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Australia contains established oil and gas provinces (Fig. 1), is politically stable, and has a fiscal regime which encourages petroleum exploration and development. These combined with infrastructure all serve to attract and maintain petroleum exploration and production investment in the established oil and gas provinces. Over the last ten years Australia has maintained 65-85% self sufficiency in oil and better than 100% sufficiency in gas as a net gas exporter through LNG. The Australian government has a new program of data acquisition in poorly explored areas and the recently announced Spatial Information and Data Access Policy requires that basic data be made available at the marginal cost of transfer, or is free if delivered via the internet. In addition, to encourage exploration in its many under-explored regions, Australia has traditionally maintained better access to geoscience and petroleum exploration data than almost anywhere else in the world. Access to petroleum exploration information has been facilitated by legislation requiring data submission and availability, and by the provision of pre-competitive studies by government agencies. This is coupled with an aggressive, globally and yearly promoted, acreage release program. Australia remains significantly under-explored and for that reason has sought to improve the very high level of access to exploration and production data that includes seismic data, well information, and regional geological studies. Ease of access is designed to attract new explorers. Australia has less than eight thousand petroleum exploration wells onshore and offshore in an area of over twelve million square kilometres and, consequently, there is considerable opportunity for further exploration. Significant discoveries of oil and gas have occurred in Australia since the 1960?s and continue to the present day. Super giant oil and gas fields have been discovered both in the southeast and northwest of Australia. Globally, Australia ranks 27 as an oil producer and 18 as a gas producer. Although under-explored, already it is assessed as containing upwards of 2% of the world?s gas reserves and 1% of the world?s oil reserves. Recently, deeper water exploration (>1200m) has occurred in Australia adjacent to major gas and oil production in the Carnarvon Basin and to major discoveries in the adjacent Browse Basin on the Northwest Shelf. Significant deep-water oil discoveries at Laverda, Vincent and Enfield, of over 200 mmbls have been made in the Carnarvon Basin, and many tens of Tcf of gas have been discovered at Gorgon and deep water fields further to the west (Longley et al 2001).

Situated just inboard of the late Neoproterozoic Australian rift margin (Tasman Line), the Broken Hill region occupies a critical position in reconstructions of Rodinia, combining an older basement (Willyama Supergroup) deformed by Paleoproterozoic-Mesoproterozoic events with a subsequent record of crustal extension, dyke intrusion and syn-rift sedimentation commencing around 827 Ma. These events not only constrain the timing and initial direction of late Neoproterozoic continental extension but provide a critical test of competing reconstructions for Rodinia in which south-central Australia is juxtaposed against western Laurentia. Contrary to some reconstructions there is no continuation of 1100-1300 Ma Grenville-age rocks into Broken Hill (SWEAT) and alternative restorations based on juxtaposition of the Broken Hill and Mojave-Oaxaca terranes along the Sonora-Mojave mega-shear (southern USA) result in misalignment of this major palaeo-transform fault with late Neoproterozoic normal faults in south-central Australia. Differences in deformational history and tectonic setting also preclude simple matching of 1.7-1.60 Ga orogenic belts in Australia and Laurentia (AUSWUS). In contrast to the southwest margin of Laurentia which was dominated by plate convergence, terrane assembly and arc magmatism throughout much of the Late Proterozoic (Yavapai and Mazatzal orogenies), the Willyama Supergroup preserves a record of 1.72-1.67 Ga intracontinental rifting and crustal extension (D1) followed by nappe emplacement and crustal thickening after 1640 Ma, culminating in the 1600 Ma Olarian orogeny (D2). Crustal thickening produced a second generation of granulite-grade mineral assemblages in the Willyama Supergroup and was superimposed on rocks initially metamorphosed under low P ? high T conditions as a result of D1 crustal thinning and associated bimodal magmatism. The resulting counterclockwise P-T-time path is evident only in the structurally higher parts of the Willyama Supergroup whereas the underlying and once more deeply buried parts of the sequence reveal evidence of decompression and metamorphism under progressively lower pressures as might be expected to occur during emplacement of a metamorphic core complex. A major mylonite zone of D1 age separates upper and lower structural levels. Validation of existing reconstructions for Rodinia requires a greater range of temporally equivalent events be present in western Laurentia than is presently recognised.

The Stuart Shelf overlies the eastern portion of the Gawler Craton. This part of the Gawler Craton is South Australia's major mineral province and contains the world-class Olympic Dam Cu-U-Au deposit and the recent Cu and Au discovery at Prominent Hill. The Stuart Shelf is several kilometres thick in places. As such, little is known of the crustal structure of the basement, its crustal evolution or its tectono-stratigraphic relationship to adjacent areas, for example the Curnamona Province in the east. There has been much effort applied to advancing our understanding of basement, mainly through the use of potential field data and deep drilling programmes; though drilling has proved very costly and very hit and miss. The Stuart Shelf area needs new data and methods to bring our knowledge of it to the next level of understanding. At a Gawler Craton seismic planning workshop held in July 2001, stakeholders from industry, government, and university stakeholders identified several criteria fundamental to undertaking any seismic survey within the Gawler Craton. These were - Location of seismic traverse across a known mineral system in order to improve understanding and enhance knowledge of the region's mineral systems. Access to surface and/or drill hole geological knowledge to link geology data with the seismic interpretation. Good coverage of potential field data, and Potential for the seismic data to stimulate area selection and exploration in the survey region.

