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Late Pleistocene-Holocene depositional history of the California Continental Borderland

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Late Pleistocene-Holocene depositional history of the California Continental Borderland

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LATE FLEBTOCENE-HOLOCENE DEFOSTTIONAL HISTORY
OF THE CALIFORNIA CONTINENTAL BORDERLAND
Rebecca Sprague Robinson.
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A Thesis Presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
I Requirements for the Degree of
| MASTER OF SCIENCE
l (Earth Sciences)
[ August 1997
Copyright 1997 Rebecca Sprague Robinson
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UMI Number: 1387829
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UNIVERSITY O F SO U TH ER N CALIFORNIA
THE GRADUATE SCHOOL
UNIVERSITY PARK
LOS ANOELES. CALIFORNIA SOOOT
This thesis, written by
under the direction of A & L — Thesis Committee,
and approved by all its members, has been pre
sented to and accepted by the Dean of The
Graduate School, in partial fulfillment of the
requirements for the degree of
J&»Jtt£JC~£JL££Asa££
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II
A cknow ledgem ents
This project has been shaped and reshaped during m y time at USC.
W ithout D onn Gorsline, it w ould not have been conceived. H e brought me
to USC and introduced me to "reading" X-rays. He taught me to w onder at
the complexities of the borderland and to love my work. Bob Douglas has
given me a num ber of things to think about while teaching me the value of
the once-living creatures in m y sam ples. Steve Lund's ever-critical m ind has
added to m y personal developm ent as a scientist as w ell as the im provem ent
of the project.
In collecting the data, I h ad help all around. Dave Drake gave m uch
needed assistance and equipm ent at the USGS Sediment Dynamics Lab. Eric
Hovanitz and Lawford A nderson allowed and helped m e to use the XRD.
Donal M anahan and Doug Pope assisted my progress and provided me w ith
coundess hours in the radioisotope lab in Hancock using a centrifuge. Will
Berelson, beyond the use of his centrifuge, spent num erous coffee breaks
discussing dogs and data. Janette Murillo and Enrique N ava answ ered
questions and gave me assistance in the lab as well as Spanish translations
w ith Anel, w ithout whom I w ould still be running carbonate analyses.
Thanks to Ron Kolpack for advice and discussion. M any thanks to Dennis
Graham, for his help at the USGS and in many other aspects of this thesis.
I owe special thanks to m y parents for their never ending
encouragm ent and love, throughout m y schooling. This project was
funded in p a rt by the National Science Foundation and the W. and D.
Zinsm eyer Endowm ent.
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Table of Contents
Acknowledgements........................................................................................................i 1
List of Figures..................................................................................................................v
List of Tables....................................................................................................................ix
Abstract............................................................................................................................x
Introduction................................................................................................................... 1
Statement of Intent.............................................................................................1
General C irculation..........................................................................................6
Previous W ork.................................................................................................. 9
M ethods.......................................................................................................................... 16
X-radiograph D escription............................................................................... 17
[ Sampling................................................................................................................ 17
[ Organic Carbon an d Carbonate........................................................................18
Grain Size A nalysis..........................................................................................19
C om position...................................................................................................... 20
Coiling Direction................................................................................................ 23
Age Models..........................................................................................................23
Potential Errors...................................................................................................28
Errors in depth below sediment-surface......................................................29
Results and Discussion................................................................................................ 31
EW9504-02PC- A nim al Basin.........................................................................31
EW9504-03PC -Descanso Plain...................................................................... 45
EW904-04PC - East C ortes............................................................................... 50
EW9504-05PC- San Clem ente........................................................................ 56
| EW9504-08PC- San Nicolas..............................................................................62
j EW9504-09PC- T anner Basin........................................................................... 70
I Synthesis......................................................................................................................... 79
I Carbonate..............................................................................................................79
f Organic Carbon an d Paleoproductivity......................................................... 82
* The question of the "partings"..........................................................................83
Regional Circulation C hanges.......................................................................85
Present and Past Regional C lim ate...........................................................................93
Application of the study to regional climate record................................. .95
Conclusions..................................................................................................................... 97
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References....................................................................................................................... 98
Appendix I.................................................................................................................... 106
Appendix H...................................................................................................................127
Appendix IH..................................................................................................................131
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List of Figures
Figure 1. Map o f California Continental Borderland. The core locations
and basin names are noted. The striped areas are exposed during times
of lowered sea-level.......................................................................................................3
Figure 2. Schematic cross-section of borderland from w est to east
(adapted from Gorsline, 1987). The sills become increasingly shallow
towards land. The sedimentation pattern changes from being
dominated by terrigenous input in the nearshore basins, to m ostly fine
grained detritus and biogenic materials far from land. Turbidity
currents in the outer basins are delivered from the basin flanks and sill
tops................... 5
Figure 3. Surface circulation in the borderland. The broad, sluggish
California C urrent passes offshore over Tanner Basin and turns
inwards tow ards Baja California. The California Counter C urrent is
traveling northw ards adjacent to the shoreline (from Hickey, 1979)...............7
Figure 4. Bottom w ater renewal occurs from the south in m ost
borderland basins. The direction of bottom water flow in the region is
complex due to the bathym etry (from Emery, 1960)..........................................8
Figure 5. Deep Pacific Ocean CaC03 record showing a record
dominated by dissolution with low carbonate during intergladal times.
The CCB record is the opposite of this pattern (from Karlin e t al 1992)..........12
Figure 6. Spatial distribution of chorite and illite in the Pacific Ocean.
Illite dominates m ost of the Pacific, particularly the m argin regions.
Chlorite is m ost im portant in polar regions, (from W eaver, 1989)................ 12
Figure 7. A representative X-ray diffraction pattern from this study
w ith peaks labeled. The shaded area indicates the peaks that are used
for the semi-quantitative analysis.............................................................................. 22
Figure 8. % C aC 03 stratigraphy versus depth. The CaC03 stratigraphy
was used in creating the age model, based on the previously established
idea that the basins display a dilution effect during glacial times. It is
not clear in all basins and absent in Animal. Oxygen isotope stages 2
and 4 are shaded by the gray swaths..........................................................................25
Figure 9.. Color reflectence records from shipboard results (Lyle et al
1995). High reflectence indicates less color absorbence and is thought to
be related to the ratio of TOC to CaC03....................................................................26
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Figure 10. Age m odel and mass accum ulation (MAR) plots. The age
versus depth curves are similar for all six basins. The MAR versus age
plot shows the different rates of flux over the region. MAR is based on
sedimentation rates and dry bulk density, which is estim ated from
porosity data also pictured...........................................................................................27
Plate 1. X-radiograph of representative interval of bioturbated facies
from the Anim al Basin core. Large burrow s and small bits of pyrite are
clearly visible. A t 10X magnification there is no clear structure or
preferred orientation of the m aterial....................................................................... 32
Figure 11. Mass accumulation rate (MAR), facies, sand percent, coiling
direction, total foraminifera, w hole/total foraminifera, biogenic silica,
fecal pellets, detritus, mean size, and clay mineralogy are all plotted
together against age for easy com parison of the Animal Basin record.............33
Plate 2. X-radiograph of representative distal turbidite deposit from
Animal Basin. The turbidite is ~9 cm thick. The top portion of
laminations show w here the finest m aterials begin to settle o u t of
suspension but are not disturbed by organisms. The basal portion has
been slightly m ixed by bioturbation...........................................................................35
Plate 3. X-radiograph of current partings from the San Clem ente B.
core. The m agnified intervals show alighnm ent of the coarse m aterials
alternating w ith deisorganized hemipelagic m uds............................................... 36
Figure 12. A. W eight percent frequency distributions of all the 16-
channel grain size d ata from Anim al Basin. The distributions change
according to the m ethod of deposition. B. The distributions from the
two major turbidite deposits in the cores. C. Distributions from the
intervals containing partings, as seen in X-radiograph, w ith one
bioturbated distribution for reference. D. Statistical param eters,
skewness and standard deviation plotted against the m ean show
f different groupings dependent on the m ode of deposition................................39
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Figure 13. TOC (A) and CaC03(B), percentage and flux (MAR), and
paleoproductivity (C) plotted against age for Animal Basin. TOC
values increase during glacials in both the percentage and the flux plots
while CaC0 3 percentage decreases due to dilution.............................................. 44
Figure 14. M ultiple param eters plotted versus age, show ing relative
contribution changes through time in Descanso.Plain....................................... 47
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Figure 15. Grain size frequency distributions and statistical param eters
from Descanso Plain. There w ere no turbidites sam pled from this core.
All but one of the samples was from a reworked interval, as both the
distributions and grouping of the statistical plot suggest.....................................49
Figure 16. TOC (A), CaC03 (B), and paleoproductivity (C), downcore
from Descanso Plain. The record is the most stable of the six studied........... 51
Figure 17. Multiple parameters plotted versus age, show ing relative
contribution changes through tim e in East Cortes Basin................................... 53
Figure 18. G rain size distributions and statistical param eters from East
Cortes Basin....................................................................................................................55
Figure 19. TOC, CaC03, and paleoproductivity versus age. East Cortes
shows very clear glacial/intergladal changes in biogenic in p u t...................... 57
Figure 20. Multiple parameters plotted versus age, show ing relative
i contribution changes through tim e in San Clemente Basin.............................. 59
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I Figure 21. G rain size distributions and textural plots for San Clemente
| Basin. The distributions from this basin vary only slightly, although
r the facies changes are clear in X -ray...........................................................................61
I Figure 22. TOC, CaC03 and paleoproductivity versus age for San
I Clem ente Basin. The intergladal/gladal scale changes are not obvious
} in this record...................................................................................................................63
[ Figure 23. M ultiple parameters plotted versus age, show ing relative
| contribution changes through tim e in San Nicolas Basin.................................. 65
t
f Figure 24. The grain-size distributions and skewness and standard
| deviation versus mean size show the variation in sedim entary fades
\ in San Nicolas Basin. There are distinct distributions and statistical
f groupings for each type.................................................................................................67
Figure 25. Ternary diagram of d a y mineralogy from all six basins.
Only San Nicolas and Tanner Basins fall outside of the m ain grouping........69
Figure 26. TOC, CaC03, and paleoproductivity versus depth in San
Nicolas Basin. Like San Clemente, regional climate variations seem to
have less of an effect on this record than local variations, since
g lad al/in terg lad al changes are not dom inant features of the record.............. 71
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Figure 27. M ultiple parameters plotted versus age, showing relative
contribution, changes through time, in Tanner Basin.......................................... 73
Figure 28. Grain size and statistical data from Tanner Basin. The three
facies types are same but the overall m ean size and shape of the
distributions are skewed towards the coarse fraction. This signals a
different population of material being deposited in Tanner Basin.................. 75
Figure 29. TOC, CaC03 and paleoproductivity records from Tanner
Basin plotted against age. There is a larger contribution of CaC03 in
this basin.........................................................................................................................77
Figure 30. Schematic representation of borderland with hypothesized
Oxygen M inim um Zone.............................................................................................89
Figure 31. Relative sill depth, as it changes w ith sea-level fluctuations,
versus the occurance of partings for Descanso Plain, East Cortes and
San Clem ente Basins. Partings do not appear during the maximum or
m inim um depths of the sills, but rather at intermediate depths.....................92
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List of Tables
Table 1. Morphometry of the distal borderland basins (Emery, 1960,
Gorsline, 1987)................................................................................................................4
Table 2. Summary of core locations and lengths (Lyle et al 1995)......................16
Table 3. Sedimentation rates downcore in each basin. Rates are based
on linear extrapolation betw een fixed dates downcore. Dates are from
M artinson et al (1987).................................................................................................... 24
Table 4. Calculated standard error for LECO analyses...........................................29
Table 5. Grain size statistics for each of the six basins. The statistics
calculated are mean, standard deviation, skewness, and kurtosis.
: ■ Skewness and standard deviation are parameters used to determ ine
I sorting of sediment. .....................................................................................................40
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Abstract
Cores from the outer and central Borderland Basins, (Animal,
Descanso Plain, East Cortes, San Nicolas, San Clemente, and Tanner), contain
three common facies. The three facies, bioturbated sediments, turbidite
deposits and current partings are recognizable in X-radiograph and grain-size
data b u t do not vary in compositional m akeup. The materials being input
into the basin are organic carbon, carbonate, fecal pellets, detritus, biogenic
silica and days.- The only distinctly differenct fades are the turbidite deposits.
Otherw ise compositional variations correspond with larger scale
gladal/intergladal climate changes and not fades changes.
The occurrence of the three fades is inconsistent between basins, aside
from a total lack of partings during the Holocene. Throughout their entire
lengths, all six cores have been bioturbated and in the older portions of the
cores the bioturbated material has been rew orked by bottom currents a n d /o r
biological action. The bottom currents appear to remove the finest m aterials,
<10 pm, and skew the size distributions tow ards the positive.
I attribute the occurrence of the partings to bottom currents intruduced
during semi-annual bottom w ater renew al events that set off a strong
counter-dockwise current along the edge of the basin floor. C ontem porary
examples of such events are docum ented in the literature for the past few
decades. The occurrence of the partings does not correspond to sea-level
extemes and so they cannot be directly related to climate forcing, but parhaps
to water-mass circulation variations on som e other time scale or else biologic
activity at the sediment w ater interface.
There are several possible explanations for the occurrence of these
structures. In general terms, if they are caused by physical means, they are a
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result of either: 1. the characteristics of the water m oving into the basin or 2.
how circulation is being forced. In the first scenario, the renewal water could
be denser and thus entering faster, or perhaps just m oving more rapidly due
to intensified currents or instability. More likely, the basin sill is at times
within the oxygen m inim um zone (OMZ), making the w ater constantly in
the basin different than w hat is there at present. The reduced oxygen levels
slow sedim ent mixing rates by benthic organisms and as a result better
preserve the structures. This requires a shift or expansion of the OMZ to
deeper depths— perhaps as a result of a thicker mixed layer at the surface that
then supresses the OMZ or higher productivity in the surface waters resulting
in greater respiration at depth and an expansion of the OMZ at depth.
In the second case, w here forcing changes, an increase in the amplitude
of vertical fluctuations in the surface waters, forced by tidal variations or
longshore w ind changes, m ay cause a greater pum ping action, which in turn
sets up stronger counter-clockwise m otion in the basin. This explanation
seems less plausible since a ten-fold increase in current velocity is required.
If the partings are the result of biological activity, their occurance may
still be related to the OMZ or perhaps to the rate of sedim ent compaction.
The non-synchronous nature of the structures occurences is likely due
to the complexity of the regional bathym etry. The bathym etry is ultimately
responsible for present patterns in bottom water oxygenation and
depositional patterns betw een basins. Local variations are amplified by
isolation of waters beneath the sill depth and as a result each record is unique.
Ultimately, the variation in tim ing of the facies can aid in identifying their
cause as well as larger scale changes in the regional oceanography.
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Introduction
Statement of Intent
The purpose of this study is to investigate the longest continuous
available records of Holocene and Late Pleistocene sedim ents collected from
six outer an d central Borderland Basins that are located beneath the path of
the California C u rren t The array of cores should provide information about
the tem poral and spatial variation in basin sedim entation patterns and how
they are affected by variations of the California Current and regional climates.
Specifically, measures of carbon, in both organic m aterial and carbonate, have
been m ade in an attem pt to estimate biogenic contributions and
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j paleoproductivity (Samthein, 1987). Paleoproductivity variations have been
$
| attributed to changes in upwelling rates in the region w hich have been linked
|
| to estimates of w ind and water circulation changes (Lyle et al 1992; Sancetta et
| al 1992; G ardner et al 1997). The extent to which land w as exposed during
| glacial periods should appear as a dilution signal in the w eight percent
| carbonate records. Changes in fine fraction contributions from land, as well
