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Foraminiferal trends and paleo-oceanography in Late Pleistocene-recent cores, Tanner Basin, California

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Foraminiferal trends and paleo-oceanography in Late Pleistocene-recent cores, Tanner Basin, California

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Content FORAMINIFERAL TRENDS AND PALEO-OCEANOGRAPHY
U
IN LATE PLEISTOCENE-RECENT CORES,
TANNER BASIN, CALIFORNIA
by
Ahmad Kheradpir
IM
A Thesis presented to the
FACULTY OF THE GRADUATE SCHOOL
UNIVERSITY OF SOUTHERN CALIFORNIA
In Partial Fulfillment of the
Requirements for the Degree
MASTER OF SCIENCE
(Geological Sciences)
September 1968
UMI Number: EP58563
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U N IV E R S IT Y O F S O U T H E R N C A L IF O R N IA
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U N IV E R S IT Y P A R K
LO S A N G E L E S , C A L IF O R N IA 9 0 0 0 7
£»e '(J\ K
V
This thesisj written by
............Alxn)a.d..Khexadpir.......... ....
under the direction of his, Thesis Committee,
and approved by all its members, has been pre
sented to and accepted by the Dean of The
Graduate Schoolj in partial fulfillm ent of the
requirements fo r the degree of
.M A STER . OF. SCIENCE
f . ~ ? n
Dean
Date....... Sep tern be r, 196 8
TABLE OF CONTENTS
Page
ABSTRACT................................................ 1
INTRODUCTION ........................................... 2
Previous work...................................... 5
Methods of study .................................. 7
ACKNOWLEDGMENTS ....................................... 8
GEOLOGY AND OCEANOGRAPHY OF TANNER BASIN ............. 10
SEDIMENTOLOGY ......................................... 15
PLANKTONIC FORAMINIFERAL ANALYSIS .................. 2 2
PALEO-OCEANOGRAPHIC VARIATIONS ....................... 36
DISCUSSION ........................................... 4 4
BENTHONIC FORAMINIFERA ................................ 50
CONCLUSIONS . 57
REFERENCES............................................. 60
LIST OF TEXT-FIGURES
Text-
Figure Page
1. Location of Tanner Basin in the continental
borderland of southern California ......... 4
2. Generalized surface current circulation and
summer surface temperature (C°) in the
North Pacific................................ 13
3. Percentage of calcium carbonate and
planktonic foraminiferal numbers in
Cores AHF-10617, 10614, and 11343 ......... 18
4. Absolute abundances of the most important
planktonic foraminiferal species in
Core AHF-10617............ . .............. 24
5. Absolute abundances of the most important
planktonic foraminiferal species in
Core AHF-10614............................. 26
6. Absolute abundances of the most important
planktonic foraminiferal species in
Core AHF-11343 29
7. Cummulative frequencies of dominant plank
tonic foraminiferal species, coiling ratio
changes of Globigerina pachyderma
(Ehrenberg) and stratigraphic changes
iii
Text-
Figure Page
of the less dominant planktonic forami
niferal species within Cores AHF-10617,
10614, and 11343 40
8. Abundances of radiolarians in specimens
per gram of sediment....................... 4 6
9. Abundances of benthonic foraminifera in
specimens per g r a m ............. 52
10. Abundances of Uvigerina peregrina in
specimens per g r a m ......................... 55
iv
Plate
1.
LIST OF ILLUSTRATIONS
Page
Part of the upper portion of Core AHF-11343 . 21
v
ABSTRACT
Microfaunas in three piston cores from Tanner Basin,
an outer basin in the continental borderland of southern
;California, were investigated to define climatic and ocean-
■ ographic variations that occurred during late Pleistocene
i to Recent times. Criteria most useful for paleo-ocean-
: ographic interpretations are changes in species composition
! of planktonic foraminiferal faunas, coiling direction
! shifts in Globigerina pachyderma, and changes in the sedi-
| ments.
| Two distinct planktonic foraminiferal faunas alter-
i nate throughout the cores: a cold-water or Subarctic fauna
, dominated by left-coiling G. pachyderma and warmer-water or
i transitional fauna characterized by dominantly right-
! coiling G. pachyderma associated with Neogloboquadrina
I dutertrei, Globorotalia inflata, Globorotalia truncatuli-
■ noides, Globigerinoides ruber, Globigerinita humi1is and
Globigerinella siphonifera. Alternations of these two
■ faunal assemblages reflect oscillations of Subarctic and
transitional water masses in response to worldwide climatic
‘ changes during the Pleistocene. The dates of the faunal
i assemblages also correlate with known eustatic changes in
: sea level. During the deposition of the sediments in the
I cores, Subarctic water masses expanded into southern Cali-
I fornia at least twice, alternating with two periods of
; warmer-water including the present. Mean surface water
| temperatures ranged between 6° C and 20° C during this
i time, and these temperatures were never warmer than the
1 present day.
Variations in absolute numbers of planktonic forami-
nifera and radiolarians in the sediments reflect changes
in rates of sedimentation, although other ecological fac
tors such as productivity may be involved. Benthonic
foraminifera occur in greater abundance in association with
the cooler-water planktonic foraminiferal faunas and are
1 probably the result of shifting of facies due to eustatic
, lowering of sea level.
i
1
INTRODUCTION
i
Various studies of the occurrences of living plank-
i
tonic foraminifera in plankton tows and of their empty
I tests in bottom sediments have been carried out by differ-
|ent investigators since the pioneering work of Murray
(1897) . These studies revealed that most planktonic fora-
jminiferal species are restricted to certain characteristic
j temperature ranges and that their relative and absolute
i abundances change with water mass characteristics (Boltov-
;skoy, 1959; Bradshaw, 1959; Be, 1959, and in press; Kus-
tanowich, 1963; Be and Hamlin, 1967; Kennett, in press).
Because of these relationships, planktonic foraminifera
have been used extensively in the interpretation of paleo-
:climatology and paleo-oceanography, especially with respect
to the Pleistocene (Schott, 1935; Ericson and Wollin, 1956;
I
Emiliani, 1957; Bandy, 1959, 1960, and in press; Emiliani,
Mayeda and Selli, 1961; Ingle, 1967).
The purpose of this study is to describe the quanti
tative trends in the stratigraphic distribution of plank
tonic foraminifera in cores from Tanner Basin (text-figure
1). These trends should in turn be informative of past
;climatic variations and of changes in the distribution of
;water masses for the time interval represented in cores of
'this area. The study is based on three piston cores
TEXT-FIGURE 1
Location of Tanner Basin in the continental
borderland of southern California.
