The Northwest Shelf of Australia is herein considered to be the part of the continental margin of Western Australia extending south westward to approximately lat. 22 °S and northeastward to approximately long. 131 °E (Figure 1). It was formed by a series of major tectonic episodes that began in the late Paleozoic and continued into the Cretaceous, and that resulted in the complete breakup of eastern Gondwana and the formation of the Indian Ocean.
Woodside Offshore Petroleum and its related predecessors have been Operator for the Northwest Shelf Joint Venture Group during more than 20 years of exploration in the region. Initially, the Group held exploration permits covering parts of all four basins of the Northwest Shelf, though these have now been substantially reduced. Most of the Joint Venture’s work has been centered on the Dampier area of the offshore northern Carnarvon basin, for which reason this chapter concentrates on the Barrow-Dampier subbasin. Discussion of the Beagle subbasin is included with that on the Barrow-Dampier subbasin because those two adjoining subbasins are similar in style. This is followed by a brief review of the Browse basin, in which the Joint Venture has also been active.
Only four wells have been drilled by the Joint Venture in the offshore Canning basin, the last one in 1971, and few wells have been drilled there by other operators. Warris (1973) summarized the geology and exploration history of the offshore Canning basin, and since then virtually no new work has been done in
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Divergent/Passive Margin Basins
All basins in the Divergent Margin class occur along continental margins near a midplate position, where they overlie and straddle rigid continental and oceanic crust. These basins are now essentially aseismic and non-volcanic. All extant divergent margins are post-Traissic and are related to the sequential breakup of Pangea. They represent the opening ocean part of the Wilson cycle of earth history ? as Pangea split, continental plates moved away from the African center. The inboard roots of divergent margin basins lie on attenuated, subsided continental crust beneath the coastal plain, continental shelf, and continental slope. Outboard, they lie on subsided oceanic crust beneath the continental slope and rise. All phases of basin development are dominated by gravity-driven extension tectonics. Hence, they are called passive, pull-apart, Atlantic-type, or divergent continental margins. This publication was initiated by the AAPG Publications Committee in 1985 and contributors were invited to write. AAPG designed their ?World Petroleum Basins? series and sought to publish the definitive volume on each of several basin types. In this volume, “Divergent/Passive Margin Basins,” a detailed overview was written about the Campos Basin (Brazil) as representative of divergent margin basins. The key paper was followed by less detailed reviews of three other selected passive margin basins: 1. Northwest Shelf of Australia 2. Gabon basin and 3. Niger Delta area. Contributors undertook to provide useful geologic information on the regional setting, stratigraphy, structure, tectonics, basin evolution, and oil and gas systems of these four basins. The goal was to develop a better understanding of the basin-forming, basin-filling, and basin-modifying processes that control hydrocarbon plays and resultant oil and gas fields in this class of basin. The volumes in the AAPG Basin Series include: 1. Divergent/Passive Margin Basins (AAPG Memoir 48) 2. Interior/Cratonic Basins (AAPG Memoir 51) 3. Active Margin Basins (AAPG Memoir 52) 4. Foreland Basins and Foldbelts (AAPG Memoir 55) 5. Interior Rift Basins (AAPG Memoir 59).