Shelf to Basin Sediment Transport from the South East Australian Continental Margin

Ron Boyd¹, Kriton Glenn², Jock Keene³, and Leharne Fountain^2
1Earth Sciences, University of Newcastle, Callaghan, NSW, Australia
²Geoscience Australia, Canberra, ACT, Australia
³University of Sydney, Sydney, NSW, Australia

The South East Australian passive margin extends for 1500 km from Bass Strait and the Gippsland Basin in the south to the Great Barrier Reef in the north. This margin consists of Paleozoic pre-rift sedimentary, volcanic and plutonic rocks forming basement, syn-rift Cretaceous basins and volcanics, and a shelf-edge wedge of Cenozoic post-rift sediments. New high-resolution multibeam and seismic data reveal a range of depositional processes for transferring siliciclastic sediments from the SE Australian shelf to the Tasman Sea slope and basin. Northward longshore transport dominates the coastline as far as Fraser Island, where a combination of wave processes, tidal currents and change in margin orientation transports coastal sands across the shelf, down the slope and 150 km along a submarine valley system onto the abyssal plain. Further south, siliciclastic supply from shelf to basin is mainly controlled by gravity processes. Here the Cretaceous rift margin is gradually subsiding and tilting seaward, resulting in steeper slopes on the outer margin, and failure at the toe of the overlying Cenozoic sediment wedge. Individual slide masses are widespread and up to 24 km long, 14.5 km wide and 0.7 km thick. Their occurrence is frequently controlled by the underlying and upslope occurrence of basement and volcanics. Quaternary lowstand deltas occur on the upper slope off major rivers such as the Hunter and Shoalhaven, and supply a network of submarine canyons and gullies beginning in 200 m water depth and continuing to the base of the lower slope in 4800 m depth.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas