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

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.

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.

pmd*CRC 2005-06 Journal articles

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. Strikingly similar geological histories and metal endowments support the view that the Broken Hill (Curnamona craton) and Mt Isa regions were once contiguous, or at least formed part of a single continuous Zn-Pb and/or IOCG mineral province, during the late Palaeoproterozoic-early Mesoproterozoic (Giles et al., 2004). Pb model ages for major Zn-Pb deposits like Broken Hill and Cannington (1675 Ma and 1665 Ma respectively) are comparable (Carr et al., 2004) and high grade metasedimentary rocks hosting these deposits are thought to have been deposited at about the same time (ca 1690-1670 Ma) in either an intra-continental rift or a back-arc extensional environment (e.g., Blake, 1987; Walters and Bailey 1998; Betts et al., 2003). High grade deformation and metamorphism at 1580-1600 Ma (e.g., Page and Sweet, 1998; Page et al. 2004) preclude unequivocal identification of the original ore-forming environment in both cases, although clues to the tectonic setting and kinematic framework are still preserved in less intensely metamorphosed rocks of equivalent age in the Mount Isa Western Succession. The Western Succession rocks developed over a 200-Myr period from 1.8 Ga to 1.6 Ga (Blake, 1987) and, thus, overlap in age with five major tectonothermal events (Claoué-Long, 2003; Scrimgeour, 2005) recognised in the Arunta-Tanami region of the NAC. Major events identified at 1810 Ma and 1770 Ma (Stafford and Yambah), 1730-1700 Ma (Strangways), ~ 1640 Ma (Leibig) and 1560-1590 Ma (Chewings) in the NAC also find expression in the Mount Isa and Broken Hill regions (Page et al., 2000; Neumann et al., 2006), inviting speculation that the crustal processes and geodynamic framework inferred for these two regions are equally pertinent to the mineral provinces in the southern and eastern NAC.

Micrometallogeny of Hydrothermal Fluids Project F3

As a consequence of the Greater Hobart Quickbird Imagery Trial project I&LS has produced a 12.5m interval DEM based on LIST 5m and 10m contours. The extent of the 12.5m DEM data over Greater Hobart Quickbird Trial area is delineated by the green box in the map image. The areas where 5m contour were used as the source data for the DEM creation (depicted by pink shaded tiles in map image) have the greater height accuracy warranting the 12.5m grid interval. The remaining area uses the same LIST 10m contour data as used for creation of the Tas 25m DEM. Extent MGA coordinates are 439987mE to 590012mE and 5169983mN to 5295008mN.

The Bremer Sub-basin is a Mid Jurassic - Late Cretaceous half-graben complex that forms the western-most depocentre of the Bight Basin. It is located across the continental slope off the southern coast of Western Australia in water depths of 100 - 4000 m and with no wells drilled in the sub-basin it is a rank frontier area for petroleum exploration. Through integrating dredge sample data with regional seismic interpretations, it has been possible to develop a structural and stratigraphic framework for the sub-basin, and assess the petroleum exploration potential using conventional basin analysis techniques. Structurally, the sub-basin comprises a series of en-echelon SW-NE trending fault-bounded half graben and a significant intra-basin fault system that developed as a result of rifting between Australia and Antarctica. Of particular importance to petroleum exploration are three major cycles of lacustrine and fluvial sedimentation in Late Jurassic - Early Cretaceous strata, which provide key petroleum system elements of both organic-rich source rocks to generate hydrocarbons, and sandstones overlain by thick mudstones that could potentially reservoir hydrocarbons. Exploration opportunities and risks vary across the sub-basin. A large potential source kitchen area occurs in the central part of the sub-basin, where sediments are between 4 - 9.5 km thick. Here, the main exploration play is fault block traps in water depths of 1000 - >2500 m. Smaller depocentres with up to 5 km of sediment fill occur in the western and eastern parts of the basin and host large anticlinal structures in water depths of 500 - 800 m.

No abstract available