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