3
U 8o00* II9 ° 0 0 '
CONTINENTAL BORDERLAND PHYSIOGRAPHY
D E P T H S IN M E T E R S
Santo Borbaro Basin
IN S E T W ITH P O S IT IO N O F C O R E S
W IT H IN T A N N E R B A S IN
LO S A N G E L E S
x
II9°00’
\ Vo
10614
JI9°20'
0617
11343
PA C l F I C
O C E A N
3 2 °0 0 ’
N A U TIC A L M IL E S X
119*40
CONTOUR IN T E R V A L IN M ETERS
2 0
N A U T IC A L M IL E S
I2 0 °0 0 '
II9 6 00' I I 8 ° 0 0 '
5
(132 samples) used in an investigation of Holocene sedimen
tation in the same basin by Gorsline, Drake and Barnes
(1968).
Bandy (1959, 1960) and Ericson (1959) have shown
that the planktonic foraminifer, Globigerina pachyderma 1
i
(Ehrenberg), changes its coiling direction with changes in
surface water temeprature. Left-coiling (sinistral) popu-
I
lations of this species now are restricted to polar and
subpolar seas, whereas the right-coiling (dextral) popula- |
tions occur in warmer waters. This discovery is of impor- '
tance in determining past climatic and oceanographic varia
tions within the stratigraphic range of the species.
Radiometric dating on basin cores off southern California
has shown that the last shift in the coiling direction of
G. pachyderma, from sinistral to dextral, occurred 11,000
to 12,000 years B.P., marking the Pleistocene-Recent bound-i
ary (Bandy, 1960, 1967). i
Previous work |
!
General characteristics of the continental border- !
I
i
land basins were summarized by Emery (1960) and Moore |
i
(1966). Several papers have been published concerning the ,
I
distribution of benthonic and/or planktonic foraminifera ;
\
in surface sediments off the coast of California (Bandy, ^
f
1953; Resig, 1958; Zalesny, 1959; Uchio, 1960; Ingle, 1967).I
6 !
Neogene planktonic foraminiferal zonation for
southern California has been proposed by Bandy (I960, 1967)
I
based on the preferential coiling direction of Globigerina
pachyderma. It was shown that dextral populations of this
species existed off the coast of California for the last
11,000 to 12,000 years and were preceded by sinistral popu
lations during the Pleistocene except for a short dextral
occurrence within the sinistral sequence. Dextral forms
occurred in the upper Pliocene, sinistral populations in
i
the middle Pliocene, and dextral populations in the lower j
I
Pliocene. Later Ingle (1963a) and Parker (1964) noted that
the sinistral form of this species also occurs within the
upper Miocene.
Gorsline, Drake and Barnes (1968) completed a de-
I
tailed study of Holocene sedimentation in Tanner Basin. !
They observed that carbonate sedimentation rates (mean of |
I
7 mg/cm2/year) were constant for the last 17,000 years but
detrital (terrigenous) sedimentation rates underwent sig
nificant changes. As determined by radiocarbon dating,
higher rates of terrigenous sedimentation (mean of 17 mg/
cm^/year) were characteristic of the period before 7,500
years B.P. and lower rates (mean of 10 mg/cm^/year) were
characteristic of the last 7,500 years. This change in
detrital sedimentation rate was explained as the result of
a period of lower sea level prior to 12,000 years B.P., j
during which a greater exposure of land area (including the
Santa Rosa-Cortes-Tanner Bank system on the eastern margin
of the basin) provided sources for the sediment. As sea
level rose, the detrital contribution decreased during the
period 12,000 to 7,500 years B.P. In the last 7,500 years,
the major contribution of terrigenous material has been in
the form of fine suspended sediment.
A study of the calcareous nannoplankton in seven
cores from Tanner Basin was carried out by Wilcoxon (in
press). From his study, it is evident that a significant
increase in reworked Eocene nannoplankton occurred below
the 12,000 B.P. horizon in each core. This increase was
also related to a change in sea level.
Distribution of living planktonic foraminifera in
the North and equatorial Pacific was outlined by Bradshaw
(1959). This will be discussed in more detail later.
Methods of study
Samples 2 to 3 cm. long were taken at 10 cm. inter
vals in the cores for foraminiferal analysis. Since the
top few centimeters of piston cores are usually missing,
the tops of trigger cores were used for details of surface
sediments. All samples were dried and weighed and then
washed on a 250-mesh Tyler screen (61 micron openings).
Prior to counting, the samples were screened on an
8
j
88 micron screen in order to eliminate very small juvenile
,specimens whose positive identification is often difficult.
I
,A modified Otto microsplitter was used to obtain a repre-
i
|sentative split of the sample. Counts were made of an
!average of 750 specimens per sample in order to determine
I the following parameters:
1 - Percentages of sinistral and dextral forms of
j Globigerina pachyderma.
, 2 - Relative and absolute abundance of planktonic
>
Iforaminiferal species.
I 3 - Planktonic and benthonic foraminiferal numbers
I
;and radiolanan numbers per gram of dry sediment.
4 - Absolute abundance of selected benthonic species.
After counting each sample fraction, the entire
'sample was studied for minor species not present in the
counted fraction, since their presence or absence may be
:significant. A few reworked foraminifera were occasionally
encountered in the samples. Reworked planktonic forms were
easily identified by their abraded surface and yellowish
color, and were not included in the counts.
ACKNOWLEDGMENTS
Appreciation is expressed to the Iranian Oil Explo
ration and Producing Company for providing financial sup
port throughout the course of study. Dr. O. L. Bandy
9
suggested the topic and provided valuable guidance during
the investigation. The samples, along with sedimentologi-
cal data, were provided by Dr. D. S. Gorsline who, with
Dr. R. 0. Stone, critically reviewed the manuscript. The
assistance of these staff members of the Department of
Geological Sciences of the University of Southern Califor
nia is gratefully acknowledged.
