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SEDIMENTATION

ACROSS THE OXYGEN MINIMUM ZONE

ON THE CONTINENTAL SLOPE

OFFSHORE CENTRAL CALIFORNIA

A Thesis

Presented to

The Faculty of the Department of Geology

San Jose State University

In Partial Fulfillment

of the Requirements for the Degree

Master of Science

By

Thomas L. Vercoutere

May, 1984

APPROVED FOR THE DEPARTMENT OF GEOLOGY

APPROVED FOR THE UNIVERSITY

ACKNOWLEDGMENTS

The undertaking of this study could not have been accomplished

without the encouragement, support, and guidance of many friends and

colleagues. Al Roberts, my friend and committee member, was the most

influential of all, providing the initial impetus for graduate work.

Committee chairman Hank Mullins provided the initial idea as well as

support and guidance throughout the study. The Petroleum Research Fund

of the American Chemical Society's ACS-PRF Type G grant #12923-GB2 to

H. T. Mullins provided financial support. Moss Landing Marine Labora-

tories provided use of the R/V CAYUSE and crew, without which this study

could not have been accomplished. A great deal of thanks goes to fellow

graduate students Dave Nagel, Rich Rasch, Dave Schwartz, and Joel

Thompson who generously assisted at sea.

I am indebted to the U.S. Geological Survey and my friends and col-..

leagues there for allowing me to use laboratory facilities where most of

the research was conducted. Special thanks are due Mike Torresan and

Kris Johnson, who provided instruction and assistance in physical

analyses of the sediments; Gerta Keller, Kris McDougall and John Barron,

who gave invaluable assistance in the identification and interpretation

of the foraminifers and diatoms; Jim Gardner and Brian Edwards, who

generously provided both unpublished data and helpful discussion; and

Karen Johnson who helped in the final preparation of the many figures in

this thesis.

I wish to thank Lorrie Duval and John Dern who labored through the

iii

manuscript in its formative stages, and to my committee membe.rs Hank

Mullins, Al Roberts and Cal Stevens for their critical review of the

manuscript.

Finally, I wish to thank Martha Dern for understanding and support

when it mattered.

iv

TABLE OF CONTENTS

ABSTRACT

INTRODUCTION

Previous Work

Study Area

Geologic Setting

Oceanographic Setting

METHODS

Field operations

Laboratories Techniques

RESULTS

Physical Properties Analyses

Carbon Analysis

Biostratigraphic Analysis

Clay Mineral Analysis

14c Analysis

X-radiography

Page

xii

1

3

4

5

5

11

11

14

14

15

15

16

17

17

18

Surface Sediments --------------------------------------- 18

Grain Size ---------------------------------------- 18

Sand Components

Carbonate and Total Organic Carbon

Clay Mineralogy

Lithostratigraphy ---------------------------------------Gravity Core Descriptions

Gravity Core Grain Size

v

18

21

21

26

26

27

Gravity Core Carbonate and Total Organic Carbon --- 27

Box Core Descriptions ----------------------------- 27

Box Core Grain Size ------------------------------- 30

Box Core Carbonate and Total Organic Carbon ------- 30

Box Core Sand Grain Constituents ------------------ 33

Biostratigraphy ----------------------------------------- 37

Planktonic Foraminifers --------------------------- 37

Diatoms ------------------------------------------- 48

Chronostratigraphy --------------------------------------

14c Age Determinations

50

50

DISCUSSION --------------------------------------------------- 51

Effect of Currents on Surface Sediment Texture

and Composition --------------------------------------- 51

Effect of Oxygen Content on Surface Sediment

Composition 55

Clay Mineral Assemblages in Surface Sediments ----------- 62

Total Organic Carbon Distribution in Surface

Sediments --------------------------------------------- 67

Correlation of Cores ------------------------------------ 68

Biostratigraphic Correlations

Carbonate Content Correlation

Lithostratigraphic Correlation

70

72

74

Clay Composition ----------------------------- 76

Sedimentation Rates ------------------------------------- 77

Rates Derived from 14c Data ----------------------- 77

vi

Rates Derived from Biostratigraphic Data ---------• 79

CONCLUSIONS -------------------------------------------------- 83

REFERENCES CITED --------------------------------------------- 86

APPENDICES --------------------------------------------------- 94

A. Description of Gravity Cores ------------------------ 94

B. Grain Size in Gravity Core Sediments ---------------- 104

C. Weight Percent of Total Organic Carbon and

Carbonate in Gravity Cores ------------------------ 106

D. Description of Box Cores ---------------------------- 108

E. Grain Size in Box Core Sediments -------------------- 119

F. Weight Percent of Total Organic Carbon and

Carbonate in Box Cores ---------------------------- 121

G. Compositional Percentage of Sand Size Material

in Box Cores -------------------------------------- 123

H. Percentage of Individual Planktonic Foraminiferal

Species in Gravity Cores 127

vii

Figure

1.

2.

3.

4.

LIST OF FIGURES

Bathymetric Map of Central California Continental Margin with Study Area. ----------------------------------

Oxygen Concentration Relative to Water Depth from Offshore Central California. -----------------------------

Central California Coast, 19 April 1979, Tiros N Satellite, VHRR Infrared Image Enhanced for Water Temperature. ---------------------------------------------

Bathymetry Map of Study Area Showing Bottom Sample

Locations. -----------------------------------------------

5. Surficial Sediment Texture from Box Cores Relative

Page

6

7

9

12

to Water Depth. ------------------------------------------ 19

6. Cumulative Percent Surficial Sand Components from Box Cores Relative to Water Depth. , --~--------------------

7. Weight Percent Total Organic Carbon and Carbonate in Surficial Sediments from Box Cores Relative to

··20

Water Depth. --------------------------------------------- 22

8.

9.

10.

Cumulative Percent Smectite, Illite, and Chlorite plus Kaolinite in Surficial Sediments from Box Cores Relative to Water Depth. ---------------------------

XRD Diffractogram of Glycolated and Magnesium Saturated Surface Clay Assemblages. ----------------------

Cumulative Percent Gravel, Sand, Silt, and Clay Relative to Depth in Core from Gravity Cores.

11. Weight Percent Total Organic Carbon (TOC) and

23

25

28

Carbonate Relative to Depth in Core from Gravity Cores. 29

12. Cumulative Percent Gravel, Sand, Silt, and Clay Relative to Depth in Core from Box Cores. ---------------- 31

13. Weight Percent Total Organic Carbon (TOC) and Carbonate Relative to Depth in Core from Box Cores. 32

14. Cumulative Percent Sand Components Relative to Depth in Core from Box Cores 1 through 4. ---------------------- 34

viii

Figure Page

15. Cumulative Percent Sand Components Relative to Depth in Core from Box Cores 5 through 8. ---------------------- 35

16. Cumulative Percent Sand Components Relative to Depth in Core from Box Cores 9 and 10. ------------------------ 36

17. Plots of Coiling Ratio of Neogloboquadrina pachyderma and Abundance of Selected Species of Planktonic Foraminifers from the Assemblages in Core GC-1. ---------- 39






23. Plots of Coiling Ratio of Neogloboquadrina pachyderma and Abundance of Selected Species ·of Planktonic Foraminifers from the Assemblages in Core GC-7. ---------- 45



26. Plots of the Abundances of Selected Species of Planktonic Foraminifers that Display Systematic Variation with Age from the Assemblage in Core V1-80-P3. -------------------- 49

ix

Figure Page

27. Diagram Showing Effects of Current Velocities of the California Undercurrent During Typical Summer Conditions on the Distribution of Surficial Sediment Texture and Sand Composition. ---------------------------- 52

28. Current Velocities Required for Erosion, Transportation, and Deposition. ------------------------------------------ 53

29. Distribution of Surficial Total Organic Carbon, Carbonate, and Sand Components Relative to Water Depth and Their Possible Relation to an Impinging Oxygen Minimum Zone. ------------------------------------- 56

30. Percentage of Benthic Foraminifers in the Sand-size Fraction of Surface Samples Relative to Water Depth and Their Relation to the Oxygen Minimum Zone. ----------- 58

31. Percentage of Fecal Pellets in the Sand-size Fraction of Surface Samples Relative to Water Depth and Their Relation to the Oxygen Minimum Zone. ----------~---------- 59

32. Percentage of glauconite in the sand-size fraction of surface samples versus water depth and their relation to the oxygen minimum zone. --------------------- 61

33. Compositional Range of Clay Mineral Assemblages from Cores in the Study Area. --------------------------------- 66

34. Biostratigraphic Correlation of Gravity Cores.

35. Correlation Chart of Box and Gravity Cores from the Continental Slope Northwest of Point Sur, California.

X

71

75

Table

1.

2.

3.

4.

5.

6.

7.

LIST OF TABLES

Station Location, Water Depth and Depth of Penetration of Cores and Camera Stations. -----------

Semiquantitative Clay Mineral Assemblages of Surficial Sediments. -----------------------------

Occurrence of Planktonic Foraminifers in

Gravity Cores. --------------------------------------

Geochemical Classification of Marine Sedimentary Environments Based on Mineral Composition. ----------

Semiquantitative Clay Mineral Assemblages of Recent and late Pleistocene Sediments. --------------

Ratio of Planktonic to Benthic Foraminifers. --------

The Biostratigraphically Derived Sediment Accumulation Rates for the Holocene and late

Pleistocene. ----------------------------------------

xi

Page

13

24

38

62

64

73

80

ABSTRACT

Sedimentation on the continental slope northwest of Point Sur,

California has been affected by northerly flow of the California

Undercurrent and a persistent oxygen minimum zone (OMZ) associated with

seasonal coastal upwelling. To document and understand the geological

processes and their products associated with the OMZ in this area, 10

. box and 9 gravity core samples were collected at approximately lOD-m

depth intervals along a transect between 300 and 1400 m of water.

The depositional regime changes from that of erosion/nondeposition

on the slope swept by the California undercurrent exceeding the thresh

old velocity needed to transport/erode fine sediment, to that of depo

sition on the slope below the effect of the undercurrent. This change

occurs between 600 to 800 m and is indicated by: (1) a decrease in

glauconite content from >30 percent at 500 m to <5 percent at 700 m;

(2) location of a mudline between approximately 750 and 800 m; and (3)

an increase in fine-sand-size mica and siliceous microfossils from <5

percent to )18 percent and <2 percent to >6 percent, respectively,

between 650 and 800 m. The clay mineral assemblage displays a down

slope increase in percent smectite and decrease in percent illite and

chlorite plus kaolinite between approximately 600 to 700 m.

The biogenic and authigenic components of surface sediments have

been affected by impingement of the OMZ. The percentage of benthic

foraminiferal tests is at a minimum between 593 and 905 m where the

lowest oxygen content of the OMZ impinges the bottom. The maximum

xii

_,

percentages of glauconite and fecal pellets are at the upper (525 m)

and lower (1025 m) boundaries of the OMZ, respectively.

Total organic carbon (TOC) content of surface sediments, Which

increases down slope from a minimum of 0.6 weight percent at 279 m to a

maximum of 2.5 weight percent at 1200 m, is predominantly controlled by

the percentage of clay-size sediment rather than by the oxygen content

in the overlying water. The correlation coefficient for weight percent

TOC and percentage of clay in the sediment is 0.95 and for weight

percent TOC and oxygen content is 0.66.

Biostratigraphic and lithostratigraphic data indicate a late

Miocene to Holocene unconformity at the boundary between a glauconitic

sand and a non-glauconitic, silty sand, 15 to 25 em beneath the

sediment-water interface in cores frPffi approximately 500 m. An uncon-

formity caused by a depositional h~atus or a slide has resulted in the

absence of approximately a 7,00D-year section of Holocene sediment.

The distribution of modern sediment on the upper continental slope

within an area of seasonal coastal upwelling, a persistent OMZ, and an

eastern oceanic boundary current displays recognizable down-slope

changes controlled by these oceanographic conditions. Recognition of

similar sedimentological features in the rock record may be useful for

the interpretation of analogous depositional environment.

xiii

INTRODUCTION

The combined interaction of photosynthesis, respiration, oxidation

of organic material, and oceanic circulation result in a nonlinear

vertical distribution of oxygen in open oceanic water columns (Sverdrup

and others, 1952). A pronounced oxygen minimum zone (OMZ) typically

occurs at intermediate water depths with higher concentrations in both

shallower and deeper water (Richards, 1957). Oxygen minimum zones tend

to be best developed and most persistent in areas of coastal upwelling

along eastern boundaries of ocean basins where surface biological

productivity is highest. Demaison and Moore (1980) used the term

"anoxic" to define water within an OMZ containing less than 0.5 ml/1 of

dissolved oxygen. The 0.5 ml/1 concentration will be utilized to define

the upper and lower limit of the OMZ in this study.

The impingement of an oxygen minimum zone on the seafloor may be

reflected in the physical, chemical, and biological characteristics of

near-surface sediments if the zone is temporally and spatially persist

ent (Diester-Haass, 1978). Authigenic minerals, such as phosphorites

(Veeh and others, 1974;_ Burnett, 1977) and glauconite (McRae, 1972; Odin

and Matter, 1981), commonly form during early diagenesis either within

or at the boundaries of oxygen minimum zones. Organic carbon content in

the sediments may also be significantly higher in OMZ's than in

surrounding regions (Diester-Haass, 1978).

Biological activity in near-surface sediments also may be affected

by the impingement of an oxygen minimum zone (Thompson and others, in

prep.). Complete anoxia may inhibit all organisms except anaerobic

bacteria (Rhoads and Morse, 1971) resulting in the preservation of

short-term variability of sediment make-up and original depositional

structures owing to a lack of bioturbation (Calvert, 1964; Codispoti,

1983; Summerhayes, 1983).

The accumulation patterns, when viewed on a secular time scale, of

some petroleum source rocks, phosphorite deposits, glauconites, biogenic

silica, and sediments enriched in elements from the biogenic cycle,

appear to be strongly influenced by oxygen concentrations and produc

tivity of the water column superjacent to the .. depositional site (Fischer

and Arthur, 1977; Baturin, 1983). Sedimentary facies and biofacies

patterns within many ancient sedimentary units in which these types of

deposits are found have been interpreted as having formed in low oxygen

environments (McRae, 1972; Fischer and Arthur, 1977; Demaison and Moore,

1980; Sheldon, 1980; Odin and Matter, 1981).

Despite the importance of OMZ's on ancient sediments, a paucity

of literature exists concerning the effect of an impinging OMZ on

sedimentation and early diagenesis of modern sediments along the upper

and middle continental slope. Such studies have never before been

conducted on the central California continental slope even though

phosphorite and glauconite are present in this area (Galliher, 1935;

Chesterman, 1952; Rein and others, 1974; Mullins and Rasch, 1981)

coincident with seasonal upwelling and a persistent oxygen minimum zone

(Hickey, 1979; Broenkow and Greene, 1981). In light of these

deficiencies, this study was conducted particularly to identify

2

solutions to the following conditions or problems:

1. What are the near-surface sediment facies patterns across an open

ocean oxygen minimum zone? Specifically, what are the sources, rates,

concentrations, and distribution of sediment in this environment?

2. What, if any, early diagenetic products occur within this zone?

What are the diagenetic facies patterns across slope and down core?

Specifically, are phosphatic, glauconitic or other authigenic sediments

actively forming? If so, what are their relationships with the OMZ?

3. Is the sediment across the OMZ enriched in organic carbon? If so,

to what level is it concentrated and how does it vary spatially and

temporally?

4. What types of sedimentary structures are present across the OMZ?

5. What effect have sea level changes had on sediment distribution and

diagenesis?

Previous Work

A comprehensive examination of coastal upwelling and its sedimen

tary record is given in a two volume publication edited by Suess and

Thiede (1983). Individual papers deal with a wide spectra of subjects

including sedimentological and geochemical features in upwelling regions

(Baturin, 1983; Summerhayes, 1983) and constituents in the water column

(Codispoti, 1983; Fischer and others, 1983)~ The continental margins

off South West Africa and Peru-Chile have well developed OMZ's and have

been the primary sites for studies on the effects of oxygen concen

tration on phosphorite formation (Burnett, 1977; Baturin, 1978) and

3

sediment composition (Calvert and Price, 1971; Krissek and oth~rs,

1980).

Previous work in the study area can be divided into two groups:

geologic and oceanographic. Published geological investigations of the

continental slope between Point Sur and Monterey Canyon are few. The

most intensive investigation to date is the study by Greene (1977)

although an investigation of the source and dispersal of clay minerals

off Point Sur was conducted by Griggs and Hein (1980). A few seismic

reflection profiles of the margin off Point Sur have been published in

reports for leasing the outer continental shelf for oil exploration

(McCulloch and others, 1980).

Oceanographic investigations in the study area have dealt with

biological, chemical, and physical oceanography. The effects of oxygen

concentration on the biological community on the slope off Point Sur

were examined by Thompson (1983). Studies on particulate flux and

nutrient levels in the water column and oceanic circulation have been

conducted as part of the VERTEX program by Moss Landing Marine Labora

tories and the California Cooperative Oceanic Fisheries Investigations.

These include works by Broenkow and Smithie (1978), Broenkow and Greene

(1981), and Martin and Knauer (1983). Investigations of the California

Current System conducted by the Naval Postgraduate School in Monterey

include work by Wickman (1975) and Traganza and Conrad (1981).

Study Area

The area of investigation for this study is located on a north-

4

westerly transect down the continental slope from Point Sur, California

to the Monterey Canyon. Water depths range between 279 and 1420 m

(Figure 1).

Geologic Setting

The geologic structure and present physiography of the central

California continental margin was developed primarily since the early

Miocene by folding, faulting, sliding, and slumping (Curray, 1966;

Silver and others, 1971; Blake and others, 1978; Howell and others,

1980). Tectonic movement and fluctuations in sea level have exposed a

variety of rocks that provide a aource of sediment for modern conti

nental slope deposits, including river and stream input, seacliff

erosion, and relict shelf sediments (Griggs and Rein, 1980). Coastal

rivers have been the major source of fine-grained sediments during the

Holocene, providing as much as 80 percent of the sediment along the

northern and central California coast (Griggs and Rein, 1980). Using

LANDSAT imagery, Griggs and Rein (1980) identified sediment disperal

plumes emanating from the Russian River, San Francisco Bay, and Salinas

River as the major sources of suspended sediment along the central

California coast; only minor contributions from other rivers and creeks

entering along the coast.

Oceanographic Setting

Dissolved oxygen concentrations seaward of the Point Sur area

display a pronounced minimum (less than 0.5 ml/1; the OMZ) between 525

and 1025 m with a low of 0.27 ml/1 at 750 m (Figure 2) beneath the

5

122°30' 37°oo~·----~~--------------~----------------------------------37°oo'

~<V

'··' ~ ·-a·,. 7- .,

0 10

F--~ km

North

.- 11 seaside

Figure 1. Bathymetric map of central California continental margin with study area indicated by box. From NOAA bathymetric map NOS 1307-11B, (contours in meters).

6

Oxygen (mill)

0 0.5 1.0 1.5 2.0

400

- 600 CIJ .... Q) -Q)

E -.s:::. .... 0. Q)

0 800 .... Q) .... co ~

1000

1200

Figure 2. Oxygen concentration relative to water depth from offshore central California. Stippled area represents oxygen concentrations of (0.5 ml/1 {the oxygen minimum zone) between 525 and 1025 m. Data from Broenkow and Greene (1981).

7

surface expression of upwelling. There is little variation in the depth

of the oxygen minimum zone for a distance of 150 km offshore (Broenkow

and Gree~e, 1981), and this OMZ has persisted for at least the past 20

years along the central California margin (Churgin and Halminski, 1974).

The California Current system, which is the eastern limb of the

North Pacific gyre, is driven primarily by wind stress patterns over the

North Pacific Ocean (Halliwell and others, 1980). Strong, persistent,

southeastward-directed wind stress during the spring and summer and the

Coriolis effect. res~lt in a net water transport of near-surface layers

away from the coast. The displaced water is replenished by upwelling of

cold, nutrient-rich water from a subsurface zone less than approximately

200 to 300m deep (Sverdrup and others, 1952; Halliwell and others,

1980). Although the pattern of upwelling is complex ( Pirie and others,

1975; Hickey, 1979), satellite thermal imagery shows coastal upwelling

waters may become large scale cyclonic or elongate plumes with sharp

thermal fronts (Traganza and Conrad, 1981). One such area of intense

upwelling occurs in the study area northwest of Point Sur, (Figure 3;

Broenkow and Smithie, 1978).

Along the west coast of the u.s., an undercurrent flows northward

at depths from 200 to 500 m or more (Hickey, 1979). This undercurrent,

known as the California Undercurrent, is a subsurface northward flow

that occurs below the main pycnocline and seaward of the continental

shelf (Hickey, 1979); its water is characterized by higher temperatures

and salinity than the surrounding water (Wickman, 1975). Mean flow

velocities are usually low, on the order of 5-10 em/sec (Schwartzlose

8

Figure 3. Central California coast, 19 April 1979, Tiros

N Satellite, VHRR infrared image enhanced for water temperature

(white, 10° C; black, 20° C).

9

and Reid, 1972; Broenkow and Greene, 1981) although Wickman (197-5) has

determined that off Monterey, California, jets of equatorial water

occurring between 200 and 500 m may have northerly flow velocities as

high as 2D-40 em/sec. When seasonal upwelling weakens or ceases during

the winter, the core of the California Undercurrent propagates upward

toward the surface to become the major flow component of the northerly

flowing Davidson Current (Hickey, 1979). Year-round ocean current

velocity data along the central California coast are rare. A sequence

of measurements conducted in less than 500 m show seasonal changes in

both direction and magnitude (Wickman, 1975; Halliwell and others,

1980). For most of the period between November 1973 to February 1974,

southward flow over the slope was between 5 and 12 em/sec. In June and

July 1974, a northward countercurrent flow below approximately 200 m

developed over the slope with flow velocities as great as 8 em/sec (data

from Wickman, 1975, in Halliwell and others, 1980). Measurements taken

during August and September of 1980 (which include deeper measurements)

in the same region (Broenkow and Greene, 1981) generally confirm the

results of Wickman.

10

METHODS

Field Operations

During 1981 and 1982 the R/V Cayuse occupied 10 sites in the study

area at water depths between 279 and 1400 m. Box core and gravity core

samples and bottom photographs were recovered at approximately 100-m

depth intervals along the transect (Figure 4; Table 1) northwest of

Point Sur where the oxygen minimum zone impinges on the bottom.

A Benthos box corer equipped with a stainless steel box (20 x 30 x

60 em) was used to recover an undisturbed portion of the sea floor and a

9-cm diameter gravity corer was used to retrieve the upper 1-2.2 m of

sediment. Approximately 10 bottom photographs were taken at each

station from 2 m above the sediment with a Benthos deep-sea camera

system.

Each recovered box core was carefully removed from the box and an

18 x 2 em longitudinal slab was taken for X-radiography and subsamples

were taken at S-cm intervals with a 100 cm3 syringe. The 8-cm liner

containing the gravity core was removed from the barrel, sealed, and

returned to the laboratory.

During the study, ship location was determined by a LORAN-e coastal

navigation system supplemented by radar triangulation and satellite

navigation fixes. Station positions were recorded at the time of bottom

impact of the corer or camera, indicated by the winch tensiometer or

sonic alarm, respectively. Water depth was determined with a 12 kHz

precision depth recorder.

• Gravity Core

1111 Box Core

;.. Bottom Camera

Figure 4. Bathymetric map of study area showing bottom sample locations. From NOAA bathymetry map NOS 1307-11B, (contours in meters).

12

13

Table 1.--Station locations, water depths, and penetration of box

cores and gravity cores, and camera station locations

Sample Water Subsurface

Number Depth Penetration Latitude Longitude

(meters) (centimeters)

Box Cores

BC-1 279 (10 122° 05.1 I w 36° 19.3 1 N BC-2 390 35 122° 05.4 1 w 36° 21.0 1 N BC-3 510 10 122° 05.4 1 w 36° 21.9 1 N BC-4 593 23 122° 05.5 1 w 36° 22.3 1 N BC-5 690 36 122° 06.3' w 36° 23.0 I N BC-6 785 44 122° 08.3' w 36° 24.1' N BC-7 905 42 122° 10.7 1 w 36° 25.1 1 N BC-8 1020 43 122° 12.0 1 w 36° 25.7 1 N BC-9 1085 43 122° 12 • 5 I w 36° 26.3 1 N BC-10 1200 42 122° 13.0 1 w 36° 27.6 1 N

Gravity Cores

GC-1 505 91 122° 05.1 1 w 36° 21.8 I N

GC-2 717 130 122° 07.0 1 w 36° 23.0 1 N GC-3 832 230 122° 08.9 1 w 36° 25.1 1 N GC-4 862 225 122° 09.6 1 w 36° 25.4 1 N

GC-5 983 200 122° 10.8 1 w 36° 25.9 1 N GC-6 1072 176 122° ll.4 I w 36° 26.8 1 N GC-7 1183 180 122° 12.1' w 36° 27.6' N

GC-8 1277 198 122° 12.4 1 w 36° 29.0 1 N

GC-9 1420 215 122° 17.0 1 w 36° 30.6 1 N

Camera Stations

C-1 300 122° 05.5' w 36° 19.8 1 N C-2 452 122° 06.0' w 36° 21.3 I N

C-3 570 122° 07.0 1 w 36° 21.7 I N C-4 688 122° 07.1 1 w 36° 22.3 1 N

C-5 801 122° 08.6' w 36° 23.9 1 N c-6 903 122° 10.8 1 w 36° 24.7 1 N

C-7 1005 122° ll.4 1 w 36° 25.7 1 N C-8 1100 122° 12.0 1 w 36° 26.5 1 N

C-9 1210 122° 14.1' w 36° 26.5 1 N

Laboratory Techniques

Core samples were brought back to the lab at the u. s. Geological

Survey and stored vertically at 4° C and 100 percent humidity until they

were split, described, X-radiographed, photographed, subsampled (10-cm

intervals for gravity cores and 5-cm intervals for box cores), and

archived.

Physical Properties Analyses

Grain size (sand, silt, and clay) was determined by wet sieve and

pipette separation following the methods of Folk (1974). Textural clas

sification of sediments follows that of Shepard (1954), and symbols used

for graphic lithology and sedimentary structures are those used in the

Deep Sea Drilling Project initial reports. The sand component of box

cores was recovered, dried, and split to approximately 300 to 400 grains

for point counts with a binocular microscope. Grains were identified

and counted as 1 of 11 categories consisting of: (1) quartz and feld

spar; (2) mica; (3) opaque minerals (including authigenic pyrite); (4)

rock fragments; (5) glauconite; (6) fecal pellets; (7) planktonic foram

inifers; (8) benthic foraminifers; (9) siliceous microfossils; (10)

macrofaunal shell fragments; and (11) unidentified material including

organic debris. The term "glauconite" will be used in the morphological

sense to describe sand-sized greenish grains. Authigenic pyrite,

present in very small quantities (< 0.5 percent) in some early Holocene

and Pleistocene sediment, was counted as an opaque mineral.

14

Carbon Analysis

Total carbon values were determined on oven dried (65° C) and

powdered bulk samples with a LECO combustion carbon analyzer following

the methods of Kolpack and Bell (1968). Inorganic carbon values were

determined using an automatic coulometric titration apparatus following

the manufacturer's instructions (Coulometrics Incorporated, 1979).

Total organic carbon is the difference in the two carbon values, and

carbonate content is calculated from the inorganic carbon content

values. Precision between runs of three replicate samples is on the

order of 2-4 percent of the value of total carbon and 1-2 percent of the

value of inorganic carbon. Measurement accuracy was checked every 20

analyses with standard carbon rings or NBS standard SCo-1. In order to

separate trend movements in gravity core profiles, which may represent

Pleistocene to Holocene changes, from cyclical or analytical error

fluctuation, a third order smoothed line is shown. The line is plotted

from the mean value of a sequence of three numbers centered on the

middle number.

Biostratigraphic Analysis

Samples for planktonic foraminiferal biostratigraphy were collected

from the gravity cores at 20-cm intervals. Samples were washed on a 250

mesh (62 micron) sieve and allowed to air dry. Splits of approximately

300 individuals greater than 150 microns were separated to eliminate the

indistinguishable juvenile foraminfers. Individuals were identified to

species and counted for quantitative frequency distribution and coiling

direction of Neogloboquadrina pachyderma. Box core slabs were also

15

selectively subsampled for planktonic foraminiferal biostratigraphy and

were analysed in the same manner.

Clay Mineral Analysis

Samples for semiquantitative X-ray diffraction analysis of clay

minerals following the methods of Rein and others (1976) were collected

from the upper 2 em in all box and gravity cores and from within a

12,500 to 15,000 year BP interval and an 18,000 to 22,000 year BP

interval (determined from planktonic foraminiferal biostratigraphy) in

gravity cores GC-3, GC-4, GC-5, GC-8, and GC-9. Oriented mounts were

made from the <2 micron size fraction using the filter-membrane peel

technique of Drever (1973). They were X-rayed from 3° to 14° 29 at 1°

per minute to identify the clay minerals and- from 24° to 26° 2e at¥4

per minute to distinguish chlorite from kaolinite after being Mg

saturated and glycolated. Peak areas were measured with a planimeter

and relative abundances of individual clay minerals were calculated by

measuring the (001) peak area, and then multiplying by the weighting

factors of Biscaye (1965) and normalizing to 100 percent. Along the

central California margin, the expandable clay phase, with its charac

teristic 14-15 A peak, is commonly a smectite/illite mixed layer clay

with an average of 74 percent expandable layers (Griggs and Rein, 1980).

The expandable phase will be referred to as smectite. Glauconite and

fecal pellets were treated with R2o2 and Morgan's Solution, ultrason

ically disaggregated and dispersed, then mounted and X-rayed in the same

manner as clay samples.

16

14c Analyses

Six samples were submitted for 14c age determinations to Geochron

Labs in Cambridge Massachusetts where clay and organic matter were

recovered from whole sediment samples, then treated with hot dilute HCl

to remove any old, detrital carbonate. The remaining material was

filtered, washed, dried, and roasted in oxygen to recover carbon dioxide

from the organic matter for the analyses.

x-radiography

X-radiographs of the box and gravity cores were taken to examine

sedimentary structures. Recognition of structures on radiographs is

possible because changes in texture and density result in changes in

contrast on the radiograph (Bouma, 1969). A light table was used to

examine X-radiographs and identify sedimentary and biogenic structures.

17

RESULTS

Surface Sediments

Surficial sediments in this study are defined as the upper 5 em of

box core samples. Samples from the top of gravity cores were not used

because of uncertainty of sediment loss on impact of the corer.

Grain Size

Surficial sediments from water depths between 279 and 600 m are

dominated by sand-size material which comprises over 88 weight percent

of the sediment (Figure 5). Below 600 m the amount of sand decreases

and there is a concomitant increase in the weight percent of silt and

clay. Maximum values of 49 weight percent silt, 41 w~ight percent clay,

and a minimum value of 10 weight percent sand occur at 1200 m.

Sand Components

The 700-m bathymetric contour approximates a significant boundary

about which surficial sand compositions change (Figure 6). The per

centage of quartz and feldspar is variable over the entire depth range

but reaches a maximum near 700 m. Mica content, less than 5 percent on

the upper slope, increases to greater than 15 percent below 700 m.

Fecal pellets are not found in sediments above 700 m but become a major

component below comprising as much as 20 percent of the sediments at

1020 m. Rock fragments are only present in sediments shallower than

700 m. Glauconite is a major component of the sediments shallower than

700 m (>30 percent between 390 and 593 m) and rapidly disappears below

-0 ... Q) -Q)

E -.r::. -c. Q)

c

400

600

800

1000

1200

Figure 5.

Cumulative Percentage of Clastic Sediment

0 25

••••••••••••••••••••••• ••••••••••••••••••••

50 75

................. . ........................... . ::::::::::::··:· .... :.:.:.:.:.:.:.:.:.:.:.:.:. :·:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.:.: ......... .· ..... ·.· ..... ·.·. ·.·.·. ·.·. ·.·.· ... ·.·.·.·.· ... ·.·.·.·.· .· .·.·.·.·.·. ....... . ................................... . .... . ..................................... . :: .· :-:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·:·: ·: ·:·:·:· :-: ·:-: ·:·:·:·:·: .. . ...................................... . . . .............................................................................. . . . ...................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

• •••••• tl tl •• tl ••••••••••••••••••••••••••• . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .....................................

::::::: r: ::r :: r:: :::: r:: r:: r r:: n: r: >:: =-· · ......................... . . . . . . . . . . . . . . . . .. . . .. . . . . ..................... . . . . . . . . . . . .. . . . . . . . .................. . . . . . . . . . . . . . . . . . ................... ................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ........... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

•••••• •••••• •••••• •••••• •••••• •••••• no~ D 6

Gravel Sand silt Clay

100

Surficial sediment texture relative to water depth.

19

,... til ... <D -<D

·e .s::. -0. <D Cl .... <D -Ill ;:

0

400

600

800

1000

1200

D

Cumulative Percentage of Sediment Components

20

Quartz +

Feldspar

Mica

Opaque

Minerals

40

~ [ill] .

II

60

Rock Fragments

Glauconite

Fecal Pellets

Planktonic Foraminifers

80 100

400

600

800

1000

1200

~ Benthic Foraminifers

Siliceous

Microfauna

Carbonate Shell Fragments

Organic Debris

Figure 6. Cumulative percentage of surficial sand components relative to water depth.

20

that depth. The percentage of benthic foraminifers reaches a-low

between 593 and 905 m and increases above and below those depths. The

percentage of planktonic foraminifers is less than 2.5 percent in all

surface sediment except at 593 m where it reaches 5 percent. Siliceous

microfaunal debris is very rare or absent above 700 m and increases to

as much as 6.5 percent below. Macrofossils are present at all depths

except 593 m and 1020 m. The maximum percentage of macrofossils occurs

at 1085 m.

Carbonate and Total Organic Carbon

Calcium carbonate weight percent in surficial sediments changes

significantly in the down slope direction as shown in Figure 7. The

lowest carbonate concentration was measured at ~93 m; the values triple

at sample locations 100 m shallower and deeper than this location.

Total organic carbon (TOC) in surficial sediments is relatively

constant at less than 1 weight percent on the slope between 400 and

700 m. However, below 700 m the TOC content increases in a nearly

linear fashion with increasing water depth, attaining a maximum of 2.49

weight percent at 1200 m (Figure 7).

Clay Mineralogy

Surficial clay mineral assemblages display a down slope change and

can be divided into two groups separated at approximately the 600-m

contour (Figure 8; Table 2). The group from less than 600 m is charac

terized by lower smectite and higher illite and chlorite + kaolinite

than the deeper water group (Figure 9). The shallower group clay

21

Weight Percent Total Organic Carbon

0 1.00 2.00 3.00 4.00

400

-Cl) ~

Q) .... Q)

600 E -.r:: .... c. Q)

Cl .... 800 Q) .... Cil

~

1000

0 1.50 3.00 4.50 6.00

Weight Percent Carbonate

T 0 C ee---ilte---ee

Carbon ate mlllll---111111111-----1111111

Figure 7. Weight percent total organic carbon and carbonate in surficial sediments relative to water depth.

22

> 4: ....I (.)

1-z w (.) 0: w a.. w > 1-4: ....I :::::> :::E :::::> (.)

75

50

25

0 • 300 400 500

a . • I I o U I •

600 700 800 900 1000 1100 1200 1300 1400

WATER DEPTH (meters)

[]] Chlorite +

Kaolinite

Illite

Smectite

Figure 8. Cumulative percent smect·ite, illite, and chlorite plus kaolinite in surficial sediments relative to water depth.

N w

24

Table 2.--Semiquantitative clay mineral assemblage of -

surficial sediments from the continental slope northwest

of Point Sur, California. Percentages determined from

corrected X-ray diffraction peak volume

[S, smectite; I, illite; C+K, chlorite + kaolinite]

WATER CORE DEPTH s I K + C

(meters) (percent) (percent) (percent)

BC-1 279 40.0±9.2 27.0±4.2 33.0±9.2

BC-2 390 50.0±2.8 27 .0±4 .2 23 .0±1.4

BC-3 .510 34.0±9.2 32.0±0.7 33.5±9.2

BC-4 59;3 45.5±9.2 29 .0±4. 2 26 .0±4 .2

mean 42.8±8.6 29.0±3.3 28.3±6.4

BC-5 690 55.5±0.7 25 .0±1.4 19.5±0.7

BC-6 785 55.0±1.4 22.0±1.4 23 .0±0. 7

BC-7 905 59 .5±2 .1 22.0±1.4 19.0±1.4

BC-8 1020 56.0±2.8 24.5±2.1 19.5±0.7

BC-9 1085 56.0±5.7 21.0±1.4 23.0±4.2

BC-10 1200 53.0±5.7 23.0±0.7 23.5±6.4

mean 55.8±3.3 23.0±1.8 21.5±3.1

combined mean 51.1±8.5 25.2±3.8 23.8±5.6

14 13

chlorite +

kaolinite

12 11 10 9 8 7 6 5 4

Degrees 2 9

Figure 9. XRD diffractogram of glycolated and magnesium saturated surface clay assemblages from upper slope (BC-1) and lower slope (BC-9).

3

assemblages are ·also more variable in composition than the deeper group

clays even though the deeper group is from a geographically larger area.

The mean clay assemblage for the upper continental slope northwest of

Point Sur is 51.1 percent smectite, 25.2 percent illite and 23.8 percent

chlorite+ kaolinite (see Table 2). Of the total chlorite+ kaolinite

percentage, chlorite comprises between 53 and 59 percent, being slightly

higher in the shallower group.

Lithostratigraphy

Gravity Core Descriptions

Lithologies, sedimentary structures, and visual descriptions of

gravity cores 1 through 9 are shown in Appendix A. The cores are

composed predominantly of silty clays and clayey silts with some clayey,

silty sand, silty sand and pebbly sand present. Sediment in most cores

is grayish olive (10Y4/2) to olive gray (5Y3/2) with some areas dusky

yellow green (5GY5/2) and moderate olive brown (5Y4/4). Most original

sedimentary structures are not recognizable on X-radiographs because

they have been bioturbated. The upper parts of the cores are typically

more intensely bioturbated or homogeneous than the lower part of the

same cores. Cores GC-1, GC-3, and GC-5 have a laminated interval

between 60 to 80 em. A sharp, irregular contact separating relatively

coarse sediment from underlying fine sediment is present at 60 em in

GC-2 and at 22 to 24 em in GC-3 and GC-4. Glauconite is concentrated

in a surface layer 10 to 20 em thick in GC-1 and is present as a minor

constituent in the upper 50 em of GC-2.

26

Gravity Core Grain Size

The sediments in the gravity cores display a wide range in sand,

silt, and clay percentages (Figure 10, Appendix B). The cores from

higher on the slope tend to contain more sand and silt than the cores

from lower on the slope. The variance in the percentages of sand, silt,

and clay decreases in the down slope direction.

Gravity Core Carbonate and Total Organic Carbon

The carbonate content in the gravity cores ranges between 1.57 and

9.65 weight percent. There is an increase down core followed by a

variable amount of fluctuation in carbonate in all cores except GC-1 in

which the carbonate content decreases down core (Figure 11, Appendix C).

The total organic carbon (TOC) in GC-1 ranges from 0.56 to 4.41

weight percent. In cores 2 through 9, the TOC ranges from 0.67 to 2.57

weight percent with only a slight decrease or no decrease down core

(Figure 11, Appendix C).

Box Core Descriptions

Lithologies, sedimentary structures, and visual descriptions of box

cores 1 through 10 are·given in Appendix D. Box cores above 700 mare

predominantly sand, pebbly sand, and silty sand; cores below 700 m are

predominantly sandy, clayey silt; clayey silt; and silty clay. Most

textural changes are gradational with overlying and underlying groups.

There are sharp, irregular contacts in box cores 2, 7, 8, and 10 sepa

rating coarser on top from finer sediment below. The sediment in most

cores is olive gray (5Y3/2) to grayish olive (10Y4/2), or olive black

27

50

'E !:!

" 0 100

u .:

" 150 .. 0

200

GC-1 (505 m) GC-2 (717 ml GC-3 (832 m) GC-4 (862 m) GC-5 (91!3 m)

Cumulative Percent Cumulative Percenl Cumulative Percent Cumulative Porconl Cumulative Percenl

0 50 100 0 50 100 0 50 100 0 50 100 0 50 100

GC-6 (1072 m) GC-7 (1183 m) GC-8 ( 1277 m) GC-9 ( 14 20 m)

illHill .

D D ~

Cumulative Percent Cumulative Percent Cumulative Percent Cumulative Percent

Gravel

Sand

'E !:!

Silt .. 0 u .: ::

Clay " " 0

Figure 10. Cumulative percent gravel, sand, silt, and clay relative to depth in core (from gravity cores 1 through 9).

0

50

100

150

200

N OJ

Gravity Cora 1 (606 rn)

TOC (wl ,.,

t.oo 2.oo J.oo •.oo a.oo

50

g :l 100 X

!

g , 150

200

2.00 4,00 1.00 1.00 10.00

Carbonate (wt '1.}

Third Order Smoothed C1rbonate

Total Organic

Carbon (TOCJ

Carbonate

tl

"' ., .... X

z n 0 :ll , n ~

50

100

150

200

Oravhy Cora 2 (717 m)

TOC (wt '1.)

1.00 2.00 :t.oo 4.oo a.oo

o 2.00 4,oo e.oo e.oo to.oo Carbonate (w1 '1.)

Gravity Coree (1072 m)

TOC (wt '1.)

o 1.00 2.oo :t.oo 4,oo a.oo

1 ~

" I

' t , ~

• 1 !

~' •

o 2.00 .t.oo a.oo a.oo 10.00

Cartlonate (wl '1.)

Gravity Core 3 (B32m)

TOC (wt 'r.)

t.OO J.OO :1,00 4.00 5.00

2.00 4.0Q 8.00 8.00 10,00

Carbonate (wl '!1.)

Gravity Core 7 ( 1183 m)

TOC (wt 'lo)

1.00 2 00 3.00 4.00 5.00

, ' I I ' I ; t j

I

. + • ;

l

o 2.00 .e.ao 8.oo a.oo 10.00

Car'""•'• (wt '!1.)

Figure 11. Weight percent total organic relative to depth in core (from gravity cores

Gravity Core "' (882 m)

TOC (wl '!1.)

1.00. 2.00 :1,00 4.00 1.00

0 2.00 ... oo 8.00 8.00 10 00

Carbonate (wl '1.)

Gravity Core 8 ( 1277 m)

TOC (wl '1.)

t.oo 2.00 3.oo .t.oo a.oo

,• ,·

0 2.00 4,00 1.00 8.00 10.00

Carbonat• (wl 11.)

carbon (TOC) and 1 through 9).

Gravity Core 6 (983 m)

TOC (wt -..)

1.00 2.00 :1.00 4.00 1.00

. I

l )o

I • ...

~ i L

' J

50

100

150

200

0 2.00 ... 00 8.00 8.00 10.00

Carbonata (wl '1.)

Gravity Core 9 ( U20 m)

TOC (wt 'lo)

1.00 2.00 :1.00 A,OO 15.00

50

100

150

200

0 2.00 ... oo 1.00 1,00 10.00

Cubonata lwl '!1.)

carbonate

(5Y4/l) where glauconite is abundant. BC-2 is the only box core that

contains faint laminations as well as convolute bedding. Burrow struc

tures are recognizable in most cores deeper than 390 m, and the density

of recognizable burrows generally increases with water depth. Glauco

nite is present as a major component above the irregular contact in

BC-2, BC-3, and BC-4. Pebble-size material in box cores 1, 2, and 3

consists of phosphorite nodules, granodiorite rocks, or metasedimentary

rocks.

Box Core Grain Size

Box core sediments display a wide range of gravel, sand, silt, and

clay percentages (Figure 12, and Appendix E). There is a general trend

of decreasing sand and gravel and increasing mud in the down-slope

direction. Sediment in box cores from the slope above 700 m contains

greater than 60 percent sand and gravel (with the notable exception of

the sediment below the irregular contact in BC-2). Sediment in box

cores below 700 m contains greater than 50 percent mud.

Box Core Carbonate and Total Organic Carbon

The carbonate content of sediments range from 0.73 to 7.88 weight

percent (Figure 13, Appendix F). Most of the cores contain a minimum

amount of carbonate in the upper 10 to 20 em of sediment, with more

below. Carbonate content throughout the sediment sampled by box cores

decreases in a down-slope direction from 390 to 593 m, where the minimum

amount is found, then increases toward 1200 m at the bottom of the

transect.

30

BC-1 (279.,) BC-2 (390 m) BC-3 (510 m) BC-4 (593 m) BC-5 (690 m)

O'llo 50'1!. 100% O'llo 50 ... 100% O'llo 50% 100% 0'11. 50'1!. 100'11. 0'11. 50% 100 'II.

0 0

e 10 10 0

.. 0 u 20 20 = .c 0. .. 0

30 30

40 40

BC-6 (765 m) BC-7 (905 m) BC-8 ( 1020 m) BC-9 ( 1085 m) BC-10 (1200 m)

0% so% 100'1!. 0% 50% 100% O% 50% 100% 0% 50% 100% 0% 50% 100%

0 0

e 10 10

u

.. ;; u 20 20

= .c 0. .. 0 30 30

40 40

rnmm Gravel 0 Sand D Slit ~ Clay .

Figure 12. Cumulative percent gravel, sand, silt, and clay relative to depth in core (from box cores 1 through 10).

Aiii&UiiW:ZUi Jiil lZi iJ£ :a: z ;,;;; a=uu:

BC- I (279 m) BC-2 {390 m)

toe (•t 'llo} TOC Cwt 1U

1.00 2'.00 :3.00 4.00 1.00 2.00 >.00 4.00

\ ' ' ~ '

"' ~ "'

o, a: 0

' 0 20

"' ; I

:X: ... • 14C >35hy ~ ..

w 0

30

40 2.00 4.00 6.00 8.00 2.00 4.00 a.oo 8.00

Carbonate (wl 'lo) Carbonate (wt '11,)

BC-6 {785 m) BC-7 {905 m)

TOC (wt "'o) TOC (wt 'a.)

I 00 2 00 300 400 1.00 2.00 3.00 4.00

r! 10 ~

~ w a:

{\

0 u 20 ; :X:

lp ... .. "' 0

30

40

2.00 4.00 6.00 8.00 2.00 4.00 6.00 8.00

Carbonate (wt 'II.) Carbonate ht·t 'A)

Total Organic Carbon o- - .... - ....

Figure 13. Weight percent depth in core (from box cores 1

BC-3 (510 m) BC-4 {593 m) BC-!5 (890 m)

TOC I• I 11.) TOC h•t 'II.) TOC (wt 'A)

1.00 2.00 3.00 4.00 1,00 2.00 3.00 •.oo 1.00 2 00 3.00 •. 00

t

2.00 4.00 e.oo 8.00 2.00 .ti.OO a.oo 8.00 2.00 •.oo a.oo 8.00

Carbonate (wl '!1.) Carbonate (•I "') Catborula (wt '-l

BC-8 (1020 m) BC-9 ( 1085 m) BC-10 (1200 m}

TOC (wt 'It) TOC (wt 'II.) TOC (wl 'II.)

1.00 f.OO 3.00 4.00 1.00 2.00 3.00 •.oo 1.00 2.00 3.00 4.00

' 4

' f.

' ' • . 2.00 4.00 ti.OO 2.00 4.00 8.00 6.00 2.00 4.00 • 00 .. Carbonala (wt 'lo) Carbonata (wl 'II.) Carbonate (wl "a.)

Carbonate

total organic carbon (TOC) through 10).

and carbonate relative

10

20

30

40

10

20

30

40

to

w N

The TOC content of box core sediments remains nearly constant from

top to bottom of each core except in BC-2 where there is a significant

increase in TOC below an unconformity where sediments have a 14c age

greater than 35,000 years. TOC content in sediments sampled by box

cores generally increases in the down-slope direction (Figure 13,

Appendix F).

Box Core Sand Grain Constituents

Down core variation in the sand-size constituents of the box cores

are shown in Figures 14, 15, and 16 and in Appendix G. Quartz and feld

spar content vary between 40 and 80 percent and show no down slope

trends. Mica content ranges from 1 to 7 percent (average 4.5 percent)

in the cores shallower than 600 m, and from 3 to 27 percent (average 14

percent) in cores 690 m and deeper. Opaque minerals range from 1 to 9

percent and display no systematic down slope trends. Pyrite is present

as an accessory opaque mineral and it constitutes less than 0.5 percent

of subsurface samples; pyrite is absent in all surface sediment

examined. Rock fragments comprise less than 2 percent of most cores

shallower than 700 m. Glauconite is present in all cores between 279

and 785 m and is completely absent in the cores deeper than 900 m. It

is a major component in the upper 10 to 15 em of cores between 390 and

593 m, but decreases in the lower 15 to 30 em. Fecal pellet occurrence

is nearly opposite that of glauconite. Except for an occurrence in

BC-1, fecal pellets are absent in the cores shallower than 785 m and

become a large component in the cores between 785 and 1200 m. The

highest percentage occurs in the upper 10 em of core BC-8 at 1020 m.

33

" c Q)

co Olll 0. E 0

(.)

E -go "' "' 0 Cll

"' "' c "' "' u 0 4) 0

[!) 0.. ....

"' >

"' :; E o

""' (.)

"' c

0 0

~0 0 0)

0. E 0

(.)

E] ~ m Cll ,._ N C

I "' u

(.) "'0 [!) 0.. ...

"' > .. :; Eo :> N (.)

0

0

0

0

0

0

"'

0

"'

0

"' 0.

"' ~ ., u. '0 c

"' N

"' :> 0

0

"'

0

"'

0

"' (w~) aJ05 ut 4tdoo

Ul

~ Q) c ~ Q) :J 0" a! a. 0

0 ....

0 ....

0 ....

~ c Q)

E Ol

"' .;:

"" u 0 0:

., c 0 u :>

"' (3

" c:

0 0

Q) 0

~ "' 0. E 0

(.)

c: .... Q) I U

(.) Q) 0 [!) 0.. ....

Q)

>

"' :; E o

" "' (.)

~ c

0 0

"' 0 c 0) 0 0. E 0 (.)

E ~ ~ 0 "' Cll

~ c M <!> I U

(.) "' 0 [!) 0.. ..,.

"' >

"' :; 0

E "' " (.)

"' u

"' u.

0

0

0

" Q)

E

"' 0 u.

ii'l11'

11il'! i!lli

:i! \1

"' c

" <ll

0

u

:i " :> 0 ., u

Cll

0

0

0

"' .0 ., 0 "'

"' .0 c ., :> 0

"' u o ·c u "' "' Ol

:::; 0

0

"'

0 N

0

"'

0

"'

0

"'

0 M

(w~) aJo:> u! 4tdao

0 ....

0 ....

0 ...

<I) .... 0 0

c: oM

.L..I c: <I) 0 .... Q) Cl..

Q)

> oM .L..I ~

..-lr-.

§: UbO

::l 0 . ....

...:r..c:: ...... .L..I

Q) ..... .... ::l g) b()Q)

oM .... t:=.. 0

0

>< 0

..c

34

"

0 0

c 0 ~ 0)

0 0. E 0 u

E ~ ~ It) "' "' f/) ....

c

"' "' I U

() 41 ~ m a.

0 0

;;; 0. .. '0 a; u. '0 c .. N

.. ::> 0 .. ... ... ...

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0

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3 0 E N

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.. c 0 "' 0) c 0 0. E 0

E ~ ~ 0 c

"' "' "'f/)

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0 u 0 Ill "' ... a.

"' ~ .. :; 0 E N

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0 0 0 N

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~.~."'.;.;·:,·"·"·~·"'·:'i- ----------------- •• :: •••••••••••• • ••••• ••••••••••••••• • ••••••• ......•.................... •............•............. ••••••••••••••••••••••••••• ...•.•..........•.......... ••••••••••••••••••••••••••• •.•..............•......... ........................... •............•............. •.............•............ ••••••••••••••••••••••••••• ••••••••••••••••••••••••••• ••••••••••••••••••••••••••• ••••••••••••••••••••••••••• ••••••••••••••••••••••••••• ...•.•..................... ........................... .•......................... •..........•............... ••••••••••••••••••••••••••• ••••••••••••••••••••••••••• .....••.................... ••••••••••••••••••••••••••• •.••.•..................... ....••..................... ••••••••••••••••••••••••••• .....•..................... ••••••••••••••••••••••••••• •.•.••..................... •..............•........... ••••••••••••••••••••••••••• •••••••••••••••••••••••••••

fl)

"§ Gl c ~ Gl :J cr ., c. 0

0 ...

0 ....

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"' .. u. -" u 0 a:

o~~·~·~·~·~·~·~·~·r·~·~·~·~·~·~·~·~·T·~·~·~•;•~·~•;•;•,•--------~ 0 0 0

"' 0

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0 ...

"' c 0 u ::>

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'" ~ "' a. a; u

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0

;';

0 0

c 0 G> ID c 0 0. E 0

e ~ o 0 c: "'

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c ID 0> I U O

u " ... m a. ., >

"' :; 0 E N

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0

0 0

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"' ::> 0

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f/)

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~ "' "' .0 c "' ::> 0 "' u o ·c

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u "' 0 m o. "' .,

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. ...... . ••.•............ . ••••••.•........ . ................ . . ...................... . . ....•.•.•..•••.••.•.•.. . ...............•••.••.•........ . .................•.•.•......... . ................•.............. . ...............•............... . ............••.•........... . .............•..•..•........ . ...............•..•......... . ..•.•.•..........•••..••.... . ........................... . . .......•.................... . .•..........•....••••••..... . ..•....................•.... . ......•.•.•................. . .•.........••••••••••.•..... . ...................•..•...... . ....•....••••................ . •.............•••.••••....... ....................•......... 0 0

N 0

"' (W~) aJO!) U! 41daQ

0 ...