I
| as detritus-carrying currents, has been estimated using clay mineralogy. X-
' radiography provides a detailed record of sedimentation modes, such as
* turbidity current activity, reworking due to bottom currents, and the extent of
I bioturbation (Hein, 1985) and act as a sampling map for the other analyses.
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' California Continental Borderland
Continental m argins combine high sedim entation rates with high
productivity due to coastal upwelling to provide a high-resolution look at
regional oceanographic changes. The California Continental Borderland
(CCB), as nam ed by Emery and Shepard, is a collection of marginal basins
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(Fig. 1) offshore of southern California. It is a 300 km -wide extension of the
continental m argin, and extends 1000 km along the Eastern Pacific margin,
from Point Conception south to Viscaino Bay, Baja California (Emery, 1960;
Gorsline and Teng, 1989). The structure of the region is a result of the
interaction betw een the N orth American Plate and the East Pacific Rise
during the mid-Tertiary. The ridge was lost upon arrival at the trench and the
boundary changed from one of a subduction regime to one of complex
transform motion. Strike-slip motion of the present boundary betw een the
N orth American and Pacific Plates occurs along the San Andreas fault system
in Southern California. The San Andreas system is oblique to the coast
creating both extension and strike-slip m otion which is responsible for the
series of "pull-apart" basins offshore (Atwater, 1989; Atwater, 1977).
The northern portion of the borderland trends east-west in agreem ent
w ith the trend of the adjacent transverse ranges. South of the northern
C hannel Islands is a series of fault-bounded blocks w hich trend northwest-
southeast due to major lateral motions betw een plates. The result of these
tw o trends is the parallelogram shape of the present configuration of the
"pull-apart" basins. Contem porary deposition began in late Miocene time,
w hen lateral m otion jum ped to the present San Andreas system (Gorsline
and Teng, 1989; Atwater, 1989). The northern borderland is now in
compression against the Transverse Ranges (Atwater, 1989).
At present, the CCB is a collection of basins, islands, and banks which
align w ith the regional northwest-southeast trend. The basins are arranged in
roughly three row s and are separated by sills which create a patchwork-like
pattern (Emery 1960). Sills increase in depth to the southeast (Table 1) (Doyle
and Gorsline, 1977) . The basins act as a series of independent sedim ent traps.
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legend:
02 Animal B. 05 San Clemente B.
03 Descanso Plain 08 San Nicolas B.
04 East Cortez B. 09 Tanner B.
120° 119° 118° 117° 116°
Figure 1. Map of the California Continental Borderland. The core locations
and basin names are noted. The striped areas w ere exposed during times
o f lowered sea-level.
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The depositional pattern in the Borderland is controlled by supply,
topography, distance from the shoreline, and circulation as well as the general
oceanographic and climatic conditions (Emery 1960; Schwalbach et al, 1993).
Basin w idth km length km depth m area km2 deepest si
02PC Animal 27 130 2020
03PC Descanso Plain 27 108 1350 1350
04PC East Cortes 27 63 1947 1320 1594
05PC San Clemente 36 108 2047 1865 1787
08PC San Nicolas 54 90 1803 3327 1089
09PC Tanner 36 108 1526 1577 1146
Table 1. Morphometry of the distal borderland basins (Emery, 1960; Gorsline, 1987)
A general distinction can be m ade between nearshore and offshore
basins in term s of sedimentation rates as well as the type of materials being
deposited w ithin the basins. Nearshore basins are dom inated by terrigenous
sedim ent input from northern and central streams such as the Santa Clara,
Ventura, Los Angeles, San Gabriel, and Santa Ana rivers. Accumulation
^ rates in the inner basins are of the order of 15-30 m g/cm 2y r (Schwalbach et al.,
I 1993). The sills which separate the inner and outer basins prevent significant
| passage of the coarse-grained terrigeneous sediment seaw ard (Fig. 2). Central
[ and outer borderland basin sedim entation is dominated by hemipelagic
j regimes. Accumulation rates are as low as 2-5 m g/cm 2yr (Schwalbach et al,
1993).
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inner borderland outer borderland
Penninsular Ranges
— Om
600
Santa Monica
SanQem ente Basin
Basin
1200
Tanner
Basin
1200
1800
2400
hemipelagic sedimentation
100 km
terrigenous input
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| Figure 2. Schematic cross-section of the borderland from the southeast to
| the northwest (adapted from Gorsline, 1987). The sills become increasingly
shallow towards land The sedimentation pattern changes from being
■ dominated by terrigenous input in the nearshore basins, to m ostly fine
grained detritus and biogenic materials further seaward Turbidity currents
in the outer basins are delivered from basin flanks and sill tops.
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General Circulation
The California Current is a broad, sluggish eastern boundary current
traveling offshore of western N orth America towards the equator. It is fed by
West Wind Drift from the Pacific Gyre (Emery, 1960; Hickey, 1979; Sancetta et
al, 1992). The California C urrent reaches its maximum velocity
approximately 300 km offshore. Along the Southern California coast, it tends
to bend offshore at Point Conception and then back inshore in the southern
borderland region (Fig. 3). As a result, it does not directly affect the nearshore
basins. Circulation within the borderland is dominated by the northward-
flowing Southern California C ounter Current, which is supposed to be a large
I ;
scale eddy in the California C urrent system (Fig. 3). There is a third current,
! the California U ndercurrent that moves deeper in the w ater colum n. The
| undercurrent flows beneath the California Current system along the entire
f west coast. In the Borderland region the Undercurrent is concentrated on the
| inshore slope and is thus spatially separated from the California Current
I (Hickey, 1979). The Undercurrent, which is deep and fast, has variable water
| properties. It’ s source waters are south of the region, and at tim es, equatorial.
I It probably has m ultiple cores in the borderland because of the variable
j topography (Fig. 4).
I The waters in the borderland are a combination of tw o w ater masses,
f the Pacific Subarctic and the Pacific Equatorial waters. Pacific subarctic, carried
by the California C urrent from the north, is characterized by low
temperatures, low salinity, high oxygen content, and high nutrient content.
In contrast, the Pacific equatorial w ater has a high tem perature, high salinity,
low oxygen and high nutrient signature. This water mass is delivered by the
U ndercurrent.
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legend:
02 Animal B. 05 San. Clemente B .
03 Descanso Plain 08 San Nicolas B .
04 East Cortes B. 09 Tanner B.
120° 119° 118° 117° 116°
Figure 3. Surface circulation in the borderland. The broad, sluggish
C a lifo rn ia Current passes offshore over Tanner Basin and turns inward
towards Baja Califoria. The California Current is traveling northwards
adjacent to the shoreline (from Hickey, 1979).
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legend:
02 Animal B. 05 San Clemente B.
03 Descanso Plain 08 San Nicolas B.
04 East Cortes B. 09 Tanner B .
120° 119° 118° 117° 116°
Figure 4. Bottom water renewal occurs from the south in most borderland
basins. The direction o f bottom water flow in the region is complex due to
the bathymetry (from Emery, 1960).
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Bottom w ater renew al in the basins is achieved by either vertical
m ixing or over-sill flow (Hickey, 1993). The water at the surface over the
basins is less dense than the incoming water and so the new water sinks and
displaces the existing bottom water. Bottom water renewal is thought to
occur from the south and thus the waters carry an Equatorial Pacific water
signal. This is true for all the basins in the Borderlands except Tanner and
Santa Barbara (Atkinson, 1986). Tanner and Santa Barbara are renewed from
the north with Pacific Subarctic water.
Upon displacem ent of the bottom water the new w ater spreads laterally
and propagates cydonically around the basin perimeter. Renewal occurs less
j. than one time per year and is a rapid process, about one m onth in length
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I (Berelson, 1991). M easurem ents of these renewal events have shown
I
synchronous flushing in m ore than one basin which m ay indicate a larger
scale surface/upper w ater column process in the region (Berelson, 1991;
!
Hickey, 1993). Flushing of the basins has biological and chemical
implications. M acrofaunal distributions, water chemistry and nutrient
contents are all affected by the renewal. The flow of water into the basins may
| also impact the bottom of the basin, causing erosional features near the sides
| w here the cyclonic pattern is strongest (Berelson, 1991; Douglas, 1981).
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I Previous Work
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: The nearshore basins have been extensively studied because of the
high resolution record they preserve as a result of high sedim entation rates
and low bottom water oxygen content which moderates or preserves
bioturbation (Kennett et al., 1995; Christienson et al., 1994). Past work in the
outer basins has tended to concentrate on one or a few basins and covers a
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I 0
range of topics not necessarily consistent between all basins. The work that
has been done in the outer borderland basins can be used to evaluate changes
in the California Current’ s more recent activity. The following chapter will
review previous studies in both the outer and inner borderlands as they
pertain to the sedimentology, stratigraphy and general paleoceanographic
setting of the region.
There are seven fine-grained facies types identified by Hein (1985) from
sedim ent cores from three borderland basins. The basic types are: 1.
Disorganized beds (predominantly bioturbated), 2. deformed beds, 3. beds w ith
fluid escape features. 4. graded beds w ith Bouma sequences (turbidites), 5.
rippled beds, 6. horizontally laminated beds, and 7. ungraded ripple cross-
■ bedding (Hein, 1985). Of the seven, facies 1 ,3 ,4 and 7, originally described by
I Hiilsem ann and Emery, (1961) are comm on in the CCB. Turbidite deposits,
} found prim arily and most extensively in the inner basins such as Santa
I Monica (Gorsline, 1996; Christienson e t al., 1994), are present in the outer
| borderland, in basins such as Tanner and San Clemente (Hein, 1985; N ardin,
f 1979; Gorsline and Teng, 1989). Evidence of such flows is seen in X-
radiography as dense packages of material in the cores. They are identified as
fine-grained turbidites which are thought to be the result of either slope
failure along the basin edges, (Nardin, 1979) or remobilization of stored bank
or shelf m aterials during low-sea level stands.
! D eposition of any fine-grained detritus w hich remains in suspension,
as well as biogenic materials, dominates the offshore basins (Douglas, 1981).
Fine-grained detritus from the California C urrent is a major source of
terrigenous materials for the outer basins (Fleischer, 1970) since it is otherwise
blocked by the landward sills.
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11
Productivity and the resulting contribution of biogenic materials, is
driven by the circulation within the borderland and upwelling regimes
within and north of the CCB (Hickey, 1993). As a result, productivity in the
surface w ater plays a major role in the outer basin sedimentation, as well as
in determ ining the relative inputs of carbon and carbonate. The carbonate
cycles in the borderland are o u t of phase w ith the open Pacific, and seemingly
m ore complicated (Gardner et aL, 1997; Karlin et al., 1992; Gorsline and
Prensky, 1975; Prensky, 1973). Typical Pacific carbonate records along the
California Current, both north of P t Conception and in equatorial regions,
reveal high carbonate mass accumulation rates (MAR) during cold periods
and low during warm times as a result of the shallow and dynamic CCD in
the Pacific Ocean (Fig. 5) (Karlin et al., 1992). It is a record of dissolution rather
than productivity (Karlin et al., 1992; Lyle et al., 1992,1988).
Carbonate records along the California C urrent in Southern California
i
! show opposite records, with lower accumulation rates during cold periods as
a result of dilution by terrigenous input due to the exposure of the
continental shelf in the region (Gardner et al., 1997; G ardner and Dartnell,
| 1995; Prensky, 1973). High mass-accumulation rates, associated with
f continental m argins are also linked to the high carbon preservation in the
j sedim ents (Gardner et al., 1997; Lyle et al., 1992). Variations in preservation
t due to oxygenation differences (Cai and Reimers, 1995) as well as in
j
accumulation rates, location and input (Berelson et al., 1996) make regional
paleoproductivity a difficult param eter to estim ate in the borderland region.
Clay mineralogy has been studied as a means of tracing past
atm ospheric and oceanic current paths (Weaver, 1989; Lange, 1982; Stein,
1995) since clays form in characteristic climate zones, based on chemical
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1 2
50 100
100
200
300 2944m
49.4° N
% CaCq»
50 100
3230m
47° N
50 100 0 0 100
4420m
15° N
Figure 5. Deep Pacific Ocean CaCOj records show ing a record dominated
by dissolution with low carbonate during interglacial times. The CCB
record is opposite of this pattern (from Karlin et al 1992).
CHLORITE ILLITE
Figure 6. Spatial distribution of chlorite, (left) an d illite in the Pacific
Ocean. Illite dominates m ost of the Pacific, particulary in margin
regions. Chlorite is most im portant in polar regions (Weaver, 1989).
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I 3
weathering rates, and can be a proxy for precipitation regimes (Fig. 6). The
California C urrent, coming from it's arctic origins, carries an assemblage rich
in chlorite dow n from the Gulf of Alaska. The chlorite/illite ratio diminishes
rapidly as the current moves south and is diluted by illite and
m ontmorillonite from local sources (Hayes et al., 1973). Illite and smectite
tend to vary inversely where smectite signals low terrigenous input (Weaver,
1989).
The fine fraction makes up about 90% of the sedim ents in the
borderland an d the clay fraction, <2pm, about 50 % of the fines (Fleischer,
1970, 1972). M ontmorillonite (smectite), illite, chlorite, quartz and feldspar
are the m ain m inerals present in the <2pm fraction in the borderland
\ (Prensky, 1973, Fleischer, 1972, and Stein, 1995) as w ell as in the entire Pacific
!
Ocean. Reischer, (1972), described the clay m ineralogy of the upper sediments
| in Santa Barbara basin in order to determine the sources of the different
I
sediment types in the near-shore basin. He was able to distinguish between
the different facies in the basin based on the m ineralogy as well as identify the
5 Santa Clara River as the primary source of the Santa Barbara flood layers
i
j (Reischer, 1972). Transgressions and regressions of the shoreline, as they are
associated w ith changing sea-levels, are responsible for the variations in
smectite and illite contributions since illite tends to reflect high input regimes
while smectite form ation occurs in areas of little detrital influx (Weaver,
1989). Stein, (1995), extended the record from Santa Barbara basin back to
160,000 years from the ODP site 893 core and noted little significant variation
in the different mineralogic contributions. Other Pacific studies have
dem onstrated m ajor changes in the North Pacific sedim ents through time
(Hayes et al., 1973).
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I 4
Up welling, driven by coast-parallel winds heading towards the equator,
is the source of the cold, nutrient-rich waters of the coastal area. Along the
west coast of N orth America, upwelling is variable as well as restricted to a
narrow band about 10-25 km wide along the shore (Huyer, 1983). There is
strong coastal upw elling centered just south of the Channel Islands off Point
Conception in Southern California (Huyer, 1983; Douglas, 1981). This
upwelling region is the m ain source of nutrients for the CCB. The upw elled
water has a Pacific Subarctic signature of low tem perature and salinity, high
oxygen and high nutrient content (Hickey, 1979). There is also m inor
upwelling occurring along the seaward side of the islands but the
contribution of nutrients is minimal relative to the am ount delivered by the
upwelling in the Santa Barbara Channel area (Douglas, 1981).
Variations in foraminiferal assemblages have been used for
monitoring global climate cycles and the resulting m igration of isotherms
(Kohfield et al., 1996; Kennett and Venz, 1995; Prensky, 1973). Cold California
Current circulation intensified during the last glacial maxim um, (CLIMAP
Project Members, 1988) shifting isotherms to the south. This shift is
associated w ith an increase in number of sinistrally-coiled Neoglobigerina
pachyderma (N. pachyderma (s).), a polar to sub-polar species, as well as other
members of present sub-polar Pacific waters (Kennett and Venz, 1995). The
present day assemblage in the region is predom inantly m ade up of dextrally
coiling, Neoglobigerina pachyderma (Neoglobigerina pachyderma (d)).
Globigerina bulliodes and Globigerina quinqueloba (Kennett and Venz, 1995).
The change from N. pachyderma (d). to N. pachyderma (s) is thought to occur
at the 10?C isotherm. Kennett and Venz’ s (1995) detailed record from Santa
Barbara Basin shows a sharp shift from -90% dextrally coiled dow n to 10%
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around 16,000 year BP. The sinistrally-coiled m orphotype is most abundant
back through 160 ky except during stage 5e, the last interglacial since the
present (Kennett and Venz, 1995). The assemblage during the rem ainder of
stage 5, is oddly sub-polar rather than warm, perhaps a result of selective
dissolution of the thinner, tropical tests, more intense upw elling, or m erely
reflecting early intrusion of cold waters into the region.
This study will concentrate on outer and central borderland basins,
nam ely Animal, East Cortez, Descanso Plain, San Nicolas, and San Clemente.
Due to their proximity to the California Current, these basins should act as
slightly isolated recorders of the current's activity w ithout the noise of the
detritus being delivered by the local streams.
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I
i
l 6
M ethods
Coring and Curating
The cores used in this study w ere taken as part of the site survey cruise
for ODP Leg 167, aboard the R.V. M. Ewing in 1995 (Table 2). The cores were
taken using a giant piston corer. Each core is approximately 500-700 cm long.
The cores w ere split aboard ship and 10 cm pore water samples w ere removed
at regular intervals. Color reflectance, m agnetic susceptibility, GRAPE, and
w et bulk density were measured. The cores were described aboard ship.
Features such as initial color, color changes, odor, and any visible primary
structures such as turbidite deposits w ere noted. After description, cores were
placed in core liners, labeled and sealed for transport; half to Oregon State
University and half to the University of Southern California. A t USC, the
cores are stored in a walk-in refrigerator.
w ater length of
02PC Animal 31° 25.92’ 117° 35.09' 2042 720
03PC Descanso Plain 32° 04.39’ 117° 21.85' 1299 400
04PC East Cortes 32° 17.01’ 118° 23.73' 1759 810
05PC San Clemente 32° 28.55’ 118° 07.49' 1818 530
08PC San Nicolas 32° 48.05’ 118° 48.0O ' 1442 490
09FC Tanner 32° 51.51’ 119° 57.48’ 1194 650
Table 2. Summary of core locations and lengths (Lyle et al 1995)
In o rder to X-ray the cores, 1 cm thick slabs were cut and placed in
labeled 25 cm-long acrylic trays. The rem aining rounded halves of the cores
w ere sealed, labeled and stored as an archive. The slabs were X-rayed in a
Penetrex industrial x-ray unit and then sealed and stored until sam pling
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L 7
began. For this study, 1/3 of the x-rayed slab was cut Iongitidinaly at 1 cm
intervals downcore and placed in labeled bags.
X-radiograph Description
The x-radiographs, which record density differences occurring in the
sedim ent column, were described in detail by both Donn Gorsline and myself.
Different m odes of deposition as well as disturbance of sediments are visible
as differences in x-ray absorption. Dense materials, such as terrigenous and
organic materials, show up as dark features, while less dense material is
lighter. The x-radiographs were scanned for features such as hemipelagic
deposition, bioturbation, laminations, turbidites, sedimentary structures, and
preserved organisms. A n approximated percentage of these features w ithin
each 5 cm interval was noted (Appendix I).
Sam pling
The reconnaissance plan subsam pled every 10 cm downcore for organic
carbon and carbonate analyses. From those detailed stratigraphies and X-
radiographs, samples were selected for coarse fraction composition, grain size,
and clay mineralogy. Each sub-sample was divided into halves that w ere both
dried in a drying oven at about 90°C. One of the sample halves was then
pow dered for carbon and carbonate analyses while the other half was
separated into fine (<63 pm) and coarse fractions (>63 pm) for later grain size
analyses.
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L 8
Organic Carbon and Carbonate
A LECO carbon determinator was used to measure both total carbon
(TC) and calcium carbonate percentages (CaC0 3 ). TC was determined by total
combustion in an induction furnace of the pow dered sam ple in a ceramic
crucible, containing iron filings and tin for added mass to ensure a total bum .
Carbonate was determ ined w ith a gasometric digestion attachm ent to the
LECO. Each sample was repeated twice, or until a replicate within 3% was
achieve using approxim ately 200-300 m g of pow dered m aterial in each run.
For a complete description, see Kolpack and Bell (1968), and Flocks (1993). For
carbonate, each individual sample is run twice to ensure complete digestion
