Tectonostratigraphic and Paleogeographic Evolution of the Northwest Australian Margin

Jeffrey U. Kraus

The evolution of Australia's rifted northwestern margin has been investigated by interpreting its stratigraphic history within the framework of a regional plate tectonic/ paleogeographic model. The Permian through Cretaceous stratigraphy of the five major basins, the Bonaparte, Browse, Canning, Carnarvon, and Perth, was summarized using a standardized nomenclature and time scale. These data were used to construct 12 subsidence profiles and to provide the lithologic and paleoecologic foundation for interpreting regional paleogeography. Subsidence analysis was performed to study varying responses to tectonism, eustatic and climatic change, as well as variations in sediment input/loading. Two types of events (unconformities) became evident through this analysis. The first ty e tend to be diachronous across the margin, becoming younger toward the Southwest. These events were primarily driven by regional tectonic forces, that were usually extensional in nature. The second type were more regionally synchronous and appear to have been related to third order changes in base level and/or variations in regional stresses. The timing and magnitude of events, as indicated by subsidence analysis and sub-basin-level structural analysis, were used to construct the paleogeographic model. The model is illustrated in a series of 10 regional paleogeographic maps depicting changing environments and zones of structural deformation from the Permian through the Cretaceous, as eastern Gondwana was disassembled. This work points out the significant effects of far-field tectonic fo ces on basin evolution and serves as a prerequisite for comprehensive investigation of petroleum systems in this prolific area.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California