0 ...

0 ...

1! til Cl)

~ t:: <l) t) ,.. <l) 0.

<l)

> ~ ~

til ~-6co ::S.t:! uoo

::s 0 . ,..

11"\.t:! ~ ~

<llll"' ,.. ::s Cl)

OO<ll ~,..

~ 0 t)

>< 0 .0

35

BC-9 ( 1085 m)

Cumulative Percent Sand Components

0 20 40 60 80 100

0 0 •••••••••••• •••••••••••••••••••••• •••••••••••••••••••••• •••••••••••••••••••••• •••••••••••••••••••••• I •••••••••••••••••••••• ••••••••••••••••••••••

10 •••••••••••••••••••••• 10 •••••••••••••••••••••• ,.. •••••••••••••••••••• E •••••••••••••••••••• 2 •••••••••••••••••••• •••••••••••••••••••• •••••••••••••••••••• ., •••••••••••••••••••• 0 •••••••••••••••••••• I •••••••••••••••••••• u 20 •••••••••••••••••••• 20

-= •••••••••••••••••••• •••••••••••••••••••••• ••••••••••••••••••••••

.&: ••••••••••••••••••••••••• •••••••••••••••••••••••••• c. •••••••••••••••••••••••••• ., •••••••••••••••••••••••••• mill 0 •••••••••••••••••••••••••

30 ••••••••••••••••••••••••• 30 Quartz and Feldspar ••••••••••••••••••••••••• • •••••••••••••••••••••• I .............•......•. ••••••••••••••••••••••• ••·••••••······•······· Mica

40 40

D Opaque Minerals

BC-10 (1200 m) • Cumulative Sand Components Fecal Pellets

Percent

0 20 40 60 80 100 1111 0 0 Foraminifers

• Siliceous Microfauna

10 10 Macrofauna! Debris

e Organic Debris .!:! ., ~

0 u 20 20

-= .&:

c. ., 0

30 30

40

Figure 16. Cumulative percent sand components relative to depth in core (from box cores 9 and 10).

36

Foraminifers are present in all cores; the lowest percentage is gener

ally between 593 and 785 m. Siliceous microfossils are present in all

cores except BC-3 and tend to increase in percentage in the down-slope

direction. A notable exception occurs at the base of BC-2 ( 14c age

)35,000 years) where they constitute 14 percent of the sand-size

sediments. Macrofossils and organic material are present in small

amounts in all cores, with a slightly larger amount in the cores from

1085 and 1200 m.

Biostratigraphi

Planktonic Foraminifers

A total of 12 different species of planktonic foraminifers were

identified in gravity cores 1 through 9 in the study area. Their occur

rence is shown in Table 3. GC-1 was devoid of planktonic foraminifers

below 10- 15 em (late Miocene age sediments), probably due to disso

lution. The quantitative distribution of species abundance is given in

Appendix H. Six species of planktonic foraminifers constitute more than

99 percent of the total population. Neogloboquadrina pachyderma

(Ehrenberg) is the dominant species in all cores and shows systematic

variation in coiling direction and abundance with depth in several

cores. Globigerina bulloides (d'Orbigny), Globigerina quadrilatera

Galloway and Wissler, Globigerina quinqueloba Natland, and Globigerinita

glutinata (Egger) are also present in significant quantity and vary

systematically with depth in most cores. The results of quantitative

analysis are shown in Figures 17 through 25. The systematic variations

37

Table 3.-- Occurrence of planktonic foraminifers in gravity cores northwest of Point ·sur,

California [x, present in core]

SPECIES CORES GC-1 GC-2 GC-3 GC-4 GC-5 GC-6 GC-7 GC-8 GC-9

Neogloboquadrina pachyderma (Ehrenberg) X X X X X X X X X

Globi~erina bulloides (d'Orbigny) X X X X X X X X X

Globigerina falconensis Blow X

Globi~erina guadrilatera Galloway and Wissler X X X X X X X X X

Globigerina guingueloba Natland X X X X X X X X

Globigerina rubescens Hofker X

Globigerina umbilicata Orr and Zaitzeff X X X X X X X

Globigerinita glutinata (Egger) X X X X X X X X

Globorotalia inflata (d'Orbigny) X X X X

Globorotalia sci tula (Brady) X X X X X X X X

Globorotaloides hexigona Natland X X X X X X X

Orbulina universa d'Orbigny X X X X X X X

GRAVITY CORE 1 (505 m}

Texture Sediment Coiling Percent Percent Percent Percent Years BP

Structure N. pachyderms N. pschydermll G. qulnqueloba G. bulloldes G. glut/nata +

G. qusdrllaters • 100~ s 50 0 0 50 100 0 10 0 20 40 0 8 16

0 s • .. .. ~

E ::!.. v w 25 sS a: 0 ~ (.) " ~ ----- devolrl devoid devoid devoid ~

" , 50 :I: Scs

1-2:' ;;

0.. w " Cl cs

:;:: 9.0 Ma c. e

75 - - .!?

Scs ~ 0

100 ~ e

convoluted

clay Sse sand silt clay sS silty sand D homogeneous

sc silty clay s sand

[]I] intensely bioturbated

cs clayey silt cS clayey sand

silt Sc sandy clay w moderately bioturbated s

Ss sandy silt c clay [JJ faintly bioturbated

sand silt w faintly laminated -

II laminated

Figure 17. Plots of coiling ratio of Neogloboquadrina pacQyderma and abundance of selected species of planktonic foraminifers from the assemblages in core GC-1. Age estimate from diatom biostratigraphy.

Texture

0

25

E ~ w a: 50

0 ss (.)

~ :X: 75 t-0.. w 0

100

125 cSs

150

GRAVITY CORE 2 (717 m)

Sediment Coiling

Structure N. pachyderms

100'll. s 50 0

I\ ~

Percent

N. pachyderms

0 50

(left)

,.

~~

I ~

100

Percent

G. qulnquelobll

0 10

Percent

G. bulla/des • +

G. quadrllaters e

r

Percent

G. glut/nata

0 I T 16

1\

Figure 18. Plots of coiling ratio of Neogloboquadrina pachyderma and abundance of selected species of planktonic foraminifers from the assemblages in core GC-2.

Texture

0 cSs

f-. -ss

25 1- -

cSs

50 Scs --- - -

75 sc

e -- --~ sS

100 - - --w cSs a: 0 (.)

~ 125 Ss J: f-ll.. >-- -w Scs Cl 150

cs - - - -cSs

175 --- --cs

- -- -200

csS

225


Sediment Coltlng


lOO'llo S 50

I J J

)

s

il

Percent

N. pachyderms

0 0 50 100

(left)

Percent

G.qulnqueloba

0 10

Percent Percent

G. bulloldea • G. glutlmJta +

G. quadrllater~l •

210 4p I 7 I

18

I~ I> II

~ r

;

j,

Years BP

10.5 ky

12.5 ky

15 ky

~ " ~ " "C

,.. ., u .c c. .. "' .. "' 0

.0

Figure 19. Plots of coiling ratio of Neogloboquadrina pachyderma and abundance of selected species of planktonic foraminifers from the assemblages in core GC-3. Age estimates from correlation with core Vl-80-P3 (Gardner and others, in press).


Texture Sediment Coiling Percent Percent

Structure N. pschyderma N. pachyderms G. qulnquelobs

100%8 50 0 0 50 1 0 0 10 0

cSs

25 cs I'

r--so

sc

E 75 ) ~ r--w ) cr cs 1"\l.N_ 0 u 100 I1VW

(right)

~ ----- )\ :I: 1- S\ a. 125 w

) Cl sc

\ /

150 s ) ----- s (

175 Scs

----- S) l cs ))

200 --

sc )

225

0

Percent

G. bulloldu •

G. qusdrllater• o

20 40

Percent

G. glurtnsts

0 l ~ I 16

,.

\ (

\

i)

.Yeara BP

~ " 9.5 ky >

" '0

"' 12.5 ky "' u

13.5 ky .c c.

"' 0

.. 15 ky

m 0

.0

Figure 20. Plots of coiling ratio of Neogloboquadrina pachyderma and abundance of selected species of planktonic foraminifers from the assemblages in core GC-4. Age estimates from correlation with core Vl-8D-P3 (Gardner and others, in press).



Structure N. pachyderms N. pachyderms G. qu/nqueloba G. bulloldes • G. glullnala

G. qusdrll•t•r• •

0 100'!1. s 50 0 0 50 100 10 0 20 40 0 -, r e

L I I 18

Scs

25 sc ))

- - ))

50 cs )

E -- --~~ } I

(right)

~ sc w a: 75 cs

., "' > ~

0 u ~

y -::t 100 sc I-

\ Ql .,

12.5 ky ,..

"' u D.. w 0

) -----125

150 cs

/ ( 1\

\ \

13.5 ky :;: c.

" "' ..

15 ky "' 0

.c

\ (left)

175 \ '

1- - - -sc

200 I

Figure 21. Plots of coiling ratio of Neogloboquadrina pachyderma and abundance of selected species of planktonic foraminifers from the assemblages in core GC-5. Age estimates from correlation with core Vl-80-PJ (Gardner and others, in press).

E ~ w a: 0 (.)

;!l; J: 1-a. w 0

0

25

so

75

100

125

150

175

200

Texture

1---sc


Sediment Coiling


100% s 50

)

)

) )

Percent Percent

N. pachyderms G. qulnqueloba

0 50 100 0 110

Percent Percent

G. bulloldes A G. glut/nata +

G. quadrllatera •

0 210 40 7 16 I I I

I\


GRAVITY CORE 7 ( 1183 m)

Texture Sediment Coiling Percent Percent Percent Percent

N. pachyderms N. pa c lryderma G. qulnquelobll G. bulloldes . G. glutlnata Structure +

G. quadrllsrerll • 100% s 50 0 0 50 100 0 10 0 20 40 0 8 18

0 ~

)\

25 \\ \)

E \\ ~ 50 \ w a: 0 (.) 75 ;?;; cs \ J: t-a. 100 w

~ 0

125

~ 150 s 175 >



Texture Sediment Coiling Percent Percent Percent Percent Veers BP

N. pBchyderma N. pachyderms G. qulnquelobs G. bulloldas . G. glullnsra Structure +

G. quadrllstera e 100% s 50 0 0 50 100 0 10 0 20 40 0 8 18

0

cs

25

50

75

sc

sc ~ 9.5 ky

w, J ~ " > m "' 10.5 ky '0

)) ( ,.,

" 0

E u

12.5 ky .t: c.

100 w

cs )S .. ~

5! 0: "' 0 (J

~ 125

.., )) 0

.0

J: 1-a. w 0 150

15 ky )~

sc )) 175

cs S\ 200

Figure 24. Plots of coiling ratio of Neogloboquadrina pachyderma and abundance of selected species of planktonic foraminifers from the assemblages in core GC-8. Age estimates from correlation with core Vl-80-P3 (Gardner and others, in press).



N. pachyderms N. pachyderm.a Structure

G. qulnquelobs G. bulloldu • G. glullnata +

G. quadrllatera o 100'!1. s 50 0 0 50 100

0 )))

0 10 16 I

0

25 %

I % % 50

cs \) E u 75 )\

12.5 ky ~ " >

" "C

,.,

' t

I( w a: )\ 0 ()

~ 100

J: ~\ .... 1-----a..

.. 0

.t= c. .. 0

.. "

w 125 ~) 0 sc 15 ky " 0

.c

150 ~) cs

)~ 175

t----- \~ sc ----200 ~ cs 1) ~

225

Figure 25. Plots of coiling ratio of Neogloboquadrina pachyderms and abundance of selected species of planktonic foraminifers from the assemblages in core GC-9. Age estimates from correlation with core Vl-8D-P3 (Gardner and others, in press).

shown in these figures are combined with 14c age determinations from the

study and are correlated with systematic variation in species abundance

from other work on the central California margin (Figure 26; Gardner and

others, in press) to assign age datums to the sediment. The variation

in species abundance is also used to make biostratigraphic correlation

between the different gravity cores. These correlations, as well as

comparisons with the work of Gardner and others (in press), are dis

cussed in the "Biostratigraphic Correlation" section.

Diatoms

The interval between 60 and 80 em in GC-1 is a laminated diato

maceous clayey silt with a 14c age )35,000 years. A smear slide of a

sample from that interval examined by John Barron (written commun.,

1983) yielded the following age diagnostic diatoms:

Actinoptychus vulgaris var. monicae

Denticulopsis hustedtii (v. rare)

Heniaulus polymorphus

Rouxia californica

Rhizosolenia barboi

Thalassionema schraderi

The age diagnostic silicoflagellate Distephanus pseudofibula was also

present. The presence of these species indicates that the sample is

late Miocene in age in the uppermost part of the Denticulopsis hustedtii

Zone-Subzone a, and approximately 9 million years in age. The diatoms

are well preserved and could not have been transported very far (John

Barron, written commun., 1983).

48

5

->-~

- 10 (])

Ol <(

15

20

V1-80-P3

Percent Percent Percent Percent Percent

N. pachyderms N. pachyderma G. bulloldes G. qulnqueloba G. glutlnata

(left) (right)

20 40 60 80 100 0 20 40 60 0 10 20 30 40 0 10 20 0 10 20

that age. Data

Figure 26. Plots of the abundances of selected species of planktonic foraminifers 4 display systematic variation with age from the assemblage in core Vl-80-PJ versus 1 C

Core is from 1600 meters of water, 60 km west of the Russian River, California. from Gardner and others (in press).

Chronostratigraphy

14c Age Determinations

Six samples were submitted to Geochron Laboratories for radiocarbon

age determination. Two samples have ages greater than 35,000 years BP.

They were from 73-78 em down core in a well laminated, diatomaceous,

clayey silt in core GC-1, the same interval that had a diatom determined

age of approximately 9 million years and from 24-26 em down core in a

silty sand just below an irregular contact with the overlying pebbly

gluaconitic sand in BC-2. Two samples from BC-7, one from a clayey,

sandy silt at 14-16 em, the other from a silty clay at 34-36 em down

core, yielded 14c dates of 2525 ± 170 years BP and 10,330 ± 340 years

BP, respectively. The two samples are separated by a sharp, irregular

contact at 30 em. Two samples were also submitted from BC-10, one from

a clayey silt at 14-16 em and the other from a sandy, clayey silt 32-34

em down core. These yielded 14c dates of 1930 ± 180 years BP and 3175 ±

185 years BP, respectively. The two samples are separated by 20 em of

bioturbated sediment with a gradational change between the lower sandy,

clayey silt and the upper clayey silt.

50

DISCUSSION

Effect ot Currents on Surface Sediment Grain Size and Composition

The California Current System contains a northerly directed

component known as the California Undercurrent with its core located

over the outer shelf-upper slope along central California (Hickey,

1979). Composite geostrophic current velocity measurements from VERTEX

1 (Broenkow and Greene, 1981) are shown in Figure 27. From this figure

it is apparent that the interval from 600 to 800 m is the most dynamic

portion of the upper continental slope with significant changes in

texture and composition. Comparison of current velocities on Figure 27

with Figure 28 shows that current velocities along the upper portion of

the slope cross the transportation field for sand and silt size material

(Heezen and Hollister, 1971).

The change in surface sediment texture is most dramatic between 600

to 800 m. The percentage of mud in the sediment increases signifi

cantly, from less than 12 percent to greater than 55 percent within this

transitional interval or zone (Figure 27). Bottom photographs show a

major change in surface texture from a dark, sandy surface to a light,

muddy surface between 700 and 750 m (Thompson and others, in prep.).

Grain size data and bottom photographs indicate the transitional zone on

the slope off Point Sur is located between approximately 600 and 800 m

and the mudline is located at the bottom of this zone at approximately

750 to 800 m (Figure 27). Stanley and Wear (1978, p. Ml9) define the

"mudline" as " ••• the lower limit of the transitional zone [and] the

-;; ~ ; E

= c. . 0

~ ;; 3:

Cumulative Percent Surficial Sand-Silt-Clay

0 25 50 75 100

400 400

600 600

BOO BOO

1000 1000

1200 1200

llilli) . Dill . D ~ Gravel Sand Silt Clay

Distance From Shore (km)

50

I I \ I I I II \

I \

25

\ 10

" .._ __ jl \.5

\ \ .: I 3 ' ~

0

I \...---- --,::_-~:.': I -.:·: Transl11on

\ · Zone

I I

1

I I I I I

Current Velocity (em/sec)

Northerly Directed Flow

Cumulative Percent Surficial Sand Components

0 20 40 60 60 100

400

600

BOO

1000

1200 1200

D [] Glauconite Slllceoua

Quartz+ Feldspar Microfauna . II IIIII Mica lW Fecal Pellets Carbonate 1111111 Shell Fragments

D Planktonic ~ Organic Debris Opaque Minerals

Foraminifers

D Rock Fragments ~ Benthic Foraminifers

Figure 27. Diagram showing effects of current velocities of the California Undercurrent during typical summer conditions on the distribution of surficial sediment texture and sand composition from box core sediments. Dashed lines are northerly directed current velocity data from Broenkow and Greene (1981) and Willia~ Broenkow, (written communication, 1983).

VI N

Current Velocity (em/sec)

0.01 0.1 1.0 10 100

Pebbles

Granules ::::::--~ ... 1.0 -,o~ C!> E

'b-.... cu E ~ .... E Sand 0 -o'~ C!> .._

c:,0 > Q) Cl) ..... Ill

0.1 Q)

.r: E 0 0 til .... ·-

Q

c: ·-til 0 0.01

.._ ..:.. 0 .... " 0 ~ 0

()

Clay ~ 0.001

Figure 28. Current velocities required for erosion, transportation and deposition (from Heezen and Hollister, 1971).

