Deep seismic reflection profiles collected offshore during a circum-navigation of Tasmania have provided fundamental information on the crustal architecture of the State. In particular, the profiles show the geometry of the boundaries between the major crustal elements, including the offshore continuation of the Arthur Lineament. These crustal element boundaries have apparent dips to the east or southeast and most of them appear to cut through the entire crust to the Moho. In eastern Tasmania, the seismic lines show an old mid-crustal extensional event followed by crustal shortening and duplexing, which probably occurred during the Cambrian-Ordovician Delamerian Orogeny. Thrusts that developed at this time were later reactivated as extensional faults during continental breakup of Pangea in the Cretaceous. Granites off the west coast have the geometry of flat, thin pancakes. In summary, the offshore seismic reflection program around Tasmania has led to a better understanding of the geometry and relationships between the basement elements of Tasmania and younger basins.

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Lithostratigraphy, grain sizes and down-hole logs of Site 1166 on the continental shelf, and Site 1167 on the upper slope, are analyzed to reconstruct glacial processes in eastern Prydz Bay and the development of the Prydz trough-mouth fan. In eastern Prydz Bay upper Pliocene-lower Pleistocene glaciomarine sediments occur interbedded with open-marine muds and grade upward into waterlaid tills and subglacial tills. Lower Pleistocene sediments of the trough-mouth fan consist of coarse-grained debrites interbedded with bottom-current deposits and hemipelagic muds, indicating repeated advances and retreats of the Lambert Glacier-Amery Ice Shelf system with respect to the shelf break. Systematic fluctuations in lithofacies and down-hole logs characterize the upper Pliocene-lower Pleistocene transition at Sites 1166 and 1167 and indicate that an ice stream advanced and retreated within the Prydz Channel until the mid Pleistocene. The record from Site 1167 shows that the grounding line of the Lambert Glacier did not extend to the shelf break after 0.78 Ma. Published ice-rafted debris records in the Southern Ocean show peak abundances in the Pliocene and the early Pleistocene, suggesting a link between the nature of the glacial drainage system as recorded by the trough-mouth fans and increased delivery of ice-rafted debris to the Southern Ocean.

1. Blevin et al.:Hydrocarbon prospectivity of the Bight Basin - petroleum systems analysis in a frontier basin 2. Boreham et al : Geochemical Comparisons Between Asphaltites on the Southern Australian Margin and Cretaceous Source Rock Analogues 3. Brown et al: Anomalous Tectonic Subsidence of the Southern Australian Passive Margin: Response to Cretaceous Dynamic Topography or Differential Lithospheric Stretching? 4. Krassay and Totterdell : Seismic stratigraphy of a large, Cretaceous shelf-margin delta complex, offshore southern Australia 5. Ruble et al : Geochemistry and Charge History of a Palaeo-Oil Column: Jerboa-1, Eyre Sub-Basin, Great Australian Bight 6. Struckmeyer et al : Character, Maturity and Distribution of Potential Cretaceous Oil Source Rocks in the Ceduna Sub-Basin, Bight Basin, Great Australian Bight 7. Struckmeyer et al: The role of shale deformation and growth faulting in the Late Cretaceous evolution of the Bight Basin, offshore southern Australia 8. Totterdell et al : A new sequence framework for the Great Australian Bight: starting with a clean slate 9. Totterdell and Bradshaw : The structural framework and tectonic evolution of the Bight Basin 10. Totterdell and Krassay : The role of shale deformation and growth faulting in the Late Cretaceous evolution of the Bight Basin, offshore southern Australia

In 2009, as part of its Onshore Energy Security Program, Geoscience Australia, in conjunction with the Northern Territory Geological Survey, acquired 373 km of vibroseis-source, deep seismic reflection, magnetotelluric and gravity data along a single north-south traverse from the Todd River in the south to nearly 30 km north of the Sandover Highway in the north. This traverse, 09GA-GA1, is referred to as the Georgina-Arunta seismic line, extends from the northeastern Amadeus Basin, across the Casey Inlier, Irindina and Aileron provinces of the Arunta Region and Georgina Basin to the southernmost Davenport Province. Here, we report the results of an initial geological interpretation of the seismic and magnetotelluric data, and discuss some preliminary geodynamic implications.

