Download ghosts of oceans past: analysis of microfossils from deep

GHOSTS OF OCEANS PAST: ANALYSIS OF MICROFOSSILS
FROM DEEP OCEAN SEDIMENTS
A Senior Scholars Thesis
by
REGINA LEA PERRY
Submitted to the Office of Undergraduate Research
Texas A&M University
in partial fulfillment of the requirements for the designation as
UNDERGRADUATE RESEARCH SCHOLAR
May 2006
Major: Wildlife and Fisheries Science
GHOSTS OF OCEANS PAST: ANALYSIS OF MICROFOSSILS
FROM DEEP SEA SEDIMENTS
A Senior Scholars Thesis
by
REGINA LEA PERRY
Submitted to the Office of Undergraduate Research
Texas A&M University
in partial fulfillment of the requirements for designation as
UNDERGRADUATE RESEARCH SCHOLAR
Approved by:
Research Advisor:
Associate Dean for Undergraduate Research:
Deborah Thomas
Robert C. Webb
May 2006
Major: Wildlife and Fisheries Science
iii
ABSTRACT
Ghosts of Oceans Past: Analysis of Microfossils from Deep Sea Sediments (May 2006)
Regina Lea Perry
Department of Wildlife and Fisheries Science
Texas A&M University
Research Advisor: Dr. Deborah Thomas
Department of Oceanography
This research focuses on the analysis of microfossils from deep-sea sediments. I am
investigating a series of deep-sea sediment cores from the South Pacific. The cores are a
vertical timeline of sedimentation, with each centimeter layer representing approximately
1,000 to 5,000 years of deposition. I subsampled each core by removing 10cc of
sediment every 150 cm. Each subsample spans 2cm. After recording the mass of each
sample, I washed and agitated each in purified water and sodium metaphosphate
(disaggregant) solution to break up any clays adhering to the fragile fossil material. After
rinsing over a 63m sieve, the samples were dried, and then transferred to a storage vial.
Each sample was examined under a low-power binocular microscope to identify and
quantify the assemblage of microfossils. I also analyzed the microfossil specimens using
the scanning electron microscope to aid in identification and capture images of the
important specimens. Results document changes in the composition of microfossil shells
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and faunal assemblages through time. In general, the dominant sediment lithology is red
clay.
However, several cores contain evidence of significant sediment variability through time.
Typically, South Pacific deep waters are corrosive to calcium carbonate, so the
preservation of carbonate fossils in the sediments reflects intervals of anomalous ocean
chemistry that in turn may reflect changes in atmospheric CO inventories. These results
show that over a relatively short geologic period, the ocean level at the coring site
fluctuated between shallower nutrient rich waters and deeper carbonate rich waters.
Future work, in collaboration with colleagues at the University of Michigan and Boise
State University, will focus on more precise determinations of the sediment layer ages
and geochemical analyses of the microfossils to determine ancient oceanic and
atmospheric circulation patterns.
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DEDICATION
To my husband, Dale
and
our son
vi
ACKNOWLEDGEMENTS
I would like to thank Dr. Deborah Thomas for inspiring me to make this more
than just a class project. I would also like to thank her for her patience and support
throughout my research.
Thanks also to Dr. Michael Pendleton for his time and expertise with the scanning
electron microscope.
Finally, thanks to my husband who is a constant source of encouragement,
support and love.
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TABLE OF CONTENTS
Page
ABSTRACT ……………………………………………………………………………iii
DEDICATION…………………………………………………………………………….v
ACKNOWLEDGEMENTS………………………………………………………………vi
TABLE OF CONTENTS………………………………………………………………..vii
LIST OF FIGURES……………………………………………………………………..viii
CHAPTER
I
INTRODUCTION………………………………………………………...1
II
METHODS………………………………………………………………..3
III
RESULTS…………………………………………………………………7
IV
SUMMARY AND CONCLUSIONS……………………………………14
REFERENCES…………………………………………………………………………..16
CONTACT INFORMATION……………………………………………………………17
viii
LIST OF FIGURES
FIGURE
Page
1
Map of South Pacific Coring Sites………………………………………...4
2
Stratigraphic Columns of Cores 7JC and 9JC……………………………..5
3
Saturnalin………………………………………………………………….9
4
Lamprocyclas sp.………………………………………………………….9
5
Actinommid……………………………………………………………….9
6
Theoperid….……………………………………………………………..10
7
Globigerina sp.…………………………………………………………..10
8
Polymorphina…………………………………………………………….10
9
Loxostomoides……………………………………………………………11
10
Silicoloculina…………………………………………………………….11
11
Rotaliina………………………………………………………………….11
12
Detail of Rotaliina aperture……………………………………………..12
13
Serrated Fish Tooth………………………………………………………12
14
Fish Tooth………………………………………………………………..12
15
Fe-Mn Nodule…………………………………………………………....13
16
Si Nodule Formed in
Foraminifera……………………………………………………………...13
17
Si Crystal…………………………………………………………………13
1
CHAPTER I
INTRODUCTION
The world’s oceans have been a source of life for as long as the earth has existed.
