The Phanerozoic geological history of Northwest Australia

Abstract

The common geological history of the Phanerozoic Canning Basin and Bonaparte Gulf Basin of northwest Australia is indicated by their continuity offshore and by the similarity of contemporaneous deposits onshore. The region has a basement of older Precambrian plutonic and metamorphic rocks, and a superstructure of flat‐lying and locally deformed younger Precambrian and Phanerozic sedimentary rocks, and minor volcanic rocks. Sedimentary rocks onshore span the Phanerozoic Eon, except the Cainozoic Era, which is possibly represented offshore by thick sediments in an elongate depression along the continental margin. The Phanerozoic sediments were deposited in three environments: on epicontinental marine shelves during the Middle Cambrian to Middle Ordovician, Late Devonian and Early Carboniferous, Middle Jurassic to Early Cretaceous, and at the present day; on paralic platforms, intermittently continental and marine, during the Late Carboniferous to Triassic; and on continental platforms in the interval Late Ordovician to early Middle Devonian. Lower Cambrian plateau basalt and Mesozoic lamproite plugs are the only igneous rocks. The structural elements are step‐ and block‐faults, and folds are rare. Because of its simple structure and its position near the Banda Arcs of Indonesia, northwest Australia is a key area for studies of wide geological interest.