53

depth of substantially increased silt and clay content below which depo-

sition prevails...... A mudline on the midslope (300 to 1,000 m) has

been recognized on the Atlantic margin off Cape Hatteras (Newton and

others, 1971; Keller and others, 1979). Active offshelf spillover of

coarse sediment along a relatively narrow shelf and continuous reworking

of sediment along the upper slope by the Gulf Stream off Cape Hatteras

depress the mudline below the effect of major Gulf Stream erosion to

approximately 800 m (Stanley and others, 1983). The sedimentological

response to physical conditions on the margin off Point Sur is similar

to the response on the margin off Cape Hatteras; the shelf is narrow,

coarse material occurs over and below the shelf break, and the mudline

occurs below the erosional or transportational effects of the California · .. ,

Undercurrent.

The change from nondeposition or erosion to deposition indicated

by the mudline is supported by compositional changes in the sand-size

fraction as well. The increase in abundance of mica between 600 and

800 m (the transitional zone) from less than 5 percent to 18 percent of

the total sand indicates a change in depositional regimes. In general,

a lack of mica (here, (5 percent shallower than 600 m) indicates non-

deposition or erosion and the presence of fine-sand-size mica (here, >15

percent deeper than 785 m) indicates deposition of fine material (Doyle

and others, 1968). On the margin off Cape Hatteras, an increase in mica

content that indicates the change from nondeposition to deposition

occurs well below the shelf break (Doyle and others, 1968, p. 387), in

close agreement with the location of regime change indicated by the

54

55

-mudline (Stanley and others, 1983). The change in glauconite abundance

in the study area also supports the location of the nondepositional-

depositional boundary between 600 and 800 m. The formation of glauco-

nite in modern environments requires exposure of incipient grains to sea

water for extended periods of time, by necessity requiring a minimum of

sediment influx and/or winnowing (Odin and Matter, 1981). The hypo-

thesis that surficial glauconite indicates environments of extremely

slow deposition or erosion is not new. Galliher (1935), a pioneer in

the study of the origin of glauconite, concluded that glauconite forming

in the Monterey Bay, California was restricted to areas of very low

sedimentation. In more recent work on glauconite in Monterey Bay, high

abundance and diverse morphology of glauconite were associated with low

sedimentation rates (Hein and others, 1974). Inspection.of Figure 27

shows that siliceous microfaunal debris in the sand-size fraction is

completely absent above 600 m and increases gradually below that depth

to approximately 6.5 percent at 1200 m. It is likely that the

California Undercurrent is strong enough to keep the bottom relatively

free of fine material on the slope above 600 to 800 m northwest of

Point Sur.

Effects of Oxygen Content on Surface Sediment Composition

Oxygen content in the water column, particularly within the oxygen

minimum zone (OMZ), appears to influence the biogenic and perhaps the

authigenic components of the sediments on the continental slope. Figure

29 shows the relationship between oxygen content and the composition of

Weight Percent Total Organic Cnrbon Oxygen (ml/1) Cumulative Percentage of Sediment Components

0 1.00 2.00 3.00 4.00 0 0.5 1.0 1.5 2.0 0 20 40 60 80 100

400 400 400

" " ; .s 600 600 -"

600 600

ii .. 0

;; ; 3: 600 800 aoo aoo

1000 1000 1000

1200 1200 1200

0 1.50 3.00 4.50 6.00

Weight Percent Carbonate [] Quartz ~Rock ~ Benthic + Fragments Foraminifers Feldspar

TOC :1:1:11 m Glauconite -~y,. Siliceous Mica ;>f// Microfauna

Carbonate D Opaque ~ Fecal Peilels II Carbonate Minerals Shell Fr agmenb

Planktonic ~ Organic Debris Foraminifers

Figure 29. Distribution of surficial total organic carbon, carbonate, and sand components from box cores versus water depth and their possible relation to an impinging oxygen minimum zone (stippled in middle figure).

the sediments. The percentage of benthic foraminifers increases above

and below a minimum between 593 and 905 m, corresponding to the lowest

oxygen values in the OMZ (Figures 29 and 30). The percentage of fecal

pellets reaches a maximum at the lower edge of the OMZ (Figures 29 and

31) and is directly related to a peak in the total number of organisms

in the upper few centimeters of sediments at the edge of the OMZ on the

continental slope west of Point Sur (Thompson, 1982).

Macrofaunal shell fragments are uncommon on the slope at Point Sur.

The minima (less than 1 percent) occur in surface sediments at 593 m and

between 785 and 1020 m, all located within the OMZ. The two maxima of

shell fragments are at 690 m and 1085 m, respectively (Appendix G). The

maximum number of living individuals with carbonate shells on the slope

off Point Sur is at 1085 m (Thompson, 1983), and represents an immediate

source for the maximum percentage of carbonate fragments at 1085 m.

Thompson also noted a relative maximum in living individuals with

carbonate shells near 600 m, yet no shell fragments were found in

surface sediments at this depth. Thompson and others (in prep.)

observed "biotransport" of non-endemic shells by hermit crabs in the

core of the OMZ off Point Sur. Downslope biotransport and perhaps creep

may combine to provide a viable means of eliminating shell and shell

fragments from the upper edge of the OMZ and relocate them lower on the

slope. The minimum carbonate content of < 1 percent at 600 m (Figure

29) corresponds with and appears to be controlled by the combined

minimum of carbonate shell fragments and benthic foraminifers at 600 m.

The occurrence of glauconite on the continental slope is centered

57

~ (/)

'-Q) ..... Q)

E

.s::::. ..... 0. Q)

0

Percent Benthic Foraminifers in Surficial Sand-size Material

12

J=====================~~------~~

-

-

Figure 30. Percentage of benthic foraminifers (striped) in the sand-size fraction of surface_ samples versus water depth and their relat~on to the oxygen minimum zone (from box cores 1 - 10).

58

,-.. (/) 1-Q) ..... Q)

E

..c ..... 0.. Q)

0

Percent Fecal Pellets in Surficial Sand -size Material

0

-10

I

20 I

30 I

40

400-

- ............................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....................................... -..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................ 60"0 _:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: r-. .......................................... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............................................ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

- ·.·.·.·.·.·.·.·.·.·.·-·-·-·-·.·-·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·-~·......... . ....... . ~<::::::::::::::: 0 x y g en Minim urn Zone:::::::::::::::::

""'"1;"T;T:T;~.,._· •: •: •: •: •: •: • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •. • • • • •. • •: •: •: •: •: •: •: •: •: I •• e e • • • e • e • • e •• • e I • • •• • I e I I I • e • • e • • e I • • • I • e

800 :::: :-:::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::-

~~·~·~·g·~·~· ~·~· ·~· ·~· "l. ·: ............................................................... .

1000

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.· ................................. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . : : : : .... -:-::::::::::::::::::::::::::::::::::::::::::::::::::::::::: ~

f!.-1.-Trf.f.f,~l'+'-t,..,.."'r'lr"trtrf.f-.lf-.F..t: !f: ~: <::..:. ~ : : : : : : : : : : :::: : :: : : :: : : : : : : : : : : : : : :: :: : : :

~·~..:.:.:·::::::::::::::::::::::::::::::-

1 2 0 0 _.....~..~..~. ......... .~..~..~...J...I..,j"-rl------r---.-----• ....-----+-0 10 20 30 40

Figure 31. Percentage of fecal pellets (patterned) in the sand-size fraction of surface samples versus water depth and their relation to the oxygen minimum zone (from box cores 1 - 10).

59

about the upper edge of the OMZ at approximately 525 m (Figure.29 and

32). McRae (1972) pointed out that most geoscientists studying the

formation of glauconite view a slightly reducing environment with modest

circulation as the most conducive for glauconitization. There is also a

delicate balance between the degree of physical confinment of a particle

and the amount of ionic exchange between the microenvironment within the

particle and the ambient open marine sea water (Odin and Matter, 1981).

Excessive confinment caused by too much mud in the sediment will prevent

formation of glauconite and insufficient confinment caused by too large

a mean grain size allows only glauconitic rinds to form. It is within a

slightly reducing and confined environment where circulation is suffi

cient for the exchange of iron necessary for glauconite formation to be

most effective. In strongly oxidizing environments, soluble iron is

precipitated and iron minerals oxidize; iron is thus largely immobi~

· lized. Glauconite also degenerates in contact with highly oxygenated

sea water (Odin and Stephan, 1982). Conversely, in strongly reducing

environments in the presence of organic matter or hydrogen sulfide, iron

is reduced and becomes soluble. The iron in solution is then either

precipitated as pyrite or migrates into sea water (Odin and Matter,

1981). Because strongly reducing environments usually require little or

no circulation to persist, iron exchange between the substrate and the

ambient sea water is insufficient and glauconite does not form (Odin and

Matter, 1981).

Berner (1981) suggested a geochemical classification of sediments

based on the presence of key minerals that enables researchers studying

60

..c ...... Q. (])

0

Percent Glauconite in Surficial Sand-size Material

0 10 20 30 40 I I I - -

400-

...... . . . . . . ::::::::::: .·. ·.:.:.: .. :-:::::::::::~ ................

. . . . ....... :-:.:-:-:-:-:-:-:.:.:-:-:.:-:-:-:-:-:-: . . . . . . . . ~ . . . . . . . . . . . . . . . . . . . . . . . . r/::::::::::: ~:::::::: :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: f-

600-

: :~-:::::::::::::::: Oxygen Minimum Zone ::::::::::::::::::

- :~.: ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: :·: ~: ~: ~ :~ :~: ~: ~: ~: 800 ~tt· .......................................... 1-

J. iii i ·iii iii iii iii i iii iii iii iii iii iii iii i iii iii iii iii iii i iii i iii iii i iii iii iii iii i iii i. ~ 100o-·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.·.··"f........................................... ·.·

-

1200~---------,,-----------~,----------~,-----------+-

Figure 32. Percentage of glauconite (patterned) in the sandsize fraction of surface samples versus water depth and their relation to the oxygen minimum zone (from box cores 1- 10).

61

the rock record to interpret oxygen and sulfide concentrations of the

depositional environment. The presence or absence of dissolved oxygen

and dissolved sulfide in the sediments at the time of authigenic mineral

formation controls the characteristic phases present in the sediments.

Table 4 is a summary of Berner's (1981) environments and characteristic

phases.

Table 4.--Geochemica1 classification of marine sedimentary

environments ba.sed on mineral composition. (After Berner, 1981).

Environment

Oxic

Anoxic

Sulfidic

Nonsulfidic

Post-oxic

Methanic

Characteristic phases

Hematite, goethite, Mn0 2-type minerals; no organic matter

Pyrite, marcasite, rhodochrosite, alabandite; organic matter

Glauconite and other Fe2+-Fe3+ silicates (also siderite, vivianite, rhodochrosite); no sulfide minerals; minor organic matter

Siderite, vivianite, rhodochrosite; earlier formed sulfide minerals; organic matter

A part of the slope between 300 and 800 m where glauconite and some

organic matter are present may belong in the post-oxic nonsulfidic

anoxic environment.

Clay Mineral Assemblages in Surface Sediments

Surficial clay mineral assemblages on the continental slope north-

62

west of Point Sur display a slight down slope change in bulk assemblage

composition. Those shallower than approximately 600 m contain a lower

mean smectite percentage and concomitant higher illite and chlorite +

kaolinite percentage than those deeper than 600 m (see Table 2). The

lower amount of smectite in samples from less than 600 m may be the

result of one or a combination of factors. First, smectite crystals are

smaller on average than illite, chlorite, or kaolinite (Gibbs, 1965),

and the lateral change in assemblage composition may be caused by

physical sorti~g of clays by size with increasing distance from shore

(Gibbs, 1977; Knebel and others, 1977). Second, the shallower assem

blage may have a different provenance from the deeper assemblage and the

difference in composition may be the result of different source area

assemblages. Third, the shallower assemblage, with affinities of the

late Pleistocene assemblages of gravity cores 3, 4, 5, 8, and 9 (see

Table 5) may be relict clays exposed on the surface by nondeposition or

erosion. Fourth, clays in the shallower assemblage may be affected by

glauconitization of the substrate. Progressive removal of smectite

occurs as authigenic glauconitic smectite forms (Odin and Matter, 1981).

Evaluation of the influence of these factors individually is not

possible. However, the location of the mudline, the change in mica

content, and other compositional changes already discussed suggest a

change from nondeposition or erosion above 600 to 800 m to deposition

below that level. The change in clay assemblages near the depositional

regime boundary suggests some kind of change is indeed occurring at that

water depth.

63

Table 5.--Semiquantitative clay mineral assemblages of Recent and late Pleistocene sediments from the continental slope

northwest of Point Sur, California. [Percentages determined from corrected X-ray diffraction peak volume. Age of sediments

based on planktonic foraminifer assemblages • S, smectite; I, illite; C + K, chlorite + kaolinite; x, not present in core]

Core Depth Surficial 12.5-15 kl BP 18-22 kl BP (meters) S% I% C+K% S% I% C+K% S% I% C+K%

GC 3 832 50 23 27 50 25 25 48 28 24

GC 4 862 54 23 23 48 25 27 48 27 25

GC 5 983 50 22 28 46 25 29 48 26 26

GC 6 1072 53 23 24 X X X X X X

GC 7 1183 56 21 23 X X X X X X

GC8 1277 53 20 19 47 25 28 47 28 25

GC 9 1420 54 22 24 44 31 25 46 24 30

mean 52.9±3.1 22±2 .o 24.0±5.0 47±2 .2 26.2±2.7 26.8±1.8 47.4±0.9 26 .6:1;1. 7 26:1;2.4

Five surficial sediment clay mineral provinces, defined py the

relative abundance of smectite, illite, and chlorite+ kaolinite have

been identified along the California coast from the Oregon border to

Point Conception (Griggs and Rein, 1980). A boundary in northern

Monterey Bay separates a province to the north (Province 2 of Griggs

and Rein, 1980) characterized by high smectite (mean, 57 percent), low

illite (mean, 18 percent), and low chlorite+ kaolinite (mean, 25

percent) from a province to the south (Province 3 of Griggs and Rein,

1980) characterized by moderate smectite (mean, 26 percent), high illite

(mean, 39 percent), and moderate chlorite+ kaolinite (mean, 35

percent). Figure 33 shows the compositional range of clay assemblages

from the seafloor, intervals from 12.5 to 15 and 18 to 22 thousand years

BP, the limits of Provinces 2 and 3, and the major clay sources. Clay

mineral assemblages from surficial sediments in the study area, geo

graphically located in the southern province, are characterized by high

smectite (mean, 51 percent), low illite (mean, 25 percent), and low

chlorite + kaolinite (mean, 24 percent) and fall well within the compo

sitional limits of Province 2 (see Table 2 and Figure 33). The compo

sition of clay assemblages in the study area correspond more closely to

clay assemblages in the northern province (Province 2) than to clay

assemblages in the southern province (Province 3), suggesting several

possibilities. First, clay-size material on the upper continental slope

northwest of Point Sur has, at least in part, the same provenance as

clay-size material on the shelf and slope between Point Reyes,

California and northern Monterey Bay. Perhaps clays were entrained and

65

II!IIIIM ! I

\ \

Illite

El Sources

Iii Province mean

Surficial clay

12.5-15 ky BP

18-22 ky BP

Age uncertain

e Miocene

Province 3

\

Russian River

fl • I Y--------. -=-•• =1·-( ..

\ \

{ . .. ..., . \ Province 2

8 Province 2 Mean

I I

I \ \.~---7~---------------J

\ I \ I

Chlorite + ~-. ...... ..___...__... _ __._......,. _ _.. _ _.... _ _.... _ _.__..;,t..._....__....__..__...__....__...__~__..____,. _ _.. Smectite Kaolinite

Figure 33. Compositional range of clay mineral assemblages from cores in the study area. Age assignments are biostratigraphically derived. Composition of source areas, province means and compositional limits of Province 2 (Pt. Reyes to northern Monterey Bay) and Province 3 (southern Monterey Bay to Pt. Buchon) are from Griggs and Hein (1980).

transported by the southerly flowing California Current. Sec9nd, the

contribution of clay minerals from rivers debauching into Monterey Bay

has not left a dominant imprint on the clay mineral assemblage of

surface sediments on the continental slope northwest of Point Sur.

Third, because the clay assemblage on the continental slope off Point

Sur bears a closer resemblance to Province 2 than to Province 3, the

boundary of Griggs and Hien (1980) in northern Monterey Bay separating

the two provinces may need to be redrawn farther south to include the

upper continental slope northwest of Point Sur in Province 2.

Total Organic Carbon Distribution in Surface Sediments

High total organic carbon (TOC) content in near surface sediments

often coincides with a minimum in dissolved oxygen in the oxygen minimum

zone (OMZ) developed in areas of coastal upwelling (Calvert and Price,

1971; Manheim and others, 1975) where surface biological productivity is

highest. In general, maximum TOC will normally occur on the upper slope

regardless of how depleted the OMZ becomes (Jones, 1983). This occurs

because slope sediments normally have a substantially smaller grain size

but often a sedimentation rate similar to that of shelf sediments, and a

comparable grain size but much higher sedimentation rates than abyssal

sediments. Increased bacterial activity in coarse-grained sediments of

shelf deposits and longer residence time of organic carbon in the water

column prior to deposition in abyssal sediments allow for oxidation of

the organic carbon (Demaison, 1981). Thus, the long-noted broad corre

lation seen between particle size and TOC content (Trask, 1932)

67

precludes coarse-grained shelf deposits from containing substantial

organic carbon under normal conditions.