The cores were collected during cruises of the Uni- j
versity of Southern California Marine Laboratory vessel, j
Velero IV, with financial support from the National Sciencej
Foundation. Radiocarbon dates were provided for core {
I
AHF-11343 by Dr. H. F. Nelson of Mobil Research and Devel- :
opment Corporation, Field Research Laboratory, Dallas,
Texas. Laboratory space and other facilities were made
available by the Allan Hancock Foundation of the University:
of Southern California. The cooperation of these organiza-i
tions is greatly appreciated. Appreciation is also ex- j
pressed for help and suggestions of Dr. J. P. Kennett, j
R. Stapleton, F. Theyer and other staff members of the
Micropaleontology Laboratory of the Allan Hancock Founda- !
tion.
i
GEOLOGY AND OCEANOGRAPHY OF TANNER BASIN
Tanner Basin is one of the outer seaward basins of
the California continental borderland. Structurally it is
a fault-controlled feature initiated in middle or late
Miocene time as a result of deformation of the contenental
margin (Emery, 1960). This basin is between latitudes
22°2 0' and 33°10' North and longitudes 119°20' and 12 0°00'
West, with maximum depth of 4180 m. along the steeper
eastern margin of the basin and of 1100 m. in the shallower
western portion. The basin is oriented northwest to south
east with a long axis of 90 km. and a short axis of 40 km.
Tanner and Cortes Banks form the eastern and south
ern wall of the basin. Dredge samples collected from these
banks contained boulders of siliceous shales, metamorphic
rocks and of a sandy siltstone containing radiolarians of
mid-Miocene and possibly late Miocene time (Gorsline, Drake
and Barnes, 1968). Basaltic rocks of the upper part of the
Patton Escarpment to the west, along with northern and
southern sills (at depths of 1100 and 1000 m. respectively)
form the other boundaries of the basin.
Along the coast of California, the southward moving
waters are known as the California Current, part of the
great clockwise circulation of the North Pacific Ocean.
Influenced by prevailing westerlies, the Subarctic Current
(Aleutian Current) at high latitudes flows eastward and
divides into two branches before reaching the American
coast (Sverdrup, Johnson and Fleming, 1942). The smaller
stream turns northward into the Gulf of Alaska, and the
larger portion of the current turns southeastward to become
the California Current, which is characterized by low tem
perature, low salinity, high oxygen and high phosphate.
These characteristics are typical of Subarctic water masses.
The current becomes warmer southwards until 25° N. where it
becomes part of the west-flowing North Equatorial Current
(text-figure 2).
The detailed oceanography of the area off southern
California is given by Sverdrup and Fleming (1941) . They
reported a deep counter current below 200 m. along the
coast, carrying large quantities of warmer and more saline
Equatorial Water northward. During the fall and early
winter, when the north winds are weak or absent, this cur
rent is at the surface as the Davidson Current, flowing
towards the north on the coastal side of the California
Current as far north as latitude 48°.
The predominance of northwesterly winds in the
spring and summer causes an offshore transport of surface
water and is an important factor in the development of
coastal upwelling (Reid, Roden and Wyllie, 1958) which
produces complex oceanographic conditions in certain areas.
TEXT-FIGURE 2
Generalized surface current circulation and
summer surface temperature (C°) in the North
Pacific. Adapted from Sverdrup, Johnson and
Fleming (1942) and Bradshaw (1959).
13
1 8 0 * IS O * l«0 * 1 4 0 *
So
Ko
No
No
Ec
1 0 0*
SURFACE CURRENTS CIRCULATION
As Alaska Current Ne North E quatorial Current
C f C alifornia Current Np North P a cific Current
Ec Equatorial Counter C urrent Sa S ubarctic Current
Ks Kuroshio C urrent
GENERALIZED SEA SURFACE TEMPERATURE (°C)
14
Upwelling returns nutrients to the euphotic zone and thus
increases surface plankton productivity.
SEDIMENTOLOGY
The most complete sedimentological data on the Tan
ner Basin are presented by Gorsline, Drake and Barnes
(1968), and most of the data given below are from their
work. Inasmuch as the present study is concerned primarily
with the stratigraphic distribution of planktonic forami
nifera in the cores, a detailed discussion of sedimentation
is not presented here.
Surface sediments throughout most of the area con
sist of light olive-gray clayey silt with a uniform mean
grain size of about 8 microns in the central part of the
basin and with coarser sediments (mean diameters of 16 to
32 microns) on the surrounding slopes. Mean diameters
throughout the cores (exclusive of turbidites) are rela
tively constant (6-10 microns) and show no significant
pattern. The coarse fraction (>61 microns) consists mainly
of foraminiferal tests (90-95 per cent), Radiolaria, sponge
spicules and small amounts of terrestrially derived sands.
Turbidites were absent in all three of the cores which were
studied. However, the 380-430 cm. section of Core AHF-
10614 may be the result of a turbidity current, inasmuch as
most of the foraminifera were crushed and discolored.
Carbonate content of surface sediment is high, but
values vary down-core. As shown in text-figure 3, carbon
ate content is relatively high in the upper part of the
cores, diminishing to a minimum at about 11,000-12,000
i
years B.P., when the last shift in coiling direction of (
G. pachyderma ocurred. At the base of the layer of uni- 1
i
formly high carbonate content in cores from different parts|
of the basin, radiocarbon dates give an age of about 7,500 ,
years B.P. Below the Pleistocene-Recent boundary, values '
are low and almost constant, except for a restricted peak .
which in one core (AHF-11343) coincides with a Carbon-14 i
date of 32,900 years B.P. j
Superimposed on the carbonate curves are the curves '
of total planktonic foraminiferal numbers. A general cor
relation exists between these two parameters, except for
the uppermost parts of the cores, indicating that tests of |
planktonic foraminifera are the main factor controlling the|
carbonate content of the sediment. The differences between 1
carbonate content and foraminiferal numbers at the tops of
the three cores are due to reworked foraminifera which are
not included in the counts, and due to the increase in j
abundances of indigenous calcareous nannoplankton in the |
F
tops of the cores (Wilcoxon, personal communication). ;
The segments of the cores with high carbonate con- <
J
tent are generally far removed from sources of terrigenous j
sediments and are almost completely composed of tests of ■
TEXT-FIGURE 3
Percentage of calcium carbonate (after Gorsline
et al., 19 68) and planktonic foraminiferal num
bers in Cores AHF-10617, 10614, and 11343. The
change in coiling direction of G. pachyderma
(Ehrenberg) from sinistral (Pleistocene) to
dextral (Recent) is the basis for designation
of the 11,000 years B.P. datum. Numbers to the
right of the cores are corrected radiocarbon
dates.
17
18
PERCENT C«CO|
AHF 10617
AHF 10614
PERCENT CoCOj OF ORY WEIGHT SEDIMENTS.
PLANKTONIC FORAMINIFERA PER GRAM OF SEDIMENTS.
19
planktonic foraminifera. This is reflected in the color
of the sediments as shown in the upper part of Core AHF-
11343 (Plate 1). The boundary between the colors in this
core segment coincides with the drop in the carbonate
curve.