as well as to flush any lurking CO2 out of the system, and the total carbonate
m easured is the sum of the two runs. Each sample is also replicated and the
resulting m ean is used. Total organic carbon (TOC) is finally calculated as a
percentage based on the following formula:
TC- Total Inorganic Carbon= TOC
where Total Inorganic carbon= CaC03/8.33
I Sam thein (1987) developed the following relationship as a reflection of
I surface water productivity:
R= 15.9 (%TOC• MAR)-66 (S(l-%TOC/100))--7l Z-32
where R= paleoproductivity, S= linear sedimentation rate, and Z= water
depth. In calculating R, I used the depth of sill for Z because this is a better
indication of bottom water oxygen content in the basins. It attem pts to
accommodate the effects that productivity, sedimentation rates and bottom
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I 9
w ater oxygenation levels have on TOC preservation and the resulting % TOC
observed. This relationship m ay be too sim ple for the borderland but it’s
m erits w ere tested regardless.
Grain Size Analysis
The dry, grain size sam ple was weighed and resuspended in 5 m l of
acetone and 5 ml of deionized water and left to soak overnight. After
decanting, the sediment was then rinsed w ith deionized water. A dilute
Calgon solution was added to serve as a defloculant. The suspended sam ple
was then passed through a 63pm screen. The >63pm fraction was dried and
w eighed and sand percentage was determined. The remaining suspension of
<63pm w as stored in a labeled tub for later use. The dried coarse fraction was
placed on a gridded tray and 100-200 grains were point counted for a semi-
quantitative compositional analysis. Any foraminifera present were scanned
for dissolution features.
The fine grain size analysis (<63 pm) was done using a 16-channel
C oulter C ounter Tn in the U nited StatesGeological Survey Sediment
Dynamic Laboratory at Menlo Park, CA. Approxim ately 10 ml of the <63 pm
portion of the material in suspension was then split again through a <38 pm
screen. The suspensions w ere used in the Coulter Counter analyses w here
the volum e and num ber of particles is determ ined by relating spherical
equivalence to electrical resistance and thus volume. Small am ounts of the
suspension are placed in an electrically conductive liquid and this m ixture is
then draw n through an orifice to measure the changes in electrical resistivity.
For a m ore complete procedure and explanation, see McCave and Jarvis,
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I
i
20
(1973). Two sizes of aperture tubes were used, the 280 pm and the 70 pm
orifice, in order to recover a complete size-distribution of fine-grained
particles ranging from 1.3 to 200 pm.
C om position
Coarse fraction sam ples were separated du rin g the fine-grain analysis
preparation. The dried and w ashed samples are then saved for a semi-
quantitative analysis. Samples are placed in a sm all point counting tray and a
m inim um of 100 grains per sam ple were counted. In samples too small to
count 100 grains, as m any grains as could be counted were. The categories
counted and a full data table for each sample counted is in Appendix A.
Samples for clay m ineralogy were prepared by first removing the
carbonate and organic m atter to achieve good x-ray diffraction patterns. The
| m ethods for sample preparation were modified from those described by
Reynolds and Moore (1989) and Fleischer (1970).
Carbonate was rem oved by digestion in a p H 5 buffered solution of
sodium acetate and acetic a d d at 85° C. The sam ple w as rinsed after digestion
| w as complete. The rinsed carbonate-free sam ples w ere then placed in 500 ml
| beakers for removal of organic matter using a 30% hydrogen peroxide
f
| solution. The samples w ere again heated to 85° C to accelerate the
procedure. The rem oval of the organics was m ade obvious by the change in
color of the sediments from olive-green to a grayish-tan. The samples w ere
rinsed by centrifugation.
To completely disperse the samples in order to separate the <2gm
fraction, the samples w ere placed in 200 ml of distilled water w ith a "pinch"
of Calgon. The samples w ere then suffitiently agitated so as to completely
t
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2 1
disperse the sam ple. The size separation was done using a centrifuge, where
gravity is accelerated according to the speed of the centrifuge, 700 rpm and the
height of the container. This procedure was performed in Dr. Donal
Manahan's laboratory at USC. The separation was complete in -9 minutes
time. This separation is repeated 3 times to remove all the clays from the
sam ple.
The clays finally have to be concentrated in order to m ake a sample
m ount for the XRD. The samples are spun in a high-speed centrifuge at 6,000
rpm for 15 min. in order to completely flocculate the clays. The resulting clay
pellets are then concentrated in a small am ount of distilled w ater and
redispersed.
The redispersed sample is vacuum filtered using a Millipore® unit
until a completely opaque layer of clay is deposited upon the filter. The filter,
clay-side down, is gently placed on a glass slide and left to d ry about 3 minutes
until the filter can be removed. This m ounting method is the m ost reliable
to obtain an oriented sample, best suited for semi-quantitative work. After a
period of drying at 60° C, this dried m ount is analyzed from 3° to 40° 2 theta in
an XRD after air-drying, and then again after an over night exposure to
ethylene glycol. Peaks were selected according to mineral cards and with
repeated heating tests for absolute confirmation between overlapping peaks
(Warshaw and Roy, 1961). The heating involved baking selected samples at
300,400, and 600° C overnight and then running them to see the collapse of
first the smectite peak, then the kaolinite and finally, after the 600° C baking,
the chlorite. The background of the peaks was then estim ated in order to
quantify peak area and semi-quantitatively compare the relative amounts of
clay minerals (Biscaye, 1965), (Fig. 7).
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Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission.
3000
sm ectite
illite T J
1
8
I
i
chlorite+ kaolinite
feld sp a r
0
5 10 15 20 25
F ig u re 7. A n rep re sen ta tiv e X -ray diffractio n p a tte rn fro m th is stu d y w ith p e a k s lableled. T h e s h a d e d
a re a s in d icate th e p e a k s u se d in th e sem i-q u an titativ e analysis.
to
to
23
Coiling Direction
The relative abundance of N. pachyderma (d) and N. pachyderma (s)
were counted as an additional fix on age. A bout 100 N. pachyderma w ere
counted in each sample. The observed shift in coiling direction has been a
significant one w ith a change from 90% to 10% dextral-coiling in a sam pling
interval. Such a sharp change allows for a relatively small num ber of counts
(100) to provide adequate precision (± 10 %) to confirm the relative age of the
sedim ents.
Age Models
i
The age model for each basin was constructed using a com bination of
*
0
| AMS C-14 dates from planktonic foraminifera analyzed at the Lawrence
| Livermore Laboratory, stratigraphy of both benthic and planktonic
foraminifera (Neum ann, pers comm), and CaC 0 3 stratigraphy (Fig. 8). The
1
combination of the three gave a good estim ate of oxygen isotope stage (OIS)
boundary locations downcore. Coiling direction changes and color
reflectance records (Figs. 9,10) were also used to support the age m odel. The
shift from dextral to sinistral coiling has been observed at "16 ky BP in Santa
| Barbara Basin w ith small variations during stage 3 and then a shift back to
I dextral in 5e (Kennett and Venz, 1995).
|
« Published dates for the boundaries of the isotope stages (M artinson et al
$
s
1987), and the length of core between each estim ated boundary, were used to
i
’ determ ine a linear sedim entation rate (Table 3, Fig. 10). The core bottom s
ranged in age from 80 ky to 190 ky in age depending on the distance of the
basins from sources. Data comparison betw een the basins became possible
once the age m odels were established.
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with permission o f th e copyright owner. Further reproduction prohibited without permission. CD
■ o
- 5
O
Q .
Q .
)IS
length
(ky)
02PC
length in
core (cm)
sed
cate
03PC
length in
con (cm)
sed
rate
04PC
length in
core (cm)
sed
rate
05PC
length in
core (cm)
sed
rate
08PC
length in
core (cm)
sed
rate
09PC
length in
core (cm)
sed
rate
1 13 90 6.92 60 4.62 100 7.69 80 6.15 110 8.46 140 10.77
2 11 80 727 60 5.45 140 12.73 80 7.27 50 455 180 16.36
3 35 160 4 5 7 70 2.00 160 457 130 3.71 175 5,00 170 4.86
4 15 70 4.67 160 10.67 200 13.33 170 11.33 125 8.33 120 8.00
5 46 80 1.74 n o 2.39 220 4.78 70 3.89
6 58 240 4.14
Table 3. Sedimentation rates downcore in each basin. Rates are based on linear extrapolation between fixed dates
downcore. Dates are from Martinson et al (1967).
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EW9504-02PC EW9504-03PC
Animal B. Descanso Plain
10 20 30 40 50 0 10 20 30 40 50 0
I I I I
EW9504-04PC
East Cortes B.
EW9504-05PC
San Clemente B.
EW9504-08PC
San Nicolas B.
10 20 30 40 50
EW9504-09PC
Tanner B„
0 10 20 30 40 50
N
§ 300
1
2 400
.5
a
V
S r
500
° J
600 -
700
800
10 20 30 40 50 (
t
10 20 30 40 50 C
I
C aC 03%
Figure 8. % CaC03 stratigraphy versus depth. The C aC 03 stratigraphy was used in creating the
age model, based on the previously established idea that the basins display a dilution effect during
glacial times. It is not clear in all basins and absent in Animal. Oxygen isotope stages 2 and 4 are
shaded by the gray swaths.
to
U \
2 6
S
t
f
2 *
S . 3
in U
£ s
c z i u
* 1 « C .
9
3
in
I
ui
§«2
i
< s
i -
in
i l i
' i r r ^ v f ' T '
■
i
8
(uo) ipdap
I
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Figure 9. Color reflecten ce reco rd s from sh ip b o ard resu lts (Lyle et al 1995). High r e f le c te n c e
in d ic a te s less color ab so rb e n c e and is th o u g h t t o be related t o the ratio of TOC t o CaCO$.
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a t
S o
( 0
50 -
1 00
150 -
200
0 100 200 300 400 500 600
depth in core (cm)
700 800
02PC Animal
03PC Descanso Plain
04PC East Cories
05PC San Clemente
08PC San Nicolas
0911 'I miner
OIS 02
SEDIMENTATION
03 04 05
RATES
08 09
1 6.92 4.62 7.69 6.15 8.46 10.77
2 7.27 5.45 12.73 7.27 4.55 16.36
3 4.57 2.00 4.57 3.71 5.00 4.86
4 4.67 10.67 13.33 11.33 8.33 8.00
5 1.74 2.39 4.78 3.89
Figure 10. Age model and mass acculation rate (MAR) plots. The age
versus depth curves are similar for all six basins. The MAR versus age
plot shows the different rates of flux in the region. MAR is based on
sedimentation rates and dry bulk density, which is estimated from porosity
data, also pictured.
0.85 0.75
porosity
mm * *
10 15
MAR (mg/cm2 ky)
20 25
N )
~ ~ 4
The age m odels were also used to determ ine mass accumulation rates.
This w as done by estimating a sm ooth porosity curve based on discreet
dow ncore m easurem ents done on the R.V. Ewing. These values were then
used to determ ine the dry bulk density of the sedim ent based on the
follow ing relationship:
sedim ent porosity (density of water)-*- (1-sediment porosity)(density of sediment)
= dry bulk density
in units of m g/cm ^. This is then m ultiplied by a linear sedimentation rate to
get a m ass accum ulation rate, a flux, in units of m g /cm ^ ky (Fig. 10).
»
• Potential Errors
| Standard error for the calcium carbonate analyses is calculated based on
1
30 runs of reagent grade CaCC>3 (Table 4). The sam ples were replicated to
reliability w ithin 3% of one another and the average values were used. There
m aybe an increase in error in samples containing less than 15% CaCC>3. This
\ is based on an increased difficulty in producing sim ilar replicates as well as in
I the overall range of variation due to sm all gas volum es. The standard error
I for these sam ples is likely 1-2% greater than those sam ples with large
F quantities of CaC03-
| Total carbon standards m ay also show this com pounded error due to
i
\ the sm all am ount of carbon, 0.82%, w ithin each standard sample ring. The
error in the actual sediment samples is likely low er due to the high total
carbon content in the basins. Standard error is calculated for both the
standards as w ell as five runs of an East Cortes Basin sample (Table 4) and the
error based on the sediment analyses was used.
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1
29
%CaC03 %TC E. Cortes Basin
reagent rings sam ple
m ean 95 0.71 4.97
standard deviation 3.04 0.07 0.05
standard error 3.19 10.6 1.15
Table 4. Calculated standard error for LECO analyses.
C ounting errors, for both the point counting an d the coiling direction
data, are as standard counting error, (l/n)*1/2. The values are recorded in the
data tables in Appendix H I.
Standard error associated w ith a sem i-quantitative clay mineralogical
analysis can be high. The presence of quartz in the borderland sam ples was
known, from Fleischer, (1970) and Stein (1995) so rather than using an
internal standard, the quartz peak was used to test for the d-spating or 2-theta
variability. As for intensity variations, replicate sam ples were made for
Anim al Basin and the areas were m easured and com pared. The maximum
error w as estimated to be ±8 % of the area. There was sim ply not enough
time to ru n replicate analyses of all clay samples and so the largest error is
supposed to be the m axim um for all samples. To m inim ize variation in area
estim ates, the areas were all m easured by scanning the peaks and tracing the
outline using Canvas. The area of the polygon is then m easured by the
com puter.
Errors in depth below sediment-surface
Piston coring typically causes a loss of high-water-content surface
sedim ents due to "flow away" by the shock wave of the free-falling core and
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30
by possible losses dur to super penetration or sm earing along the core walls.
Depths of core samples from Animal, East Cortes and Tanner basins are
adjusted to account for 20 cm of lost material from the top. This is estim ated
by com paring the CaC03 records from the pilot cores to those from the piston
cores. Depth of samples from Descanso and San Clem ente and San Nicolas
are from core-top and some Holocene record is missing. They could not be
adjusted because their records could not be matched. The MAR for the top
portions of these cores are possibly lower than the true values, depending on
the am ount missing from the core-top.
i
r
t
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3 I
Results and D iscussion
EW9504-02PC- Animal Basin
Initial core descriptions of Animal Basin state that the sedim ent is a
hom ogenous, dark-olive gray, silty-clay containing abundant foraminifera
and nanno fossils. There are two sandy turbidites in the core from 320-345
and 617-633 cm depth. Below 633, betw een 662 and 692 there is also a more
significant silt component.
The Animal Basin core records approxim ately 190 ky. The
sedim entation rate is highest (7.3 cm /ky) during stage 2 and at a m inim um
(1.74 cm /ky) during stage 5, a warm intergladal (Fig. 11, Table 3). These rates
I fit the established concept that sedim ent delivery offshore is increased during
S cold periods, w hen the shelf is exposed due to lower sea-level. The rate
i
appears nearly constant through stages 3 and 4, suggesting that the slight
increase in sea-level associated with the w arm glacial time did not change the
sedim entation regime in the basin. The high rate of -7 c m /k y during the
Holocene is more likely a reflection of the increased productivity regime of
the m odem era (Sancetta et al., 1992; Lyle et al., 1992) w ithout the effects of
‘
terrigenous dilution.
X-radiographs of the entire length of core allow for a detailed look at
the stratigraphy. There are three m ain facies in the Animal Basin core:
i
i bioturbated material, turbidite deposits, and structures that will be called
current partings. The majority of the core is bioturbated w ith a strong
diagenetic overprint evidenced by extensive remineralization of burrow
linings and foraminifera throughout (Plate 1). There are two dense turbidite
deposits, located at 65 and 200 ky BP. Both display the characteristic basal
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66.5 cm
Plate 1. X-radiograph of representative interval of the bioturbated facies from
the Animal Basin core. Large burrows and small bits of pyrite are clearly
visible. At 10X magnification there is no clear structure or preferred
orientation of the material.
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0
50
f 1 0 0
60
150
200
Figure 11. Mass accumulation rate, facies, sand percent, coiling direction, total
forams, w hole/ total forams, biogenic silica, fecal pellets, detritus, mean size,
and clay mineralogy are plotted together against age above for easy comparison
of the Animal Basin record.
u>
u >
K ey :
structures; detritus:
......... n\ic,\
.... % partings
— » quartz
biogenic silica: clay mineralogy:
diatoms wt'K. illite
♦ ■ ■ ■ ■ ■ spicules
----------wt.% smectite
-wt % chi tk.io
EW9504-02PC Animal Basin
(N.Pachyderm)
coiling
direction % forams
hole/total % W«8enic % fecal
forams silica
clay
pellets % detritus % pyrite mean size mineralogy
MAR facies sand
►
1111
11,1,1 I I
(g/cm^ky) % structures weight % ratio% ratio%
pm
34
scour and lam inated upper portion (Plate 2). The third facies is a type of
current structure or ripple cross-bedding (Plate 3) that is present
interm ittently in the core, appearing betw een 50 and 100 ky as well as again at
the base around 190 ky BP (Fig. 11). The appearance of the younger partings
begins during the end of stage 5 and extends through stage 4. Late stage 5 sea-
level fluctuates greatly and during the final stages, is lower than at present
and stage 4 sea-level is nearly 100 m below the present, based on the
SPECMAP isotope curve (Martinson et al., 1987). The rapid fall in sea-level
associated w ith the intergladal-gladal transitions m ay be related to the
appearance of partings in the basin, representing intensified bottom currents
o r general instability in the water column.
f
« The w eight percent sand downcore varies between 0 and 5% (Fig. 11).
The only significant sand contributions occur at the intervals of the turbidite
deposits. The turbidite at the base of stage 4, 60 ky BP, contains 11% sand, and
the larger turbidite at 165 ky BP, during stage 6, contains over 40%.
The m ajor components of the coarse fraction, as determined by point
i
counting, are foraminifera, broken and whole, fecal pellets, quartz and mica,
and in one interval, pyrite (Fig. 11). The two turbidites (Plate 2), at 60 and 165
I
ky BP, have quartz and mica dominating the coarse fraction. The lack of any
biogenic m aterial in the turbidites suggest that they are coming from Eocene
continental deposits exposed during the low stands rather than from the shelf
1
o r slope deposits or is possibly due to a sorting effect where light microfossils
are m ore readily removed.
Foraminifera (Fig. 11) are abundant between 100 and 150 ky and from
50 ky to the present. The w hole/total foram curve parallels the total
foraminfera curve and is probably a result of dissolution rather than artificial
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3 5
hemi-pelagic,
bioturbated material
Laminated interval
very dense, coarse
material
beginning of
bioturbation at base
Plate 2. X-radiograph of representative distal turbidite deposit from
Animal Basin. The turbidite is ~9 cm thick. The top portion of
laminations show where the finest materials begin to settle o u t of
suspension but are not disturbed by organims. The basal portion
has been slightly mixed by bioturbation.
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450.6 c m
Plate 3. X-radiograph of current partings from the San Clemente B. core. The
magnified intervals show alignment of the coarse materials alternating with
disorganized hemipelagic muds.
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37
breakage. Detail is lost in the dissolution/preservation signal provided by the
w hole/total foraminfera ratio because there is not seperation of benthic and
planktonic species. The two have different shell thicknesses and resisitivity
to disolution. Fecal pellets are a major contributor throughout the core with
distinct m inim a coinciding with the turbidite deposits (Fig. 11). Biogenic
silica, including diatom s, sponge spicules, and radiolaria, make up only a
sm all fraction of the coarse fraction (Fig. 11). This is likely due to low
preservation of silica in the borderland as well as a product of sam pling.
Since biogenic silica is fragile and tends to fragment, looking a t only the
coarse fraction may eliminate much of the silica from the sample. Regardless,
there are tw o distinct peaks in the silica a t 49 and 150 ky BP. The peaks occur
during glacial times and could suggest an increase in nutrient availability due
to enhanced upw elling or perhaps im proved preservation due to increased
MAR (G ardner et al., 1997). The younger silica peak coincides w ith a foram
m inim um and the older, 160 ky peak correlates with a m axim um in
foraminifera during stage 6. There is a m ajor pyrite spike of 35% at 115 ky
(Fig. 11). Pyrite remineralization signals reducing conditions in the sediment
where there is enough iron and sulfate to form pyrite. This interval also
corresponds to a m inim um in foram counts b u t high foram breakage. The
pyrite m ineralization and high breakage indicated active dissolution on the
basin floor.
Coiling directions of N. pachyderma, as previously docum ented,
change around 16 ky BP from 90% dextral to ~20% dextral (Fig. 11). This is
due to a shift in surface water isotherms in the region. There is a slight
increase in the percent dextral during stage 5e and a significant increase at the
base of the core during stage 7. The docum ented shift from dom inantly
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38
sinistra! during glacials to dextral during 5e is not completely clear in Animal
Basin. This is likely a result of bioturbation sm earing the signal due to the
low sedimentation rate. The interval containing stage 5e is ~ 4 ky in length or
<7 cm in length. It is likely to be diluted by mixing in super and subadjacent
sediment. A sam ple at 453 cm, approxim ately 5e, contains some tropical and
w arm water species of foraminifera and ~30 % dextral coiling N. pachyderma,
while the superjacent and subjacent sam ples look distinctly like polar fauna
(Robert Douglas, pers comm.). This suggests a relatively strong influx of
w arm er waters during this time. The older shift is m uch stronger and
