Original paper

Cenozoic progradation in the Barrow-Dampier Subbasin, Northwest Shelf of Australia

Westphal, Hildegard

Abstract

From the Permian to the Present, the Barrow-Dampier Subbasin (Northwest Shelf of Australia) developed from a continental sedimentary basin, located in the interior of the Gondwana continent, to a rift graben that was abandoned in the Upper Jurassic, and finally to a passive continental margin after the Separation of Australia from India in the Cretaceous. In this study, the Cenozoic succession that is characterized by pronounced progradation has been investigated. The interpretation of about 600 km of seismic profiles led to the characterization of four Cenozoic sequences. Each of the four sequences shows prograding foresets. They are bounded by obvious erosional unconformities that locally cut deep into the foresets of the preceding sequences. In some cases, however, nicely developed topsets are preserved. This suggests a continuing subsidence during their formation. Subsidence curves of several wells in the study area show a pattern unusual for passive continental margins. Instead of the concave-upward shape typical for passive margins, the curves exhibit a convex-upward shape. This is interpreted to be the result of the Cenozoic subduction regime to the North of the study area, that causes a distally influenced subsidence. The convex-upward shape becomes less pronounced towards the continent. In the same direction, the total amount of subsidence decreases. The influence of the tectonic movements on subsidence is buffered by the structurally weakened former Barrow-Dampier rift graben.