PLATE 1
Part of the upper portion of Core AHF-11343.
The light color in the upper segment of the
core is caused by very high numbers of
planktonic foraminifera.
2 0
21
PLATE 1
Cm.
I
123
133
143
PLANKTONIC FORAMINIFERAL ANALYSIS
Two assemblages of planktonic foraminifera were rec
ognized in the cores of Tanner Basin: (1) a cold-water or
Subarctic fauna characterized by dominantly left-coiling
Globigerina pachyderma; and (2) a warmer water or transi
tional (temperate) fauna characterized by dominantly right
coiling G. pachyderma and by Neogloboquadrina dutertrei,
Globigerinoides ruber, Globorotalia truncatulinoides,
Globorotalia inflata, Globigerinita humi1is, and Globige-
rinella siphonifera.
Associated with both groups are Globigerina quinque
loba, Globigerina bulloides, Globigerinita uvula, Globige
rinita glutinata, Globigerinita iota, Globorotalia scitula
Globoquadrina hexagona, and "Orbulina" chambers. Figures
of all these species have been presented and their taxono
mies discussed by Parker (1962) and Bradshaw (1959).
Text-figures 4-6 show the absolute abundance of the
most important planktonic foraminiferal species in Cores
AHF-10617, AHF-10614 and AHF-11343 respectively. Dextral
and sinistral zones of G. pachyderma are superimposed on
the frequency curves of G. pachyderma and N. dutertrei.
The change from sinistral to dextral in the upper portion
of the cores occurred at 11,000 B.P., the Pleistocene-
Recent boundary. A second dextral zone appears in the
lower portion of two cores. This zone is absent in Core
TEXT-FIGURE 4
Absolute abundances of the most important plank
tonic foraminiferal species in Core AHF-10617.
Dextral and sinistral zones of Globigerina
pachyderma (Ehrenberg) are superimposed on the
frequency curves of G. pachyderma and Neoglo-
boquadrina dutertrei (d'Orbigny).
23
AHF 10617
-5 0
' N. DUTERTREI
— SINISTRAL---------
-8 0
DEX
0
-5 0
G. HUMILtS
-100
-150
: \
r
G. TRUNCATULINOIDES \
- 5 0
1
- 8 0
-5 0
G. RUBER
-8 0
0
-5 0
ORBULINA
-8 0
N C E N T I M E T E R S
O
-2000
G. PACHYDERMA
-5 0 0 0
SINISTRAL DEXTRAL
c
-2000
- 6 0 0 0
G . QUINQUELOBA
-10000
-2000
G. UVULA
-4 0 0 0
0
2000
G. BULLOIDES
GRAM
TEXT-FIGURE 5
Absolute abundances of the most important plank
tonic foraminiferal species in Core AHF-10614.
Dextral and sinistral zones of Globigerina
pachyderma (Ehrenberg) are superimposed on the
frequency curves of G. pachyderma and N. duter
trei (d'Orbigny).
25
CORE LENGTH C E N T I M E T E R S
G. PACHYDERMA
|»SIN .V-^—4*DEX.*j«-----------------------------SINISTRAL-
'-2000
•5000
•DEXTRAL*
>
X
T |
o
0)
-2000
5000
QUINQUELOBA
- 1 0 0 0 0
0
-2000
G. UVULA
-5 0 0 0
0
-2000
BULLOIDES
N>
-50
N. DUTERTREI
- 1 0 0
-150
SINISTRAL-
X
- 5 0
• -----------------------
G. TRUNCATULINOIDES
- 5 0
- 1 0 0
RUBER
-150
-200
ORBULIN A
- 1 0 0
L Z
TEXT-FIGURE 6
Absolute abundances of the most important plank
tonic foraminiferal species in Core AHF-11343.
Dextral and sinistral zones of Globigerina
pachyderma (Ehrenberg) are superimposed on the
frequency curves of G. pachyderma and N. duter
trei (d'Orbigny).
CORE LEN GT H IN C E N T I M E T E R S
o >
-2000
PACHYDERMA
- 5 0 0 0
S IN IS T R A L D E X T R A L " - S I N I S T R A L
- 0
-2000
- 5 0 0 0
QUINQUELOBA
-10000
-2000
UVULA
5 0 0 0
= -0
BULLOIDES
2000
to
■ S C O
NUMBER O F SPECIMENS PER GRAM
ro
- 5 0
DUTERTREI
-S IN . — DEXTRAL -100.
0
HUM I LIS
100
0 s
TRUNCATULINOIDES
20
G. RUBER
80
-20
ORBULIN A
- 4 0
u>
o
AHF 11343
31
I
• AHF-10617 because it lies below the depth of penetration
'of this core. Between these two dextral zones, sinistral
i forms of G. pachyderma are dominant; however, a minor de-
i
crease in the percentage of sinistral forms occurs within
the sequence as shown in the coiling ratio curves of G.
pachyderma (text-figure 7). This decrease occurs in most
cores within the California Borderland basins (Bandy, 1960)
<
| at a level dated by the radio carbon method at about 17,000
r
B.P. Similar alternating dextral and sinistral coiling
1 changes in G. pachyderma also were reported by Jenkins
(1967) from the Pleistocene of New Zealand.
Globigerina pachyderma is one of the most abundant
species, and throughout most of the length of cores it makes
; up 30 to 40 per cent of the total planktonic foraminiferal
j assemblage. However, a significant increase in frequency,
I to about 70 per cent, occurs at a horizon in the cores imme-
i
! diately above the second dextral coiling zone (text-figure 7).
The number of specimens of G. pachyderma per gram
of dry sediment (absolute abundance) also shows significant
I
i
trends. On all three cores, values for the segments above
i the Pleistocene-Recent boundary are much higher (average
5,000 specimens) than the values below this boundary (aver-
age 2,500) except in one core (AHF-10614). In this core,
a horizon of high values (8,000 specimens) occurs at the
base of the core. This horizon was absent from Core AHF-
! 11343, and Core AHF-10617 did not penetrate to this depth.
! 32 |
i
■ Globigerina quinqueloba Natland is another common
! species, making up 30 to 40 per cent of the total planktonic
| foraminiferal assemblage throughout most of the length of ■
!the cores. Although its relative abundance varies, its
i frequency is higher in the right-coiling zones of G. pachy- I
' derma. Trends in absolute abundance of G. quinqueloba show
i
| a well-developed pattern. High numbers of specimens (13,000-
i
|19,000 per gram) occur in the Recent core segments while
i
jnumbers are greatly reduced (2,000-3,000 per gram) below
i
; the Pleistocene-Recent boundary. In Core AHF-10614, there 1
\ ,
I is a second large increase in numbers of G. quinqueloba, j
I '
!occurring in the lowest segments of the core, immediately j
I i
below the second dextral zone of G. pachyderma. A similar
i —
but much smaller increase occurs in Core AHF-11343, but in
this core the increase coincides with the coiling shift.
