Annular to crescent-shaped low back scatter SAR slicks over carbonate reefs and shoals in the Timor Sea with slick `feathering', and within the coral spawning period for the region, are interpreted to be caused by a coral spawn event. In contrast, ocean current data and detailed swath bathymetry of the sea floor to the southeast of the coral spawn slicks suggest that elongate repeating slicks in this area are related to current flow over submarine channels. Assessment of these slicks in association with ancillary data, such as bathymetry, current velocities, weather and timing of scene capture allow a more robust interpretation of their origins. Through differentiating coral spawn and bathymetric slicks from oil and other biological slicks in shallow carbonate systems, such as the Timor Sea, petroleum and environmental assessments for these areas can be improved.

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 variability in the inherent optical properties along an estuary-coast-ocean continuum in tropical Australia has been studied. The study area, the Fitzroy Estuary and Keppel Bay system, is a shallow coastal environment (depth < 30 m) with highly turbid waters in the estuary and blue oceanic waters in the bay and subject to macrotides. Biogeochemical and inherent optical properties (IOPs) were sampled in the near-surface layer spatially and across the tidal phase during the dry season. These determinations included continuous measurements of spectral absorption, scattering and backscattering coefficients, together with discrete measurements of spectral absorption coefficients of phytoplankton, nonalgal particles and colored dissolved organic matter, and concentrations of phytoplankton pigments and suspended matter. Because of a large variability in the characteristics of the water components on short spatial and temporal scales, we observe a large variability in the associated optical properties. From the estuary to the bay, particle scattering and dissolved absorption decreased by 2 orders of magnitude, and nonalgal particle absorption decreased by 3 orders of magnitude. We also observed a strong variability in particle single scattering albedo and backscattering efficiency (by a factor of 6) and in specific IOPs (IOPs normalized by the relevant constituent concentration) such as suspended matter-specific particle scattering and chlorophyll-specific phytoplankton absorption. Superimposed on this strong spatial variability is the effect of the semidiurnal tide, which affects the spatial distribution of all measured properties. These results emphasize the need for spatially and temporally adjusted algorithms for remote sensing in complex coastal systems.

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

Australia's nickel sulfide industry has had a fluctuating history since the discovery in 1966 of massive sulfides at Kambalda in the Eastern Goldfields of Western Australia. Periods of buoyant nickel prices and high demand, speculative exploration, and frenetic investment (the 'nickel boom' years) have been interspersed by protracted periods of relatively depressed metal prices, exploration inactivity, and low discovery rates. Despite this unpredictable evolution, the industry has had a significant impact on the world nickel scene with Australia having a global resource of nickel metal from sulfide ores of not, vert, similar 12.9 Mt, five world-class deposits (> 1 Mt contained Ni), and a production status of number three after Russia and Canada. More than 90% of the nation's known global resources of nickel metal from sulfide sources were discovered during the relative short period of 1966 to 1973. Australia's nickel sulfide deposits are associated with ultramafic and/or mafic igneous rocks in three major geotectonic settings: (1) Archean komatiites emplaced in rift zones of granite-greenstone belts; (2) Precambrian tholeiitic mafic-ultramafic intrusions emplaced in rift zones of Archean cratons and Proterozoic orogens; and (3) hydrothermal-remobilized deposits of various ages and settings. The komatiitic association is economically by far the most important, accounting for more than 95% of the nation's identified nickel sulfide resources. The ages of Australian komatiitic- and tholeiitic-hosted deposits generally correlate with three major global-scale nickel-metallogenic events at not, vert, similar 3000 Ma, not, vert, similar 2700 Ma, and not, vert, similar 1900 Ma. These events are interpreted to correspond to periods of juvenile crustal growth and the development of large volumes of primitive komatiitic and tholeiitic magmas caused by large-scale mantle overturn and mantle plume activities. There is considerable potential for the further discovery of komatiite-hosted deposits in Archean granite-greenstone terranes including both large, and smaller high-grade (5 to 9% Ni) deposits, that may be enriched in PGEs (2 to 5 g/t), especially where the host ultramafic sequences are poorly exposed. Analysis of the major komatiite provinces of the world reveals that fertile komatiitic sequences are generally of late Archean (not, vert, similar 2700 Ma) or Paleoproterozoic (not, vert, similar 1900 Ma) age, have dominantly Al-undepleted (Al2O3/TiO2 = 15 to 25) chemical affinities, and often occur with sulfur-bearing country rocks in dynamic high-magma-flux environments, such as compound sheet flows with internal pathways facies (Kambalda-type) or dunitic compound sheet flow facies (Mt Keith-type). Most Precambrian provinces in Australia, particularly the Proterozoic orogenic belts, contain an abundance of sulfur-saturated tholeiitic mafic ± ultramafic intrusions that have not been fully investigated for their potential to host basal Ni-Cu sulfides (Voisey's Bay-type mineralization). The major exploration challenges for finding these deposits are to determine the pre-deformational geometries and younging directions of the intrusions, and to locate structural depressions in the basal contacts and feeder conduits under cover. Stratabound PGE-Ni-Cu ± Cr deposits hosted by large Archean-Proterozoic layered mafic-ultramafic intrusions (Munni Munni, Panton) of tholeiitic affinity have comparable global nickel resources to many komatiite deposits, but low-grades (< 0.2% Ni). There are also hydrothermal nickel sulfide deposits, including the unusual Avebury deposit in western Tasmania, and some potential for 'Noril'sk-type' Ni-Cu-PGE deposits associated with major flood basaltic provinces in western and northern Australia.