On the Washington and Oregon continental margin, the highest TOC

values (approximately 3.2 percent) are on the middle and upper slope

where the oxygen deficient OMZ and generally fine-grained deposits

co-exist (Gross and others, 1972). An analogous situation occurs on the

margin off Point Sur, California. The highest TOC content in surficial

sediments is on the upper slope where fine-grained sediment and low

oxygen content co~exist (see Figures 27 and 29). It is noteworthy that

the highest TOC value (2.5 weight percent) is almost 200 m below the

OMZ where oxygen conditions are low but not at a minimum. TOC in the

sediments between 279 and 1200 m display a strong correlation with the

percentage of clay (compare Figures 7 and 6) and weak correlation with

the oxygen content of overlying water. The correlation coefficient for

percent clay and weight percent TOC is 0.95, whereas the correlation

coefficient for o2 content and TOC is 0.66. It therefore appears that

the TOC content of sediment on the slope off Point Sur is controlled

primarily by the percentage of clay in the sediment and not by the o2

content of the water impinging on the slope.

Correlation of Cores

Systematic change of several measured parameters and visible

features with depth in the cores are useful for correlating the cores.

Planktonic foraminiferal biostratigraphic correlation is reliable for

regional and interregional correlation because changes in species

68

abundance and morphology occur in response to changes in oceanic

conditions (Keller, 1978). The coiling direction of Neog1oboquadrina

pachyderms, shown to be a temperature-related trait (Ericson, 1959;

Bandy, 1960), is useful for both biostratigraphic correlation and

paleoclimatic interpretation. The change in coiling direction from the

late Pleistocene sinistral-dominated population to the Holocene dextral

dominated population of~· pachyderma between 11,000 and 12,000 years BP

(Bandy and Ingle, 1970; Ingle, 1973a) was caused by southward and north

ward shifts of critical ocean surface isotherms within the California

Current (Ingle, 1967, 1973a, 1973b).

Gardner and others (in press) assigned age datum lines determined

from 14c to intervals of change in coiling direction and abundance of

N. pachyderms and variations in the relative abundance of other key

planktonic foraminiferal species in core V1-80-P3 (Figure 26) taken from

1600 m of water west of the Russian River, California. Similar

variations are observed in many of the cores in the present study area,

and tentative age assignments have been made (see Biostratigraphic

Correlation section).

Carbonate content in hemipelagic sediments, controlled by a complex

interaction of productivity, dilution, and dissolution, has been shown

to exhibit systematic variation with depth in cores, and it was used to

correlate intervals in cores (Gorsline and others, 1968) and to identify

the Holocene-Pleistocene boundary (Gorsline and Prensky, 1975). A com

bination of low carbonate content ((10 weight percent) and low level

variation in content in the cores of the study area makes carbonate

69

correlation difficult and tentative. Nevertheless, some features are

evident (see Carbonate Content Correlation section).

Biostratigraphic Correlations

Systematic variation in planktonic foraminiferal species abundance

versus 14c ages from core Vl-80-P3 is shown in Figure 26. When similar

variations such as the peaks in~. quinqueloba and G. glutinata at

15,000 years BP, the low in left coiling~· pachyderma at 13,000 years

BP, and the maximum in~. quinqueloba at 9,500 years BP were observed in

the cores from off Point Sur, appropriate age datum lines were assigned.

The variation in planktonic foraminiferal species abundance in GC-3

between 80 em and 180 em exhibits a close correspondence with observed

variations in core Vl-8G-P3 for the 9,500 to 15,000 years BP interval

and correlations have been made (Figure 18). Similar correlations have

also been made with gravity cores 2, 4, 7, and 8, and are shown individ

ually in Figures 19 through 25 and collectively in Figure 34. Plank

tonic foraminifer species abundance in gravity cores 1, 2, 6, and 7 do

not exhibit recognizable systematic variation that can be correlated

with core V1-80-P3 or the other cores. Perhaps slumps, slides, creep,

or different accumulation rates during the Holocene covered those parts

of the slope so that the recognizable interval was not penetrated by the

cores. Nevertheless, the change in the rate of increase of left coiling

N. pachyderma and a corresponding change in the ratio of left coiling

and right coiling N. pachyderma at approximately 140 em in GC-6 and 150

em in GC-7 suggest a possible correlation between the two cores. The

relative abundance of other key planktonic foraminiferal species in

70

0

25 Ul

Q; 50 4i

.5 "' 75

0 u .5

100

.c c. 125 Ql 0

150

175

200

225

GC-1 GC-2 GC-3 GC-4

(505 m) (717 m) (832 m) (882 m)

sS Ma

cSs

--12.5 ky-?-··

cs

sc

ss '<> css ·.s

-----"' -l-.s.,

cs

Ss ~ .S sc

- ~C_! -+.J..

cs

cSs

cs

csS

Biostratigraphic correlatiOn wlfh ass1gned age, Quened where age uncertain ,dolled where

not J[.IOhcable to core: ky =thousand years. Ma • mdhon yef'Jrs,

GC-5

(983 m)

GC-6 GC-7 GC-8 GC-9

(1072 m) (1183 m) (1277 m) (1420 m)

. -9.5 -1/ .,"' cs

IJ..• " --?--···· cs···· ··12.5 ky·· ·· cs· · --?

cs

.. 15 ky .. _....\ "''1-~ sc

sc cs

cs sc

cs

clay Sse snnd slit cldy sS silty sand

sc silly clay sand


slit Sc sandy clily

Ss sundy silt clay

Figure 34. Biostratigraphic correlation of gravity cores. Ages determined from correlation of planktonic foraminifers in gravity cores with core Vl-8D-P3 of Gardner and others (in press).

two cores suggests that the sediments are less than 12,000 years old,

perhaps 7,000 years or less.

The 9 million year age assigned to the lower portion of.GC-1, based

on the diatom assemblage, combined with an absence of planktonic foram

inifers precludes correlation with the Quaternary biostratigraphy of

core V1-80-P3 or the cores in the study area.

Carbonate Content Correlation

A systematic variation in carbonate content enables correlation to

be made between three gravity cores and two box cores collected between

832 and 1020 m. In BC-7 and BC-8, and GC-3, GC-4, and GC-5, the reduc

tion of carbonate by one hal~ from that of deeper sediments occurs in

the interval from 35 to 15 em; in GC-5 the interval is 65 to 15 em (see

Figure 11). The decrease in carbonate may reflect any one or a combi

nation of: (1) a decrease in carbonate productivity, (2) dissolution,

and (3) dilution. The ratio of planktonic to benthic foraminifers given

in Table 6 shows a distinct drop in the percentage of planktonic foram

inifers occurring between 35 and 15 em. The decrease in planktonic

foraminifers above approximately 35 em is probably the result of prefer

ential dissolution of the thin tests of planktonic foraminifers (Berger,

1979). Also occurring within this interval is a textural facies change

from silty clay and clayey silt to sandy, clayey silt separated by a

sharp contact. A 14c date in BC-7 at 34-36 em (just below the sharp

contact) is 10,330 years BP. Correlations between the gravity cores and

box cores indicate that the textural change and decrease in carbonate

content have occurred less than 10,000 years BP. Gardner and others (in

72

73

Table 6.--Ratios of planktonic foraminifers to benthic foraminifers

in box cores 7 and 8 and gravity cores 3, 4, and 5 from 0 to 65 em

Ratio of planktonic to benthic foraminifers

Depth GC-3 GC-4 BC-7 GC-5 BC-8 (em) (832 m) (862 m) ( 905 m) (983 m) (1020 m)

0 7:93 13:87

5 5:95 2:98 4:96

10 9:91 15:85

15 3:97 1:99 9:91

20 10:90 21:79

25 4:96 32:68 31:69

30 1:99

35 19:81 37:63 59:41 58:42

40 42:58

45 21:79 51:49 52:48

50

55 23:77 64:36

60

65 15:85 46:54

press) have tentatively interpreted the interval from 0 to o,SOO years

BP in core V1-80-P3 to be dissolution affected. The onset of disso

lution less than approximately 10,000 years BP may have resulted from

changes in oceanographic conditions that followed rapid deglaciation

and sea level rise. Secular carbonate dissolution cycles have been

correlated with deglaciation throughout the Pleistocene (Shackleton and

Opdyke, 1973, 1976). The last four periods of maximum warming and sea

level rise are associated with dissolution minima (a preservation

spike). The preservation spike at the end of the Pleistocene was

followed immediately by the present period of dissolution--the Holocene

dissolution pulse (Thompson and Saito, 1974). Thompson and Saito (1974)

used oxygen isotope data to correlate the beginning of the Holocene

dissolution pulse (10,000 ±2,500 years BP) with the oxygen isotope Stage

1-2 boundary (13,000 years BP) of Shackleton and Opdyke (1973). The low

carbonate content and low planktonic to benthic foraminiferal ratio in

the tops of cores between 832 and 1020 m off Point Sur may represent the

Holocene dissolution pulse brought about by deglaciation and correlate

with the oxygen isotope Stage 1-2 boundary of Shackleton and Opdyke

(1973, 1976). However, without oxygen isotope data from the present

study area, this correlation cannot be confirmed.

Lithostratigraphic Correlation

Systematic distribution of textural and compositional facies and

depositional structures enable tentative correlations to be made between

box and gravity cores. These correlations are shown on Figure 35.

The glauconitic sand facies is present in the upper 10 to 25 em of

74

200

400

600

BOO

1000

1200

1400

0 5

~ --3 Horizontal Distance (km)

GC-9

- _') ____ _

Lithologic corretation, dashed where inferred, QUetied where uncertain,

dotted where not applicable due to ol!set ot cores on cross section

Carbonate content correlation

lithologic facies change

Approximate contact ol Miocene sediment with

younger Terliary and Quaternary sediment

- '-

I I

I

' ' I

Clay

Silt

200

400

600

I BOO I

I I

I I I I 0 I 1000

I Clay

50

Sc Sandy clay 'E u 1200

100 m cS Clayey sand 0

(.)

.<: s Sand 150 = c.

m

sS Silty sand 0

200

Ss Sandy silt

Silt 250

cs Clayey silt

sc Silty clay

Sse Sand, slit, clay

Figure 35. Correlation chart of box and gravity cores from the continental slope northwest of Point Sur, California. Textural nomenclature from Shepard (1954).

cores between 350 to 750 m. An irregular erosional contact approx

imately 20 em beneath the surface separates the glauconitic sand from

Miocene nonglauconitic, silty sand in GC-1 and BC-2.

A silty sand that grades into sandy, clayey silt down slope is

present in the upper 20 to 60 em of cores between 690 and 1085 m. A

strong correlation of that layer can be made between cores from 832 to

1020 m, based on similar carbonate content and juxtaposition of the

layer to an irregular contact with silty clay or clayey silt already

discussed in the Carbonate Content Correlation section. Correlation of

the uppermost clayey, sandy silt and silty s~nd of GC-3 with the rela

tively coarse material in cores between 690 and 785 m is uncertain.

Laminated sediments in GC-3 and GC-5 at 78 em and 75 em down core,

respectively, appear to correlate. Both are at approximately the same

depth and are located 10 to 15 em above the 12,500 year BP datum.

Planktonic foraminifers in GC-3 su~gest a 10,500 years BP age for the

laminated zone.

A questionable correlation of a sandy, clayey silt interval 30 to

35 em down core, below a clayey silt, is made in BC-9, BC-10, and GC-8.

The interval in BC-10 has a 14c age of 3,175 yr BP. Another question

able correlation between a )70 em thick, clayey silt and underlying

silty clay is made in GC-5, GC-8, and GC-9. The boundary appears to be

time-transgressive, becoming younger with distance from shore.

Clay Composition. A change in the clay mineral assemblage on the

slope northwest of Point Sur has occurred with time. The assemblage

displays a decrease in the amount of smectite, an increase in the amount

76

of illite, and an increase in the amount of chlorite + koalinite

relative to surficial sediments of the same core (see Table 5). The

change may represent a change in provenance of fine grained material

from the late Pleistocene to the Holocene. With a lower sea level

during the late Pleistocene glacial interval, sediment carried by the

Sacramento and San Joaquin river systems could have bypassed San

Francisco Bay and the exposed shelf and debouched directly into coastal

waters. Clays emanating from the San Francisco Bay have a lower

percentage of smectite (see Figure 33). The suspended sediment from

this source may have been entrained in the California Current and

transported south, lowering the smectite percentage of the assemblages

deposited off Point Sur during the late Pleistocene. As sea level rose

and flooded San Francisco Bay, beginning 10,000-11,000 years ago, much

of the clay in the rivers entering the bay was impounded (Atwater and

others, 1977). The Russian River then became the dominant source of

clays in Province 2 during the Holocene {Griggs and Rein, 1980).

Sedimentation Rates

Rates Derived From 14c Data

The 14c dates in excess of 35,000 years BP in GC-1 and BC-2 are

from a glauconite-rich, mud-poor layer that contains a high percentage

of transported and broken foraminifers (Kristin McDougall, written

commun., 1983). These attributes suggest erosion, nondeposition, or

extremely low sedimentation rates on the slope between 390 and 505 m

of water.

77

An average accumulation rate of 2.6 cm/ky is derived for the

interval between 14-16 em (2,525 yr BP) and 34-36 em (10,330 yr BP) in

BC-7. The two samples submitted for 14c ages are separated by a sharp

irregular contact. The amount of bioturbation and preserved burrow

structures, identified on X-radiographs, are different in the sediments

above and below the contact and may be the result of different thixo

tropic response of the sediments to biogenic disturbances (Edwards, in

press) or to a change in the type and rate of sedimentation. The change

in sediment texture at this sharp, irregular contact along with the

change in burrow recognizability and lack of significant burrowing

across the boundary suggests either erosion or a period of nondeposition

followed by a change in the texture of sedimentation, or the base of a

fluidal sediment gravity deposit. The sinking of heavier into lighter

sediment resulted in load structures on the irregular contact. In

either case, the contact marks an interval of discontinuous sedimen

tation. However, because the irregular contact separating the two

samples is present in all cores between 832 and 1020 m, the accumulation

rate of 2.6 cm/ky is representative for the time interval between 10,000

and 2,500 years between those depths. This value is in close agreement

with a hemipelagic sedimentation rate of approximately 2.0 cm/ky calcu

lated from a water column total particulate flux value of 150 mg/m2/day

(assuming an average sediment density of 2.7 g/cm3 ) measured in 900 m of

water west of Point Sur (Martin and Knauer, 1983). This particulate

flux value does not appear to be anomalous for the Point Sur margin,

because similar values have been reported at sites off northern

78

California as well (Fischer and others, 1983).

An average accumulation rate of 16.1 cm/ky is derived for the

interval between 14-16 em (1,930 years BP) and 32-34 em (3,175 years BP)

in BC-10. The two samples are separated by 20 em of bioturbated sed

iment with a gradational change between the lower sandy, clayey silt and

the upper clayey silt. The gradational change in textural type between

the two dated intervals suggests continuous sedimentation. The rate of

16.1 cm/ky is therefore considered to be a representive sedimentation

rate during the last 3,000 years for the slope at 1200 m off Point Sur,

California.

The 16.1 cm/ky value derived from 14c differs by an order of

magnitude from the particulate flux derived rate (2.0 cm/ky), but it

is close to some of the rates calculated from biostratigraphically

identified intervals (see s~ction on biostratigraphically derived

sedimentation rates). It is also very close to a 14.7 cm/ky rate

estimated from 14c dates in sediments from the continental slope off

northern California (Gardner and others, in press).

Rates Derived From Biostratigraphic Data

The correlation of gravity cores from the continental slope north

west of Point Sur with core Vl-80-P3 allows tentative age assignments

to be made on individual cores. From these age datum lines, sediment

accumulation rates for 0 to 12,500 and 12,500 to 15,000 years BP have

been calculated. Three features are readily apparent after analyzing

the data in Table 7. First, the accumulation rate for the 12,500 to

15,000 year BP interval is greater than the rate for the 0 to 12,500

79

year BP interval. The higher sediment accumulation rates from 12,500 to

15,000 years BP, particularly evident in the deeper cores, have also

been observed off southern California where accumulation was 2 to 10

times greater during the colder period from 12,000 to 17,000 years BP

than during the Holocene (Gorsline and Prensky, 1975). Off the Russian

River, accumulation rates increased from 14.4 cm/ky during 0 to 11,200

years BP to 27.9 cm/ky between 11,200 and 14,800 years BP (Gardner and

others, in press) Second, the accumulation rate during the 12,500 to

15,000 year BP interval increases with distance from shore, possibly a

shadow effect of the California Undercurrent. Third, the accumulation

rate during the 0 to 12,500 year BP interval displays a slight decrease

with distance from shore.

Table 7.-- The biostratigraphically derived sediment accumulation

rates (cm/ky) in gravity cores from the upper continental slope

northwest of Point Sur, California.

Gravity Cores

Age Intervals GC-3 GC-4 GC-5 GC-8 GC-9 Depth in Core (832 m) (862 m) (983 m) (1277 m) (1420 m)

(ky)

0-12.5 7 10 8 7 4

12.5-15 10 14 15 20 31

The discrepancy between the biostratigraphic accumulation rate of

approximately 7 cm/ky for the last 12,500 years and the 14c accumulation

rate of 16.1 cm/ky for the last 3,000 years at approximately the same

80

water depth is perplexing. Possible explanations include an increase in

the accumulation rate from early Holocene to late Holocene so the

average for the entire period is lower, the occurrence of a depositional

hiatus of several thousand years with resumption of sedimentation at the

higher rate, or the occurrence of a slide that removed several thousand

years of accumulated sediment and no change in sedimentation rate.

Evidence in support of a hiatus or a slide include: (1) a sharp,

irr~ular contact in cores between 832 and 1020 m, (2) a change in

texture and carbonate content across the contact, and (3) preferential

dissolution of planktonic foraminifers above but not below the contact.

If the sedimentation rate of 16 cm/ky is used to extrapolate back in

time in BC-7 from the 2,500 year BP 14c age of sed-iments 14-16 em down

core to the irregular contact 30 em down core, the approximate age of

the sediment immediately above the contact is 3,500 years BP. The age

of the slide or the duration of the hiatus can then be calculated. The

slide would have occurred approximately 3,500 years ago and removed

7,000 years of accumulated sediment. The hiatus, marked by the sharp,

irregular contact in BC-7, has a duration of approximately 7,000 years;

the duration is based on the separation of two 14c dates: the estimated

age above the contact is 3,500 years BP and the age below is 10,330

years BP. A more detailed 14c investigation is needed to confirm the

estimate. Additional support for a slide in preference to a hiatus may

be the lack of correlatable variation in abundance of planktonic

foraminiferal species in cores GC-6 and GC-7 with other gravity cores.

