Salient Features in the Stratigraphy, Tectonic Structure, and Physiography of the Commonwealth of Australia1

Abstract

A BRIEF summary of the salient features of the stratigraphy of the Commonwealth is essential for understanding its tectonic structure. Pre-Cambrian rocks are developed in Western, Central, and South Australia. The Proterozoic rocks of Northern Australia are partly formed of thick dolomites, possibly a forerunner of the Great Barrier Reef of to-day. Basic lavas and tuffs, 3000 feet thick, preceded a great ice-age in late Proterozoic or early Cambrian time. Marine Cambrian strata occur chiefly in Northern and Central Australia and South Australia, with patches in Victoria, Tasmania, and Queensland. Ordovician rocks attain a thickness of 40,000 feet in Victoria and Central Australia. Igneous intrusions and unconformity separate the Ordovician rocks from the Silurian. In the Devonian rocks of Queensland, coralline limestone, 7000 feet thick, is probably another ancestor of the Great Barrier Reef. In Carboniferous time a south-eastern shore of ‘the Tethys Sea’ is well defined in the northwest of Western Australia. Carboniferous and Devonian time were periods of granitic intrusions and effusive rocks. In Permo-Carboniferous time half Australia was under ice. This was the chief coal-forming epoch, followed by more coal (in Triassic and in Jurassic times) developed in immense epi-continental lakes in eastern and central Australia, near which carnivorous deinosaurs existed.