New seabed survey off eastern Australia
A recently completed survey of the seabed off eastern Australia has revealed that things are much the same as they were when dinosaurs roamed the Earth.
The research expedition was conducted by scientists from the Australian Geological Survey Organisation (AGSO), the CSIRO and the Universities of Sydney and Melbourne.
The team returned to Hobart in Tasmania yesterday on the expedition vessel Franklin with profiles and cores of the seabed at the edge of the Australian continent.
Australia's island continent separated from the rest of the ancient supercontinent Gondwana around 85 million years ago. The continental margin collapsed into the sea after a period of heating, uplifting and volcanic outpouring which accompanied the breakup of Gondwana.
"This poorly known part of Australia extends 100 kilometres offshore with its outer limit 4,500 metres deep, and is one-third the size of Tasmania," said Dr Neville Exon, AGSO's chief scientist.
"The margin supports a fishing industry and has some potential for petroleum, but our main aim was to better define its nature and its history."
One of the most surprising findings is that, unlike many other such continental margins around the world, the Australian continent is not covered by a thick blanket of younger sediment.
"The granites, basalts, metamorphic rocks and sandstones familiar to many east coast Tasmanians are right there at the sea bed," Dr Exon said.
The expedition also collected core samples more than eight metres long from the ancient Bass Lake which existed where Bass Strait is now situated following the last ice age.
"It will enable us to study past climates as the lake came and went over thousands of years," said Professor Jock Keene for the University of Sydney.
"This all occurred when Aborigines were living and walking across Bass Strait."
Professor Keene and research students have already used shorter cores to determine that Bass Strait flooded 9,000 years ago as the sea level rose from the melting of the ice sheets. This new and longer core sample will go back to older ice-ages and allow studies of the Tasmanian and Victorian climates during this time.
Andrea Leach, a PhD student from the University of Melbourne, is studying canyons formed in another part of Bass Strait called the Otway margin off Port Campbell and Portland. Using seismic profile, she has already shown that the canyons first formed about 30 million years ago, shortly after the Australian continental margin first collapsed.
Her aim on this expedition is to sample the sediments moving down the canyons to see if the canyons are being filled or cutting deeper.