Legacy product - no abstract available

Legacy product - no abstract available

In January 2000, the Australian Geological Survey Organisation (AGSO) completed a major, 25-day seabed swath-mapping and geophysical survey off southeast Australia for the National Oceans Office (NOO) and Environment Australia (EA). The survey, named AUSTREA-l and designated as AGSO Cruise 222, used the 85-m French oceanographic and geoscience research vessel L 'Ata/ante, departing Noumea on 18 December 1999 and ending in Hobart on 11 January 2000. The survey covered 11,000 km and mapped about 120,000 km2 of seabed - an area about 1.5 times the size of Tasmania. The work was done for marine zone planning and management, for assessment of seabed living and non-living (petroleum and mineral) resources, and geological and biological research, as a major step towards implementation of Australia's Oceans Policy and Australia's Marine Science and Technology Plan, and in particular, the development of the Southeast Regional Marine Plan by the National Oceans Office. Data collected included Simrad EM 12D swath-bathymetry and backscatter imagery, 6- channel GI-gun seismic, digital 3.5 kHz sub-bottom profiles, gravity and total field magnetics. Also collected was oceanographic information - XBTs to 1800 m depth and underway ADCP (current), sea surface temperature and salinity measurements. Weather and sea conditions were generally favourable, though stormy conditions with 30-35 knot winds and associated rough seas were encountered at times. Data quality was mostly excellent. The survey mapped the volcanic slopes of Lord Howe Island and Ball's Pyramid to the 12 nautical mile outer limits of a proposed Marine Protected Area, revealing a rugged terrain of volcanic cones, flows and canyons likely to harbour diverse benthic communities. The steep and narrow rifted continental margin off the NSW South Coast was shown to be deeply dissected by canyons and to contain gigantic continental fauit blocks fuld ?syw-ift volcanic seamounts and ridges. The survey completed mapping of the huge Bass Canyon complex off southeast Victoria, revealing detailed morphology of tributary canyons up to 1000 m deep adjacent to the Gippsland oil fields. Important fishing grounds of the Southeast Trawl Fishery were mapped off Tasmania, including volcanic and carbonate pinnacle terrain off St Helens, volcanic seamounts of the Southern Hills, and the heads of canyon systems incised into the sedimented upper slope off west Tasmania. Mapping of the Tasmanian Seamounts Marine Protected Area, south of Hobart, was completed, with thirty additional volcanic seamounts found just east and north of the MP A. The seismic profiles confirmed the existence of potential frontier petroleum basins off the east, southern and west coasts of Tasmania. Parts of the deeply-canyoned upper and mid slope of the Otway Basin were mapped off northwest Tasmania, Victoria and South Australia. The Great Australian Bight Benthic Protected Area of the GAB Marine Park was fully surveyed below the 500 m isobath and was shown to be generally a uniform slope, with the gigantic Nullarbor Canyon crossing its southeastern comer, gouged into deformed Late Cretaceous sediments. A full set of shipboard maps was provided to the National Oceans Office; copies of the digital swath-data are held for NOO at AGSO. All data from the cruise will be jointly managed by AGSO, NOO and EA.

Legacy product - no abstract available

Overall, the cruise met its objectives of studying rift and drift sedimentation, and obtaining cores for palaeo-oceanography. The east Tasmanian seismic program was completely successful. The planned sampling program was somewhat curtailed by bad weather, equipment failures and other factors. It was least successful off east Tasmania. A total of about 1300 km of 8-fold multichannel seismic data were acquired along 8 transects across the east Tasmanian margin. The quality of the seismic profiles was excellent, with good resolution and penetration, given the bad weather and the limitations of the acquisition system. The seismic source comprised 2 GI airguns (each 45/105 cu. in. capacity) giving a penetration of 2-2.5 s twt (2.5-3 km) in places. The seismic profiles indicate a structurally complex margin with rugged basement relief that includes large-scale horst/graben structures and volcanic intrusions. The sedimentary section on the continental slope is at least 1.5 s twt thick in some graben and includes Campanian-Paleocene early sag-phase deposits, which are 0.5-1.0 s twt thick. Regional compressive tectonism in the Late Paleocene-Early Eocene has produced widespread inversion (folding/faulting) in this succession. A wedge of Neogene shallow-water carbonates underlies the continental shelf. It shows seaward progradation and attains a maximum thickness of ~700 m beneath the shelf edge. Oceanic basement (?Campanian) adjacent to the margin lies at a depth of 7.0-7.5 s twt. The continental rise and Tasman Abyssal Plain in this zone are underlain by 1.5-2.0 s twt of post-breakup sedimentary section. The East Tasman Saddle is underlain by `transitional? basement and contains a sedimentary section of similar thickness. During the sampling program 58 of 86 stations were successful: 38 gravity cores (21 successful), 4 piston cores (3), 16 dredges (7) and 28 grabs (28). Total core recovery was 81.4 metres from the 16 successful cores taken in soft sediments, an average recovery of about 5 metres. The fairly low success rate with the gravity corer can be ascribed to problems with foram sand east of Tasmania, and shelly sand in Storm Bay. The low success rate with the dredge was related to the lightness of the gear. The deployment of the heavy piston corer for the first time on Franklin was successful. However, we did not attempt to piston core in deep water. East of Tasmania we recovered 8 gravity cores, and 7 dredge hauls. Deepwater dredging and coring were surprisingly unsuccessful. The upper slope stations, designed to sample older rocks, were reasonably successful. From these results and some existing information, general conclusions can be drawn about changes along the margin with increasing water depth. The shelf and upper slope wedge of Neogene, seaward-prograding sediments was sampled out to 1640 m. The sediments recovered include muddy sand, clayey sandstone with siliceous nodules, siliceous sandstone and calcarenite. The calcarenite is presumably part of the Middle Miocene shelf limestone sequence that is widespread off St Helens. Somewhat deeper on the upper slope, basement outcrops occur in steep slopes: granite, arkose, metasediments, conglomerate, quartz sandstone and gritty mudstone. The granites are probably from Devonian batholiths like those onshore up the east coast. Volcanic rocks and conglomerate form a basement block in deeper water on a ridge off northeast Tasmania at ~3750m. Deepwater outcrop ridges support manganese nodules and crusts. Nannofossil oozes cling to the slope, particularly in local basins, and are ubiquitous in deep water. The East Australian Current apparently winnows many of the oozes to form a blanket of foram sand.

