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  • Presentation delivered on 9 March 2012 by Marita Bradshaw.

  • The Capel and Faust basins are located in a remote part of deepwater offshore eastern Australia. They are largely Cretaceous rifts formed within a 1600 km long ribbon of continental crust (the Lord Howe Rise) that became detached from Australia during the fragmentation of the eastern Gondwana plate margin and the opening of the Tasman Basin. As part of Geoscience Australia (GA)'s ongoing work to identify and evaluate the resource potential of Australia's offshore frontier basins, approximately 6 000 km of industry-standard, 106-fold 2D seismic data was acquired over the Capel and Faust basins during late 2006 and early 2007. These data supplemented earlier, sparse regional seismic data and were complemented by the acquisition of approximately 24 000 km2 of multibeam bathymetry and 11 000 line kilometres of shipboard gravity and magnetic data by GA in late 2007. This record details the interpretation of the seismic data and is intended to complement the release of a digital version of the interpretations in workstation formats (GeoFrame, Kingdom). Scientific conclusions drawn from the seismic interpretations and, very importantly, from an integration of the seismic, potential field and other data sets are beyond the scope of this record and are published in other GA Records, scientific papers and conference proceedings volumes.

  • The Capel and Faust basins are located on the northern Lord Howe Rise in water depths of 1300-2500 m. Geoscience Australia recently completed a geological and petroleum prospectivity assessment of the area based on new seismic, potential field, multibeam bathymetry and rock sample data. The data sets were acquired under Australian Geovernment initiatives aimed at providing pre-competitive information to industry.

  • Passive margins worldwide record the combined effects of faulting and magmatism that achieve stretching within the crust, but their relative contributions are difficult to evaluate. The ~1000 km-long Great Australian Bight margin appears to be magma starved, yet its moderate breadth and deepwater setting indicates unusually large amounts of heating during rifting, raising questions concerning the significance and timing of magmatism, the along-strike variability of strain, and the factors causing the localization of rifting along these margins. We re-evaluate existing onshore and offshore gravity, magnetic, seismic reflection, and well data from the Australian margin to investigate the evolution of the margin from rift initiation to breakup and the onset of seafloor spreading. Our results indicate that the southern Australian margin evolved through at least two phases of extension prior to breakup, and that the stretching is spatially and temporally distinct. Rift systems along the Australian margin were established between 165-140 Ma. The rift basins are generally simple, widely-distributed half-graben structures. Strain localized within the centre of this broad rift zone, to a short-lived, possibly magmatic, narrow rift system between 92-83 Ma, immediately prior to the onset of seafloor spreading between Australia and Antarctica. Structural and stratigraphic relations indicate that seafloor spreading initiated at ~83 Ma within the centre of the Great Australian Bight, and then propagated both to the east and west. To the east, or northern sector of the Otway Basin continental rifting continued until approximately 65 Ma. Euler deconvolution and analytical signal results calibrated by seismic reflection data indicate that magmatism commenced immediately before or during Stage-2 rifting (92-83 Ma). Significant crustal thinning accompanied the two rift phases, magmatism during the late stages of rifting may explain the deepwater setting of the Bight Basin.

  • Over the last 10 years there has been a rapid expansion in the coal seam gas industry in Australia. Exploration and production of coal seam gas is primarily focused on sedimentary basins along Australia's eastern seaboard. To provide a sound basis for a national assessment of coal seam gas resources, Geoscience Australia is identifying and mapping the distribution of coal in Australia's onshore sedimentary basins into a single Geographical Information System (GIS). Data are being collated for the three key geological time periods for coal, i.e. the Permian-Triassic, Jurassic-Cretaceous and Cenozoic. Information is being sourced from a wide range of publications and publicly available datasets and includes the distribution, thickness and depth of coal measures, and key attributes such as thermal maturity/rank, water content, porosity/permeability and depositional environment. Other relevant national datasets such as basin polygons, wells, mines and cultural data are also being compiled. While national in scale, work to date has focused on coal measures in the key eastern Australian basins, such as the Permian coals of the Bowen, Gunnedah, Sydney and Galilee basins, and the Jurassic Walloon Coal Measures in the Surat and Clarence-Moreton basins. The GIS forms a fundamental tool for Geoscience Australia's national unconventional hydrocarbon resources assessment. This compilation for the first time provides a single, national-scale coal basins dataset for use by government, industry and the public, reflecting Geoscience Australia's role to improve the information available to support the exploration and management of Australia's hydrocarbon resources. Abstract presented to 2012 Eastern Australasian Basins Symposium (EABS) IV Conference

  • The Capel and Faust basins are located over the northern part of the Lord Howe Rise, a large offshore frontier region containing a number of basins with untested petroleum prospectivity. Recent data acquisition by Geoscience Australia has significantly improved geological knowledge of these basins. Given the diversity of acquired data, comparative sparseness of data coverage, lack of deep drilling control, and complexity of geological structure, effective data integration and analysis methods were essential for a meaningful geological interpretation of the Capel and Faust basins. By using the 3D visualisation and modelling environment provided by GOCAD, the datasets were captured, processed and interpreted to create an integrated 3D model that enabled key geological and prospectivity questions to be answered. This presentation summarises the construction methodology and the resulting geological and prospectivity implications of the Capel-Faust 3D geological model.

  • Legacy product - no abstract available

  • Geoscience Australia is currently conducting a study under the National CO2 Infrastructure Plan (NCIP) to assess suitability of the Vlaming Sub-basin for CO2 storage. It involves characterisation of the potential seal, the Early Cretaceous South Perth Shale (SPS), by integrating seismic and well log interpretation into a sequence stratigraphic framework. The SPS, conventionally described as a regional seal deposited during a post-rift thermal subsidence phase, consists of a series of prograding units deposited in a deltaic to shallow marine setting. Mapping of the SPS has revealed differences in the geometries of progradational sequences between the northern and southern areas, related to the type and distance to the sediment source as well as the seafloor morphology. In the northern area, deltaic progradation and aggradation occurred over a flat topography between the two uplifted blocks. The succession is composed of prograding sequences commonly exhibiting sigmoidal to oblique geometries, prograding from the north-east to south-west. In the southern area the topography is more complex due to the presence of several paleotopographic highs associated with pre-existing structures. These sequences are sigmoidal to oblique in cross section. They were deposited in fan shaped lobes, successively infilling paleotopographic lows. Direction of the progradation is from southwest to northeast. The thickness of the SPS varies from 200 m between topographic highs to 700 m in the lows. Sedimentary facies are interpreted to vary from sandy delta front to muddy slope and prodelta deposits. These findings will be used in a 3D geological model for assessing CO2 storage potential.

  • The seismic stacking velocity data in the Otway Basin are a useful dataset for calculating depths and sediment thicknesses. This work presents time-depth relationships computed from unsmoothed stacking velocities and compares these with functions obtained from sonobuoy refraction data and exploration well sonic logs. The comparison suggests that a total sediment thickness over-estimate for the Otway Basin of about 15% can be expected from the depths derived from stacking velocities alone. On the other hand, for sediment thickness calculations down to ~3 s two-way travel time below sea floor, stacking velocity data give comparable depths to those obtained from the sonic logs. A piece-wise formula is offered which scales the time-depth function for the Otway Basin in order to compensate for the depth overestimate inherent in using stacking velocities to calculate total sediment thickness.