A new sequence stratigraphic framework has been developed for the Otway Basin based on the interpretation and integration of offshore wells, key onshore wells, new biostratigraphic results and a regional grid of 2D seismic data. In the new tectonostratigraphic framework, seven major basin phases and their eight component supersequences are recognised as follows: 1) Tithonian?-Barremian rifting of the Crayfish Supersequence 2) Aptian-Albian post-rift deposition of the Eumeralla Supersequence 3) mid-Cretaceous compression and inversion 4) Late Cretaceous rifting of the Shipwreck and Sherbrook Supersequences 5) latest Maastrichtian to Middle Eocene basin reorganisation and early thermal subsidence of the Wangerrip Supersequence 6) local inversion and thermal subsidence of the Nirranda Supersequence (Middle Eocene to Early Oligocene) followed by thermal subsidence and progressive compression of the Heytesbury Supersequence (Late Oligocene to Late Miocene) leading to Late Miocene uplift and erosion and 7) Plio-Pleistocene deposition of the Whalers Bluff Supersequence. Basin phases are distinguished by their different tectonic driving mechanisms as the primary control on the creation of accommodation space. The supersequences are bounded by regional unconformities and define major episodes of sedimentation within each basin phase. Supersequences are related to second-order transgressive-regressive cycles within the basin and are regionally mappable. The new sequence stratigraphic framework is then used as the basis for correlation to deep-water regions where well-control is limited or absent. The framework is also used to help place existing, complex, facies-dependent lithostratigraphic schemes into depositional and petroleum systems context.

In 2010 and 2011, the Australian Government released exploration acreage in the Perth, Mentelle and Southern Carnarvon basins off the southwest margin of Australia. This release was underpinned by two new marine geophysical surveys (GA-310 and GA-2476) that were conducted by Geoscience Australia in late 2008 and early 2009 as part of the Australian Government's Offshore Energy Security Program. These surveys acquired a range of pre-competitive geological and geophysical data that included seismic reflection, gravity, magnetic and swath bathymetry measurements, as well as seafloor dredge samples. The new surveys provided a total of about 26 000 line km of new gravity and magnetic data that add to existing data from around 150 previous marine surveys conducted off the southwest margin since 1960. This Record describes the integration and levelling of the new gravity and magnetic data with existing data, both offshore and onshore, to produce a unified gravity and magnetic dataset for use in constraining regional tectonics, basin structure and petroleum prospectivity. Levelling is a key step in processing ship-borne gravity and magnetic data. This process minimises the mistie errors at ship-track cross-overs that arise from factors such as positioning errors, instrument drift and lack of diurnal corrections to magnetic data. Without accounting for these cross-over errors, gridded data can be rendered un-interpretable by artefacts and distortions at line cross-overs.

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.

Legacy product - no abstract available

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.

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.

The Ceduna Sub-basin of the deep-water frontier Bight Basin contains a Middle Jurassic-Late Cretaceous sedimentary succession in excess of 15 km thick. Nine offshore exploration wells have been drilled in the basin, mostly clustered around the inboard edge of the Ceduna Sub-basin. As a result, the distal mid-Late Cretaceous strata predicted to contain potential source rock facies, had previously not been sampled. The presence of high quality source rocks in the basin was therefore an open question. 2D seismic data was used to delineate targets for sampling of the pre-Campanian section of the basin. Identified targets included potential source intervals of Albian-Santonian age at locations on the seaward edge of the Ceduna and Eyre Terrace where canyon formation, slumping and faulting have exposed the section. Also, a series of sites were selected to test for potential hydrocarbon seepage in the basin. These sites include areas where recently reactivated deep-seated faults were exposed at the seafloor, basin margin areas where facies thin, and areas where possible seepage was identified from Synthetic Aperture Radar (SAR) data. In February and March 2007, a 3-week marine acquisition programme was carried out on the RV Southern Surveyor. Potential dredge targets were first surveyed with 30 kHz EM300 swath bathymetry and observed with Topaz 3.5 kHz sub-bottom profiler. Near-live swath processing and slope analysis techniques enabled site specific dredge sampling of seafloor terrains where Cretaceous section outcropped or slopes were sufficient to ensure only a thin cover of overlying sediments. Targets include fault scarps and eroded sides of canyons. A better-than-expected number of successful dredges were collected (total of 37) from water depths ranging from 1600-4500m. Geochemical analysis of 259 dredge samples for total organic carbon (TOC) and pyrolysis yields (Rock Eval) identified good to very good organic richness in 13 samples, with TOC values between 2.1% and 6.2%. Of these, seven show liquids potential with Hydrocarbon Index (HI) values ranging between 274 and 479 (mgHC/TOC). The rocks with the best source rock characteristics came from high priority sampling sites in the westernmost Ceduna Sub-basin. Organic geochemical analysis has provided evidence for preservation of organic matter under anoxic conditions close to or at the sediment-water interface. Biostratigraphic analysis of these organic-rich rocks has yielded an age around the Cenomanian-Turonian boundary. Although the dredged rocks are immature for hydrocarbon generation, interpretation of an extensive seismic grid across the basin and petroleum system modelling have shown that this succession occurs with the oil window in the central Ceduna Sub-basin. The results of this study provide the best evidence to date for the presence of good quality liquids-prone source rocks in the basin, successfully addressing a key industry concern in this petroleum exploration frontier.

The paper discusses the results from the GA-302 2D seismic survey and GA-2436 (RV Tangaroa) marine reconnaissance survey over the Capel and Faust basins, northern Tasman Sea. The integration of seismic, potential field and bathymetric data sets in 3D space at an early stage in the project workflow has assisted in the visualisation of the basin architecture, the interpolation of data between the seismic lines, and the iterative refinement of interpretations. The data sets confirm the presence of multiple depocentres, as previously interpreted from satellite gravity data, with a maximum sediment thickness of 5-7 km. Preliminary interpretation of the seismic data has identified two predominantly Cretaceous syn-rift and two Upper Cretaceous to Neogene sag megasequences overlying a heterogeneous pre-rift basement. The comparison of seismic facies and tectonostratigraphic history with offshore New Zealand and eastern Australian basins suggests the presence of possible Jurassic to Upper Cretaceous coaly and lacustrine source rocks in the pre- and syn-rift, and fluvio-deltaic to shallow marine reservoir rocks in the syn-rift to early post-rift successions. Preliminary 1D basin modelling suggests that the deeper depocentres of the Capel and Faust basins are within the oil and gas windows. Large potential stratigraphic and structural traps are also present.

No abstract available

Poorly exposed Paleoproterozoic sandstones and siltstones of the Killi Killi Formation record developement of a large turbidite complex. Killi Killi Formation sediments were eroded from the uplifted ~1860 Ma Nimbuwah and Hooper Orogens as indicated by detrital zircons with sediment deposition at ~1840 Ma. Facies analysis, isopach maps and detrital zircon populations, combined with Sm-Nd data from the Tanami region and Halls Creek Orogen, confirm the previously suggested correlation of the Paleoproterozoic successions in the Eastern zone of the Halls Creek Orogen and the Tanami region. Detrital zircons from the Aileron Province suggest the turbidite complex extends into the Arunta region, however, high metamorphic grade precludes direct facies comparisons in the Arunta region. Portions of the turbidite complex in the Tanami region are dominated by mudstones, consisting of low-density turbidites and associated hemipelagites, that potentially acted as a redox boundary to gold-bearing fluid. Gold prospectivity in turbiditic systems is increased within these mudstone sequences with the potential for further gold discoveries.