When one thinks of the fossil record, usually visions of dinosaurs or land-dwelling
creatures come to mind. Interestingly, there is just as much to be learned from the soil
beneath the ocean as there is on dry land. By studying cores from deep ocean sediments,
we can determine the ages of the rocks from the fossils found in the cores, what type of
ocean environment existed at that time period, and even some of the atmospheric
conditions at that time.
Each layer of the core taken is similar to a chapter in a history book. The cores in
this study range over approximately 24 million years. Core 7JC tells a story of nutrient
rich waters that flourished with radiolarians. Modern day radiolarians “prefer oceanic
conditions….in regions where divergent surface currents bring up nutrients from the
depths and planktonic food is available” (Armstrong and Brasier). Their numbers
respond to environmental conditions, namely the composition of the water masses they
live in (Armstrong and Brasier). Shallower waters tend to be silica poor and, in turn, lead
to dissolution of a majority of siliceous organisms as they filter through the water
column. Therefore, in sediments with high silica content, we can conclude that at the time
of deposition, there was an overabundance of siliceous organisms in highly productive
waters, which allowed some of them to actually filter through the water column and make
2
it to the ocean bottom. Silica deposition is controlled oceanographically, not
geochemically (Armstrong and Brasier).
In core 9JC, we see a change from carbonate rich sediments, to a siliceous ooze,
and back to a carbonate ooze. Carbonates, in contrast with siliceous oozes, are
geochemically controlled. Factors such as the atmosphere, hydrosphere and lithosphere
all affect the amount of CO2 in the ocean (Kennett). The oceans are a reservoir for CO2,
and, therefore, have a direct impact on whether a large or small amount of carbonate
organisms actually suffer dissolution or are preserved. The level at which the
concentration of calcium carbonate is 10% is called the critical compensation depth
(CCD). This is the level at which carbonate sediments start to be replaced with red clays
(Funnell).
3
__________
This thesis follows the style of Micropaleontology.
4
CHAPTER 2
METHODS
Cores were taken from several sites in the South Pacific (Figure 1) from the
research vessel Melville. Piston coring was used to obtain the cores, 7JC (Lat. 46
degrees 26.95’S) and 9JC (Long. 139 degrees 26.83’ W), which accounts for the slight
variability in core length.
Small 2 cm samples were taken from each of the cores in 150 cm intervals. The
samples were then washed in a solution of purified water and sodium metaphosphate
(disaggregant) to break up any clays adhering to the fragile fossil material. After
carefully rinsing the samples through a 63 m sieve, the debris that remained was dried
in a low temperature oven. This process left a majority of microscopic fossil material and
some mineral nodules.
Analysis of each vial of material was performed under a low power binocular
microscope to quantify the assemblage of fossils and make generalizations regarding the
core strata. Figure 2 displays the stratigraphic columns from each of the cores. Core 7JC
is made up of a majority of siliceous fossil material, while 9JC varies from carbonate to
siliceous and back to carbonate oozes. The better fossils from each core were then
separated and identified.
5
Figure 1 Map of Coring Sites in South Pacific
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STRATIGRAPHIC COLUMNS
KEY
Clay
Carbonate Ooze
Siliceous Ooze
Fe-Mn Nodule
Depth (cm)
0
225
250
295580
600
610730
7311640
7JC
7
Depth (cm)
0
9JC
198620
621830
831956
9571195
11961410
Figure 2 Stratigraphic Columns of Cores 7JC and 9JC
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CHAPTER 3
RESULTS
Since most ocean organisms contain more fleshy, or soft, than hard parts, it is
difficult to look at fossil assemblages for every species. Only species with hard skeletons
are able to be preserved, and even then it is difficult to achieve preservation in the
harshness of the ocean environment. The two fossil groups that were seen most in the
cores were grouped into either a siliceous ooze or a carbonate ooze. Oozes are sediments
containing at least 30 percent of the remains of a certain type of organism. Core 7JC had
an abundance of siliceous organisms, like radiolarians and diatoms. Core 9JC varied
from carbonate organisms, such as foraminifera, to a siliceous ooze, and back to
carbonate ooze. Occasionally, iron-manganese nodules were found interspersed with the
oozes.
