using carbonate stable isotopes to identify …
TRANSCRIPT
Nicholas M. Ellis; Thomas S. TobinThe University of Alabama
Distance along shell (mm)
-0.3
-0.2
-0.1
0
0.1
0.2
Best Fit Linear
95% Bounds
Distance along shell (mm)
-1.5
-1
-0.5
0
0.5
1
1.5
Best Fit Sine
95% Bounds
Distance along shell (mm)
Best Fit Linear
95% Bounds
Distance along shell (mm)
-0.2
-0.1
0
0.1
0.2
0.3
δ1
8O
(‰
VP
DB
)
Best Fit Sine
95% Bounds
Distance along shell (mm)
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4Best Fit Sine95% Bounds
Distance along shell (mm)
-4.5
-4
-3.5
-3
-2.5
-2 Best Fit Linear
95% Bounds
Distance along shell (mm)
Distance along shell (mm)
95% BoundsBest Fit Linear
393 mm 332 mm 107 mm 185 mm
62
mm
54
mm
35
mm
30
mm
60
mm
320 mm
The locations represented by the ammonites studied during this
investigation are projected onto a reconstruction of the WIS.
CC-1 CC-2 WY-1 MT-1
0 50 100 150 200 250 300 350 400
0 50 100 150 200 250 300 350 400 0 50 100 150 200 250 300
0 50 100 150 200 250 300 0 20 40 60 80 100
0 20 40 60 80 100
0 20 40 60 80 100 120 140 160 180
0 20 40 60 80 100 120 140 160 180
Acknowledgments
Results and Conclusions
Literature Cited
MethodsIntroduction
Specimen
Name
Specimen
Length (mm)
Period of Best Fit
(mm)
CC-1
367 ± 27320
393
332
107
185
373 ± 47
No Sine Fit
No Sine Fit
No Sine Fit No Sine Fit
No Sine Fit
No Sine Fit
No Sine Fit
No Sine Fit
No Sine Fit
No Sine Fit
0.225 ± 0.066
1.671 ± 0.156 0.94
0.73
0.02
339 ± 69
0.8314 ± 0.340
0.3100 ± 0.108
1.2204 ± 0.224
0.07
0.43
0.52
0.33
0.44
331 ± 54
334 ± 73
0.42
0.34
Fatheree
WY-1
MT-1
CC-2
Amplitude of Best Fit
(‰ VPBD)Amplitude of Best Fit
(‰ VPBD)
Period of Best Fit
(mm)
δ18O
R2 R2
δ13CTable 1
-2.4
-2.3
-2.2
-2.1
-2
-1.9
-1.8
-1.7
-1.6
-1.5
-1.4 Best Fit Linear95% Bounds
δ1
8O
(‰
VP
DB
)
δ1
8O
(‰
VP
DB
)
δ1
8O
(‰
VP
DB
)
δ1
3C
(‰
VP
DB
)
δ1
3C
(‰
VP
DB
)
δ1
3C
(‰
VP
DB
)
δ1
3C
(‰
VP
DB
)y = (0.01684)sin(0.01473x + 0.07002)
y = (0.155)sin(0.01597x + 0.1933)
y = 0.001727x - 0.03637
y = (0.6102)sin(0.01856x - 1.122)
y = -0.00569x + 0.4787
y = 0.005046x - 2.191
y = 0.0003414x
- 0.1668
Isotope data from Baculites undatus specimen from the Coon Creek formation
(35.35218 °N, 88.42043 °W) is shown. Oxygen and carbon isotope data were
normalized to 0 using means: δ18O = 0.4294; δ13C = 0.3979.
Isotope data from Baculites undatus specimen from the Coon Creek formation
(35.35218 °N, 88.42043 °W) is shown. Carbon isotope data were normalized to
0 using mean: δ13C = -0.1215. A sine curve could not be extrapolated from the
oxygen data series, so a linear fit was used.
Isotope data from Baculites clinolobatus specimen from Northern Wyoming
(44.75 °N, 108.5 °W) is shown. The unidirectional trends could represent a
portion of the seasonal cycle given the shorter length of this specimen. Sine
curves could not be extrapolated from the datasets, so linear fits were used.
Isotope data from Baculites sp. specimen from the Bear Paw Shale at Hell
Creek in Eastern Montana (47.6314 °N, -106.8688 °W) is shown. The signals in
this specimen are rather noisy, and no meaningful or significant trends were
identified.
y = -0.004121x - 2.399
Distance along shell (mm)
δ1
8O
(‰
VP
DB
)
0 50 100 150 200 250 300-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1Best Fit Sine
95% Bounds
Distance along shell (mm)
δ1
3C
(‰
VP
DB
)
0 50 100 150 200 250 300
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
Best Fit Sine
95% Bounds
y = (0.8355)sin(0.0171x + 0.1562)
y = (0.4157)sin(0.01879x + 1.784)
Figure 2
Figure 1
Cochran, J.K., Kallenberg, K., Landman, N.H., Harries, P.J., Weinreb, D., Turekian, K.K., Beck, A.J., and Cobban, W.A., 2010, Effect of diagenesis
on the Sr, O, and C isotope composition of late Cretaceous mollusks from the Western Interior Seaway of North America: American
Journal of Science, v. 310, p. 69–88, doi: 10.2475/02.2010.01.
