The Naturaliste Plateau is a large marginal plateau located immediately west of the southwestern tip of the Australian mainland from which it is separated by the N-S trending Naturaliste Trough. It has an area of about 90 000 km2, extending for about 400 km E-W and 250 km N-S in water depths of 2000 to 5000 m. Results of a recent study of the Naturaliste Plateau based on new and reprocessed seismic data and RV Marion Dufresne cruise 110 (1998) dredging results indicate that large parts of the plateau are underpinned by Proterozoic metamorphic basement similar to the Leeuwin Block of southwestern Australia. The Naturaliste Plateau is a structurally complex terrain that was rifted in the Jurassic-Early Cretaceous and modified by volcanism towards the end of the Early Cretaceous. A number of variable-size rift basins are imaged on seismic profiles on the plateau. Most of these basins are half-grabens bounded by steep ENE-trending normal faults that dip S or SE. The basins extend for up to 120 km along strike, and are from 10-30 km wide. The largest basin (the western Mentelle Basin) lies beneath the Naturaliste Trough and contains more than 5 km of sediment. Basin development probably commenced with the N-S oriented Permian intracratonic rifting that characterises the western and northwestern Australian margins. These Palaeozoic structures were then reactivated by the Jurassic to Early Cretaceous rifting that preceded breakup between Greater India, and Australia-Antarctica (A-A). However, this structural fabric has been subsequently overprinted by E-W trending rifting, reflecting the Early Cretaceous stress regime developed leading to the Late Cretaceous breakup of Australia and Antarctica. A large number of smaller E-W trending rift basins formed across the southern part of the Naturaliste Plateau during this time. In the Valanginian the Naturaliste Plateau separated from Greater India along its northern and western margins. This breakup was accompanied by widespread volcanism, which partly overprinted pre-existing extensional structures. The southern margin of the plateau was formed during the Late Cretaceous A-A breakup which is interpreted to have commenced in the Santonian with a phase of very slow-spreading. A deep-seismic line extending south from the Naturaliste Plateau across the Diamantina Zone imaged a broad (250 km wide) structurally complex zone, which has been interpreted as a continent-ocean transitional zone. The inboard part of this zone appears to contain a mixture of magmatic and continental crust, while further oceanward, it is dominated by peridotite ridges alternating with basaltic intrusions, producing the characteristic rough bathymetry of the Diamantina Zone. This crust could be alternatively interpreted as an ultra-slow spreading crust or highly extended continental crust with partly unroofed mantle and it is significantly different from the slow-spreading crust described on the southern Australian margin

New geophysical data acquired by Geoscience Australia during the Southwest Margins 2D seismic survey in 2008-09 has been used to interpret the tectonic and depositional history of the Mentelle Basin. The Mentelle Basin is a large, potentially prospective frontier basin located between the Yallingup Shelf and the Naturaliste Plateau. It comprises several shallow water depocentres (500-1500 m) in the east (eastern Mentelle Basin) and a large ultra deep-water depocentre (3000-3500 m) in the west (western Mentelle Basin). Interpretation of the new data revealed that initial rifting in the Mentelle Basin occurred in the Early Permian as part of the Perth Basin extensional system. This was followed by Late Permian to Early Jurassic thermal subsidence. Half-graben structures with Permo-Triassic fill have been mapped in the eastern Mentelle Basin. The main depositional phase in the western Mentelle Basin has been interpreted to correlate with Late Jurassic to Early Cretaceous extension in the Perth Basin and on the Southern Margin. New structural interpretation shows that in the northern part of the western Mentelle Basin, major structures are trending N-S similar to the Perth Basin, whereas in the south most structures are trending SW-NE, which is consistent with the orientation of the extensional basins on the Southern Margin. The proximity of the Southern Margin rift system not only affected the structure of the Mentelle Basin but also resulted in major fault reactivation, inversion and margin collapse in the Eocene corresponding to the onset of fast spreading in the Southern Ocean.

The compilation and processing of GA's single and multibeam bathymetry data in the Gippsland Basin was produced following a request by an internal client in November 2013. It is an updated version of the 2012 bathymetry grid of the Gippsland basin.

