Abstract for initial submission, pending acceptance by convention technical program committee.

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A recent Geoscience Australia sampling survey in the Bight Basin recovered hundreds of dredge samples of Early Cenomanian to Late Maastrichtian age. Given the location of these samples near the updip northern edge of the Ceduna Sub-basin, they are all immature for hydrocarbon generation with vitrinite reflectance - 0.5% RVmax, Tmax < 440oC and PI < 0.1. Excellent hydrocarbon generative potential is seen for marine, outer shelf, black shales and mudstones with TOC to 6.9% and HI up to 479 mg hydrocarbons/g TOC. These sediments are exclusively of Late Cenomanian-Early Turonian (C/T) in age. The high hydrocarbon potential of the C/T dredge samples is further supported by a dominance of the hydrogen-rich exinite maceral group (liptinite, lamalginite and telalginite macerals), where samples with the highest HI (> 200 mg hydrocarbons/g TOC) contain > 70% of the exinite maceral group. Pyrolysis-gas chromatography and pyrolysis-gas chromatography mass spectrometry of the C/T kerogens reveal moderate levels of sulphur compounds and the relative abundances of aliphatic and aromatic hydrocarbons predict the generation of a paraffinic-naphthenic-aromatic low wax oil in nature. Not enough oom for rest of Abstract

Australia's North West Shelf (NW Shelf) has been the premier hydrocarbon exploration and production province for over 30 years. Despite the large number of geological studies completed in this region, numerous geological questions remain to be answered such as the provenance of reservoir units and how this relates to reservoir quality, extent and correlation. Submission of offshore sample material by explorers on the NW Shelf has allowed U-Pb age results to be determined; providing insights into the potential provenance and sedimentary transport pathways of various Triassic to Cretaceous reservoir facies. Initial results reveal that the proximal Pilbara, Yilgarn and Kimberly cratons were not major proto-sources during the Middle to Upper Triassic. The prospective, Mungaroo Formation appears to display a Triassic volcanic signature; the source of which remains enigmatic, but numerous grain characteristics suggest a source proximal to the Exmouth Plateau. Many samples show a Gondwana Assemblage age. Sediment sources of this age are absent on the Australian continent suggesting a distal origin - most likely the Antarctic and Indian blocks. Transport pathways, for the Triassic Mungaroo Formation, are interpreted as possibly northward through a proto-Perth Basin or north-westward through the Gascoyne-Hamersley-Pilbara regions. Other results suggest subtle differences in provenance of the sediments between the Exmouth Plateau and Rankin Platform, and that the provenance signatures of the Bonaparte, Canning and Perth basins show distinctively different provenance signatures.

The Onshore Energy Security Program, funded by the Australian Government, has been a five year program (2006-2011) conducted by Geoscience Australia in conjunction with the Australian state and Northern Territory geological surveys. Its aim was to provide new geological information on frontier onshore sedimentary basins in Australia, and, as part of this program, deep seismic reflection data have been acquired across several basins, to provide fundamental information on the stratigraphic and structural architecture of the basins and to stimulate hydrocarbon exploration. Reflection data were acquired over the Darling, Arrowie, Georgina (Queensland and Northern Territory), Amadeus, Arckaringa, Officer (Western Australia and South Australia) and southern Carnarvon Basins. This program also discovered and imaged a previously unknown basin, the Millungera Basin, in northwestern Queensland. Ranging from the Neoproterozoic to Cretaceous, these basins encompass segments of the Centralian Superbasin and later phases of basins that have built the Australia continent. Key results of this work include description of the architecture and internal geometries of each basin, settings imaged include mostly extensional basins, many which are later subject to contraction either by inversion (Arrowie Basin) or thrusting (Amadeus Basin) and, an example of a strike-slip basin, the Moorilyanna Graben, in the Officer Basin. The interpretation of stratigraphy used a sequence stratigraphic approach providing a basis for 1D petroleum systems modelling of the Millungera, Arrowie, Georgina (QLD) and Darling Basins. In total, 10 deep seismic profiles across 8 basins have been interpreted, hopefully contributing to an increase in onshore exploration activity.

Three-dimensional gravity models are a useful part of improving the geological understanding of large areas in various geological settings. Such models can assist seismic interpretation, particularly in areas of poor seismic coverage. In general, forward modelling and inversion are conducted until a single model is derived that fits well to the observed gravity field. However, the value of such a model is limited because it shows only one possible solution that depends on a fixed set of underlying assumptions. These underlying assumptions are not always clear to the interpreter and an arguably more useful approach is to prepare multiple models that test various scenarios under a range of different assumptions. The misfit between observed and calculated gravity for these various models helps to highlight flaws in the assumptions behind a particular choice of physical parameters or model geometry. Identifying these flaws helps to guide improvements in the geological understanding of the area. We present case studies for sedimentary basins off western Africa and western Australia. The flawed models have been used to rethink assumptions related to the geology, crustal structure and isostatic state associated with the basins, and also to identify areas where seismic interpretation might need to be revised. The result is a more reliable interpretation in which key uncertainties are more clearly evident.

The Early Permian to Middle Triassic Bowen and Gunnedah Basins and the Early Jurassic to Early Cretaceous Surat Basin exhibit a complex subsidence history over a period of about two hundred million years. Backstripped tectonic subsidence curves, constructed by removing the effects of processes such as sediment loading, loading due to the water column, and sediment compaction allow the subsidence histories of the basin to be examined in terms of the tectonic drivers that caused the subsidence of the basins. In the Early Permian, rapid subsidence was driven by mechanical extension, forming a series of half grabens along the western margin of the Bowen and Gunnedah Basins. Mechanical extension ceased at about 280 Ma, being replaced by a phase of passive thermal subsidence, resulting in more widespread, uniform sedimentation, with reduced tectonic subsidence rates. At the start of the Late Permian, the passive thermal subsidence phase was interrupted by the onset of lithospheric flexure during a foreland basin phase, driven by convergence and thrust loading to the east in the New England Orogen. Initially, dynamic loading, caused by viscous corner flow in the asthenospheric wedge above the west-dipping subducting plate, led to limited tectonic subsidence. Later in the Late Permian, the dynamic loading was overwhelmed by static loading, caused by the developing retroforeland thrust belt in New England, leading to very high rates of tectonic subsidence, and the development of a major retroforeland basin. Peneplanation in the Late Triassic was followed by sedimentation at the start of the Jurassic, forming the Surat Basin, where the tectonic subsidence can again be interpreted in terms of dynamically-induced platform tilting. Subduction ceased at about 95 Ma, resulting in rapid uplift, due the rebound of the lithosphere following cessation of subduction, or it stepping well to the outboard of Australia.

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Processed seismic data (SEG-Y format) and TIFF images for the 2008 Rankins Springs Seismic Survey (L188), acquired by Geoscience Australia (GA) under the Onshore Energy Security Program (OESP), in conjunction with the New South Wales Department of Primary Industries (NSWDPI). Stack and migrated data are included for lines 08GA-RS1 and 08GA-RS2, as well as CDP coordinates. Raw data for this survey are available on request from clientservices@ga.gov.au

The Naturaliste Plateau is a large marginal plateau located immediately west of the southwestern tip of the Australian mainland from which it is separated by the N-S trending Naturaliste Trough. It has an area of about 90 000 km2, extending for about 400 km E-W and 250 km N-S in water depths of 2000 to 5000 m. Results of a recent study of the Naturaliste Plateau based on new and reprocessed seismic data and RV Marion Dufresne cruise 110 (1998) dredging results indicate that large parts of the plateau are underpinned by Proterozoic metamorphic basement similar to the Leeuwin Block of southwestern Australia. The Naturaliste Plateau is a structurally complex terrain that was rifted in the Jurassic-Early Cretaceous and modified by volcanism towards the end of the Early Cretaceous. A number of variable-size rift basins are imaged on seismic profiles on the plateau. Most of these basins are half-grabens bounded by steep ENE-trending normal faults that dip S or SE. The basins extend for up to 120 km along strike, and are from 10-30 km wide. The largest basin (the western Mentelle Basin) lies beneath the Naturaliste Trough and contains more than 5 km of sediment. Basin development probably commenced with the N-S oriented Permian intracratonic rifting that characterises the western and northwestern Australian margins. These Palaeozoic structures were then reactivated by the Jurassic to Early Cretaceous rifting that preceded breakup between Greater India, and Australia-Antarctica (A-A). However, this structural fabric has been subsequently overprinted by E-W trending rifting, reflecting the Early Cretaceous stress regime developed leading to the Late Cretaceous breakup of Australia and Antarctica. A large number of smaller E-W trending rift basins formed across the southern part of the Naturaliste Plateau during this time. In the Valanginian the Naturaliste Plateau separated from Greater India along its northern and western margins. This breakup was accompanied by widespread volcanism, which partly overprinted pre-existing extensional structures. The southern margin of the plateau was formed during the Late Cretaceous A-A breakup which is interpreted to have commenced in the Santonian with a phase of very slow-spreading. A deep-seismic line extending south from the Naturaliste Plateau across the Diamantina Zone imaged a broad (250 km wide) structurally complex zone, which has been interpreted as a continent-ocean transitional zone. The inboard part of this zone appears to contain a mixture of magmatic and continental crust, while further oceanward, it is dominated by peridotite ridges alternating with basaltic intrusions, producing the characteristic rough bathymetry of the Diamantina Zone. This crust could be alternatively interpreted as an ultra-slow spreading crust or highly extended continental crust with partly unroofed mantle and it is significantly different from the slow-spreading crust described on the southern Australian margin