Seafloor mapping of the south-east region and adjacent waters : AUSTREA-1 cruise report : Lord Howe Island, south-east Australian margin and central Great Australian Bight

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.

Tags: AU-NSW, AU-TAS, AU-VIC, Earth Sciences, GA Publication, Published_External, Record, continental margins, geophysics, marine
Organization: Australian Ocean Data Network