Fatherree, J.W., Harries, P.J., and Quinn, T.M., 1998, Oxygen and Carbon Isotopic "Dissection" of Baculites compressus (Mollusca: Cephalopoda)
from the Pierre Shale (Upper Campanian) of South Dakota: Implications for Paleoenvironmental Reconstructions: Palaios, v. 13,
p. 376–385, doi: 10.2307/3515325.
Grossman, E., 1986, Oxygen and carbon isotope fractionation in biogenic aragonite: Temperature effects: Chemical Geology, v. 59, p. 59–74,
doi: 10.1016/0168-9622(86)90057-6.
We acknowledge the generous support of the Undergraduate Creativity
and Research Academy and The University of Alabama Department of
Geological Sciences for providing financial assistance for this project. We
thank the Alabama Stable Isotope Laboratory for processing our samples.
We thank the United States Geological Survey and the Pink Palace
Museum for providing specimens used in this project. We especially thank
Tamara Braithwaite and Louella Weaver of the Pink Palace Museum
for assistance with collections and sampling permission.
Fatherree CC-1
7.84 1.06 ≥2.43 >3.33 n/a
CC-2 WY-1 HC-1
Calculated Annual ∆T (°C)
Specimen NameTable 2
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
0.5
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
Baculites specimen CC-1 and the specimen described by Fatherree et al. (1998) show sinusoidal
δ18O signals with similar periods around 370 mm and have overlapping error ranges (see Table 1).
Baculites specimens CC-1, CC-2, and the specimen described by Fatherree et al. (1998) show
sinusoidal δ13C signals with very similar periods around 335 mm. Error ranges overlap with each
other and the period lengths produced from δ18O (see Table 1).
The consistency in period length is suggestive of common cause, which could be explained by a
seasonal trend since δ18O is temperature dependent and δ13C may reflect seasonal variation in
organism behavior, metabolism, and/or activity.
The lengths of these periods suggest that Baculites grow at extremely fast rates (>300 mm/yr).
Baculites may be r-strategists that grow rapidly, live short lives, and produce large amounts of
offspring, or they may simply reach their mature size quickly and stop growing.
The amplitude of the δ18O signal from the specimen CC-1 is small which may indicate low
magnitude seasonal cycles, agreeing with a shallow subtropical shelf environment.
The amplitude of the Fatheree et al. (2010) specimen’s δ18O signal is several times greater than that
of CC-1 as expected at a much higher paleolatitude.
Seasonal amplitude could be reduced due to organism behavior, such as seasonal geographic
migration or vertical migration in the water column.
Powdered shell samples were generated for isotopic analysis of ontogenetic sequences
using a handheld Foredam drill.
Carbon and oxygen isotope values were measured using a Thermo Scientific Delta V Plus
isotope ratio mass spectrometer equipped with a GasBench II autosampler.
Best fit sine functions (representing seasonal cyclicity) were found using the curve fitting
toolbox in MATLAB. Datasets with insufficient data, such as unidirectional trends, were fit
with linear functions.
δ18O and δ13C data with apparent sinusoidal patterns were normalized to a mean of 0 by
subtracting the mean of the sample data as required by MATLAB.
Seasonal temperature differentials were calculated by assuming a constant δ18O for
seawater and multiplying the peak-to-peak amplitude of the δ18O sine function by 4.69
as defined by Grossman and Ku (1986).
All specimens preserve primary aragonite as indicated by their iridescence.
Samples are currently being imaged with a scanning electron microscope to assess their
preservation quality using the preservation index established by Cochran et al. (2010).
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Fatherree et al. (1998) measured δ18O and
δ13C in an ontogenetic sequence on a single
Baculites compressus collected from the
Pierre Shale in Northern Wyoming
(43.9333 °N, 102.8167 °W).
A sinusoidal δ18O trend over the length of
the shell (320 mm) was recognized to be
approximately one seasonal cycle.
We reanalyzed their data for sinusoidal fits
with MATLAB using the same methods by
which our data was processed (see
Methods) to produce functions for their
δ18O and δ13C signals.
The periods of these functions are similar to
those we were able to fit to our specimens,
CC-1 and CC-2 (see Table 1).
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An SEM image of the the Fatherree (1998)
Baculites’ well-preserved microstructure
Mollusks are typically thought to precipitate
carbonate shell material in equilibrium with
seawater.
Little is known about the lifespan or habits of
extinct ammonite species. Most postulations are
made based on their modern analog - the Nautilus.
The uncoiled morphology of Baculites makes the
genus an easy target for sclerochronological
isotopic analysis.
Seasonal temperature signals may be preserved in
oxygen isotope content as shell material is
deposited over time.
Carbon isotope content may also preserve seasonal
signals depending on organism behavior.
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Using Carbonate Stable Isotopes to Identify Seasonal Trends in Late Cretaceous Ammonites
160 320800Miles
Middle Campanian Reconstruction
Colorado Plateau Geosystems Inc.
Western Interior Seaway (WIS)
MT-1
Fatherree
CC-1, CC-2
WY-1
N