Journal of Petroleum Geology, Vol.15, No.4, pp. 435-450, 1992

©Copyright 2000 Scientific Press, Ltd.

POTENTIAL PETROLEUM SOURCE ROCKS IN TRIASSIC
LACUSTRINE-DELTA SEDIMENTS OF THE
GUNNEDAH BASIN, EASTERN AUSTRALIA

M. Smyth*, Feng Xu Jian** and C. R. Ward**

* CSIRO Division of Exploration Geoscience, P.O. Box 136, North Ryde, N.S.W., 2113, Australia.

** Department of Applied Geology, University of New South Wales, P.O. Box 1, Kensington, N.S.W., 2033, Australia.

Abstract

Integration of lithofacies, inferred depositional environments and organic petrology of a lacustrine delta sequence in the Permo-Triassic Gunnedah Basin of eastern Australia has provided a logical explanation for the patterns of distribution of the dispersed organic matter. The data show that: (i) sedimentary processes, such as size sorting and transportation, control the association of maceral assemblages in the dispersed organic matter with depositional environments; (ii) the extent of oxidation of organic matter increases downstream, from floodplain lake to interdistributary bay, delta front, prodelta and off-shore lake deposits; (iii) coarse, woody material, mostly oxidised to semifusinite, is concentrated in the delta-front environment; (iv) leaf material is transported preferentially to the prodelta, via the delta front. On the basis of organic matter type, the prodelta was probably the most favourable environment in this depositional system for the accumulation of oil-prone source beds.