I
The difference in magnitude between the two increases may |
I
(be caused by higher sedimentation rates in the vicinity of j
Core AHF-11343 while the difference in the stratigraphic
horizon of occurrence may be due to reworking by organisms. ;
t
It should be noticed that this latter difference represents i
i
I less than 15-20 cm. of core length. j
Coiling ratios of G. quinqueloba are variable and
i
dextral and sinistral varieties occur in approximately
equal proportions throughout the cores.
Distribution of Globigerinita uvula (Ehrenberg) |
throughout the cores varies, but on the average this species j
33
1 makes up about 10 per cent of the total population. Its
]greatest abundance (40 per cent) was recorded in Core AHF-
I
11343 within the lower zone of dextral G. pachyderma.
Globigerina bulloides d'Orbigny usually comprises
less than 10 per cent of the fauna throughout the cores.
Forms similar to Globigerina falconensis Blow were encoun
tered randomly in the samples. However, due to morphologi
cal intergrading between the two species, G. falconensis
was included in counts of G. bulloides.
No apparent trends were found in the coiling direc
tion of G. bulloides. Throughout the cores, populations
ihave coiling ratios ranging between 60 and 80 per cent
sinistral. The same trends in the number of specimens per
gram, which were noted above for G. pachyderma and G. quin
queloba, also apply to G. bulloides.
Neogloboquadrina dutertrei (d'Orbigny) is an uncom-
|inon species, never making up more than 6 per cent of the
jpopulation, although it does occur within the right-coiling
jzones of G. pachyderma (text-figures 4-6). This form also
!is occasionally present within the left-coiling sequence,
i •
where the left-coiling ratio is 60-70 per cent. It is of
I interest to note that though this species is usually re
stricted to the right-coiling zones, its greatest abundance
(100-27 0 specimens per gram) occurs- above the Pleistocene-
Recent boundary. Coiling direction is 99-10 0 per cent
idextral and none of the specimens had umbilical teeth.
The name Neogloboquadrina dutertrei has been tenta-
34
tively used in synonymy with Globigerina eggeri Rhumbler,
Globigerina subcretacea Lomnicki and Globoguadrina duter
trei (d'Orbigny). There appear to be morphological simi
larities between this species and right-coiling G. pachy-
^ i
derma and, as Be (in press) noted, it is possible that a ;
continuous gradient exists from sinistral coiling to dex-
tral coiling populations of G. pachyderma and that the
latter grade into N. dutertrei. However, more evidence is ,
i
needed before conclusions can be drawn. The generic as
signment follows the usage of Bandy, et_ a^. (1967) . !
Globigerinita humilis (Brady) and Globorotalia trun-
catulinoides (d'Orbigny) are rare (<1 per cent) and show
the same trends as N. dutertrei. Both species occur within
the right-coiling zones of G. pachyderma and usually have
their maximum abundance above the Pleistocene-Recent
boundary. There are too few specimens of G. truncatuli-
nojdes to give significant coiling direction ratios.
Globigerinoides ruber (d'Orbigny) and "Qrbulina"
chambers are rare (<1 per cent) but persistent throughout
the length of the cores. Their highest frequencies (100-
200 specimens per gram) occur within the right-coiling
zones of G. pachyderma (text-figures 4-6).
Globorotalia inflata d'Orbigny is either rare (<1
per cent) or absent in most parts of the cores. As shown
in text-figure 7, this species occurs within the right-
i
coiling zones of G. pachyderma and is usually absent within j
!the left-coiling sequences. Although there were too few
specimens to give significant coiling ratios (100 speci
mens) , all the specimens observed were coiled sinistrally.
Globigerinita glutinata (Egger) has a relatively
i i
i uniform and continuous distribution throughout the length ,
!of the cores, with frequencies ranging from 2 to 5 per cent
1 of the total planktonic foraminifera. Although no measure-;
ments were undertaken, forms of this species associated
with the left-coiling form of G. pachyderma appear to be
1 larger than those associated with dextral G. pachyderma.
! Globorotalia scitula Brady and Globigerinita iota j
| i 1
I Parker are found throughout the cores, but their individual|
■ i
' frequencies are seldom more than 1 per cent of the total pop
ulations. A few specimens resembling Globorotalia hirsuta
(d'Orbigny) were also noticed, but due to uncertainty of
identification they were included in counts of G. scitula.
< Globorotaloides hexagonus (Natland) is a very rare
(
i
species and its frequency never exceeds more than 1 per 1
cent of the total population. It occurs in most parts of
the cores, but it is more abundant within the right-coilingi
t
, zones of G. pachyderma. |
i
Globigerinella siphonifera (d'Orbigny), Globigeri-
noides conglobatus (Brady) and Globorotalia menardii
>
1 (d'Orbigny) are extremely rare. Only a few specimens of
these species were observed, all within the right-coiling
! !
i i
| zones of G. pachyderma. i
PALEO-OCEANOGRAPHIC VARIATIONS '
I
Any attempt to explain changes in past climatic and I
oceanographic variations by using planktonic foraminifera |
j requires a preliminary examination of distribution trends i
I I
'in modern assemblages and relationships between such assem-■ ;
1blages and present oceanographic conditions.
The distribution of living planktonic foraminifera
in the North and equatorial Pacific was described by Brad-
1shaw (1959) who divided the species present into three gen- !
eral groups: a northern cold-water or Subarctic fauna, a ' ■
I j
transitional fauna, and a southern or warm-water fauna. j
i i
The cold-water or Subarctic fauna is characterized
i
!by G. pachyderma, G. quinqueloba, G. bulloides, G. uvula,
I
j (Globigerinoides cf. G. minuta of Bradshaw) and G. gluti- ^
I
nata, species which are generally found north of the Sub-
i
I arctic Convergence at 40°-45° N. latitude. When the con-
I
•vergence is not distinct, the 15° surface summer isotherm i
,(text-figure 2) marks the southern boundary of this fauna.
1 The transitional fauna contains a mixture of the
I Subarctic fauna and the southern warm-water faunas. The
i
I
most common species are G. quinqueloba, G. bulloides, large j
'specimens of G. eggeri (N. dutertrei of this paper), G.
f ,
jruber and Orbulina universa. Northern and southern limits
■ of this fauna are marked by the 15° and 20° C summer \
37
isotherms respectively.
