Clinton B. Foster1,
Graham Logan1
(1) Australian Geological Survey Organisation, Canberra, Australia
Abstract: Carbon isotopes, Tmax and EOM as environmental proxies: application to oil/source correlation – examples from the Permian-Triassic of Australia
The carbon isotopic composition
of kerogens from the Permian–Triassic from eastern and western Australia appears
to be controlled by the contribution of woody organic matter. Wood-dominated
organics, as determined from palynological preparations, are typically
isotopically enriched, 13C
-24 %o; while non-woody material, comprising typically of spores, pollen and
spinose acritarchs is significantly lighter (
13C
-30 %o). Tmax data, from standard Rock-Eval, for the same sample set, show
patterns of reworking and can be associated with the amount of isotopically
enriched, refractory woody tissue. Extractable organic matter (EOM) from the
wood-dominated samples is, as might be expected, low. Evidence from
Permian-Triassic boundary sections in Australia, China and Russia confirms that
the primary control on organic carbon isotopic composition is its biological
source; secular causes may also be present, but are difficult to isolate. These
three data sets (
13C,
Tmax, and EOM) combine to give a proxy for sea level change, and biofacies. The
kerogen
13C values can be
modelled and used to predict biofacies, which in turn is correlated to the
compound specific carbon isotopic analysis of oils (CSIA) and used to predict a
likely organic source. This is a novel, relatively inexpensive, and useful tool
for hydrocarbon exploration.
AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana