EVOLUTION OF THE PERTH AND CARNARVON BASINS

Abstract

Along the present southwest Australian margin, in the Perth and Carnarvon Basins, the wholly nonmarine Permian, Triassic, and Jurassic sedimentary rocks of the southern Perth Basin pass northwards into paralic and marine equivalents of the Carnarvon Basin, which additionally contains marine Silurian, Devonian, and Carboniferous rocks. These contrasts are interpreted in terms of the re-assembly of Australia in Gondwanaland: the southern Perth Basin lay alongside India in the interior of Gondwanaland, and the northern Carnarvon Basin faced a gulf of Tethys.

According to this model, southwest Australia was arched in the Late Carboniferous, and the arch collapsed by rifting in the Permian, Triassic, and Jurassic, with the accumulation of thick nonmarine (in the south) to paralic and marine sediments (in the north). Rupture from India was marked by the eruption of basalt in the earliest Cretaceous, and dispersal of India and Australia was marked by rapid marginal subsidence in the Late Cretaceous. This model, derived from stratigraphical and faciological data, is supported by the ridge-and-rift structure of southwest Australia.