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  • Product no longer exists, please refer to GeoCat #30413 for the data

  • Product no longer exists, please refer to GeoCat #30413 for the data

  • Product no longer exists, please refer to GeoCat #30413 for the data

  • Product no longer exists, please refer to GeoCat #30413 for the data

  • Current metre deployments, suspended sediment measurements and surface sediment samples were collected from three locations within distributary channels of the tidally dominated Fly River delta in southern Papua New Guinea.

  • Product no longer exists, please refer to GeoCat #30413 for the data

  • Product no longer exists, please refer to GeoCat #30413 for the data

  • 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.

  • The presence of relatively abundant bedded sulfate deposits before 3.2 Ga and after 1.8 Ga, the peak in iron formation abundance between 3.2 Ga and 1.8 Ga, and the aqueous geochemistry of sulfur and iron together suggest that the redox state, and the abundances of sulfur and iron in the hydrosphere varied widely during the Archean and Proterozoic. We propose a layered hydrosphere prior to 3.2 Ga in which sulfate produced by atmospheric photolytic reactions was enriched in an upper layer, whereas the underlying layer was reduced and sulfur-poor. Between 3.2 Ga and 2.4 Ga, sulfate reduction removed sulfate from the upper layer, producing broadly uniform, reduced, sulfur-poor and iron-rich oceans. As a result of increasing atmospheric oxygenation around 2.4 Ga, the flux of sulfate into the hydrosphere by oxidative weathering was greatly enhanced, producing layered oceans, with sulfate-enriched, iron-poor surface waters and reduced, sulfur-poor and iron-rich bottom waters. The rate at which this process proceeded varied between basins depending on the size and local environment of the basin. By 1.8 Ga, the hydrosphere was, relatively sulfate-rich and iron-poor throughout. Variations in sulfur and iron abundances suggest that the redox state of the oceans was buffered by iron before 2.4 Ga and by sulfur after 1.8 Ga.

  • PowerPoint Presentation: 3D structural model for the northern Leichhardt River Fault Trough and adjacent Lawn Hill Platform, Mt Isa. Sponsors, meeting, Barossa Valley, SA (June, 2004).