The warm-water fauna is divided into two subassem
blages: (1) a central-water assemblage, characterized by
— • inflata and G. truncatulinoides, which occurs in the
Central Water masses (as defined by Bradshaw) of the North
Pacific. These species are not present in the surface
water of the equatorial region. (2) An equatorial west-
central assemblage, consisting of those species confined to
water of the most tropical character, and which includes
Globigerina conglomerata, Globorotalia tumida, Pulleniatina
obliguiloculata and Sphaeroidinella dehiscens.
Associated with both subassemblages are G. hirsuta,
G. scitula, G. menardii, G. conglobatus, G. ruber, G.
sacculifera, G. hexagonus, G. glutinata, G. siphonifera (G.
aequilateralis of Bradshaw), Candeina nitida, Hastigerina
pelagica and Hastigerinella rhumbleri. The 20° C summer
isotherm marks the northern and also presumably the south
ern extent of the warm-water fauna in the North and South
Pacific. According to Bradshaw, the distribution of most
species shows a general agreement with latitude, but an
even better correlation exists with sea surface tempera
tures .
No report was provided by Bradshaw on the coiling
direction of G. pachyderma. However, the change from domi
nantly sinistral to dominantly dextral populations today
occurs at about 45° N. latitude for the eastern North
Pacific (Ingle, 1967), so that right-coiling G. pachyderma
( is largely confined to the transitional zone. Furthermore,
'this change in coiling direction coincides with the 15° C
I '
summer isotherm (Enbysk, personal communication). It
! i
■ should be remembered that the boundary between these sinis- j
i
tral and dextral populations is gradational and currents,
i
divergences and convergences play an important role in I
shaping the species distribution. For example, the Cali-
jfornia Current carries the dextrally coiled transitional j
faunas southward to about 20°-25° N. latitude.
Text-figure 7 shows the cummulative frequencies of
'common planktonic foraminiferal species, coiling ratio
|changes of G. pachyderma, and stratigraphic ranges of the
|less common planktonic foraminiferal species within Cores
AHF-10617, AHF-10614 and AHF-11343. As is shown, G. pachy- j
derma, G. quinqueloba, G. bulloides and G. uvula are the 1
dominant species throughout the cores. However, the upper j
I
zones of the three cores are characterized by a transitionali
fauna which includes dominantly dextral G. pachyderma and '
I !
!low abundance of N. dutertrei, G. humilis, G. ruber, G. 1
; truncatulinoides and G. inflata. There is a change from
this fauna to the Subarctic fauna of Bradshaw (character
ized by colder water species such as left-coiling G. pachy
derma) below the Pleistocene-Recent boundary. This change ,
TEXT-FIGURE 7
Cummulative frequencies of dominant planktonic
foraminiferal species, coiling ratio changes of
Globigerina pachyderma (Ehrenberg) and strati-
graphic changes of the less dominant planktonic
foraminiferal species within Cores AHF-10617,
10614, and 11343. The upper solid line repre
sents the Pleistocene-Recent boundary. The lower
solid line marks the correlation of the Pleisto
cene segments in Cores AHF-10614 and 11343.
39
C O R E L EN G T H I N
8
CENTI M ETERS
8
------
>
X
\ G. PACHYDERMA /
~ n \ # v .
o
c r > \
\ G. QUINQUELOBA
///////M IS C . S P E C IE S /
GLOBIGERINITA GLUTINATA -------------
GLOBOROTALIA SCITULA ---------------
"ORBULINA" CHAMBERS ---------------
GLOBIGERINITA IOTA ---------------
GLOBOROTALOIDES HEXAGONUS--------------
GLOBIGERINOIDES RUBER -------
NEOGLOBOQUADINA DUTERTREI -
GLOBOROTALIA IN PLATA
G. TRUNCATULINOIDES
GLOBIGERINITA HUMILIS
o
£
0 2
C *»
1 5
Z -a
>
X
~ n
o
g >
GLOBIGERINITA GLUTINATA
GLOBOROTALIA SCITULA
"ORBULINA" CHAMBERS
GLOBIGERINITA IOTA
GLOBOROTALOIDES HEXAGONUS
GLOBIGERINOIDES RUBER
NEOGLOBOQUADRINA DUTERTREI -
GLOBOROTALIA INFLATA
G. TRUNCATULINOIDES
GLOBIGERINITA HUMILIS
GLOBIGERINELLA SIPHONIFERA
GLOBOROTALIA MENARDII
GLOBIGERINOIDES CONGLOBATUS
BULLOIDES
G. PACHYDERMA
G. QUINQUELOBA
UVULA
MISC. SPECIES
>
X
~ n
m
*
OJ
u i o
G. BULLOIDES
G . PACHYDERMA
G . QUINQUELOBA
G. UVULA
' Z T Z Z z z Z Z Z Z Z Z Z A
/M IS C . SPECIES
GLOBIGERINITA GLUTINATA------------------
GLOBOROTALIA SCITULA ------------------
"ORBULINA" CHAMBERS ------------------
GLOBIGERINITA IOTA ------------------
GLOBOROTALOIDES HEXAGONUS
GLOBIGERINOIDES RUBER
NEOGLOBOQUADRINA DUTERTREI
GLOBOROTALIA INFLATA
G. TRUNCATULINOIDES
GLOBIGERINITA HUMILIS
GLOBIGERINELLA SIPHONIFERA
41 ;
is best illustrated by the coiling direction of G. pachy
derma which down the cores abruptly switches from dextral
to sinistral in the absence of temperate fauna.
