQUIREMENTS FOR SMITHSONIAN SERIES PUBLICATION

Manuscripts intended for series publication receive substantive review within their
originating Smithsonian museums or offices and are submitted to the Smithsonian Institution
Press with approval of the appropriate museum authority on Form SI-36. Requests for
special treatment—use of color, foldouts, casebound covers, etc.—require, on the same
form, the added approval of designated committees or museum directors.

Review of manuscripts and art by the Press for requirements of series format and style,
completeness and clarity of copy, and arrangement of all material, as outlined below, will
govern, within the judgment of the Press, acceptance or rejection of the manuscripts and art.

Copy must be typewritten, double-spaced, on one side of standard white bond paper,
with 114” margins, submitted as ribbon copy (not carbon or xerox), in loose sheets (not
stapled or bound), and accompanied by original art. Minimum acceptable length is 30 pages.

Front matter (preceding the text) should include: title page with only title and author
and no other information, abstract page with auttior/title/series/etc., following the establish-
ed format, table of contents with indents reflecting the heads and structure of the paper.

First page of text should carry the title and author at the top of the page andan unnum-
bered footnote at the bottom consisting of author’s name and pro;essional mailing address.

Center heads of whatever level should be typed with initial caps of major words, with
extra space above and delow the head, but with no other preparation (such as all caps or
underline). Run-in paragraph heads should use period/dashes or colons as necessary.

Tabulations within text (lists of data, often in parallel columns) can be typed on the text
page where they occur, but they should not contain rules or formal, numbered table heads.

Formal tables (numbered, with table heads, boxheads, stubs, rules) should be sub-
mitted as camera copy, but the author must contact the series section of the Press for edito-
rial attention and preparation assistance before final typing of this matter.

Taxonomic keys in natural history papers should use the alined-couplet form in the
zoology and paleobiology series and the multi-level indent form in the botany series. If
cross-referencing is required between key and text, do not include page references within the
key, but number the keyed-out taxa with their corresponding heads in the text.

Synonymy in the zoology and paleobiology series must use the short form (taxon,
author, year:page), with a full reference at the end of the paper under ‘“‘Literature Cited.”’
For the botany series, the long form (taxon, author, abbreviated journal or book title, volume,
Page, year, with no reference in the ‘‘Literature Cited’’) is optional.

Footnotes, when few in number, whether annotative or bibliographic, should be typed
at the bottom of the text page on which the reference occurs. Extensive notes must appear at
the end of the text in a netes section. If bibliographic footnotes are required, use the short
form (author/brief title/page) with the full reference in the bibliography.

Text-reference system (author/year/page within the text, with the full reference in a
“Literature Cited”’ at the end of the text) must be used in place of bibliographic footnotes in
all scientific series and is strongly recommended in the history and technology series:
“(JJones, 1910:122)”’ or “*... . Jones (1910:122).”’

Bibliography, depending upon use, is termed ‘‘References,’’ ‘‘Selected References,” or
“Literature Cited.’’ Spell out book, journal, and article titles, using initial caps in all major
words. For capitalization of titles in foreign languages, follow the national practice of each
language. Underline (for italics) book and journal titles. Use the colon-parentheses system
for volume/number/page citations: “‘10(2):5-9."" For alinement and arrangement of
elements, follow the format of the series for which the manuscript is intended.

Legends for illustrations must not be attached to the art nor included within the text but
must be submitted at the end of the manuscript—with as many legends typed, double-
spaced, to a page as convenient.

Illustrations must not be included within the manuscript but must be submitted sepa-
rately as original art (not copies). All illustrations (photographs, line drawings, maps, etc.)
can be intermixed throughout the printed text. They should be termed Figures and should
be numbered consecutively. If several ‘‘figures’’ are treated as components of a single larger
figure, they should be designated by lowercase italic letters (underlined in copy) on the illus-
tration, in the legend, and in text references: ‘‘Figure 9b.”’ If illustrations are intended to be
printed separately on coated stock following the text, they should be termed Plates and any
components should be lettered as in figures: ‘“‘Plate 9b.’’ Keys to any symbols within an
illustration should appear on the art and not in the legend.

A few points of style: (1) Do not use periods after such abbreviations as ‘‘mm, ft,
yds, USNM, NNE, AM, BC.’’ (2) Use hyphens in spelled-out fractions: “‘two-thirds.’’ (3)
Spell out numbers “‘one’”’ through ‘‘nine’’ in expository text, but use numerals in all other
cases if possible. (4) Use the metric system of measurement, where possible, instead of
the English system. (5) Use the decimal system, where possible, in place of fractions.
(6) Use day/month/year sequence for dates: ‘‘9 April 1976."’ (7) For months in tabular list-
ings or data sections, use three-letter abbreviations with no periods: ‘‘Jan, Mar, Jun,”’ etc.

Arrange and paginate sequentially EVERY sheet of manuscript—including ALL front
matter and ALL legends, etc., at the back of the text—in the following order: (1) title page,
(2) abstract, (3) table of contents, (4) foreword and/or preface, (5) text, (6) appendixes,
(7) notes, (8) glossary, (9) bibliography, (10) index, (11) legends.