Legacy product - no abstract available

Legacy product - no abstract available

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 Australian Southern Margin SEEBASE® Compilation represents many years of work by SRK in southern Australia in the petroleum, mineral and coal sectors. During this time SRK has undertaken numerous projects in southern Australia with both the private and government sectors. These projects have resulted in the development of a model of the geological evolution of southern Australia from Archean to Recent that is summarised in this GIS and report. The model is consistent with a wide range of datasets including airborne and satellite remote sensing, seismic, well and outcrop observations. The basins of Australia's Southern margin formed by the repeated reactivation of long-lived basement structures. By understanding the genesis and geometry of the old basement structures, we have produced a model for the evolution of the Southern Margin basins that explains their structural framework and architecture. This SEEBASE model and structural interpretation can now be used as the basis for a new understanding of the sequence stratigraphy and petroleum systems of the margin.

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.

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.

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.

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.

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.

Presentation delivered on 8 March 2012 at the Tasman Frontier Petroleum Industry Workshop, 8-9 March 2012, Geoscience Australia, Canberra.