A DEPOSITIONAL MODEL FOR THE DUPUY MEMBER AND THE BARROW GROUP IN THE BARROW SUB-BASIN, NORTHWESTERN AUSTRALIA

Abstract

A detailed sedimentological study of the Dupuy Member and the Barrow Group has resulted in a regional model for the deposition of these Upper Jurassic to Lower Cretaceous reservoir sequences in the Barrow Sub-basin. The Dupuy Member is interpreted as a prograding offshore slope sequence of turbidite sandstones and debris flows, which built laterally into the Barrow Sub-basin from along its eastern margin. This slope sequence contains bentonite markers in its upper part. The overlying Barrow Group was deposited by a delta which prograded along the length of the Barrow Sub-basin from the southwest and onlapped the Dupuy Member along the eastern side of the sub-basin. The topsets of the delta are fluvial to shallow marine sandstones, the foresets are offshore claystones, and the bottomsets are submarine mass-flow sandstones. After 8 million years of progradation, the delta was starved of sediment by continental breakup south of the Exmouth Plateau and stopped with its last foreset trending in an east-west arc from Barrow Island across the Exmouth Plateau. The Barrow Group delta was then gradually transgressed by the sea and blanketed by the Muderong Shale. Structural growth of the Barrow Island anticline took place during deltaic deposition and caused anomalous relationships between foresets and bottomsets under the north of Barrow Island. Known hydrocarbon accumulations and common shows in the Dupuy Member and the Barrow Group make these sequences attractive exploration targets.