probably corresponds to interglacial stage 7.
The m ean grain-size downcore is 8.0 pm (Fig. 11). The two major
i peaks in the fine-grain fraction correspond to the two turbidite deposits as
| seen in the initial core descriptions, X-radiographs and coarse fractions. W ith
»
| the coarse-grained turbidite sample-means rem oved, the overall m ean for the
f core is reduced to 6.0 pm (Table 5). There is only one significant increase in
[: size and that is from 6 pm at 42 ky to 8 pm by 86 ky BP. Size falls off again by
f 98 ky. The lowest value, 4.7, occurs during the transition between the Last
f Glacial Maxima and the Holocene. The two other low values, of 5.0 and 5.7
r pm occur during stages 3 and 5, when coarser m aterial is being trapped on the
I flooded or partially flooded shelf.
f Completely hemi-pelagic fine-size fractions show a broad size
distribution, peaking in the fines between 2 and 10 pm with little or no tail
past 40 pm other than the possible tail in the sand fraction, which reflects
foram shells (Fig. 12). Turbidite deposits have distributions with a sharp peak
in the sand fraction 8-80 pm and contain little to no fine materials and have
strongly positive skewness values (Table 5; Fig. 12). The turbidite at 165 ky
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lb
’ 8
*
15
02PC- All
10
5
0
10
pm
100
* 3
*
15
intervals
with partings bioturbated
5
0
100 10 1
15
P 10
5
0
iiri i i
10 100 1
pm
H 3
&
| 2.5
i 2
.2
^ 1 5
I '
n 0.5
■ 1 0
1-0.5
10 100 1
pm
mean pm
Figure 12. A. Weight percent frequency distributions of ail the 16-channel grain size data from Animal Basin.
The distribtuions change according to the method of deposition. B. The distributions from the two major
turbidite deposits of the core. C. Distributions from the intervals containing partings, as seen in X-radiograph,
with one bioturbated distribution for reference. D. Statistical parameters, skewness and standard deviation, w
plotted against the mean show different groupings according to mode of deposition.
v £ >
40
Table 5. Grain size statistics for each o f the six basins. The statistics
calculated are mean, standard deviation, skewness, and kurtosis.
Skewness and standard deviation are param eters used to describe
the sorting of sediment.
EW9504-02PC Animal Basin
age (ky) depth mean (phi) mean (pm) st.deviation (phi) skewness (phi) kurtosis (phi)
2.9 0.5 7.43 5.79 2.13 -0.56 1.58
14.5 80.5 7.73 4.73 2.20 -0.90 1.78
19 1105 750 6.00 2.14 -0.65 1.63
29 170.5 7.45 5.73 2.13 -058 1.59
42 2305 7.35 6.13 2-12 -0.45 1.53
64 3305 6.16 13.98 2.45 0.90 1.40
86 4005 6.92 8.25 2-15 0.15 1.35
98 4205 7.64 5.03 2.17 -0.81 1.72
134 5005 7.41 5.89 2.13 -0.53 1.57
141 5305 7.35 6.12 2.12 -0.46 1.53
165 6305 5.42 23.38 2.97 1.12 1.44
182 7005 7.41 5.90 2.13 -0.53 156
190 7505 7.19 6.87 2.12 -0.23 1.44
mean ((an) = 7.98
EW9504-03PC Descanso Plain
age (ky) depth mean (phi) mean (pm) st.deviation (phi) skewness (phi) kurtosis (phi)
5 15 7.07 7.45 2.12 -0.06 1.39
34 1415 6.82 8.83 2.17 0.28 1.33
62.8 2315 6.60 10.34 2.24 0.55 1.33
70.3 3115 6.74 9.37 2.19 0.38 1.33
82.4 3715 6.77 9.18 2.18 0.35 1.33
115.8 4515 6.84 8.73 2.16 0.26 1.33
mean pm= 8.98
EW9504-04PC East Cortes
age (ky) depth mean (phi) mean (pm) st.deviation (phi) skewness (phi) kurtosis (phi)
3.9 29.5 7.37 6.04 2.12 -0.48 1.54
11.7 685 6.63 10.12 2.23 0.51 1.33
15.4 1085 6.90 8.40 215 0.18 1.34
23.2 2115 6.94 8.16 2.14 0.13 1.35
48.1 3305 7.31 6.30 2.12 -0.40 150
59 3815 6.97 7.97 214 0.08 1.36
69.5 5195 7.17 6.97 212 -0.20 1.43
75.5 6055 7.15 7.03 212 -0.18 1.42
80 6605 6.75 9.30 219 0.37 1.33
81 6705 6.88 8.46 215 0.20 1.34
87.2 742.5 7.01 7.77 213 0.03 1.37
110 835.5 7.00 7.83 2.13 0.04 1.36
meanpm= 7.86
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Table 5 (cont.)
EW9504-05PC San Clemente
age (ky) depth mean (phi) mean (pm) st.deviation (phi) skewness (phi) kurtosis (phi)
8 503 7.60 5.16 2.16 -0.77 1.69
24 160.5 7.31 6.30 2.12 -0.40 130
40 2203 7.44 5.77 2.13 -0.57 1.58
56 2803 7.45 5.71 2.13 -0.59 1.60
63 3403 7.40 5.91 2.13 -0.53 1.56
69 4003 7.47 5.65 2.14 -0.61 1.60
79 480.5 7.40 5.91 2.13 -0.53 136
meanpm= 5.77
EW9504-08PC San Nicolas
age (ky) depth mean (phi) mean (pm) st.deviation (phi) skewness (phi) kurtosis (phi)
0.5 6.45 11.43 2.30 0.69 1.35
3.5 303 7.41 5.88 2.13 -0.54 1.57
7.1 603 7.16 6.99 2.12 -0.19 1.42
15.2 120.5 7.05 735 2.13 -0.03 1.38
32.8 200.5 7.55 5.35 2.15 -0.71 1.66
40 236.5 7.10 7.30 2.12 -0.10 1.40
53 2903 6.87 8 3 7 2.16 0.22 1.34
63 340.5 6.42 11.69 2.31 0.72 1.36
71 381.5 6.94 8.14 2.14 0.12 1.35
81 466.5 7.05 735 2.13 -0.03 1.38
meanpm= 8.10
EW9504-09PC Tanner
age (ky) depth mean (phi) mean (pm) st.deviation (phi) skewness (phi) kurtosis (phi)
3.7 203 6.44 1131 2.30 0.70 1.35
4.6 303 6.78 9.11 2.18 0.34 1.33
9.3 80.5 6.75 9.28 2.19 0.37 1.33
14.2 1403 6.59 10.42 2.24 0.56 1.33
17.9 200.5 6.68 9.77 2.21 0.46 1.33
30.2 3303 6.72 932 2.20 0.41 1.33
34.3 3503 6.88 8.47 2.15 0.20 1.34
48.7 420.5 6.95 8.07 2.14 0.10 1.35
67.8 5403 6.48 11.23 2.28 0.67 1.35
75.3 600.5 634 10.74 2.26 0.60 1.34
83 6903 6.50 11.02 2.27 0.64 1.34
meanpm= 9.92
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i
i
42
looks different from the one at 60 ky. The 64 ky turbidite has a fairly strong
shoulder in the coarse silts and tail in the fines while the 165 ky turbidite has
only a small fraction of silts with no appreciable clay material (Fig. 12B).
This could be a reflection of the difference in the sample location w ith respect
to the basal scour of the turbidite or a change in source material for the
turbidite to one more fine grained. The 64 ky sam ple is likely from quite far
above the base of the deposit in the core, representing late stage
sedim entation, from a residual suspension which reflects the reduction of
speed n the mass gravity flow and the onset of deposition of suspended fines.
The 160 ky sam ple only shows a small amount of day, perhaps m aterial sw ept
up by the sands and caught within the sandy layer, or just a small fraction of
settling m aterial from the upper portion of the flow. The samples from the
rew orked fades appear to show more positively skewed distributions and a
slightly tighter peak, between 4 and 20 pm w ith a small tail in the coarser 40-
60 pm range (Fig. 12C). The tighter distribution indicates that the sediment
has been sorted. The sorting could be the result of a bottom current which is
winnowing aw ay finer materials and thus creating a distinct structure. After
integrating four areas under the distributions a distinct pattern is visible in
each core, the days and fine silts, <10 pm, appear to be lost in the older
regions of the core. This could indicate changes in source materials or in the
carrying capadty of bottom currents within the basin.
Clay m ineral composition in Animal Basin seems to have rem ained
nearly stable over the last 160 ky (Fig. 11). The basin sediments are
dom inantly illite and smectite w ith a small -10% contribution from chlorite
and kaolinite. The chlorite and kaolinite do not appear to vary w ith depth in
the core. Only between 15 and 60 ky, does smectite become less abundant than
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43
illite, and this is by <10%. The increase in illite during a cold period is a
reflection of increased terrigenous input (Weaver, 1989). Animal Basin is the
deepest and m ost distal of all the basins sampled and its overall lack of
variation in clays may be an indication that it reflects a m ore stable,
sedim entation regime than som e of the other more proxim al borderland
basins.
TOC m ass accumulation rates range from 0-19 m g /cm 2 ky (Fig. 13A)
w ith a m inim a.of 0 at 27 ky BP during late stage 3. The highest organic
carbon accumulation occurred imm ediately following the m inim a w ith
I sim ilar high values during the Holocene. Sediment accum ulation rate
\ greatly emphasizes changes in the TOC record.
| C aC 03 accumulation rate varies from 0- 100 m g /cm 2ky and the curve
| parallels the percentage curve (Fig. 13B). The intervals w hich contain no
I carbonate correspond with the turbidite deposits. There is a major shift from
I low to high accumulation rates at about 170 ky BP and C aC 03 flux remains
I high for about 40 ky, into stage 5 and then drops. The values remain low
!
until a sharp jum p between 40 and 30 ky BP. This jump leads into a high but
variable rate of carbonate accumulation. Accumulation reaches a m aximum
at present. CaCC>3 may be a reflection of productivity, dilution, or
i dissolution. In Animal Basin, it is possibly some combination of the three.
I Anim al has a deep sill, ~2000 m, that at times may have been open to Pacific
Deep water, which is highly corrosive. CaCC>3 is very low during much of
stage 5 when sea-level was high enough to bring this w ater mass into the
basin. Sea-level was at least as high as at present and the sill depth has
changed, relative to the water mass due to tectonics. Tectonic uplift is
estim ated to be 130-300 m m /k y and so in the past 100 ky the sill depth has
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44
EW9504-02PC
A. TOC%
0 5 10 15
0 5 10 15 20 25 30
MAR TOC m g /c m 2 ky
0 20
CaC03%
40 60 80 100
0 20 40 60 80 100 120
MAR CaCO, g/cm2 ky
Figure 13. TOC (A) an d CaC03 (B), percentage and flux against age
for Animal Basin.
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I
1
4 5
changed 13-30 m (Ortleib, 1989). This alone is not enough to change the
C aC 03 preservation pattern from one characteristic of the deep Pacific to one
typical of other m argin basins in the borderland. Changes in the depth of
Deep Pacific W ater are more likely resposible for the shift in the Animal
preservation regime. During the recent glacials (Stages 2 &3), CaC 0 3 is
diluted by the incom ing terrigenous m aterials. While calculating fluxes does
m itigate some of the dilution signal, it rem ains strong in Animal. But,
Animal has it’ s highest CaC03 values, both percentage and MAR during stage
6, like much of the Pacific, but unlike the rest of the borderland. It m ay be
acting more like the deep Pacific records, due to a sill depth in the
\ undersaturated region of the water column.
i
• The overall picture of productivity is very similar to TOC. Productivity
(Fig. 13C) fluctuates considerably throughout the core, with high am plitude
changes, but the general trend of peaks during stage 2 and 4, w ith a relative
high in 3 as com pared to 5. There is a distinct trough during the w arm 5 w ith
a peak again after 130 ky BP. If it is reflecting productivity, it fits generally
w ith the idea that surface circulation and w inds are stronger during glacial
times and thus upw elling and productivity are enhanced. But, since TOC
input is generally m ore complex than sim ply falling from the surface waters,
TOC is probably a complex proxy.
i
I
t EW9504-03PC- Descanso Plain
s
The Descanso Plain sediment recovered is a homogenous dark olive
marl. The sedim ent is m ade up of angular silt grains in a clay m atrix w ith
abundant nannofossils, fish fragments, and spicules. There are discrete
intervals which contain abundant carbonate debris. Below 221 cm, there are
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46
intervals of increased silt content. The sediment is m ore variable between
220 and 370 cm and lacks visible foraminifera. The bottom of the core is
hom ogenous w ith foram and nanno fossil debris in a silty clay matrix (Lyle et
al., 1995).
The Descanso Plain core record appears to extend back to about 120 ky
BP. The sedimentation rate has been relatively constant, 4-5 cm /ky, for the
last 24 ky, just as seen in Animal. Stage 3 and 5 appear to have similar
sedim entation rates of ~2 cm /ky. The highest rate, -11 cm /ky, again occurs
during stage 4 (Table 3; Fig. 10).
Three of the four main facies types described in Anim al occur in
Descanso (Fig. 14). The upper half of the core, until 50 ky BP, is dom inated by
j
[ bioturbated sediment w ith weak, intermittent rew orking evidenced by
| partings. Prior to that, back to 120 ky BP, partings dom inate the X-rays. There
| is a small turbidite at 120. The partings begin sporadically in stage four but
I appear to be almost constant during 5, as though reworking by bottom
| currents was continuous for nearly 40 ky.
» W eight percent sand down-core has three major peaks, horn 18-25 ky,
| 63-75 ky, and finally at about 90 ky (Fig. 14). The peaks do not correspond to
e
| distal turbidites in the X-rays b u t are more likely reflecting input onto the
| slope during low stand times. Descanso is the most landw ard site and the
| core is not from a basin but rather a starved basin floor (D. Gorsline, pers.
comm). The final interval of high sand as well as the turbidite near the base
occur during stage 5. Both intervals are perhaps occurring during one of the
rapid climate changes during stage 5 (Dansgaard et al., 1993).
Fecal pellets and foraminifera remain stable throughout the core
with the exception of -70 and 120 ky (Fig. 14) for the foraminifera and 120 ky
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Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission.
EW9504-03PC Descanso Plain
MAR facies sand
3
(N.Pucliyilfniin)
coiling whole/total % biogenic % fecal clay
direction %forams forams silica pellets % detritus % pyrite mean size mineralogy
20
40
§ 6 0
I
80
100
120
140
-
1 1 1 1 1 1 1 1 1 ‘ 1 1 1 1 1 1 1 J_L ■ 1 I 1 I I 1 I J I ,LI I I I I I
2 6 10 14 0 40 80 0 20 40 0 40 80 0 40 80 0 40 80 0 8 0 40 80 0 20 40 0 8 0 10 20 0 40 80
(g/cm2ky) % weight % ratio% % ratio% % % % % pm weight %
Key:
structures: detritus;
■ % turbiditcs
-% partings
biogenic silica;
••••• -diatoms
■ spicules
m ic a
• 4 quartz
clay mineralogy:
_ _ w l% illite
wt.% smectite
-wl'iuchltkao
Figure 14. Multiple parameters plotted versus age showing relative
contribution changes through time in Descanso Plain.
-j
48
for pellets (Fig. 14). These lows are a result of dilution from land. The
foraminifera are fragm ented, either as a result of dissolution or mechanical
breakage (Fig. 14). Q uartz and mica appear to make up a greater portion of the
sand fraction during the times of high sand input (Fig. 14). There is a huge
quartz peak corresponding w ith the turbidite, w hich is likely coming from the
shelf. There is an increase in pyrite during times of high terrigenous input
suggesting that the rapid burial creates reducing conditions that allow for the
authigenic growth of pyrite (Fig. 14). Biogenic silica fragments appear to be
coincident with the intervals of high terrigenous input; a result of
preservation by burial due to the higher observed MAR during stages 2, 4, and
r the Holocene, and by the turbidite (Fig. 14).
\ Coiling directions of N. pachyderma in Descanso indicate that the 10° C
E
| isotherm passed below the area before 20 ky BP and remained south of it
| throughout the length of the core until the bottom -m ost sample (Fig. 14).
if
i This core appears to reach stage 5e at 600 cm depth, where coiling ratios
" change from 20% dextral to nearly 60%.
It is very clear that all but one of the fine fraction grain size sam ples
cam e from a w innow ed interval of the core (Fig. 15). The bioturbated interval
at about 500 yrs. BP has a broad distribution w ith greater contributions in the
I fine fraction than those from winnowed intervals. The winnowed sam ples
| are very tightly peaked a t about 15 (im. There is a separation of the tw o types
i __
in the m ean versus skewness and standard deviation plot as well. The
w innow ed samples are som ew hat better sorted and more positively skewed,
w ith the most skewed sam ple at 63 ky, being the interval with the strongest
apparent structures in the X-radiographs.
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Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission.
II y HB j m IIM > . « 1 H « WW ^fW — H * n- v T ^ n HW *1 . • - v ; — **•«*
03PC-A11
intervals
with partings
0.5 Ky
34 Ky
63 K y
70 Ky
8 2 Ky
116 ky
bioturbated
10
p m
2.5
1
| 2
o st deviation
1
• ->
_□ skewness
s
i 15
S
- -
§ 1
• J 3
_ -
< u 0.5
T3
-
J ^ | current partings
£ o
-
(□ ] bioturbated
$-0.5
i
10
pm
100
Figure 15. Grain size frequency distributions and statistical
parameters from Descanso Plain. There were no turbidites
sampled from this core. All of the samples but one were from
reworked intervals, as both the distributions and the grouping
of the statisticalplot suggest.
100
vO
50
Descanso Plain is the more nearshore basin of the set of cores and it
appears to record local changes in mineralogy (Fig. 14). Chlorite and kaolinite
abundance increases downcore, while sm ectite and illite vary conversely and
fluctuate more rapidly. The increase in kaolinite +chlorite occurs during low
sea-levels when the shelf is exposed. Metamorphic basem ent rocks of Baja
California are likely a source for the tertiary shelf deposits which were then
remobilized during lowered sea-levels an d deposited on Descanso Plain
(Doyle and Gorsline, 1977).
Both percentage and MAR curves o f CaC0 3 and TOC parallel one
another (Fig. 16) throughout most of the core. TOC flux increases by greater
than 20 m g/cm ^ky into stage 2 and then shifts to a low, stable period nearly 50
ky in length. There is a second increase, at 59 ky through stage 4.
CaC 0 3 flux is highest during these same intervals despite the dilution signal
in the carbonate percentage curve during stage 4. The paleoproductivity
estim ate suggests that productivity in the area has been relatively high for the
last 80 ky (Fig. 16C). It was highest during stage 4 and at a minim a during the
Holocene climatic optim a, when w ind-driven upwelling was slowed.
EW904-04PC - East Cortes
The East Cortes core contains hom ogenous dark olive marl. The upper
300 cm is made up of foraminifera and nannos in a clay matrix. Below 330 cm
there is an increase in mica content which persists through to about 500 cm
depth.
The core from East Cortes Basin has the second longest record from the
suite of cores, spanning at least 128 ky through stage 5 (Fig. 10, Table 3). The
sedimentation rate in East Cortes is highest during stages 2 and 4 at -13
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
EW9504-03PC
TOC%
5 10 15
B - CaC03%
20 20 40 60 80
C- productivity
200 400 600 800
<
100
120
100 150 50 50 10 30
MAR TOC g/cm 2 ky MAR CaCO , mg/cm ky
Figure 16. TOC (A), CaC0 3(B), and paleoproductivity (C), downcore from Descanso
Plain. The record is the most stable of the six studied. (B)
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
52
cm /ky. Sedimentation during 5 and 3 occured at a rate of ~5 cm /ky. It is
slightly higher during the Holocene, reaching 7.7 cm /ky.
X-radiography in East Cortes shows bioturbated material dom inating
the top half of the core with intermittent, m oderate reworking (Fig. 17). Prior
to 40 ky BP, evidence of reworking dominates. There are also turbidite
deposits at 75 ky. The reworking is slightly dim inished in early stage 5.
C urrent partings suggest an increase in bottom current activity, likely a result
of changing circulation conditions in the borderland. The shift does not
appear to be solely related to sea-level changes. It suggests a shift of
circulation regimes since 40 ky BP into the present, where bottom circulation
has slowed.
The sand fraction makes up only about 2% of the material throughout
the core (Fig. 17). Foraminifera and fecal pellets dom inate the coarse fraction
and are inversely related downcore. High incidence in total foraminifera
again coincide w ith high w hole/total foram ratios, suggesting that there is
again a dissolution signal in the basin along w ith a dilution by terrigenous
materials. The turbidite at 75 ky, containing 10% sand, is likely derived from
a nearby sill. The m aterial in this interval is prim arily made up of quartz and
[ pyrite grains. The finer, lighter materials, such as m ica and foram tests were
| probably carried along or remained in suspension to be deposited in a higher
F
| horizon. There is a mica peak, which does not correspond to a quartz peak, at
f
; 50 ky BP, as well as a later quartz peak, w ith no related mica, at 23 ky. The
mica peak corresponds to a high in biogenic silica (Fig. 17) and fecal pellets
(Fig. 17) and m oderate foram counts (Fig. 18). Since there is relatively little
accompanying quartz being delivered at this time, it m ay be either a change in
the source of the coarse fraction or possibly a result of sorting, either in the
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission.
EW9504-04PC East Cortes Basin
MAR facies
(N.I’fldiyiferow)
coiling whole/total % biogenic % fecal clay
sand direction %forams forams silica pellets % detritus % pyrite mean size mineralogy
9
to o
120
140
4 8 12 0 40 80 0 20 40 0 40 80 0 40 80 0 40 80 0 8 16 0 40 80 0 20 40 0 8
0 10 20 0 40 80
(g/cm^ky) % structures weight % ratio% % ratio% % % % pm weight %
Key:
structures: detritus:
— ..... % turbidite* roic*
■ ■ % partings
^ quartz
biogenic silica: clay mineralogy:
........ diatoms w t'V .. illite
» spicules
---------wt.7o smectite
-wllnchltkrin
Figure 17. Multiple parameter plot for the East Cortes Basin showing
the relative contribution changes through tim e.
u>
54
basin or the surface waters, if a current carried the platy mica along after
losing the quartz.
The grain size distributions in East Cortes are slightly different from
the other basins (Fig. 18). They show a multi-modal, prim arily bi-modal,
distribution, indicating there are m ultiple populations being mixed. The
m ost pronounced two have average grain sizes of -6 fim and 20 fim. The 6
pm population could be an eolian contribution or perhaps some type of
nanno-fossil. The most positively skewed sample with a broad but coarse
distribution comes from a bioturbated region of the core that, in X-radiograph,
is considerably denser than the surrounding material. It is likely a fine
grained turbidite that has been subsequently chewed up by large organisms in
the sediment. There is no distinct grouping of the facies w hen com paring
f
i m ean and skewness. This m ay be a result of the mixing populations, or that
| there is some sort of continuum of sorting, that is increasing down-core.
| Mineralogy in East Cortes is out of phase with most of the borderland,
j It shows an increase in illite content into the present w ith a reduced
| abundance during stages 2 and 3 (Fig. 17). The sample at the 3 /4 boundary
I show s converging value of smectite and illite suggesting a tapering of input
! from land or perhaps exposure of localized volcanics which m ay lead to
( smectite formation (Doyle and Gorsline, 1977). Chlorite and kaolinite is most
\
i abundant at the stages 2 /3 and 4 /5 boundary, when sea-levels are supposed to
