THE STRATIGRAPHY OF THE BASAL TRIASSIC SANDSTONE, NORTH PERTH BASIN, WESTERN AUSTRALIA

Abstract

The Basal Triassic Sandstone is the basal member of the Lower Triassic Kockatea Shale. It is widely distributed adjacent to, and on the Precambrian Greenough Block in the northern Perth Basin, Western Australia. This member is lowermost Lower Triassic in age in the subsurface of the Don-gara gas field. In outcrop on the Greenough Block, the member is represented by a thin basal conglomerate, conformably overlain by upper Lower Triassic Kockatea Shale. In this stratigraphic study, detailed well-to-well correlations and lithologic studies were integrated to reconstruct the depositional history of the interval encompassing the Basal Triassic Sandstone. This sandstone is a composite of near-shore marine, and strand line accumulations deposited around the flanks and on the Greenough Block during a Lower Triassic marine transgression. The sandstone bodies were deposited on a drowned, topography of low relief, on progressively truncated Permian formations and Precambrian basement. The topography was formed following uplift and tilting of the Greenough Block and the overlying Lower Permian formations during mild Upper Permian tectonism.