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ABSTRACT: Petroleum Systems in the Australian Offshore Region

BRADSHAW, MARITA T., Bureau of Mineral Resources, Canberra, Australian Capital Territory, Australia

Phanerozoic Australian sedimentary sequences can be grouped into six broad petroleum systems termed the Larapintine, Gondwanan, Westralian, Austral, Capricorn, and Murta systems. Establishing this framework stresses the linkages between coeval basins of similar paleogeographic and tectonic setting; reservoir, seal, and source facies; trap formation and maturation histories; and thus, hydrocarbon prospectivity. In this way, the correspondences between the basins in a petroleum system are recognized and knowledge from more explored areas can be used predictively in frontier regions.

All of the petroleum systems are represented on Australia's continental shelf. The Larapintine system is best known from onshore Australia where it is characterized by lower Paleozoic marine facies,

including carbonates, evaporites, and excellent marine source rocks. The Arafura basin is recognized as a less explored, offshore extension of the Larapintine system.

The Gondwanan system includes those sequences dominated by the late Carboniferous/Early Permian Gondwanan glaciation. The basins along the North West Shelf are part of the Westralian system. They share Triassic to Cretaceous reservoirs, Jurassic marine source rocks, and a Cretaceous regional seal. The development of the southern margin as Australia and Antarctica separated has influenced the basins of the Austral system. They have similar nonmarine Mesozoic rift valley sequences followed by marine Late Cretaceous and Cainozoic sediments. The Capricorn system is related to the opening of the Coral Sea and includes onshore Tertiary oil shale deposits and the offshore basins of northeast Australia. The Mesozoic interior sag sequences of Murta system extend into the Gulf of Carpentaria.

 

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)