Geomorphology and surficial sediments of the southeast Australian continental margin

The southeast Australian continental margin stretches 1500 km north from Bass Strait to the Great Barrier Reef. This part of the Australian margin represents a distinct oceanographic, climatic and geological province. Recent initiatives by the Australian Hydrographic Office, Geoscience Australia and the Environmental Geoscience Group at the University of Newcastle have provided a new digital database of bathymetric soundings and surface-sediment distribution for the southeast Australian margin. This database is used here to provide the first detailed digital 3-D representations of the southeast Australian margin, leading to new morphological classifications and integrated sedimentation models. As a result of its tectonic history of asymmetric passive margin rifting, the continental margin as a whole is narrow, steep and sediment deficient. The shelf can be divided into an inner zone with bedrock cropping out or close to the surface, and an outer zone that represents the top of a Cenozoic sediment wedge. The continental shelf and slope can be classified into a variety of morphological units based on detailed analysis of geometry and slope. These units include a succession of shore-normal zones (shoreface, inner plain, inner and mid-slope, outer plain and continental slope) and a number of local regions (mounds, lobes, tongues, depressions, deltas and bedrock). Sediments are generally siliciclastic in composition on the inner margin and carbonate-rich on the outer margin, reflecting carbonate production at low sea-levels on the outer shelf/continental slope and terrestrial sediment input to the inner shelf. Fine-grained sediments are rare on the shelf north from Port Stephens, and occur draped across the inner and mid-slope further south. Outer shelf carbonate sediments are coarse grained with a patchy distribution related to winnowing by the East Australian Current. The East Australian Current also produces erosional depressions and southward prograding sediment tongues and lobes where it separates from the shelf off Port Stephens. The margin character varies markedly from south to north in terms of fine-sediment distribution, depth to the shelf break and width of the outer shelf. These outer shelf features reflect an inherited palaeotopography from underlying Cenozoic sediment wedges that are better developed on the southern margin