The frontier deepwater Otway and Sorell basins lie offshore of south-western Victoria and western Tasmania at the eastern end of Australia's Southern Rift System. The basins developed during rifting and continental separation between Australia and Antarctica from the Cretaceous to Cenozoic. The complex structural and depositional history of the basins reflects their location in the transition from an orthogonal-obliquely rifted continental margin (western-central Otway Basin) to a transform continental margin (southern Sorell Basin). Despite good 2D seismic data coverage, these basins remain relatively untested and their prospectivity poorly understood. The deepwater (>500 m) section of the Otway Basin has been tested by two wells, of which Somerset 1 recorded minor gas shows. Three wells have been drilled in the Sorell Basin, where minor oil shows were recorded near the base of Cape Sorell 1. As part of the Federal Government funded Offshore Energy Security Program, Geoscience Australia has acquired new aeromagnetic data and utilised open file seismic datasets to undertake an integrated regional study of the deepwater Otway and Sorell basins. Structural interpretation of the new aeromagnetic data and potential field modelling provide new insights into the basement architecture and tectonic history, and highlights the role of pre-existing structural fabric in controlling the evolution of the basins. Regional scale mapping of key sequence stratigraphic surfaces across the basins, integration of the regional structural analysis, and petroleum systems modelling have resulted in a clearer understanding of the tectonostratigraphic evolution and petroleum prospectivity of this complex basin system.

As part of the Offshore Energy Security Program (2007-2011), Geoscience Australia (GA) undertook an integrated regional study of the deepwater Otway and Sorell basins to improve the understanding of the geology and petroleum prospectivity of the region. Major outputs of this study include: - New interpretations of basement architecture and structural fabric resulting in the recognition of the Avoca-Sorell Fault System as a major control on sedimentary basin development, - Extension of the tectonostratigraphic framework of Krassay et. al. (2004) into the deepwater Otway and Sorell basins, leading to new insights into their structural and accommodation histories of both basins, and - Petroleum systems modelling indicating that these basins are mature for oil and gas generation.

The Sedimentary basins of eastern Australia project undertook structural and sequence stratigraphic mapping of a regional grid of seismic reflection data in the Bowen, Gunnedah and Surat Basins (usually 4 seconds two-way travel time data, with about 15,000 line km of data on about 1200 individual seismic lines). The seismic mapping was used to define the interplate and intraplate tectonic events that have helped to create the accommodation space and also to define the stratal geometry of the sedimentary units. Thus, the mapping provided the overall geometry of the basin system as well as the geometry of several of the sequence boundaries, resulting in the development of a new sequence stratigraphic framework for the basins. These results were also compiled into a series of structure contour and isopach maps, which have been used to build a 3D geological map of the Bowen Gunnedah and Surat Basins.

The 2012 Australian offshore acreage release includes exploration areas in four southern margin basins. Three large Release Areas in the frontier Ceduna Sub-basin lie adjacent to four exploration permits granted in 2011. The petroleum prospectivity of the Ceduna Sub-basin is controlled by the distribution of Upper Cretaceous marine and deltaic facies and a structural framework established by Cenomanian growth faulting. These Release Areas offer a range of plays charged by Cretaceous marine and coaly source rocks and Jurassic lacustrine sediments. In the westernmost part of the gas-producing Otway Basin, a large Release Area offers numerous opportunites to test exisiting and new play concepts in underexplored areas beyond the continental shelf. Gas and oil shows in the eastern part of the Release Area confirm the presence of at least two working petroleum systems. In the eastern Otway Basin, several Release Areas are offered in shallow water on the eastern flank of the highly prospective Shipwreck Trough and provide untested targets along the eastern basin margin southward into Tasmanian waters. To the south, a large Release Area in the frontier Sorell Basin provides the opportunity to explore a range of untested targets in depocentres that formed along the western Tasmanian transform continental margin. This year, two Release Areas offer exploration potential in the under-explored eastern deep-water part of the Gippsland Basin. Geological control is provided by several successful wells indicating the presence of both gas and liquids in the northern area, while the southern area represents the remaining frontier of the basin.

This document is a professional opinion, presenting an assessment of the macrofossils present in well CKAD0001, located in the Northern Territory in the Georgina Basin.