Mesozoic Evolution of the West Australian Margin: A Landlubber's View

Abstract

Despite the large dataset available from petroleum exploration of the North West Shelf, the distribution and age of Mesozoic strata in much of Western Australia remains poorly understood thereby limiting the resolution of palaeogeographic reconstructions that include such peripheral provinces. For this reason just 8 divisions of the Mesozoic can be constructed to cover the entire western part of the Australian Plate. Whereas basin subdivisions across Western Australia have been delineated according to their present structural configuration, the concerns that they are of minor palaeogeographic or palaeobathymetric relevance is contradicted by regional isopach maps that show many were long-lived depocentres. At the end of the Permian the interior seaway which had extended along the eastern part of the Southern Carnarvon Basin into the Perth Basin was disrupted with deposition shifting to the present offshore part of the State, except in the Perth Basin that continued as a set of major depocentres controlled by the Darling Fault System and faults along the west, and to the south, of the Beagle Ridge. Most other onshore basins became transit zones with minimal accommodation across which sediment was carried to the west and northwest but, based on provenance studies utilizing zircon dates, with little apparent input from adjacent basement terrains. Late Triassic – Jurassic tectonism, evident as a break in deposition in the Canning Basin (Fitzroy Movement), was associated with drift of the Lhasa Block and other terrains now in southeastern Asia away from the Australian Craton. In effect Triassic–Jurassic deposition across the present onshore part of the State was dominated by thin fluvial sediments, which likely represent highstand deposits that encroached across older strata and basement. By comparison, far more complete (and better dated), dominantly deltaic to shelfal sequences were ubiquitous along the North West Shelf prior to breakup in the Early Cretaceous. Following breakup marine deposition extended across most basins and eventually well into central Australia, albeit significantly shallower and thinner than in the present offshore areas, and sediment contribution from adjacent basement terrains increased substantially. A notable exception was in the northern–central Canning Basin that appears to have been little influenced by breakup, possibly due to its main structural elements being virtually orthogonal to those of the North West Shelf.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015