25th International Meeting on Organic Geochemistry IMOG 2011

O-53
Biomarkers and stable isotopes of euxinia and their role in fossil
preservation
Ines Melendez 1 , Kliti Grice 1 , Kate Trinajstic 1 , Katherine Thompson 1 , Mojgan Ladjaverdi 1 ,
Arndt Schimmelmann 2 , Paul Greenwood 3
1 WA Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University of Technology,
Perth, Australia, 2 Indiana University, Dept. of Geological Sciences, Bloomington, United States of America,
3 University of Western Australia, Perth, Australia (corresponding author:ines.melendez@curtin.edu.au)
The Gogo Formation, located in the Canning Basin,
north-western Western Australia, shows remarkable
preservation of a Late Devonian (380 MYA) reef
fauna. The exceptional preservation, including original
bone and mineralized soft tissues, has resulted from a
combination of rapid burial and cementation within a
relatively tectonically stable environment. Soft-tissues,
including muscle bundles, nerve cells, and umbilical
structures, have been identified and described in the
vertebrate fauna (1, 2, 3). Through improved sampling
and preparation techniques extensive areas of soft
tissue have now been recovered from the Gogo
Formation. However, the exact mode of preservation
is yet to be determined.
To determine the palaeoenvironmental conditions that
resulted in the exceptional preservation of the ―Gogo‖
Formation an invertebrate fossil, containing soft
tissue, and the carbonate nodule were investigated
for the presence of biomarkers.
The nodule was divided in two with only one half used
for the experiments described below. The fossil was
extracted and separated into different fractions.
Dominant n-alkanes ranging from C15 to C32
(maximizing at n-C18 and n-C25) were identified. Their
� 13 C (-34 ‰ to -40 ‰) and �D values considering Denrichment
produced by thermal maturity (-230 ‰ to
270 ‰) are consistent with a source from
chemotrophic sulfate reducing bacteria (4, 5, 6). In
addition, the fossilised matrix was dominated by
cholestane (with a � 13 C value of -30.5 ‰) �bearing the
22R isomer (biological stereoisomer, reflecting an
immature signal) and high relative amounts of
phytane (� 13 C value of -34 ‰) probably derived from
sterols and chlorophyll of phytoplankton, respectively
in the upper water column on which the crustacean
used for its diet (7).
The desulfurised polar fraction (using Raney Nickel)
yielded a similar distribution of biomarkers to those
found in the free bitumen fraction. This observation is
remarkable for a sample 380 million years old. This
data supports rapid burial and preservation through
sulfurisation during the early stages of diagenesis.
Consistent with this hypothesis is the presence of
abundant Chlorobi biomarkers present in both the free
bitumen and sulfurised polar fraction. Markers of
Chlorobi, like isorenieratane and derivatives
therefrom, globally identified across Permian/Triassic
mass extinction boundary, have also been identified
here also supporting photic zone euxinic conditions
(H2S and light) in the water column (8, 9).These
results also support a recent study (10) which has
demonstrated that the Gogo Formation, Western
Australia, and the equivalent aged - Duvernay
Formation, western Canada (and their associated
oils) were deposited under highly euxinic conditions
based on the presence of biomarkers associated with
Chlorobi.
In marked contrast to the immaturity reflected by the
sterane distributions, the Ts/Tm ratio (0.62) of the
sample supports late thermal maturity. In order to
investigate the variations in maturity reflected by
these different biomarkers the second bitumen (after
isolation of kerogen) through heavy mineral
separation has been performed and compared with
the other fractions from the free bitumen (cf. work
carried out by 11).
(1) K. Trinajstic et al., Biology Letters 3(2),197-200 (2007)
(2) J. A. Long et al., Nature 453:650–652 (2008)
(3) J. A. Long and K. Trinajstic, Annual Reviews of Earth and
Planetary Sciences 38, 255- 270 (2010)
(4) K. Londry and D. Des Marais. Appl. Environ. Microbiol.
69:2942–2949 (2003)
(5) K. Londry et al., Appl. Environ. Microbiol. 70:745–751 (2004)
(6) X. Zhang et al., PNAS 106(31):12580-12586 (2009)
(7) K. Grice et al., Paleoceanography 13, 686-693 (1998)
(8) K, Grice et al., (2005) Science 307, 706-709.
(9) B. Nabbefeld et al., Earth and Planetary Science Letters 291,
84–96 (2010a)
(10) E. Maslen et al., Organic Geochemistry 49, 1–17 (2009)
(11) B. Nabbefeld et al., Organic Geochemistry 41, 78–87 (2010b)
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