Understanding of the depth of cover is poor across large areas of Australia. The spectral method is an efficient method of producing reliable depth to magnetic basement estimates across large regions of the continent. A semi-automated work-flow has been created that enables the generation of depth to magnetic source estimates from windowed magnetic data using the Spector and Grant method. The work-flow allows for the correction of the power spectra prior to the picking of straight-line segments to account for the fractal distribution of magnetic sources. The fractal parameter (ß) varies with depth and was determined by picking multiple depth estimates in regions of outcropping magnetic basement which have been upward continued to different levels in order to simulate different amounts of burial beneath non-magnetic sediments. A power law function best approximates the decay of ß with depth. An iterative schema has been incorporated into the workflow which is used to determine the optimum ß where the depths of magnetic sources are unknown. Preliminary testing in a region of known magnetic basement depth has produced encouraging results, although further testing is required. The decrease of ß with increasing depth suggests that the fractal distribution of magnetisation becomes more correlated over larger volumes of observation.

The Onshore Energy Security Program, funded by the Australian Government, Geoscience Australia has acquired deep seismic reflection data across several frontier sedimentary basins to stimulate interest in petroleum exploration in onshore Australia. Detailed interpretation of deep seismic reflection profiles from four onshore basins, focusing on overall basin geometry and internal sequence stratigraphy will be presented here, with the aim of assessing the petroleum potential of the basins. At the Southern end of the exposed part of the Mt Isa Province, northwest Queensland, a deep seismic line (06GA-M6) crosses the Burke River Structural Zone of the Georgina Basin. The basin here is >50 km wide, with a half graben geometry, and bound in the west by a rift border fault. The Millungera Basin in northwest Queensland is completely covered by the thin Eromanga basin and was unknown prior to being detected on two seismic lines (06GA-M4 and 06GA-M5) acquired in 2006. Following this, seismic line 07GA-IG1 imaged a 65 km wide section of the basin. The geometry of internal stratigraphic sequences and post-depositional thrust margin indicate that the original succession was much thicker than preserved today. The Yathong Trough in the southeast part of the Darling Basin in NSW has been imaged in seismic line 08GA-RS2 and interpreted in detail using sequence stratigraphic principles, with several sequences being mapped. The upper part of this basin contains Devonian sediments, with potential source rocks at depth.

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.

Twenty-four samples provided by Geoscience Australia were analysed using screening methods to provide a preliminary insight into the gas shale potential of the Amadeus and Georgina Basins, Australia. Eleven samples from the Amadeus Basin include the Bitter Springs Formation (Late Neoproterozoic), Lower Giles Creek Dolomite (Middle Cambrian), Goyder Formation (Middle Cambrian) and Horn Valley Siltstone (Early Ordovician). Thirteen samples of core from the Georgina Basin are from the Middle Cambrian, and most of them from the "hot shale" of the Arthur Creek Formation. Results indicate that samples from both the Amadeus and Georgina basins have high potential for gas shale.

Increased loads of land-based pollutants associated with land use change are a major threat to coastal-marine ecosystems globally. Identifying the affected areas and the scale of influence on marine ecosystems is critical to assess the ecological impacts of degraded water quality and to inform planning for catchment management and marine conservation. Studies using remotely-sensed data have contributed to our understanding of the occurrence and extent of influence of river plumes, as well as to assess exposure of ecosystems to river-borne pollutants. However, refinement of plume modelling techniques is required to improve risk assessments. We developed a novel approach to model exposure of coastal-marine ecosystems to river-borne pollutants. The model is based on supervised classification of true-colour satellite imagery to map the extent of plumes and to qualitatively assess the dispersal of pollutants in plumes. We use the Great Barrier Reef (GBR) to test our approach. We combined frequency of plume occurrence with spatially-distributed loads (based on a cost-distance function) to create maps of exposure to suspended sediment and dissolved inorganic nitrogen. We then compared annual exposure maps (2007-2011) to assess inter-annual variability in the exposure of coral reefs and seagrass beds. Our findings indicate that classification of true colour satellite images is useful to map plumes and to qualitatively assess exposure to river-borne pollutants. This approach should be considered complementary to remote sensing methods based on ocean colour products used to characterise surface water in plumes. The proposed exposure model is useful to study the spatial and temporal variation in exposure of coastal-marine ecosystems to riverine plumes. Observed inter-annual variation in exposure of habitats to pollutants stresses the need to incorporate the temporal component in exposure and risk models.

