The modern southern Australian continental margin constitutes the largest cool-water carbonate platform on Earth. Seismic stratigraphic analysis of the offshore succession in the western GAB shows that the Eucla basin contains a discontinuous record of predominantly cool-water carbonate sedimentation throughout the Cenozoic, and that deposition was controlled by the interaction between sea level fluctuations and tectonic and paleo-oceanographic processes. This analysis indicates that the earliest Cenozoic sequence was a Paleocene(?)-middle Eocene progradational siliciclastic wedge with reflector geometry dictated by accommodation constraints. This analysis also indicates that deposition of this sequence was controlled by the interaction between sea level fluctuations and tectonic movements associated with formation of the Eyre sub-basin. The overlying middle Eocene-early middle Miocene carbonate shelf evolved from an extensive cool-water ramp to a warm-water rimmed platform as a consequence of (1) influx of open-oceanic cool waters resulting from development of the Southern Ocean basin following separation of Australia and Antarctica, (2) restriction of terrigenous sediment input arising from the tectonic stability of the basin hinterland, and (3) the transition to a warm-water environment during the early middle Miocene climatic optimum, with the possible contribution of warm waters by the Leeuwin Current. Late middle Miocene tilting and uplift of the platform and a eustatic fall in sea level resulted in the middle(?) late Miocene debris apron at the foot of the steepest part of the subaerially exposed platform rim. Cool-water, lowstand deposition during the late Miocene-early Pliocene was restricted to the outer shelf seaward of the reef escarpment, and was terminated by a major erosional episode. The final depositional phase reflects Pliocene-Quaternary highstand cool-water deposition in a swell-dominated paleo-oceanographic regime, and resulted in an extensive seaward-prograding ramp with numerous biogenic mounds.
We conclude that in the western Great Australian Bight, paleo-oceanographic variations produced seismic geometries that are strikingly different depending on sea-surface temperature. Broad, low-relief buildups and ramp morphology resulted from cool-water depositional processes, contrasting with higher relief reefs and rimmed platform morphology resulting from warmer water deposition. In the case of these ramps, organic growth potential apparently was distributed over a much greater water depth range and, accordingly, over a much broader area compared with the warmer water platform where the reefs that formed the platform rim concentrated organic growth potential into a narrow zone close to sea level.