The interpretation of two regional seismic reflection profiles and the construction of a balanced cross section through the southern Australian margin (Bight Basin) are designed to analyze the influence of the Australia-Antarctica continental breakup process on the kinematic evolution of the Cretaceous Ceduna delta system. The data shows that the structural architecture of this delta system consists of two stacked sub-delta systems. The lower White Pointer delta system (Late Albian-Santonian) is an unstable tectonic wedge, regionally detached seaward above Late Albian ductile shales. Sequential restorations suggest that the overall gravitational sliding behavior of the White Pointer delta wedge (~45 km of seaward extension, i.e., ~25%) is partially balanced by the tectonic denudation of the subcontinental mantle. We are able to estimate the horizontal stretching rate of the mantle exhumation between ~2 km Ma-1and 5 km Ma-1. The associated uplift of the distal part of the margin and associated flexural subsidence in the proximal part of the basin are partially responsible for the decrease of the gravitational sliding of the White Pointer delta system. Lithospheric failure occurs at ~84 Ma through the rapid exhumation of the mantle. The upper Hammerhead delta system (Late Santonian-Maastrichtian) forms a stable tectonic wedge developed during initial, slow seafloor spreading and sag basin evolution of the Australian side margin. Lateral variation of basin slope (related to the geometry of the underlying White Pointer delta wedge) is associated with distal raft tectonic structures sustained by high sedimentation rates. Finally, we propose a conceptual low-angle detachment fault model for the evolution of the Australian-Antarctica conjugate margins, in which the Antarctica margin corresponds to the upper plate and the Australian margin to the lower plate.

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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

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The Onshore Energy Security Program, funded by the Australian Government and conducted by Geoscience Australia, has acquired deep seismic reflection data, in conjunction with State and Territory geological surveys, across several frontier sedimentary basins to stimulate petroleum exploration in onshore Australia. Here, we present data from two seismic lines collected in South Australia and the Northern Territory. Seismic line 08GA-OM1 crossed the Carboniferous to Permian Arckaringa Basin is imaged as a series of depocentres forming the Phillipson and Penrhyn Troughs, with a much thinner succession connecting the depocentres, and extending well to the north. Seismic line 08GA-OM1 also crosses the Neoproterozoic to Devonian eastern Officer Basin. The basin is structurally complex in this area, being dominated by south-directed thrust faults and fault-related folds, providing potential for underthrust petroleum plays. Seismic line 08GA-OM1 also images the southern margin of the Amadeus Basin Seismic line 09GA-GA1 crossed the northeastern part of the Amadeus Basin and the complete width of the southern Georgina Basin in the Northern Territory. Structural and sequence stratigraphic interpretations of the seismic lines will be presented here, to be followed by an assessment of the petroleum potential of the basins. In the northeast, seismic line 09GA-GA1 crosses two parts of the basin separated by the Paleoproteroozic to Mesoproterozoic Casey Inlier. Seismic line 09GA-GA1 was positioned to cross that part of the southern Georgina Basin where the basin has a complex southern margin, with Neoproterozoic stratigraphy being thrust interleaved with basement rocks of the Arunta Region.

This report was Commissioned by Geoscience Australia for the Western Tasmania Regional Minerals Program (WTRMP). It was completed by SRK Consulting, and is listed as Report AG701. The report covers the interpretation of economic basement in the Bass Basin, and documents the production of a SEEBASE model.

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