Geoscience Australia marine reconnaissance survey GA2476 to the west Australian continental margin was undertaken as part of the Australian Government's Offshore Energy Program between 25 October 2008 and 19 January 2009 using the German research vessel RV Sonne. The survey acquired geological, geophysical, oceanographic and biological data over poorly known areas of Australia's western continental margin in order to improve knowledge of frontier sedimentary basins and marginal plateaus, and allow assessment of their petroleum prospectivity and environmental significance. Four key areas were targeted: the Zeewyck and Houtman sub-basins (Perth Basin), the Cuvier margin (northwest of the Southern Carnarvon Basin), and the Cuvier Plateau (a sub-feature of the Wallaby Plateau). These areas were mapped using multi-beam sonar, shallow seismic, magnetics and gravity. Over the duration of the survey a total of 229,000 km2 (26,500 line-km) of seabed was mapped with the multibeam sonar, 25,000 line-km of digital shallow seismic reflection data and 25,000 line-km of gravity and magnetic data. Sampling sites covering a range of seabed features were identified from the preliminary analysis of the multi-beam bathymetry grids and pre-existing geophysical data (seismic and gravity). A variety of sampling equipment was deployed over the duration of the survey, including ocean floor observation systems (OFOS), deep-sea TV controlled grab (BODO), boxcores, rock dredges, conductivity-temperature depth profilers (CTD), and epibenthic sleds. Different combinations of equipment were used at each station depending on the morphology of the seabed and objectives of each site. A total of 62 stations were examined throughout the survey, including 16 over the Houtman Sub-basin, 16 over the Zeewyck Subbasin, 13 in the Cuvier margin, 12 over the Cuvier Plateau and four in the Indian Ocean. This dataset comprises total chlorin concentrations and chlorin indices measured on the upper 2 cm of seabed sediments. For more information: Daniell, J., Jorgensen, D.C., Anderson, T., Borissova, I., Burq, S., Heap, A.D., Hughes, M., Mantle, D., Nelson, G., Nichol, S., Nicholson, C., Payne, D., Przeslawski, R., Radke, L., Siwabessy, J., Smith, C., and Shipboard Party, (2010). Frontier Basins of the West Australian Continental Margin: Post-survey Report of Marine Reconnaissance and Geological Sampling Survey GA2476. Geoscience Australia, Record 2009/38, 229pp

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The Antarctic continental slope spans the depths from the shelf break (usually between 500-1000 m) to ~3000 m, is very steep, overlain by 'warm' Circumpolar Deep Water and life there is poorly studied. This study investigates whether life on Antarctica's continental slope is essentially an extension of the shelf or the deep-sea fauna, a transition zone between these or clearly distinct in its own right. Using data from several cruises to the Weddell and Scotia sea, including the ANDEEP (ANtarctic benthic DEEP-sea biodiversity, colonisation history and recent community patterns) I-III and BIOPEARL (BIOdiversity, Phylogeny, Evolution and Adaptive Radiation of Life in Antarctica) 1 and EASIZ II cruises as well as current data bases (SOMBASE, SCAR-MarBIN), we selected four different taxa (i.e. cheilostome bryozoans, isopod and ostracod crustaceans, and echinoid echinoderms) and two areas, the Weddell and the Scotia Sea, to examine faunal composition, richness and affinities. The answer has important ramifications to the link between physical oceanography and ecology, and the potential of the slope to act as a refuge and resupply zone to the shelf during glaciations (and therefore support or not glaciological reconstructions of ice sheets covering continental shelves).

The Bremer Sub-basin on the rifted southwestern continental margin of Australia is a frontier basin in which no wells have been drilled. The petroleum potential of such frontier basins is generally limited to theoretical assessments from seismic data and analogues. However, a series of submarine canyons have incised the Bremer Sub-basin, allowing geological sampling of the upper 2.5 km of the basin succession. Geochemical, petrographic and palaeontological analyses of 136 rock samples recovered from 30 dredge sites, integrated with interpretation from a regional seismic grid, indicate that the Bremer Sub-basin contains a succession of up to 7km of Jurassic to Tertiary age sediments containing the essential petroleum system elements (source, reservoir and seal) to generate and trap hydrocarbons. Source rock analyses indicate Early Cretaceous coaly and lacustrine organic facies have the best oil potential with hydrogen indices (HI) up to 370 mg hydrocarbons/g TOC. Similar fluvio-lacustrine organic facies are recognised sources for oil in the adjacent Perth and eastern Bight basins. Furthermore, the identification of late Early Cretaceous marine anoxic organic facies in the Bremer Sub-basin supports the concept of a local southern Australian margin origin for widespread coastal bitumens termed asphaltites. Berriasian to Hauterivian age strata within the Bremer Sub-basin have the greatest potential to reservoir hydrocarbons, where lacustrine mudstones overlie fluvial sandstones in anticlines and fault block traps. The largest anticline may be capable of trapping up to 500 million barrels of oil in-place (P50 estimate; 900 million barrels P10 estimate).

