PALAEOGEOGRAPHY OF THE AUSTRALIAN PERMIAN IN RELATION TO OIL SEARCH

Abstract

Aspects of Permian glaciomarine sedimentation in Australia in relation to petroleum generation are treated in the light of the "Gondwana-land" hypothesis and recent studies in palaeolatitudinal distribution of Tertiary oilfields. The Permian segment of the Gondwana (U. Dev. to Trias.) succession is characterised by Glossopteris-Gangamopteris flora, glacial. glaciomarine and glaciofluvial sediments, coal measures and cyclothems.

Evolution of the Hunter-Bowen Geosyncline of eastern Australia was accompanied by major volcanic activity along an arc-like archipelago. Sedimentation in this longitudinal ortho-geosynclinal belt linked acrosn the continent via shallow infra-basins and intra-cratonic basins to a series of graben-troughs (Perth, Carnarvon, Fitzroy and Bonaparte) developing about the western margin of Neo-Australia. These latter elongate and generally extremely deep "basins" were early manifestations of, and incipient riftings related to, the embryonic Indian Ocean.

The Permian (south) palaeomagnetic pole was located approximately 30 degrees of are west of south from Melbourne, placing Australia in relatively high southern latitudes. Middle to Upper Tertiary oilfields of the Northern Hemisphere on the other hand have been indicated elsewhere to be products of tropical palaeolatitudes from which it has been implied that warm temperatures may be critical in oil formation.

Recent investigations indicate that, acre for acre, Antarctic waters are potentially richer in organic life than any other. This is related primarily to abundance of nitrates and phosphates brought into sunlit (20 or more hours per day in summer) waters by upwelling currents. In consequence a high nutrient status of marine waters may be more important than palaeolatitudes in facilitating organic build-up in accumulating sediments. More research into contemporaneous sedimentation in relation to "Antarctic Convergence" in continental shelf settings is undoubtedly desirable.

The great variety of Australian palaeo-environments of Permian age includes those of the open sea, continental shelf, hinge-line, barred embayment and alternating marine to fresh water basin. These offer a range of settings favourable to the entombment of organic matter under a variety of conditions presumed favourable to the formation of petroleum source-beds. Encouraging discoveries at Yardarino (W.A.), Gidgealpa (S.A.) and Cabawin (Qld.) justify accelerated exploration for commercial petroleum in the Australian Permian.