Those two cores may not have been in the area affected by the slide.

81

However, without high-resolution seismic reflection profiles, a positive

identification and location of the slide cannot be established. A

possible cause for the hiatus in cores between 830 and 1020 m was

sediment bypassing owing to shelf edge and upper slope turbulence

combined with an early Holocene lowering of the erosional- or

nondepositional-depositional regime boundary, presently located between

approximately 600 and 800 m. Curray (1965) noted that the rise in sea

level was so rapid during the interval from 18,000 to 7,000 years BP

that deposition of shelf facies (and shelf spillover) " ••• did not

commence until about 7,000 years ago or even later." In any event, the

data on hand are inconclusive and either a slide or a depositional

hiatus are possible.

82

CONCLUSIONS

1. Sediments of the upper slope northwest of Point Sur, California

display a down-slope decrease in mean grain size. A glauconitic sand

facies is present between 350 and 650 m. Below 650 m the sediment is

composed primarily of terrigenous material with a biogenic and authi

genic component.

2. A change from erosion or nondeposition to deposition occurs between

600 and 800 m indicated by: a change in texture through the transition

zone and location of. the mudline at 800 m, an increase in fine-sand-size

mica and siliceous microfossils, and the presence of surficial

glauconite.

3. Oxygen content affects the composition of surficial sand-size

sediment. Benthic foraminifers are at a minimum in the middle of the

OMZ, increasing up and down slope with increasing oxygen content.

Glauconite is concentrated at the upper edge of the OMZ, whereas fecal

pellets are concentrated at the lower edge.

4. Total organic carbon in surficial sediments appears to be controlled

more by sediment grain size than oxygen content. The greatest amount of

total organic carbon is at 1200 min the most clay-rich sediment. The

correlation coefficient for percent clay and weight percent total

organic carbon is 0.95. The correlation coefficient between oxygen

content and percent total organic carbon is 0.66.

5. Surficial clay minerals in water shallower than approximately 600 m

have a slightly different assemblage than those deeper than 600 m.

The shallower group has less smectite and more illite and chlorite plus

kaolinite than the deeper group. Possible reasons for the differing

assemblages include: physical sorting by size, different provenance, or

diagenetic loss of smectite during glauconitization of the substrate.

Diagenetic loss of smectite during glauconitization of the substrate

may be the major cause for the different assemblages.

6. The average late Pleistocene clay assemblage in cores 832 m and

deeper contain less smectite and more illite and chlorite plus kaolinite

than average surficial clays from the same cores. The change may rep

resent a change in provenance from the San Francisco Bay river system to

the Russian River when sea level rose, flooded the bay and impounded

much of the clay mineral load.

7. Biostratigraphic analyses of box and gravity cores indicate that a

Miocene-Holocene (?) unconformity of unknown origin is present in the

shallow subsurface at water depths between 390 and 505 m. Deeper cores

contain only Holocene and late Pleistocene sediments.

8. Biostratigraphic and lithostratigraphic correlations combined with

l4c analyses indicate that sediment accumulation rates during the late

Pleistocene increased with increasing water depth from 10 cm/ky at 832 m

to 31 cm/ky at 1400 m. Accumulation rates were also more rapid in the

late Pleistocene than during the Holocene (7 cm/ky for the Holocene and

10 cm/ky for the late Pleistocene at 832 m; 4 cm/ky for the Holocene and

31 cm/ky for the late Pleistocene at 1400 m).

9. A sharp, irregular contact in Holocene sediments is presently 20

to 30 em beneath the sediment-water interface in cores between 832 and

84

1020 m. The origin of the irregular contact is uncertain, but it may

be a slide surface upon which approximately a 7,00Q-year accumulation of

sediment was removed, or a depositional hiatus of a 7,000-year duration

resulting from a combination of sediment bypassing owing to shelf edge

and upper slope turbulence and an early Holocene lowering of the

erosional- or nondepositional-depositional regime boundary.

85

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Stanley, D. J., Addy, s. K., and Behrens, E. w., 1983, The mudline: variability of its position relative to shelfbreak, in Stanley, D. J., and Moore, G. T., eds., The Shelfbreak: Critical Interface on Continental Margins: Society of Economic Paleontologists and Mineralogists Special Publication No. 33, p. 279-298.

92

Summerhayes, c. P., 1983, Sedimentation of organic matter in upwelling regimes, in Suess, E., and Thiede, J., eds., Coastal Upwelling: Its Sediment Record, Part B.: NATO Advanced Research Institute on Coastal Upwelling and Its Sediment Record, New York, Plenum Press, P• 29-71.

Suess, E., and Thiede, J., 1983, eds., Coastal Upwelling: Its Sediment Record, NATO Advanced Research Institute on Coastal Upwelling and Its Sediment Record, New York, Plenum Press, Part A, 604 p.; Part B, 613 P•

Sverdrup, H. U., Johnson, M. W., and Fleming, R. H., 1952, The Oceans: their physics, chemistry, and general biology: New York, PrenticeHall, 1087 P•

Thompson, J. B., 1982, Low oxygen macroinvertebrate assemblages: central California continental slope [C}b.S •. ] : Long Beach, California, Western Society of Naturalists Annual Meeting, December 27-30, 1982.

1983, Analysis of macrofauna! assemblages across the oxygen ----,-minimum zone offshore central California: Sacramento, California, California State University Sacramento, Masters Thesis, 77 p.

Thompson, J. B., Mullins, H. T., Newton, c. R., and Vercoutere, T. L., (in prep.), Alternative biofacies model for low-oxygen communities.

Thompson, P. R., and Saito, T., 1974, Pacific Pleistocene sediments: planktonic foraminifera dissolution cycles and geochronology: Geology, v. 2, p. 333-335.

Traganza, E. D., and Conrad, J. c., 1981, Satellite observations of a cyclonic upwelling system and giant plume in the California Current, in, Richards, F. A., ed., Coastal Upwelling: Coastal and Estuarine Sciences 1, American Geophysical Union, p. 228-241.

Trask, P. D., 1932, Origin and Environment of Source Sediments of Petroleum: Houston, Gulf Publishing Company, 323 p.

Veeh, H. H., uranium shelf:

Calvert, s. E., and Price, N. B., 1974, Accumulation of in sediments and phosphorites on the southwest African Marine Chemistry, v. 2, p. 189-202.

Wickham, J. B., 1975, Observations of the California Countercurrent: Journal Marine Research, v. 33, no. 3, p. 325-340.

93

94

APPENDIX A

Description of Gravity Cores

Texture Sediment

Structure

0 s

E v ~ w 25 sS a: 0 0

~ -----::I: 50 1-

Scs a. - -w c cs

75 --Scs

100

clay

GRAVITY CORE 1 (505 m) .

GLAUCONITE SAND, mica- and foraminifer-bearing, olive black (SY 2/1); homogeneous; contains irregular bored PHOSPHORITE PEBBLES and bivalve shell fragments. sharp, irregular contact

SILTY SAND, olive gray (SY 3/2); convoluted laminae; few burrows, sharp walled, infilled with laminated micaceous CLAYEY SILT.

SANDY, CLAYEY SILT, olive gray; faintly laminated.

diatomaceous CLAYEY SILT, olive gray; laminated.

SANDY, CLAYEY SILT, olive gray; faintly laminated.

~ convoluted

Sse sand silt clay sS silty sand D homogeneous


[ill] intensely bioturbated


Sc sandy cia y w moderately bio•urbated s silt

Ss sandy silt c clay OJ faintly bioturbated

silt ~ faintly laminated -

iii laminated

0

25

E ~ w 0:

50

0 ()

~ :I: 75 1-a. w 0

100

125

150

Texture

sS

r-----cSs

Sediment

Structure

)

)

)

~

~

GRAVITY CORE 2 (71 7 m)

SILTY SAND, foraminifer- and mica-bearing, grayish olive (lOY 4/2) to olive brown (5Y 4/1); mottled with dark gray (N2) patches; bivalve shell fragments at 54 and 63 em; foraminifer-filled burrow at 68 em.

CLAYEY, SANDY SILT, grayish olive; mottled.

Texture

0 cSs

t-- - - -ss

25 1- - - - -

cSs

50 Scs --- - -

75 sc

E -- - -.:!. sS UJ 100 a: 0

- - - -cSs

- - - -()

~ 125 Ss :I: 1-Q. UJ 0

150

J-- -Scs - - - -cs

- - - -cSs

175 -- - - -cs

t-- - - -200

csS

225

Sediment

Structure

)

) )

s s


CLAYEY, SANDY SILT, gray~sh olive (lOY 4/2); homogeneous. SILTY SAND, mica-bearing, grayish olive.

CLAYEY, SANDY SILT, grayish olive; bioturbated and mottled; bivalve shell fragment at 40 em. sharp irregular contact SANDY, CLAYEY SILT, mica-bearing, light olive gray (5Y 5/2); faintly laminated; bivalve shell fragment at 60 em. SILTY CLAY, foraminifer rich silty clay at 80 to 83 em; laminated.

SILTY SAND; homogeneous CLAYEY, SANDY SILT, foraminifer-bearing, dusky yellow green (5GY 5/2); homogeneous to mottled.

SANDY SILT, wood fragment at 123 em.

SANDY, CLAYEY SILT; mottled. CLAYEY SILT, light olive gray; mottled.

CLAYEY, SANDY SILT; mottled; wood fragment at 170 em.

CLAYEY SILTY; mottled to homogeneous.

CLAYEY, SILTY SAND; homogeneous

Texture

0

cSs

25 cs

r--

50 sc

E 75 0 r-----w c: cs 0 () 100

~ 1-----

J: 1-a. 125 w 0 sc

150

1-----175 Scs

1-----

cs 200

--sc

225

Sediment

Structure

)) )\

)

) )

ruJ1.Q_ rM1J \)

)) s

ss ss


CLAYEY, SANDY SILT, mica-bearing, olive gray (SY 3/2); homogeneous, open burrow (2 em in diameter) at 10 em. sharp, irregular contact CLAYEY SILT, mica-bearing, grayish olive (lOY 4/2); bioturbated with distinct infilled burrows (0.3 em across).

SILTY CLAY, foraminifer bearing, grayish olive; mottled with distinct infilled burrows (<S em across); bivalve shell at 75 em.

CLAYEY SILT, grayish olive, convoluted laminae.

SILTY CLAY, foraminifer-bearing, grayish olive; bioturbated; wood and shell fragments at 125 em and bivalve shell at 144 em.

SANDY, CLAYEY SILT, grayish olive, bioturbated.

CLAYEY SILT, grayish olive; mottled with greenish black (5GY 2/1) irregular laminae.

SILTY CLAY, grayish olive; mottled; wood fragment at 210 em.

Texture

0

Scs

25 sc

1- -

50 cs

E 1--- - -0 sc w 1- - -- -a: 75 cs 0 1- - - - -(.J

~ J: 1-

100 sc

a. w 0

1-- -- -125

150 cs

175

1-----sc

200

Sediment

Structure


SANDY, CLAYEY SILT, mica-bearing, grayish olive (lOY 4/2); homogeneous; wood fragment at 10 em. sharp irregular contact

~ SILTY CLAY, mica-bearing, light olive gray (SY 5/2); mottled with )\ grayish olive patches; bivalve shell at 30 em.

) l CLAYEY SILT, grayish olive.

SILTEY CLAY, light olive gray; laminated. CLAYEY SILT; laminated.

SILTY CLAY; bioturbated to faintly laminated.

CLAYEY SILT; mottled to faintly laminated.

SILTY CLAY; faintly laminated to lightly mottled.

1.0 1.0

Texture

0

25

E 50 ~ w 0: 0 0 75 cs ~ J: t-a. 100 w 0

125

150

f-----sc

175

200

Sediment

Structure

)

)

~

\ ( I

( )

)

)

) )

)


CLAYEY SILT, grayish olive (lOY 4/2); bioturbated; open burrow (1 em across) at 10 em down core; bivalve (?) shell at 61 em; rock fragment (0.4 em across) at 76 em down core; wood chip at 144 em.

SILTY CLAY, grayish olive; bioturbated.

1-' 0 0

0

25

E 50 ()

w a: 0 (.) 75 ~ :X: 1-0. 100 w 0

125

150

Texture Sediment

Structure

§ ~\

~) ~)

f( ))

\

cs


CLAYEY SILT, grayish olive green (SGY 3/2) to grayish olive (lOY 4/2); bioturbated; unknown biogenic fragments((.S em across) at 12 and 16 em down core, bivalve shell fragment at 42 em; foraminifer-bearing layer (4 em thick) at 90 em.

Texture

0 cs

-----sc

25 -----Scs r-----sc r-----

50

75

E u

100 cs w a: 0 ()

~ 125

:X: r-D.. w 0 150

-----sc ------

175

cs

200

Sediment

Structure

))<;

m ))

)~

))

)~

)~

S\


CLAYEY SILT, grayish olive (lOY 4/2); mottled with medium dark gray (N4) burrows (1 em across) at 6 and 10 em down core. SILTY CLAY, grayish olive; homogeneous. SANDY CLAYEY SILT, grayish olive; homogeneous. SILTY CLAY, grayish olive; homogeneous.

CLAYEY SILT, light olive gray (5Y 5/2) to grayish olive; bioturbated and mottled with dark gray (N4) patches; burrows (2 to 5 em across) at 70 and 77 em infilled with pelletal mud; shell fragments at 115 and 120 em.

SILTY CLAY, grayish olive; bioturbated.

CLAYEY SILT, grayish olive, bioturbated.

1-' 0 N


Texture Sediment

Structure

0 )})

25 ~~~ ))\

50 )))

cs )) CLAYEY SILT, olive gray (5Y 3/2); bioturbated and mottled; shell fragments at 95 and 105 G

E em. 1.) 75 )\ -w a:

)\ 0 0

~ 100

J: ~\ 1- 1-----0.. w 125 \) SILTY CLAY, olive gray; bioturbated. 0 sc

150 ~) cs )) CLAYEY SILT, olive gray; bioturbated; shell fragment at 175 em.

175

1----- \~ SILTY CLAY, olive gray; bioturbated. sc 1-----

200 ~\ CLAYEY SILT, olive gray; bioturbated. cs

225

104

APPENDIX B

Grain Size in Gravity Core Sediments

Depth

ln c~re

GC-1 GC-2

Percent acavel. aand. silt. aod clay 1n gravity core aedllaents

(grv, gravel; end, ttand; alt, allt; ely, clay]

GC-3 GC-4 GC-5 GC-6 GC-7 GC-6 GC-9

(ca) 11rv •nJ •It ely and •It ely and sit ely and alt ely and slt ely and alt ely snd sit ely and a1t ely and alt ely

1S

2'i

15

55

b'i

75

85

95

lllj

115

125

135

14S

155

165

IH

IdS

195

205

215

6 8H

57 J I 12

28 51 20

42 41 17

26 51 2l

21 54 26

14 52 3.\

14 48 38

20 49 32

b] 2 3 10

68 23

6 7 24 10

64 24 12

65 25 10

66 24 11

49 36 16

52 34 ll

52 33 I 5

57 27 16

so 35 14

53 30 18

34 4 5 21

38 42 20

44 39 18

43 38 19

39 39 22

34 39 27

u 43 34

44 46

39 56

l1 42 41

44 40 17

34 45 21

JS 55 10

48 37 15

25 56 19

20 SO JO

l) 51 36

32 46 22

4 5 34 21

18 47 JS

44 35 21

48 3 I 21

37 36 27

33 44 22

21 54 25

56 16

12 52 36

48 so

45 s 1

8 45 47

12 42 46

54 42

20 46 34

12 46 42

40 56

9 44 47

43 53

39 57

44 52

JO 40 29

32 44 24

11 52 37

so 47

47 so

2 J 48 29

26 46 28

4 5 48

6 43 51

12 54 34

l) 46 41

11 44 46

11 48 41

4 5 51

42 ))

40 54

43 54

15 49 37

18 so 33

55 36

12 53 35

15 51 34

12 53 36

53 43

47 49

11 58 31

8 58 34

58 34

10 57 ))

10 56 14

12 56 32

11 59 30

I 3 60 27

14 52 33

14 52 33

12 56 32

14 56 30

8 51 41

60 32

56 39

53 41

41 56

1 'i 'iS 30

46 46

52 41

8 )5 36

10 'iS 12

10 so 39

11 49 41

11 'il 36

14 53 33

13 51 36

12 52 36

8 56 36

59 33

54 42

so 47

8 53 40

53 42

51 46

12 46 42

14 38 48

26 43 ll

14 41 45

1 3 46 41

12 4H 40

48 48

51 41

so 43

52 4 3

52 44

48 44

48 43

48 43

10 48 42

10 43 47

49 44

49 44

11 57 32

11 60 29

10 59 ll

58 39

62 14

60 18

60 38

56 39

11 62 27

61 )6

62 36

46 49

46 52

45 51

8 so 41

49 45

51 45

48 48

44 48

11 46 44

48 47

...... 0 U'l

APPENDIX C

Weight Percent Organic Carbon and Carbonate

in Gravity Cores

106

Depth

ln core

(ca)

