Marita Bradshaw, 2005. "Divergent Continental Margin Basins—The Habitat of Australian Petroleum Systems", Petroleum Systems of Divergent Continental Margin Basins, Paul J. Post, Norman C. Rosen, Donald L. Olson, Stephen L. Palmes, Kevin T. Lyons, Geoffrey B. Newton
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The majority of the initial oil reserves (3.8 billion barrels of the 6.2 billion barrels of Australia’s initial commercial crude oil reserves) were discovered in just one of these basins, the Gippsland, located offshore, southeastern Australia. Other significant volumes of oil were discovered in the Carnarvon and Bonaparte basins on the North West Shelf; as well as major gas reserves, estimated in 2004 at over 100 trillion cubic feet. Australia ranked 30th and 13th in oil and gas global reserves, and 28th and 17th in oil and gas production at year end 2002 (Petrie et al., 2005).
Australia’s continental margin basins are the legacy of the breakup of Gondwana. The character and timing of the breakup varied along the margin and is reflected in the petroleum systems. The North West margin has a marine history extending back into the early Paleozoic. Successive continental slivers rifted away during the formation of the various incarnations of Tethys, continuing through to the development of the Indian Ocean in the Late Jurassic and Early Cretaceous. North West Shelf petroleum systems are characterized by marine shales providing oil source rocks and regional seals for fluvio-deltaic to shallow marine sandstone reservoirs. In contrast, the late Mesozoic breakup along the Southern Margin occurred between the two major continental blocks of Australia and Antarctica. Non-marine facies characterize the petroleum systems with coals and carbonaceous shales sourcing the hydrocarbons trapped in siliciclastic reservoirs.
Several kilometers of marine Jurassic sediments were deposited in these sub-basins that are age-equivalent to sections a few meters thick on the Exmouth Plateau. Breakup on the northern margin of the Exmouth Plateau during the Callovian was associated with the formation of the Argo Abyssal Plain and produced further movement on the faults bounding the sub-basins. Restricted, deep-marine environments were established in the subsiding troughs, and the primary oil source rock facies of the Dingo Claystone was deposited during the Late Jurassic (Bishop, 1999; Bradshaw et al., 1998; Longley et al., 2002).
On the southeastern continental margin of Australia, the Gippsland basin is one of Australia’s most prolific and mature petroleum provinces. The basin is an intact rift preserved from the later stages of Gondwana breakup. It was initiated as part of the east-west directed Early Cretaceous breakup rift system between Antarctica and Australia. In the Late Cretaceous, the oil kitchen and main depocenter of the Central Deep was established during renewed extension associated with the opening of the Tasman Sea (Bernecker, et al 2001; Norvick et al 2001). The first marine incursion occurred in the late Santonian. However, the lower coastal plain and coal swamp facies deposited in the Central Deep during the Late Cretaceous are regarded as the major source rocks for the billion-barrel accumulations of the Gippsland basin (Burns et al., 1984; Rahmanian et al., 1990).