The 1999 release of offshore petroleum exploration acreage in the Great Australian Bight and the acquisition of high quality seismic datasets covering the Bight and Duntroon Basins, have provided a timely opportunity to reassess the stratigraphic and tectonic evolution of the area. A sequence stratigraphic framework for the Great Australian Bight region has been developed based on the interpretation of exploration wells in the Bight and Duntroon basins and a grid of new and reprocessed seismic data in the Bight Basin. Previous formation-based nomenclature has emphasised lithostratigraphic correlations rather than the chronostratigraphic relationships. The new sequence framework underpins an analysis of play elements and petroleum systems and is helping to identify new exploration opportunities.Deposition in the Bight and Duntroon Basins commenced in the Late Jurassic during a period of lithospheric extension. Extensive half graben systems were filled with fluvial and lacustrine clastic sediments (Sea Lion and Minke supersequences). Potential source rocks within these supersequences are immature at Jerboa-1 in the Eyre Sub-basin, however higher maturities are expected within adjacent half graben and in the Ceduna and Recherche Sub-basins. The syn-rift successions are overlain by widespread Berriasian to Albian fluvio-lacustrine to marine sediments of the Southern Right and Bronze Whaler supersequences. The onlapping sag-fill geometry of these Early Cretaceous packages in the Eyre, Ceduna and inner Recherche Sub-basins suggests that they were deposited during a period of thermal subsidence.Accelerated subsidence commencing in the late Albian led to the deposition of the marine shales of the Blue Whale supersequence, followed by a period of gravity-controlled faulting and deformation in the Cenomanian. The White Pointer supersequence is characterised by growth strata associated with a series of listric faults that sole out in underlying ductile shales of the Blue Whale supersequence. Open marine conditions during the Turonian-Santonian (Tiger supersequence) were followed by the development of massive shelf margin delta complexes in the late Santonian-Maastrichtian (Hammerhead supersequence). The progradational to aggradational stratal geometries within the Hammerhead supersequence suggest initial high rates of sediment input that subsequently waned during this period. An overall transgressive phase of sedimentation in the Early Tertiary (Wobbegong supersequence) was followed by the establishment of open marine carbonate shelf conditions from the Early Eocene onward (Dugong supersequence). Organic geochemical studies show that the Bronze Whaler to White Pointer supersequences have good source rock potential in the relatively proximal facies intersected by existing petroleum exploration wells. Our sequence stratigraphic model predicts the likelihood of widespread late Aptian, Albian, Cenomanian-Santonian, and Campanian marine shales, which underpin four potential marine petroleum systems.

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We document the interpretation of three crustal sections from coincident deep seismic reflection, gravity and magnetic data acquired on Australia's southern margin: one section from the Naturaliste Plateau and the Diamantina Zone; and two in the Great Australian Bight (GAB). Interpretations are based on an integrated study of deep multichannel seismic, gravity and magnetic data, together with sparse sonobuoy and dredging information.All interpreted sections of the margin show a transition from thinned continental crust, through a wide continent ocean transition zone (COTZ). In the GAB the transition is to slow sea-floor spreading oceanic crust that dates from breakup in the Campanian (c. 83 Ma); in the Naturaliste-Diamantina margin the earliest oceanic crust is undated. The COTZ on these margins is geologically and geophysically complex, but interpretation of all data, including dredge hauls, is consistent with the presence of a mixture of modified continental lower crust, breakup related volcanics and exhumed continental mantle. Serpentinized detachment faults are not well imaged, but have been inferred from high-amplitude magnetic signatures interpreted to arise from magnetite associated with the hydration of peridotites. Alternative models for the structure of the COTZ, involving either mafic underplating or aborted sea-floor spreading, have been explored, but are considered unlikely on this margin.Similarity in the final architecture of these margins has major implications for the nature of rifting in the Southern Rift System, and may point to the entire 4000 km-long system being non-volcanic in character.Second-order differences in geometry and morphology of the two areas studied are unlikely to be a function of strain rate. Instead, they probably reflect complexities owing to the multiple tectonic events that occurred during final Gondwanide fragmentation. The most dramatic of these is the impact of hotspot activity in the Kerguelen Plateau, which commenced some 50 Ma prior to final breakup in that sector.

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