Figures 3-6 are examples of organisms in a siliceous ooze. They are all
radiolarians, or planktonic single celled organisms. Radiolarians are important to the
geologic record due to their abundance and diversity (Kennett 573), and date back as far
as the Cambrian. The radiolarians were “apparently as diverse and widespread in the
Paleozoic as they are now” (Haq and Boersma).
Figures 7-12 are foraminifera. Foraminifera, or forams, are carbonate organisms.
The forams with the particular bulbous body type in figure 7 are considered planktonic,
or free floating organisms found at shallower depths. The planktonic forams have a
lighter and coarser test, allowing them to float in the water column. Figures 8-12 are
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benthic forams, found at deeper depths. Notice the change in the type and texture of the
skeletons between the planktonic and benthic forms. Figure 12 is a detailed look at the
apertures and smoothness of the test of the organism in figure 11.
Figures 13 and 14 are microscopic fish teeth. Figures 15 is an iron-manganese
nodule. Figure 16 is a silicate nodule that formed in the test of a foram and 17 is a silicate
crystal. All of these particular samples are found in environments that are too harsh to
preserve either siliceous or carbonate ooze.
10
Figure 3 Saturnalin
Figure 4 Lamprocyclas sp.
Figure 5 Actinommid
11
Figure 6 Theoperid
Figure 7 Globigerina sp.
Figure 8 Polymorphina
12
Figure 9 Loxostomoides
Figure 10 Silicoloculina
Figure 11 Rotaliina
13
Figure 12 Detail of Rotaliina aperture
Figure 13 Serrated Fish Tooth
Figure 14 Fish Tooth
14
Figure 15 Fe-Mn Nodule
Figure 16 Si Nodule formed in Foraminifera
Figure 17 Si Crystal
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CHAPTER 4
RESULTS AND CONCLUSIONS
In looking at core 7JC, we can see that the assemblage of fossils and other
material includes mostly siliceous ooze and red clays. The presence of siliceous
organisms implies high biological activity at the time of deposition. Because the upper
layers of the water column are silica poor, most of the silica bearing organisms are
dissolved as they filter through the water column. Only when there is an overabundance
of these organisms can they make it through the shallower waters to greater depths to be
fossilized.
The red clay layers are where the fish teeth and Fe-Mn and silicate nodules are
found. Conditions in these layers were too harsh for the preservation of siliceous or
carbonate oozes, and the strontium in the fish teeth is strong enough to stand up to the
corrosiveness of the deep waters. The same can be said for the nodules.
For core 9JC, we see carbonate ooze at the top and bottom of the core, with
siliceous ooze and red clays in between. Carbonate oozes are indicative of preservation
at depth. Calcium carbonate tends to be undersaturated at greater depths; therefore, when
conditions favor greater calcium carbonate levels at depth, the carbonate organisms can
sink to the sea floor without dissolution to be fossilized. The conditions for core 9JC
fluctuated to allow for carbonate preservation, followed by and undersaturation, and
finally back to greater calcium carbonate levels again. The calcium carbonate levels in
the oceans are directly affected by atmospheric conditions, particularly the amount of
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carbon dioxide in the air. So, we can make general assumptions regarding
paleoenvironmental conditions based on the fossil assemblages studied. Further research
will focus on more precise determinations of sediment layer ages and geochemical
analyses of the microfossils to determine ancient oceanic and atmospheric circulation
patterns.
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REFERENCES
Armstrong, Howard A. and Martin D. Brasier. Microfossils. Blackwell
Publishing, 2005.
Funnell, B.M. and W.R. Reidel. The Micropaleontology of Oceans.
Cambridge at the University Press, 1971.
Haq, Bilal U. and Anne Boersma. Introduction to Marine
Micropaleontology. Elsevier. 1998.
Kennett, James P. Marine Geology. Prentice Hall. 1982.
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CONTACT INFORMATION
Name:
Regina Lea Perry
Address:
Department of Oceanography
Texas A&M University
College Station, TX 77843-3146
[email protected]
Education: B.S. Wildlife and Fisheries Science, Minor Geology, Texas
A&M University (in progress)