r
i
be rapidly hilling. These highs m ay reflect a sudden increase in California
C urrent contributions, w hich eventually stabilizes, or perhaps an influx of
chlorite from the local m etam orphic sources. The sudden exposure of islands
and banks as well as the shelf off Baja California may cause the nearly
instantaneous rem obilization of w eathered metamorphic material.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission.
12
04PC- All
10
i:
4
2
0
'3
*
1 0
10
fim
100
fim
12
7 (1 k\‘
80 ky
ky intervals with
partings y
■ lM ky 6.5 ky
15.4 ky
—• — V I ky
bioturbated J
10
8
6
4
2
0
100
< / >
8
i
i
§
B
a >
'O
■ a
1
in
IS
2
0
_□
---------------------------1 ---------------
.standard dev
skewness •
-
1.5
- -
1
- -
0.5 □
.
0
□
B
0.5
□
---------------------B -»---------------
10
mean
100
F ig u r e 18. G r a in s iz e d is t r ib u t io n s a n d s ta tis tic a l
p a r a m e te r s f r o m E a s t C o r te s B a s in . T h e e f f e c t o f th e
r e w o r k i n g v a r ie s s o t h a t th e r e is a le s s d i s t i n c t g r o u p i n g
in t h e s ta tis tic s a n d m o r e o f a c o n ti n u u m .
U l
U \
(
I
56
The TOC, in percent and flux, nearly parallel one another dow n core
(Fig. 19A). During stages 4 and 2, TOC accumulation is significantly enhanced
by high sedimentation rates. The flux is low during stage 3, as demonstrated
by the convergence of the two curves. The CaC 0 3 curves alm ost converge
during stage 3 as well (Fig. 19B). During stages 2 and 4, CaC0 3 MAR is three
times greater than accumulation during stage 3. The CaC03 curves diverge
far more than TOC. This suggests that while carbonate percentages are
regularly diluted during cold times, either high productivity or terrigenous
input is contributing organic carbon to the basin. Productivity estim ates (Fig.
19C) again suggest an increase during cold periods with a more significant low
in stage 5 than during 3, a relatively cool "warm".
r
EW9504-05PC- San Clemente
Sediment in San Clemente is a hom ogenous dark olive gray silty clay
containing foraminifera and abundant nannofossils. There are three distinct
color cycles between 400 and 530 cm depth w here the sediment changes from
black to dark olive gray. The bottom of the core, below 530 cm, contains flow-
in m aterial (Lyle et al., 1995).
c
| The piston core from San Clemente extends back through stage 4 or
approxim ately 80 ky. The age m odel reveals a sharp decrease in
sedim entation rate at 59 ky, from 11 to under 4 cm /ky during the transition
i
from stage 4 into stage 3 (Table 3; Fig. 10). Sedimentation increased to 7cm /ky
into stage 2 and remains nearly the sam e until the present.
There are again three major facies types in San Clemente (Fig. 20). The
turbidites are in the upper portion of the core a t about 6,10, and 13 ky BP. The
occurrence of the partings is nearly synchronous with those in Descanso and
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
t
5 7
EW9504-04PC
A .
T O C %
5 10 15
B.
0
C a C 0 3%
40 80
C- productivity
350 550
o o
iod
ioo o 60 20
200 400
MAR TOC m g /cm 2 ky MAR C aC 03 m g /cm 2 ky
Figure 19. TOC, CaC03, and paleoproductivity versus age for East Cortes Basin.
There are clear glacial / interglacial changes in biogenic input.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
58
East Cortes extending from the base of the core to about 40 ky BP where they
begin to disappear.
The weight percent o f sand in San Clemente is the lowest of all the
basins m aking up only 0-2% of the core, w ith the maxim um occurring at 40
ky (Fig. 20). Coarse fraction components, foraminifera and fecal pellets
dom inate the entire length of the core (Fig. 20). Fecal pellets are lowest at 45
ky in an interval which corresponds to one of increased detritus,
foraminifera, biogenic silica, and pyrite. It may be that the fecal pellets are
being pyritized. Within the sam e broad pyrite peak, following the m im im a
in pellets, there is a low in foraminifera and a slight increase in the w eight
percent sand. The pyrite is replacing both the foram tests as well as burrow
linings and it seems clear that the slight, 1-2% increase in sand percent reflects
j the replacem ent of relatively light CaC0 3 w ith the heavier FeS2- There is an
I
increase in broken foram inifera relative to the total, which coincides w ith a
peak in quartz and mica. In this instance, the current which is concentrating
the detritus is perhaps responsible for delivering m ore corrosive water to the
basin floor. Biogenic silica is high at same time as quartz and mica, reflecting
} rapid burial and removal from the system before the silica was recycled. But
it is also high during stage 4, one of high MAR, and coincident w ith a
maxima in total foraminifera, perhaps an indication of high productivity as
well as preservation. The coiling directions of N. pachyderma change sharply
around 18 ky from 100% dextral to 20%. The ratio rem ains stable and low
through to the base of the core, suggesting that the bottom is still in stage 4 or
late stage 5 (Fig. 20).
M ean grain size data, (Table 4), shows very little variation (Fig. 20). At
24 ky, the sample is slightly m ore coarse grained as well as more positively
*
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission.
- •- J* V r»
EW9504-05PC San Clemente Basin
(N, Pachyderma)
coiling whole / total % biogenic % fecal clay
MAR facies % sand direction % foram* forams silica pellets % detritus 7u pyrite mean size mineralogy
20
40
u
so
A
60
8 0
1 0 0
1 I I 1 I I 1 1 « 1 » i ■ * i i Ll I I I i i i i i i i i i___ i i
5 15 0 40 80 0 20 40 0 40
g/cm 2ky % % ratio %
Key:
structures;
detritus:
% partings
f quartz
biogenic silica: clay mineralogy:
--•■-•■diatoms
♦ spicules
wt% illite
wt% smectite
V- -wl chltkan
ratio %
% % pm weight %
Figure 20. Multiple parameter plot for the San Clemente Basin showing
the relative contribution changes through tim e.
< -n
V O
60
skewed than the rest of the core samples (Fig. 21). There are also two samples
slightly coarser than the mean which are also more positively skewed, in
older intervals in the core. These samples are coincident with intervals of
high remineralization as seen in the x-rays as well as in the pyrite counts (Fig.
21).
The frequency distribution at 24 ky shows a broad peak from 3-20 (im
(Fig. 21). Surrounding sam ples show slightly tighter distributions w ith peaks
contained prim arily below 10 (im. The distribution at 280 cm shows a small
tail at the coarse end, betw een 60 and 70 (im. The peaks broaden beyond
10|im again at 72 ky. The increase in skewness m ay again be associated w ith
the remineralization of burrow s and foraminifera in this interval, as a
t function of the pore w ater chemistry or it could be an indication of
| hydrodynam ic sorting and concentration of these heavier grains. At 24 ky,
|
! the most positively skew ed distribution shows a broad but slightly double-
I
| hum ped distribution w hich is shifted distinctly to the right when compared
I to the 8 ky, hemi-pelagic sam ple distribution. At 63 ky, the distribution is
I tight w ith a sharp peak at 10 (im and no tail. The distribution at 79 ky is
*
j; broader than at 10 (im w ith a tail in the coarse fraction. The slight variability
I
( - in the distributions is likely a combination of two factors, multiple
t
| populations and current reworking. The strong presence of pyrite is obvious
I
f both from the coarse fractions as well as the X-radiographs. The overall
t
positive shift of the distribution curves could be the result of hydrodynamic
sorting. The irregularity of the distributions, such as the extreme peakedness
of the 63 ky sample, m ay be show ing that rem ineralization in this interval is
specific to some size fraction. Its increased contributions could be an
indication of a geochemical boundary rather than prim arily physical effects.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission.
05PC-AII
t 10 -
8.
I
*
1 0 1 00 1
8.
I)
•3
pm
15
■ « ■ 8.0 ky
— « — 24.0 K y
— 4-— 63.0 k y .
— 7‘ JOKy
“bioturbated
10
intervals
with partings
5
0
2.5
< X D
100
mean pm
F ig u r e 2 1 . G r a in s iz e d is t r ib u t io n s a n d t e x t u r a l p l o t f o r S a n
C le m e n te B a s in . T h e d i s t r ib u t io n s f r o m t h is b a s in v a r y v e r y
little , a l t h o u g h th e fa c ie s c h a n g e s a r e c le a r in X -ra y .
10
pm
10 0
O N
62
But, separating their effects is difficult since pyrite is hydrodynamically
heavier and would be concentrated w hen the current removed the fine
grained m atrix.
TOC MAR in San Clem ente diverges from the percent curve during
stages 2 and 4, but remains nearly parallel otherwise (Fig. 22A). The high
C aC 03 flux occurs during stages 4 and 2, sim ilar to TOC but also in the
Holocene, where TOC flux is not quite so high (Fig. 22B). The
paleoproductivity curve is very irregular b u t does show relatively high
productivity in stage 4 (Fig. 22C). San Clemente lacks the high productivity
signal that shows up in stage 2 in Descanso and East Cortes.
EW9504-08PC- San Nicolas
The core from San Nicolas contains calcareous silty clay which is
olive gray in color. There are carbonate fragments, foraminifera, sponge
spicules and nannofossils as w ell as angular silt grains in a clay matrix. There
are color changes in the lower half of the core beginning at 460 cm. The
change from dark gray-black to olive gray. Below 500 cm, the core material is
disturbed from recovery.
The 537 cm core from San Nicolas Basin extends back about 80 ky (Fig.
10, Table 4). Sedimentation in San Nicolas during the Holocene and stage 4,
is a rapid 8.5 cm /ky. During stages 2 and 3 the rate is lower at about 5 cm /ky.
There is no distinct change at the transition into stage 2, as in other basins, but
rather there is an increase at the base of the Holocene. San Nicolas'
anom alous sedimentation patterns probably indicate a nearly complete
isolation of the basin during the m axim um period of low sea-level, during
glacial periods.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
6 3
E W 9504-05PC
TOC% B. CaC03 % C productivity
200 400 600
eo
100
300 100 200 80 0 40 0
MAR TOC mg/cm 2 ^ MAR CaCO 3 mg/cm2 ky
Figure 22. TOC, CaC0 3 , and paleoproductivity versus age for
San Clemente Basin. The interglacial/gladal scale changes are
not obvious in this record.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
There is 537 cm of undisturbed core in San Nicolas Basin. The X-
radiographs reveal the same three facies types, bioturbated, turbidite deposits,
and rew orked materials found in the other basins (Fig. 23). Evidence of
rem ineralization is considerably less than that seen in the other basins.
Turbidite deposits are smaller but m ore abundant than in other basins. They
are present at 20,59 and then in a pocket from 75-80 ky BP. The turbidites are
occurring at times of lowered sea level and are likely coming off the recently
em erged Channel Island banks. The prim arily bioturbated portion of the
core is limited to only the last 20 ky. Before that, the sediments were
increasingly reworked downcore. The reworking lasts through stage 3 in San
Nicolas Basin. The bathym etry around San Nicolas is such that a sm all drop
in sea-level cuts out a large percentage of the surface water height above the
.r
| sill. Perhaps with this vertical area reduced, water coming over the sill begins
[ t
cycling around the basin edges at a quickened pace, resulting in the current
I partings. The affect of the glacial epoch w ould be greater on this basin than
f t
I East Cortes or San Clemente, w ith their deeper sills.
I The greatest contribution of sand-sized materials in San Nicolas is
if
£ occurring at present, with a low during the Holocene (Fig. 23). The sand
| fraction nearly disappears betw een 60 and 80 ky BP. The interval w ith the
| least sand, is that with the highest quartz counts as well as a sharp peak in
pyrite (Fig. 23). This oldest interval, at 80 ky, contains the least foraminifera
and the lowest ratio of whole to broken foraminifera. Otherwise,
foram inifera make up about 50% of the coarse fraction throughout the length
of the core. Fecal pellets show an inverse relationship with foraminifera, and
consistently make up between 10 and 30% of the sand fraction. Sponge
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Reproduced with permission o f th e copyright owner. Further reproduction prohibited without permission.
EW9504-08PC San Nicolas
0
20
~ 40
£
&
I S
60
80
100
8 12 0 40 80 0 20 40 0 40 80 0 40 80 0 40 80 5 IS 0 40 80 0 20 40 5 15 0 10 20 0 40 80
(m g/cn& y) % % ratio % % ratio % % % % % |im weight%
Figure 23. Multiple parameter plot for the San Nicolas Basin showing
the relative contribution changes through tim e.
0\
C r »
Key:
structures: detritus:
mi«
— + quartz
biogenic silica: clay mineralogy:
diatoms — will, illite
♦ spicules
---------wt.% smectite
-wt'iudiltkao
(N. fw chym m a)
coiling whole/total % biogenic % fecal day
MAR facies ^ % sand direction % foranis forams silica pellets % detritus %pyrite mean size mineralogy
L L U LXXX
\ I
i i i i i i
i i i
X I I I
T I I I
V
xxxx
66
spicules are better preserved in San Nicolas than other basins, or possibly
more abundant. There is a strong biogenic silica peak, in both diatoms and
spicules and radiolarian, at about 52 ky, that does not appear to be related to a
turbidite deposit or a significantly greater sedimentation rate than in other
intervals and that coincides w ith a peak in foraminifera as well as low
dissolution/ fracture of foraminifera (Fig. 23). Perhaps it is a result of a local
productivity peak due to upw elling around the islands. There is a more
gradual coiling direction change in the N. pachyderma assemblage beginning
w ith a shift from 90% to 60% about 18 ky BP (Fig. 23). The shift continues to
about 20% dextral by 30 ky BP. The less dramatic shift at 18 ky is likely an
artifact of bioturbation. The younger, dextral coiling assemblage is probably
diluting the older, sinestral-dom inated horizon. The core does not appear to
reach back into stage 5, w here more dextral coiling individuals occur.
There is a slight increase in m ean grain-size in San Nicolas, from
-5.9pm to -8 pm, through tim e (Fig. 23) The trend is interrupted by two
peaks up to 11pm corresponding to sam pled turbidites in the core.
Distributions of the finer sam ples, betw een 3 and 30 ky, show a broad
distribution which spans from 2- 20 pm (Fig. 24). The increase in mean size
is accompanied by increasingly positive values of skewness as well as tight
frequency distribution peaks betw een 7 and 20 pm (Fig. 24). The fine fraction
| distributions as well as the coarse fraction composition counts indicate a
£
coarsening downcore. The coarsening m ay be from current rew orking rather
or a change in input. An overall increase in input of terrigenous material
due to a sea-level fall w ould contribute a more positively skew ed distribution
of materials as the basin is approached by the shoreline as sea level falls. The
breadth of the distribution should rem ain similar. The observed tightening
Reproduced with permission o f the copyright owner. Further reproduction prohibited without permission.
io n o f th e copyright owner. Further reproduction prohibited without permission.
1 5
5
1 0
u
I
5
*
0
1 0 100 1
Jim
I
3
*
|im
15
intervals
with partings
10
biotuihated
5
0
100 1 10
I
1 5
5
0
100
pm
fa-2 5
( / ) o
I
I 1.5
1 1
§ 0 5
•s
s o
T3
T3
S-0.5
1
w
“i------ 1 — i — i— r r r 1 1 "
Q D < & 8 >
i ------------->— t ' t i r * r i ,
O stdev
□ skew
I
| | j | turbidites
current partings
m
bioturbated
■ ■ *__i 1 . 1 1 1 _____ ■ ■ ■ ■ ■ ■ ■ ■
10
mean pm
100
F i g u r e 24. G r a in s iz e d i s t r i b u t i o n s a n d s ta tis tic a l p a r a m e t e r s f ro m S a n N ic o la s B a s in . T h e d is tin c t
d i s t r ib u t io n s a n d s ta tis tic a l g r o u p s s h o w th e v a r i a ti o n in th e s e d im e n ta r y fa c ie s in t h e b a s in .
O N
^4
68
and reduction of fines (Fig. 24) suggests reworking. Hemi-pelagic material
dom inates between 45 ky to the present, w ith a mean of approxim ately 6.5
jim. The distributions have a small tail in the coarse fraction w hich is m ade
up of foraminifera and fecal pellets. A distinctly high m ean size of 11.5 J i m
occurs at the core top and accompanies a distribution which peaks between 10
and 60 pm with a strong peak in the sand. This is likely indicating the
presence of a turbidite which is barely noticeable in the X-radiographs.
Another turbidite downcore, at 63 ky, has a peak between 20 and 70 pm w ith a
shoulder in the sands. This is likely a fine-grained turbidite from the shelf or
possibly a sample spanning a turbidite as well as some hemi-pelagic material.
The statistical parameters of m ean and skewness show three separate groups
which coincide with the three distributions and facies types m entioned above.
They appear to fall on a line, w here turbidites and bioturbated m aterials are
the end-members and the rew orked materials are a mixture of a well-sorted
and a thoroughly mixed sedim ent distribution (Fig. 24).
Despite a lack of clay mineralogy data in San Nicolas Basin, there
appears to be an overall increase in chlorite between 20 and 40 ky which
persists through to the base (Fig. 23). This overall increase as well a generally
higher abundance than seen in other basins (Fig. 25), m ay be reflecting input
from nearby metamorphic island sources or perhaps a decrease in overall
smectite and illite contributions. San Nicolas Basin is sheltered by the
Channel Islands and during times of low sea-level, is nearly cut-off. This
"barrier" m ay impede the input of materials from the Santa Clara and
Ventura Rivers, the m ain contributor of illite, into the waters over San
Nicolas since currents flow north through Santa Barbara Channel (Fig. 3) in
this region.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
♦ EW9504- 02PC Animal B.
g EW9504-03PC Descanso Plain
■ EW9504-04PC East Cortes B.
♦ EW9504-05PC San Clemente B.
□ EW9504- 08PC San Nicolas B.
♦ EW9504-09PC Tanner B.
chlorite and kaolinite
0
0 smectite .6 .2 1 .4 .8
Figure 25. Ternary diagram of clay minerals, illite, chlorite+kaolinite,
and smectite. Only San Nicolas and Tanner Basins show consistantly
different mineralogies, with high chlorite+kaolinite relative to the
other basins.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
70
The TOC record in San Nicolas Basin shows little systematic variation
(Fig. 26A). The percentage and flux records parallel one another quite closely.
There is a decrease in TOC from the present to 10 ky BP. The record remains
stable through stages 2 and 3. TOC is high and variable from early 3 back until
the end of the core. The CaC03 record, similar in pattern as the TOC record,
shows a decrease an d stabilization of CaC 0 3 between 65 and 20 ky (Fig. 26B).
During the Holocene major shifts occur from high to low occur. There are
not any systematic changes in pdeoproductivity (Fig. 26C), b u t rather, a lot of
variation w ith values hovering essentially around 400. This is slightly higher
than what is seen in other basins, and correlates generally w ith w hat would
] be termed their productivity highs, during stages 2 and 4. It is possible that
| w ith a very small, localized upwelling center off the Channel Islands,
I productivity rem ains consistently high in San Nicolas, regardless of changes
in upwelling rates off Pt. Conception, the nutrient supplier for m ost of the
borderland. With its shallower sill and more complex topography, San
I
Nicolas has different bottom water oxygenation values and could be receiving
more m aterials from lateral transport, m aking it a more complex system than
Sam thein's estim ate can accommodate.
EW9504-09PC- Tanner Basin
Tanner Basin sediments are a m ade up of a foram and nannofossil
j marl in a predom inantly clay matrix. The core is interrupted by black to olive
gray color cycles in the lower portion, as are the San Nicolas and San
Clemente basin cores.
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j
EW9504-08PC
7 1
A. -
■ %TOC
B.
% CaCO, q productivity
100 400 800
6 0
iod
50 150 250 350
■ M AR TOC m g/cm 2 ky MAR C a C O 3 m g /cm ky
Figure 26. TOC, CaC0 3 and paleoproductivity versus depth in San
Nicolas Basin. Like San Clemente, the regional climate changes have
less of an effect than local variations.
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72
The core in Tanner is approximately 700 cm in length but extends back
less than 80 ky (Fig. 10, Table 3). Sedimentation rates are consistently high,
w ith a maximum, 16 cm /ky, in stage 2 during the Holocene and a similarly
high rate of 11 c m / ky extending into the Holocene. Stage 3 rates are reduced
to about 5 c m /k y while during stage 4 they are up to about 8 cm /ky. The high
sedim entation rate in Tanner, despite it’ s distance from land, is a
com bination of very high biogenic inputs, excellent preservation, and input
of detritus carried by the California Current off Point Conception.
The X-radiographs show the presence of the three main facies types:
and, again, the younger portion of the core is predom inantly bioturbated.
There is a num ber of small turbidites between 3 and 8 ky BP (Fig. 27). Before
this time, there is a gradual weakening of current reworking structures into
the present. They become interspersed with bioturbated materials. Reworked
m aterial completely dominates the older portion of the core beginning at
about 60 ky. There is a relatively small am ount of visible pyrite
rem ineralization relative to other cores.
Sand m akes up only a small percent of the sediment w eight in Tanner,
probably a result of it's distance from shore (Fig. 27). The Tanner Basin coarse
fraction was dom inated by foraminifera, predom inantly whole, and fecal
pellets. The recent turbidite deposits have significant contributions by quartz
and mica as well as the previously associated peak in sponge spicules and
pyrite (Fig. 27). Foraminifera and fecal pellets show an inverse relationship.
Foraminifera m ake up from 90-50% of the coarse materials while pellets
range from 10 to 40%. Fecal pellets appear to dom inate the fraction where
foraminifera are low and the ratio w hole/total foraminifera is also low. This
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with permission o f th e copyright owner. Further reproduction prohibited without permission. ■ o
- 5
o
Q.
C
o
CD
Q.
EW9504-09PCTanner Basin
(N M tyknm )
coiling
direction % forams
whole/total % biogenic % fecal
forams silica MAR sand forams pellets %detritus % pyrite
I
- - I
to
1 0 0
weight % ratk>% % % % % % % weight %
• i
p m
K e y
strucfeires; detritus;
mica
0 quartz
biogenic silica; cby mineralogy:
diatoms — wt'tiiillilo
