MARINE GEOLOGY OF THE CONTINENTAL
MARGIN OFF SOUTHERN OREGON

Joseph John Spigai

DUDLEY KNOX LIBRARY

I POSTGRADUATE SCHOOL

MONTEREY, CALIFORNIA 93943-5002

Marine Geology of the Continental Margin
Off Southern Oregon

by

Joseph John Spigai

A THESIS

submitted to

Oregon State University

in partial fulfillment of
the requirements for the
degree of

Doctor of Philosophy

June 1971

GRADUATE SCHOOB
CALIF. 93940"

APPROVED:

Associate Professor of Oceanography

in charge of major

Chairman of the Department of Oceanography-

Dean of the Graduate School

Date thesis is presented

Typed by Gwendolyn Hansen for Joseph John Spigai

ACKNOWLEDGMENTS

I would like to express sincere gratitude to Dr. LaVerne D.
Kulm, my major professor, for his judicious advice and patient
guidance during the entire course of this study. His generosity in
giving so freely of his time and in critically reviewing this manuscript
is greatly appreciated.

Discussions with many people stimulated my thinking and helped
me to formulate many of the ideas presented here. In this regard,
thanks are due William Bales, and Drs. Richard Couch, Gerald A.
Fowler, Michael S. Longuet-Higgins, and Eli A. Silver. Many fellow
graduate students unselfishly contributed their knowledge and assistance
to this work; thanks go especially to Drs. David W. Allen, John R.
Duncan, Jr. , and Gary B. Griggs, and to David M. Chambers, Roger
H. Neudeck, Robert E. Peterson, James B. Phipps, Robert C. Roush,
and Kenneth F. Scheidegger.

I am indebted to Dr. Gerald A. Fowler for providing the identifi-
cation and correlation of the rock fauna, and to Dr. G. Ross Heath for
his assistance in the analysis and interpretation of the clay minerals.
I am also grateful to Miss Anastasia Sotiropoulos for her excellent work
in drafting many of the figures. Appreciation is extended to the staff
and students of the Department of Oceanography, Oregon State Univer-
sity, and to the personnel of the R/V Yaquina for their invaluable

assistance in the collection of data at sea.

I am very grateful to my wife, Frances, for her enduring patience
and for the unlimited help and encouragement she provided me during
the course of the study. To my parents, whose sacrifices made my
education possible, I am ever grateful.

The opportunity to undertake this graduate study was made pos-
sible by the United States Navy, under its Postgraduate Education
Program; personal financial support was also provided by the Navy.
The research pertaining to this study was made possible by grants
from the United States Geological Survey made to Oregon State
University (Contracts 14-08-0001-107 66, -11941, and -1287). Initial
support for the research and ship time was provided by the Office of
Naval Research (ContractNonr 1286 (10)).

TABLE OF CONTENTS

Page

INTRODUCTION 1

SUBMARINE PHYSIOGRAPHY 5

General Physiographic Features 5

Physiographic Provinces of the Southern Oregon

Continental Margin 9

Continental Shelf 12

Upper Continental Slope 13

Klamath Plateau 13

Cape Blanco Bench 15

Middle Bench 1 6

Lower Continental Slope 16

Rogue Submarine Canyon 17

REGIONAL GEOLOGY 22

General Geology of Southwestern Oregon and

Northern California 22
Coastal Features and the History of Sea Level

Fluctuations 31

SAMPLING AND ANALYTICAL PROCEDURES 33

Sample Collection and Processing 33

Laboratory Analyses 36

STRUCTURAL FEATURES OF THE SOUTHERN OREGON MARGIN 40

Regional Setting 40

Gravity 40

Magnetics 44

Heat Flow 47

Seismicity 48

Interpretation of the Tectonic Pattern 50

Continental Margin Structure 51

General Structural Trends 51

Continental Shelf 55

Upper Slope and Benches 58

Page

Lower Slope 65

Rogue Submarine Canyon 67
Continental Margin Structure in Relation to the

Regional Setting 7 0

STRATIGRAPHY 74

Unconsolidated Sediments 74

Planktonic Foraminifera-Radiolaria Abundance 74

Mazama Ash 78

Radiocarbon Dating 79

Faunal Stratigraphy of Consolidated Sediments 79

Rates of Sediment Accumulation 81

SEDIMENTOLOGY 85

Unconsolidated Sediments 85

Classification and Distribution of Sediment Types 85

Olive Gray Lutite 88

Gray Lutite 95

Sand-Silt Layers 96

Minor Sediment Types 97

The Present Sediment Pattern 99

Textural Relationships 100

Mineralogy 102

Light Minerals 106

Heavy Minerals 109

Clay Minerals 114

Organic Carbon 119

Consolidated Sediments 122

Classification and Distribution of Rock Types 122

PROCESSES OF SEDIMENTATION 128

A Proposed Model for Modern Sediment Transport

on the Southern Oregon Continental Margin 128

The Initial Regime of Sedimentation 128

The Concept of Lutum Transport 133

The Oceanographic Regime 134
Turbid Layer Formation and Transport

Across the Shelf 141

Transport Down the Slope 145

Deposition of Lutum on the Lower Slope 150

The Late Pleistocene and Holocene Sedimentation Patterns 153

SUMMARY AND CONCLUSIONS

Development of the Structural Framework

Pre-Tertiary History

Tertiary History
Quaternary History of Sedimentation

Pleistocene

Holocene and Modern

BIBLIOGRAPHY
APPENDICES

Legend for Appendices

Appendix 1. Piston core and rock dredge station
locations

Appendix 2. Radiocarbon age determinations from
selected cores

Appendix 3. Coarse-fraction composition of sedi-
ment samples

Appendix 4. Textural analyses of sediment samples

Appendix 5. Light mineral composition of the sand
fraction in selected sediment samples

Appendix 6. Heavy mineral composition of the sand
fraction in selected sediment samples

Appendix 7. Quantitative analyses of the major clay

minerals from X-ray diffraction records

of selected samples 211

Appendix 8. Mineralogy of the major rock types

from dredge hauls 212

Page

157

157

157

158

162

162

164

168

183

183

184

185

186

198

207

208

LIST OF FIGURES

Figure Page

1. Oregon continental margin and adjacent deep-sea areas. 3

2. Bathymetry of the southern Oregon continental margin. 7

3. Precision Depth Recorder track lines in the area

of investigation. 8

4. Physiographic provinces of the southern Oregon

continental margin. 10

5. Selected bathymetric profiles of the continental margin. 11

6. Generalized bathymetry and selected profiles across

the Rogue Submarine Canyon. 19

7. Geographic and drainage features of southwestern

Oregon and northern California. 23

8. Geologic map of southwestern Oregon and northern
California. 26

9. Location of piston core and dredge samples. 34

10. Flow chart for core processing and sample analysis. 35

11. Major tectonic features and earthquake epicenters

in the northeast Pacific. 41

12. Free -air gravity anomaly map west of the southern
Oregon-northern California coast. 43

13. Magnetic anomaly patterns off southern Oregon and

northern California. 45

14. Fault-plane solutions of earthquakes and possible
displacements from first motion studies in the

northeast Pacific. 49

15. Track line map of continuous seismic profiles. 52

Figure Page

16. Major structural features of the southern Oregon

margin. 53

17. Sparker profiles across the southern Oregon shelf

and upper slope. 57

18. EDO subbottom profiles across the southern Oregon

shelf edge and base of slope. 59

19. Sparker profile across Cape Blanco Bench. 60

20. EDO subbottom profile across the upper continental

slope. 62

21. Sparker profile across the entire southern Oregon

slope. 63

22. Sparker profile across the upper continental slope
illustrating slumping. 64

23. Reflection profiles of the southern Oregon and

northern California continental margins. 66

24. North-south Sparker profile across the Upper Rogue

Canyon. 68

25. Summary of lithologic and stratigraphic information
from piston cores from the southern Oregon margin

and adjacent Blanco Valley. 7 6

26. Textural classification of unconsolidated sediments. 87

27. Coarse-fraction constituents of unconsolidated sediments. 89

28. Lithology of piston cores from the southern Oregon
continental shelf. 90

29. Lithology of piston cores from the upper continental

slope and benches. 91

30. Lithology of piston cores from the lower slope. 92

31. Lithology of piston cores from the Rogue Submarine

Canyon. 93

Figure Page

32. Distribution of surface sediment types on the southern

Oregon margin. 101

33. Phi Mean Diameter versus Phi Deviation. 103

34. Phi Mean Diameter versus Phi Skewness according

to depositional environment. 104

35. Phi Mean Diameter versus Phi Skewness according

to sediment type. 105

36. Light mineral composition of selected sediments and
sedimentary rocks. 107

37. Major drainage basins of northwestern United States. 110

38. Clay mineral composition of selected sediments from

the continental margin and major Oregon rivers. 115

39. Rock types from the southern Oregon margin. 123

40. Schematic model of modern sediment transport

processes on the southern Oregon margin. 129

41. Schematic model of the oceanographic conditions
over the southern Oregon margin in winter and

summer. 135

42. Idealized cross -section of the late Pleistocene

sediment distribution on the southern Oregon margin. 154

43. Idealized cross -section of the Holocene and modern

sediment distribution on the southern Oregon margin. 156

LIST OF TABLES

Table Page

1. Age, correlation and paleo-depth of Foraminifera from
selected consolidated sediments on the southern Oregon
continental margin. 80

2. Sedimentation rates from the southern Oregon continental
margin, 82

3. A comparison of the light mineral composition of
selected margin sediments with southwestern Oregon
sandstones. 108

4. Comparison of the heavy mineral suites and pyroxene/
amphibole ratios of southern Oregon margin environ-
ments with continental drainage basins. 112

5. Total carbon, organic carbon and calcium carbonate

in selected margin sediments. 120

MARINE GEOLOGY OF THE CONTINENTAL MARGIN
OFF SOUTHERN OREGON

INTRODUCTION

Investigations of the world's continental margins have expanded
in recent years owing to increased political awareness, economic need,
and a more sophisticated technology. More important, however, is the
fact that both interest and understanding of continental margins have
increased due to a deeper scientific insight into the basic processes of
margin development and due to an awareness of the importance of con-
tinental margins in the evolution of both continents and ocean basins.
Recent theories concerning sea-floor spreading and plate tectonics
(e. g. Vine, 1966; Isacks, e_t aL , 1968; Le Pichon, 1968) have had a
major influence on the interpretation of both the geology of ocean
basins and the geologic structure and evolution of the adjoining con-
tinents. Because of these theories, new attention has been focused on
the continental margins as the critical zones of transition between
interacting continental and oceanic plates. An understanding of the
tectonic history of continental margins in the light of sea-floor spread-
ing must now be an essential prerequisite to help explain the processes
of growth and development of ocean basins and continental masses.

The continental margin off the state of Oregon has been the sub-
ject of detailed investigation since 1962. The early work on the geo-
morphology of the Oregon margin by Byrne (1962, 1963a, b) was

followed by more detailed studies (Kulm and Byrne, 19 66; Byrne, e_t al . ,
1966) as well as a number of other works. Geophysical studies have
also been carried out on, or adjacent to, the Oregon margin (Dehlinger,
etal., 1967, 1968; Emilia, etal., 1968; McManus, 1965; Shor, etal.,
1968; Silver, 1969a, b).

The Department of Oceanography, Oregon State University, in a
joint effort with the United States Geological Survey (USGS), has sought
to gain further and more detailed information about the Oregon con-
tinental margin since 1967. Under this program an intensive and
systematic study of the sediments and structure of this area is being
carried out in an effort to better understand its geologic history, the
dynamics of sediment movement in the water column and on the sea
floor, and its possible economic mineral potential. Several published
and unpublished reports describe preliminary findings of this program
(Kulm, etal., 1968a, b; Clifton, 1968; Chambers, 1968; Mackay,
19 69; Bales and Kulm, 19 69; Kulm and Bales, 19 69; Spigai and Kulm,
1969; Roush, 1970; Neudeck, 1970).

The present study of the continental margin off southern Oregon
(Figure 1) is part of the overall USGS-sponsored program. Emphasis
in this study has been placed on the sediments and structure of the con-
tinental slope. Data concerning the continental shelf, derived from
unpublished research, will be used as supplementary information to
provide a more comprehensive picture of the margin as a whole.

Figure 1. Oregon continental margin and adjacent deep-sea areas.

Area of investigation is indicated by the horizontal rulings

The objectives of this study are:

1. to determine the structure of the continental slope, its rela-
tion to the structure of the entire margin, and its influence
on the present geomorphology of the slope;

2. to delineate the major bathymetric features of the slope and
determine their influence on the sedimentary processes
acting on the slope, both past and present; and

3. to develop a three-dimensional picture of the surface and
subsurface sediment distribution pattern, and relate this
pattern to the dynamic sedimentary processes operating in
the water column over the continental slope and on the sea
floor below.

SUBMARINE PHYSIOGRAPHY
General Physiographic Features

The geomorphology of the Oregon continental margin was first
described in detail by- Byrne (1962, 1963a, b). The continental mar-
gin off Oregon was called a continental terrace by Byrne and includes
only the continental shelf and slope. The Oregon shelf is narrower,
steeper and has its outer edge (the shelf break) in deeper water than
the world's "average" shelf as given by Shepard (1963). It is also con-
siderably wider in the north than it is in the south. The continental
slope extends from the shelf break to a depth of approximately 3000 m,
and is also wider, and has a gentler gradient, in the north than in the
south.

In general terms, the northern Oregon margin is marked by the
appearance of the Astoria Canyon and Fan system, a ridge -trough com-
plex below 800 m, and a prominent bench below 500 m, while the cen-
tral margin is characterized by submarine banks such as Heceta,
Stonewall, and Coquille (Maloney, 19 65). The southern margin is
noted for the numerous slope benches at various depths, the Rogue
Canyon, and numerous small submarine valleys.

In describing the southern Oregon margin, Byrne (1963b) noted
the appearance of "terraces" at various depths as well as the numerous

6
submarine valleys, including the Rogue Canyon. He also noted the
apparent antecedent nature of the "terraces" in relation to the sub-
marine valleys, implying that the valleys have subsequently dissected
the pre-existing "terraces. " Byrne (1963b) compiled a bathymetric
map in fathoms of the southern Oregon margin utilizing United States
Coast and Geodetic Survey (USC&GS) smooth sheets of surveys done
mostly in the mid- and late-1920's. More recently (1968), the USC&GS
issued a bathymetric chart of the same region (USC&GS Chart 1308N-
17). This chart was reconstructed from the data of the 1920 surveys
and recontoured in meters. It gives a somewhat more detailed picture
of the submarine physiography. The southern half of this chart, which
includes only the area of this study from Cape Blanco to the Oregon-
California border (42°00'N to 42°50'N) is used as the bathymetric base
map (Figure 2).

Twenty-five hundred kilometers of bathymetric profiles were
made on four Yaquina cruises (6706, 6708, 6711 and 6802) conducted
during the course of this study, utilizing a Precision Depth Recorder.
They have been used to supplement the existing bathymetric information
(Figure 3). Navigational control was obtained using dual Loran A
receivers and standard radar and navigational procedures which gave
a maximum positioning error of ± 2 km.

BLANCO

— 42° 30'

VALLEY

PORT ORFORD

0 5 0 10

w m n i ^3

KILOMETERS

CONTOURS \
IN
METERS

42° 30'-

Figure 3. Precision Depth Recorder track lines in the area of
investigation.

Physiographic Provinces of the Southern Oregon
Continental Margin

An analysis and comparison of previous work with the newer
bathymetric data described above and combined with sub-bottom pro-
files has enabled the writer to subdivide the southern Oregon continental
margin into a number of discrete physiographic provinces (Figure 4).
The provinces can be grouped as follows:

Continental Shelf

Upper Continental Slope
Klamath Plateau
Upper and Lower Plateau Slope
Cape Blanco Bench
Middle Bench

Lower Continental Slope
Lower Bench
Minor Submarine Valleys

Rogue Submarine Canyon

As can be seen from Figure 4, the boundaries have been

generalized somewhat to approximate the underlying structural limits

rather than follow the exact bathymetric contours, which only indicate

the boundaries of the present dissected surface. A number of selected

bathymetric profiles across the margin, which show the relation of the

various physiographic provinces with depth, are shown in Figure 5.

10

BLANCO

—42° 30'

VALLEY

PHYSIOGRAPHIC
PROVINCES

'CAPE BLANCO
PORT ORFORD

KILOMETERS

CONTINENTAL

ER

TEAU

I
SLOPE

SHELF

42° 30' -

124° 30

Figure 4. Physiographic provinces of the southern Oregon
continental margin.

11

KILOMETERS

rAPf
BLANCO

PORT ORFORD

42° 03' \ BROOKINGS

Figure 5. Selected bathymetric profiles of the continental margin.

12
Continental Shelf

The continental shelf off southern Oregon extends to depths vary-
ing between 120 m off the Rogue River to 200 m off Port Orford.
Directly off Cape Blanco the shelf break is difficult to determine
because the Cape Blanco Bench abuts the shelf edge and results in a
gradually decreasing gradient of approximately 1 ° down to a depth of
nearly 500 m before the first sharp break in slope (Figure 5, profile
at 42°50'N)„ In the area of investigation the slope width varies from
15 to 30 km; it is narrowest off Port Orford and Cape Sebastian and
widest near the California border and just north of the Rogue River
mouth.

Chambers (1968) has described the southern Oregon shelf between
42°20'N and 42°40'N„ He particularly noted the meandering contours
in this area, which indicates a thin sediment cover, and the exposure
of bedrock such as the Rogue River Reefs. Similar outcrops or shoals,
such as the Blanco Reef, occur southwest of Cape Blanco. Chambers
also noted the occurrence of submerged terraces which are especially
well defined at latitude 42°21'N. Here terraces occur at 35, 60, 70,
85, 100, 120 and 145 meters (± 5 m) and were most likely formed
during stillstands of sea level which interrupted the last major trans-
gression of the sea.

13
Upper Continental Slope

With the exception of the continental shelf, all of the physio-
graphic provinces recognized in this study lie within the boundaries
of the southern Oregon continental slope between 42°00'N and 42°50'N.
The slope is widest just off Cape Blanco and also south of Cape
Sebastian (Figure 5). The steepness of the slope ranges from an
average of 2° on the upper slope (above 1000 m) to an average of 5° on
the lower slope (below 1000 m) because of the presence of benches.

The upper slope is characterized by the presence of benches,
plateau slopes, and the Upper Rogue Canyon. It extends from the shelf
break to depths varying from 750 to 1250 m. The lower boundary is
the lowest extent of the gently inclined benches and/or the beginning
of the steeper lower slope. The benches are distinctive not only
because they occupy the greatest area of the upper slope, but also
because their gentler gradient suggests a different structural origin
from the steep escarpments above and below (Figure 5).

Klamath Plateau

The largest bench on the southern Oregon margin lies between
500 and 750 m within the southern part of the upper slope between Cape
Sebastian and the California border (Figure 5, profiles at 42°00'N to
42°17'N). This feature is the continuation of a large marginal plateau

14
which extends unto the upper slope off northern California as far south
as 41°10'N. It has been named the Klamath Plateau by Silver (1969a)
and this name is used here. The profiles of Figure 5 illustrate the
moderate steepness (1°30') and relief of the Klamath Plateau and show
how its width narrows from 25 km at 42°00'N to 1 0 km west of Cape
Sebastian. Silver (1 969a, p. 1 1 ) noted a maximum width of 30 km for
the Plateau on the northern California margin and also found that the
Plateau slopes gently to the south.

The relatively flat topography and bench-like appearance of the
Plateau terminates abruptly with the appearance of a topographic high,
or a series of highs, which mark its western edge (Figure 5, profiles
at 42°03'N, 42°10'N, and42°17'N). Silver ( 19 69a) and Kulm and Bales
(19 69 ) suggest that such topographic highs on the Klamath Plateau
represent anticlinal folds. These folds have dammed, or ponded, the
sediments behind them and have tended to smooth any underlying topo-
graphic irregularities. Other benches on the upper slope probably
have a similar origin; this underlying structural control may in fact
be more extensive and continuous than the boundaries of the Klamath
Plateau (Figure 4) would indicate. The Klamath Plateau, the Cape
Blanco Bench (Figure 4; Figure 5, profile at 42°50'N) and the large
bench areas on the upper slope north of Coquille Bank (Byrne, 1963b)
may actually represent a single bench controlled by a single anticlinal
fold system. The folds may even be contemporaneous in origin. The

15
ponded sediments have formed a single bench which has since been
partially obscured by slumping and dissected by submarine valleys.

Immediately above and below the Klamath Plateau are the Upper
and Lower Plateau Slope respectively (Figure 5, profile at 42°03'N).
The Upper Plateau Slope forms a transitional zone between the con-
tinental shelf and the Klamath Plateau, while the Lower Plateau Slope
forms a transition between the Plateau and Middle Bench.

Cape Blanco Bench

The Cape Blanco Bench is named after Cape Blanco on the
Oregon coast (Figures 2, 4, and 5). Although there is an almost con-
tinuous slope of about 1° from the shoreline at Cape Blanco down to a
depth of about 500 m, the Cape Blanco Bench extends from about 250
to 500 m. As was previously noted, the Cape Blanco Bench and the
Klamath Plateau may have formed as parts of a single bench system,
the connecting segment between the two having since been obscured by
the Upper Rogue Canyon and by slumping on the upper slope.

The extremely dissected nature of the Cape Blanco Bench dif-
ferentiates it from the Klamath Plateau. This can readily be seen in
the profiles at 42°45'N and 42°43'N (Figure 5). The dissected nature of
the Bench appears to be the result of a number of small north-south
trending channels which are restricted to this portion of the Bench and
may be structurally controlled.

16
Middle Bench

The Middle Bench is so named because of its occurrence midway
down the continental slope. It is exposed in the southern part of the
slope below 42°05'N at depths between 1000 and 1250 m and occurs
again at approximately the same depth at 42°3 6'N (Figure 5). It is
apparent that the two exposures of the Middle Bench are part of a con-
tinuous system, representing the second in a series of at least three
bench systems which extend the length of the southern Oregon margin
and probably beyond. From physiographic data alone, however, it is
not possible to determine whether these three systems also represent
three different structural episodes. The southerly exposure of the
Middle Bench marks the transition of the upper to the lower slope on
the southernmost Oregon margin.

Lower Continental Slope

The lower continental slope extends from a depth of 1000 to 1250
m down to 3000 to 3050 m where it meets the abyssal plain. However,
south of Cape Blanco Bench the lower slope may begin at depths as
shallow as 750 m. Between Cape Blanco and the Oregon-California
border the lower slope has an inclination from 4° 20' to 8° 10'.

In general the lower slope is marked by the existence of a num-
ber of small submarine valleys which extend from the upper reaches

17
of the lower slope down to the abyssal plain. There are approximately
eleven such submarine valley systems, excluding the Rogue Submarine
Canyon. The two most prominent valley systems are called the Blanco
Seavalley at 42°45'N, and the Brookings Seavalley at 42°05'N (Figures
2 and 4). Most of the valley systems drain only the lower slope,
extending from a depth of about 1000 to 1250 m. They terminate on the
sea floor at a depth of about 3000 m. Their average gradient is about
4°.

The Lower Bench is also exposed on the lower slope between
42°05'N and 42° 15'N at a depth between 2250 and 2500 m (Figure 5).
The topography shown in Figure 5 suggests that this bench may also be
part of a continuous system at this level, the third such system
identified on the southern Oregon slope. Exposures of this bench fur-
ther to the north on the lower slope may be absent due to sedimentation.
Byrne (1963b) cites other exposures of benches, or in his terminology
"terraces, " at various depths, such as those occurring at 1600 to 1700
m at 42°50'N.

Rogue Submarine Canyon

Byrne (1963b) recognized the Rogue Submarine Valley and placed
its terminus at a depth of approximately 1100 to 1200 m. However,
the present study shows that this depth only marks what is now termed
the Upper Rogue Canyon, and that this valley system is continuous to

18
the base of the slope to a depth of 3050 m„ The Upper Rogue Canyon
heads on the continental shelf at a depth of 145 meters and is located
some 12 miles northwest of the mouth of the Rogue River. From here
it continues to a depth of about 1500 m in a generally east-west direc-
tion. The Lower Rogue Canyon extends from this depth down to 3050 m
at the base of the slope (Figure 2), and has a general northeast-
southwest trend. As can be seen from Figure 2, the Lower Rogue Can-
yon is actually a continuation of a northeast-southwest-trending swale
which lies to the north of the Canyon and enters it at approximately
1500 m.

The writer believes that the Canyon system is continuous, and
although it may not be structurally continuous in its entirety, it is a
single valley system from shelf break to base of slope. Figure 6 shows
the major contours of the Rogue Canyon system together with a series
of north-south profiles across the axis and a longitudinal profile down-
axis. Structural control on the Upper Rogue Canyon is suggested in
the profiles C-C, F-F', G-G1, and I-I', which show a notch or bench-
like feature; this characteristic is not apparent on the profiles of the
Lower Canyon. The north side of the Upper Canyon slopes 8°, the
south side 15°; the steepness of both the northwest and southeast walls
of the Lower Canyon averages 12°. The entrance of the swale, which
marks the beginning of the Lower Rogue Canyon, is a gradual one. It
occurs between 1500 and 1750 m (profiles J-J' and K-K1, Figure 6),

19

CONTOURS '*«

-42° 30

DEPTHS 8 CONTOURS
IN METERS

VE X20

Figure 6. Generalized bathymetry and selected profiles across the
Rogue Submarine Canyon.

20
but a noticeable change in the axial profile is evident in profiles K-K'
and L-L,1.

