Abstract

Topographic features in the western and north-western continental slopes of Australia arose in two ways. Along the major part, bordering the Indian Ocean, extensive pre-Cretaceous block-faulting formed horsts and grabens. These were covered by a sedimentary mantle in Mesozoic and Tertiary times. In the Timor Sea, the continental slope topography developed through gentle downwarping of shallow-water deposits in the late Tertiary.

The Naturaliste Plateau was least affected by block-faulting and may have been retained at or near shelf level in the continental slope until early Tertiary time. The Wallaby Plateau and the Carnarvon Terrace (new name) were formed as Mesozoic and Tertiary sedimentary mantles over a series of linear and arcuate horst blocks. Oceanic material forms the western margin of the Wallaby Plateau; the plateau's eastern margin is almost detached from the base of the slope. The Exmouth Plateau forms an extensive area of block-faulted Triassic and Permian rocks with Cretaceous and Tertiary sedimentary cover. A northeasterly trend in the central Exmouth Plateau is truncated in the north by a dextral fault and east-west structures which isolate at least three sedimentary blocks on the northern margin. The plateau's southern margin has a northwest trend which controls some early Mesozoic deposition. The Scott Plateau contains a narrow sedimentary horst and a western region of oceanic material. On the east of the Scott Plateau, the Ashmore Terrace (new name) is formed of pre-Cretaceous horsts near the shelf break.

The Timor Trough has formed since the Pliocene with shelf structures gently downwarped into the axis of the trough. Diapiric structures (probably salt intrusions) along the trough axis are present near the line of over-thrusting of the Outer Banda Arc over the downwarped Sahul Shelf.