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The Early Mesoproterozoic (1600 Ma - 1570 Ma) was a period of widespread compressional tectonism and high geothermal gradient metamorphism in the Australian Proterozoic. In the eastern half of the North Australian Craton, the bulk of Palaeoproterozoic terrains underwent high-temperature tectonism between 1600 Ma to 1550 Ma. In central Australia, the Chewings Orogeny (1600 Ma - 1570 Ma) was associated with approximately north-south shortening coeval with regional low-pressure high-temperature metamorphism up to granulite grade. In northeastern Australia, the Early Isan (1600 Ma - 1580 Ma), and Ewamin-Janan Orogenies (1585 Ma - 1555 Ma) in the Mt Isa and Georgetown and Yambo Inliers, respectively, were also associated with approximately north-south shortening and high geothermal gradient metamorphism. In the southern Australian Proterozoic, the Olarian Orogeny (1610 Ma - 1585 Ma) in the Curnamona Province was also characterised by high geothermal gradient metamorphism. <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 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>

A seismic survey using Australian National Seismic Imaging Resource (ANSIR) Hemi60 Vibroseis vehicles, ARAM24 acquisition equipment and Pelton controllers was carried in the Curnamona province of South Australia over two periods, August 2003 and July 2004. A total of 197.6 km of 2-D data was collected to 18 seconds two way time over a single line at 60 fold CDP coverage. The project was undertaken to meet the objectives of ANSIR proposal 03-02R as lodged by researchers from Primary Industries and Resource, South Australia (PIRSA), Office of Minerals, Energy and Petroleum, SA. The principal scientific objective of this survey was to provide a regional crustal seismic image of the Curnamona Province. This dataset will assist in the understanding of the geological architecture and resource potential of the region particularly in areas under cover. This line links with a seismic transect in the Broken Hill Block undertaken by Australian Geological Survey Organisation (AGSO) in 1996 and provides a future opportunity for an eventual east-west continuation across the Adelaide Geosyncline and the Gawler Craton. The survey was funded by PIRSA, Office of Minerals, Energy and Petroleum, SA and the Predictive Minerals Discovery Cooperative Research Centre (pmd*CRC) with project supervision undertaken by ANSIR and in-kind support from Geoscience Australia (GA).

The biological data used in this study was collected by Museum Victoria in an extensive survey of the fauna of Bass Strait between 1979 and 1983. Additional sediment sampling and swath mapping of parts of Bass Strait were undertaken on GA Survey 226 and Australian Hydrographic Office Survey HI339, in which Geoscience Australia personnel participated (GA Survey 233). Survey HI339 also collected underwater video footage. Biological material from a range of taxonomic groups was identified as a basis for identification and analysis of biological communities. The results indicate that Bass Strait supports a particularly diverse fauna. A high degree of small-scale variation occurs, with even adjacent samples having low similarity. Video footage from sites to the east of Bass Strait corroborates the high degree of faunal diversity over small spatial scales. Analysis of physical variables, derived from data collected on the original survey and supplemented by more recent data, show that longitude and depth are important factors in explaining the biological diversity. Despite this, overall correlation of faunal composition with physical factors is poor, indicating that other environmental variables influence the composition of benthic assemblages, and that different groups of species react to different environmental variables. It is likely that the biota reflect a series of intergrading assemblages rather than a group of discrete and repeatable species associations. Sediment facies identified can be correlated with facies from the Otway margin (Boreen et al., 1993) and those mapped previously in Bass Strait (Jones and Davies, 1983). Analysis of sediments taken from sites previously targeted by Jones and Davies (1983) indicate that sampling technique has had little impact on retention of fines. Rather, the lack of fines is a reflection of the high energy environment of much of Bass Strait. Examination of the composition of sand and gravel fractions indicates that extensive bioerosion acts in concert with physical processes to produce carbonate mud. Biogenic content in sediments shows little correlation with living communities, due in part to the abundance of soft-bodied organisms in the biota, as well as the strong imprint of post-depositional processes on sediments. The biological patterns identified in this study broadly support the divisions of the current Interim Marine and Coastal Regionalisation of Australia (IMCRA Technical Group, 1998) for Bass Strait. However, the biological assemblages are not consistent enough to be mapped. The lack of relationships between biota and sediments over the scale of the study area may reflect the scale of the study area and limitations of the statistical analyses used.

This report presents the interpretive results of a comprehensive geological framework study based on new and existing available well and seismic data. The study was initiated in 2003, as part of Geoscience Australia's Big New Oil Program to address exploration risks in a shallow water frontier basin.