THE QUEENSLAND TROUGH: ITS PETROLEUM POTENTIAL BASED ON SOME RECENT GEOPHYSICAL RESULTS

Abstract

The Queensland Trough, about 130 km wide, lies between Queensland and the Coral Sea Plateau. It runs from a water depth of 1000 m off Townsville to 3000 m opposite Cape Melville.

The most extensive and systematic geophysical survey of the area to date is that conducted by the BMR during 1971 as part of the survey of the Australian continental margin.

The BMR sparker seismic sections show a rugged and eroded basement surface. It is concluded that this represents the top of mildly metamorphosed Palaeozoic sediments of the Tasman Geosyncline which were uplifted, folded, and faulted during the Permian and were subsequently severely eroded. In places coral reefs have grown from this basement surface. Some are now buried and some, especially those atop basement highs, are still growing.

The Eocene/Oligocene unconformity encountered in the DSPD hole 209 on the outer edge of the Coral Sea Plateau can be traced as an unconformity over the entire trough and as a conformable Eocene seismic horizon over most of the trough. This horizon lies close to the basement over much of the plateau and at least 1.5 km above the basement in the centre of the trough. It is overlain by about 0.5 km of sediments over both the trough and the plateau.

It appears that the trough was low relative to the plateau and the mainland since the beginning of the Mesozoic and received terrestrial and shallow marine sediments.

Regional subsidence of the trough and plateau probably began in the Early Eocene. Small basins on the trough's eastern margin and on the plateau were formed by differential subsidence along rejuvenated basement faults. These small basins contain lower to middle Eocene shallow marine sediments.

Petroleum prospects appear favourable in the south of the trough, especially in the trough's marginal reef development and in the region of pre-Eocene pinch-out against Palaeozoic basement.