The axial slope of the Rogue Canyon varies over its extent, with
the axis divided into five segments (Figure 6). The steepness of the
axis varies down canyon from only 1°50' at segment AB to a very steep
14° at EF, the lowest segment. The steepness of the Upper Canyon
is similar to that for the upper slope (2°, or 5° if the benches are .
ignored) which indicates that the Upper Canyon may be more or less in
equilibrium, or at grade with the surrounding upper slope. This would
tend to indicate either that the lower slope is accreting or up -building
faster than the Lower Rogue Canyon, or that the Lower Rogue Canyon
may in fact be down-cutting. These generalizations do not take into
account the added effects of uplift or subsidence. For example, during
a period of uplift the Lower Canyon would down-cut faster and thus have
a steeper gradient than the surrounding slope.

The axis configuration of the Rogue Canyon may also be an
important factor in determining whether a particular segment is eroding
or accreting. The axis is distinctly V-shaped in the upper reaches of
the Canyon, particularly between segments AB and BC. This suggests
an erosional character, but this is not particularly borne out by the
axial slope of these segments. The Upper Rogue Canyon may then owe
its V-shape to a structural origin. The Lower Rogue Canyon has a
generally more rounded shape. This indicates that sediment may be

21
accumulating in the axis of the Lower Canyon, although the steepness
seemingly contradicts this. In short, physiographic evidence alone may
not be sufficient to determine the character of the Rogue Canyon; how-
ever, sedimentological and structural evidence to be presented later
indicates that the Upper Rogue is stable or slightly erosional, while the
Lower Rogue Canyon appears to be accumulating sediment.

22

REGIONAL GEOLOGY

General Geology of Southwestern Oregon
and Northern California

The geologic history of the continental margin off southern
Oregon is directly or indirectly related to the adjacent geologic
provinces of the continent which lies landward of the margin. It is
pertinent, therefore, to review the geology not only of the possible
sediment source areas, but also of those areas whose geology and
structural history may be related to that of the margin. All or part of
the southern Oregon Coast Ranges, the Klamath Mountains, the Cas-
cade Mountains, and the northern California Coast Ranges lie within
southwestern Oregon and northern California (Figure 7).

Oregon's Coast Ranges are a series of coastal hills composed of
thick sequences of Tertiary volcanic and sedimentary rocks. They are
divided into northern and southern ranges which together stretch for
about 250 miles along western Oregon. The southern Coast Ranges
consist mainly of Eocene sedimentary and volcanic rocks, with younger
Mio-Pliocene and Quaternary formations present only near Coos Bay
and Cape Blanco. The Siuslaw, Umpqua, Coos, and Coquille are the
main rivers which drain this portion of the Coast Ranges. The middle
fork of the Coquille River is considered to be the province's southern
boundary (Figure 7). Structurally, the southern Coast Ranges consist

23

I24c

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123°

NORTHERN BOUNDARY
OF THE KLAMATH MT.
PROVINCE, INCLUDING OUTLIERS

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Figure 7. Geographic and drainage features of southwestern Oregon
and northern California.

24
of folded and faulted sediments and volcanics which were uplifted during
the mid-Tertiary to form a series of low hills with an average elevation
of 1500 feet.

Two formations within the southern Oregon Coast Ranges are
worthy of note. The oldest formation in this province is the Umpqua
Formation (Early to Middle Eocene) which consists mainly of inter-
bedded basalt and sandstones, with minor amounts of siltstones and
conglomerates. The Tyee Formation unconformably overlies the
Umpqua Formation and is the most widespread formation in the Coast
Ranges. It consists mainly of rhythmically-bedded micaceous sand-
stones and siltstones which grade upward into siltstones (rhythmites)
and are locally argillaceous.

The Klamath Mountains occupy the extreme southwestern corner
of Oregon south of the southern Coast Ranges and west of the Cascade
Range and extend into northwestern California (Figure 7). In Oregon,
the Klamath Mountains are drained by the Sixes, Elk, Rogue, Pistol
and Chetco Rivers, and in California by the Smith and Klamath Rivers.
These drainages are comprised of rugged hills and mountains with 2000
to 5000 feet of relief, and consist mostly of folded and faulted pre-
Tertiary strata which in places have been intruded by granitic and
serpentized ultrabasic rocks. The Klamath Mountains are much older
than any other part of western Oregon and probably contain the oldest
formations in the state. Both Paleozoic and Mesozoic volcanic and

25
sedimentary rocks are present, which have been altered locally to
schist, phyllite and marble. Irwin (1966) has applied the term "sub-
jacent" to denote the entire sequence of eugeosynclinal and plutonic
rocks within the Klamath Mountains which were folded and thrust-
faulted during the Late Jurassic Nevadan orogeny. They are dis-
tinguished from the sequence of younger rocks which unconformably
overlie them, to which he has applied the term "superjacent. "

The subjacent eugeosynclinal rocks range in age from Ordovician
to Late Jurassic (Kimmeridgean) and consist mainly of graywacke sand-
stones, mudstones, greenstones, radiolarian cherts, minor amounts
of limestone, as well as metamorphic equivalents of the foregoing and
abundant granitic and ultramafic intrusives. Irwin (1966) describes
the pattern of distribution of the rocks in the Klamath Mountains as
one of concentric, rudely arcuate belts, -which he divides from east to
west into the eastern Klamath, central metamorphic, western Paleozoic
and Triassic, and western Jurassic (Figure 8). All belts, except the
eastern Klamath, contain outliers of adjacent belts and contain some-
what linear ultramafic and granitic bodies which generally conform to
the arcuate pattern. The Western Jurassic belt in Oregon consists of
the Dothan, Rogue, and Galice Formations; the last, the youngest
known subjacent formation, is made up of slaty detrital rocks and a
schist which forms the western boundary of this belt and of the entire
Klamath Mountain province. The Dothan Formation is predominantly

EXriANAT ION

SUPERJACENT ROCKS

□

Rock* of Cenoioic age

Rock, of Lite Juraaaic

(Tithonien) to L»te

Cretaceous age

SUBJACENT ROCKS

Western Jurassic belt

Western Paleozoic and Triaasic
belt

Central met amorphic belt

_.

^

Eaatera Klamath belt

Granitic rocks

Ultramafic rocks, in both

subjacent and auparjacant

ter ranea

Includes iok gaooroic

roeas

10

20 30

40 MILES

Biology coapllsd and aodiflid
I roa St rand (1862 and I 864).
• il It and Pack (I 661 ), and

rain ( I 08 0 I

Figure 8. Geologic map of southwestern Oregon and

northern California.

27
a medium-grained, indurated sandstone with interbeds of dark-gray
or black mudstone, shale, siltstone, chert, and volcanics. These
formations, all Late Jurassic in age, were folded and thrust-faulted
during the Nevadan orogeny and were intruded by ultramafic, chiefly
peridotite, and granitic bodies mostly of quartz diorite composition.
The superjacent rocks are uppermost Late Jurassic or Early
Cretaceous in age and in Oregon consist of a pair of formations known
as the Myrtle Group. Middle and Late Cretaceous formations, the
latter at Cape Sebastian, cap the Mesozoic sequence of the Klamath
Mountains in Oregon, with later Cenozoic marine and river formations
forming the youngest overlying deposits.

The arcuate, concentric distribution of the lithic belts of the sub-
jacent rocks is the most obvious large-scale structural feature of the
Klamath Mountains (Irwin, 1966; Wells and Peck, 1961). The lithic
belts are separated by faults or by linear ultramafic and granitic bodies,
These faults are thrusts which commonly dip eastward and separate
eastward-dipping strata. They probably resulted from compressional
forces normal to the arcuate trend, accompanied by westward over-
riding of low angle thrust plates which occurred in pulses during the
Late Jurassic Nevadan orogeny and also in Late Cretaceous time.
Dott (1965) has noted that the predominant north-northeast thrust
pattern of the Klamath Mountains has been superimposed by a pre-
dominantly north-northeast pattern of intense shears in northern

28
California and southwestern Oregon. These shears occurred during
the late Cenozoic Cascadan orogeny (Dott, 1965).

The sediments and structure of the continental margin off southern
Oregon may reflect the complexity of southwestern Oregon, particurly
the varied geology and structural history of the Klamath Mountains.
The dominance of the Klamath Mountain rock types, and the fact that
they are drained by the major streams in the area, indicate that the
Klamath Mountains are the most likely source of sediment found on the
southern Oregon continental margin. Structurally, what is now the mar-
gin has probably also been affected by the major orogenies from the
Nevadan to the Cascadan, and may still be actively involved in
geologically recent movements.

The Cascade Mountains, the dividing line between eastern and
western Oregon, are a line of high volcanic peaks running north-south
the length of the state. In southern Oregon they are bounded on the
east by the Basin and Range Province and on the west by the Klamath
Mountains and are divided into two physiographic sub-provinces, the
Western Cascades and the High Cascades.

The rocks of the Western Cascades, which range in age from
Eocene to Pliocene (Peck, e_t al . , 19 64), include lava flows of pyroxene
andesite and beds of pyroclastic debris, both interbedded in places with
non-marine and shallow marine sediments. High Cascade Range rocks
are also predominantly pyroxene andesite and range in age from

29
Pliocene to Recent. The Klamath and Rogue Rivers have their head-
waters in these rocks, and flow westward from this source across the
Klamath Mountains of southwestern Oregon and northern California
(Figure 7).

Volcanic rocks in the Western Cascades differ from those in most
of the High Cascades; the former have a greater variety of petrographic
types and a larger proportion of pyroclastic rocks. A characteristic
greenish hue is also noted in most of the Western Cascade rocks due
to widespread chloritic alteration which resulted from late Miocene
uplift and erosion.

The northern California Coast Ranges, like most of the Coast
Range province in California, is a region of many separate ranges,
coalescing mountain masses and major structural valleys. It consists
of two different core complexes, one being the Franciscan rocks which
are a complex Jurassic-Cretaceous eugeosynclinal assemblage, and
the other consisting of Early Cretaceous granitic intrusions and older
metamorphic rocks (Page, 1966). The two core complexes lie adjacent
to one another separated by large-scale faults. Covering the core
material are thick sequences of Late Cretaceous and Cenozoic clastic
sediments which tend to conceal much of the complexity of the under-
lying "basement" core. The entire province is marked by continuing
crustal disturbances represented by folds, thrust faults, steep reverse
faults and strike -slip faults. These complex geology and structural

30
relationships have been studied by Reed (1933) and by Bailey, et al.
(1964). Extensive Mesozoic rocks peripheral to the Coast Range core
represent continuous thick sequences from the Upper Jurassic to the
Upper Cretaceous. Overlying these are the Cenozoic shelf and slope
deposits where marine sedimentary formations of nearly every epoch
and stage from early Paleocene to Pleistocene are represented in thick
accumulations (Taliaferro, 1943; Ogle, 1953; Christensen, 1966).

Page (1966) has recognized four major structural boundaries in
the California Coast Range; three of which, the Nacimiento Fault Zone,
the San Andreas Fault and the Sierran-Franciscan boundary, separate
the granitic-metamorphic core complex from the Franciscan core.
The fourth structural boundary is represented by the continental-
oceanic boundary at the base of the present continental slope, and
abruptly truncates the continental rocks and structures and separates
them from the ocean basin (Hanna, 1952; Uchupi and Emery, 1963;
Rusnak, 1966; Curray, 1966). The Sierran-Franciscan boundary is
represented by the South Fork Mountain Fault, a 300-mile long east-
ward-dipping thrust that separates the Klamath terrane from the
Franciscan complex of the Coast Ranges (Figure 7). The San Andreas
is presently active (Meade and Small, 1 9 66), but the Nacimiento Fault
is not (Page, 1966).

31

Coastal Features and the History of Sea Level Fluctuations

In addition to the resistant headlands of the southern Oregon
coast, such as Cape Blanco, Humbug Mountain and Cape Sebastian, the
most prominent coastal features of southern Oregon are the numerous
elevated marine terraces. These terraces were first studied by Diller
(1902) and later by Griggs (1945) and Baldwin (1945), and most
recently by Janda (1969). There are at least four prominent terraces
in the vicinity of Cape Blanco. The lowest, the Elk River Terrace,
which correlates with the Whiskey Run Terrace of Griggs, ranges in
elevation from 65 m above sea level near Cape Blanco to a point
below sea level south of Cape Blanco. Above this terrace, in ascend-
ing order, are the Pioneer, Seven Devils, Bills Peak, and Blue Ridge
terraces. The last terrace is elevated more than 1500 feet above sea
level in southern Oregon. Pleistocene sea level fluctuations are most
probably recorded by these terraces, as is evidence of regional dif-
ferential uplift and warping.

Faunal studies by Addicott (1964) and Richards and Thurber (1966)
on mollusk shells from the Elk River Terrace indicate a minimum age
for this level of 33, 000 years. Janda (1969) reports a 45, 000 year
minimum age for this same level. This evidence indicates the Elk
River Terrace to be late Pleistocene in age. Comparison of this data
with the sea level rise curves of Curray (1964) and Milliman and Emery

32
(1968) suggest uplift of this terrace at the rate of 2 m/1000 years.
Since the Elk River Terrace dips near, or below sea level south of
Cape Blanco, uplift is minimal in this area. The highest marine ter-
race, the "unnamed" terrace of Janda (1969), which may correlate
with the Bills Peak or Blue Ridge Terrace of Baldwin and Griggs, is
most probably Early Pleistocene or even Late Pliocene in age. The
rate of uplift on this level remains indeterminate, until it can be
precisely dated.

The rise of sea level which followed the last glacial advance and
which marked both the end of the Pleistocene and the beginning of the
Holocene is assumed to have begun about 18,000 years B. P. (Before
the Present) (Curray, 1965). This Holocene transgression of the sea
from about 125 m below present sea level to the present sea level may
have been interrupted by several minor regressions (Curray, 1965).
Assuming that these regressions did occur, they would have resulted
in stillstands of the sea at 18, 40, 65, 87, and 125 m below sea level,
according to Curray. These stillstands may be recorded as the sub-
merged terraces which are to be found at 35, 60, 70, 85, 100, 120,
and 145 m (± 5 m) on the southern Oregon shelf (Chambers, 1968). The
effects of uplift or subsidence along the southern Oregon coast preclude
precise correlation of these latter depths with the former; however,
possible placer accumulations found by Kulm e_t ah (1968a) at similar
depths suggest that these may be ancient shorelines.

33

SAMPLING AND ANALYTICAL PROCEDURES

Sample Collection and Processing

A total of 23 piston cores and ten dredge hauls was collected on
the continental margin off southern Oregon. All of the piston cores and
dredge samples were collected on cruises of the R/V Yaquina in 1967
and 1968 (Figure 9). The sample details are given in Appendix 1. A
modified Ewing piston corer, utilizing a multiple corer (Fowler and
Kulm, 19 66) as a trip weight, was employed for coring. The cores
were collected in plastic liners and cut into 3-meter sections aboard
ship. Each section was sealed, placed in a galvanized downspout and
kept at a temperature of 4°C until processed. Representative sedimen-
tary rocks were selected from each dredge haul, thin-sectioned and
described petrographically. A number of surface samples were taken
on the southern Oregon shelf and slope at selected stations with a
Shipek bucket-type sampler and a box corer. The shelf sediment
samples have been analyzed and described by Chambers (1968). The
core processing procedure is outlined in the flow chart in Figure 10.
Cores were sampled at various intervals for the different lithologies
and sediment textures, and at least every 50 centimers.

34

124*
— ,4<J«

CONTOURS IN METERS

— 142"
I24*

Figure 9. Location of piston core and dredge samples,

35

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36
Laboratory Analyses

Textural analyses were made on 305 samples to determine the
grain size distributions and variations for each of the sediment types.
A fine -grain analysis was made by utilizing a vacuum-operated pipette
and following standard techniques (Krumbein and Pettijohn, 1938).
Sand textural analysis (> 62 u) was made with a standard Emery
settling tube (Emery, 1938) as modified by Poole (1957). The per-
centages of sand, silt and clay were determined for each sample; in
addition, standard grain size parameters (Inman, 1952) were computed
for each sample using a CDC 3300 computer (Appendix 4). Coarse -
fraction analyses were made on approximately 350 samples to determine
the compositional variations of the major sediment types within each
core (Appendix 3). A split of at least 300 grains were identified and
counted using a binocular microscope following a grid pattern. A
count of the Radiolarian and planktonic Foraminiferan faunas was made
on all samples where it was possible to obtain a combined count of at
least 100 specimens for the two groups.

Heavy mineral analyses were made on 33 selected samples.
The heavy minerals were concentrated using tetrabromethane (specific
gravity 2. 96). The concentrate was mounted on a glass slide in Aroclor
(R. I. 1. 66) and at least 200-300 grains were identified and counted
(Appendix 6). The majority of the mineral grains had a median

37
diameter between 62 and 125 u, but no attempt was made to determine
the exact size variations within mineral groups or among various
samples. The light mineralogy of twelve selected samples was
analyzed using the feldspar staining techniques of Bailey and Stevens
(I960); the tabulated results are given in Appendix 5.

Organic carbon and calcium carbonate determinations were made
on 1 6 selected samples representing the various sedimentary environ-
ments using a LECO Automatic Carbon Analyzer. The method outlined
by Peterson (1969, p. 44) was followed in preparing the samples; the
formulas used in computing the percent total carbon, organic carbon
and calcium carbonate were also taken from Peterson (1969). These
values are recorded in Table 5 (see Sedimentology ), together with
those samples taken from cores 6711-2 and 6706-5, which were
analyzed by Peterson (1969).

The clay mineralogy of 22 samples was determined using X-ray
diffraction techniques; the samples were treated and prepared for
examination according to the methods outlined by Heath (19 68) except
for the use of the silver plug sample holder and the sample spinner
described below. The treated suspensate from the < 62 (a fraction of
each sample was allowed to settle until only the < 2 (jl fraction remained
in suspension. Only this fraction was collected and used in subsequent
analyses. In order to minimize differential segregation of the clay
mineral particles, approximately 1-1.5 milliliter of the clay suspension

38

was applied by means of a replicating pipette to the surface of a porous
silver plug which served as the sample holder. This procedure pro-
duced a thin highly-oriented aggregate. A solution of 60% glycerol and
40% 0. 3 molar magnesium chloride was sprayed on the oriented sample,
then dried for at least one -half hour and analyzed. This latter pro-
cedure enhanced detection of the montmorillonite clays by expanding
their lattices.

All the clay mineral samples were analyzed on a Phillips -Norelco
diffractometer with a Geiger-Muller counting tube. Samples were
scanned from 2° to 14° 29 at a goniometer speed of 1/2° 20 /minute,
and from 24° to 26° 20 at a goniometer speed of 1/ 8° 29 /minute. The
resulting diffractograms were produced on a linear scale strip chart
recorder running at 1/2 inch/minute. A sample spinner was employed
which spun samples in the plane of reflection.

The presence of montmorillonite, illite and chlorite was deter-
mined from the diffractograms by identifying the peaks at 16. 8 A,
9. 95 A, and 7. 05 A, respectively. Using the criteria of Biscaye (1964),
and comparing the 3. 54 A chlorite peak with the 3. 58 A kaolinite peak,
it was concluded that no kaolinite was present in any of the samples
and that this latter peak represented only chlorite. The semi-quantita-
tive method of Biscaye (1965) for determining the relative proportions
of montmorillonite, illite and chlorite by means of weighting factors was
employed to interpret the diffractograms. The resulting percentages

39
for each of the three major clay minerals in each sample are provided
in Appendix 7. Persistent minor peaks on several of the diffracto-
grams were identified as amphiboles.

40

STRUCTURAL FEATURES OF THE SOUTHERN
OREGON MARGIN

Regional Setting

The structural and tectonic pattern in the northeast Pacific
adjacent to Oregon and California has been examined and interpreted
by McManus (1965), Wilson (1965a, b), Vine and Wilson (1965), and
most recently by Tobin and Sykes (1968), Menard and Atwater (1968,
1969), McKenzie and Morgan (1969), Silver (1969a, b), and Atwater
and Menard (1970). The two fracture zones which lie directly west of
southern Oregon and northern California are the Blanco Fracture Zone
(Figures 1 and 11 A) and the Mendocino Fracture Zone (Figure 11A),
respectively. The former is a transform fault (Wilson, 1965b) which
separates the Juan de Fuca Ridge and the Cascadia Basin on the north-
west from the Gorda Ridge to the southeast (Figure 1). The ocean area
immediately north of the Mendocino Fracture Zone is one of active sea-
floor spreading at present (Vine, 1966) and this undoubtedly has had an
effect on the continental margin off northern California and southern
Oregon.

Gravity

Gravity data for the southern Oregon margin and the adjacent
ocean basin has been analyzed by Dehlinger (1969) and Dehlinger,

41

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ID

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1/5

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42
e_t al . (1967, 1968, 1970), The area west of southern Oregon has near-
zero average free-air anomalies (Figure 12) which indicates that the
area is essentially in isostatic equilibrium (Dehlinger, e_t al_ . , 1970).
In addition, the Blanco Fracture Zone does not appear to affect the
bathymetry of the southern Oregon margin (McManus, 1965) nor the
pattern of gravity anomalies (Figure 12).

On the other hand, the southern Oregon margin does exhibit a
pattern of three distinct gravity anomalies (Couch, 1970). A high nega-
tive anomaly (-80 to -100 mgal) is located over the base of the southern
Oregon continental slope (Figure 12). This anomaly may be due to the
dip of the Moho beneath the continent and the overlying wedge of sedi-
ments at the base of the slope which appear to thicken northward of
42°00'N (Couch, 1970). A positive anomaly of +1 to 410 mgal is
situated near the edge of the continental shelf and suggests the presence
of a structural high. Another negative anomaly (-40 to -60 mgal) is
situated over the continental shelf south of 42°30'N and is especially
well developed over the northern California shelf at about 41°00'N
(Figure 12). Couch (1970) suggests that this anomaly could represent
a large depression such as a basin or down-faulted structure which
may be filled with sediment. A small positive anomaly of +20 mgal
is present immediately southwest of Cape Blanco over the shelf and
upper slope and may be related to a structural high.

A distinct break in the gravity anomaly pattern is present on

43

44°r

if I CAPE BLANCO

124'

123"

44c

43*

g; CAPE MENDOCINO

42"

41'

40*

I27«

126*

125'

124'

123*

Figure 12. Free-air gravity anomaly map west of the southern
Oregon-northern California coast. After Dehlinger,
et al. , (1970). Shaded pattern denotes continental
slope. Arrow (A) indicates the position of the surface
trace of the west-southwest unconformity on the shelf.

44
the southern Oregon shelf (Figure 12, arrow A). The location and trend
of this break corresponds to that of a west-southwest unconformity
which Bales and Kulm (1969) have recognized as the dividing line
between two regions of differing structural character.

Magnetics

The pattern of magnetic anomalies off the southern Oregon and
northern California continental margins has been interpreted by
Emilia, et al. ( 1968) and Silver ( 1969a, b). Silver ( 1969a) notes the
presence of magnetic anomaly 3 (5 million years, Vine, 1966) near the
base of the continental slope off northern California (Figure 13, D).
He cites this as evidence for underthrusting of the continental margin
in late Cenozoic time.

Emilia, et al . (1968) have noted the anomalous magnetic character
of the crust off northern Oregon and the presence of high susceptibility
material which dips in toward the continent near the Mendocino Frac-
ture Zone (Figure 13, A). Only minor negative and positive anomalies
are observed over the continental shelf and slope off southern Oregon.
The small 100 to 150 gamma negative anomaly is the only distinctive
negative feature (Figure 13, A), while only small positive anomalies are
seen at the base of the continental slope (Figure 13, B). It is not clear
whether these small positive anomalies are a continuation of anomaly 2
(Emilia, et al. 1968; Figure 13, B and C) or whether they represent

Magnetic anomaly patterns off southern Oregon and northern California. A.
Total magnetic field. B. Positive magnetic anomalies. C. Magnetic anomalies
in the northeast Pacific. Anomaly 3 (arrow) is the westernmost positive anomaly
adjacent to the continental margin. D. Anomaly 3 as mapped on the continental
slope. E. Water-depth contour map off Oregon (700 m contour interval). Shaded
portion indicates shelf. Numbers indicate stations where source depths were cal-
culated. F. Source depths to magnetic anomalies. Contours in 2 km intervals;
source depths to nearest hundred m. A, B, E, and F after Emilia et aj.. (1968);
(modified after Raff, 1966); D after Silver (1969b).

46
anomaly 3 noted by Silver (Figure 13, C and D). It is also not clear
whether anomaly 2 of Emilia, et al . (1968), and anomaly 3 noted by
Silver are the same.

The source depth of the magnetic anomalies (Figure 13, E and F)
on the southern Oregon and northern California continental slope vary
between 3. 4 and 4. 5 km (Emilia, et al. , 1968), which agrees with
similar calculations made by Silver (1969a) for anomaly 3. This would
place the anomalies, depending upon water depth, within the second
layer (consolidated sediments and basalts). According to Vine and
Wilson (1965), the bulk of the magnetization rests in this thin (1 to 2
km) layer of basalts (layer 2) which overlies the main oceanic crust.
Deeper anomalies have been noted by Emilia, et al. at the base of the
slope off the Eel River in northern California (10. 1 km), and on the
northern Oregon margin (12. 5 and 14. 6 km). The sources for these
latter anomalies are deeper within the oceanic crustal layer.

Figure 13, B indicates the distinct difference between the mag-
netic character of the northern and southern Oregon continental shelf.
Large positive anomalies are observed over the northern Oregon shelf,
probably due to the presence of coastal volcanics which extend beneath
the shelf of this area (Emilia, ejt al . , 1968). In contrast, the southern
Oregon shelf is nearly barren of such anomalies which may reflect the
low magnetic susceptibility of the probable metamorphic rocks beneath
the southern shelf. Kulm, et al. (1968a) have analyzed magnetic data

47
of a more detailed nature for the continental shelf adjacent to the Rogue
River and have interpreted the anomalies as possible evidence for
placer deposits.