1~

2~

3S

4~

5~

65

H

8~

9~

10~

ll5

125

135

145

155

16S

175

185

195

20~

215

CC-1

roc

0.56

1.92

3.02

2.19

2.85

3.18

4.41

4.17

3.79

3.48

2.46

2.43

2.18

2.58

2.12

2.25

2.08

1. 76

GC-2

1.05 2.67

.91 2.50

1.02 1.57

1.17 2.24

.85 3. 74

.94 2.57

.73 6.54

.85 7 .68

.86 7.18

.80 8.05

.83 4.59

1.04 5.41

1.05 4.07

Weight percent total organlc carbon and carbonate in gravity corea

GC-3

TOC

1.52

l.H

1.14

1.28

1.48

1.36

1. 76

1.59

1.47

1.01

2.61

2.29

2. 55

3.98

4.15

4.56

6.18

5.62

6.29

6.00

.95 6.26

.89 6. 26

.84 7.49

1.17

1.33

1.16

.94

.94

1.48

.67

5. 53

5.44

7.14

5.33

6.23

5.23

8.77

.70 9.06

.78 9.17

[toe. total organlc carbon

GC-4

TOC

1.49

1.37

l. 70

1.62

I. 74

1.69

1.71

1.62

1.82

1.36

2.18

2.16

5. 94

7.22

8.19

7 .41

6.08

6.88

6.61

6.00

1.77 6.74

1.75 5.71

1.71 6.81

1.85 7.16

1.77 6.89

1.85 6.97

1.19 8.26

.93 7.63

1.40 6.66

1.58 5.95

1.64 5.78

l.ll 2.72

GC-5

TOC

1.91

1.58

l. 72

1.38

1.88

1.95

1.71

1.80

3.77

2.86

5. 7 4

6. 3 5

6.67

7.03

7.16

6.76

1.74 7.24

1.96 4.61

1.54 5.24

1.23

1.48

1.89

l. 7 5

l. 25

1.37

1.33

5.68

5.33

6.05

6.86

7.01

5.n 5.88

co3 , carbonate 1

GC-6

TOC

2.33

2.46

2.35

2.14

2.14

2.02

1.93

1. 74

1.77

1.81

4.16

4.94

5.39

4.80

4.99

5.05

4.78

4.30

5.19

6.36

1.76 6.26

1.66 5.43

1.81 6.16

1.56 7.18

1.61 8.56

1.58 9.50

1.78 9.50

CC-7

TOC

2.47

2.54

2. 57

2.44

2.27

2.19

2.27

2.19

2 .as 2.01

7.03

6.87

7. 41

7.96

8.35

9.65

8.65

9.60

8.39

7.92

1.92 6.21

2.00 6.88

1.84 7.06

1.84 6.39

1.98 6.64

1.72 6.75

1.66 8.71

1.70 9.19

GC-8

TOC

2.2J

2.48

l. ~ 5

1.78

1.60

1.48

1.63

1.35

1.41

5.15

~.01

6.60

7.22

7.51

6.73

5.16

5.90

7.23

1.52 6.44

1.31 8.11

1.35 6.81

1.39 7.23

1.47 7.15

1.39 7.36

1.)0 7.19

1.52 6.32

1.47 6.32

GC-9

2.53 2.13

2.24 2.75

1.86 3.77

1.55 4.94

1.41 5.36

1 .4 7 3.61

1.36 3.18

l. 39 2.83

1.56 ).47

1.44 4.07

1.39 3.23

1.14 3.73

1.25 4.51

1.35

1.39

1.31

1.22

1.34

1.24

1.32

5.12

6.91

4.59

4.59

4.50

4.46

4.28

1.27 4.04

108

APPENDIX D

Description of Box Cores

0

5

E 10 0

w a: 15 0 (.)

20 ~ J: 25 t-a. w 30 0

35

40

45

Box Core 1 (279 m)

Graphic Lithology Structure

. . . . 0. 0 .. 0 . o.. . ·. G .. 0. "f.\ . . . . . 0 . \V . 0 ..•.

0 .. o ..•. · o.G.

sand

~ convoluted

D homogeneous

D clay

[ill] intensely bioturbated

GRAVELLY SAND, PHOSPHORITE NODULES, GRANODIORITE and metasedimentary rock pebbles and granules, foraminiferrich, mica-, mafic mineral-, and GLAUCONITE-bearing, olive gray (SY 3/2); homogeneous.

Sse sand silt clay sS silty sand



s si It Sc sandy clay

Ss sandy silt c clay

silt

w moderately bioturbated iii laminated

[I] faintly bioturbated

-ru faintly laminated t-' 0 1.0

0

5

E 10 0

w 0:: 15 0 (.)

20 ~ :::c 25 1-0.. w 30 0

35

40

45

Box Core 2 {390 m)

Graphic lithology Structure

G G

G ~Gr;J G S G G

0

sS

GLAUCONITE SAND, foraminifer-rich, mica- and mafic mineral- bearing, olive black (SY 4/1); homogeneous; metasedimentary pebble at 2 em, PHOSPHORITE and GRANODIORITE pebbles at 5 to 12 em.

sharp irregular contact

SILTY SAND, mica-, mafic mineral-, GLAUCONITE-, and foraminifer-bearing, olive gray (SY 3/2); convoluted to faintly laminated; mottled with greenish gray {SGY 6/1), silty sand and sand patches.

t-' t-' 0

0

5

E (J 10

w 0: 15 0 0

20 ~ :::c 25 1-Q. w 30 0

35

40

45

Box Core 3 (510 m)


G

G

G

GRAVELLY GLAUCONITE SAND, PHOSPHORITE and GRANODIORITE pebbles and granules, mica-, mafic mineral-, and foraminifer-bearing, olive gray (SY 3/2); homogeneous.

0

5

E 10 u

w a: 15 0 (.)

~ 20

::c 1-

25 0.. w 30 0

35

40

45

Box Core 4 (59 3m)


G G G G G

e> G G G

G G G

s G G

G G

GLAUCONITE SAND, mica-, mafic-, and foraminifer-bearing, olive gray (SY 3/2) to brownish black (5YR 2/1); bioturbated to homogeneous; open burrow containing several gastopod and bivalve shells at 5 to 7 em down core; wood chips at 6 and 15 em; several burrows ( (0.2cm across) between 20 and 25 em.

t-' t-' N

0

5

E 10 u

LU a: 15 0 (.)

20 z :c 25 t-a. LU 30 0

35

40

45

Box Core 5 (690 m)


sS

5 I-- - -- --

s

SILTY SAND, mafic mineral-, GLAUCONITE-, and foraminifer-bearing, dark greenish gray (SGY 4/1); bioturbated; burrows (<O.l em across) in upper 6 em.

SAND, mica-, mafic mineral-, GLAUCONITE-, and foraminifer-bearing, dark greenish gray; homogeneous.

0

5

E 10 (J

UJ a: 15 0 0

20 z ::c 25 1-a. UJ 30 0

35

40

45

Box Core 6 (7'85 m)

Graphic lithology

sS 1--

cSs

1--- - - -

sS

Structure

5

s s

SILTY SAND, mica- and fecal pellet-bearing, light olive gray (SY 5/2); homogeneous.

CLAYEY SANDY SILT, mica- and foraminifer-bearing, light olive gray; bioturbated.

SILTY SAND, mica- and mafic mineral-bearing, light olive gray; bioturbated; burrows {<0.2 em across) at 14, 20 and 26 em.

0

5

E 10 ()

w a: 15 0 0

20 ~ J: 25 t-0. w 30 0

35

40

45

Box Core 7 (905 m)


cSs ))

sc

CLAYEY SANDY SILT, mica- and fecal pellet-bearing, grayish olive green (SGY 3/2); bioturbated and mottled with light olive gray (SY 5/2) patches of same material as below contact.

sharp irregular contact

SILTY CLAY, foraminifer-bearing, light olive gray; bioturbated and mottled with material from above contact.

0

5

E 10 0

w a: 15 0 0

20 ~ :::t: 25 1-a. w 30 0

35

40

45

Box Core 8 (1020 m)

Graphic Lithology

Scs

sc

Structure

))

)) SANDY CLAYEY SILT, mica-, fecal pellet-, and foraminifer-bearing, light olive gray (5Y 5/2); bioturbated.

sharp irregular contact SILTY CLAY, light olive gray; homogeneous.

0

5

E (.) 10

w a: 15 0 ()

~ 20

J: 25 t-a. w 30 0

35

40

45

Box Core 9 ( 1085 m)


Scs f------ ~~s s~~

sss )~)

cs sss ~5)

SS\ -- --Scs ~~

SANDY CLAYEY SILT, mica- and fecal pellet-bearing, grayish olive (lOY 4/2); bioturbated.

CLAYEY SILT, grayish olive; bioturbated; worm tubes (0.5 em in diameter with .1 em thick walls) 10 em down core.

SANDY CLAYEY SILT, mica- and foraminifer-bearing, grayish olive; bioturbated.

0

5

E 10 (,)

w a: 15 0 u

20 ~ J: 25 1-ll. w 30 0

35

40

45

Box Core 10 (1200 m)


))~

)~~ cs )~

))

1------ )\

Scs

~ ~) cs

CLAYEY SILT, grayish olive (lOY 4/2); bioturbated; burrows ((0.2 em across) at 10 and 17 em; bivalve shell fragment at 15 em.

SANDY ~LAYEY SILT, mica- and foraminifer-bearing, grayish olive; bioturbated.

sharp irregular contact CLAYEY SILT, grayish olive; homogeneous.

1-' 1-' 00

119

APPENDIX E

Grain Size in Box Core Sediments

Percent gravel, sand, silt, and clay in box core sediments

[grv, gravel; and, sand; alt, silt; ely, clay]

Depth BC-1 BC-2 BC-3 BC-4 BC-5 BC-6 BC-7 BC-8 BC-9 BC-10

in Core

(ca) grv and slt ely grv snd slt ely snd slt ely and slt ely snd slt ely and slt ely and slt ely and slt ely ond slt ely snd slt ely

0 41 56 2 92 3 89 8 3 89 3 8 69 18 13 41 40 19 37 39 24 22 48 31 20 49 31 10 49 41

5 40 56 2 4 91 2 2 96 2 92 2 6 76 16 8 36 44 20 34 43 23 26 42 32 16 53 31 7 50 43

10 38 52 6 4 2 78 15 5 85 10 6 85 8 8 80 10 10 33 44 24 32 44 22 20 51 28 12 53 35 51 41

' 15 32 56 12 82 11 6 86 76 14 10 45 37 18 30 48 22 20 55 25 14 so 36 4 51 45

20 44 47 9 74 14 12 76 17 42 41 18 29 50 21 22 53 25 14 49 37 4 51 44

25 35 55 9 80 11 10 77 12 11 43 41 17 34 46 21 24 53 23 16 48 36 4 53 43

30 38 52 10 76 13 10 43 37 19 8 45 47 25 so 26 13 60 27 22 40 37

35 48 35 17 5 43 53 27 49 24 24 49 28 10 52 38

40 14 43 43 25 46 29 8 53 39

t-' N 0

APPENDIX F

Weight Percent Organic Carbon and Carbonate

in Box Cores

121

Depth BC-1 BC-2 BC-3

in core

(CIII) TOC TOC TOC

0 1.17 2.91 0.41 5.19 0.62

5 1.68 4.18 .45 5.10 .61

10 1.93 4.89 .62 7.04 .57

15 .72 7.59

20 2.68 7.22

25 2.85 6.89

30 2.65 6.54

35

40

Weight percent total organic carbon and carbonate in box corea

(TOC, total organic carbon co3, carbonate)

BC-4 BC-5 BC-6 BC-7

roc TOC TOC TOC

2.41 0.50 0.73 0.68 2.45 1.37 3.75 1.72 4.73

2.82 .49 .7 7 .66 2.27 1.41 3.44 1.88 4.28

2.52 .69 .94 .69 2.06 1.33 2.90 1.74 3.20

.47 2.53 .68 2.16 1.10 2.81 1.59 3.30

.52 1.71 .62 2.36 1.15 2.88 1.46 2.69

.41 1.09 .64 2.61 1.09 2.80 1.75 4.48

.64 2.59 1.10 3.08 1.73 7.54

1.21. 3.73 1.82 i.88

1.41 6.73

BC-8 80-9

roc roc

2.16 4.13 2.10 4.41

2.23 4.18 2.41 4.18

1.98 3.50 2.27 4.49

2.03 3.58 2.12 4.84

1.78 3.19 2.04 4.98

1.83 3.39 2.13 5.36

1.68 4.06 1.94 4.47

1. 75 6.79 1.57 4.54

BC-10

roc

2.49 4.72

2.13 4.37

2.77 5.16

2.64 5.33

2.41 5.94

2.67 6.09

2.49 6.51

2.46 6.45

,_. N N

APPENDIX G

Compositional Percentage of Sand-size

Material in Box Cores

123

O~pth

Cou ln core! Q+F Mi Om Rf G1 Fp Bf Pf Sm em u .. (em)

0 64 15 0 0

71 0 0 0

10 68 14 0 6 0

15

BC-6 20 78 8 0 0 0 0

2S

10 67 17 8 0 0

15 67 lb 9 0 0 0

0 bO 15 6 0 0 12 0

58 17 0 0 0 0

10 58 15 6 0 0 II 4 0 0

IS 11 11 0 0 2 0

BC-7 20 ]) 6 0 0 0 4 0 0

25

10 61 lb 0 0 14 0

15 42 11 0 0 JO

0 42 lb 0 0 26 6 0 0

46 18 0 0 20 0

10

15 54 19 6 0 0 9 2

BC-8 20

25 55 27 0 0 8 0

30

)5 11 6 6 0 0 11 0 0

0 56 15 0 0 11 8

52 14 4 0 0 9 8

10 53 22 0 0 0 0 0

15

BC-9 20 47 17 8 0 0 10 0 0

25 62 11 0 0

30 b2 1) 0 0

15 59 19 4 0 0 0 1-' N V1

Depth Core in core Q+F M1 Om Rf Gl Fp Bf Pf Sm c. Um

(em)

0 52 19 3 0 0 9 6 2 0

5 56 21 0 0 9 4 0

10 44 17 0 0 13 11 8

BQ-10 15

20 54 17 0 0 6 10 3 8 2

25 61 10 0 0 9 6 3 0

30

35 45 17 4 0 0 10 10 8 3 2

APPENDIX H

Percentage of Individual Planktonic Foraminiferal

Species in Gravity Cores

127

The percentage of individual planktonic foraminiferal species in gravity corea

(Npl, Neogloboquadrina pachyderm&, left coiling; Npr, Neogloboquadrina pachyderaa, right coiling;

Gb, Globigerina bulloides; Gf, Globigerina falconenais; Gqd, Globigerina quadrilatera;

Gqn, Globigerina quinqueloba; Gr, Globigerina rubeocens; Gu, Globigerina uabilicata;

Gg, Globigerinita glutinata; Gi, Globorotalia inflata; Gs, Globorotalia scitula;

Gh, Globorota1oides hexigona; Ou, Orbulina universe]

Core

Depth

in core

(em)

5

25

GC-1 45

GC-2

GC-3

GC-4

65

85

5

35

55

75

95

115

45

55

65

85

105

140

180

220

25

45

65

85

105

118

128

138

148

168

188

Np1 Npr Gb

85

77

71

80

64

70

77

17

20

28

55

59

64

53

71

12

14

14

20

19

10

28

31

28

68

60

6

8

16

5

10

9

5

69

47

34

26

19

11

14

6

75

63

61

61

69

53

43

29

22

16

20

5

9

7

7

8

9

4

12

3

8

13

11

6

2

8

3

2

14

4

17

12

5

Gf

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Gqd Gqn Gr

4

6

3

3

5

(1

10

5

5

6

3

13

8

4

10

12

6

3

16

11

14

17

3

0

0

0

2

9

3

9

12

6

8

3

2

2

5

6

3

5

3

13

2

3

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Gu

0

0

0

0

0

0

0

0

0

0

(l

0

0

0

0

0

0

0

0

0

0

0

Gg

0

0

3

3

2

2

4

2

3

0

0

3

0

4

Gi

0

0

0

0

0

0

0

0

(l

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

<l

3

0

3

4

2

4

0

(1

2

0

3

4

4

(1

0

Gh

0

0

0

0

0

0

<l

(l

0

(1

2

0

(l

3

(1

2

3

(1

0

Ou

0

0

0

0

0

0

0

0

2

2

0

0

0

0

0

0

(1

0

0

2

(1

(1

0

128

Core

GC-5

GC-6

GC-7

GC-8

GC-9

Depth

in core

(Clll)

15

35

55

75

95

120

140

160

180

200

20

60

100

140

160

10

30

50

70

90

110

130

150

170

20

40

60

80

105

125

145

165

25

45

65

85

105

125

145

165

185

205

Np1 Npr Gb

47

21

23

20

30

28

57

60

69

68

54

44

36

30

10

65

41

54

33

53

36

35

33

14

51

17

26

58

49

41

60

51

42

49

57

49

50

35

50

47

62

73

50

57

58

50

36

42

18

14

8

10

41

53

53

54

56

29

52

34

50

29

45

40

44

58

31

67

47

8

3

4

8

5

21

5

3

3

(1

2

4

3

2

10

10

8

13

5

5

5

5

7

3

0

7

14

3

7

10

8

11

14

12

16

12

6

9

22

35

3

26

9

11

22

29

29

37

28

31

34

7

Gf

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

<1

(1

0

0

0

0

0

0

0

0

Gqd Gqn Gr

0

2

6

10

9

10

0

5

7

4

0

10

0

0

2

3

1

3

5

0

2

2

9

9

2

5

3

11

11

11

14

14

16

13

11

2

3

(1

7

3

5

9

8

6

3

7

0

3

0

4

6

3

0

4

3

1

3

1

6

7

4

3

6

8

2

5

6

2

4

2

1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Gu

2

0

0

2

0

0

0

0

0

3

0

2

0

2

0

0

0

0

4

0

1

0

(1

<1

2

0

0

0

2

(1

2

2

5

6

6

2

0

0

0

0

2

0

2

4

3

0

6

11

9

10

13

4

11

16

3

4

8

4

6

6

Gi

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

(1

0

0

0

(1

(1

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

4

6

3

3

(1

0

0

0

0

0

0

2

0

0

(l

1

2

0

0

0

(1

0

0

(1

Gh

(l

2

0

0

0

0

0

(l

0

2

0

0

2

3

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

Ou

0

0

0

0

(l

0

0

0

0

0

0

0

0

0

0

0

0

0

0

2

(1

(1

(1

0

0

0

0

0

0

0

0

0

0

129

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