Benthic habitats on the continental shelf are strongly influenced by exposure to the effects of surface ocean waves, and tidal, wind and density driven ocean currents. These processes combine to induce a combined flow bed shear stress upon the seabed which can mobilise sediments or directly influence organisms disturbing the benthic environment. Output from a suite of numerical models predicting these oceanic processes have been utilised to compute the combined flow bed shear stresses over the entire Australian continental shelf for an 8-year period (March 1997- February 2005 inclusive). To quantify the relative influence of extreme or catastrophic combined flow bed shear stress events and more frequent events of smaller magnitude, three methods of classifying the oceanographic levels of exposure are presented: 1. A spectral regionalisation method, 2. A method based on the shape of the probability distribution function, and 3. A method which assesses the balance between the amount of work a stress does on the seabed, and the frequency with which it occurs. Significant relationships occur between the three regionalisation maps indicating seabed exposure to oceanographic processes and physical sediment properties (mean grain size and bulk carbonate content), and water depth, particularly when distinction is made between regions dominated by high-frequency (diurnal or semi-diurnal) events and low-frequency (synoptic or annual) events. It is concluded that both magnitude and frequency of combined-flow bed shear stresses must be considered when characterising the benthic environment. The regionalisation outputs of the Australian continental shelf presented in this study are expected to be of benefit to quantifying exposure of seabed habitats on the continental shelf to oceanographic processes in future habitat classification schemes for marine planning and policy procedures.

The characterisation of benthic habitats based on their abiotic (physical and chemical) attributes remains poorly defined in the marine environment, but is becoming increasingly central in the development of marine management plans in Australia and elsewhere in the world. The current study tested this link between physical and biological datasets for the southern Gulf of Carpentaria, Australia. The results presented were based on a range of physical factors, including the sediment composition (grain size and carbonate content), sediment mobility, water depth and organic carbon flux, and their relationship to the distribution and diversity of benthic macrofauna was tested. The results reveal the importance of process-based indices, such as sediment mobility, in addition to other environmental factors in defining the distribution of the benthic macrofauna. The distribution of the benthic macrofauna changes gradationally across the south-eastern Gulf, associated with changes in the per cent mud and gravel, the seabed exposure and the water depth. Patterns of diversity also reveal the importance of physical processes such as sediment mobility in defining benthic habitats. The species' environment relationships observed at the small scale of the current study are consistent with broader associations observed for other organisms within the Gulf.

40Ar/39Ar dating of mica-bearing pyrite from thermally overprinted Archean gold deposits

Decrepitation and degassing behaviour of quartz up to 1560 °C: Analysis of noble gases and halogens in complex fluid inclusion assemblages

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The North Australia Project of Geoscience Australia had, as its starting point, the review of event chronology in the Arunta Region compiled by Collins and Shaw (1995) and only sparse dating coverage in the Tanami and Tennant regions. The knowledge-base was still dominated by younger systems, which overprinted the Palaeoproterozoic rocks. Early attempts to unravel the pre-1700 Ma evolution with SHRIMP U-Pb dating had not yet identified all of the major event systems and their scope. In the absence of detailed timing constraints, regional correlations were conjectural or based on perceived litholigical links. The prevailing model was that the earliest evolution across the Proterozoic inliers of northern Australia comprised two major basin phases separated by a single correlated orogenic episode, the 'Barramundi Orogeny', which created and defined the North Australian Craton as a tectonic domain (Etheridge et al., 1987, Meyers et al., 1996). Detailed regional re-mapping, combined with a program of imaging-assisted SHRIMP U-Pb dating studies, has led to a new understanding. Several distinct events are now recognised and there are many basin phases separated by a variety of stratigraphic and/or tectonic surfaces. Although major issues are yet to be resolved, there is greater confidence in reconstructing the evolution and metallogeny of individual regions. Some key inter-region correlations can now be demonstrated at the scale of individual formations, unconformities or events. <p>Related product:<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=64764">Evolution and metallogenesis of the North Australian Craton Conference Abstracts</p>

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The 2005 Tanami Seismic Collaborative Research Project was developed to provide a better understanding of the crustal architecture and mineral systems of the Tanami region within Western Australia and the Northern Territory. This was achieved through the acquisition of four regional scale deep crustal seismic reflection profiles. The Tanami Seismic Collaborative Research Project involved Geoscience Australia, the Northern Territory Geological Survey, the Geological Survey Western Australia, Newmont Exploration Pty Ltd and Tanami Gold NL. <p>Related product:<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=64764">Evolution and metallogenesis of the North Australian Craton Conference Abstracts</p>

The HyLogger hyperspectral core-mapping instrument, developed by CSIRO's Mineral Mapping Technologies Group (MMTG), can log up to 1000 m of core per day (more for chips) and has automated core tray handling, digital imaging and spectral scanning and specialised mineral identification software for rapid logging capability. The Central Gawler Gold Province HyLogger project is a collaborative undertaking between the collaborators/developers: CSIRO MMTG, Primary Industries and Resources South Australia (PIRSA) / Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRC LEME) and Geoscience Australia. The Tunkillia prospect, part of the Central Gawler Gold Province, is located some 250 km South of Coober Pedy, and is a regolith-dominated landscape with up to 300m of cover. The area delineated as a de-magnetised zone by earlier studies, was extensively drilled with Diamond and RC drilling. Selected diamond holes from Tunkillia were selected for this HyLogger investigation. At Tunkillia, high gold shows some correlation with white mica composition (phengite-muscovite), as well as mica crystallinity and spectral absorption feature wavelength shifts, possibly representing an increasing in acidity due to mixing of metamorphic muscovite and hydrothermal fluid in the altered granitic host rocks. Alteration occurring in mafic dykes, are well delineated by chlorite-carbonate minerals which can be easily mapped. Gold is predominantly confined to a granitic host, high gold in mafic rocks appears to occur in nearly all cases on margins / fracture zones between the dyke and the host rock. This talk was presented at the Workshop on iron oxide copper-gold systems of the Gawler Craton, held at the AMF Centre, Adelaide on 24 February, 2006.

Reply to comment by Brian Stevens on Evidence and timing of crustal extension versus shortening in the early tectonothermal evolution of a Proterozoic continental rift sequence at Broken Hill, Australia

Decrepitation and degassing behaviour of quartz up to 1560 °C: Analysis of noble gases and halogens in complex fluid inclusion assemblages

Evaluation of 40Ar 39Ar quartz ages: Implications for fluid inclusion retentivity and determination of initial 40Ar/36Ar values in Proterozoic samples