Heat Flow

Dehlinger, e_t al. (1970) report the heat flow values from 76 sta-
tions measured in the northeast Pacific. Those stations north of the

2
Mendocino escarpment have an average heat flow value of 2. 4 |j.cal/cm

sec. , which is one-third greater than the average for ocean ridges and
nearly double the value for ocean basins. Mesecar (1968) and Korgen
(19 69) have studied the sediment temperature gradients and heat flow
values over the Oregon continental slope. Mesecar measured heat flow
values at eight stations down the continental slope and on the adjacent
abyssal plain and noted a linear increase in the value of both the sedi-
ment temperature gradient and the heat flow with depth. He found the

2
mean heat flow values on the slope to be 2. 0 ucal/cm sec. and that

2
on the abyssal plain to be 3. 2 ucal/cm sec. Thus the continental

slope, and the deep sea environment adjacent to it are areas where the

heat flow is higher than normal, reflecting the presence of high heat

sources, which in turn may suggest the presence of a low density con-

vecting mantle.

48

Seismicity

The seismicity of the areas adjacent to the southern Oregon mar-
gin has been examined by Tobin and Sykes (1968) and Bolt, e_t al . (1968).
Earthquake epicenters concentrate along the Gorda Ridge, the
Mendocino Fracture Zone east of Gorda Ridge, and the Blanco Fracture
Zone between Juan de Fuca and Gorda Ridges (Figure 11, B). Accord-
ing to Dehlinger (1969), fault-plane solutions (Figure 14) indicate that
all but one of the relative motions in this area are consistent with ten-
sion in an east-west direction. Hamilton (1969) also postulates that
crustal extension has been the dominant tectonic movement during most
of Cenozoic time along the western United States. Bolt, et al. (1968)
postulate that the fault-plane solutions on the shelf north of Cape
Mendocino and in Gorda Basin are consistent with a right-lateral
strike-slip which trends about N40°W. They suggest that distortion
of the oceanic crust within Gorda Basin, as well as some degree of
underthrusting along the continental margin may account for the east-
ward component of strike-slip.

Dehlinger's interpretation (1969) of tension in an east-west direc-
tion negates the existence of regional compression and casts doubt on
the possibility of underthrusting along the southern Oregon-northern
California margin. However, Byrne, e_t al . ( 19 66) and Silver (1969a, b)
have cited evidence of compressional features on the margin off central

132° 130° 128° 126° 124° 122'

49

Figure 14. Fault-plane solutions of earthquakes (numbers 1-23) and
possible displacements from first motion studies (num-
bers 24-34) in the northeast Pacific. Arrows indicate
horizontal component of displacement; N indicates nor-
mal faulting. After Dehlinger, et^ al. , (1970).

50
Oregon and northern California, respectively. Silver (19 69a) notes
that the presence of anticlinal and synclinal folds on the northern
California margin corroborates his view of underthrusting in that area.
Compressional features on the margin may also be attributable to local
vertical forces rather than to large-scale underthrusting; hence, the
origin of these features is an open question at present and one which
requires further analysis.

Interpretation of the Tectonic Pattern

The tectonic pattern of the northeast Pacific is a complex one.
Silver (1969a, b), Dehlinger, et al . (1970), Bolt, et al . (1968), Menard
and Atwater (1968, 1969), Atwater and Menard (1970), and others have
developed various theories for the large-scale tectonic movements
involving the interaction of oceanic and continental lithospheric plates.

A general consensus of these workers indicates a predominantly
east-west direction of movement of these plates prior to Miocene time.
From Miocene time to the present, however, the movement of oceanic
and continental plates (i. e. the Pacific andNorth American plates, respec-
tively) with respect to one another has shifted direction to a northwest-
southeast trend. This major component of movement is a right lateral
strike-slip motion along the San Andreas -Queen Charlotte Fault systems
(Figure 11, A) accompanied by a smaller component of eastward under-
thrusting of the oceanic plate against the continent.

51
Continental Margin Structure

The structure of the continental margin off southern Oregon has
been investigated with the aid of detailed continuous seismic-profiling
surveys conducted during 1967, 1968, and 1969. Approximately 2000
km of track lines have been made off the southern Oregon shelf and
slope between Cape Blanco and the Oregon-California border (Figure
15). The profiling equipment used included an EG&G Sparker with both
5, 000 and 10, 000 joule capacity, a 20 cu. in. Bolt air gun and a 3. 5
KHz Edo transducer. Based on an analysis of these continuous seismic
profiles, a map has been compiled (Figure 16) which illustrates the
major structural features of the southern Oregon margin. The struc-
ture of the continental shelf illustrated in Figure 16 has been derived
from the interpretation of Bales and Kulm (1969).

General Structural Trends

The trend of both the major fault and fold systems on the margin
is generally north-south, parallel or sub-parallel to the margin (Bales
and Kulm, 1969). The major exceptions to this trend are the east-west
faults running through the Upper Rogue Canyon and the several east-
west folds on the continental shelf south of Cape Sebastian. It appears
from Figure 16 that the continental shelf and upper slope are character-
ized by folds, whereas the lower slope topography may owe its origin

52

Figure 15. Track line map of continuous seismic profiles. Shaded
area denotes the continental slope. After Kulm and
Fowler (1970).

53

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54
to large-scale faulting. A number of small-scale anticlinal folds
appear on the reflection profiles on the lower slope which have not been
plotted in Figure 16. These folds are smaller in amplitude and wave-
length than those of the upper slope and do not appear to detract from
the general trend noted above.

Nearly all of the faults determined, or inferred, from the reflec-
tion profiles and shown on Figure 16 appear to strike in a north-south
direction. They apparently are high-angle or nearly vertical and down-
thrown to the west. This has also been observed by Silver (1969a, p.
24). These faults appear to be normal faults; although data sufficient
to determine their true dip directions and attitude is lacking. The fault
pattern on the lower slope appears to be one of a typical block-faulted
region. Maloney (1965) classified similar faults off central Oregon as
step faults and the intervening benches and hills as step fault blocks,
although he was unable to determine if any displacement had occurred.
Step faults differ from normal faults in that they are compressional in
nature and both the hanging wall and foot wall move up, the foot wall
moving up farther than the hanging wall. The net displacement is
similar to that of a normal fault.

The faults on the southern Oregon margin appear to be normal
faults which are tensional in origin. If this is correct, then it must
be reconciled with the apparently compressional origin of the folds
which exist on the same margin (Figure 16). Even if both faults and

55
folds result from compressional forces, then the interpretation of
east-west tension noted earlier from fault-plane solutions (Dehlinger,
19 69) would still have to be explained.

A solution to this problem might be found by assuming a mech-
anism where both tension and compression are possible. Such a
mechanism has been postulated by Malahoff (1970) to account for
simultaneous underthrusting of oceanic crust under island arcs and
the formation of gravity faults in trenches; he suggests that a trans-
formed thrust mechanism may exist under trenches, whereby a gravity
fault located at the trench surface would become a thrust fault at depths
of 30 to 40 km beneath the island arc. Assuming that the southern
Oregon continental margin at its interface with the adjacent ocean
basin presents an analogous situation, then the existence of normal
gravity faults in an area of active underthrusting can be explained.

Continental Shelf

The southern Oregon continental shelf can be divided into two
regions which do not appear to be structurally related (Bales and Kulm,
19 69). The dividing line of the two regions is the surface trace of a
west-southwest trending angular unconformity within the late Cenozoic
sedimentary sequence between the Rogue River and Cape Sebastian
(Figure 16). This division can also be noted on the gravity map
(Figure 12, arrow A). A series of parallel and subparallel

56
northwest-southeast trending folds characterize the northern region,
with folds becoming gentler on the outer shelf and increasing in number
towards the coastline. The Gold Beach shear zone may extend off-
shore in a similar northwest-southeast trend. This latter feature
reflects the northwest-southeast trend of shears found in northwestern
California which were formed during the late Cenozoic Cascadan orogeny.

A north-south trending angular unconformity between the late
Cenozoic sedimentary sequence and the later Quaternary deposits is
present along the shelf break southwest of Port Orford (Figure 17, A,
at 26 km). The wedge of sediment above the unconformity suggests
that the shelf may be prograding in this area. The unconformity
apparently terminates north of the head of the Upper Rogue Canyon and
is not observed south of the Canyon.

The southern part of the shelf is characterized by a southwest-
trending basin off Cape Sebastian which extends westward across the
entire shelf (Figure 17, B) and southward to the southernmost portion
of the shelf (Figure 16). It appears to be only slightly deformed by
local folding and warping near the coastline (Bales and Kulm, 19 69;
Figure 16). West of this basin, an anticlinal fold underlies the shelf
edge (Figures 16 and 17, B). A north-south unconformity, similar to
the one in the northern region, lies between this anticline and the upper
slope (Figure 1 6).

Several prominent reflectors observed on the seismic records at

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the shelf break (Figure 18, A and C) suggest that the shelf is pro-
grading. The truncated surface (Figure 17, A) suggests that erosion
of the shelf has also occurred in some places off southern Oregon.
The erosion was caused by the numerous transgressions and regres-
sions resulting from Pleistocene glaciation. In addition, these sea-
level fluctuations were superimposed on a tectonically active area,
which could account for the complex structure of the shelf. Since
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sion, the shelf has prograded.

Upper Slope and Benches

The upper slope is characterized by bench-like features such as
the Cape Blanco Bench and the Klamath Plateau. In general these
benches are formed by the ponding of sediment, some of which is
slumped, behind anticlinal folds. The structure underlying Cape
Blanco Bench appears to fit this pattern (Figure 19). A synclinal
basin underlies the main part of the bench, while the anticline observed
at a depth of 350 m marks the western edge of the bench. The origin
of the small submarine valleys running north-south along the bench
surface is unclear. They appear to have originated from small faults
or between small folds within the synclinal basin which do not appear
at the surface. However, their present surface topographic expres-
sion appears to be mainly the result of erosion and small amounts of

59

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Figure 18. EDO subbottom profiles across the southern Oregon shelf
and base of slope. A. Shelf edge (42°46'N). B. Base of
slope (42°46'N). C. Shelf edge (42°40'N). D. Base of
slope (42°37'N).

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61
erosion and small amounts of valley filling.

The Klamath Plateau is the largest bench-like structure on the
southern Oregon margin (Figures 5, 20 and 21). Starting at latitude
42°10'N, it continues south on the margin to about 41°00'N (Silver,
1969a). Its western edge is marked by a large anticline, behind which
a substantial amount of sediment has ponded (Figure 21, at 36-37 km).
The flat-lying sediments which give rise to the Plateau are approxi-
mately 100 to 150 m thick, and thin to only a few meters immediately
behind the anticline. In comparison, approximately 150 to 200 m of
sediment are found on Cape Blanco Bench. The western flank of the
Plateau is a normal fault (Figure 21 at 41 km). Another normal fault
is inferred at the base of the Upper Plateau Slope at the extreme eastern
edge of the Klamath Plateau (Figure 17, B).

Slumping of sediment from the outer shelf down the upper slope
and Upper Plateau Slope may account for a number of small-scale, but
thick, sediment accumulations found along the upper slope (Figure 21
at 42 to 45 km; Figure 22 at 30 km). The Middle Bench (1000 to 1250
m) is a smaller -scale example of sediment ponding behind anticlinal
folds (Figures 20 and 21); normal faults also occur within the Middle
Bench (Figure 16).

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Lower Slope

The lower slope consists of small-scale, north-south trending
anticlinal folds and normal faults down-dropped to the west. They form
a series of sediment traps and step fault blocks down to the base of the
slope. The Lower Bench (2250 to 2500 m) is the most prominent bench-
like structure on the lower slope. The most prominent normal fault is
that forming a marginal escarpment at the base of the slope (Figure 21
at 64 km). Silver (1969a) also postulated the existence of such a fault
and others similar to it on the northern California margin. He finds
structural trends similar to those off southern Oregon (Figure 23).
He has recognized the Klamath Plateau and other ponded sediment
basins and benches and has described the northern California margin
as a series of north-south trending anticlinal folds and high-angle
normal faults down-dropped to the west (Figure 23). He believes his
interpretation of the structure is consistent with compression and
underthrusting directed broadly from the west.

In general the sediment cover drapes conformably over the under-
lying structures on the lower slope and appears to thicken near its
base. The thickest section is found at the base of the lower slope and
on the adjacent abyssal floor (Figures 18, A and D and 21). This thick
section (Figure 23, lineO) consists of flat-lying, relatively undeformed
strata which conformably overlie the irregular basement topography;

67
however, deformation of the sediments appears to increase with depth.

A continental rise is not well developed off southern Oregon and
probably reflects the lower sediment supply from the Rogue, Klamath
and other rivers which feed the area. In contrast, the continental rise
off the east coast of the United States results from the much larger
influx of sediment supplied by the numerous large coastal rivers.

Rogue Submarine Canyon

The Upper Rogue Canyon, situated from 150 to approximately
1500 m, is an east-west trending submarine canyon that is predomi-
nantly structurally controlled but exhibits erosional features (Figure
24). The Upper Canyon has about 400 m of relief and a distinctly sharp
V-shape. An east-west fault can be inferred from the rapidly-
steepening dips observed on either side of the Canyon which suggest
down-dragged strata, in addition to what appears to be a fault sliver
on the south wall (Figure 24). Other seismic reflection profiles across
the Upper Canyon show similar fault features. The fault is possibly
split into two branches: one strikes along the axis of the Canyon and
the other along the steeper south wall which has been down-dropped to
the north forming a small bench along part of the channelway (Figure
24). The fault terminates eastward on the shelf against a series of
small-scale en echelon faults at the head of the Canyon (Figure 16).
Little, if any, sediment accumulation exists in the Upper Rogue Canyon,

ROGUE CANYON

N

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Rogue Canyon (SP-71, 124°50'W).

69
suggesting that it may still be erosional in nature.

The Lower Rogue Canyon, trends in a northwest-southwest
direction and extends from 1500 to 3000 m. It has a much broader
cross-sectional profile (e.g., Figure 6, profiles K-K' and L-L') in
contrast to the Upper Canyon. It is at least in part an extension of the
northeast-southwest trending swale (Figure 2) which is located to the
north of the Rogue Canyon. The two valleys join at about 1500 m and
continue down to the base of the slope as one system. Good seismic
reflection profiles from the Lower Canyon are lacking, but it appears
from cores taken in the axis of the Lower Canyon that this portion may
be filling. The Lower Canyon does not appear to be offset by the Upper
Canyon fault and hence may be younger than the Upper Canyon.

The writer concurs with Bales (1969) in the belief that the fault
in the Upper Canyon may be of late Tertiary age, as is the S-shaped
anticline west of the Rogue River mouth (Figure 16). Erosion of the
Rogue Canyon was probably due to the influx of coarse clastic sediment
during the late Pleistocene, when sea level was only slightly above
150 m. Other evidence (See Sedimentology) indicates that the late
Pleistocene coarse sediment may have poured into the incipient faulted
channelway during this time, initiating the development of the Upper
Rogue Canyon.

No buried channels have been found on the continental shelf to
indicate a possible connection between the Rogue River mouth and the

70
head of the Rogue Canyon (Kulm, et al . , 1968a). However, the eastern
flank of the S- shaped anticline to the west of the Rogue River could have
acted as a pathway for sediment transport, during a lowered sea level.
In a similar manner, other shelf structures, such as those now
observed southeast of Port Orford, could have acted as pathways for
sediment transport north along the shelf by-passing the Upper Rogue
Canyon. If such a flow were diverted southwestward across the slope
by banks or rock reefs, a feature similar to the swale on the
could easily have formed.

Continental Margin Structure in Relation to the Regional Setting

Various theories can be developed to explain the evolution of the
southern Oregon margin, each of which is dependent upon a different
interpretation of the regional tectonics in the northeast Pacific. One
interpretation of the magnetic data suggests that ocean-floor spreading
is occurring eastward from the Juan de Fuca and Gorda Ridges and
that this new crust is underthrusting beneath the southern Oregon
and northern California continental margin (Silver, 1969b). However,
based on fault plane solutions Dehlinger, (19 69) and Dehlinger, et al.
(1970) believe that the region is presently experiencing tension in an
east-west direction.

The structure of the southern Oregon margin does not resolve
this dilemma. The north-south fold system indicates compression

71
directed from the west, while the north-south faults are ambiguous in
that they appear to be normal tensional faults down-dropped to the west.
They may also be compressional step faults (i„ e. vertical faults where
the movement is mainly in the horizontal plane) or simply slump
features produced by sediment loading. If underthrusing is occurring
along the southern Oregon margin, the leading edge of the descending
oceanic lithspheric plate could produce components of both tension and
compression. Tension would result in subsidence and down-dragging
at the base of the slope, giving rise to normal gravity faults. Compres
sion would produce uplift directed to the east forming compressional
north-south trending folds. If such a mechanism operated along a
structural hinge line along the present shelf break or upper slope, the
resultant structural pattern would be similar to that mapped in Figure
16. In an analogous situation that was described previously, Malahoff
(1970) was able to reconcile both tension and compression existing in
an area of active underthrusting. It would appear then that the com-
plex of structures on the southern margin are compatible with under-
thrusting.

Several additional points need to be considered in attempting to
explain the margin structural pattern. First, the margin off southern
Oregon and northern California may have been more affected by com-
pression than the margin off central and northern Oregon. Second,
the warped coastal marine terraces near Cape Blanco indicate

72
differential uplift in the vicinity of Cape Blanco. Third, faunal studies
(See Stratigraphy) indicate that both uplift and subsidence has occurred
on the southern Oregon margin. These facts indicate a complex struc-
tural history for the southern Oregon margin; one that has varied with
time.

Several current interpretations of the regional tectonics do take
into account changing structural trends with both direction and time,
and may serve to explain many of the complex structures on the southern
Oregon margin. Dehlinger (1969) has postulated that much of the move-
ment of crustal plates, especially between the Gorda and North American
plates, may be due to differential slippage caused by the varying effects
of tidal friction on the low velocity layer between the plates. He also
notes that the interaction of two plates at the continental margin need
not be resolved by underthrusting alone, but can also be accounted for
by local vertical uplifts. These uplifts may express themselves as
fold-like diapiric structures which are not compressional in nature,
and probably not unlike the small-scale folds observed on the margin
in Figures 20 and 21. Silver (1969b) has postulated a general eastward
movement of the Gorda Plate, but with a larger component of right
lateral slip of the plate along the continental margin which moves the
plate mostly in a north-northwest direction. Wilson (1965a) first
theorized that sea-floor spreading and the resulting direction of plate
motion has changed to its present northwest-southeast sense due to

73
rapid outbuilding of the margin sometime in the mid-Teriary, perhaps
since Miocene time. Atwater and Menard (1970) have shown that this
change in direction of sea-floor spreading may have begun as early as
55 million years ago (Eocene time).

These theories suggest that some degree of spreading and under-
thrusting occurred on the margin prior to mid-Tertiary time. Sub-
sequent to mid-Tertiary time the direction of movement of continental
and oceanic plates shifted to the northwest-southeast. Late Pliocene
or early Pleistocene may have been a time of renewed underthrusting
(Silver, 1969a); if so evidence for this episode should be found in the
structure and unconformities on the northern California and southern
Oregon margin. The current effects of underthrusting are considered
by Silver (1969b), Dehlinger (1969), and others to involve only the
southern portion of the Gorda Plate, affecting only that part of the mar-
gin lying between Cape Sebastian (Oregon) and Cape Mendocino. The
northern part of the Gorda Plate above Cape Sebastian may not be
actively underthrusting at present, as is suggested by the fact that sedi
ments have begun to accumulate at the base of the northern Oregon-
southern Washington slope in the form of submarine fans, which may
eventually coalesce to form an incipient continental rise. Localized
uplift and subsidence may also play an important role in the present
structural evolution of the southern Oregon margin.

74
STRATIGRAPHY

Unconsolidated Sediments

The geologic history of the southern Oregon margin can be inter-
preted through a correlation of the various sedimentary units which
occur on the margin and their continental counterparts. The strati-
graphic work of Duncan (1968), Duncan, et al. (1970), and Griggs, et al.
(1970) in the deep-sea environments west of the Oregon margin provide
a basis for comparison with the results of this study and with other
interpretations of the faunal stratigraphy of the Oregon margin,

Planktonic Foraminifera-Radiolaria Abundance

Duncan (1968) and Duncan, et al. (1970) reported the development
of the first paleoclimatic stratigraphy for the deep-sea environments
off Oregon, which is based mainly on the Radiolaria (R)/planktonic
Foraminifera (P) ratios during the late Pleistocene and Holocene.
Griggs (1969) and Griggs, et^ al. (1970) expanded this stratigraphy to
give a more detailed paleoclimatic curve for the last 12, 500 years in
Cascadia Basin. The stratigraphy developed by both Duncan and Griggs
closely matches the glacial advances and retreats noted by Armstong,
e_t al_. (1965) on the continent. Since 35,000 years Before the Present
(B. P. ), there have been three warm periods recognized within the
Pleistocene and marked by an increase in Radiolaria within the pre-
dominant planktonic Foraminifera interval. These have been dated at

75
34, 000 years B. P. , 28, 000 to 25, 000 years B. P. , and 18, 000 to 16, 000
years B. P. The most abrupt change in the fauna occurred about 12, 500
years B. P. in Cascadia Basin and is considered the end of the Pleisto-
cene and the beginning of the Holocene (or post-glacial) in this area
(Duncan, 1968). The pelagic and hemipelagic sediments high in plank-
tonic Foraminifera, principally Globigerina pachyderma and G. bulloides,
characterize cooler or glacial periods, while Radiolaria-rich sediments
characterize the warmer or interglacial periods. The abruptness of the
transition depends on the sedimentation rate, which determines the length
of the transitional interval between the Holocene and late Pleistocene.

Griggs ( 1 9 69 ) and Griggs, et al_. (1970) noted that several cooler
periods, marked by Globigerina-rich intervals, occur within the
Holocene since 12,500 years B. P. These have been dated at 5000 to
4000 years B. P. and 2000 years B. P. ; the former can be dated
precisely since it usually occurs just above a Mazema ash layer which
dates at 6600 years B. P. , while the latter is somewhat tenuous.

In an effort to determine whether or not these stratigraphic hori-
zons occur in the continental margin deposits, an analysis similar to
that performed by Griggs and Duncan was employed with the sediments
examined in this study. Figure 25 illustrates the R/P ratios deter-
mined for five cores (6706-2, 6711-1, 6711-2, 6711-6, and 6711-8).
In each core a combined count of at least 100 Radiolaria and/or
planktonic Foraminifera were obtained. The high sedimentation rates,

LOWER SLOPE

ROGUE CANYON

.-*.-_.

zzr^r

^

^

CONTINENTAL SHELF

1

□

Figure 25. Summary of lithologic and stratigraphic information from piston cores from the
continental margin and adjacent Blanco Valley. Data for box cores 6708-44 and
6802-BCB after Chambers (1968).

77
particularly evident in the lower slope cores, caused the dilution of the
biologic material by detrital grains and precluded the calculation of
R/P ratios in most other cores. The variation in the R/P ratio in
cores 6706-2, 6711-1 and 6711-2 have been dated using radiocarbon
dates and/or the presence of Mazama ash.

As can be noted from Figure 25, the R/P ratios in core 6706-2
(upper slope and benches) indicate an age for the core which ranges
from 28, 000 to 25, 000 years B. P. near the bottom to 18, 000 to 1 6, 000
years B. P. near its surface. Since the top of the core is considered
to be present, it appears that the surface sediment in this core and
that from the surrounding area may be relict sediment of Pleistocene
age. The low R/P ratio in cores 6711-1 and 6711-2 (lower slope)
probably represents the 5000 to 4000 years B. P. interval of Griggs,
et_ al . (1970). This interval correlates with a similar interval in cores
6604-12 and 6604-11 from Blanco Valley (Figure 25), and reflects
similar sedimentation rates for the two environments. The ages
inferred by the R/P ratios plotted for cores 6711-6 (lower Rogue
Canyon) and 6711-8 (lower slope) have not been confirmed by dating.
The topmost Foraminifera-rich zone in each core may represent the
last cool period in the Holocene (2000 years B. P. ); however, this
would produce an unreasonably high rate of sedimentation. It is more
reasonable to assume they represent the 5000 to 4000 years B. P.
interval until more precise dating can confirm their age.

78
Mazama Ash

The Mazama ash which erupted from Mt. Mazama (Crater Lake,
Oregon) 6600 years ago and blanketed large areas of the Pacific North-
west is a good stratigraphic horizon in deep-sea and continental mar-
gin sediments because of its widespread occurrence. Nelson, et al.
(19 68 ) describe the occurrence of the ash in the various deep-sea
environments of Cascadia Basin and postulate that ash deposition was
effected by turbidity currents and not through aerial fallout. They sug-
gest that the ash accumulated on the continental margin prior to its
transport to the deep sea. The ash identified in this study has been
verified as Mazama ash through comparison of its refractive index
(1. 505) with known samples as identified by Nelson (1968), Duncan
(1968) and others. The depth of maximum abundance of the ash has
been used as the stratigraphic horizon dating approximating 6600
years B. P. in six cores (6711-1, 6711-2, and 6708-38, lower slope;
6706-6, upper slope; and 6708-23 and 6708-25, shelf) from the con-
tinental margin (Figure 25). While the depth of occurrence of the ash
varies within the margin or deep-sea environments, it does reflect
differences in sedimentation rates. It is significant to note that the
ash was found in only one upper slope core (6706-6) which suggests
that older sediments persist to the surface in upper slope environments,
or at least that the sedimentation rate is markedly lower here.