— • — spicules
---------wt.% smectite
-wl%chltkao
Figure 27.Multiple parameter plot for the Tanner Basin showing the
relative contribution changes through tim e.
^4
U >
74
m ay indicate increased dissolution of foram tests while productivity is still
sufficiently high to contribute pellets to the coarse fraction (Fig. 27). O r that
benthic organisms are responsible for the high foram breakage as well as the
increased contribution of the fecal pellets in the basin. Coiling directions
confirm the high sedim entation rates in Tanner. It does not appear to extend
back to stage 5, since the N. pachyderma assemblage remains predom inantly
sinestral coiling (Fig. 26). Dextral coiling individuals dominate in the
Holocene and then there is a shift towards lower % dextral in the surface of
the core, indicating a very recent migration of the 10°C isotherm south of
T anner Basin.
Tanner overall has a coarser population than the other basins. The
distributions, w hether bioturbated or w innow ed are all positively skew ed
(Fig. 28). There is a distinct peak at 30 pm in som e intervals, regardless of
facies, which is likely some kind of biogenic contribution. Then there are
other intervals which do not contain this com ponent, but have a strong fine
com ponent from -15 pm. Most of the Tanner core has been rew orked
slightly and this is apparent in the lack of broad, unsorted material. There is a
bioturbated sample, at 20 cm, which is extremely well sorted, as though it is
only receiving m aterial of one size fraction at 30 pm. This again suggests the
presence of a slightly bioturbated distal turbidite which is still generally sorted
an d coarser than the surrounding materials. The other samples w ith the
skew ed distributions are from intervals w ith partings, supporting the idea of
w innow ing as the m ain mechanism for fine fraction removal. It is possible
that the partings are a result of biogenic activity. The inverse relationship of
foram to fecal pellet counts m ay signal that benthic organisms are rem oving
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o f th e copyright owner. Further reproduction prohibited without permission.
09PC-AII
I
8.
I
12
10
intervals -
.with parting:
8
6
4
bioturbated
2
0
1 0
pm
1 0 0
2 25
£? o standard deviation
□skewness
•3 1.5
a >
£ 0.5
T
/
1 0 100
mean pm
Figure 28. Grain size and statistical data from Tanner Basin.
The overall size of material in Tanner is coarser than in the
other basins. This signals a different population of material
being deposited in Tanner.
76
the fines as they peiietize the sediment and leave distince repetative traces on
the sea-floor.
The California Current does appear to contribute a greater am ount of
chlorite overall to Tanner Basin (Fig. 25). The chlorite and kaoiinite
abundance at 60 ky is reduced compared to the other two samples (Fig. 27).
This m ay be a reflection of increased illite and smectite contributions from
land during low sea-level stands. The effect is one of dilution of chlorite
despite the fact that the California Current is likely stronger during the glacial
periods. Higher sea-levels act as a buffer between Tanner and the land,
making interglacial times a m ore simple reflection of inputs from the surface
w ater w hile glacial signals are confused w ith terrigenous influx.
Tanner shows the highest level of TOC and carbonate accumulation of
all the basins analyzed. TOC accumulation occurred at a very variable rate
during stage 4 (Fig. 29 A). The accumulation of TOC is reduced to less than 50
m g/cm ^ky during stage 3 but rises up to about 50 m g/cm ^ ky at about 35 ky. It
appears to fluctuate around 50 into the present time. Carbonate accumulation
is high and variable in stage 4 and then quite stable in 3 (Fig. 29B). The rise in
TOC at 35 ky corresponds to a moderate rise in the CaC03 record. By looking
carefully at the m any peaks and troughs within the general trends, it appears
that the lowest values of CaC03 correspond to a peak in TOC at about 41 ky.
here is also a similar inverse correlation at 4 ky. Productivity in Tanner Basin
is consistantly higher than the other cores studied and more stable.
There is a change in the frequency of the variation, where from 25-60 ky, the
record was more stable (Fig. 29B). The productivity being high and fairly
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77
EW9504-09PC
A.
0
% TOC
20
40
V
60
( O
60 _
80
100
15
B.
0
% CaCO,
40 80
C.
0
productivity
200 400 600
f }
_ _ _ *
•si—* * *
"k
— -
^ m m r n ---
■ *
------------ 1 ------------- 1
___ 1 _ _ J __ _ 1 __ _ 1 ___ 1 ___ 1 ___
50 100 150 100 300 500 700
MAR TOC mg/cm 2 ky MAR CaC03 mg/cm2 ky
Figure 29. TOC, CaCO3 and paleoproductivity records from Tanner Basin
plotted against age. There are greater contributions of CaC0 3 in this basin,
perhaps the change in biogenics is responsible for the population difference
in the size data.
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stable is reflecting Tanner's proxim ity to Point Conception. It’ s location puts
it directly dow nstream of Point Conception's nutrients as well as it’ s super-
productive surface waters so that organism s are carried along w ith the current
and are entering the borderland over Tanner Basin.
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79
Synthesis
The 6 basins studied share sim ilar surface waters, those of the
California C urrent, and most receive similar bottom w ater from the Pacific
Equatorial w ater mass. W ithin this generalized setting, there are many small
scale features peculiar to each basin which effect depositional patterns. The
basins vary in biogenic input, preservation rates of both inorganic and organic
carbon, am ount, size and composition of terrigenous m aterials, as well as
forces acting upon the basin edge after deposition.
Carbonate
; The carbonate cycles in the borderland have been described num erous
I times (eg. Prensky, 1973): the basins show a pattern of high CaC0 3 content
v
’
during intergladal times and low during glacials, due to dilution by detrital
materials. Dissolution is not thought to dominate the sedimentation pattern
since the sill depths for all the basins are above the lysodine, but it is
occurring at some rate, due to the input and oxidation of organic material.
The pattern of dilution during glacial times appears in five out of the six
basins (Fig. 9). In Animal Basin, there is high CaCC>3 during the Holocene
and a low during the last glacial maximum, in keeping w ith the region. The
C aC 03 does not appear to rise again until stage 6, not only after the last
intergladal b u t during a gladal. The pattern appears to change during the late
] Pleistocene, to one that conforms w ith those observed in deep Pacific cores
along the California Current, both north (Karlin et al., 1992) and south
(Weber et al., 1995) of the Borderland. It seems that during the last
intergladal (stage 5e) sea-level m ay have been high enough to bring highly
corrosive, deep Pacific water, over the sill into Animal Basin. There has also
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80
been a m inim um of 15 m of uplift in the past 120 ky, which could help to
place the sill depth within this range, b u t m ore likely the change is due to a
shift in the Deep Pacific Water.
The other cores in this study show that their respective basins fit with
the previously proposed model for carbonate sedimentation. Overall,
Tanner Basin consistently has the highest C aC03 content of any of the basins
because o f it's proximity to the nutrient and plankton plum e off of Point
Conception. Tanner basin sits directly below the California Current, south of
the major upw elling center and it is essentially catching the m aterial carried
by the current as it enters the borderland region. East Cortes, the second most
proximal basin to the nutrient and plankton carrying current, contains only
slightly low er carbonate contents than Tanner during stages 1-3. Dilution
appears to be stronger in East Cortes during stage 4, perhaps because it is both
closer to land and w ith less irregular bathym etry between it and shoreline
them Tanner. San Nicolas, in particular, but also San Clemente, Basins, have
more irregular CaC0 3 patterns as well as lower overall contents. Both basins
sit in a central position in the borderlands w ith respect to the California
Current an d the Counter current as well as slightly blocked by the Channel
Islands. Their "isolation" from a direct current path and closer proxim ity to
shore, com bined w ith local upwelling centers along the islands, is likely
responsible for the less distinct glacial intergladal patterns and m ore variable
records. Both surface and bottom water circulation is likely altered in these
basins during gladal times because of their shallow sill depths. Descanso
Plain show s the most stable CaC03 record although lower. This core is
located on a starved, open shelf that receives little input from land during
intergladals but is probably very dose to a source of detritus during gladals.
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8 1
W hether there are actual increases in CaCC>3 input, preservational
variations, or both, is still in question. The com parison of broken to whole
foraminifera is an attem pt to look at dissolution changes but this method is
biased w ithout distinguishing benthic from planktonic species since they
have variable resistance to dissolution. In Animal, the ratio overall is quite
low, dem onstrating that dissolution is likely active from 80 to 110 ky BP as
well as during the Holocene. In Descanso Plain, whole foraminifera make
up no more than 40% show ing possible evidence for dissolution, with the
best preservation at 100 ky. This peak at 100 ky is visible in East Cortes basin
as well. It is just before a long period of reduced preservation. In San Nicolas
the ratio increased b u t is highly variable. The cores do not reach 100 ky so
comparison of this peak is impossible. San Nicolas does show a broad high
which coincides w ith a low in East Cortez. Tanner show s a similar pattern to
San Nicolas. Tanner receives different bottom w ater than the rest of the
borderland and so it m ay have an overall different preservation potential.
Benthic organisms have broken up the shells during predation. Bioturbation
by benthic organim s is evidence in the X-radiographs as well as in the
sm earing of the N. pachyderma curves.
In San Nicolas Basin, sedimentation rates are likely the dom inating
factor. Removal from the system by rapid sedim entation probably controls
the dissolution patterns. Descanso Plain and Anim al Basin are the lowest
\ sedim entation rate cores w ith the most fractured foraminifera while San
Nicolas and Tanner have the highest rates and the best preservation.
Alternative ideas are that the northernm ost basins (Tanner, San
Clem ente and San Nicolas) have overall m ore w hole foraminifera than the
southern basins (Animal, Descanso, and East Cortes) because of faunal
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82
variation in shell production, w here the southern basins have overall more
tropical species which are most easily dissolved. It m ay reflect local inputs of
coarse silt and sand w hich may cause either enhanced preservation, if it
comes in as a turbidite and prevents bioturbation, or breakage, if it is abrading
the tests during mixing. O r it m ay be an indication of current reworking
w ithin the basins. Sample handling may also contribute to the broken foram
contributions and artificially change the measure.
Organic Carbon and Paleoproductivity
TOC content is variable in all six of the records. There is a general
pattern of high TOC accumulation during cold periods, stages 2, and 4, (and in
►
t Animal: 6), and the Holocene. This is likely a reflection o f enhanced
preservation due to the increase in sedimentation rates associated w ith these
times. Organic carbon input into the borderland basins is considered to be
from surface w aters as well as through lateral transport and horizontal
focusing of sediments (Berelson et al., 1996). Thus, TOC is not directly a
m easure of surface w ater productivity as is assum ed for other regions
(Samthein, 1987; Mix, 1989). It is also a difficult property to compare in basin
sedim ents w hich could have been deposited under variable oxygenation
regim es that control preservation of organic materials (Cai and Reimers, 1995,
Berelson et al., 1996). Productivity estimates, such as Sam thien's (1987), that
| consider %TOC , sedim entation rate, accumulation rate, and depth or bottom
w ater oxygenation, and then calibrate to a m odem standard, attem pt to give
an approxim ation of productivity. Samthien's estim ate, one for high TOC
percent sediments, creates a picture of productivity very sim ilar to the %TOC
data, w ith a slight increase in the amplitude of the changes. The borderland
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83
basins are probably too complex to be treated w ith such a generalized estimate.
Both lateral inputs, from basin slopes, and preservation are undoubtedly
enhanced d ue to increased accumulation rates. There is too much
uncertainty in the inputs and preservation changes in TOC measures to make
a detailed story about productivity changes. The data in four out of the six
basins support the general idea that productivity is greater during stages 2,4, 6
and the late-Holocene and that is it reduced during stages 3 and 5. There are
two basins, San Nicolas and San Clemente that do not show any
gladal/interglacial scale changes in their TOC records. Productivity in the
basins m ay be better estimated using biogenic silica or another chemical
proxy. A lthough again, silica preservation m ay be enhanced by rapid burial.
f t The question of the "partings";
f W hat could be responsible for the partings? The structures in the X-
I
radiographs (Plate 3) do not look like prim ary laminations or turbidites. They
seem too regular to be created by benthic organisms, although it is a
| possibility. The grain-size data show more positively skewed distributions
I coincident w ith the occurrence of the structures (Table 4). There are two
i
*
. w ays to alter a distribution: reworking o r a change in input (Rea and Hovan,
1995; McCave and Jarvis, 1973). Sea-level falls, during glacials, cause a strong
shift of the shoreline and, in effect, bring the basins closer to the source of
terrigenous materials. This change should allow the input of coarser
m aterials from the shelf out into the borderland. Shelf material is well sorted
and thus has a distinct distribution; one that is more positively skewed than
sedim ents from the more distal basins. The coarsening of the mean and the
tightened distributions could therefore be a result of an input of resuspended
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84
shelf m aterials which then pull the distributions to the right and make them
look like a well sorted deposit This idea suggests that the input would be
fairly uniform throughout the borderland and so the shift in the distributions
should be synchronous as well as of similar m agnitude (with some
adjustm ent for variations in distance from shore). But this is not the case.
Because we are dealing w ith distal, restricted basins, the significant
change in coarse fraction input is likely restricted to the inner basins. Clay
and fine silt m ay be the only material m aking it past the sills and into the
outer basins in an increased m anner. The increase in illite at the base of the
Holocene is a signal for increased terrigenous flux while smectite, a signal for
low terrigenous input settings, is decreasing. While the clay mineralogy
signals increased input, the actual weight percent clay is diminishing down
core, suggesting that it is being removed. This, combined w ith the skewed
distributions being coincident w ith the current-like structures, current
activity seem s to be responsible. The irregularity of the distributions can be
attributed to the fact that the partings are sm all structures which are mixed in
w ith hemi-pelagic materials. A sample interval is about 1 cm^ and is likely
combining both facies types. It seems that this m ethod gives a conservative
estimate o f the changes, and yet the variations are still quite distinct.
It is possible that organisms are creating the structures and removing
fines from the sediment and pelletizing them. For example, the structures
could be from a biomound. This would account for the changing
distributions as well as the variability in tim e and space. It would seen that
the structures would be in more compact intervals, unless they too were
being erased. More likely, the role of benthic organisms is that of
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85
resuspending material and enhancing the particle density in the nepheloid
layer, thereby making the m aterial easier to rework by currents.
W hy are the partings not present in the Holocene? The absence of the
structures in the Holocene m ay be a result of compaction. The structures m ay
be enhanced by increased w ater loss due to compaction. It is possible that after
the Holocene material has been buried by several m eters of sediment the
parting m ay become visible.
Regional Circulation Changes
M odem borderland basins show a fairly continuous but sluggish, (<5
cm /s) contour current along edges of the basin floors. This quiet regime is
r occasionally interrupted by strong influxes of dense w ater that sinks to the
if floor and circles around the edges (Hickey, 1979). The current partings,
skew ed and tightened distributions, and som ewhat sorted coarse fractions
i together are strong evidence that the six borderland basins studied all were
affected by frequent bottom current activity, fast enough to move and
redistribute sediment during the late Pleistocene. To achieve this type of
i
| record, the current need not be continuous for the entire span of the partings,
i
!
but rather, intermittently strong enough to rew ork the top centimeter of
m aterial along the basin edge. In the m odem setting, bottom water renew al is
| thought to occur almost yearly, where dense w ater travels over the sill and
f
. rapidly sinks to the floor and begins a counterclockwise trip around the basin
!
edge (Hickey, 1993; Berelson, 1991). It has been suggested that the sinking
w ater causes some erosion on the basin floor (Hein, 1985). If in the past,
bottom w ater renewal was m ore frequent or faster, because the entering w ater
was already moving more rapidly or was significantly denser than seen today,
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it m ay be able to initiate a contour current fast enough to rework sediment
u n d e r it’ s path more frequently than during the Holocene.
The continuous slow-current cycling around the basin edges is the
result of vertical m otions in the surface waters. Long wave-length "coastal
trapped waves" as w ell as sub-tidal fluctuations drive the counter-clockwise
m otion in the deeper basin waters (Hickey, 1993). D uring glacial times
surface circulation is thought to be more vigorous and sea-level is lowered.
The cross-sectional area between the sill and surface w ater is reduced. It is
possible that the decreased area combined w ith vigorous surface circulation,
characteristic of a glacial time, may result in a n acceleration of bottom
currents and resuspension of materials.
The main question is: is the water entering the basin changing or is the
driving force behind the background motion stronger? During the
Pleistocene, N orth Atlantic Deep water transport is reduced and Antarctic
Bottom W ater (AABW) is driving deep ocean circulation (Broecker, 1989).
There is evidence for velocity increases in deep water flow in the western
Pacific which results in sedim ent erosion a n d /o r the form ation of bedforms
in passages or over ridges (Mammerickx, 1985; Mangini et al., 1982). Mangini
e t al. (1982) specifically identify the end of stage 5 and early stage 4 as a period
o f sedim ent redistribution in the equatorial N orth Pacific. If the AABW
filling the deep Pacific takes up a greater portion of the w ater column than it
does at present (Kennett, 1982), it may peek above the basin sills and drive the
flushings. Or AABW m ay be the source of a m ore dense Intermediate water
that would also sink faster, and thus set off a bottom current capable of
rew orking high w ater content basin sediments.
permission of the copyright owner. Further reproduction prohibited without permission.
87
Another scenario is that the basins sills may have been within the
Oxygen M inim um Zone (OMZ) and the current partings are merely
preserved as a reflection of low background oxygen content in the basins. The
creation of the current partings is likely still a product of flushing events and
possibly ones sim ilar to those seen in the m odem . They are being removed
more effectively in the Holocene and more interm ittently in the past. The
difference in the record would be due to low oxygen contents in the bottom
waters. Santa Monica and Santa Barbara Basins are m odem basins with sills
in the OMZ. Low-oxygen water fills the basins constantly, apart from semi
annual renewal events, and as a result, all the oxygen is used during
; respiration, creating anoxic conditions and lam inated sediments.
» Sedimentation rates are an order of m agnitude lower in the outer basins,
i
| m aking annual to decadal signals only millimeters thick. And, the basins
S
were not anoxic; there is a clear record of bioturbation throughout the cores.
More likely, as oxygen levels dropped, m ixing rates in the sedim ent column
| slowed. The differing sill depths as well as changing sea-levels could easily
1 explain the lack of synchroneity of the partings betw een cores. The
I occurrence in stage 5 may simply be an indication of different water mass
* structure then seen at present and the partings are representing the different
f
l levels of oxygenation in the basins during the Pleistocene. W hen comparing
f the density of partings within an entire core w ith m odem bottom-water
l
oxygenation level, there is a strong correlation (William Berelson, pers
comm).
G ardner and Hemphill-Haley, (1985) identified a stronger OMZ under
the California C urrent, north of Pt. Conception, during the late Pleistocene
and attributed it to increased productivity; an enhanced upwelling regime. A
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88
sim ilar situation, could be present in the Borderland. In Santa Barbara Basins,
during gladals, the bottom waters become oxic. Kennett and Ingram, (1995)
proposed that OMZ is weak because of mixing due to vigorous circulation.