Below the Pleistocene-Recent boundary, left-coiling
G. pachyderma with its associated fauna remains dominant.
G. pachyderma reaches its maximum frequency (average 65 per.
cent of the total population) and then changes its coiling ;
direction to give the second dextral zone in Cores AHF- ;
10614 and AHF-11343. Temperate species, including N. j
i
dutertrei, G. truncatulinoides, G. humilis, G. ruber and ;
G. inflata, appear in low abundance after their absence
during the predominance of the Subarctic fauna. Further- j
more, some warm-water species such as G. menardii, G. con-
globatus and G. siphonifera were observed occasionally
within the temperate fauna. However, these species are rare
and their presence may not be signigicant. Below this tem
perature zone G. pachyderma again changes coiling direction
from dextral to sinistral. Simultaneously, the temperate
fauna disappears and G. pachyderma increases in abundance. :
According to Bradshaw (1959) the region offshore
from southern California today is occupied by a transitional
i
planktonic foraminiferal assemblage, separating dominantly
Subarctic faunas to the north and warm temperate faunas to
the south. The observed alternations of transitional and
Subarctic planktonic foraminiferal faunas within the Tanner;
Basin cores is attributed to the result of northward and
southward migration of Subarctic and transitional water
masses and their respective planktonic faunas. The inva
sion of the Subarctic fauna into the southern California
region in response to significant cooling during the Pleis
tocene previously has been shown by Bandy (1967). During
glacial periods, the Subarctic fauna, characterized by a
sinistral coiling population of G. pachyderma, extended
further south off the southern California region. Con
versely, during periods of glacial retreat, the transi
tional fauna occurred off southern California as it does
today. Fowler and Duncan (1967) examined long deep-sea
sediment cores off Oregon and found that G. pachyderma is
dominantly sinistral throughout the entire length of the
cores, representing the last 50,000-70,000 years. At no
horizon in the cores did they find a transitional fauna and
thus transitional water masses with their characteristic
fauna never extended as far north as the coast of Oregon
during the time of deposition of the sediment of the cores.
The cores examined for Tanner Basin show that there
were at least two periods of Subarctic surface water tem
peratures during late Pleistocene and Recent time. The
absence, in the Tanner Basin cores, of the warm-water fauna
of Bradshaw (1959) which is characteristic of temperatures
above 20° C shows that surface water temperatures were at
43
no time during deposition of the cores warmer than those
of the present day. Furthermore, the absence of an Arctic
planktonic fauna, composed entirely of G. pachyderma
(sinistral) implies that the surface water temperature was
not at any time less than 6° C. Mean surface water temper
atures have thus ranged between 6° and 20° C during the
glacial advances and retreats which are represented in the
Tanner Basin cores. These values agree reasonably well
with the paleotemperature curve obtained from oxygen iso
tope ratios at planktonic foraminiferal tests from other
cores of the same basin (Gorsline and Drake, in prepara
tion) .
DISCUSSION
Comparisons of rates of sedimentation and trends in
absolute abundance of planktonic foraminiferal species in
the cores of Tanner Basin reveal that certain general rela
tionships exist between these two parameters. As noted
earlier, for most species high numbers of specimens per
gram of sediment occur within the Recent portions of the
cores, with lower values occurring below the Pleistocene-
Recent boundary. These low values remain constant for most
portions of the cores except for the second dextral zones
of G. pachyderma, where the number of specimens per gram
increases although usually not to the high values of the
Recent parts of the cores.
Radiolarians showed the same trends as the plank
tonic foraminifera, being abundant (300-1,000 specimens per
gram) in the tops of the cores and diminishing (10-20
specimens per gram) below the Pleistocene-Recent boundary
(text-figure 8). This trend has been reported for the ma
jor offshore basins by Bandy (1967). A minor increase in
the number of radiolarians per gram was also noticed in
Core AHF-11343 within the second zone of G. pachyderma.
A considerable change in the number of remains of
planktonic faunas in an undisturbed stratigraphic sequence
is a function either of the rate of sedimentation, or of
44
TEXT-FIGURE 8
Abundances of radiolarians in specimens per
gram of sediment.
45
46
R A D IO LA R IA N S PER GRAM
§ °
8 2
7“"
100-
u j 200-
300-
400 -
_ i
AHF 10614
500 -
AHF 10617
AHF 11343
600 -
700 -
47
the rate of surface plankton productivity. From studies of
sedimentation in Tanner Basin, Gorsline (1967) concluded
that carbonate sedimentation rates were nearly constant
during the time represented by deposition of the cores but
that terrigenous sedimentation rates have varied signifi
cantly. Gorsline also reported a converse relationship
between detrital sedimentation rate and carbonate content
of the sediments. The rate of detrital contribution was
low during the high peak in the carbonate curve at 32,900
B.P., then increased until it reached a high value at about ,
12,000 years ago, decreasing again to a minimum at 7,500
years B.P., remaining low to the present. Furthermore,
Uchupi and Emery (1963), in a study of deep-sea cores of
the continental slope and rise off southern California,
stated that sedimentation rates were eight times higher
during the late Pleistocene than in the Recent.
Thus, it seems reasonable to assume that the abso
lute abundances of planktonic foraminifera and radiolarians .
in the sediments is controlled to a large extent by sedi
mentation rates. The high number of specimens per gram in I
the upper portions of the cores and within the second dex-
tral zones of G. pachyderma are due to the lower sedimenta
tion rates, whereas the low numbers in those Pleistocene
segments associated with left-coiling G. pachyderma are 1
caused by a considerably higher rate of sedimentation.
48
However, it should be remembered that the only occurrences
of certain rare temperate species such as N. dutertrei, G.
truncatulinoides, G. humilis, G. inflata and G. siphonifera
are within right-coiling zones of G. pachyderma, whereas
these species are absent from the left-coiling zones. This
cannot be due to dilution by the sediments, but is the re
sult of changes in water mass boundaries. Similar changes
in planktonic foraminifera during the late Pleistocene and
Recent have been reported by Caralp (1967) in a core from
the Bay of Biscay. The core was taken in 1800 m., at the
base of the continental slope at 45°09' N. and 3°23' W.
The same temperate fauna which occurs in the Tanner Basin
cores was found in this core where, as in Tanner Basin, it
is restricted to the right-coiling zones of G. pachyderma
and is absent within the left-coiling zone.
Although it seems likely that rate of sedimentation
is the main factor controlling species abundances, there
are a number of exceptions. The top 2 0 cm. in all three
cores are characterized by very low numbers of planktonic
foraminifera, indicating the effects of factors other than
sedimentation rates. Trends in the number of total ben-
thonic foraminifera also showed a converse relationship to
the sedimentation rate as will be discussed later.
Changes in terrigenous sedimentation rate for the
last 12,000 years in Tanner Basin have been correlated by
49
Gorsline et al. (1968) with the curves of sea level varia
tion summarized by Curray (19 61), and by Shepard and Curray
(1967). Both these authors have shown that prior to 30,000
B.P., sea level began to rise from a low level, reaching
-20 ± 4 m. from the present level at about 30,000 B.P. Sea
level then dropped to -125 m. approximately 18,000 to
20,000 B.P. in response to major ice advances, then rose to
-15 m. at 7,000 B.P. and reached present levels about 3,000
years ago. It appears that the second dextral zone of G.
pachyderma, which is characterized by a relatively low
detrital sedimentation rate, high carbonate content and
temperate faunas, can also be correlated with the high
stand of sea level at the 30,000 B.P. interstadial. Sup
port for this concept comes from the Carbon-14 date of
32,900 years at the 640-650 cm. interval in Core AHF-11343.