79
Radiocarbon Dating

In order to establish the absolute ages of certain lithologic or

biologic events recorded in the cores, and to facilitate correlation

14 12
among cores, the radiocarbon (C /C ) dating method was employed.

Samples from five selected cores (6706-2 and 6706-3, upper slope;
6711-2, lower slope; 6708-37, Rogue Canyon; 6708-42, shelf) were
dated utilizing the total carbon content (Figure 25; Appendix 2). Two
other dates were obtained by Chambers (1968) from box cores taken
on the southern Oregon shelf (6708-44 (42°35. l'N, 124°41.0'W, 150 m)
and 6802-BCB (42°35. l'N, 124°41. l'W, 150 m)); these utilized car-
bonate carbon from mollusk shells found in the cores.

Faunal Stratigraphy of Consolidated Sediments

The benthic and planktonic Foraminifera in two selected dredge
haul samples (6708-36-1 and 6802-D3-1) and from consolidated rock
fragments in the basal 20 cm in one piston core (6706-3) were identified
and described in detail by Fowler (1970). His conclusions regarding the
faunal assemblages are shown in Table 1.

Both uplift and subsidence are inferred from the nature of the
faunal assemblages in the consolidated rocks. In the two samples from
the upper slope (6708-36-1 and 6706-3-11-2) the faunal data suggest that
uplift has occurred on the southern Oregon margin. These data

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81
corroborate the findings of Byrne, e_t al . (19 66). Although the amount
of uplift is less than the maximum reported by Byrne, et al. , for the
central Oregon margin (60 m to over 1000 m), it is within their lower
range of values.

Faunal data from the lower slope sample (6802-D3-1) suggest that
a significant amount of down-faulting or subsidence has occurred on the
lower margin. Movement and deformation on the margin was subsequent
to either "early Pliocene" or "mid-Pliocene. " However, the three
samples are all approximately the same age (Table 1). This suggests
that both local uplift and subsidence could have occurred at about the
same time, with the uplift restricted to the upper slope and shelf and
the down-faulting or subsidence restricted to the deeper portions of the
slope.

Rates of Sediment Accumulation

The stratigraphic horizons established at various depths within
the unconsolidated sediment section permit the calculation of approxi-
mate rates of deposition. By noting the depth interval between a par-
ticular horizon and the surface (which is assumed to be at zero or
present time) and by averaging this interval over the time represented,
an estimate can be obtained of the sedimentation rates within the dif-
ferent depositional environments (Table 2).

The sedimentation rates determined for the upper slope, benches,

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83
and the Upper Rogue Canyon are moderate, averaging about 10 cm/ 1000
years (Figures 29 and 31). In contrast, the lower slope is experiencing
the highest rates of sediment accumulation, on the order of 40 to 50
cm/1000 years (Figures 30 and 31). Sedimentation on the shelf varies
widely from a very low to a moderately high rate and ranges from 5 to
approximately 50 cm/1000 years (Table 2; Figure 28). These com-
parisons assume that the surface of all cores represents present time,
and that sedimentation continued uniformly at the calculated rate during
the stated time interval. If the surface or near -surface sediment of
the upper slope cores (670602, 6706-3, 6708-37) and the shelf core
(6708-42) is assumed to be late Pleistocene in age as stratigraphic
data suggest, then the calculated rates would have to be increased to
about 15 cm/1000 years in each core (25 cm/1000 years in the case
of core 6708-42) and would represent only late Pleistocene sedimenta-
tion. Consequently, the Holocene sedimentation rate for these shelf
and upper slope cores would be nil. In any case, the upper slope
environments appear to be receiving less sediment than the lower slope.
This is also demonstrated in the Rogue Canyon, where the rate cal-
culated in the lower Canyon (core 6711-6) is eight times greater than
that determined from the upper Canyon (core 6708-37). This suggests
that the lower Canyon may be more closely related to the rapidly-filling
swale (core 6708-38) than to the upper Canyon, and hence the lower
Canyon is filling much faster than the upper Canyon.

84
Estimates of the Holocene sedimentation rate on continental
slopes vary widely. Gorsline and Emery (1959) calculated that the
green muds of the southern California Borderland province deposit
at a rate equivalent to 72 cm/1000 years, while the estimates given by
Moore (1966) for the total basin-fill in the same area range from 4 to
160 cm/ 1000 years. Carlson (1968) notes that the rate of deposition on
the floor of Astoria Canyon on the northern Oregon margin ranges
from about 50 cm/1000 years near the mouth to more than 75 cm/
1000 years near the head, but he estimates a 10 cm/1000 years
average for the hemipelagic deposition on the adjacent protected con-
tinental slope. Duncan (1968) calculated postglacial (Holocene) rates
of deposition ranging from 29 cm/1000 years to 100 cm/1000 years in
the deep-sea area adjacent to the base of the continental slope. Thus
the rates shown in Table 2, especially those from the lower slope,
are not unreasonable when compared to the foregoing estimates. It is
therefore suggested that the lower slope is presently accumulating
sediment three to four times faster than the upper slope.

85

SEDIMENTOLOGY

The sedimentological character of continental margin deposits
can provide important clues to the provenance and dispersal paths of
the sediments, as well as to the physiographic and tectonic framework
of sedimentation in the margin environment. In turn, a knowledge of
margin sedimentation patterns, particularly with regard to the role of
the continental slope as a temporary resting place for sediments during
their transport from shelves to final deposition in deep-sea basins, is
an essential link in the interpretation of the complete cycle of oceanic
sedimentation.

Unconsolidated Sediments

Classification and Distribution of Sediment Types

Three main sediment types were observed in the cores taken on
the southern Oregon margin. These are olive gray lutite, gray lutite,
and sand-silt layers. Although not part of a particular classification,
these terms have been used previously (Duncan, 1968; Griggs, 1969)
to describe similar deposits, and are based primarily on character-
istics observed by megascopic examination supplemented with the use
of a binocular microscope. The term lutite (Ericson, e_t al_ . 1961;
Heezen, e_t al . , 1966) implies a sediment composed chiefly of silt-

86
and clay-size particles, or mud. The proportion of the two con-
stituents may vary over a wide range from a nearly pure clay to a
sediment composed almost entirely of silt, but most often the lutite
in this study is a clayey silt (< 50% clay) or silty clay (< 50% silt)
according to Shepard's classification (1954). The distinction between
olive gray lutite and gray lutite is based solely on color. Sand-silt
layers refer to terrigenous sand or coarse silt-size particles com-
posed chiefly of detrital mineral grains.

At this point it is important to note that in most cases a physio-
graphic province corresponds to an environment of deposition. There-
fore, in subsequent discussions relating to the margin sediments, the
term "physiographic province" will also imply the depositional environ-
ment represented by that province, and conversely, the term
"depositional environment" will also imply the particular physiographic
province which includes that depositional environment. Any exception
to this will be explained fully in subsequent discussion.

Using the data from the textural analysis, and plotting each
sample according to its sediment type, depositional environment and
age, the sediments were grouped according to the textural classifica-
tion of Shepard (1954) (Figure 26). Similarly, the coarse -fraction
constituents of each sample are plotted on a triangular diagram whose
three end-members are grouped according to origin and hydrodynamic
character: the detrital group consists of those mineral grains and

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rock fragments (except mica) requiring strong transporting currents;
mica-plant fibers -volcanic glass are platy and/or low-density grains
sensitive to current action; the biologic-authigenic group consists of
material which accumulates in situ such as benthic and planktonic
Foraminifera, Radiolaria, fecal pellets, glauconite and pyrite
(Figure 27). The location and distribution of the major and minor
sediment types within each core illustrated for the four main physio-
graphic provinces: shelf (Figure 28), upper slope and benches (Figure 29),
lower slope (Figure 30) and Rogue Canyon (Figure 31).

Olive Gray Lutite

Olive gray lutite is the most widespread and abundant sediment
type (Figures 28-31). It varies slightly in color, from olive gray
(5Y 3/2, Geological Society of America Rock Color Chart, 1963) to
light olive gray (5 Y 4/2). The texture also varies, but it is typically
a homogeneous, poorly sorted silty clay or clayey silt, with occasional
coarse constituents (Figure 26). The olive gray lutite is character-
istically poorly consolidated and relatively high in organic matter and
moisture content. Although found in every environment, it especially
dominates the lower slope (Figure 30), where the coarse fraction com-
monly is composed of more than 50% biologic material (Figure 27).
In contrast, the majority of the coarse fraction in samples from the
upper slope and benches consists of detrital minerals (Figure 27).

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Figure 28. Lithology of piston cores from the southern
Oregon continental shelf. Sediment ages are
indicated next to the core. Circled numbers
indicate rates of sedimentation. Physiogra-
phic province boundaries reflect present dis-
sected surface of margin. Data for box core
6802-BCB after Chambers (1968).

UPPER SLOPE
AND BENCHES

5 O 5 10

HUH !— =]

KILOMETERS

LEGEND

= ASH

_ OLIVE GRAY
" LUTITE

= SAND-SILT
= GRAY LUTITE
3 =FORAMS

= GLAUCONITE

ROCK
FRAGMENTS

Figure 29. Lithology of piston cores from the upper con-
tinental slope and benches. Sediment ages are
indicated next to the core. Circled numbers
indicate rates of sedimentation. Physiographic
province boundaries reflect present dissected
surface of margin.

Figure 30. Lithology of piston cores from the lower slope.
See legend and caption of Figure 29 for explan-
ation.

Figure 31. Lithology of piston cores from the Rogue Sub-
marine Canyon. See legend and caption of
Figure 29 for explanation.

94
Mica, plant fibers and glass are rarely more than 20% of the coarse
fraction in any sample.

All of the olive gray lutite observed by Duncan (1968) in the
adjacent deep sea was postglacial (Holocene); however, at least some
of that sampled from the upper slope and Upper Rogue Canyon (cores
6706-2 and 6708-37, Figures 25, 29 and 30) may be late Pleistocene
in age. In both cases gray lutite occurs at the base of the core. As
Duncan (1968), Carlson (1968) and Nelson (1968) have observed, the
change from gray lutite to olive gray lutite may mark a significant
time boundary, the transition from late Pleistocene to postglacial
(Holocene) time. If the R/P faunal ratio indicates that this transition
took place about 12,500 years B. P. (Duncan, et al . , 1970) than the
gray to olive transition should have occurred at about the same time
and would be observed at approximately the same depth as the shift
from abundant planktonic Foraminifera to abundant Radiolaria. A
transitional type sediment, light olive gray, lutite often occurs between
the gray and olive varieties in the deep sea, but appears to be
restricted to postglacial time (Duncan, 1968).

The color transition has been noted in four slope cores (6706-1
and 6706-2 from the upper slope; 6706-4 and 6708-37 from the Upper
Rogue Canyon), with one other core (6706-3 from the Klamath Plateau)
composed almost entirely of gray lutite (Figures 25, 29 and 31). Two
of these cores (6706-1 and 6706-4) lack sufficient stratigraphic

95
information to confirm the above hypothesis. However, a core adjacent
to each of these from a similar environment (6706-2 and 6708-37,
Figures 29 and 31, respectively) clearly indicates that the color shift
occurs earlier than 12,500 years B. P. (Figure 26). This indicates
that either the deposition of olive gray lutite began much earlier in the
upper margin environments than in the deep sea and hence may be as
old as late Pleistocene, or that the olive gray lutite in cores 6708-37
and 6706-2 should have been classed as gray lutite, a distinction not
apparent from either megascopic examination or subsequent analyses
(Figures 26 and 27).

Gray Lutite

Gray lutite commonly occurs as a clayey silt or silty clay
(Figure 27) and varies in color from olive gray (5Y 4/1) to dark
greenish gray (5GY 4/1) or medium dark gray (N4). It is generally
cohesive and stiffly compacted, and hence tends to be better con-
solidated than the olive gray lutite. The coarse fraction content of
the gray lutite comprise only two or three percent of the total sedi-
ment, and consist mainly of detrital grains with only 25 to 40%
biologic material (Figure 27). As noted above, gray lutite was
penetrated only in cores from the upper slope and Upper Rogue Can-
yon. If it is indicative of the late Pleistocene, it probably underlies
the thicker accumulation of Holocene sediment on the lower slope.

96
In continental margin environments, gray lutite cannot be distinguished
from olive gray lutite on the basis of texture (Figure 26) or coarse
fraction (Figure 27). It may be distinctive initially only in its color
until its age can be established. Gray lutite from the continental mar-
gin is similar texturally to that found by Duncan (19 68) in adjacent
deep-sea environments, and closely resembles the gray clay found by
Griggs (1969) in Cascadia Channel. However, the coarse fraction in
these latter types often contains 75% or more biologic material,
principally planktonic Foraminifera and Radiolaria, as compared to
the lesser amounts found in gray lutite from the margin. This reflects
the increased pelagic rain of shells and tests and the smaller amount
of detrital material found in deeper and more distant environments.

Sand-Silt Layers

Terrigenous sand and coarse silt occur in all environments and in all
cores except 6711-1 (Figures 28-31). It is the dominant sediment type
in cores from the continental shelf (including 6706-7 from the head of
the Rogue Canyon) and from the Cape Blanco Bench. It occurs in these
latter environments in thick sequences, and in all other environments
as distinct layers with sharp and well-defined contacts interbedded
with olive gray lutite or gray lutite. X-radiographs revealed that all of
the sands sampled were essentially featureless and structureless with
no grading observed within a unit or layer except for some minor

97
grading noted in core 6706-5 from the Upper Rogue Canyon. Texturally,
this type varies from sandy silt to sand, but still can easily be dis-
tinguished from the lutites (Figure 26). Generally the coarse fraction
consists of more than 75% detritals.

The age of the sand-silt layers in the various environments is
more difficult to determine, and can be either Holocene or late
Pleistocene. Coarse fraction analyses reveal an abundance of iron-
staining, solution pitting, and alteration in the sand-silt materials
from the surface of both the shelf and Cape Blanco Bench, but these
characteristics are absent from other parts of the slope. The thick
accumulations of sand-silt on Cape Blanco Bench are more suggestive
of shelf sands than of the thinner sand-silt layers on the lower slope.
Chambers (1968) recognized staining and alteration in sands from the
southern Oregon shelf; Emery (1965, 1968) notes that staining and
alteration of shelf sands may be indicative of their relict nature. It
is postulated here that the sand-silt on the surface of Cape Blanco
Bench is also of a relict nature, and may be late Pleistocene in age.
However, all of the sand-silt layers in the cores from the lower slope
are Holocene.

Minor Sediment Types

Several minor sediment types were observed which were dis-
tinctly different from the three main types just described, but were not

98
widespread enough either vertically or areally to warrant their clas-
sification as major sediment types. These types usually consist of
sediments whose coarse fractions contain appreciable amounts of
distinctive constituents. The most important of these were:

Foraminifera-rich lutite (6706-2 from the upper slope; 6711-1

and 6711-2 from the lower slope);
volcanic ash-rich layers, usually lutite (6708-23 and 6708-25
from the shelf; 6706-6 from the wall of the Upper Rogue
Canyon; 6711-1, 6711-2, and 6708-38 from the lower slope);
shell layers (6708-42 from the shelf);

rock fragments (6706-3 from the Klamath Plateau); and
glauconitic layers, usually sandy (6706-1 from Middle Bench,
6706-3 from the Klamath Plateau, and 6706-4 from the
Upper Rogue Canyon).
The glauconitic layers occur at the surface of two cores from
the upper slope close to the relict surface sediments. Glauconite is
normally authigenic, or formed in place, and is often relict (Emery,
1968). Because of its association with relict, or possibly relict
sediments, it is postulated that the glauconite found in the upper slope
cores is also relict (i. e. a sediment formed out of equilibrium with
existing conditions). The tentative relict age of the olive gray lutite
at the surface of core 6706-2 may also apply to the adjacent olive gray
lutite and surface glauconite in core 6706-1. Similarly, the late

99
Pleistocene age of the gray lutite in core 6706-3 (Figure 25) also
suggests that the surface glauconite in this core is not modern but
relict. The coarse sand in core 6706-7 from the head of the Upper
Rogue Canyon, the late Pleistocene age of the olive gray lutite in
core 6708-37, and the surface glauconite in core 6706-4 (Figure 31),
all suggest that the Upper Rogue Canyon may be another relict area
on the upper slope.

Without additional evidence for the absolute ages of the surface
sediment in cores 6706-1, 6706-3, and 6706-4, it is difficult to state
with certainty that these sediments are late Pleistocene in age,
although the existing evidence suggests that they may be. Relict sedi-
ments need not all be of late Pleistocene age, they could have formed
early in Holocene time under different conditions than those encountered
today.

The Present Sediment Pattern

The stratigraphic and sedimentological evidence from the upper
slope environments, especially the benches, strongly suggests that the
surface sediment in these areas is both modern and relict in nature.
Certain areas, such as Cape Blanco Bench and the Klamath Plateau,
may be covered entirely with relict sediment while other upper slope
areas contain patches of both modern and relict material. The data
of Chambers (1968) suggest that the continental shelf off southern

100
Oregon is also surfaced with both modern and relict sediment. In
contrast, the lower slope appears to be completely mantled by modern
mud.

By combining the data available on the surface sediments of the
southern Oregon margin, a generalized genetic classification emerges.
Figure 32 illustrates six types thought to be present on the margin.
Modern sand occurs on the inner shelf and modern mud is found on both
the central shelf and lower slope. Mixed sand and mud and the relict
sand found on the shelf have their analogs in the mixed modern and
relict deposits and the relict sand found on the upper slope. The
shelf, upper slope, and lower slope are distinct physiographically and
as sedimentary environments. The upper slope appears to be more
closely related to the shelf than to the lower slope, and could be
thought of as a transition zone between the two, not unlike the sedi-
mentary regime of the Borderland province off southern California
(Gorsline and Emery, 1959; Moore, 1966).

Textural Relationships

Certain statistical measures related to the texture of the sedi-
ment have been examined in an attempt to test whether or not the
three environments (shelf, upper slope, lower slope) can be dis-
tinguished more precisely. Mean diameter (M ) has been plotted

9

against both the phi deviation (cr ) and phi skewness (a ) with respect

9 9

Figure 3 2. Distribution of surface sediment types on the
southern Oregon margin.

102
to environment (Figures 33, A and 34) and sediment type (Figures 33,
B and 35).

The sorting of the majority of sediments, particularly the olive
gray lutites from the lower slope, is generally poor (Figure 33). No
sharp demarcation can be made between sand-silt layers and lutites on
this basis, either environmentally or by sediment type. A division of
the sediments into two groups is apparent in both Figures 34 and 35.
One group represents sand-silt layers, which are coarse-grained
and extremely fine -skewed, and both olive gray and gray lutite appear
as another group which is fine-grained and coarse -skewed. The
coarse (negative) skewness of the lutite may be attributable to the
presence of sand-sized tests or shells of Foraminifera or other
pelagic organisms. No environmental distinction can be made among
any of the three sediment types which would indicate their particular
environment of deposition. Conversely, it also appears that no clear
textural subdivisions can be made among the various environments
which would indicate the presence of a distinct sediment type.

Mineralogy

An analysis of the mineralogy of the margin sediments can be
most useful, not only in distinguishing among the various sediment
types, but also in determining the provenance of the sediment and its
dispersal patterns.

103

9r

o SHELF

• UPPER SLOPE

□ BENCH

a UPPER ROGUE CANYON

g 6 _ ♦ LOWER SLOPE ^

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PHI MEAN DIAMETER (M0)

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PHI MEAN DIAMETER (M0)

Figure 33. Phi Mean Diameter versus Phi Deviation according to
(A) depositional environment and (B) sediment type.

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104

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23456789
PHI MEAN DIAMETER (M0)

10

Figure 34. Phi Mean Diameter versus Phi Skewness according to
depositional environment.

105

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Figure 35. Phi Mean Diameter versus Phi Skewness according to
sediment type.

12

106
Light Minerals

Inasmuch as the texture of the sediments tends to reflect the
depositional environment for the most part, rather than the source area
of the sediment (van Andel, 1964), an examination of light minerals of
the sediment coarse fraction can provide a better clue to the rock com-
position and tectonic stability of the source areas. The light mineral
suites from 12 samples selected from the various physiographic
provinces include quartz, potash feldspar, plagioclase feldspar, rock
fragments and volcanic glass. Using the classification of Williams,
Turner and Gilbert (1954), these constituents have been plotted on a
ternary diagram (Figure 36, A) to show the relative amounts of stable
(quartz, chert, quartzite) and unstable (feldspar, rock fragments ) grains

The light mineral fraction of southern Oregon margin sediments
is chiefly arkosic, volcanic or lithic sand, with the arkosic sands pre-
dominating. All sediments have less than 50% stable grains (Figure 36,
A) suggesting a tectonically unstable source area that has possibly under-
gone rapid erosion. The unconsolidated sediments contain higher per-
centages of unstable constituents than those found in various Jurassic
and Cretaceous rocks of southwestern Oregon (Figure 36, B)by Dott
(1965). His analysis indicates an increase in both potash feldspars and
total feldspars with decreasing age (Table 3). This trend is continued in
the unconsolidated sediments (Figure 36, A; Table 3) whichare younger
than the rocks and which contain an even higher percentage of feldspars.

107

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Table 3. A comparison of the light mineral composition of selected
margin sediments with southwestern Oregon sandstones.

Location

Percent of Composition

Plagioclase Potash
Quartz Feldspar Feldspar

Southern Oregon Continental Margin

Shelf sediments (3) 30

Upper slope and benche

sediments (7) 33

Lower slope sediments (2) Zl

30

26
15

15

21

42

Southwestern Oregon Rocks
Eocene (38)
Upper Cretaceous (42)
"Myrtle Rocks"
Dothan Formation (50)

25

14

6-25

48

20

10-20

--

--

1-10

17

18

< 1

"Composition does not total 100% because other constituents not listed
here (rock fragments, volcanic glass, etc. ) have been excluded.

(N) - Number of samples,

Data from Dott (1965).

109
Heavy Minerals

One of the best indicators of the provenance of continental mar-
gin sediments is the heavy mineral assemblage. The distinctive assem-
blage found in the sediments from the southern Oregon margin provides
a particularly clear indication of their source area and source rocks.

The dominant heavy mineral groups observed were the amphiboles
(especially blue-green hornblende and actinolite -tremolite ), epidote,
and opaque minerals (including hematite and limonite). Next in impor-
tance were the pyroxenes, olivine and garnets. Glaucophane, a mineral
diagnositic of metamorphic provenance (Kulm, et al, , 1968), was also
present in minor amounts in the assemblage.

The four continental drainage basins providing sediment to the
Oregon continental margin are the Columbia River Basin, the North
Coast Basin, the Umpqua Mid-Coast Basins, and the Klamath-South
Coast Basins (Figure 37). The various rivers in each of the basins
have been examined to determine their heavy mineral assemblages and
source rocks (Kulm, e_t aL , 1968b; Duncan, 1968). The Klamath-
South Coast Basins, particularly those of the Rogue and Klamath
Rivers, are the principal basins draining southwestern Oregon and
northern California. They appear to be the principal contributors of
sediment to the southern Oregon continental margin.

The Paleozoic and Mesozoic meta-sedimentary, meta-volcanic,
and sedimentary rocks of the Klamath Mountains which have been
intruded by granitoid and ultrabasic rocks (Baldwin, 1964) are
responsible for the distinctive mineralogy found in Klamath-South

1 10

Ill

Coast drainages. The rivers of the Klamath-South Coast Basins are
characterized by an amphibole assemblage, consisting principally of
blue-green hornblende and actinolite-tremolite. In addition to these,
the epidote group is also present in nearly all the rivers. Glaucophane,
although present only in small amounts, occurs only in the Rogue and
Klamath drainages, and is therefore diagnostic of the Klamath-South
Coast Basins. The glaucophane probably is derived from the
glaucophane -bearing schists of the Franciscan Formation of northern
California and the Dothan Formation of Oregon (Irwin, 19 66). Some
rivers of the Klamath-South Coast Basins such as the Coos, Coquille,
Sixes and Elk Rivers, and the major rivers of the Umpqua Mid-Coast
Basins drain the late Tertiary and Quaternary volcanic and sedi-
mentary formations of the central and southern Oregon Coast Range
(Figure 7 ).

The similarity of the heavy mineral assemblages from the
southern Oregon margin and the Klamath-South Coast Basins is shown
in Table 4. The low percentage of pyroxene minerals in the margin
sediments compares closely with that present in the Klamath-South
Coast Basins, and is very close to the amount present in the adjacent
deep sea. The average amount of blue-green hornblende (29%) present
in the Klamath-South Coast Basins assemblage (Kulm, et al. , 1968b)
is very close to the average obtained from the margin assemblages
(25%). Glaucophane, found only in the Klamath-South Coast Basins,
is present in at least one sample from every margin environment.

112

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113
The relative abundance of pyroxene and amphibole is a consistent
indicator of the source area contributing sediment to the margin
environments. The minerals included in the pyroxene to amphibole
ratio (P/H ratio) constitute the majority of the non-opaque, non-
micaceous and unweathered constituents and therefore adequately
represent the entire heavy mineral suite. The average P/A ratio in
the margin environments is similar to that obtained for the Klamath-
South Coast Basins (Table 4).