Instead, I propose that the OM Z remained strong b u t was supressed in the
w ater column, as a result of mixed layer expansion. And it was expanded in
thickness due to enhanced productivity (Fig. 30). This could easily result in a
ventilation of the nearshore, shallow-silled basins and a choking of the
deeper, usually oxic basins. The change in the OM Z seems to be the best
explanation for the occurrence of the structures.
If w hat is entering the basins remained the sam e through time, then
the partings would have to be a result of a changing forcing mechanism, such
as the long wavelength coastal trapped waves or sub-tidal vertical
fluctuations. In the case of the coastal trapped waves, generated by longshore
w inds, the increase in the pum ping action driving the circulation could be
the result of a larger tem perature gradient from south to north. The change
w ould have to be drastic to accommodate the increase in constant velocity
necessary to rework sediments. The observed m otion of the continuous
current, I cm /s, was in a nearshore basin at a depth of -900 m (Hickey, 1993).
Tidal fluctuations on glacial time scales are related to the change in the
volum e capacity due to the drop in sea-level. A fall allows for more frictional
contact between the tides and the sea-floor, but the effects of this are not likely
to be seen off the shelf. The variations in the tim ing of the partings may be
som ew hat explained by variations in sill depth or in basin floor depth but not
directly. The shallower sills and basins appear to have more partings than the
deeper ones.
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Reproduced w ith permission o f th e copyright owner. Further reproduction prohibited without permission.
NE
resent sea level
m n i
■ ' I S i '
' w .v,X ..
Flux from surface water including: organic material, CaC03, silica, pellets
terrigenous input (illite, chlorite, quartz, mica, feldspars...,)
Figure 30. Hypothesized scenario for preserving current partings. If the oxygen minimum zone (OMZ)
is supressed and/or expanded at times not necessarily corresponding to sea-level variations, but
perhaps to instability or enhanced productivity, the evidence of reworking may have been preserved
by decreased rates of mixing by benthic organisms.
oo
V O
»
90
Evidence of the partings is n o t synchronous betw een the basins nor
does it clearly coincide with either glacial or intergladal periods. Variations
in the topography around each of the basins probably contributes to the
irregularity of the record. The partings appear in San Nicolas, East Cortes and
Tanner Basins during stage 2 and are intermittent but persistent through to
the base of the cores. These three basins have shallower sill depths than do
San Clemente and Animal Basins, suggesting that the persistence of the
partings may be a function of sill d ep th (Table 1). The core location, whether
, on the basin plain or the flanks, very likely plays a role in the occurrence of
j the partings. For comparison, the Descanso core is from the closer to the
t
| basin plain w hile in East Cortes it is from the flanks. Bioturbation m ay also
I be a factor, or even the controlling factor, since variable rates of sediment
m ixing from basin to basin may m ean that the record is being altered or
!
erased. The variability in time and space may also be explained by the idea
that the partings are created by benthic organims on the basin floor.
| hi all o f the basins, the evidence of reworking is not limited to sea-
( level m inim um s but rather during intermediate sea-levels (Fig. 31). The
f longest records, East Cortes and Descanso, show that the reworking persists
I through m ost of stage 5, a supposed, w arm period, and possibly in 5e, the true
| intergladal at the base. In both of these cores, 5e is a short interval just at the
■ base where the partings appear to taper out. Since the current partings are
' probably a result of intermittent events that are able to alter a record
hundreds of years in length, it is difficult to say if the record from 5e was
rew orked during or after deposition because it may have been altered. In
Animal, there is no major evidence for partings that cointide with the
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
t
t
t
i
9 L
highest sea-level. This evidence, combined with coiling directions both from
this stu d y and those from Kennett and Venz (1995) suggest that the instability
of stage 5 (Dansgaard et al., 1993) created a record in this region that looks very
sim ilar to that of a glacial period during most of stage 5. O r perhaps, the
overall instability that is associated with stages 3 and 4 as glacials, as well as
stage 5, is responsible for the bottom current activity. Since the partings do
not appear during absolute glacial maximas, they m ay be initiated as a result
of changing circulation regimes during the transitions- perhaps the shifting
depths of water masses, such as AABW or the OMZ. The record varies from
basin to basin, but consistently shows an abrupt end to the partings during the
Holocene, a time of anomalous stability (Dansgaard et al., 1993; Broecker,
1997).
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Descanso Plain
100 • •
( A
ec
c
h m
fZ
a.
3 5
1250 1200 1300 1350
so
e
■ a
W
< 3
Q .
120
100
80
60
40
20
1 ' r 1 ■ ■
• • •
• v
East Cortes Basin
- i ~ r v 1 1 * i
0
1400
m m 9 V • m •
• ■ ■ ■ 1 * » ■ 1 ■ ■ * ■
1450 1500 1550 1600
San Clemente Basin
I O O
m
1800 1700 1750 1650 1600
sill depth (m)
Figure 31. Relative sill depth as it changes with sea-level fluctuations
versus the occurence of partings for Descanso Plain, East Cortes and San Clemente
Basins. Partings do not appear at maximum or minimum depths of sills, but rather
at intermediate levels.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
93
Present and Past Regional Climate
Present-day climatic conditions of the N orthern Hem isphere are
thought to be characteristic of the Holocene. Permanent ice caps are restricted
to Greenland and Antarctica. North American weather is dom inated by the
westerly jet stream w hich is located at about 50°N latitude. There is a
subtropical high-pressure system controlling sum m er circulation, and
A leutian and Icelandic lows dominate w inter conditions over their respective
ocean basins.
The California C urrent is the eastern boundary current which runs
dow n the western coast of the N orth America. Coastal upw elling is occurring
j along the eastern edge of the N orth Pacific, from W ashington to Baja
| California, controlled by northerly winds driven by the N orth Pacific high
| pressure cell. The northern region of the coast undergoes a seasonal
I upw elling but upw elling rem ains year-round in Southern California and
I Mexico. The seasonality is due to the presence of the Aleutian Low during
I the w inter months.
f Present Holocene climatic conditions are characterized by an increase
t
| in productivity evidenced in both the carbonate and the siliceous record, the
\ presence of tem perate pollens, lower levels of bulk organic carbon, and
*
1 decreased input of rock detritus into the coastal ocean after about 8,000 yrs. BP
i
? (Sancetta et al., 1992). The increases in productivity are attributed to coastal
*
1 upwelling and thus to w ind patterns that can be associated w ith a regional
cooling since the climatic optim um . Redwoods and oaks are present in
N orthern California regions which have coastal fog, a result of the upwelling
of cold water to the surface (Heusser, 1994). O n land, the American
Southwest is semi-arid to arid (Smith, 1984), w ith few lakes and low runoff
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
94
rates. In Southern California precipitation records for the past 100 years show
a small degree of variation with a range from 5-40 inches per year (Hall, 1996).
Stream flow in Southern California is dictated by precipitation and this is
reflected in the am ount of sediment input into the Pacific Ocean from local
rivers. The frequency of major floods, as observed in the Santa Barbara gray
layer record as well as by historical means, is about 30 years (Fleischer, 1972).
Before the rapid transition into the Holocene, the highly variable,
glacial conditions of the Pleistocene prevailed. From about 200 ky to the
Holocene, the earth underw ent several m ajor climate oscillations which were
caused by variations in incoming solar radiation. Globally, at the peak of the
last glaciation, 18 ky BP, ice sheets and N orth Atlantic sea ice were at their
maximum. N orthern ocean surface waters are estim ated to have been about
10° C cooler and a cold water foraminifera species, N. Pachyderma, (left
coiling), extended far south of its present know n range (Prensky, 1973;
Kennett and Venz, 1995). Late Pleistocene records from coastal Oregon,
show California C urrent conditions to be quite different from today. The
upwelling regime w as weakened. Productivity was low, w ith reduced input
of carbonate and siliceous tests (Lyle et al., 1992; Sancetta et al., 1992). The
pollen record, dom inated by pine and m ountain hemlock at 22,000 to 16,000
yrs, shows that tem peratures were at their lowest. This is thought to be
during the initiation of the Fraser Glaciation (Sancetta et al., 1992). There was
a lack of tem perate spruce and oak forests, due to the cold, dry conditions and
extensive perm afrost (COHMAP, 1988). The Cordilleran Ice Sheet reached its
maximum at 14,000 yrs BP when grasses and herbs dom inated the flora taxa
and then degladation began, leading into the Holocene (Sancetta et al. 1992).
Extended records from Searies Lake, of the Southwestern Great Basin, show
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95
that further inland, the Pleistocene was a time of varying conditions from wet
to dry and lake levels and salinities changed drastically (Smith, 1984). The
Pleistocene in the Sierra Nevada area, from the Owens Lake record OL-92,
represents a time of fresh-water lucustrine deposition, indicating high
precipitaion regimes (Owens Lake Core Study Team, 1994). Amongst all this
change, coastal Southern California vegetation did not appear to m igrate
laterally during glacial times (Heusser, 1994)
Globally, the 3 ^ 0 records of SPECMAP and the Greenland ice cores, at
different scales, show the m agnitude of variablility of sea-level/tem perature
changes (Martinson et al., 1989; Dansgaard et al., 1993). The Summit ice core
t record extends back nearly 250 ky and allowed a very detailed study of ocean
1 and atmospheric circulation proxies such as stable isotope and dust records
I (Dansgaard et al., 1993). The sum m it record shows the Holocene stability to
| be highly irregular and that during past glacial and intergladal periods, the
| global ice volume, as measured by 3lsO, as well atmospheric moisture
S
f conditions have fluctuated drastically, espetially during stage 5, a so-called
intergladal (Dansgaard et al., 1993). Stage 5e appears to be the only truly high
sea-level time equivalant to the Holocene intergladal.
Application of the study to regional climate record
The records recovered from the outer borderland support the general
picture of global climate that has previously been documented. G ladal times
accompanied increased terrigenous input, increased productivity, and
changing current regimes. The low rainfall record of the Holocene is clearly
pictured in the borderland region's percent CaC03 record. But w hy the high
productivity or MAR that also accompany the lack of rainfall that apparantly
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persisted throughout the Holocene? Reduced rainfall should result in
reduced upwelling and lowered productivity as well as a drop in the MAR
due to decreased detrital input from land.
The spatial variation in the records from California during the Late
Pleistocene, such as the Searles Lake record of rapid fluctutations and variable
conditions, the consistant increase in rainfall at Owens Lake, and the lack of
change in the Southern California pollen from Late Pleistocene to Holocene,
is m atched by the local variations seen in the cores in this study. The six
individual records in this study dem onstrate the complexity of the regional
climate system of the Southern California margin.
>
i
i
i
I
\
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97
Conclusions
1. TOC and CaC03 records in the region vary on m ultiple scales up to
glacial/intergladal and create a picture of variable biogenic input in the
borderland region since the Late Pleistocene.
2. Productivity appears to have increased during glacial times, especially
beneath the California Current, but a more careful study of some other proxy
would be better suited for the basins, since TOC has m ultiple sources.
3. G rain size and facies types suggest there are three sedimentary facies
present in all six basins: bioturbated sediments, turbidite deposits, and current
partings. Each facies has a distinct grain-size distribution that is attributed to
the m ode of deposition.
4. The current partings have not been previously observed as a common
facies in the region. They are not synchronous in tim e or space throughout
the borderland cores. They do not correspond to m ajor climate cycles.
5. The best explanation for there formation and preservation is that they are
created during bottom -water renewal events and preserved when the basins
had reduced background oxygen contents in their waters. This explanation
suggests a shift or expansion of the Oxygen M inimum Zone to deeper depths.
6. O ther explanations for the partings are: they are the result of biological
activity, compaction of the sediments, or due to increased vertical
fluctuations in the surface waters which drive continuous counter-clockwise
currents at depth.
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
98
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Appendix L Table of estimated percentage of fades per 5 cm interval.
EW9504-02PC Animal Basin S tratig rap h y
age (ky) depth in cote (cm)% bioturbated % turbidites % partings laminations
036 2 3 100 0 0 0
1.09 7 5 30 20 0 50
1.81 125 100 0 0 0
2.54 17 5 100 0 0 0
3.26 225 100 0 0 0
3.99 2 7 5 80 20 0 0
4.71 325 100 0 0 0
5.43 37 5 100 0 0 0
6.16 425 100 0 0 0
6.88 47.5 100 0 0 0
7.61 523 100 0 0 0
8.33 573 100 0 0 0
9.06 623 100 0 0 0
9.78 673 100 0 0 0
1031 723 100 0 0 0
11.23 773 100 0 0 0
11.96 823 100 0 0 0
12.68 873 100 0 0 0
1337 923 100 0 0 0
1406 973 100 0 0 0
14.74 1023 100 0 0 0
15.43 1073 100 0 0 0
16.12 1123 100 0 0 0
16.81 1173 100 0 0 0
17.50 1223 100 0 0 0
18.18 1273 100 0 0 0
18.87 1323 100 0 0 0
19.56 13 7 3 100 0 0 0
20.25 1423 100 0 0 0
20.93 1473 100 0 0 0
21.62 1523 100 0 0 0
2231 1573 100 0 0 0
23.00 1623 100 0 0 0
24.08 1673 100 0 0 0
2477 1723 100 0 0 0
25.86 1773 100 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
26.95 1825 100 0 0 0
28.03 1875 100 0 0 0
29.12 1925 100 0 0 0
30.21 1975 100 0 0 0
31.29 2025 100 0 0 0
32.38 2075 100 0 0 0
33.47 2125 100 0 0 0
34.55 2175 100 0 0 0
35.64 2225 100 0 0 0
36.73 2275 100 0 0 0
37.82 2325 100 0 0 0
38.90 2375 100 0 0 0
39.99 2425 100 0 0 0
41.08 2475 100 0 0 0
42.16 2525 100 0 0 0
43.25 2575 100 0 0 0
44.34 2625 100 0 0 0
45.42 2675 100 0 0 0
46.51 2725 100 0 0 0
47.60 2775 100 0 0 0
48.69 2825 100 0 0 0
49.77 2875 100 0 0 0
50.86 2925 100 0 0 0
51.95 2975 100 0 0 0
53.03 3025 100 0 0 0
54.12 3075 100 0 0 0
55.21 3125 100 0 0 0
56.29 3175 100 0 0 0
57.61 3225 0 0 100 0
58.93 3275 0 0 100 0
59.99 3325 80 10 10 0
61.05 3375 100 0 0 0
62.12 3425 100 0 0 0
63.18 3475 90 0 10 0
64.24 3525 100 0 0 0
65.31 3575 100 0 0 0
6637 3625 90 0 10 0
67.44 3675 100 0 0 0
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age (ky) depth in. core (cm)% bioturbated % turbidltes % partings laminations
6850 3725 100 0 0 0
6956 3775 70 0 30 0
70.63 3825 100 0 0 0
71.69 3875 100 0 0 0
72.76 3925 100 0 0 0
73.82 3975 100 0 0 0
74.88 4025 100 0 0 0
77.82 4075 90 0 5 0
80.77 4125 100 0 0 0
83.71 4175 100 0 0 0
86.65 4225 95 0 5 0
8959 4275 100 0 0 0
9253 4325 95 0 5 0
95.47 4375 95 0 5 0
98.41 4425 95 0 5 0
10155 4475 100 0 0 0
104.29 4525 100 0 0 0
10754 4575 100 0 0 0
110.18 4625 100 0 0 0
113.12 4675 98 0 2 0
116.06 4725 100 0 0 0
119.00 4775 100 0 0 0
121.94 4825 100 0 0 0
124.88 4875 100 0 0 0
127.82 4925 100 0 0 0
130.77 4975 100 0 0 0
131.97 5025 100 0 0 0
133.18 5075 100 0 0 0
13459 5125 95 0 5 0
135.60 5175 100 0 0 0
136.80 5225 100 0 0 0
138.01 5275 95 0 5 0
139.22 5325 100 0 0 0
140.43 5375 100 0 0 0
141.63 5425 100 0 0 0
142.84 5475 100 0 0 0
144.05 5525 100 0 0 0
145.26 5575 100 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings lamina1
146.47 5623 100 0 0 0
147.67 5673 100 0 0 0
148.88 5723 100 0 0 0
150.09 5773 100 0 0 0
15130 5823 100 0 0 0
15230 5873 100 0 0 0
153.71 5923 100 0 0 0
154.92 5973 100 0 0 0
156.13 6023 100 0 0 0
15734 6073 100 0 0 0
15834 6123 100 0 0 0
159.75 6173 100 0 0 0
160.96 6223 100 0 0 0
162.17 6273 60 20 20 0
16337 6323 25 75 0 0
16438 6373 100 0 0 0
165.79 6423 100 0 0 0
167.00 6473 100 0 0 0
168.20 6523 100 0 0 0
169.41 6573 100 0 0 0
170.62 6623 100 0 0 0
171.83 6673 100 0 0 0
173.04 6723 100 0 0 0
17434 6773 100 0 0 0
175.45 6823 100 0 0 0
176.66 6873 100 0 0 0
177.87 692.5 100 0 0 0
179.07 6973 100 0 0 0
180.28 7023 100 0 0 0
181.49 7073 100 0 0 . 0
182.70 7123 100 0 0 0
183.91 7173 90 0 10 0
185.11 7223 100 0 0 0
18632 7273 70 0 30 0
18733 7323 100 0 0 0
188.74 7373 100 0 0 0
189.94 7423 20 0 80 0
191.15 7473 80 0 20 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
19236 7523 90 0 10 0
19337 7573 75 0 25 0
194.78 7623 75 0 25 0
EW9504-03PC Descanso Plain Stratigraphy
034 2 3 100 0 0 0
1.63 73 100 0 0 0
172 123 100 0 0 0
3.80 173 100 0 0 0
4.89 223 100 0 0 0
5.98 273 100 0 0 0
7.07 323 100 0 0 0
8.15 373 100 0 0 0
9.24 415 100 0 0 0
10.33 473 100 0 0 0
11.41 523 100 0 0 0
1230 573 70 0 30 0
1339 623 100 0 0 0
1430 673 95 0 5 0
15.41 723 100 0 0 0
16.31 773 100 0 0 0
1722 823 100 0 0 0
18.13 873 60 0 40 0
19.04 923 75 0 25 0
19.95 973 70 0 30 0
20.86 1015 70 0 30 0
21.77 1073 60 0 40 0
2168 1123 100 0 0 0
2339 1173 95 0 5 0
2430 1215 90 0 10 0
27.00 1273 100 0 0 0
2930 1323 100 0 0 0
3200 13 7 3 100 0 0 0
3430 1415 100 0 0 0
37.00 1473 90 0 10 0
3930 1523 90 0 10 0
4100. 1573 100 0 0 0
4430 1615 100 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
47.00 1675 100 0 0 0
4950 1725 100 0 0 0
52.00 1775 85 0 15 0
5450 1825 100 0 0 0
57.00 1875 100 0 0 0
5950 1925 100 0 0 0
59.96 1975 100 0 0 0
60.43 2025 90 0 10 0
60.90 2075 100 0 0 0
6157 2125 100 0 0 0
61.83 2175 100 0 0 0
6250
777 5
100 0 0 0
62.77 2275 100 0 0 0
63.23 2325 80 0 20 0
63.70 2375 70 0 30 0
64.17 2425 100 0 0 0
64.64 2475 100 0 0 0
65.10 2525 80 0 20 0
6557 2575 100 0 0 0
66.04 2625 100 0 0 0
6651 2675 100 0 0 0
66.97 2725 100 0 0 0
67.44 2775 100 0 0 0
67.91 2825 100 0 0 0
6857 2875 50 0 50 0
68.84 2925 100 0 0 0
6951 2975 0 0 100 0
69.78 3025 0 0 100 0
7054 3075 70 0 30 0
70.71 3125 100 0 0 0
71.18 3175 100 0 0 0
71.65 3225 60 0 40 0
72.11 3275 100 0 0 0
7258 3325 40 0 60 0
73.05 3375 30 0 70 0
7351 3425 10 0 90 0
73.98 3475 100 0 0 0
74.45 3525 50 0 50 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in. core (cm)% bioturbated % turbidites % partings laminations
74.92 357 5 80 0 20 0
7538 3 6 2 3 40 0 60 0
75.85 3 6 7 3 10 0 90 0
7 6 3 2 3 7 2 3 30 0 70 0
78.40 377 3 0 0 100 0
80.49 382.5 20 0 80 0
82-57 3875 0 0 100 0
84.65 3925 0 0 100 0
86.74 3975 20 0 80 0
88.82 4025 0 0 100 0
90.90 4075 50 0 50 0
92.99 4125 0 0 100 0
95.07 4175 30 0 70 0
97.15 4225 0 0 100 0
9924 4275 10 0 90 0
101.32 4325 10 0 90 0
103.40 4375 0 0 100 0
105.49 4425 0 0 100 0
10757 4475 10 0 90 0
109.65 4525 20 0 80 0
111.74 4575 0 0 100 0
113.82 4625 0 0 100 0
115.90 4675 10 50 40 0
117.99 4725 50 50 0 0
120.07 4775 30 0 70 0
122.15 4825 0 0 100 0
124.24 4875 0 0 100 0
126.32 4925 40 0 60 0
EW9504-04PC East Cortes Basin Stratigraphy
032 2 5 100 0 0 0
0.97 7 5 100 0 0 0
1.62 125 100 0 0 0
2.26 175 100 0 0 0
2.91 225 100 0 0 0
336 275 100 0 0 0
4.20 325 100 0 0 0
4.85 375 100 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
530 423 100 0 0 0
6.14 473 100 0 0 0
6.79 523 100 0 0 0
7.44 573 100 0 0 0
8.09 623 100 0 0 0
8.73 673 100 0 0 0
9.38 723 100 0 0 0
10.03 773 100 0 0 0
10.67 823 100 0 0 0
1132 873 100 0 0 0
11.97 923 80 0 20 0
12.61 973 75 0 25 0
13.01 1023 80 0 20 0
13.40 1073 90 0 10 0
13.79 1123 80 0 20 0
14.19 1173 80 0 20 0
1438 1223 20 0 80 0
14.98 1273 60 0 40 0
1537 1323 100 0 0 0
15.76 13 7 3 100 0 0 0
16.16 1423 95 0 5 0
1635 1473 100 0 0 0
16.94 1523 100 0 0 0
1734 1573 100 0 0 0
17.73 1623 100 0 0 0
18.13 1673 90 0 10 0
1832 1723 100 0 0 0
18.91 1773 100 0 0 0
1931 1823 100 0 0 0
19.70 1873 90 0 10 0
20.09 1923 100 0 0 0
20.49 1973 100 0 0 0
20.88 2023 100 0 0 0
2137 2073 95 0 5 0
21.67 2123 90 0 10 0
22.06 2173 90 0 10 0
22.46 2223 80 0 20 0
22.85 2273 95 0 5 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age(ky) depth in core (cm)% bioturbated % turbidites % partings laminations 114
23.24 2323 100 0 0 0
23.64 2 3 7 5 90 0 10 0
24.72 2 4 2 5 100 0 0 0
25.81 247 5 90 0 10 0
26.90 2 5 2 5 100 0 0 0
27.98 2 5 7 5 100 0 0 0
29.07 2 6 2 5 80 0 20 0
30.16 2 6 7 5 85 0 15 0
31.25 2725 70 0 30 0
3133 2 7 7 5 85 0 15 0
33.42 2 3 2 5 90 0 10 0
34.51 287 5 100 0 0 0
3539 2 9 2 5 80 0 20 0
36.68 2 9 7 5 100 0 0 0
37.77 3025 80 0 20 0
38.85 3 0 7 5 100 0 0 0
39.94 3125 100 0 0 0
41.03 317 5 100 0 0 0
42.12 3225 85 0 15 0
4310 327 5 90 0 10 0
44.29 3325 95 0 5 0
4538 337 5 90 0 10 0
46.46 3425 75 0 25 0
4735 347 5 70 0 30 0
48.64 3 5 2 5 75 0 25 0
49.72 3 5 7 5 90 0 10 0
50.81 3 6 2 5 50 0 50 0
51.90 3 6 7 5 50 0 50 0
52.98 3 7 2 5 70 0 30 0
54.07 3 7 7 5 50 0 50 0
55.16 3823 60 0 40 0
5615 3 8 7 5 30 0 70 0
5733 3923 50 0 50 0
58.42 3973 70 0 30 0
58.74 4023 30 0 70 0
59.07 4073 70 0 30 0
5939 4123 50 0 50 0
59.72 4173 70 0 30 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in. core (cm)% bioturbated % turbidites % partings laminations
60.04 4223 75 0 25 0
6037 4273 85 0 15 0
60.69 4323 80 0 20 0
61.02 4373 90 0 10 0
6134 4423 75 0 25 0
61.67 4473 70 0 30 0
61.99 4523 80 0 20 0
6232 4573 75 0 25 0
62.64 4623 90 0 10 0
62.96 4673 10 0 90 0
6339 4723 60 0 40 0
63.61 4773 80 0 20 0
63.94 4823 0 0 0 0
64.26 4873 0 0 0 0
6439 4923 0 0 0 0
64.91 4973 0 0 100 0
65.24 5023 0 0 100 0
6536 5073 0 0 100 0
65.89 5123 0 0 100 0
66.21 5173 0 0 100 0
6634 5223 5 0 95 0
66.86 5273 0 0 100 0
67.19 5323 0 0 100 0
6731 5373 0 0 0 0
67.84 5423 0 0 0 0
68.16 5473 0 0 0 0
68.48 5523 0 0 0 0
68.81 5573 0 0 0 0
69.13 5623 0 0 0 0
69.46 5673 0 0 0 0
69.78 5723 0 0 0 0
70.11 5773 0 0 0 0
70.43 5823 20 0 80 0
70.76 5873 25 0 75 0
71.08 5923 70 0 30 0
71.41 5973 50 0 50 0
71.73. 6023 70 0 30 0
72.06 6073 100 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
