--> Abstract: The Upper Cretaceous of the Bight Basin, Australia: A Large Deltaic System in a Greenhouse World, by Peter J. McCabe and Jennifer M. Totterdell; #90124 (2011)

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Making the Next Giant Leap in Geosciences
April 10-13, 2011, Houston, Texas, USA

The Upper Cretaceous of the Bight Basin, Australia: A Large Deltaic System in a Greenhouse World

Peter J. McCabe1; Jennifer M. Totterdell2

(1) CSIRO, North Ryde, NSW, Australia.

(2) Geoscience Australia, Canberra, ACT, Australia.

The Bight Basin offshore southern Australia is one of the few remaining major frontier basins in the world. Following the initiation of sea-floor spreading between Australia and Antarctica in the late Santonian a large deltaic system, known as the Hammerhead Delta, built out into the Ceduna Sub-basin. At the end of the Cretaceous the influx of siliciclastic sediment ceased. Most of the area of the former delta has been subsequently dominated by marly sedimentation in relatively deepwater. The Hammerhead delta strata extend over an area of over 100,000 km2 and are up to 5000m thick.

Although the Hammerhead Delta built out on a continental margin, the strata have a number of marked differences to strata in well-documented late Cenozoic deltas that built out in such settings. There is a very limited progradation of the Upper Cretaceous shelf break in the Ceduna Sub-basin. Instead there is a high preservation of the delta topset strata which are composed predominantly of highstand system tracts with progradational and aggradational parasequence sets. Coal-bearing strata occur landward of the shoreface deposits. In places the parasequence stacking patterns result in large clinoform structures that are up to 700 m in amplitude. The scale of these clinoforms suggest the possibility that they were steep enough for the generation of turbidity currents ; consequently, submarine fan deposits may well be preserved at the base of the clinoforms, landward of the Upper Cretaceous shelf break.

The differences in stratal geometry are interpreted to be largely due to the fact that the Hammerhead was deposited during a greenhouse regime rather than the transitional and icehouse regimes that existed during the late Cenozoic. The lower magnitude and frequency of sea-level changes over time in a greenhouse world permits the accumulation of thick highstand deposits and may limit the size of deepwater lowstand deposits. Future petroleum exploration in this region needs careful consideration of appropriate analogs for source rocks, reservoir rocks, and seals. In many regards the stratal patterns seen in the Hammerhead Delta have more similarities to the Upper Cretaceous strata of the North American Western Interior Basin than strata in continental margin deltas of Miocene to Recent age.