The P/A ratios indicate that the sediments in all margin environ'
ments are influenced more by the mineral assemblages in the Klamath
South Coast Basins than those from any other basin. Despite the fact
that the river runoff of the Columbia Basin is over seven times that
for the Klamath-South Coast Basin (Figure 37), the distinctive
assemblage of the latter basin still appears to dominate the southern
Oregon margin environments. It may be argued from the data of
Table 4 that the lower slope, which has a relatively high P/A ratio of
0. 7, is also influenced by sediments from the Umpqua Mid-Coast
Basins and/or the Columbia River. However, the clay mineralogy
suggests that only the sediments from the Umpqua Mid-Coast Basins
have any noticeable effect on the lower slope off southern Oregon.

In general, surface sediments from the benches and upper slope
exhibit higher percentages of hematite and limonite in their heavy
mineral fractions than do sediments of other environments.

114
Considerable iron staining, pitting, and alteration is also evident in
the light mineral fractions from these environments, especially from
the benches. As previously noted, this evidence may be an indication
of the relict nature of the benches sediments, and to a lesser extent
of most upper slope sediments. Shelf sediments show a higher
average percentage of heavy minerals, particularly opaque grains,
than do the other environments. Chambers (1968) has plotted the
zones of high heavy mineral concentration on the shelf; he has
also noted that opaque grains may be indicative of stillstands of sea
level due to their high specific gravity and resistance to offshore
transport. The shelf samples examined in this study are within, or
adjacent to, high heavy mineral zones mapped by Chambers and the
results from these samples appear to be consistent with his data.

Clay Minerals

The clay mineralogy reinforces the hypothesis that the Klamath-
South Coast Basins are the most important source for the sediments
of the southern Oregon margin. The clay fraction from 18 sediment
samples representing shelf, upper slope and lower slope environments,
and from three rock dredges was examined to determine the per-
centages of the various clay minerals present (Figure 38). The clay
minerals from all the environments on the southern Oregon margin
consist predominantly of chlorite and illite, with only minor amounts

115

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116
of montmorillonite. No kaolinite was found. The presence of
amphiboles of clay size was also noted in six of the sediment samples
and all the rock samples examined. In all sediments and sedimentary-
rocks, chlorite is the most abundant mineral (average 60%), with
lesser amounts of illite (average 35%). Only minor amounts of mont-
morillonite occur in the sediments (average 5%).

The Rogue River, which drains the metamorphic terrane of the
Klamath Mountains, is noted for its high chlorite content. Duncan
(1968) and Duncan, et al. (1970) examined the clays from this river
and obtained values of 5 1 /o chlorite, 26% illite, and 23% montmoril-
lonite; Drake (1969) obtained similar values in her analysis (43%
chlorite, 38% illite, and 19% montmorillonite ) (Figure 38). When
compared to the clay mineralogy of the Umpqua River of any of the
Columbia River sub-basins (Figure 38), the Rogue River appears to
be the dominant influence affecting the clay mineralogy of all sediments
on the southern Oregon margin. Other rivers draining the Klamath
Mountains may also be chlorite -rich and may contribute to the relative
uniformity of the clay mineral content of margin sediments. The fact
that all the samples examined are so nearly alike in clay mineral com-
position attests to the pervasive influence of chlorite -rich sediments
from the Klamath Mountains, which masks any influence from the
Columbia sub-basins, and to a lesser extent, from the Umpqua
Mid-Coast Basins.

117
Russell (1967), Duncan (1968), Duncan, et al . (1970), and
Harlett (1969) have all noted that diffractograms of late Pleistocene
deep-sea clays exhibit sharper peaks than those of Holocene deep-
sea clays. Duncan et al. (1970) report that more illite than chlorite
is present in late Pleistocene deep-sea clays than in the Holocene
clays. They postulate that the change in character between the late
Pleistocene and Holocene clays is probably due to variations in the
relative rates at which the Columbia River and Snake River sub-
basins contributed their clay mineral assemblage to the sediment load
of the Columbia River. They state further that the Upper Columbia
River sub-basin was a major source for the illite-rich deep-sea
sediments during the Pleistocene, but as the region emerged from
glaciation montmorillonite -rich sediments of the Lower Columbia and
Snake River sub-basins began to dominate the sediment load. This
change is abrupt, and not due to more gradual marine diagenetic
processes; it is associated with the late Pleistocene -Holocene faunal
boundary (ca. 12, 500 years B. P. ) and has been verified quantitatively
by similar abrupt increases in the chlorite -illite and montmorillonite -
illite ratios (Duncan, 1968; Duncan, et al. , 1970). Chlorite -illite
ratios were calculated for the samples examined in this study; the
samples represent the tops and bottoms of nine cores from the various
environments (Appendix 7). Although the Pleistocene-Holocene
boundary was not evident in the cores examined the chlorite -illite ratio

118
did increase upward in all but two cores, a trend which is in general
agreement with Duncan's data.

In addition to determining the change in clay mineral character
with depth, Duncan (1968) noted that three Holocene clay mineral
groups are evident in the deep-sea which radiate outward from the
Columbia River. The montmorillonite content decreases while chlorite,
and to a lesser extent, illite, increase with distance from the river.
Group three, in the deep sea off central and southern Oregon, contains
the most chlorite (mean value 40%) and the least montmorillonite
(mean value 32%). The clay minerals from the continental margin
appear to belong to this group. However, the higher chlorite content
of margin sediments compared to those in group three suggest either
that a significant amount of chlorite is retained on the margin and may
never reach the deep-sea environment, or that the chlorite is diluted
as the clays move seaward.

The occurrence of amphibole in the clay mineral fraction from
three cores and three dredge samples (Appendix 7), representing
mostly upper slope environments, may be significant. Heath (1969)
suggests that the amphibole may have been produced as glacial rock
flour during the late Pleistocene and may have deposited on the mar-
gin in that form. However, except for a few valley glaciers that may
have been present, the region was not glaciated during the Pleistocene.
In addition, the sediment in these samples is not all Pleistocene in

119
age. A fuller explanation for the presence of amphibole must await
a more detailed examination.

Organic Carbon

Sedimentation rates in late Pleistocene was at least six times
higher than that in the Holocene in the deep-sea environments off
Oregon (Duncan, 1968). Duncan found that the organic carbon content
of postglacial lutite is up to five times higher than that of the late
Pleistocene lutites. He attributed this apparently reversed trend to
the higher influx of sediments in the late Pleistocene masking the
organic carbon content of these older sediments. Peterson (1969)

reached the same conclusion by calculating sediment and organic car-

2
bon accumulations in terms of gm/cm /1000 years. From his cal-
culations, Peterson found that although the sedimentation rate and
organic carbon influx was higher during the late Pleistocene, the
absolute amount of organic carbon preserved in the older sediments
was less due to dilution, differences in preservation, and depth of
burial.

In this study, samples from near the top and bottom of eight
cores representing different depositional environments were analyzed
for their percent total carbon, organic carbon, and calcium carbonate
(Table 5). Two additional cores were more fully examined by
Peterson (1969).

120

Table 5. Total carbon, organic carbon and calcium carbonate in selected margin sediments.

Percent

Percent

Sample

Depth in

Depositional

. b
Age

Sediment

total

organic

Percent

number

core (cm)

environment

typec

carbon

carbon

CaC03a

6708-25-4

230

Shelf

H

OGL

1. 16

0.90

2. 17

6708-25-16

583

H

OGL

0. 95

0.63

2.67

6708-42-1

230

Shelf

H

S-S

0. 53

0.44

0.76

6708-42-2

454

LP

S-S

1.02

0. 54

3.97

d
6706-5-(l)

6706-5-(2)

17
183

Upper Rogue
Canyon

LP
LP

OGL
OGL

1. 41
0.69

1.36

0. 47

0.48
1. 77

6706-5-(3)

255

LP

OGL

0.70

0. 53

1.35

6708-37-1

15

Upper Rogue

LP

OGL

1. 70

1.57

1.03

6708-37-7

575

Canyon

LP

GL

1. 56

1. 14

3.50

6706-3-1

5

Klamath

LP

GL

1.00

0. 95

0.41

6706-3-10

377

Plateau

LT

GL

0.84

0.67

1. 44

6706-2-12

302

Middle

LP

OGL

1.34

0.85

4.08

6706-2-17

375

Bench

LP

GL

1. 18

0.74

3.66

6706-6-8

155

Upper

H

OGL

1. 14

0. 94

1.53

6706-6-15

355+

Slope

H

OGL

1. 18

0. 89

2. 47

6711-6-1

10

Lower Rogue

H

OGL

2.30

2.00

2.45

6711-6-8

340+

Canyon

H

OGL

2.22

1.84

3.00

6708-38-1

5

Lower

H

OGL

1.82

1.60

1.82

6708-38-21

472

Slope

H

OGL

1. 52

1.32

1.62

d
6711-2-(l)

19

Lower

H

OGL

2.06

1.42

5. 32

6711-2-(5)

154

Slope

H

OGL

1.06

0.97

0.62

6711-2-(10)

410

H

OGL

1.33

1.20

1. 16

Percent by weight

LP -late Pleistocene, H - Holocene, LT - Late Tertiary.

OGL - olive gray lutite, GL - gray lutite, S-S - sand-silt layers.

i
Data and sample number designations after Peterson (1969)

121

In those margin cores where the surface, or near-surface,
samples were examined, the average percent organic carbon was
found to be 1. 3, with surface samples from the lower slope being
among the highest values recorded (1. 6% and 2. 0%). These values
compare favorably with the 1. 6% median value from the adjacent con-
tinental slope at 41059'N, reported by Gross, et al. (1970). Sediments
accumulating on the continental slope are thought to have high organic -
carbon concentrations where the oxygen-minimum zone impinges on
the bottom. Off Oregon the oxygen minimum zone extends to depths
of 500 to 2000 m and appears to coincide with the high organic carbon
content of slope sediments in this depth range.

All but one core (6708-42, a sandy core from the shelf) showed
an increasing percentage of organic carbon upwards, and all but three
cores (6711-2, 6708-38, and 6706-2) showed a decreasing percentage
of calcium carbonate upwards in the core. In terms of absolute values
of organic carbon, samples from cores considered to be entirely
Holocene in age showed generally higher values of organic carbon and
lower values of calcium carbonate than cores considered to be entirely
late Pleistocene in age. It is not possible to determine whether this
increase is abrupt. Although the Holocene sedimentation rates com-
puted in this study are high (Table 2), it is possible, as Duncan has
noted, that Pleistocene rates could have been several times higher
both on the margin and in the deep sea. If this hypothesis is correct,

122
then the decrease in sedimentation rate from Pleistocene to Holocene
time may not have occurred as abruptly on the margin as in the deep
sea.

Consolidated Sediments

Classification and Distribution of Rock Types

A comparison of the consolidated rocks recovered from the
dredge hauls with the unconsolidated sediments from the cores reveals
certain trends which may provide a clearer understanding of the
geological events that have occurred on the margin. Figure 39 shows
the location and major lithology of the rock types collected in the ten
dredge hauls. Samples from nine of the rock types were sufficiently
coarse-grained to permit a detailed petrographic examination
(Appendix 8); these have been grouped according to the classification
of Williams, Turner and Gilbert (1954) and are shown in Figure 36, C.
The remaining samples were too fine-grained for petrographic identi-
fication (Figure 39; Appendix 8).

The lithified samples fall into two groups: coarse-grained
impure sandstones, mostly arkosic and lithic wacke (Figure 36, C),
all but one of which are from the shelf and upper slope, and fine-
grained mudstones and siltstones from the lower slope (Figure 39),
some of which are calcareous. When one compares the light mineral

ARKOSE/ARKOSIC
WACKE

V LITHIC WACKE
FELDSPATHIC V_^\

WACKE ^m ^ .-SHELLS

DENOTES LENGTH
AND DIRECTION
OF DREDGE HAUL

Figure 39. Rock types from the southern Oregon margin

Numbers next to circles denote percent of each
rock type.

124
composition of the unconsolidated sediments (Figure 36, A) with that
of the consolidated sediments (Figure 36, C), it is apparent that the
unconsolidated sediments have a higher percentage of unstable grains
than do the lithified sediments. This would seem reasonable since the
sediments lose much of their unstable elements during the various
stages of diagenesis and repeated cycling as they become lithified. In
general, both the unconsolidated and consolidated sediments are
arkosic in character. A comparison of the light mineralogy of the
consolidated sediments on the margin with that of southwestern Oregon
continental rocks examined by Dott (1965) (Figure 36, B) shows that
the composition of the shelf and upper slope sedimentary rocks are
similar to those of the Upper Cretaceous Series and the Dothan
Formation. This suggests that the late Tertiary rocks of the shelf
and upper slope could have been derived from either the Jurassic or
Late Cretaceous rocks of the Klamath Mountains.

A complex of Tertiary and pre-Tertiary strata crop out in the
coastal and near-coastal regions of southwestern Oregon. These have
been described in detail previously (see Regional Geology). The early
Tertiary strata exposed along the southern Oregon Coast Range were
folded and faulted during the late Tertiary Cascadan orogeny (Dott,
1965), and the resulting north-south-trending anticlines and synclines
probably extend westward from the coast offshore and underlie the
shelf and upper slope, and perhaps the lower slope. All but the most

125
resistant Tertiary strata probably occur only in synclinal basins or
down-faulted blocks, and most likely only the younger Mio-Pliocene
strata are widespread, or exposed, on the upper margin. Maloney
(1965) reports only Miocene and Pliocene rocks from the shelf,
banks, and slope off central Oregon. The age of three rocks recovered
from the margin off southern Oregon date back to the early or mid-
Pliocene (Table 1). Most, if not all, of the predominantly arkosic
rocks from the shelf and upper slope (6708-22, 6708-36, 6708-41,
6711-D1; Figure 39) may also be Mio-Pliocene in age, although it
cannot be stated with certainty that they are from contiguous strata.

The calcareous, nodular mudstones (6711-D2 and 6711-D3)
may be widespread on the upper slope, particularly on the Klamath
Plateau, since similar rocks have been recovered by Silver (1969a)
on the Klamath Plateau off northern California. The rocks are
probably concretionary in origin, but the time of their formation is
unknown. Rock fragments in the base of core 6706-3 (Figure 39)
have been dated as mid-Pliocene (Table 1). This suggests that a
distinct unconformity, probably a result of tectonism, exists between
the Tertiary rocks at the base of the core and the overlying late
Pleistocene sediments. In general, the lithology and age of the rocks
recovered by Silver (1969a) from the northern California margin
are similar to those found in this study.

Clay mineral contents of the three rock samples from the slope

126
(6802-D3-1, 6802-D2, and 6706-3-11-1; Figure 38) show the same high
chlorite percentages as unconsolidated sediments from the slope,
which indicates that the contribution of the chlorite-rich sediments
from the Klamath Mountains has been strong, at least since the Mio-
Pliocene. The large difference in the chlorite-illite ratio in core
6706-3 between the mudstone fragments at the base (C/I = 3. 9) and
the immediately overlying gray lutite (C/I =1.5) reinforces the
evidence of a distinct erosional boundary at that depth in the core.

In general, the grain-to-matrix ratio of the consolidated sedi-
ments from the margin approximates the sand-mud ratio of the over-
lying sediments. On the shelf, the grain-matrix ratio of the rocks
approaches one and the sand-mud ratio of shelf sediments is also
commonly one or slightly greater. In the remaining margin environ-
ments, both the grain-matrix ratio of the rocks and the sand-mud ratio
of the overlying sediments are usually less than one, reflecting an
absence of coarse constituents in these environments.

In examining the composition of the consolidated and unconsoli-
dated sediments of the southern Oregon margin, certain generaliza-
tions can be made. First, the light mineral composition of the sedi-
ment samples is generally similar to the rocks, but the latter have
more stable constituents. Second, the upper slope sediments and
rocks have a composition more closely approaching that of the Upper
Cretaceous Series and Dothan Formation of the Klamath Mountains

127

than that of the Eocene or other early Tertiary strata of the southern
Oregon Coast Range. Third, the lower slope sediments and rocks
have a higher percentage of unstable constituents, particularly
feldspars, than do those of the upper slope. They tend to reflect the
influence of the early Tertiary strata of the southern Oregon Coast
Range as well as that of the Klamath Mountains.

These relationships suggest an orderly sequence of events.
The Mio-Pliocene strata exposed or underlying the shelf and upper
slope were apparently derived from the uplift and erosion of pre-
Tertiary Klamath Mountain strata, probably during the Nevadan
orogeny or late Cretaceous disturbance. The Quaternary sediments
exposed or underlying the lower slope were probably derived in part
from a later uplift and erosion of mid- and late Tertiary sediments,
probably during the Cascadan orogeny, and in part from the pre-
existing Klamath Mountain strata.

128

PROCESSES OF SEDIMENTATION

A Proposed Model for Modern Sediment Transport on the
Southern Oregon Continental Margin

Many factors influence sedimentation on the southern Oregon con-
tinental margin. These include the character of the source rocks,
climatic effects, the quantity of sediment supplied by the continental
drainage, the influence of coastal morphology and submarine topography,
and the various oceanographic conditions which prevail over the margin.
A generalized model of modern sediment transport processes (Figure
40) is proposed which attempts to relate these factors to the sediment
distribution pattern presently found on the margin, and to that present
during the late Pleistocene and early Holocene.

The Initial Regime of Sedimentation

The major sources of the unconsolidated sediments on the
southern Oregon margin lies in the adjacent coastal complex of pre-
Tertiary and Tertiary rocks of the Klamath Mountains and southern
Oregon Coast Range. The relative dominance of sediments from the
metamorphic terrane of the Klamath Mountains throughout the entire
margin has already been shown. To a lesser extent, sediments from
the Tertiary rocks of the southern Oregon Coast Range are contributed
to the margin, but this contribution is more noticeable on the lower

FLUVIAL TRANSPORT
LONGSHORE DRIFT

LUTUM TRANSPORT
SUSPENSATE

BOTTOM TURBID
w LAYER

SLUMPING

Figure 40. Schematic model of modern sediment transport
processes on the southern Oregon margin.

130
slope than in other margin environments.

The major drainage complex supplying sediment to the margin is
that of the Klamath-South Coast Basins. Additional sediment may be
added to the southern Oregon margin by the major streams of the
Umpqua Mid-Coast Basins, particularly by the Umpqua River, which
drains portions of the northern edge of the Klamath Mountains as well
as the southern Oregon Coast Range. River runoff data for these
streams has been compiled by Hagenstein, et al. (1966) and by the
U. S. Geological Survey (1964, 1966). Over 87 % (21 . 5 million acre
feet) of the total runoff of the Klamath-South Coast Basins comes from
the Klamath and Rogue Rivers; one-half (7. 5 million acre feet) of the
total runoff of the Umpqua Mid-Coast Basins is supplied by the Umpqua
River (Figure 37). The runoff of all the streams in both basins is only
20-25% of that supplied by the Columbia River (Lockett, 1965). How-
ever, mineralogical analyses in this study have shown that the influence
of the Columbia River, and that of the North Coast Basins to the south
of it, have a relatively minor affect on the sediments of the southern
Oregon margin.

The amount of rainfall over southwestern Oregon varies widely
with seasons, but is greatest during winter months, which is reflected
in the stream runoff. For example, although the average discharge at
the mouth of the Rogue River is approximately 3000 to 4000 cubic feet
per second (cfs) for the entire year, it reaches a maximum of 15, 000

131

to 16, 000 cfs in January, and a minimum of 1500 cfs in September,
following the low summer rainfall season. Since the amount and size
of sediment discharge from a river is a function of the rate of flow of
the river (Postma, 1967), the Rogue River discharges more sediment
in winter, by an order of magnitude, than in summer.

The last rise of sea level has created numerous bays and
estuaries at the mouth of the major streams along the northern Califor-
nia and southern Oregon coasts. These features have a marked
influence on the supply of sediment to the southern Oregon margin.
Fluctuating tides influence the interaction of the discharging fresh river
water and the encroaching oceanic salt water within these bays and
estuaries. According to Postma (1967) various accumulation mech-
anisms, particularly settling- and scour-lag effects, tend to trap
sediment inside these basins or at leas-t restrict their movement to the
near-shore regions. Kulm and Byrne (1966) have shown this to be the
case in Yaquina Bay, Oregon. Postma noted that this sediment trapping
is most effective for relatively fine-grained sediment, but may vary
between wide limits depending on local conditions to any size between
five to ten \i and 100 u.

As Chambers (1968) has noted, the Holocene sea level rise has
caused the trapping and restriction of sand-sized sediment on the con-
tinental shelf off the Rogue River. A belt of sand is present from the
shoreline to a depth of about 50-75 m, but only sand shoaler than

132
15-20 m (modern sand) is considered to be in equilibrium with the
present environment (Figure 32). The sand between 20 and 70 m is
probably relict sand of Pleistocene age. Dietz (1963) and Vernon (1966)
conclude that modern beach sand is generally not transported offshore
to depths greater than 20 m, except where the heads of submarine can-
yon extend into this depth. No work later than that of Chambers,
including the present study, has detected any appreciable quantities of
modern Holocene sand at the surface in margin environments deeper
than the inner shelf, although Roush (1970) and Neudeck (1970) have
cited evidence from sedimentary structures and from oceanographic
conditions which indicate that sand movements to depths of 80-90 m or
deeper may be possible.

The Holocene sea-level rise on the southern Oregon margin pro-
duced the following: 1. large accumulations of relict Pleistocene sand
on the submerged benches and the deposition of large quantities of
Holocene mud on the lower slope; 2. a six-times greater Pleistocene
sedimentation rate in the deep sea compared to the Holocene (Duncan,
1968); 3. non-deposition of Holocene and modern sands on much of the
outer shelf due to trapping in the bays and estuaries. This evidence
all points to a large influx of coarse-grained sediment on the margin
during the late Pleistocene when sea level was lower, followed by a
greatly reduced and finer-grained influx of sediment deposited in
Holocene time as a consequence of rising sea level.

133

The Concept of Lutum Transport

The initial premise upon which the present sediment transport
model (Figure 40) is based is that since the modern time (3000 years
B. P. to the present, when sea level is assumed to have been at about
the same level it is today), and indeed since the beginning of Holocene
time (12,500 years B„ P. ), the sediment influx to the margin has been
primarily one of fine-grained silts and clays, or lutum. Lutum here
refers to fine-grained sediment still in transport or suspension, as
distinguished from lutite, which is fine-grained sediment that has been
deposited. As opposed to the late Pleistocene, when great quantities
of coarse sediment blanketed the margin and deep sea, very little
modern sand reaches depths greater than 20-30 m. As this study has
shown, Holocene (including modern) lutites are ubiquitous on the mar-
gin, but the thickest accumulations are found on the lower slope.
These lutites are generally uniform in character with no visible grading,
as are the sand-silt layers interbedded with them. These sand-silt
layers were probably deposited by mass downslope gravity movements,
such as slumping; it is also possible that they are winnowed deposits,
or even the finer-grained tails of unrecognizable turbidites. However,
the evidence precludes a turbidity current origin for much, if not all,
of the Holocene deposits, and suggests instead that a process of large-
scale lutum transport must be called for to account for the Holocene

134
and modern deposits. Such a process has been described by Moore
(1970) to account for much of the basin-filling occurring on the southern
California Borderland. A similar process is postulated to occur on
the southern Oregon margin.

The Oceanographic Regime

In order to fully understand lutum transport on the southern
Oregon margin, it is also necessary to understand the oceanographic
regime in which it operates. The oceanographic factors play a major
role in determining the routes of sediment transport and dispersal,
and consequently the ultimate sites of deposition. Many of the
oceanographic factors that are important to sediment transport vary
seasonally and shift in direction in response to the changing wind pat-
terns. Sea and swell and many of the currents on the margin change
direction in this manner; therefore, it is important to distinguish be-
tween the oceanographic regime in the winter (Figure 41, left) and that
which exists in the summer (Figure 41, right).

The Westwind Drift is a major ocean surface current which moves
eastward across the North Pacific Ocean. As it approaches North
America at a point about 500 km west of the continent near 45° N
latitude it divides into two parts: one part of the Drift flows north and
one part south as the California Current (Dodimead, Favorite, and
Hirano, 19 63). The Davidson Current flows northward as a subsurface

Figure 41. Schematic diagram of the major ocean currents on the southern Oregon margii
Left, represents winter conditions; right, summer conditions.

136
current on the coastal side of the California Current (Figure 41) and
breaks through to the surface during the winter months (Sverdrup,
et al_. , 1942); it has been reported as far north as 50° during January
and February (Burt and Wyatt, 1964).

Stevenson, et al. (1969) report a subsurface current flowing
about 70 km offshore from Oregon which has a southerly component of
movement from the surface to 500 m during the entire year except for
some slight northward movement during the winter months (Figure 41,
left). They measured velocities averaging 5-10 cm/sec, but reported
no velocities greater than 18 cm/sec below 50 m. Maughan (1963)
measured velocities as great as 25. 8 cm/sec at a depth of 10 m over
the central Oregon continental slope. Collins (19 67) measured northerly
subsurface currents with velocities of 1 3 to 27 cm/sec on the central
Oregon shelf at depths of 10, 20, and 60 m during the winter months
(Figure 41, left), but reported a southerly movement at these same
depths during the summer (Figure 41, right). However, throughout any
year the net movement was to the north over the shelf.

Longuet-Higgins (1969a), in studying mass transport by time-
varying ocean currents, determined that in regions of large bottom
gradient the Stokes velocity factor (the difference between Eulerian
mean velocity and Lagrangian mean velocity at a given point) may be an
important consideration. He stated that the Stokes velocity may at
times be opposite in direction to that of the surface wave propagation

137
direction, and hence the resulting mass transport may be opposite in
direction to that expected from the wave propagation direction. He
farther reasoned (1969b) that such a situation may exist along the con-
tinental shelf-slope transition off Oregon, where a significant Stokes
jet may give rise to a southerly mass transport along the upper slope
with the flow being opposite to the wave-generated northerly mass
transport over the shelf (Figure 41 ).