The Capel and Faust basins lie at water depths of 1500-3000 metres, 800 km east of Brisbane. Geoscience Australia began a petroleum prospectivity study of these remote frontier basins with acquisition of reflection and refraction seismic, gravity, magnetic and multi-beam bathymetry data across an area of 87,000 km2 during 2006/07. The approach mapped a complex distribution of sub-basins through an integration of traditional 2D reflection seismic interpretation techniques with 3D mapping and gravity modelling. Forward and inverse gravity models were used to inform the ongoing reflection seismic interpretation and test the identification of basement. Gravity models had three sediment layers with average densities inferred from refraction velocity modelling of 1.85, 2.13, 2.31 t/m3 overlying a pre-rift basement of density 2.54 t/m3, itself considered to consist in part of intruded older basin material. Depth conversion of horizon travel times was achieved using a function derived from models of refraction data. Gravity modelling of the simple density model arising from the initial interpretation of reflection seismic data indicated a first order agreement between observed and calculated data. The second order misfits could be accounted for by a combination of adjustments to the density values assigned to each of the layers, localised adjustments to the basin depths, and heterogeneity in the basement density values. The study concluded that sediment of average velocity 3500 m/s exceeds 6000 m thickness in the northwest of the area, which is sufficient for potential petroleum generation.

The Early Permian to Middle Triassic Bowen and Gunnedah basins in eastern Australia developed in response to a series of interplate and intraplate tectonic events located to the east of the basin system. The initial event was extensional and stretched the continental crust to form part of the major Early Permian East Australian Rift System that stretched at least from far north Queensland to southern New South Wales. The most commercially important of the rift-related features are a series of half graben that form the Denison Trough, now the site of several producing gas fields. The eastern part of the rift system commenced at about 305 Ma and was volcanic dominated. In contrast, the half graben in, and to the west of, the Bowen Basin were non-volcanic, and appear to have initiated at about 285 Ma. These half graben are essentially north-south in length with an extension direction of approximately east-northeast. Mechanical extension appears to have ceased at about 280 Ma, when subsidence became driven by thermal relaxation. The extension occurred in a backarc setting, in response to far field stresses that propagated from the west-dipping subduction system at the convergent plate margin of East Gondwana that was located to the east of the East Australian Rift System.

The Proterozoic Mount Isa Inlier records an extensive history of sedimentation, magmatism, tectonism, and mineralisation. SHRIMP geochronology has been integrated with sequence stratigraphy and facies analysis to develop a regional chronostratigraphic framework for sedimentary packages of the Leichhardt and Calvert Superbasins in the Western Fold Belt. Determining the depositional age and regional extent of these packages is important because they are possible source regions for younger Pb mineralising systems, and because the geometries of these basins have an important control on the migration of fluids and on the development of the overlying ca. 1670 to 1575 Ma Isa Superbasin. New SHRIMP geochronology integrated with basin analysis recognises three supersequences in the Leichhardt Superbasin .....

No abstract available

The Bremer Sub-basin, which forms part of the Bight Basin off the southern coast of Western Australia, is a deep-water (100-4000 m water depth) frontier area for petroleum exploration. No wells have been drilled to test the sub-basin's petroleum potential, with company exploration limited to a regional seismic survey by Esso Australia Ltd in 1974. Early studies identified the Bremer Subbasin as a series of Middle Jurassic-Early Cretaceous half graben, which contain potentially prospective structures for trapping hydrocarbons. However, a lack of sub-surface geological data, along with the deep-water setting, discouraged exploration of this area for over 30 years. In 2003, the Bremer Sub-basin was identified as a key frontier area in Geoscience Australia's New Oil Program where new exploration opportunities might occur. Subsequently, Geoscience Australia's Bremer Sub-basin Study commenced in 2004 with an aim to determine if the sub-basin formed under suitable geological conditions to generate and trap large volumes of hydrocarbons.