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A companion volume to 'The geology and petroleum potential of the Clarernce-Moreton Basin, New South Wales and Queensland' compiled and edited by A.T. Wells and P.E. O'Brien, Australian Geological Survey Organisation bulletin 241(1994).

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Surprisingly few natural hydrocarbon seeps have been identified in Australia's offshore basins despite studies spanning thirty years. Initial studies of natural hydrocarbon seepage around the Australian margin were generally based around the geochemical analysis of stranded bitumens, water column geochemical `sniffer' sampling, synthetic aperture radar or airborne laser fluorsensor. Later studies involved the integration of these remote sensing and geochemical techniques with mutli-channel and shallow seismic. A review of these earlier studies indicates that many seepage interpretations need to be re-evaluated and that previous data sets, when set in a global context, often represent normal background hydrocarbon levels. Relatively few sites of proven natural hydrocarbon seepage in Australia's offshore sedimentary basins can be reconciled with the dominantly passive margin setting and low recent sedimentation rates, which are not favourable for high rates of seepage, and difficulties in proving seepage on high energy, shallow carbonate shelves, where seabed features may be rapidly reworked and modern marine signatures are overprinted on authigenic seep carbonates. Active thermogenic methane seepage on the Yampi Shelf, the only proven documented occurrence in Australia, is driven by deposition of a thick Late Tertiary carbonate succession and Late Miocene tectonic reactivation. Therefore, to increase the success of detecting and correctly interpreting natural hydrocarbon seepage, data need to be analysed and integrated within the context of the local geological setting, and with an understanding of what is observed globally.

Between 2006 and 2011, Geoscience Australia acquired deep crustal seismic reflection and magnetotelluric surveys as a major component of the Australian Government's Onshore Energy Security Program (OESP). All surveys have been conducted in collaboration with the relevant state or NT geological survey. The Seismic Acquisition and Processing Project provides precompetitive data for developing new geological frameworks for assessment of onshore hydrocarbon, geothermal and uranium resources. The Onshore Petroleum Project provides interpretation of the seismic data in frontier basins with petroleum potential and an assessment of the petroleum prospectivity of some of these basins. Seismic data can reveal basin and crustal architecture for potential hydrocarbons, image potential hot rocks (granites), and identify potential uranium deposit settings, such as craton margins and unconformities.

The Exmouth Plateau lies oceanward of Australia's Northwest Shelf petroleum province, in water depths of 800 to 2000 m, and is flanked by the abyssal plains of the Wharton Basin. Its area is 150 000 km2 and the adjacent lower continental slopes, also considered in this study, cover another 150 000 km2 . The southwest and northwest margins of the plateau are fault-bounded escarpments, but the northern margin consists of spurs and subplateaux separated by deep troughs. Our interpretation of the area is based on 12 000 km of BMR seismic reflection, magnetic, and gravity profiles, and 6000 km of seismic reflection profiles provided by petroleum exploration companies. Initially, eight major seismic horizons were identified over the profile network. They were then related to the nearest known stratigraphy by means of seismic tie-lines to wells on the Northwest Shelf. Additional information came from magnetic and gravimetric studies and deep-sea drill holes on the adjacent abyssal plains.

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