Upwelling has been noted to occur along the Oregon coast (Smith,
1964), and is particularly well developed off southern Oregon (Pattullo
and Denner, 1965; Smith, e_t ah , 1966). The upwelling is explained by
the seasonal shift in wind direction off the Oregon coast. During the
late spring and summer, the predominant winds are from the north-
northwest and blow onshore to drive the surface water offshore. This
surface water is then replaced by upwelling subsurface water (Figure
41). During the winter the winds and surface water movement reverses
direction and the upwelling ceases. Neudeck (1970) has postulated that
upwelling may be a significant factor in inhibiting the offshore and down-
slope flow of bottom turbid layers.

The strongest winds occur off Oregon during the winter months,
when severe storms produce high energy wind and wave conditions
(Cooper, 1958; Kulm and Byrne, 1966). Neudeck (1970) has related the
occurrence of greater amounts of more competent waves in winter to an
increase in the maximum depth of rippling of bottom shelf sediment.

138
He has shown that rippling occurs roughly parallel to the coastline to
maximum depths of about 200 m in winter and only 50-100 m in summer.

The seasonal shift in winds produces similar shifts in the pattern
of waves and in the resulting littoral drift directions along the coast.
During the winter months wave directions due to sea are from the
south-southwest (Figure 41); however, the prevailing swell comes
from the south-southwest a majority of the time only during January
and February (Kulm and Byrne, 1966). During the summer, both sea
and swell come from the north-northwest a majority of the time
(Figure 41, right). Thus, it can be inferred that littoral drift along
the Oregon coast is to the south during the summer and north during
the winter (Figure 41). Quantitatively, the northerly drift in winter
appears to be greater due to the larger sediment influx, during this season and
the higher energy waves available to move it. The existence of a net
northward littoral drift over the Oregon shelf has been verified by
textural studies (Gross and Nelson, 1966; Gross, et al . , 1967) and
heavy mineral patterns (Kulm, et al . , 1968b; Chambers, 1968). The
work of Collins, cited above, and Mooers, e_t ah (1968) also suggest
that a net northward movement exists over the Oregon shelf during the
year.

Tides along the Oregon coast are mixed semi-diurnal with a range
of 6 to 10 feet (Pattullo and Burt, 1962). Mooers, etal. (1968) believe
that the tidal influence accounts for a large percentage of the current

139
speeds measured on the Oregon shelf, and although these tidal current
speeds average less than 10 cm/sec, they may cause turbulence or
instability at the pycnocline due to shear. Tidal currents may be
related to internal waves and internal tides which Mooers (1968)
believes may be a contributing factor to subsurface turbulence at the
shelf edge. Normal alternating tides and tidal currents may have a
pronounced effect on the movement of suspended sediment within the
water column and on the bottom sediment down as far as abyssal depths
(Swift, 1969; Johnson and Belderson, 1969). However it is significant
to note that Neudeck (1970) has considered these normal tides rela-
tively un-important compared to the influence of surface waves,
especially long-period swell, in forming ripples and in generating a
turbid transport system on the Oregon shelf. Storm tides may affect
the bottom; however, these are exceptions to the normally predicted
tides.

Bottom photographic studies have been made by Neudeck (1970)
on the Oregon margin to determine the extent of bottom current
activity. He found indirect evidence of current directions (no current
velocity measurements were made) in the trends of rippling, scouring,
and in the movements of benthic organisms. On the upper slope off
southern Oregon, Neudeck found indications of both a southwest-moving
bottom current and scouring at a depth of 1000 m in two nearby stations
within the swale to the north of the Upper Rogue Canyon (Kulm, 19 69).

140
Korgen (19 69) has actually measured near-bottom current velocities
(but not directions) on the central Oregon slope. He recorded
velocities at depths of 700-900 m which range from 8. 4-17. 4 cm/sec
(at 75 cm above the bottom) to 9. 6-45. 0 cm/sec (at 300-350 cm above
the bottom). At another station, at a depth of 1600 m, he recorded
velocities of 0. 4-12. 9 cm/sec (at 150-200 cm above the bottom).
Harlett (1970) has verified a southerly bottom current direction on the
upper slope, but was unsuccessful in recording its velocity.

Neudeck has observed many areas of north-south trending bottom
ripples on the southern Oregon shelf, which he has related to long-
period swell. He also observed extensive areas of near-bottom turbid
layers over the southern Oregon shelf and slope. His results show
that: 1. in general the turbidity decreases with distance offshore,
but increases sharply within 10 to 20 m off the bottom; 2. relatively
turbid waters were observed on the upper slope in the swale north of
the Upper Rogue Canyon, and in the Upper Canyon itself, while the
■water over submarine banks was relatively clear; 3. marked seasonal
changes were evident in the turbidity of surface waters due to planktonic
organisms, but the turbidity was usually higher during summer upwel-
ling; 4. although near-bottom turbid layers were dense over the shelf
during the entire year, bottom turbidity was more evident over the
upper slope in winter when its generation by waves was greater and
when the downslope movement of the bottom turbid layers was

141
unopposed by upwelling.

Based on all previous work it is evident that the predominant
surface, subsurface, and bottom current direction, as well as the
resultant net transport, is to the south on the upper slope, while the
predominant current directions at all depths over the shelf are to the
north (Figure 41). Normal tides superimpose an oscillatory east-
west component of movement on this system, possibly at all depths,
while upwelling superimposes a west-to-east, subsurface to surface
transport during the summer.

Turbid Layer Formation and Transport Across the Shelf

The mechanism of lutum transport described by Moore (1970)
calls for the downslope transport of fine-grained lutum as bottom or
near-bottom low-density turbid layers. These turbid layers are often
thin and relatively slow-moving, without sufficient erosive power to
remove fine sand or the tests of Foraminifera into deeper water.
Depending on topographic or other conditions, they may be channelized
into thicker, faster flows, or may remain as un-channelized sheet
flows.

In the initial formation of turbid layers mixed sand and mud of
the southern Oregon rivers reaches the bays and estuaries. Much of
the coarse material is separated from the lutum in the bay immediately
seaward of the river mouth; part of the sand is restricted to channel

142
banks or tidal flats inside the bay (Kulm and Byrne, 1966), or sub-
jected to alternating littoral drift and restricted to the beaches or the
inner shelf shallower than 20-30 m (modern shelf sand, Figure 32).
The lutum fraction is separated into a very fine-grained clay and
colloidal suspensate (Figure 40) which often contains entrapped organic
debris, and a silt, clayey silt, or silty clay fraction which eventually
becomes the bottom turbid layer. The finest fraction (the suspensate)
is carried slowly westward in suspension in the water column by
alternating tidal currents, by-passing the shelf and upper slope and
settling in the manner of hemipelagic sediments to deposit on the
lower slope or adjacent deep sea (Figure 40).

Part of the lutum fraction may remain in the bay or estuary; how-
ever, most of it deposits over a wide area relatively near the river
mouth (Modern Shelf Mud, Figure 32). This newly deposited lutum
is subjected to re-suspension by long-period swell, and if the re-
suspended cloud is of sufficient density, it will form a bottom or near-
bottom turbid layer. Since long-period swell is most dominant during
the winter when the sediment supply is greatest, turbid layers are most
apt to form during this season. Long-period swell is a more effective
agent for re-suspending the lutum than normal sea waves. It is mostly
this former type of wave, with a period of 8-12 sec and frequently
greater than 14 sec off Oregon (National Marine Consultants, 1961),
that may attain sufficient bottom orbital velocity over all shelf depths

143
to erode fine sand and the finer-grained sediment. Inman (1957) has
demonstrated that it is the long-period waves, of both sea and swell,
which most often attain the critical orbital velocity of 1 0 cm/sec neces-
sary to erode or ripple fine sand. Moore (1966) has also suggested that
the long-period swell is the prime agent responsible for re-suspending
lutum. Neudeck (1970) suggests that certain trends are evident when
the frequency of long-period swell increases during the winter, among
these is a corresponding increase in turbidity and turbid layer formation.

Sundborg (1956) calculated that a minimum velocity of 10 cm/sec
is necessary to erode very fine sand (62 fj.). Postma (1967) notes that
the "critical erosion velocity" for fine-grained silt and clay varies
according to its degree of consolidation (i. e. , water content). For
example, a freshly deposited medium silt (30 (jl diameter) containing 90%
water would require a velocity of 15-20 cm/sec to initaite movement,
whereas the same size sediment containing 50% water would require a
velocity over 100 cm/sec. In each case, a somewhat lower velocity is
required to maintain the sediment in suspension. Thus, it is only the
long-period waves, mostly swell, which can provide the necessary
velocity for re-suspending recently deposited lutum on the southern
Oregon shelf.

Once the lutum is re -suspended into the water column as a near-
bottom turbid cloud, it is subjected to the influence of coastal currents.
A small part may move south over the shelf in the summer, but the

144
bulk of the material moves north in response to the net mass transport
over the shelf (Figure 40). During the winter, when the sediment
supply and coastal current velocities are greatest, the near-bottom
turbid cloud more nearly approaches a very low-density current which
moves northward under the action of coastal currents and westward
across the relatively steep shelf under the action of gravity.

The bottom turbid current continues to move in this fashion until
one of several events occurs. It may continue to move north until it
impinges against a natural topographic barrier, such as a headland or
a rock reef. Numerous resistant headlands, chains of sea stacks, and
rock reefs, are present along the southern Oregon coast. Cape Blanco,
Humbug Mountain, Cape Sebastian, and Cape Ferrelo are examples of
the first, and the rock reefs off the southern end of Cape Blanco and
off the Rogue River are examples of the last (Figure 2). These barriers
may tend to constrict the northward flow and temporarily increase the
density of the current, or they may disperse or divert the flow. In
either of these cases, the action of alternating tides together with the
shelf gradient will gradually move the turbid water outward to the shelf
edge. In summer when the northward coastal currents are weak, or if
the re-suspended turbid cloud is initially in a less-dense dispersed
state, the westward component of movement may be stronger than the
northern component. In this event, the turbid cloud will move as a
sheet flow directly, but more slowly, westward across the shelf to the

145
shelf edge. Thus as a consequence of the various oceanographic con-
ditions in both winter and summer, together with the influence of bot-
tom topography, the bottom turbid layer may reach the shelf edge most
often as a broad sheet-like cloud (Moore, 1966).

Transport Down the Slope

Upon reaching the edge of the shelf the turbid cloud is subjected
to: 1. the increased gradient of the upper slope; 2. the influence of
a predominantly southerly mass transport and a resulting component
of southwesterly bottom currents; and 3. possible turbulence arising
from internal waves, a factor which may keep the turbid layer stirred
up enough to prevent deposition on the outer edge of the shelf. In addi-
tion, topographic features may be present which would tend to channel
or divert the flow.

The submarine topography of the southern Oregon continental
slope reveals many features which may serve as natural barriers or
channelways to sediment movement (Figures 2, 4 and 5). The most
obvious of these are the numerous east-west trending submarine
valleys, especially the Rogue Canyon, Brookings Seavalley and Blanco
Seavalley. These valleys serve to channel sediment from the upper to
the lower slope. Another important valley is the unnamed swale to
the north of the Upper Rogue Canyon; this swale trends northeast-
southwest and probably feeds sediment into the Lower Rogue Canyon.

146
The topography of the southern end of Cape Blanco Bench (Figure 5)
strongly suggests that a system of north-south channels is present
which may also serve to channel sediment. Less obvious, but perhaps
as important, is the character of the continental slope itself. The
downslope gradient of the continental slope gives rise to normal down-
ward gravity flow and slumping of sediment from the shelf edge to the
upper slope, and from the upper to the lower slope.

The benches on the upper slope, which interrupt the steadily
descending gradient of the continental slope, can be considered as rela-
tive "highs" because of their less steep gradient (approximately l°-2°
versus an average of 3° 37'). In effect, this may have several con-
sequences depending on the direction and velocity of sediment-laden
currents or water masses which may move over such "highs. "
Downslope -moving bottom or near-bottom sediment loads tend to
deposit coarser-grained particles on these benches upon reaching the
abruptly decreased gradient. Any other slope currents would tend to
flow faster over these "highs" than over the lower slope, since the
"high, " in effect, has constrained the current to a narrower space in
the water column. From a topographic viewpoint, the benches, and
much of the upper slope, may be regimes of coarse sediment from
which the fine sediment is being continually removed or winnowed.

As the turbid bottom layer progresses down the slope it is often
5-10 m thick (Neudeck, 1970), and may become channelized by entering

147
sea valleys such as the Upper Rogue Canyon, the swale, or other val-
ley systems (Figure 40). Neudeck has found high turbidity in both the
swale and the Upper Rogue Canyon. In the swale, he also observed
indications of southwest-trending bottom currents and scouring at the
same station (970 m) where a significant amount of turbid water was
observed. He postulates that the scouring and current activity were
probably generated by the turbid, more dense, near-bottom waters
flowing down the swale in response to gravity. This explains the
relatively low Holocene sedimentation rate (9 cm/ 1000 years, Table 2)
determined for the Upper Rogue Canyon, as well as the scouring
observed in the swale to the north of the Canyon. One must assume that
the velocity of the turbid layer increases down-canyon due to an
increased thickness and density of the layer, and/or due to an increased
gradient.

Moore (1970) suggests that the velocity of the turbid layer
increases only slightly above 10 cm/sec in its transit, and this is not
sufficient to transport shallow-water foraminiferal tests into deeper
water. But Neudeck and others (Owens and Emery, 1967; Stanley
and Kelling, 1968) suggest that the velocity of such turbid layers may
increase enough to cause distinct scouring. It is evident that whatever
the resultant velocity of the turbid layer may be, it is enough to pre-
vent significant deposition of lutum in the upper reaches of the Rogue
Canyon, and perhaps in the shoaler portions of other valleys. The

148
northward-flowing lutum may have sufficient velocity to by-pass the
Canyon head and eventually divert into the swale to the north. In any
case, large quantities of lutum do become funneled, or channelized,
and eventually deposit on the lower slope. This process may be the
most important mode of supply for the fine-grained sediment on the
lower slope. When combined with the by-passed suspensate fraction,
the two probably account for the total Holocene and modern lutite cover
on the lower slope.

That portion of the bottom turbid layer which does not become
channelized probably flows down the upper slope in a sheet-like man-
ner. It has been established that the Holocene sediment cover on the
upper slope is thin, and often patchy enough to reveal "windows" of
older, late Pleistocene, relict sediment (Figure 32). This is true of
the Upper Plateau Slope as well as the benches. Moore (1966) contends
that once lutum has deposited, it forms a fairly stable mass and is not
prone to failure by slumping. If this assumption is correct, then the
slumping observed on the Upper Plateau Slope (Figures 21 and 22) is
probably a Pleistocene phenomenon, due to the failure of great masses
of sediment deposited there during lowered sea level. It is postulated
that this process did occur, which left large areas of still older
Pleistocene material exposed on the upper slope. The unchannelized
flows of Holocene and modern lutum do not deposit at as high a rate as
the channelized flows reaching the lower slope (10 cm/1000 years

149
versus 50 cm/1000 years); hence they have failed to cover the under-
lying Pleistocene material completely, leaving a patchy sediment dis-
tribution pattern. In addition, the increased gradient from the shelf
edge to the Upper Plateau Slope and the possibility of a Stokes "jet"
here may be sufficient to prevent deposition of all but the coarsest
lutum fraction on the Upper Plateau Slope.

The greater portion of the un-channelized lutum reaches the less-
steep bench areas on the upper slope, and is subjected to further diver-
sion, mostly in a southerly direction. The channels on the Cape Blanco
Bench may serve as routes of north-south transport for lutum from the
Umpqua drainage. Whatever quantity does move south within these
channels is fed into the swale to the north of the Rogue Canyon.
Silver (1969a) has observed similar channels on the southern Klamath
Plateau which empty into Trinidad Seavalley. He believes that they are
routes of sediment transport into Gorda Basin. Although no such
channels are evident on the Klamath Plateau off southern Oregon, the
southerly mass transport over this region may sweep much of the lutum
into Brookings Seavalley, which carries it to the lower slope. Core
6711-1, from Brookings Seavalley, shows the highest rates of deposition
(60 cm/1000 years) of any core on the lower slope.

Although it appears that the abruptly decreased gradient from
the Upper Plateau Slope to the benches on the upper slope would give
rise to the deposition of much of the lutum, several facts contradict

150

this. First, the southerly mass transport mentioned previously may
sweep the lutum into an available downslope valley; second, the sedi-
ment distribution pattern itself (Figure 32) shows that little Holocene
or modern lutite is present on the benches; third, the near-bottom
current velocities measured by Korgen (8. 4 to 45. 0 cm/sec at a
depth of 700-900 m) indicate that the velocities are high enough on the
upper slope to keep the bottom turbid layer in transit, or even to
winnow any newly deposited lutum from the bench surface. Topographic
highs, such as those at the western edge of the Klamath Plateau are
another factor which affects turbid layer movement. These highs
effectively dam any westward-flowing lutum, and give rise to a thicker
ponded accumulation behind the high. Although this undoubtedly occurs,
part of this accumulation may also be winnowed and diverted into down-
slope channels.

Deposition of Lutum on the Lower Slope

The distribution of Holocene and modern lutite on the lower slope
and the computed Holocene sedimentation rates (50 cm/ 1000 years
average, Table 2) attest to the fact that the lower slope receives the
major portion of lutum generated from southern Oregon drainages.
Lutum reaching the upper slope is either channelized directly and
funneled onto the lower slope, or it may deposit on the upper slope for
a brief period and later become re-suspended and channelized. In

151
either case, much of the lutum eventually funnels into the major dis-
tributary channels and accumulates on the lower slope.

Much of the lutum from the Upper Rogue Canyon and from the
swale to the north feeds into the Lower Rogue Canyon. Sedimentation
rates suggest that the Lower Rogue Canyon (core 6711-6, approxi-
mately 75 cm/ 1 000 years ), the swale (core 6708-38, 38 cm/ 1 000 years),
and Brookings Seavalley (core 6711-1, 60 cm/1000 years) are rapidly
filling with lutum. Thus it is not unreasonable to assume that all the
seavalleys on the lower slope, and the inter-valley areas as well, are
also filling as rapidly. The entire lower slope is growing and out-
building in this manner. Duncan (1968) has examined the Holocene
sediment in Blanco Valley adjacent to the southern Oregon slope, and
has calculated Holocene sedimentation rates ranging from 44 to 100
cm/1000 years in four cores from this area. The Holocene section in
these cores suggests that a distinct bulge of Holocene sediment is
building up at the base of the southern Oregon slope. Data presented
here Indicates that the lower slope is upbuilding in a similar manner.

Downslope gravitational processes, both within valleys and in
intervalley areas, are the dominant mechanism for transport of lutum
on the lower slope (Dott, 1963; Shepard, 1965; Moore, 1970). Although
bottom currents are probably present in the lower slope valleys, none
have been adequately measured. The newly-deposited lutum may be a
stable mass, as Moore (1970) has suggested. However, the margin is

152
relatively active tectonically, and the lower slope possesses a fairly
steep gradient (up to 8°); both of these facts suggest that considerable
slumping may occur on the lower slope, such as that observed in
Figure 21. This slumping is not as large-scale as that postulated to
have occurred on the upper slope during the Pleistocene, but it still
may be quantitatively important. Locally, the numerous small anti-
clines on the lower slope may serve as dams which give rise to a num-
ber of thickly ponded areas behind them. This is similar to the ponding
noted on the upper slope, but on a smaller scale.

The mineralogy of the lower slope sediments indicates a greater
influence from Tertiary rocks than do the sediments from other environ-
ments. Much of this may come from the Umpqua Mid- Coast Basins,
especially from the Umpqua River. If this assumption is correct, and
a similar turbid transport mechanism operates north of Cape Blanco,
as Neudeck (1970) suggests, then some Umpqua sediments may be
diverted to the south around Coquille Bank and onto the southern Oregon
margin. Blanco Seavalley would be expected to collect much of this
sediment and funnel it into the deep sea. However, no core has been
taken in Blanco Seavalley to test this hypothesis, and Duncan's cores
(1968) in the adjacent deep sea do not reflect this. However, it is sig-
nificant to note that one core near the mouth of Blanco Seavalley
(6604-12, Figure 25) exhibits the thickest Holocene section of any of
Duncan's cores. Consequently, it is not unreasonable to suggest that

153
Blanco Seavalley contributes the major portion of this Holocene material
in the form of lutum.

The Late Pleistocene and Holocene Sedimentation Patterns

The great influx of sediments during the Pleistocene originally-
covered much of the southern Oregon shelf, upper slope, and lower
slope (Figure 42). The benches are primarily Pleistocene phenomena,
having formed by the ponding of Pleistocene sediment behind anticlinal
folds on the upper slope. The Upper Rogue Canyon, although struc-
turally controlled, was primarily cut during the Pleistocene, as were
the majority of channels and valleys. Evidence from glacial marine
sediments in the adjacent deep sea (Griggs and Kulm, 1969) suggests
that the paleo-oceanographic regime was essentially the same in the
late Pleistocene as it is today. If the major winds and currents were
essentially the same, then it is not unreasonable to assume that the
paleo-oceanographic regime over the continental margin was also
similar.

As a consequence of the rise of sea level during the Holocene,
the deposition of coarse-grained material was greatly reduced. Even
so, a uniform Holocene sedimentation rate of 50 cm/1000 years over
the entire margin should have covered all the environments with a
sediment cover approximately six meters thick since the start of
Holocene time. However, the model of lutum transport just described

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has shown that such a uniform sediment distribution does not exist. A
thin Holocene cover, averaging only about 3-4 m thick, is present on
the upper slope, benches, and in the Upper Rogue Canyon, and a much
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157
SUMMARY AND CONCLUSIONS

Development of the Structural Framework
Pre-Tertiary History

The present structural pattern of the southern Oregon continental
margin is the end result of several large-scale orogenic events which
have occurred mostly since Mesozoic time. Southwestern Oregon and
northern California lie at the westernmost edge of the Cordilleran
mobile belt. This belt extends to the continental margin in these areas
and has been generally eugeosynclinal throughout most of the Paleozoic
and Mesozoic to late Cenozoic time (Dott, 1965). Initially, during
Paleozoic and much of Mesozoic time, the area over what is now the
present margin received thousands of feet of sediment, which formed
graywackes and associated volcanics. During the Nevadan orogeny of
late Jurassic and the later Mesozoic orogenies the area reached a peak
of metamorphism and plutonism and the geosynclinal sediments, such
as the Dothan, Rogue and Galice formations, were uplifted, intruded,
and metamorphosed to form the present Klamath Mountains. A dis-
tinctive arcuate low-angle thrust pattern was developed in these moun-
tains (Irwin, 1966) which remained intact despite the further warping
that took place at the end of Mesozoic time. Marine sedimentation
continued into Cretaceous time, but by the Late Cretaceous volcanism

158
had ceased and the deposition of the more mature non-turbidite sand
and mud ensued (Dott, 1965). Irwin (1966) has called these rocks the
superjacent sequence. The complex Mesozoic strata which probably
extend westward to form the underlying basement of the present
southern Oregon and northern California margins is believed to be the
result of the underflow of oceanic mantle beneath the earlier margin
of the continent (Hamilton, 1969; Silver, 1969a).

Tertiary History

Early in the Tertiary, probably beginning during Eocene time,
the sea transgressed to the northwestern edge of the Klamath Mountains.
This was followed by the deposition of mud and sand and was accompanied
by minor volcanism. Deposition continued throughout the Eocene and
Oligocene and resulted in the formation of many rhythmically-bedded
units, including turbidites such as those found in the Tyee Formation.
The source for this material was the pre-Tertiary complex of the
Klamath Mountains; these mountains no doubt supplied all of the sedi-
ments during the Tertiary.

Rocks dredged from the continental shelf and slope indicate that
the Tertiary strata extend westward under the southern Oregon margin
and lie between the older Mesozoic basement and the younger
Quaternary sediments. They may be exposed, or only thinly covered
by overlying sediments, atop several of the anticlinal folds which mark

159
the western edge of benches on the upper slope. The older Tertiary
strata, however, may be deeply buried beneath the southern Oregon
margin since the rocks recovered from that part of the margin are all
Pliocene in age, and no rocks older than middle Miocene have been
recovered from the Oregon margin to date (Kulm and Fowler, 1970).

The rocks recovered from the southern Oregon margin have a
lower percentage of unstable constituents than the overlying sediments
and fall into two groups. The first group consist of coarse-grained
impure sandstones, mostly arkosic and lithic wacke, from the shelf
and upper slope. The composition of these sandstones is similar to the
pre-Tertiary complex of Klamath Mountains, particularly the Upper
Cretaceous Series and the Dothan Formation, which suggests that the
source for the late Tertiary upper slope rocks was either the Jurassic
or Late Cretaceous strata of the Klamath Mountains. The second
group consists of fine-grained siltstones and mudstones from the lower
slope, some of which are calcareous. They have a higher percentage
of unstable constituents than the upper slope sediments and rocks and
their composition reflects the influence of the early Tertiary strata of
the southern Oregon Coast Range as well as that of the Klamath
Mountains.

