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The AAPG/Datapages Combined Publications Database

CSPG Special Publications


Facts and Principles of World Petroleum Occurrence — Memoir 6, 1980
Pages 989-989
Symposium Abstracts

Hydrocarbons of the Mesozoic Basins of Western Australia: Abstract

John K. Geary1

The tectonic events related to the rifting and drifting of Eastern Gondwanaland directly control the distribution of hydrocarbon source and reservoir rocks in the Mesozoic basins of the continental margin of Western Australia. Directly or indirectly, the tensional forces involved are responsible for most entrapment situations. Exploratory drilling has been carried out in the Perth, Carnarvon, Canning, Browse and Bonaparte Basins. Of these only the offshore Canning Basin has so far failed to yield hydrocarbons. Undrilled areas, which are indicated by seismic to have thick Mesozoic sections, are the Houtman Sub-Basin and the Exmouth Plateau. These are located in deep water west of the Carnarvon Basin. Initial rifting of the Gondwana continent began in late Permian. This was followed by a widespread marine transgression and shale deposition in Lower Triassic. From Middle Triassic to Middle Jurassic a regressive deltaic cycle prevailed. Major rifting in early Upper Jurassic produced a series of deep linear troughs in which thick marine shale sequences were deposited, except in the Perth Basin where continental arenaceous deposition occurred. This rifting phase preceded the drifting apart of the Gondwana continent. Concomitant with drifting the marine transgression extended and by early Upper Cretaceous all the positive areas were covered. From this period until late Tertiary, open marine deposition prevailed, interspersed by several hiatuses. Hydrocarbon source rock analyses indicate that sediments from Lower Triassic to Lower Cretaceous can yield oil as well as gas. The number of oil and gas discoveries is approximately equal. However, in magnitude of reserves, gas predominates. Chemical analyses show that two basic types of oil exist, believed to be derived from marine and terrestrial sources respectively. The latter type is the more frequently occurring. This could mean that oil generated from the great volume of marine sediments in the area remains largely undiscovered.

Acknowledgments and Associated Footnotes

1 19 Mitchell Street, Karrinyup, Western Australia 6018

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