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  • As Australia separated from Antarctica and drifted northward the Tasmanian Gateway opened, allowing the Antarctic Circumpolar Current to develop. This current began to isolate Antarctica from the influence of warm surface currents from the north, and an ice cap started to form. Eventually, deepwater conduits led to deepwater circulation between the southern Indian and Pacific Oceans. The existence of these conduits ultimately allowed ocean conveyor circulation. Continuing Antarctic thermal isolation, caused by the continental separation, contributed to the evolution of global climate from relatively warm early Cenozoic ?Greenhouse? to late Cenozoic ?Icehouse? climates. ODP Leg 189 addressed the interrelationships of plate tectonics in the gateway, circum-polar current circulation, climate and sedimentation, and global climatic changes. DSDP drilling had led to a basic framework of paleoenvironmental changes associated with gateway opening, but was not a full test of the various interrelationships. Using the DSDP results, Kennett, Houtz et al. (1975) proposed that climatic cooling and an Antarctic ice sheet (cryosphere) developed from ~33.5 Ma as the ACC progressively isolated Antarctica thermally. They suggested that development of the Antarctic cryosphere led to the formation of the cold deep ocean and intensified thermohaline circulation. Leg 189 gathered data that support this hypothesis. Leg 189 continuously cored sediments in the gateway, which was once part of a Tasmanian land bridge between Australia and Antarctica. The bridge separated the Australo-Antarctic Gulf in the west from the proto-Pacific Ocean to the east. This region is one of the few in the Southern Ocean where almost complete Cenozoic marine sequences could be drilled in paleo-water depths that were shallow enough to allow preservation of calcareous micro-organisms for isotopic studies. The Leg 189 sequences described by Exon, Kennett, Malone et al. (2001) reflect the evolution of a tightly integrated and dynamically evolving system over the past 70 million years, involving the lithosphere, hydrosphere, atmosphere, cryosphere and biosphere. The most conspicuous changes in the region occurred over the Eocene-Oligocene transition (Figure 1) when Australia and Antarctica finally separated. Before the separation, the combination of a warm climate, nearby continental highlands, and considerable rainfall and erosion, flooded the region with siliciclastic debris. Deposition kept up with subsidence. After separation, a cool climate, smaller more distant landmasses, and little rainfall and erosion, cut off the siliciclastic supply. Pelagic carbonate deposition could not keep up with subsidence. Leg 189 confirmed that Cenozoic Antarctic-Australia separation brought many changes. The regional changes included: warm to cool climate, shallow to deep water deposition, poorly ventilated basins to well-ventilated open ocean, dark deltaic mudstone to light pelagic carbonate deposition, microfossil assemblages dominated by dinoflagellates to ones dominated by calcareous pelagic microfossils, and sediments rich in organic carbon to ones poor in organic carbon.

  • Geoscience Australia conducted a marine mapping survey between October 2008 and January 2009 to document the seabed environments and sub-surface geology of the Zeewyck, Houtman and Exmouth sub-basins and the deep-water Wallaby (Cuvier) Plateau, in Western Australia. The seabed mapping survey was the second and largest mapping survey of the Commonwealth Government's Offshore Energy Security Program. The survey documented seabed environments using multibeam sonar and sub-bottom profiler data, and characterised benthic habitats and biota from towed video footage and seabed samples. Preliminary analysis indicates that the seabed of the three sub-basins comprises carbonate mud that supports relatively sparse infaunal assemblages, while the numerous submarine canyons that incise the basins are characterised by steep rock walls that support sparse assemblages of suspension feeding organisms, such as sponges and gorgonians. Three volcanic (basaltic) peaks on the upper slopes of the sub-basins (rising 200 m above the seabed) were also mapped and surveyed, with relic coral communities recorded within their sediments. Data collected from the survey are being analysed in conjunction with existing environmental data to describe the key seabed habitats and biota for the offshore basins through a series of environmental summaries that will be made available to support future acreage release in the sub-basins. This research was undertaken concurrent to a regional 2D seismic survey to provide a broader understanding of the region. The environmental summaries of these and other Australian Frontier regions will be available to support future acreage release as part of the Offshore Energy Security Program.

  • Geoscience Australia contributes to a greater understanding of natural hazard and disaster exposure through observations of water from space. This supports Australia's capability to reduce the economic, social and environmental impacts of flood events.

  • No abstract available

  • This article investigates the use of the AuSREM 3D velocity model for earthquake location in Australia. The result is that this method can significantly improve the location accuracy as compared to a simple 1D model.

  • In 2007-08 scientists from Australia, Japan and France set out to survey the marine life and habitats in the region adjacent to Terre Adelie and George V Land in East Antarctica (Australian Antarctic Magazine 14: 2-13, 2008). The Collaborative East Antarctic Marine Census (CEAMARC) - part of Australia's contribution to the International Polar Year - aimed to understand the processes that have lead to the evolution and survival of marine life existing in the region today, so that scientists can predict how these organisms may respond to future climate-related changes in their environment. Scientists involved in the census are now finalising the collation and analysis of data and the following pages (13-18) provide an insight into some of the results. The team aims to publish its findings as a series of papers in a special volume of a scientific journal in late 2010.

  • The distribution of zinc deposits through time is periodic, with relatively short periods of high productivity and long periods of low zinc productivity. This distribution is mostly related the the geodynamic evolution of Earth. Most deposits are associated with the assembly and break-up of supercontinents, with stratiform deposits hosted by volcanic-dominated succession and Mississippi Valley-type deposits mostly associated supercontinent assembly, whereas stratiform deposits hosted by clastic-dominated successions are associated with both assembly and break-up of supercontinents. The temporal distribution of other types of zinc deposits reflect preservation. Volcanic-dominated deposits formed at mid-oceanic ridges and deposits formed on advancing accretionary orogens are unlikely to be preserved. Skarn and related deposits are generally a young feature; this distribution is likely a consequence of their poor preservation potential. Although changes in the composition of the atmosphere and hydrosphere are an important control on some characteristics of zinc ores, they are second-order controls on the temporal distribution of zinc. The main change of importance is the oxidation of the atmosphere and portions of the hydrosphere that occurred in the Paleoproterozoic, the Great Oxidation Event. After this event, oxidized fluids evolved in basins, which allowed the formation of Mississippi Valley-type and some clastic-hosted deposits. The other effects of changes in the hydrosphere relate mainly to gangue mineralogy and sulfur isotopes. After the Great Oxidation Event, barite became an important gangue mineral in many zinc deposits, and the sulfur isotope characteristics became more variable, reflecting the characteristics of coeval seawater sulfate.

  • In a collaborative effort with the regional sub-commissions within IAG sub-commission 1.3 'Regional Reference Frames', the IAG Working Group (WG) on 'Regional Dense Velocity Fields' (see http://epncb.oma.be/IAG) has made a first attempt to create a dense global velocity field. GNSS-based velocity solutions for more than 6000 continuous and episodic GNSS tracking stations, were proposed to the WG in reply to the first call for participation issued in November 2008. The combination of a part of these solutions was done in a two-step approach: first at the regional level, and secondly at the global level. Comparisons between different velocity solutions show an RMS agreement between 0.3 mm/yr and 0.5 mm/yr resp. for the horizontal and vertical velocities. In some cases, significant disagreements between the velocities of some of the networks are seen, but these are primarily caused by the inconsistent handling of discontinuity epochs and solution numbers. In the future, the WG will re-visit the procedures in order to develop a combination process that is efficient, automated, transparent, and not more complex than it needs to be.