Minor uplifting and folding began early in the Tertiary, and
although it continues on the margin and in coastal areas today, it
reached its peak during mid- and late Tertiary time (Mio-Pliocene)

160
with the onset of the Cascadan orogeny and the beginning of formation
of the southern Oregon Coast Ranges. A marked change in the structure
and in the pattern of coastal faults occurred during the mid- to late
Tertiary orogeny. Intense high-angle, north-south shears developed
in the Klamath Mountains and Coast Ranges, probably as a result of a
major shift in the direction of movement of the Pacific plate in relation
to the North American plate (i. e. a change in the direction of sea-
floor spreading). The direction of spreading shifted from a primarily
west-to-east direction to one that was primarily northwest-southeast;
Atwater and Menard (1970) have documented this shift as beginning as
early as 55 million years ago (Eocene time). Silver (1969a) has cal-
culated that the present relative motions between the Gorda and North
American plates is still in a northwest-southeast direction. The
intense shears developed on the continent, such as the Gold Beach
Shear Zone (Dott, 1962), superimposed a north-south pattern upon
the arcuate low-angle thrusts of the Klamath Mountains. Coastal
rocks became increasingly fragmented by this intense faulting. The
Franciscan complex of California was structurally juxtaposed against
the Klamath Mountains by shearing within the California Coast Ranges.

A renewed episode of sea-floor spreading and underthrusting
began in late Tertiary time, perhaps as late as Plio-Pleistocene
(Silver, 1969a). This resulted in compression against the continent
from the west and probably produced the north-south pattern of folds

161
on the southern Oregon and northern California margins. The high-
angle normal faults which cut the margin strata developed simultane-
ously, or shortly thereafter during the latest Pliocene and early
Pleistocene.

Evidence suggests that the continental crust of the western
United States and the adjacent oceanic crust have been undergoing
tension and extension since early in the Cenozoic (Hamilton, 1969).
However, it has been postulated that both underthrusting, producing
compressional features, and extension of the crust, producing high-
angle normal gravity faults, can co-exist over an oceanic-island
arc complex (Malahoff, 1970) or a continental margin-oceanic com-
plex (Silver, 1969a). This explanation would appear to fit the struc-
tural patterns observed on the southern Oregon margin.

Byrne, et al. (19 66) calculated that significant uplift of late
Tertiary sediments (as much as 1000 m) occurred along the seaward
portion of the central Oregon continental margin, and they suggested
that appreciable accretion to the continent has taken place during,
and since, the Pliocene. This evidence is in agreement with Silver's
hypothesis of underthrusting along the northern California and south-
western Oregon margins. Continued tectonic and structural mobility
is evidenced on the southern Oregon margin by the rocks which have
been recovered from it. From 80 to 300 m of uplift, and up to 225 m

162
of downwarp, are indicated from paleo-depth determinations using the
Pliocene fauna in these rocks.

Quaternary History of Sedimentation

Pleistocene

Although tectonic activity has continued on the margin since the
end of the Tertiary period to the present time, the history of the
Quaternary period on the southern Oregon margin is characterized by
a record of extensive deposition, changing regimes of sedimentation,
and sedimentary out-building and up-building. The glacial and inter-
glacial stages in the Pleistocene were accompanied by retreats and
advances of the sea, the latter are recorded in the elevated marine
terraces along the southern Oregon coast. At no time could the sea
level have been 500 m above its present level, which is the elevation
of the highest terrace level along the southern Oregon coast. Faunal
studies and radiometric dating indicate a rate of uplift of 2 m/1000
years has accompanied the formation of the terraces.

Sea level was lowered about 120-130 m below its present level
during the last stage of glaciation in the late Pleistocene, and vast
quantities of coarse elastics were deposited on the outer continental
shelf and slope. Reflection profiles indicate numerous truncated
structures. One or more unconformities exist beneath the southern

163
Oregon shelf and at the shelf edge. These unconformities, particularly
the one at the edge of the shelf, are probably Plio-Pleistocene (Bales
and Kulm, 1969). The wedge of sediment which unconformably over-
lies the truncated shelf edge was probably deposited during the last
major regression associated with the Wisconsin glaciation, and sug-
gests that the shelf began prograding at that time.

The coarse-grained sediments deposited on the margin during the
late Pleistocene continued to reflect a Klamath Mountain source; this
source probably still provided the greatest amount of sediment to the
margin. The development of the marginal plateau physiography began
in the Pleistocene when large quantities of coarse sediment began fil-
ling in synclinal basins and down-faulted structures on the upper slope.
The Upper Rogue Canyon began forming as a channel which was cut
along the trace of the older east-west fault at the shelf edge. Many of
the lower slope valleys also developed during this time.

Turbidity current deposition was prevalent during the Pleistocene
and many of the sand-silt layers which dominate the Pleistocene sec-
tion were probably laid down in this manner, Lesser amounts of mud
(which is now found as gray lutite) accompanied the sand-silt deposition.
Slumping of large sediment masses occurred during the late Pleistocene,
especially along what is now the Upper Plateau Slope. Pleistocene
sediments accumulated at about six times the rate of Holocene sedi-
ments, and may reach thicknesses of 100-200 m or more on the upper

164
continental slope and several hundred meters or more on the lower con-
tinental slope.

Holocene and Modern

The rise of sea level during the Holocene, probably began about
15, 000 years B. P. and may have been interrupted by several minor
regressions. The submerged terrace levels identified on the southern
Oregon shelf may reflect these periods of regression. Coarse-clastic
deposition on the outer margin ceased about 7, 000 years B. P. , as much
of it was trapped in newly-formed bays and estuaries. As a result, the
regime of sedimentation changed to one that was mainly characterized
by the transport and deposition of fine-grained silts and clays by bottom
turbid layers and a fine-particle suspensate (i. e. lutum transport).
This process produced the large quantities of olive gray lutite now
found on the margin.

The changes in Radiolaria/planktonic Foraminifera abundance
which mark late Pleistocene-Holocene boundary and other stratigraphic
horizons in deep-sea are also evident on the margin. Although all the
faunally-determined horizons within the late Pleistocene and Holocene
are probably present in margin sediments, only two late Pleistocene
horizons and one Holocene horizon were identified. The latter, the
5000-4000 years B. P. horizon, was the only one useful in correlation.

Volcanic ash from the eruption of Mt. Mazama (6600 years B. P. )

165
is present in several cores from both the shelf and slope off southern
Oregon; its occurrence suggests that the margin was an area of
accumulation for the ash prior to its eventual deposition on the deep
sea (Nelson, e_t aj_. , 1968). The Mazama ash is a distinct, stratigraphic
horizon in margin sediments and has been used for correlating upper
slope and shelf cores.

The abundance of blue-green hornblende and other minerals
indicative of metamorphic sources, together with an abundance of
chlorite in the clay fraction, indicate that the Klamath Mountains are
still the dominant source of sediments on the margin. However, the
mineralogy of Holocene sediments on the lower slope suggest that this
environment is receiving sediments from the Tertiary strata of the
southern Oregon Coast Range to a greater extent than other margin
environments. Lower slope sediments have a relatively high feldspar
content and exhibit a higher pyroxene to amphibole ratio than the other
environments .

This latter trend is significant, since finer -grained lower slope
sediments normally should exhibit low P/A ratios because of the ten-
dency for amphiboles to be found in the finer sediment sizes. Hence
a source other than the Klamath Mountains must be supplying
pyroxene to the lower slope in sufficient quantities to effect a noticeable
change in the P/A ratio. In addition to these trends, the only sample
in which the percent illite exceeded chlorite was that from a lower

166
slope core (6711-6-8).

The Columbia River, because of its large runoff, would normally
be thought of as a sediment contributor to the southern margin; how-
ever, the mineralogy of lower slope sediments more strongly suggests
that nearby Tertiary strata of the southern Coast Ranges are the more
probable secondary source, and that since Holocene time Columbia
River sediments have not reached far enough south to affect either the
southern margin, or the adjacent deep sea (Duncan, 1968).

Organic carbon preserved in margin sediments averages 1. 3%,
with lower slope sediments containing higher values than sediments
from other environments. The percent organic carbon increases up-
wards in margin cores, but only gradually; this fact may not reflect an
abrupt decrease in margin sedimentation from late Pleistocene to
Holocene time similar to that observed in the deep sea by Duncan ( 1 9 68 ^

Sedimentation rates obtained from margin cores suggest that the
lower slope is accumulating sediment, mostly of the olive gray lutite
type, at an average rate four to five times faster than the upper slope
environment (50 cm/1000 years versus 10 cm/1000 years). The result-
ing Holocene cover is unevenly distributed: an average of 3 m on the
upper slope versus 1 0 m on the lower slope. As additional evidence,
the transport processes which have operated during the Holocene have
given rise to a patchy Holocene cover on the surface of the upper slope
and benches, where large areas of relict Pleistocene (?) sediments

167
are still exposed which have not been covered by later Holocene or
modern deposits.

Oceanographic conditions existing today indicate that the net
transport over the southern Oregon shelf is to the north and that over
the upper slope and much of the lower slope is to the south. In addi-
tion, documented seasonal changes in the river runoff and oceanographic
conditions together with a knowledge of bottom topography suggest the
formation and net transport of lutum by bottom turbid layers can be
traced adequately throughout the margin.

A model of modern lutum transport by bottom turbid layers
and fine-particle suspensate is proposed for the southern Oregon mar-
gin. Bottom turbid layers are formed on the southern Oregon shelf and
move north and west under the influence of shelf currents and long-
period swell. The turbid layers are funnelled into submarine valleys
and transported to the lower slope. Lutum deposited on the upper
slope is eventually winnowed by southerly bottom currents and fed to
available downslope valleys and very little remains on the upper
slope. Slumping and other gravitational processes contributes addi-
tional lutite deposits to the lower slope. The end result of modern
lutum transport is the continual up-building and out-building of the
lower slope.

168

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183

LEGEND FOR APPENDICES

Sediment Age H Holocene

LP Late Pleistocene

Sediment Type OGL Olive Gray Lutite

GL Gray Lutite
S-S Sand -Silt Layers

Physiographic Province SH Continental Shelf

US Upper Continental Slope
CBB Cape Blanco Bench
KP Klamath Plateau
LS Lower Continental Slope
URC Upper Rogue Canyon
LRC Lower Rogue Canyon
MB Middle Bench
LB Lower Bench
UPS Upper Plateau Slope
LPS Lower Plateau Slope
URCW Upper Rogue Canyon Wall

'T" denotes less than one percent (trace).

184

APPENDIX 1. PISTON CORE AND ROCK DREDGE STATION LOCATIONS

OSU Station
number

Latitude
(north)

Longitude
(west)

Water

depth

(meters)

Physiographic
province

Length

of core

(cm)

6706-1

6706-2

6706-3

6706-4

6706-5

6706-6

6706-7

6706-8

6708-20

6708-23

6708-25

6708-33

6708-37

6708-38

6708-39

6708-40

6708-42

6708-43

6711-1

6711-2

6711-5

6711-6

6711-8

6708-22

6708-36

6708-41

6711-D1

6711-D2

6711-D3

6802-D1

6802-D2

6802-D3

6802-D4

PISTON CORE STATIONS

42*05.5'
42*09. 61
42*14.5'
42*31.5'
42*31.3'
42*31.0'
42*32.2'
42*49.4'
42*26.4'
42*21.6'
42*17.1'
42*29.8'
42*30.4'
42*35.2'
42*42.1'
42*45.8'
42*41.9'
42*35.9'
42*03.8'
42*07.3'
42*25.3'
42*29.8'
42*36.6'

42*23.2'
42*24.2'
42*30.5'
42*29.7'
42*44.0'
42*44.7'
42*04. 2'
42*04.5'
42*03. 9'
42*03.9'
42*08.1'
42*09.0'
42*17.5'
42*17.5'
42*43.0'
42*43.4'
42*27.3'
42*29.1'
42*36.8'
42*37.7'

124*56.0'
124*56.2'
124*47.8'
124*52.0'
124*45.7'
124*45.0'
124*39.0'
124*48.6'
124*42.5'
124*33.3'
124*35.0'
124*38.6'
124*50.3'
124*50.4'
124*50.0'
124*45.5'
124*37.3'
124*41.0'
125*06.9*
124*58.7*
124*56.9'
125*04.8'
125*01.5'

1183

1060

544

1060

540

420

150

316

118

100

165

104

769

988

658

443

121

148

2012

1365

1770

1776

1390

ROCK DREDGE STATIONS

124*40.3'
124*40.1'
124*43.2'
124*43.4'
124*40.0'
124*40.8'
125*03.5'
124*59.7'
124*49.3'
124*48.7'
124*57.8'
124*56.8'
124*48.5'
124*45.0'
124*50.8'
124*49.6*
124*55.6'
124*54.7'
125*01.4'
125*00.0'

US

MB

KP

URC

URC

URCW(US)

URC(SH)

CBB

SH

SH

SH

SH

URC

LS

CBB

CBB

SH

SH

LS

LS

LS

LRC(LS)

LS

430
390
377
150
273
355
465
375
110
243
610

65
583
472
427
152
455

50
408
430
516
340
560

125-130

SH

250-330

URCW(US)

110-150

SH

1450-1200

LS-MB

730-640

LPS-KP

1000-1200

MB

550-450

KP-UPS

460-550

CBB

1100

LS

1100

LS

185

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APPENDIX 4. TEXTURAL ANALYSES OF SEDIMENT SAMPLES

198

Depth

osua

Interval

M^

V

V

Sample

in cores

Sediment

Percent

Percent

Percent

Textural

Number

(cm)

Type

Sand

Silt

Clay

Classification

6706-1-1

0-5

OGL

6. 51

2. 17

-0.05

5.2

67. 5

27.3

CLSL

6706-1-2

8-11

S-S

5.75

2.22

0.08

55.2

28.7

16. 1

SLSN

6706-1-3

55-60

OGL

7.15

2.38

-0.08

8.6

50.9

40.5

CLSL

6706-1-4

100-105

OGL

7.40

2. 10

-0.08

1.6

55.0

43. 4

CLSL

6706-1-5

145-150

OGL

7.83

2.04

-0.04

3.0

47.6

49. 4

SLCL

6706-1-6

200-205

OGL

10.58

5.41

-1.00

2.4

25. 9

71.7

SLCL

6706-1-7

250-255

OGL

8.85

1.52

0.00

1.8

28.3

69. 9

SLCL

6706-1-8

300-305

OGL

9.02

3.88

0.58

1.8

58.7

39. 5

CLSL

6706-1-9

346-352

GL

8.71

4.99

0.23

30. 2

22.2

47.6

SSC

6706-1-10

405-410

GL

10.08

5. 92

-0.13

15.0

20. 9

64.0

SLCL

6706-1-11

425-430

GL

10.00

6.00

1.00

2.0

98.0

0

SL

6706-1-12

430+

GL

10.83

5. 17

-1.00

1.4

31.4

67.2

SLCL

6706-2-1

0-5

OGL

5.62

2.72

-0.61

29.3

42. 8

27. 9

SSC

6706-2-2

45-50

OGL

6.74

2.43

0.38

3.0

66.9

30.1

CLSL

6706-2-3

110-115

OGL

7.23

2.41

-0. 17

5. 9

49.4

44.7

CLSL

6706-2-4

150-155

OGL

8.43

2.20

0.02

4.3

39.4

56.3

SLCL

6706-2-5

185-190

OGL

9.70

3.66

0. 10

3.5

35.0

61. 5

SLCL

6706-2-6

196-198

OGL

No data

6706-2-7

200-205

OGL

8.00

2.66

0. 18

5.7

49.3

45.0

CLSL

6706-2-8

223-224

S-S

2.80

1.04

-0. 10

100.0

0

0

SN

6706-2-9

245-250

OGL

6.36

2.58

-0.17

22.2

46.0

31.8

SSC

6706-2-10

253-254

OGL

6.84

2.94

-0.06

19.3

42.4

38.3

CLSL

6706-2-11

282-283

S-S

2.75

1.03

-0.09

100.0

0

0

SN

6706-2-12

295-302

OGL

6.90

2.51

-0.21

3.8

55.3

40.9

CLSL

6706-2-13

300-315

OGL

7.36

2.22

-0.08

6. 1

50. 9

43.0

CLSL

6706-2-14

320-321

OGL

7.22

2.32

-0.09

11.2

46.3

43. 5

CLSL

6706-2-15

330-335

OGL

6.57

2.51

-0.20

15.8

49. 4

34.8

CLSL

6706-2-16

355-360

OGL

8.22

3.28

0.20

4.3

49.3

46.4

CLSL

6706-2-17

370-375

GL

8.06

1.43

-0.06

3. 1

42.6

54.4

SLCL

199

Appendix 4. (Continued)

Depth

osua

Interval

Sample

in cores

Sediment

M +

%

%

Percent

Percent

Percent

Textural

Number

(cm)

Type

Sand

Silt

Clay

Classification

6706-2-18

6706-2-19

6706-3-1

6706-3-2

6706-3-3

6706-3-4

6706-3-5

6706-3-6

6706-3-7

6706-3-8

6706-3-9

6706-3-10

6706-3-11

6706-3-12

6706-4-1*

6706-4-2

6706-4-3

6706-4-4

6706-4-5

6706-4-6

6706-5-1

6706-5-2*

6706-5-3

6706-5-4

6706-5-5

6706-5-6

6706-5-7

6706-5-8

6706-5-9

6706-5-10

385-390
390+
0-5
50-55
100-105
118

150-155

200-205

250-255

300-305

350-355

375-377

377+

380+

0-10

60-65

92-97

108-112

145-150

150+

0-10

25-30

85-90

90-91

93-95

96-97

107-110

115-117

120-121

125-127

GL
GL
GL
GL
GL

GL

GL

GL

GL

GL

GL

GL

GL

OGL

OGL

OGL

S-S

GL

GL

OGL

OGL

OGL

S-S

S-S

S-S

OGL

OGL

S-S

OGL

7.44
7.36
6.95
7.11
5.73

7.29
7.80
7.54
8.39
7.71
7.02
8.49
6.84
7.23
7.61
7.53
2.12
7.54
7.67
6.94
6.81
9.51
2.93
2.71
2.62
7.11
6.83
3.81
6.56

2.29
2.62
2.73
2.27
1.43

2.36
2.54
2.47
3.74
2. 96
2.56
4.85
2.69
2.41
2.01
2.62
1.01

2. 10
2.41
2.62

3. 11
5.63
2. 10
1.00
1.21
2. 15
2.53
1.43
2.54

-0.04
-0. 12
-0.07

0.01

0.47

No data

0.07

0.06

0.04

0.47

0.25

0.00

0.62

0.00
-0.08

0.03
-0.02
-0.03
-0.04
-0.08

0.06

0.04

0.53
-0.01

0.04

5.3

4.5

14.6

7.0

1. 9

4.4

5.0

6. 1

6. 1

7.2

11.0

21.0

14.0

4.3

5. 1

2.9

99.7

3.2

3.6

12. 8

14.2

16.7

96.3

94.7

0.03 100.0
-0.08 9.3

0.21
0.05
0. 13

10.0
95. 1
15.7

51.4
50.0
46.4
56.0
85.9

57.0
49. 1
50.8
56.3
51. 9
51.4
44.9
51.0
49.9
41.3
52.6
0.3
41.5
38.3
52.2
48.3
45.3

2. 1
1.7
0

40.2
37.2

3. 1
55.3

43.3
45.6
39.0
37.0
12.2

38.6
45.9

43. 1
37.6
40. 8
37. 5
34.0
35.0
46.8
54.6

44. 5
0

56.3
59. 1
35.0
37. 5
38.0

1.6

3.6

0
50.5
53. 8

1.8
28.9

CLSL
CLSL
CLSL
CLSL
SL

CLSL

CLSL

CLSL

CLSL

CLSL

CLSL

SSC

CLSL

CLSL

SLCL

CLSL

SN

SLCL

SLCL

CLSL

CLSL

CLSL

SN

SN

SN

SLCL

SLCL

SN

CLSL

200

Appendix 4. (Continued)

Depth

osua

Interval

Sample
Number

in cores
(cm)

Sediment
Type

%

cr

a+

9

Percent
Sand

Percent
Silt

Percent
Clay

Textural

c
Classification

6706-5-11

138-140

OGL

6.71

2.63

0.09

11.-3

44.2

44.5

SLCL

6706-5-12

145-148

S-S

2.92

1.61

0.07

97.3

2.2

0.5

SN

6706-5-13

185-187

OGL

6.47

2.58

0.27

18. 3

55.6

26. 1

CLSL

6706-5-14

207-210

OGL

6.70

2.53

0.43

11.6

61.4

27.0

CLSL

6706-5-15

227-230

OGL

6.82

2.67

0.08

8.3

53.6

38.1

CLSL

6706-5-16

243-245

OGL

7.15

2. 16

-0.03

7.4

41.3

51.3

SLCL

6706-5-17

270-273

OGL

6.93

2.61

0.05

11.6

40.8

47.6

SLCL

6706-5-18

273+

OGL

5.83

2.44

0.31

9.3

51.0

39.7

CLSL

6706-6-1

0-5

OGL

5.50

2. 19

0.54

3.9

41. 1

55.0

SLCL

6706-6-2

15-20

OGL

6.89

2.14

0.04

6.3

61.3

32.4

CLSL

6706-6-3

35-38

OGL

7.20

2.12

0.21

6. 1

60.6

33.3

CLSL

6706-6-4

60-65

OGL

7.09

1.71

0.16

2.2

68.5

29.3

CLSL

6706-6-5

80-83

OGL

6.95

1.35

-0.17

2.6

71.4

25.9

CLSL

6706-6-6

100-103

OGL

6.45

2.34

-0.08

15.0

56.8

28.2

CLSL

6706-6-7

125-127

S-S

3.14

0.66

-0.41

100.0

0

0

SN

6706-6-8

150-155

OGL

8.01

3.39

0.40

4.8

58.0

37.4

CLSL

6706-6-9

190-193

OGL

7.20

1.86

-0.10

11.5

50.4

38. 1

CLSL

6706-6-10

199-201

S-S

3.17

0.67

0.07

100.0

0

0

SN

6706-6-11

250-255

OGL

7.05

2.29

-0.02

7.4

55. 8

36.8

CLSL

6706-6-12

285-288

OGL

6.56

2.09

0. 12

7. 7

67.7

24.6

CLSL

6706-6-13

320-323

OGL

7.50

3.24

0. 18

13. 58

46. 1

40. 4

CLSL

6706-6-14

350-355

OGL

6.93

2. 48

0.04

10. 4

54. 3

35.2

CLSL

6706-6-15

335+

OGL

7. 19

2.65

0.22

9. 2

56.4

34. 4

CLSL

6706-7-1

0-5

S-S

5.25

2. 33

0.81

67. 4

18. 4

14.2

SLSN

6706-7-2

40-45

S-S

10.28

7. 35

0.77

45. 1

16.8

38. 1

CLSN

6706-7-3

70-75

S-S

5.28

2. 39

0.82

63.3

21. 7

15.0

SLSN

6706-7-4

120-125

S-S

5.15

2.41

0.74

65.0

20. 2

14.8

SLSN

6706-7-5

171

S-S

5.23

2.40

0.81

64. 9

20.3

14.8

SLSN

6706-7-6

195-200

S-S

4.78

1. 90

0.76

71.8

16.0

12.2

SLSN

6706-7-7

225-230

S-S

5.01

2.21

0.70

68.2

12. 8

19.0

CLSN

201

Appendix 4. (Continued)

a
OSU

Depth

Interval

Sample
Number

in cores
(cm)

Sediment
Type

9

\

•>

Percent
Sand

Percent
Silt

Percent
Clay

Textural

c
Classification

6706-7-8 253 S-S 5.53 2.53 0.78 64.6 18.9 16.5 SLSN

6706-7-9 275-280 S-S 5.18 2.20 0.80 65.7 10.2 24.1 CLSN

6706-7-10 285-290 S-S 4.83 1.92 0.77 63.9 25.4 10.7 SLSN

6706-7-11 315-320 S-S 5.11 2.21 0.80 64.5 23.0 12.5 SLSN

6706-7-12 345-350 S-S 5.61 1.88 0.84 63.4 12.8 23.8 CLSN

6706-7-13 385-390 S-S 5.09 2.21 0.79 66.9 20.1 13.0 SLSN

6706-7-14 410-415 S-S 4.75 1.86 0.83 66.1 25.3 8.5 SLSN

6706-7-15 445-450 S-S 4.96 2.09 0.77 67.8 22.0 10.2 SLSN

6706-7-16 465 S-S 5.32 2.41 0.74 56.2 28.3 15.5 SLSN

6706-8-1* 0-10 S-S 3.64 0.57 0.40 83.9 8.3 7.8 SN

6706-8-2* 35-40 S-S 6.68 3.75 0.81 63.2 16.8 20.1 CLSN

6706-8-3 95-100 S-S 3.40 0.54 0.04 89.7 7.8 2.4 SN

6706-8-4 250-255 OGL 6.23 2.41 -0.32 18.2 51.7 30.1 CLSL

6706-8-5 355-360 OGL 6.13 3.26 0.43 35.5 34.0 30.5 SSC

6706-8-6 375 OGL 6.55 2.60 -0.29 17.3 45.0 37.7 CLSL

6708-20-1 0-5 S-S 3.82 1.77 0.31 83.6 9.0 7.8 SN

6708-23-A 4-6 S-S 4.52 2.16 0.59 51.6 36.3 12.1 SLSN

6708-23-B 50-52 S-S 5.49 2.21 0.38 42.9 42.4 14.7 SLSN

6708-23-C 75-77 S-S 4.31 1.98 0.51 48.9 39.2 11.9 SLSN

6708-23-D 98-100 S-S 4.29 2.38 0.59 52.8 34.8 12.4 SLSN

6708-23-E 124-126 S-S 4.93 2.31 0.37 43.9 41.8 14.3 SLSN

6708-23-F 168-170 S-S 5.28 2.15 0.31 36.0 49.0 15.0 SNSL

6708-23-G 200-202 S-S 4.36 2.17 0.39 53.9 34.7 11.4 SLSN

6708-23-H 205-207 S-S 4.71 2.98 0.57 52.8 36.7 10.5 SLSN

6708-23-1 213-215 S-S 5.62 1.99 0.10 20.2 62.8 17.0 SNSL

6708-23-J 241-243 S-S 5.41 1.89 0.13 19.3 66.0 14.1 SNSL

6708-25-1 0-5 OGL 7.18 1.18 -0.07 1.7 70.0 28.2 CLSL

6708-25-2 75-80 OGL 6. 70 1. 95 -0. 29 8. 5 58. 9 32. 7 CLSL

6708-25-3 150-155 OGL 7.17 2.22 -0.13 3.5 55.4 41.1 CLSL

6708-25-4 225-230 OGL 6.62 2.01 0.09 6.0 68.7 25.3 CLSL

Appendix 4. (Continued)