AUSCAN (Australian Canyons), a major research expedition that investigated Australia's southern margin from southern Tasmania in the east to off Cape Leeuwin in the west, successfully completed its mission in March 2003. The investigation included multibeam swath-mapping, geophysical profiling, geological and biological sampling, as well as oceanographic measurements. The data were collected to support marine environmental planning and management, to help model the structural and sedimentological evolution of the margin, and to assist understanding the climatic, oceanographic and environmental changes that affected the region during the late Quaternary. Important objectives were to map in detail and study the geomorphology and origins of the gigantic, but poorly known, canyon systems that exist beyond the continental shelf. The spectacular Murray Canyons south of Kangaroo Island, with their complex and extensive channel systems and 2-km high cliffs, were a special focus of the investigation. The information collected and resulting research will assist 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. The new data, integrated with the pre-existing seabed data sets, provide the basis for environmental management strategies and plans, and also provide framework information to support future biological and physical scientific field studies and research. AUSCAN was completed as two cruise legs totalling 3 weeks using the 120-m R/V Marion Dufresne of the French Polar Institute (IPEV). The survey used a range of geophysical, sampling and oceanographic equipment carried on the ship, but vital to the AUSCAN program were the ship's Thales Sea Falcon 11 multibeam sonar swath-mapper and its giant piston corer, `Calypso?. The multibeam system produces high-resolution bathymetric and backscatter images of the sea floor at 15 knots across a swath up to 20 km wide in deep water, while `Calypso' is capable of recovering deepsea sediment cores up to 60 m long. The cruise was based on excellent international scientific cooperation, and included scientists from Australia, France, Germany, other European countries, and the USA. IPEV was the main French organisation involved, while Australian institutions included Geoscience Australia (GA), the Australian National University, SARDI (South Australian Research & Development Institute) and the National Oceans Office (NOO). CSIRO Marine Research (Hobart) also provided input during the planning phase. NOO provided much of the Australian funding and support because of AUSCAN's direct and important relevance to current regional marine planning and environmental management initiatives, including development of National Bioregionalisation and the South-east Regional Marine Plan. GA managed the project for NOO. The AUSCAN program was designed to build on earlier major swath-mapping surveys involving French-Australian cooperation (GA and IPEV/IFREMER), such as TASMANTE off west Tasmania and on the South Tasman Rise, MARGAU off southwest Western Australia, and AUSTREA-1 off southeast and southern Australia. AUSCAN swath-mapped 70,000 km of seabed (about the size of Tasmania), filling many of the existing data gaps along the southern margin and now allowing detailed maps and images of almost the entire continental slope from Western Australia to Tasmania to be produced for the first time. AUSCAN also acquired 3.5 kHz sub-bottom profiler, gravity, magnetics and oceanographic data along 9,000 km of survey line.

This paper presents tectonic elements maps for the continental margin of East Antarctica, from 38-164E, together with brief descriptions of all the major tectonic elements.

Legacy product - no abstract available

Cold seeps and hydrothermal vents can be detected by a number of oceanographic and geophysical techniques as well as the recovery of characteristic organisms. While the definitive identification of a seep or vent and its accompanying fauna is seldom unequivocal without significant effort. We suggest an approach to identifying associated VMEs in the CCAMLR region that uses the results of scientific surveys to identify confirmed features while documenting a series of criteria that can be used by fishing vessels to reduce the accidental disturbance of seep communities.

The rifting history of the magma-poor conjugate margins of Australia (Great Australian Bight) and Antarctica (Terre Adélie) is still a controversial issue. In this paper, we present a model for lithosphere-scale rifting and deformation history from initial rifting to breakup, based on the interpretation of two regional conjugate seismic profiles of the margins, and the construction of a lithosphere-scale, balanced cross section, sequentially restored through time. The model scenario highlights the symmetric pattern of initial stretching resulting to pure shear at lithospheric-scale accompanied by the development of four conjugate detachments and crustal half-graben systems. This system progressively evolves to completely asymmetric shearing along a single south-dipping detachment at the scale of the lithosphere. The detachment accounts for the exhumation of the mantle part of the Australian lithosphere, and the isolation of a crustal klippe separated from the margin by a peridotite ridge. Antarctica plays the role of the upper plate with the formation of an external crustal high separated from the unstretched continental crust by a highly extended zone still active during the Australian exhumation phase. The total elongation amount of the Australian-Antarctic conjugate system reaches ~413km (61%). Elongation was partitioned through time: ~189km and ~224km during symmetric and asymmetric stages, respectively. During symmetric stage, both margins suffered relatively the same elongation accommodated by crustal stretching (~105km (45%) and ~84km (38%) for Australia and Antarctica, respectively). Again, both margins accommodated relatively the same elongation during the asymmetric stage: the Antarctic upper plate records an elongation amount of ~225km (40%) as crustal tectonic stretching, above the inferred low-angle south dipping detachment zone, whereas the Australian lower plate suffered ~206km (61%) of elongation through mantle exhumation.