The opening of the Tasmanian Gateway between Australia and Antarctica at the Eocene-Oligocene boundary (~33.5 Ma) was a profoundly important event that affected global oceanographic circulation and climate. Ocean Drilling Program Leg 189 (in the gateway), together with other geoscience information, has increased our understanding of the tectonic and depositional history of the region from the Late Cretaceous until the present day. From the mid-Cretaceous until the latest Eocene, Australia and Antarctica faced each other across an ever-widening Australo-Australian Gulf, terminated to the east by a Tasmanian land bridge (Tasmania and South Tasman Rise [STR]). Siliciclastic sediments poured into the rifts from Antarctica, Australia and parts of the land bridge, forming deltas in a low-oxygen environment. Sedimentation kept up with subsidence, except on oceanic crust in the spreading Tasman Sea. Until the Paleocene/Eocene boundary (~55 Ma), Australia moved northwestward along a fracture west of the land bridge. Thereafter, Australia-Antarctic motion changed to N-S along the Tasman Fracture Zone west of STR, and an oceanic basin opened south of eastern STR. In the middle Eocene (~43 Ma), spreading rates increased between Australia and Antarctica, and Tasman Sea spreading ceased. By the latest Eocene, the STR had subsided until parts of it were current swept, and winnowing reduced sedimentation rates there and on ETP. Rapid and major increases in subsidence marked the final (earliest Oligocene) separation of STR and Antarctica. In the Pacific Ocean, strong currents eroded the shelves and opening straits, and a latest Eocene to early Oligocene hiatus was followed by deposition of bathyal carbonate oozes. The Indian Ocean was different. In nearby areas of Antarctica, non-marine and shelfal siliciclastic sedimentation gave way to glacigene detrital or diatomaceous sedimentation at the Eocene/Oligocene transition. Along the southern margin of mainland Australia, the siliciclastic-carbonate transition came at different times, but largely in the late Eocene and early Oligocene. The west Tasmanian margin ODP site had gradual increases in carbonate content through the Oligocene.

Genetic relationships, identified using a combination of molecular and isotopic (carbon and hydrogen) compositions, have been found between natural gases, oils, oil stains, bitumens and potential source rocks in the onshore and offshore Otway Basin. The gas-gas, gas-oil and oil-source correlations herein challenge the validity of some previously accepted oil families and re-enforces the strong compartmentalisation of petroleum systems in the Otway Basin. Previous geochemical studies in the Otway Basin, mainly focussed on the oils and oil stains, have established that the Otway Basin hosts the most diverse array of petroleum systems within Australia. Up to five different oil families have previously been identified. These oils are sourced from a wide range of depositional environments from fresh to saline lacustrine, fluvio-lacustrine to peat swamp and marine, with suspected effective source rock ages from Late Jurassic to Late Cretaceous. Such depositional settings are consistent with the progressive development of source rocks facies intimately linked to basin development from initial rifting to thermal sag. It is now concluded that there is no indigenous representation of the saline lacustrine oil population in the Otway Basin. The geochemical signal is attributed to downhole contamination from gilsonite; a solid bitumen from the Eocene Green River Formation, USA. Oils stains are thought to be a result of primary migration from mature source rocks into juxtaposed sands and are not a strong advocate for secondary oil migration fairways. The natural gases show a strong geochemical association with their respective oils, suggesting that both are generated together from the same source. Also the gases and oils and their effective source rocks have a strong stratigraphic and geographic relationship, indicating mainly short- to medium-range migration distances from source to trap. Gas and oil in the western Otway Basin are sourced from the fluvio-lacustrine Casterton Formation?Crayfish Group sediments while in the eastern Otway Basin the gas and oil from the Shipwreck Trough and its onshore extension are from the coaly Eumeralla Formation sediments. Gas and oil in the central Otway Basin have a mixed source but predominantly are of Eumeralla Formation source Multiple charge histories are also evident with the widespread influx of overmature, dry gas focused in the western Otway Basin and more recently magmatic CO2 influx. Successive natural gas charges have the potential to displace and/or alter the composition of the pre-existing reservoired gas and oil. In-reservoir biodegradation of oil is seen in the shallower reservoirs but this is not a significant risk in the Otway Basin since nearly all reservoired petroleum is below the temperature/depth limits for biologically sustainable life.

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Despite the clear unambiguous link between gold mineralisation and structural control in the well-endowed eastern Yilgarn Craton (EYC), the tectonic history of this region remains controversial. The current paradigm describes the tectonic history to have evolved in a relatively simple progressive manner with the main `D2? and subsequent events (D3 and D4) being the result of maximum shortening oriented ~E?W or ENE?WSW. Although most previous studies have focussed on the structural geology of the greenstones, both greenstones and granites (Fig. 1) have been assumed to have experienced the same event history (Swager, 1997: Precambrian Research 83, 11-41). This article outlines a new approach taken to better understand the tectonic and geodynamic evolution of this important part of Australia.