202

Depth
OSU Interval

Sample i

in cores !

sediment

M*

0"

4>

a*

Percent

Percent

Percent

Number

(cm)

Type

Sand

Silt

Clay

c
Classification

6708-25-5

287

OGL

7.65

3.42

0.52

12.8

67.6

19.6

CLSL

6708-25-6

320-325

OGL

7.38

2.06

0.09

2.8

59.0

38. 2

CLSL

6708-25-7

350-355

OGL

6.63

1.91

-0.33

3.6

64. 9

31.4

CLSL

6708-25-8

395-400

OGL

6. 13

1.62

-0.24

9.6

81. 9

8.5

SL

6708-25-9

420-425

OGL

6.89

2.53

0.01

5.3

59.4

35.3

CLSL

6708-25-10 440-445

OGL

6.81

2.29

0.08

7.3

56. 1

36.6

CLSL

6708-25-11

460-465

OGL

6.86

2.09

-0.41

9.0

48.3

42.7

CLSL

6708-25-12 480-485

OGL

6.41

2.48

-0.36

17.0

47.2

35.8

CLSL

6708-25-13

500-505

OGL

8.01

3.28

-0.21

10. 9

29. 5

59. 5

SLCL

6708-25-14 520-525

OGL

7.95

3.98

0.64

16. 2

46.8

37.0

CLSL

6708-25-15 540-545

OGL

7.22

3.29

-0.12

18. 2

35.8

46.0

SLCL

6708-25-16 578-580

OGL

7.24

3.35

0.03

17.0

41. 1

41. 9

SLCL

6708-25-17 610

OGL

7.88

3. 95

-0. 17

17. 5

26. 5

56.0

SLCL

6708-33A

1-3

S-S

3.48

0.67

0.48

81.8

12.4

5.8

SN

6708-33B

21-23

S-S

4.03

1. 26

0.73

77. 9

2. 1

7.0

SN

6708-33C

41-43

S-S

2.97

0.31

0.22

91. 1

10. 9

6.8

SN

6708-33D

61-63

S-S

3.47

0.70

0.54

82. 4

27.3

6.7

SN

6708-37-1

10-15

OGL

7.41

2.08

0. 15

2. 1

60. 1

37.7

CLSL

6708-37-2

100-105

OGL

7.68

2.33

0.31

2.5

58.8

38.7

CLSL

6708-37-3

200-205

OGL

7. 14

2.21

0. 12

4.0

61.6

34. 5

CLSL

6708-37-4

300-305

OGL

7.42

3. 12

0.46

2.5

61. 7

35. 9

CLSL

6708-37-5

400-405

GL

7.39

2.48

0.20

1.6

61.0

37. 5

CLSL

6708-37-6

505-510

GL

7.41

2.30

0.17

3.2

58.7

38. 1

CLSL

6708-37-7

570-575

GL

7.59

2.08

0.08

1. 1

57.0

41.9

CLSL

6708-37-8

583

GL

7.54

2.45

0.22

1.0

59.9

39. 1

CLSL

6708-38-1

0-5

OGL

8.44

2.32

0.06

0.5

44.8

54.7

SLCL

6708-38-3

55-60

OGL

8.33

2.80

0.17

1. 1

50. 1

48.9

CLSL

6708-38-5

100-105

OGL

7.41

2.28

0.26

2. 3

61. 9

35.7

CLSL

6708-38-7

150-155

OGL

7.96

2.33

0.11

1. 1

52.4

46.5

CLSL

6708-38-9

200-205

OGL

7.56

2.70

0.08

4.6

52. 5

42.8

CLSL

Appendix 4. (Continued)

203

Depth
OSU Interval

Sample in cores S
Number (cm)

ediment
Type

M

%

a+

Percent
Sand

Percent

sat

Percent
Clay

Textural

c
Classification

6708-38-11

250-255

OCL

8.52

2.97

0.39

1.2

53. 8

45.0

CLSL

6708-38-13

300-305

OGL

8.23

2. 93

0.42

1. 5

56. 5

42.0

CLSL

6708-38-15

350-355

OGL

7.40

2.45

0.04

1.3

57.6

41. 1

CLSL

6708-38-17

400-405

OGL

10.63

5.37

0.60

1.8

50.4

47.8

CLSL

6708-38-19

450-455

OGL

7.53

2.31

0.18

1.2

59.4

39.4

CLSL

6708-38-21

469-472

OGL

9.93

4.84

0.51

0.7

51.6

47.7

CLSL

6708-38-22

472+

OGL

10.68

5.32

-1.0

1.3

40.2

58.5

SLCL

6708-39-1*

0-10

S-S

5.87

3.03

0.65

55.7

23.2

21. 1

SLSN

6708-39-2*

25-30

S-S

6.57

3. 17

0.21

30.9

39.2

29.9

SSC

6708-39-3

65-70

S-S

4.77

2. 59

0.58

72.3

11. 9

15.7

CLSN

6708-39-4

113-115

S-S

4.93

2.42

0.41

70.9

8.0

21. 1

CLSN

6708-39-5

125-130

S-S

7.33

2. 16

-0.04

4.6

54.6

40.8

CLSL

6708-39-6

130-135

S-S

3.62

0.37

0.05

84. 5

6.2

9.3

SN

6708-39-7

180-185

S-S

8.48

5. 11

0.76

35. 8

39.8

24.4

SSC

6708-39-8

230-235

S-S

7.39

3.37

0.39

15.6

50.4

34.0

CLSN

6708-39-9

280-285

S-S

3.87

0.56

0.41

82.7

7.2

10.1

SN

6708-39-10

330-335

S-S

3.12

0.20

-0.18

73.8

6.0

20.2

CLSN

6708-39-11

380-385

S-S

4.85

1.52

0.74

68.4

17.3

14.3

SLSN

6708-39-12

412-417

S-S

9.85

6. 15

0.73

22.4

43.1

34.5

SSC

6708-39-13

427

S-S

5.83

3.07

0.87

67. 5

15.6

16.8

CLSN

6708-40-1

0-5

S-S

8.67

5. 32

0.62

46. 1

13. 9

40.0

CLSN

6708-40-2

30-35

S-S

9. 71

6. 25

0.24

29. 1

19.7

51.2

SNCL

6708-40-3

40-42

S-S

5.02

1. 94

0.78

72. 9

16. 5

10.6

SLSN

6708-40-4

87-92

S-S

9.62

6.38

0.73

45.6

13. 3

41. 1

CLSN

6708-40-5

123-127

S-S

8.59

5.23

0.63

46.0

15. 4

38.6

CLSN

6708-42-1

225-230

S-S

3.42

0.62

0.21

93.6

4.8

1.6

SN

6708-42-2

434-454

S-S

3. 10

0. 31

0. 11

98.8

1.2

0

SN

6708-43A

0-10

S-S

3.15

0.36

0.45

89.7

7.8

2.5

SN

6708-43B

10-20

S-S

3. 12

0.33

0.05

93.8

4.2

2.0

SN

6708-43C

20-30

S-S

3.26

0.38

0. 17

89.4

7. 7

2.9

SN

204

Appendix 4. (Continued)

Depth

osua ]

Interval

Sample
Number

in cores S
(cm)

ediment
Type

M

0"

Q*

Percent
Sand

Percent
Silt

Percent
Clay

Textural

c
Classification

6708-43D

30-40

S-S

3.23

0.41

0.21

90. 9

7.4

1.7

SN

6711-1-1

0-5

OGL

6.67

2.20

-0.08

0.2

68.6

31.2

CLSL

6711-1-2

45-50

OCL

7. 19

2.44

-0.09

0.3

58. 2

41. 5

CLSL

6711-1-3

95-100

OGL

6.68

1. 50

-0.30

0.3

76.7

23. 1

SL

6711-1-4

145-150

OGL

7.63

1. 78

-0.28

0.2

58.9

40. 9

CLSL

6711-1-5

195-200

OGL

8.20

2.21

-0.01

0. 1

45. 9

54. 1

SLCL

6711-1-6

248-252

OGL

6.66

1. 98

-0.01

0. 1

70. 9

29.0

CLSL

6711-1-7

295-300

OGL

6.46

1.70

-0.03

0. 5

78. 9

20.6

SL

6711-1-8

345-350

OGL

8.32

2.89

0.27

0.3

53. 7

46.0

CLSL

6711-1-9

363

OGL

6.43

2.06

0.04

5.6

71.0

23.4

CLSL

6711-1-10

375-378

OGL

6.31

1.84

0.37

0.8

81.0

18. 2

SL

6711-1-11

385-388

OGL

8.30

4.46

0.05

18. 9

30. 1

51.0

SLCL

6711-1-12

390-392

OGL

7.34

1. 75

-0.04

0. 9

60. 2

38. 9

CLSL

6711-1-13

397-399

OGL

6.92

1.69

-0. 13

0.7

68. 5

30.8

CLSL

6711-1-14

404-408

OGL

9.36

3.42

-0.03

0. 8

33.9

65.3

SLCL

6711-2-1

0-5

OGL

5.98

4.45

-0.42

17.6

33.6

48.8

SLCL

6711-2-2

25-30

OGL

9.77

6.23

0.32

16. 3

34.0

49.7

SLCL

6711-2-3

50-55

OGL

7.78

2.64

0.01

6.3

46.6

47. 1

SLCL

6711-2-4

72-80

OGL

7.28

2. 19

0.04

8. 1

47.6

44.3

CLSL

6711-2-5

103-108

OGL

8.01

2.42

0.21

7.3

50.0

42.7

CLSL

6711-2-6

125-130

OGL

8.22

1.99

0.30

6.8

40.2

53.0

SLCL

6711-2-7

135-145

OGL

7.24

2.02

-0.23

8.8

46.9

44. 4

CLSL

6711-2-8

180-185

OGL

8.26

1. 87

-0.05

4. 1

38.6

57. 2

SLCL

6711-2-9

217-223

OGL

8.31

2.30

0.03

0. 9

45. 2

53. 9

SLCL

6711-2-10

260-265

OGL

8.60

3.68

0.24

0.4

51.6

48. 1

CLSL

6711-2-11

280-285

OGL

8.81

3.09

0. 14

0.5

45.6

53. 9

SLCL

6711-2-12

305-313

OGL

8.74

3.48

0.06

0.7

44.2

55. 1

SLCL

6711-2-13

320-324

OGL

8.00

2.48

-0.01

1.0

48. 2

50.8

SLCL

6711-2-14

342-348

OGL

8.55

3.05

0.28

1.3

51. 2

47. 5

CLSL

6711-2-15

360-365

OGL

10.96

5.04

0.34

0. 9

44.4

54.6

SLCL

205

Appendix 4. (Continued)

Depth

OSU Interval

Sample in cores S

ediment

M

U

q Percent

Percent

Percent

Textural

Number

(cm)

Type

4>

4>

4>

Sand

Silt

Clay

c
Classification

6711-2-16

387-393

OGL

8. 17

3.25

-0. 10

1.6

42. 5

56.0

SLCL

6711-2-17

415-420

OGL

8.50

2.45

0. 14

2. 2

45.6

52.3

SLCL

6711-2-18

430

OGL

9.07

2. 74

0.05

0. 9

37.5

61.6

SLCL

6711-5-1

0-5

OGL

7.84

1.61

-0.03

0.8

50. 9

48. 3

CLSL

6711-5-2

35-40

OGL

8.22

1.81

-0.08

0.4

41.6

58.0

SLCL

6711-5-3

70-75

OGL

8.37

2.55

0. 24

0. 5

51. 9

47. 7

CLSL

6711-5-4

105-110

OGL

8.45

1.80

-0.04

0.6

38.6

60.8

SLCL

6711-5-5

140-145

OGL

8.89

3. 35

0. 15

0.2

46. 2

53.6

SLCL

6711-5-6

175-180

OGL

8.93

3. 18

0.06

0.3

41. 9

57. 7

SLCL

6711-5-7

195-200

OGL

7.93

1.42

-0.07

0.3

48.3

51. 4

SLCL

6711-5-8

210-215

OGL

8. 15

1. 93

0. 10

0.5

49.8

49. 7

CLSL

6711-5-9

250-255

OGL

9.43

3.22

0.22

0. 1

43.2

56.6

SLCL

6711-5-10

280-285

OGL

10.22

4.66

0.25

0.2

43.4

56.3

SLCL

6711-5-11

315

OGL

No data

6711-5-12

315-320

OGL

8.20

1.99

-0.03

0. 1

44.6

55.3

SLCL

6711-5-13

350-355

OGL

8.80

2. 94

0. 10

0. 1

44. 1

55. 8

SLCL

6711-5-14

375-380

OGL

8.40

1. 99

-0.03

0. 1

41.0

58.9

SLCL

6711-5-15

410-415

OGL

10.78

4.58

0.24

0.2

39.6

60. 2

SLCL

6711-5-16

445-450

OGL

8.03

2. 15

0.00

4.4

44.8

50.8

SLCL

6711-5-17

475-480

OGL

8.35

2.03

0.09

0.6

46.3

53. 1

SLCL

6711-5-18

490

OGL

No data

6711-5-19

500-516

OGL

8.36

2.43

0. 14

2.4

46.9

50.7

SLCL

6711-5-20

516+

OGL

10.28

4. 18

0.57

1.0

49.4

49. 7

SLCL

6711-6-1

0-10

OGL

10.85

5. 15

-0.02

3.7

29.0

67.3

SLCL

6711-6-2

50-55

OGL

11. 16

4.84

-1.00

0.2

22.3

77. 5

CL

6711-6-3

100-105

OGL

11.77

4.23

-0.66

0.8

17.3

81. 9

CL

6711-6-4

150-155

OGL

11.93

4.07

-0.22

1. 5

15.2

83.2

CL

6711-6-5

200-205

OGL

11.41

4. 59

-1.00

0.5

19. 3

80. 1

CL

6711-6-6

255-260

S-S

7.63

3. 79

-0.36

16.4

19.2

64. 4

SLCL

6711-6-7

335-340

OGL

10.34

4. 25

-0.03

1. 5

27.7

70.8

SLCL

206

Appendix 4. (Continued)

Depth

osua

Interval

Sample

in cores S

ediment

M

4>

<T

a

Percent

Percent

Percent

Textural

Number

(cm)

Type

<t>

4>

Sand

Silt

Clay

c
Classification

6711-6-8

340+

OGL

12.35

3.65

-1.00

1. 5

11.3

87.2

CL

6711-8-1

0-5

OGL

8.22

2.58

0.07

0.3

48. 7

51.0

SLCL

6711-8-2

50-55

OGL

7.82

3. 10

0. 10

0.3

54.3

45.4

CLSL

6711-8-3

100-105

OGL

8.83

2.72

0.42

0.2

52. 2

47.5

CLSL

6711-8-4

150-155

OGL

8.91

2.92

0.60

0. 3

55.6

44. 1

CLSL

6711-8-5

200-205

OGL

7.25

1.75

-0.27

0. 2

56.3

43. 5

CLSL

6711-8-6

245-250

OGL

7.45

1. 92

0.03

0.3

59.6

40. 1

CLSL

6711-8-7

300-305

OGL

7.02

2.36

-0. 17

0.2

59.2

40.6

CLSL

6711-8-8

350-355

OGL

8.92

3.66

0.44

0.6

53.7

45. 7

CLSL

6711-8-9

400-405

OGL

10.69

5. 31

0.72

1. 4

54.0

44.6

CLSL

6711-8-10

410-412

S-S

5.20

2.22

0.39

37.7

49. 7

12.6

CLSL

6711-8-11

415-416

OGL

7.53

3.57

0.20

17. 1

43. 4

39.5

CLSL

6711-8-12

417-419

OGL

9.05

4. 26

0.35

3.0

49. 5

47. 5

CLSL

6711-8-13

430-431

OGL

11.84

4. 16

-0.71

2.4

15. 3

82.3

SLCL

6711-8-14

450-455

OGL

8. 14

2.38

0.02

1. 1

47.2

51. 7

SLCL

6711-8-15

500-505

OGL

7.43

1. 72

-0.06

1. 8

57. 3

40. 9

CLSL

6711-8-16

555-560

OGL

10.95

5.05

-1.00

0.7

39. 1

60.2

SLCL

6711-8-16

560+

OGL

9.73

4.02

0.33

0.4

46.9

52. 8

SLCL

Asterisk after sample number indicates Phleger core sample from multiple corer trip weight; all other

samples are from piston cores.

b
M+)= Phi Mean Diameter; 0"^ = Phi Standard Deviation (Sorting); qi - Phi Skewness; computed from

equations of Inman (1952).

"SN = sand; SL ~ silt; CL = clay; SSC ~ sand-silt-clay; SNCL = sandy clay; SLCL = silty clay; SLSN =
silty sand; CLSN = clayey sand; SNSL = sandy silt; CLSL = clayey silt; textural classification after
Shepard (1954).

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210

Appendix 6. (Continued) NOTES

a
Only 62(jl - 125(a portion of the sand fraction counted; mineral quantities expressed

as percents of total count.

b

Pyroxene/Amphibole (Clinopyroxene/Hornblende) ratio.

Numbers in parentheses refer to the percentage sub-total for that particular mineral group
or sub-group.

d
Includes ilmenite, magnetite, chromite and pyrite.

e
Includes minerals that occur in minor amounts: chloritoid, dumorierite, serpentine,

spodumene and all unidentified minerals.

211

APPENDIX 7. QUANTITATIVE ANALYSES OF THE MAJOR CLAY MINERALS FROM
X-RAY DIFFRACTION RECORDS OF SELECTED SAMPLES

Sample Number

E

s

o

a

f

Q

0>

a
>.

*->

a

g
3

1/3

<

Physiographic
province

0)
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a
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i-i
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s

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S
2?

Chlorite/ illite
(C/I) ratio

Other minerals
present

6711-2-1

5

OGL

H

LS

62

30

8

2. 1

6711-2-12

313

OGL

H

LS

58

41

1

1.4

6706-3-1

5

CL

P

KP

57

41

2

1.4

amphiboles

6706-3-10

377

GL

P

KP

59

39

2

1.5

amphiboles

6711-6-1

10

OGL

H

LRC(LS)

52

43

5

1.2

6711-6-8

345

OGL

H

LRC(LS)

49

49

2

0.9

6708-37-1

15

OGL

LP

URC

71

26

3

2.7

6708-37-7

575

GL

LP

URC

56

43

1

1.3

6708-25-4

230

OGL

H

SH

53

43

4

1.3

amphiboles

6708-25-16

580

OGL

H

SH

62

37

1.

1.7

amphiboles

6706-1-1

5

OGL

H

US

61

36

3

1.7

6706-1-11

430

GL

LP

US

63

35

2

1.7

6706-2-12

302

OGL

LP

MB

57

40

3

1.4

6706-2-17

375

GL

LP

MB

56

42

2

1.3

6708-38-1

5

OGL

H

LS

64

33

2

1.9

6708-38-21

472

OGL

H

LS

58

40

2

1. 5

6706-6-8

155

OGL

H

URCW(US)

69

29

2

2.4

amphiboles

6706-6-15

355

OGL

H

URCW(US)

68

32

1

2. 1

amphiboles

6802-D3-1

a

c

d
LT

LS

67

31

2

2. 1

amphiboles

6802-D2

a

c

H

CBB

64

32

4

2.0

amphiboles

6706-3-11-2

377+b

c

e
LT

KP

78

20

2

3.9

amphiboles

Sample from dredge haul.

Rock fragment from piston core cutting head.

'6802-D3-1 = Mudstone; 6802-D2 = Mud; 6706-3-11-2 = Mudstone.
Early Pliocene.
Mid-Pliocene.

212

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214

Appendix 8. (Continued) NOTES

a
Other--includes: heavy minerals, authigenic minerals, opaque grains and all unidentified grains.

b ,
Nomenclature assigned to all samples examined petrographically according to the classification of

impure sandstones of Williams, Turner and Gilbert (1954).

c
Shell fragments comprised 25% of haul.

d , ,
Number in parentheses indicates a re-computed percentage, wherein only quartz, feldspar and

rock fragments are assumed to constitute 100% of the sample.

e
All samples of this rock type contain < 10% grains, and are too fine-grained for petrographic

examination; identification based on megascopic and binocular-microscopic examination.

Samples are from rock fragments in basal portion and cutting head of piston core 6706-3; 50%
of fragments are siltstone and 50% are mudstone.

AN ABSTRACT OF THE THESIS OF

JOSEPH JOHN SPIGAI for the DOCTOR OF PHILOSOPHY

(Name) (Degree)

in OCEANOGRAPHY presented on

(Major) (Date)

Title: MARINE GEOLOGY OF THE CONTINENTAL MARGIN OFF

SOUTHERN OREGON

Abstract approved:

L. D. Kulm

The continental margin off southern Oregon, which includes the
shelf and slope from Cape Blanco to the Oregon-California border,
exhibits a distinctive marginal-plateau structural pattern which divides
the margin into the continental shelf, the upper continental slope and
its associated benches, and the lower continental slope. Lutum trans-
port and deposition have dominated the sedimentary processes on the
margin since the start of Holocene time.

The structure of the southern Oregon margin is characterized by
north-south trending compressional folds, and near-vertical faults
which have been down-dropped to the west. Large-scale folds on the
upper slope have ponded sediments behind them resulting in the forma-
tion of the Klamath Plateau, Cape Blanco Bench, and other bench-like
features. Development of the structural pattern is most likely a result
of the compressive underthrusting of the oceanic lithospheric plate
beneath the southernmost Oregon-northern California margin and the

crustal extension which exists throughout the nearby continent and
ocean basin.

Useful stratigraphic horizons within the late Pleistocene and
Holocene margin deposits include Mazama Ash (6600 years B. P. ) and
several recognizable shifts in the abundance of Radiolaria and plank-
tonic Foraminifera, particularly one dating from 5000-4000 years
B. P. Holocene sedimentation rates vary from an average of 10 cm/
1000 years on the upper slope to an average of 50 cm/1000 years on
the lower slope, indicating that the lower slope is out-building and up-
building more rapidly than the upper slope. The paleo-depth range of
Pliocene fauna in sedimentary rocks from the margin suggests that
subsequent to their deposition both uplift and subsidence occurred on
the southern Oregon margin.

Sediments from the southern Oregon margin consist primarily
of olive gray lutite, gray lutite, and sand-silt layers. Olive gray
lutite is Holocene in age and is ubiquitous on the margin, with the
thickest accumulation (10 m average) found on the lower slope, while
the distribution of Holocene lutite on the upper slope is thin and patchy
(3-4 m or less). The gray lutite appears to be a late Pleistocene
deposit, and the sand-silt layers reflect both ages. The surface sedi-
ment distribution pattern on the shelf consists of modern inner shelf
sand, modern central shelf mud, and mixed deposits of both types.
Relict deposits are present at the shelf edge. The lower slope consists
entirely of modern mud, but the surface sediment on the upper slope

and benches consists of both modern and relict deposits, and mixtures
of the two.

The mineralogy of the unconsolidated and consolidated sediments
from the margin indicates that the Klamath Mountains have been the
dominant source for these deposits since early Tertiary time. This
is reflected in the abundance of blue-green hornblende and other heavy
minerals indicative of the Mesozoic rocks of the Klamath Mountains;
the same source is suggested for the abundant chlorite found in the clay
fraction of margin sediments and rocks. There are indications in the
mineralogy of lower slope sediments which suggest that the Tertiary
strata of the southern Oregon Coast Ranges may be a secondary source
for the deposits in this environment. When compared to the upper
slope sediments, those from the lower slope have a higher feldspar
content, a higher pyroxene -to-amphibole ratio, and an apparently
higher illite content.

As a result of the Holocene rise in sea level, the deposition of
coarse elastics on the southern Oregon margin has been restricted to
the inner shelf. Consequently, only the fine-grained lutum discharged
from rivers is deposited on the outer margin environments. Sub-
marine topography, oceanographic conditions, and gravity are impor-
tant factors which effect transport and deposition of lutum on the mar-
gin. A model of modern lutum transport by bottom turbid layers and
fine -particle suspensate is proposed for the southern Oregon margin.
Long-period swell is believed to be responsible for much of the

formation of bottom turbid layers on the shelf. Once formed, these
turbid layers move north and west over the shelf under the influence of
shelf currents, alternating tidal action, and gravity; upon reaching the
slope they are funneled into submarine valleys and deposited on the
lower slope and adjacent deep sea. Lutum deposited on the upper slope
is eventually re-suspended and transported by southerly bottom cur-
rents into down-slope valleys; very little lutum remains behind on the
upper slope. Deposition of the fine-particle suspensate as well as
slumping and other gravitational processes contribute to the lower
slope sediments. The end result of modern lutum transport is the
continual up-building and out-building of the lower slope.

CASE BINDER

^^3 Syracuse, N. V.
Stockton, Calif.

SpVgai

Thesis II

S66845 Spigai

Marine aeoloav of thp
continental margin off
southern Oregon.

thesS66845

Marine geology of the continent* margin

3 2768 002 01580 2

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