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In January/February 2000, the Australian Geological Survey Organisation (AGSO) completed a 2S-day seabed swath-mapping and geophysical survey off south and south-east Tasmania and south of Macquarie Island for the National Oceans Office and Environment Australia. The survey, which is named AUSTREA-2 and designated as AGSO Cruise 223, used the 8S-m French oceanographic and geoscience research vessel N/O L 'Atalante, which departed Hobart on January IS and arrived in Bluff, New Zealand, on February 9. The survey covered about 10,200 km and mapped about 140,000 km2 of seabed. The initial impetus for the work was to map the foot-of-slope position in several areas to support definition of Australia's legal Continental Shelf under the United Nations Convention on the Law of the Sea. A significant additional but complementary aspect was to support marine zone planning and management, and assessment of seabed living and non-living (petroleum and mineral) resources, as an important step towards implementation of Australia's Oceans Policy and Australia's Marine Science and Technology Plan, and, in particular, the development of the South-east Regional Marine Plan by the National Oceans Office. Geophysical data collected included Simrad EM12D swath bathymetry and backscatter, 6-channel GI-gun seismic, 3.S kHz sub-bottom profiling, and gravity and magnetic profiles. This was augmented by a suite of oceanographic data, such as seawater temperature, and both current and salinity depth profiles. Weather and sea conditions were highly favourable, particularly in the more southern latitudes. Occasional periods of rough weather resulted in higher noise levels, but did not seriously affect acquisition, and data quality was generally excellent. The work conducted off Tasmania was mostly to fill in and extend previous swath coverage, and map the foot-of-slope along the eastern margin of the South Tasman Rise. It highlighted features such as the major development of slope canyons down the eastern Tasmanian margin, and the complex character of the Cascade Seamount and other seamounts adjacent to the South Tasman Rise. The work conducted over the southern Macquarie Ridge Complex highlighted features such as: a high-relief axial valley adjoining the deep Hjort Trench; the broadening to the south of the submerged Hjort Ridge, east of the Hjort Trench; the development of seafloor spreading tectonic fabric across the Hjort Ridge summit; and the presence of a linear trough/ridge feature that obliquely truncates the southern end of the Hjort Trench and adjoining axial valley. A full set of shipboard maps are held by the National Oceans Office and AGSO, and copies of the digital data are stored at AGSO. All data from the survey will be managed jointly by AGSO and the National Oceans Office.

We use seismic-reflection and rock-sample data to propose that the first-order physiography of New Caledonia Trough and Norfolk Ridge formed in Eocene to Miocene time, and was associated with the onset of subduction and back-arc spreading at the Australia-Pacific plate boundary. Our tectonic model involves an initial Cretaceous rift that is strongly modified by Cenozoic subduction initiation and hence we are able to explain: complex sedimentary basins of inferred Mesozoic age; a prominent unconformity and onlap surface of Middle Eocene to Early Miocene age at the base of flat-lying sediments beneath the axis of New Caledonia Trough; gently-dipping, variable thickness, and locally deformed Late Cretaceous strata along the margins of the trough; platform morphology and unconformities on either side of the trough that indicate a phase of Late Eocene to Early Miocene uplift to near sea level, followed by rapid Oligocene and Miocene subsidence of c. 1100-1800 m; and seismic-reflection facies tied to boreholes that suggest absolute tectonic subsidence at the southern end of New Caledonia Trough by 1800-2200 m since Eocene time. The Cenozoic part of the model involves delamination and subduction initiation followed by rapid foundering and rollback of the slab. This created a deep (>2 km) enclosed oceanic trough c. 2000 km long and 200-300 km across in Eocene and Oligocene time as the lower crust detached, with simultaneous uplift and local land development along basin flanks. Disruption of Late Cretaceous and Paleogene strata was minimal during this Cenozoic phase and involved only subtle tilting and local reverse faulting or folding. Basin formation was possible through the action of at least one detachment fault that allowed the lower crust to either be subducted into the mantle or exhumed eastward into Norfolk Basin. We suggest that delamination of the lithosphere, with possible mixing of the lower crust back into the mantle, is more widespread than previously thought.