Thus, in the Tanner Basin cores, the two periods character
ized by Subarctic fauna are synchronous with periods of
glacial advance, high detrital sedimentation and low stands
of sea level, whereas the two warm phases, characterized
by temperate fauna, are synchronous with waning glaciation,
lower detrital sedimentation and high stands of sea level.
BENTHONIC FORAMINIFERA 1
Although the major investigation was concerned with ;
I
planktonic species, some observations were made on the
benthonic foraminifera. Benthonic populations are present j
throughout the cores, usually comprising less than 20 per i
cent of the total foraminiferal population. Among the most
significant species are:
|
Uvigerina peregrina Cushman
Uvigerina hispida Schwager I
i
Bulimina striata mexicana Cushman i
Bulimina subacuminata Cushman and Stewart j
Cassidulina delicata Cushman
Cassidulina californica Cushman and Hughes
Cassidulina limbata Cushman and Hughes
Epistominella pacifica smithi (R. E. and K. C. '
Stewart) j
Valvulineria araucana (d'Orbigny) '
Gyroidina altiformis R. E. and K. C. Stewart
Hoeglundina elegans (d'Orbigny) j
I
Bolivina sp.
_____ (
1
Trends in the number of total benthonic foraminifera I
(text-figure 9) showed converse relationships to the sedi
mentation rate. High numbers of specimens per gram occur
below the Pleistocene-Recent boundary, whereas low values
occur in the Recent parts of the cores. This is best
TEXT-FIGURE 9
Abundances of benthonic foraminifera in
specimens per gram.
51
52
NUMB ER OF BENTHONIC FORAMINIFERA
IIOOO
100 100
YRS BP
IIOOO YRS BP
200 - 200
300
AHF 10617
400
500-
AHF 10614
PER G RA M
1 0 0 -
1 1 0 0 0
YRS BP
200-
300-
400-
500-
600-
700-
AHF 11343
53
reflected in the number of specimens per gram of Uvigerina
peregrina (text-figure 10) which makes up 30 to 40 per cent
of the total benthonic foraminifera below the Pleistocene-
Recent boundary.
Uvigerina peregrina has an upper limit of occurrence
of 100 ± 50 m. in most oceanic areas (Bandy and Chierici,
1966) and its lower depth boundaries vary from place to
place. Off southern California, this species ranges
through the upper and middle bathyal zones, but its highest
frequencies usually occur below 1,000 m. The three cores
which were studied in this investigation were taken at
about 1,200 m. depth of water. A possible explanation for
low numbers of specimens per gram of U. peregrina within
the Recent part of the cores could be the high stands of
sea level which change the depth of greatest abundance of
this species during this time. However, this is specula
tion and other factors may be involved.
Random occurrences of species which have been dis
placed from shallow depths were noticed throughout the
cores. These displaced specimens are much more abundant
within the Pleistocene segment of the cores. Other dis
placed specimens occur and are often difficult to identify,
sometimes resulting in higher figures for populations than
is in fact the case. Finally, changes in environmental
factors such as nutrients may also account for the high
0
TEXT-FIGURE 10
Abundances of Uvigerina peregrina in
specimens per gram.
54
55 GRAM
IIOOO YRS BP
AHFI1343
O F S P E C IM E N S PE
IIOOO YRS BP
AHF 10614
v >
01
LJ
t-
UJ
IIOOO YRS BP
100“
z
u
o
z
200-
U J
_i
300 -
U J
oc
o
o
AHFI06I7
56
values of total benthonic foraminifera within the Pleis
tocene segments.
CONCLUSIONS
1 - Two distinct assemblages of planktonic forami
nifera are recognized in piston cores from Tanner Basin; a
cold-water, or Subarctic fauna characterized by dominantly
left-coiling G. pachyderma and a warm-water, or transi
tional fauna characterized by dominantly right-coiling G.
pachyderma associated with N. dutertrei, G. ruber, G. in-
flata, G. truncatulinoides, G. humilis and G. siphonifera.
2 - Alternations of these Subarctic and transitional
foraminiferal assemblages within the length of the cores
reflect a series of oscillations of Subarctic and transi
tional water masses in response to worldwide climatic
changes. During glacial periods the Subarctic fauna oc
curred off southern California, whereas the transitional
fauna prevailed during periods of glacial retreat. During
late Pleistocene to Recent time there were at least two
periods characterized by Subarctic water temperatures, and
two periods of temperate surface water temperatures off
southern California.
3 - The planktonic foraminiferal faunas throughout
the cores indicate that surface water temperatures were
never warmer than those of the present, during the periods
of time represented by the cores. Mean surface water tem
peratures ranged between 6° C and 20° C during this period.
57
' 58
4 - Absolute abundances of planktonic foraminifera
i
:and radiolarians in the sediments are controlled mainly by
I
the sedimentation rate. However, other factors such as
|productivity variations are known to be important in some
i cases.
5 - Planktonic foraminiferal faunal variations
throughout the cores correlate with eustatic changes of sea
level summarized by Curray (1961), and Shepard and Curray
(1967). The two periods characterized by Subarctic faunas
are synchronous with low stands of sea level. The two
warm periods, characterized by temperate faunas, are syn-
' chronous with high stands of sea level.
6 - Benthonic foraminiferal numbers are generally
much higher within the section of cores characterized by
i cooler-water planktonic assemblages. High benthonic num-
1 bers are probably the result of shallowing of facies due to
! eustatic lowering of sea level, increasing the standing
crops of benthonic forms.
i
i
i
R E F E R E N C E S
59
REFERENCES
Bandy, O.L.
1953
1959
1960
1967
(in press)
Bandy, O.L.
1966
Bandy, O.L.
1967
Be, A.W.H.
1959
(in press)
- Ecology and paleoecology of some California
foraminifera; Part I - The frequency distribu
tion of Recent foraminifera off California.
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Creator Kheradpir, Ahmad (author)

Core Title Foraminiferal trends and paleo-oceanography in Late Pleistocene-recent cores, Tanner Basin, California

Contributor Digitized by ProQuest (provenance)

Degree Master of Science

Degree Program Geological Sciences

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

Tag Marine Geology,OAI-PMH Harvest,paleontology

Language English

Permanent Link (DOI) https://doi.org/10.25549/usctheses-c30-115561

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