25th International Meeting on Organic Geochemistry IMOG 2011

O-36
Highest resolution for oil dating (≤ 10 Ma): implications for the
paleocene-eocene thermal maximum from stable isotope data
Christiane Eiserbeck 1 , Kliti Grice 1 , Joseph Curiale 2
1 Curtin University, Perth, Australia, 2 Chevron Energy Technology Company, Houston, United States of
America (corresponding author:christiane.eiserbeck@gmail.com)
The Tertiary was dominated by global warming
periods with the Paleocene-Eocene Thermal
Maximum (PETM) being the most dramatic global
warming event in Earth‘s history. The sudden
warming of about 5°C caused the release of massive
amounts of isotopically light methane from the melting
gas hydrates [1].
The Tertiary was also the period of the rise and
diversification of the angiosperms towards becoming
the dominant land plants.
Both characteristics of the Tertiary have great
potential to be significant age signals for samples
deposited during that period.
Biomarkers like oleanoids, lupanoids and ursanoids
have been attributed to angiosperms and shown to
become more prominent from the Late Cretaceous
onwards. Their abundance in geological samples
increased significantly with decreasing age [2].
We examined the molecular and compound specific
isotope composition (� 13 C and �D) of biomarkers in a
number of Tertiary deltaic crude oils and source rocks
from different localities (mainly from the Arctic).
We established several angiosperm-gymnosperm
indices (AGI) all including an exhaustive number of
oleanoids, ursanoids and lupanoids (saturated, ring-
A-degraded, tri- and tetraaromatic, di-and triaromatic
ring-A-degraded).
All AGI‘s increase with decreasing age which is in
perfect agreement with the increasing predominance
of angiosperm fossil pollen records over gymnosperm
pollen records. This AGI correlation with age taken
from sediment samples of known age could very
successfully be applied to date age-unknown oils with
detectable angiosperm input with a resolution of 5-10
Ma.
� 13 C and �D of pristane (Pr) and phytane (Ph)
revealed an increase of ��D of Ph to Pr (�DPh – �DPr)
with decreasing age (Fig. 1). �DPh values were
depleted by -15 ‰ compared to �DPr supporting the
release of isotopically light freshwater from the
melting of gas hydrates as well as the ice caps at high
latitudes.
Fig. 1. ��D of Ph to Pr with age.
Complementary correlations with age could also be
established from chemometric analyses of an
extensive molecular (including GCxGC-TOF data)
and isotopic data set completing a suite of age
relationships for Tertiary crude oils and source rocks.
References
[1] Pancost, R.D., et al., Nature, 2007. 449(7160): p.
332.
[2] Moldowan, J.M., et al., Science, 1994. 265(5173):
p. 768-771.
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