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Out of Gondwana Marita Bradshaw, Jennie Totterdell, George Gibson, irina Borissova, John Kennard 'Out of Gondwana' is a chapter of the new book on Australia's geology being published by Geoscience Australia for the 34th International Geological Congress (IGC) to be held in Brisbane in 2012. As part of this book, Shaping a continent-building a nation: a geology of Australia, this chapter will tell the story of the break up and creation of Australia as the island continent, and how this unique geology has impacted the Australian people. Geoffrey Blainey recognises climate and distance as the two major influences on the historical development of Australia and Australians; and the 'tyranny of distance' was established with the separation from Gondwana. But the Gondwanan history has also bestowed resource riches - coal, gas and oil - which power the Australian economy today.

New seismic, gravity and magnetic data over the Capel and Faust basins have allowed improved resolution of the basin architecture and a better appreciation of the stratigraphy, terrane evolution and palaeogeography. Preliminary interpretation suggests that the Capel Basin contains several depocentres with up to 4 seconds two-way time (s TWT) sediment thickness, up to 150 km long and 40 km wide. Grabens appear to contain Lower Cretaceous syn-rift volcanics, Turonian-Maastrichtian syn-rift clastic megasequences and a Maastrichtian-Recent bathyal post-rift phase. There may also be a Lower-Middle Jurassic pre-rift sequence, possibly an equivalent of the Clarence-Moreton coal measures. Total Jurassic-Recent sediment thickness may be as much as 6-7 km. A number of smaller grabens characterise the Faust Basin to the east and the southern part of the Capel Basin. Stratigraphic complexity was driven by multiple extension events. Subsequent discrete seafloor spreading events resulted in the sequential formation of the Tasman Sea, and possibly the Middleton Basin, proto-Loyalty Basin, and central New Caledonia Basin. Plate reconstructions indicate that the Capel Basin was located adjacent to the northern edge of the Sydney Basin prior to breakup. The junction between the Capel and Faust Basins is a major fault system, which may have exploited a Middle Triassic collision suture between the New England Orogen and equivalents of the Maitai Murihiku terranes of New Zealand. The interpreted Lower Cretaceous volcanics are expected to correlate with the Lower Cretaceous igneous complexes and associated volcanogenic sediments in Queensland, Bass Strait and New Zealand. Sediment analogues of the mid-Cretaceous rift fill in the Capel-Faust area can possibly be found in Gippsland and the Great South Basin, but exact correlations will be difficult because of the diachronous breakup of Tasman continental ribbons. The Capel Basin in particular may contain sediments capable of generating gas and perhaps some liquids such as those seen in Clarence-Moreton and Great South basins.

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Legacy product - no abstract available

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The Early Cretaceous Gage Sandstone and South Perth Shale formations are a prospective reservoir-seal pair in the Vlaming Sub-basin. Plays include post-breakup pinch-outs in the Gage Sandstone with the South Perth Shale forming top seal. The Gage reservoir has porosities of 18-25% and permeabilities of 1-1340 mD. It was deposited in palaeotopographic lows of the Valanginian breakup unconformity and is the lowstand component of the thick deltaic South Perth (SP) Supersequence. To characterise the reservoir-seal pair, a detailed sequence stratigraphic analysis was conducted by integrating 2D seismic interpretation, well log analysis and new biostratigraphic data. Palaeogeographic reconstructions for the SP Supersequence were derived from mapping higher-order prograding packages and establishing changes in sea level and sediment supply. Higher resolution Gage reservoir reconstructions were based on seismic facies mapping. The Gage reservoir forms part of a sand-rich submarine fan system similar to model proposed by Richards et al (1998). It ranges from canyon confined inner fan deposits to middle fan deposits on a basin plain. Directions of sediment supply are complex, with major sediment contributions from a northern and southern canyon adjacent to the Badaminna Fault Zone. The characteristics of the SP Supersequence differ markedly between the northern and southern parts of the sub-basin due to variations in palaeotopography and sediment supply. Palaeogeographic reconstructions reveal a series of regressions and transgressions leading to infilling of the palaeo-depression. Palaeogeographic reconstructions for the SP Supersequence portray a complex early post-rift depositional history in the central Vlaming Sub-basin. The developed approach is applicable for detailed studies of other sedimentary basins. APPEA

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