73.10 6125 80 0 20 0
74.14 6175 90 0 10 0
75.18 6225 100 0 0 0
76.22 6275 95 0 5 0
7 7 2 6 6325 100 0 0 0
7 8 3 1 6375 50 0 50 0
7 9 3 5 6425 70 0 30 0
8 0 3 9 6475 75 0 25 0
81.43 6525 90 0 10 0
82.47 6575 100 0 0 0
8351 6625 65 0 35 0
84.56 6675 50 0 50 0
85.60 6725 35 0 65 0
86.64 6775 90 0 10 0
87.68 6825 100 0 0 0
88.72 6875 50 0 50 0
89.76 6925 100 0 0 0
90.81 6975 100 0 0 0
91.85 7025 100 0 0 0
92.89 7075 30 0 70 0
93.93 7125 60 0 40 0
94.97 7175 70 0 30 0
96.01 7225 50 0 50 0
97.06 7275 75 0 25 0
98.10 7325 60 0 40 0
99.14 7375 40 0 60 0
100.18 7425 40 0 60 0
101.22 7475 70 0 30 0
10226 7525 40 0 60 0
103.31 7575 40 0 60 0
104.35 7625 30 0 70 0
10539 7675 100 0 0 0
106.43 7725 60 0 40 0
107.47 7775 40 0 60 0
10851 7825 70 0 30 0
10956 7875 40 0 60 0
110.60 7925 30 0 70 0
111.64 7975 0 0 100 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
112.68 8023 10 0 90 0
113.72 8073 50 0 50 0
114.76 8123 50 0 50 0
115.81 8173 75 0 25 0
116.85 8223 90 0 10 0
117.89 8273 100 0 0 0
118.93 8323 100 0 0 0
119.97 8373 80 0 20 0
121.01 842.5 75 0 25 0
122.06 8473 100 0 0 0
123.10 8523 0 0 0 0
124.14 8573 0 0 0 0
EW9504-05PC San Clemente Basin Stratigraphy
0.40 23 100 0 0 0
1 2 1 7 3 100 0 0 0
2.02 123 100 0 0 0
2.82 173 100 0 0 0
3.63 223 100 0 0 0
4.44 273 100 0 0 0
524 323 100 0 0 0
6.05 373 70 30 0 0
6.85 423 40 60 0 0
7.66 473 0 100 0 0
8.47 523 100 0 0 0
9.27 573 100 0 0 0
10.08 623 70 30 0 0
10.89 673 100 0 0 0
11.69 723 10 90 0 0
1230 773 80 20 0 0
13.31 823 100 0 0 0
13.99 873 90 0 10 0
14.68 923 100 0 0 0
15.36 973 100 0 0 0
16.05 1023 100 0 0 0
16.73 1073 90 0 10 0
17.42 1123 100 0 0 0
18.10 1173 100 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations 118
18.79 1225 100 0 0 0
19.47 1275 95 0 5 0
20.16 1325 90 0 10 0
20.84 1375 100 0 0 0
2153 1425 95 0 5 0
22^1 1475 90 0 10 0
22.90 1525 100 0 0 0
2358 15 7 5 100 0 0 0
2427 1625 100 0 0 0
25.62 1675 100 0 0 0
26.97 1725 90 0 10 0
2852 1775 90 0 10 0
29.67 1825 100 0 0 0
31.02 1875 100 0 0 0
3257 1925 100 0 0 0
33.72 1975 100 0 0 0
35.08 2025 100 0 0 0
36.43 2075 100 0 0 0
37.78 2125 90 0 10 0
39.13 2175 90 0 10 0
40.48 2225 100 0 0 0
41.83 2275 100 0 0 0
43.18 2325 100 0 0 0
4454 2375 100 0 0 0
45.89 2425 95 0 5 0
4754 2475 95 0 5 0
4859 2525 100 0 0 0
49.94 2575 95 0 5 0
51.29 2625 90 0 10 0
52.64 2675 95 0 5 0
54.00 2725 95 0 5 0
55.35 2775 100 0 0 0
56.70 2825 80 0 20 0
58.05 2875 90 0 10 0
59.40 2925 90 0 10 0
59.78 2975 80 0 20 0
60.16 3025 90 0 10 0
6055 3075 95 0 5 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
60.93 3123 70 0 30 0
6131 3173 70 0 30 0
61.69 3223 100 0 0 0
62.07 3273 50 0 50 0
62.45 3323 80 0 20 0
62.84 3373 60 0 40 0
63.22 3423 50 0 50 0
63.60 3473 50 0 50 0
63.98 3523 60 0 40 0
6436 3573 100 0 0 0
64.74 3623 90 0 10 0
65.13 3673 100 0 0 0
6531 3723 70 0 30 0
65.89 3773 50 0 50 0
6627 3823 80 0 20 0
66.65 3873 80 0 20 0
67.03 3923 100 0 0 0
67.42 3973 50 0 50 0
67.80 4023 40 0 60 0
68.18 4073 50 0 50 0
6836 4123 70 0 30 0
68.94 4173 80 0 20 0
6932 4223 0 0 100 0
69.71 4273 0 0 100 0
70.09 4323 100 0 0 0
70.47 4373 80 0 20 0
70.85 4423 75 0 25 0
7123 4473 40 0 60 0
71.61 4523 50 0 50 0
72.00 4573 40 0 60 0
7238 4623 70 0 30 0
72.76 4673 0 0 100 0
74.04 4723 0 0 100 0
7532 4773 0 0 100 0
76.61 4823 10 0 90 0
77.89 4873 40 0 60 0
79.17 4923 50 0 50 0
80.45 4973 40 0 60 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
ige(ky) depth in core (cm)% bioturbated % turbidites % partings lamina
81.73 5025 70 0 30 0
83.02 5075 90 0 10 0
84.30 5125 80 0 20 0
V9504-08PC San Nicolas Basin Stratigraphy
0.29 2 5 100 0 0 0
0.88 75 100 0 0 0
1.47 125 100 0 0 0
2.06 175 100 0 0 0
2.65 225 100 0 0 0
3.24 275 100 0 0 0
3.82 325 100 0 0 0
4.41 375 100 0 0 0
5.00 425 100 0 0 0
559 475 100 0 0 0
6.18 525 100 0 0 0
6.76 575 100 0 0 0
735 625 100 0 0 0
7.94 675 100 0 0 0
853 725 100 0 0 0
9.12 775 100 0 0 0
9.71 825 100 0 0 0
10.29 875 100 0 0 0
10.88 925 100 0 0 0
11.47 975 100 0 0 0
12.06 1025 70 0 30 0
12.65 1075 75 0 25 0
13.73 1125 100 0 0 0
1482 1175 75 0 25 0
15.91 1225 100 0 0 0
16.99 1275 100 0 0 0
18.08 1325 100 0 0 0
19.17 1375 100 0 0 0
20.26 1425 80 0 20 0
2134 1475 75 25 0 0
22.43 1525 100 0 0 0
2352 15 75 60 0 40 0
24.60 1625 100 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
25.60 1675 80 0 20 0
26.60 1725 75 0 25 0
27.60 1775 70 0 30 0
28.60 1825 50 0 50 0
29.60 1875 40 0 60 0
30.60 1925 50 0 50 0
31.60 1975 85 0 15 0
32.60 2025 75 0 25 0
33.60 2075 100 0 0 0
34.60 2125 100 0 0 0
35.60 2175 40 0 60 0
36.60 2225 30 0 70 0
37.60 2275 40 0 60 0
38.60 2325 80 0 20 0
39.60 2375 75 0 25 0
40.60 2425 100 0 0 0
41.60 2475 80 0 20 0
42.60 2525 100 0 0 0
43.60 2575 100 0 0 0
44.60 2625 80 0 20 0
45.60 2675 70 0 30 0
46.60 2725 100 0 0 0
47.60 2775 50 0 50 0
48.60 2825 100 0 0 0
49.60 2875 85 0 15 0
50.60 2925 100 0 0 0
51.60 2975 100 0 0 0
52.60 3025 20 0 80 0
53.60 3075 30 0 70 0
54.60 3125 100 0 0 0
55.60 3175 100 0 0 0
56.60 3225 70 0 30 0
57.60 3275 100 0 0 0
58.60 3325 70 0 30 0
59.60 3375 10 20 70 0
60.12 3425 100 0 0 0
60.65 3475 100 0 0 0
61.17 3525 40 o - 60 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings lamina
61.69 3575 10 0 90 0
62.21 3625 100 0 0 0
62.73 3675 100 0 0 0
63.25 3725 100 0 0 0
63.77 3775 100 0 0 0
64.29 3825 100 0 0 0
64.81 3875 0 0 100 0
6533 3925 0 0 100 0
65.85 3975 0 0 100 0
66.37 4025 80 0 20 0
66.90 4075 100 0 0 0
67.42 4125 30 0 70 0
67.94 4175 0 0 100 0
68.46 4225 0 0 100 0
68.98 4275 0 0 100 0
<
6950 4325 20 0 80 0
V
70.02 4375 0 0 100 0
s
i
7054 4425 0 100 0 0
f
71.06 4475 100 0 0 0
c
7158 4525 50 0 50 0
J s
f c
5 72.10 4575 0 0 100 0
5 :
k
i
72.62 4625 0 0 100 0
73.15 4675 0 0 100 0
73.67 4725 50 0 50 0
1
K
1
74.19 4775 0 0 100 0
74.71 4825 0 10 90 0
75.23 4875 40 10 50 0
f
75.75 4925 0 10 90 0
£
t
76.27 4975 0 0 100 0
I
76.79 5025 0 0 100 0
? ■
7731 5075 0 0 100 0
77.83 5125 0 10 90 0
7835 5175 0 20 80 0
78.87 5225 0 0 100 0
79.40 5275 0 0 100 0
79.92 5325 0 100 0 0
80.44 5375 0 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
EW9504-09PC Tanner Basin Stratigraphy
0.05 0 5 0 0 0 0
0.23 2 5 100 0 0 0
0.70 7 5 100 0 0 0
1.16 125 100 0 0 0
1.62 175 100 0 0 0
2.09 225 100 0 0 0
2.55 275 100 0 0 0
3.02 325 100 0 0 0
3.48 375 70 30 0 0
3.95 425 40 60 0 0
4.41 475 0 100 0 0
4.87 525 100 0 0 0
5.34 575 100 0 0 0
5.80 625 70 30 0 0
6 2 7 675 100 0 0 0
6.73 725 10 90 0 0
7.20 775 80 20 0 0
7.66 825 100 0 0 0
8.12 875 90 0 10 0
8.59 925 100 0 0 0
9.05 975 100 0 0 0
952 1025 100 0 0 0
9.98 1075 90 0 10 0
10.45 1125 100 0 0 0
11.37 1225 100 0 0 0
11.84 1275 95 0 5 0
12.30 1325 90 0 10 0
12.77 1375 100 0 0 0
13.07 1425 95 0 5 0
13.38 1475 90 0 10 0
13.68 1525 100 0 0 0
13.99 15 7 5 100 0 0 0
14.29 1625 100 0 0 0
14.60 1675 100 0 0 0
14.90 1725 90 0 10 0
15.21 • 1775 90 0 10 0
1551 1825 100 0 0 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations 124
15.82 1875 100 0 0 0
16.12 1925 100 0 0 0
16.43 1975 100 0 0 0
16.73 2025 100 0 0 0
17.04 2075 100 0 0 0
17.34 2125 90 0 10 0
17.64 2175 90 0 10 0
17.95 2225 100 0 0 0
18.25 2275 100 0 0 0
18.56 2325 100 0 0 0
18.86 2375 100 0 0 0
19.17 2425 95 0 5 0
19.47 2475 95 0 5 0
19.78 2525 100 0 0 0
20.08 2575 95 0 5 0
20.39 2625 90 0 10 0
20.69 2675 95 0 5 0
21.00 2725 95 0 5 0
21 JO 2775 100 0 0 0
21.61 2825 80 0 20 0
21.91 2875 90 0 10 0
?? ?2 2925 90 0 10 0
2252 2975 80 0 20 0
22.83 3025 90 0 10 0
23.13 3075 95 0 5 0
23.44 3125 70 0 30 0
23.74 3175 70 0 30 0
24.05 3225 100 0 0 0
25.07 3275 50 0 50 0
26.09 3325 80 0 20 0
27.11 3375 60 0 40 0
28.13 3425 50 0 50 0
29.15 3475 50 0 50 0
30.17 3525 60 0 40 0
31.19 3575 100 0 0 0
32.21 3625 90 0 10 0
33.23 3675 100 0 0 0
34.25 3725 70 0 30 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
3527 3773 50 0 50 0
3629 3823 80 0 20 0
3731 3873 80 0 20 0
3833 3923 100 0 0 0
3935 3973 50 0 50 0
4037 4023 40 0 60 0
4139 4073 50 0 50 0
42.41 4123 70 0 30 0
43.44 4173 80 0 20 0
44.46 4223 0 0 100 0
45.48 4273 0 0 100 0
4630 4323 100 0 0 0
4732 4373 80 0 20 0
4834 4423 75 0 25 0
4936 4473 40 0 60 0
5038 4523 50 0 50 0
51.60 4573 40 0 60 0
52.62 4623 70 0 30 0
53.64 4673 0 0 100 0
54.66 4723 0 0 100 0
55.68 4773 0 0 100 0
56.70 4823 10 0 90 0
57.72 4873 40 0 60 0
58.74 4923 50 0 50 0
5928 4973 40 0 60 0
59.82 5023 70 0 30 0
60.37 5073 90 0 10 0
60.91 5123 80 0 20 0
61.45 5173 50 0 50 0
61.99 5223 80 0 20 0
6233 5273 90 0 10 0
63.08 5323 40 0 60 0
63.62 5373 60 0 40 0
64.16 5423 90 0 10 0
64.70 5473 90 0 10 0
6524 5523 40 0 60 0
65.78 5573 90 0 10 0
66.33 5623 90 0 10 0
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) depth in core (cm)% bioturbated % turbidites % partings laminations
66.87 567 5 60 0 40 0
67.41 5723 60 0 40 0
67.95 577 5 90 0 10 0
68.49 5823 70 0 30 0
69.03 5873 60 0 40 0
69.58 5923 80 0 20 0
70.12 5973 70 0 30 0
70.66 6023 60 0 40 0
71.20 6073 60 0 40 0
71.74 6123 40 0 60 0
7 2 2 8 6173 50 0 50 0
72.83 6223 100 0 0 0
73.37 6273 20 0 80 0
73.91 6323 20 0 80 0
74.45 6373 20 0 80 0
74.99 6423 0 0 100 0
f
V
i
t
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Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Appendix H. Point counting data for all six basins. The data are in the form of calculate!
percents for each sample counted. The average number counted was 150.
age (ky) sample numbers % w hole forams% broken foraim% forams total% diatoms
EW9504-02PC- Animal Basin
2.9 02 0 5 3.91 29.69 3359 0.00
14.4 0280.45 2273 18.18 40.91 0.00
185 021105 1654 630 2283 0.00
19.9 021205 71.90 5.79 77.69 0.00
29.2 021705 4159 23.89 65.49 0.88
423 022305 0.00 244 244 0.00
64.1 023305 0.00 261 261 0.00
863 024005 0.93 556 6.48 0.00
97.8 024205 1.68 5.88 756 0.00
1093 024405 139 15.97 1736 0.00
134.0 025005 35.14 6.76 41.89 1.35
141.0 025305 3456 27.94 6250 4.41
165.0 026305 0.00 0.00 0.00 0.00
1820 027005 8.77 16.67 25.44 0.00
188.0 027505 26.14 18.75 44.89 0.00
V9504-03PC-- Descanso Plain
0.5 0315 6.85 2260 29.45 0.00
15.0 03 715 1850 33.48 51.98 0.00
34.0 031415 14.29 28.00 4229 057
61.8 03 2215 1295 33.81 46.76 0.00
68.4 03 2915 0.00 10.79 10.79 0.00
78.2 033615 11.03 30.88 41.91 0.00
99.1 034115 36.45 46.73 83.18 0.00
124.0 034715 0.60 120 1.80 0.00
I EW9504-04PC- East Cortes Basin
11.7 04685 28.18 38.18 6636 0.00
15.4 041085 60.91 21.82 8273 0.00
232 042115 15.87 34.92 50.79 0.00
48.1 043305 15.00 25.00 40.00 0.00
59.0 043815 10.17 3051 40.68 0.00
695 045195 4.90 26.47 3137 0.00
76.0 046055 3.94 2283 26.77 0.00
80.8 046705 5833 26.67 85.00 0.00
815 046805 53.78 21.01 74.79 0.00
91.4 047425 40.00 750 4750 0.00
106.0 048355 29.73 48.65 7838 0.00
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
% sponge spicules % fecal pellets % mica % quartz % Iithics % pyrite error
EW9504-02PC- Animal Basin
0.00 5234 0.00 5.47 0.00 7.03 8.84
132 48.48 0.00 3.03 435 132 1231
0.00 70.87 0.79 3.15 0.79 137 8.87
0.83 4.96 0.83 15.70 0.00 0.00 9.09
0.88 23.89 0.88 531 1.77 0.88 9.41
4.88 5834 732 21.95 4.88 0.00 15.62
2.61 1.74 3217 59.13 1.74 0.00 933
0.93 6739 0.93 2037 0.00 3.70 9.62
0.00 85.71 0.84 252 0.84 252 9.17
139 27.78 3.47 13.89 0.69 35.42 833
0.68 45.27 5.41 4.05 0.68 0.68 8.22
0.00 19.12 0.74 6.62 0.00 6.62 837
0.00 0.00 29.46 66.07 4.46 0.00 9.45
0.88 38.60 0.88 25.44 0.00 8.77 9.37
1.14 3636 3.41 832 0.00 5.68 734
EW9504-03PC- Descanso Plain
4.11 5822 5.48 137 0.00 1.37 828
3.96 22.91 14.10 4.85 0.00 220 6.64
1.14 40.00 9.14 5.14 0.00 1.71 7.56
5.04 28.06 1223 288 0.00 5.04 8.48
332 40.66 18.67 23.65 0.00 290 6.44
4.41 28.92 4.90 13.48 637 0.00 4.95
1.40 234 7.94 1.40 0.00 3.74 6.84
539 539 2036 6287 4.19 0.00 7.74
EW9504-04PC- East Cortes Basin
7.27 21.82 1.82 1.82 0.00 0.91 933
0.91 9.09 1.82 3.64 1.82 0.00 933
139 2937 0.79 11.90 3.17 238 8.91
7.00 45.00 5.00 3.00 0.00 0.00 10.00
5.08 46.61 3.39 339 0.85 0.00 921
0.00 50.98 0.98 3.92 1275 0.00 9.90
0.00 24.41 0.79 7.87 0.00 40.16 8.87
3.33 10.83 0.00 0.83 0.00 0.00 9.13
232 14.29 252 252 252 0.84 9.17
5.00 4333 0.83 0.83 0.00 230 9.13
5.00 5.41 1.80 270 0.90 4.50 9.49
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
age (ky) sample numbers % whole forams% broken foranu% fora ms total% diatoms
EW9504-05PC- San Clemente Basin
I
I
<
8.1 0550.5 30.70 21.93 52.63 0.00
24.0 051605 1429 17.01 3129 0.00
40.2 052205 1853 750 25.83 250
4 5 5 052365 1029 30.88 41.18 1.47
5 6 3 052805 23.08 20.00 43.08 154
63.4 053405 7.94 4.76 12.70 0.00
68.7 054005 2.15 450 6.45 0.00
79.1 054805 3653 23.95 60.48 0.00
V9504-08PC-■ San N icolas Basin
0 2 08 0 5 2328 2328 4655 0.00
3 5 08 305 1353 28.15 41.48 0.00
7.1 08 605 34.15 39.84 73.98 0.00
32.8 082005 3459 16.98 5157 0.00
41.0 08 2365 40.24 24.85 65.09 0.00
52.6 08 2905 43.97 2857 7254 426
632 08 3405 13.11 33.61 46.72 0.00
712 08 3815 34.34 33.73 68.07 1.20
80.0 084665 2.05 23.97 26.03 3.42
V9504-09PC-• Tanner Basin
3.7 09 205 13.19 1528 28.47 0.00
4.6 09 305 424 38.98 43.22 0.00
142 091405 70.09 1558 85.47 0.00
17.9 09 2005 20.74 31.85 5259 0.00
302 09 3305 30.72
22.89 53.61 0.00
34.4 09 3505 35.94 32.03 67.97 0.00
48.7 09 4205 29.85 53.73 8358 0.00
64.4 09 5405 153 5420 55.73 0.00
80.0 09 6905 67.48 22.76 90.24 1.63
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
ige spicules % fecal pellets % mica % quartz
J4-05PC- San Clem ente Basin
% Iithics % pyrite error
1.75 35.09 1.75 7.02 0.88 0.88 93 7
2.72 38.10 136 7.48 0.68 1837 8.25
0.83 45.00 0.83 333 0.00 21.67 9.13
4.41 25.00 11.76 8.82 735 0.00 12.13
231 36.92 3.08 9.23 0.00 3.85 8.77
238 45.24 4.76 18.25 0.79 15.87 8.91
0.00 69.89 2.15 538 2.15 13.98 1037
4.19 1557 1.80 339 1.20 13.17 7.74
130
EW9504-08PC- San N icolas Basin
3.45 4052 3.45 5.17 0.86 0.00 928
222 45.19 0.00 8.89 0.74 1.48 8.61
4.88 15.45 0.81 1.63 0.00 325 9.02
6.29 3208 252 5.03 252 0.00 7.93
1.78 30.77 0.00 0.00 059 1.78 7.69
1206 7.09 355 0.71 0.00 0.00 8.42
1.64 36.07 246 820 0.00 4.92 9.05
3.61 9.04 3.01 1024 120 3.61 7.76
6.85 6.85 4.11 3356 4.11 15.07 828
04-09PC- Tanner Basin
0.00 45.83 0.00 23.61 208 0.00 833
254 932 254 3136 254 8.47 921
256 11.97 0.00 0.00 0.00 0.00 9.25
0.00 37.78 0.00 8.15 0.00 1.48 8.61
3.01 3434 0.60 4.82 0.60 241 7.76
156 28.13 0.00 0.78 0.78 0.78 8.84
0.00 11.19 0.00 4.48 0.75 0.00 8.64
0.76 3206 0.00 7.63 153 229 8.74
0.81 325 0.00 0.81 3.25 0.00 9.02
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Appendix I I L Complete data table of CaC03 and T O C for each basin, against
both depth and age.
depth Animal Basin-02PC Descanso Plain-03 PC
in core (cm) age (ky) CaC03% %TOC age (ky) %CaC03 %TOC
0.50 0.00 050 12.90 3.45
1050 1.44 2.17 13.00 3.15
20.50 2.89 12.74 1.71 453 15.80 2.80
30.50 453 10.91 2.40 650 15.40 259
4050 5.78 10.00 2.17 8.67 28.00 1.49
5050 752 7.66 0.76 10.83 18.62 256
6050 8.67 7.91 1.81 13.00 1657 2.64
7050 10.11 750 151 14.83 11.99 255
8050 1156 5.83 1.03 16.67 14.28 258
9050 13.00 5.00 1.44 1850 15.20 2.01
10050 1458 4.33 1.62 20.33 8.81 2.84
11050 15.75 6.66 153 22.17 7.12 3.01
12050 17.13 5.83 2.20 24.00 9.18 2.96
13050 1850 8.33 150 29.00 10.14 1.84
14050 19.88 34.00 11.49 259
15050 21.25 250 2.66 39.00 13.17 2.82
16050 22.63 853 1.84 44.00 10.76 255
17050 24.81 9.16 1.47 49.00 11.91 2.80
18050 27.00 0.00 0.00 54.00 13.61 3.19
19050 29.19 10.00 153 59.00 13.49 2.41
20050 3158 750 1.11 59.94 1458 2.42
21050 3356 6.66 1.62 60.88 10.27 2.47
22050 35.75 0.00 1.85 61.81 10.06 1.94
23050 37.94 5.00 159 62.75 5.93 224
24050 40.13 1.67 1.49 63.69 3.82 234
25050 4251 0.83 1.79 64.63 3.82 325
26050 4450 0.83 1.76 6556 10.25 3.19
27050 46.69 1.67 1.90 6650 5.47 284
28050 48.88 1.67 1.76 67.44 1.70 2.73
29050 51.06 1.67 1.85 6858 250 3.73
30050 53.25 0.83 1.84 6951 353 3.47
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
depth Animal Basin-02PC Descanso Plain-03PC
in core (cm) age (ky) CaC03% %TOC age(ky) %CaC03 %TOC
310-50 55.44 250 7055 7.17 3.00
320.50 57.63 1.67 0.91 71.19 3.13 3.45
33050 59.77 0.00 1.43 72.13 3.64 2.62
34050 61.91 250 0.48 73.06 358 3.29
35050 64.05 0.00 0.79 74.00 6.74 1.87
36050 66.20 0.00 059 78.18 10.96 0.88
37050 6854 0.83 155 8256 1058 1.91
38050 70.48 1.67 1.16 8655 11-92 2.64
39050 72.63 1.67 0.82 90.73 13.61 1.82
40050 74.77 1.67 0.77 94.91 1253 1.76
41050 8052 250 0.83 99.09 13.95 1.46
42050 86.27 6.66 0.80 10357 16.18 2.21
43050 92.02 1.67 1.45 107.45 11.44 250
44050 97.77 1.67 0.99 111.64 7.16 1.84
45050 10352 4.17 1.40 115.82 5.15 2.16
46050 109.27 0.00 0.00 120.00 0.63 2.45
47050 115.02 0.00 0.00 124.18 0.72 254
48050 120.77 14.16 1.41 12856 1352 1.88
49050 12652 14.16 153 13.89 159
50050 128.93 14.99 0.80
51050 13155 1353 1.15
52050 133.76 14.16 1.16
53050 136.18 11.66 1.07
54050 138.60 11.66 1.15
55050 141.01 14.16 1.20
56050 143.43 10.83
57050 145.84 250
58050 14856 1.67 1.18
59050 150.67 0.00 1.47
60050 153.09 0.00 156
61050 15550 0.84
62050 157.92 0.83 155
63050 16053 0.83 055
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
depth Animal Basin-02PC
in cote (cm) age (ky) CaC03% %TOC
64050 162.75 250 150
65050 165.17 0.00 2.80
66050 16758 0.83 1.60
67050 170.00 5.83 0.95
68050 172.41 353 1.02
69050 174.83 5.83
70050 177.24 1.67
71050 179.66 1.67
72050 182.07
184.49
186.90
i
*
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
East Cortes-04PC San Clemente Basin-05PC
age (ky) %CaC03 %TOC age(ky) %CaC03 %TOC
0.00 0.00 1430 119
130 1.63 1630 147
2.60 30.90 2.78 335 1630 188
3.90 20.83 2.71 4.88 17.90 0.72
530 2934 3.01 630 2160 239
630 29.07 8.13 2330 1.76
7.80 28.66 3.67 9.75 6.00 180
9.10 29.90 2.82 1138 9.80 336
10.40 36.07 2.77 13.00 1530 154
11.70 27.07 1438 13.40 331
13.00 25.49 3.02 15.75 1630 171
13.79 24.82 335 17.13 15.10 3.07
1437 22.49 1.72 1830 630 470
1536 21.66 2.86 19.88 11.90 1.60
16.14 18.99 431 2135 1130 236
16.93 16.99 332 2163 10.60 100
17.71 21.66 435 2400 10.60 235
1830 18.91 333 26.69 7.70 142
19.29 28.82 2.42 29.38 9.40 118
20.07 20.83 409 3108 9.60 3.43
20.86 1233 3.19 34.77 14.30 1.99
21.64 18.49 101 37.46 1130 238
22.43 14.83 331 40.15 9.90 0.01
23.21 20.41 4185 13.00 3.11
24.00 20.74 1.98 4534 1160 230
26.19 2407 4833 10.40 113
2838 20.49 50.92 1330 169
3036 17.49 53.62 13.90 134
32.75 22.49 5631 10.60 100
34.94 24.16 59.00 10.00 1.79
37.13 18.66 111 59.88 730 113
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
East Cortes-04PC San Clemente Basin-05PC
age(ky)
%CaC03 %TOC age (ky) %CaC03 %TOC
3931 25.16 60.76 6.00 1.17
4130 2232 2.09 61.65 430 2.60
43.69 19.08 2.85 6233 230 331
45.88 1938 2.83 63.41 4.80 371
48.06 18.91 1.89 64.29 530 360
50.25 11.16 65.18 330 3.16
52.44 12.00 135 66.06 1.80 3.43
54.63 9.66 66.94 1.10 4.05
56.81 8.83 2.24 67.82 530 3.46
59.00 5.00 68.71 3.70 1.92
59.75 9.16 3.62 6939 7.40 311
6030 13.83 70.47 4.40 437
61.25 930 406 7135 5.90 1.71
62.00 830 2.81 7234 6.00 3.68
62.75 5.83 73.12 7.70 335
6330 633 2.67 74.00 15.10 1.62
64.25 11.75 5.11 7637 5.10 236
65.00 6.83 79.14 7.70
65.75 10.41 334 81.71 930
6630 10.00 3.00
67.25 11.83 2.98
68.00 13.91 3.02
68.75 17.49
6930 1938 1.46
70.25 19.99 132
71.00 21.66 1.93
71.75 19.74
7230 18.08 3.45
73.25 19.16
74.00 21.82 334
74.75 2137 3.40
7530 2332 232
76.25 2837 234
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
East Cortes-04PC
age(ky) %CaC03 %TOC
77.00 25.24 2.33
77.75 25.41 231
78.50 2632 1.81
79.25 23.16 242
80.00 27.99 1.97
80.75 24.99 220
8150 26.91 1.89
82.25 27.74 2.47
83.00 25.99 352
85.09 2124 454
87.18 19.83 3.14
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
137
San Nicolas Basin-08PC Tanner Basin-09 PC
age (ky) %CaC03 %TOC age (ky) %CaC03 %TOC
050 23.80 6.49
1.18 1250 5.91 0.93 42.48 2.80
256 1850 555 1.86 34.99
355 4.70 652 2.79 16.99 7.76
4.73 29.10 352 3.71 45.82 3.40
5.91 27.00 3.66 4.64 41.90 3.47
7.09 2750 407 5 57 39.15 3.60
8.27 28.60 2.49 650 39.15 3.83
9.45 17.80 3.03 7.43 3852 5.10
10.64 856 3957 3.95
1
f 11.82 21.80 3.79 959 2852 550
s
t
13.00 20.80 2.92 1051 20.83 4.40
1550 7.90 450 11.14 21.66 3.90
17.40 3.90 551 12.07 20.83 451
19.60 18.80 3.96 13.00 19.99 350
21.80 17.10 3.80 13.61 19.16 450
F
24.00 17.60 350 1452 19.16 5.10
26.20 9.90 4.11 14.83 22.49 3.05
;
28.40 17.70 352 15.44 21.66 4.90
30.60 12.80 4.86 16.06 22.49 450
32.80 1550 3.92 16.67 19.16 490
35.00 1650 358 1758 16.66 3.01
I
1
3750 12.00 401 17.89 15.83 650
f
| 39.40 1050 4.09 1850 23.32 4.40
41.60 16.40 4.06 19.11 22.49 353
43.80 19.40 355 19.72 19.16 3.10
46.00 13.90 152 2053 24.16 450
4850 14.80 481 20.94 22.99 3.84
50.40 2150 457 2156 21.66 450
52.60 3.30 1051 22.17 2416 2.00
54.80 20.00 4.18 22.78 21.66 4.30
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
San Nicolas Basin-08PC
age(ky> %CaC03 %TOC
57.00 18.70 428
59.20 19 JO 3.61
6120 3.80 335
6320 1620 287
6520 2.60 440
6720
6920 9.90 453
7120 820 497
72.40 1280 452
73.60 1130 413
74.80 7.10 481
76.00 10.00 5.73
7720 17.00 3.98
78.40 17.60 4.06
79.60 2320 224
80.80 4.50 3.45
82.00 7.60 4.65
8320 19 JO 535
84.40 17.80 245
66 JO 19J0 233
Tanner Basin-09 PC
age(ky) %CaC03 %TOC
2339 24.16 460
2400 2332 3.18
26.06 2832 1.40
28.12 26.66 3.00
30.18 1499 5.80
3224 2249 531
34.29 24.16 3.84
3635 26.66 285
38.41 25.82 1.94
40.47 2457 335
4253 30.40 4.45
44J9 29.99 3.10
46.65 2832 5.90
48.71 24.99 5.74
50.76 25.82 3.60
5282 20.83 4.80
5488 25.82 4.60
56.94 2282 336
59.00 19.99 3.70
60.25 19.41 6.87
6130 16.66 4.62
6275 24.16 290
64.00 20.83 3.70
6525 16.66 3.60
66 JO 14.16 528
67.75 24.16 730
69.00 2249 326
70.25 2249 530
71 JO 2249 434
7275 14.99 6.60
74.00 14.16 430
7525 17.49 3.10
7630 20.83 5.40
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
Tanner Basin-09PC
age (ky) %CaC03 %TOC
77.75 3932 3.60
79.00 2832 5.80
80.25 19.99 430
8130 14.66 434
82.75 17.49 2.70
29.16
32.74 337
0.00
►
:
!
i
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.

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Asset Metadata

Creator Robinson, Rebecca Sprague (author)

Core Title Late Pleistocene-Holocene depositional history of the California Continental Borderland

Degree Master of Science

Degree Program Earth Sciences

Publisher University of Southern California (original), University of Southern California. Libraries (digital)

Tag Geology,OAI-PMH Harvest,physical oceanography

Language English

Contributor Digitized by ProQuest (provenance)

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c16-16350

Unique identifier UC11336847

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Legacy Identifier 1387829.pdf

Dmrecord 16350

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Rights Robinson, Rebecca Sprague

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Source University of Southern California (contributing entity), University of Southern California Dissertations and Theses (collection)

Access Conditions The author retains rights to his/her dissertation, thesis or other graduate work according to U.S. copyright law. Electronic access is being provided by the USC Libraries in agreement with the au...

Repository Name University of Southern California Digital Library

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