Palaeogeographic evolution of the Triassic succession, central North West Shelf

Triassic deposition on the central North West Shelf (CNWS) mainly took place in a large depocentre comprising the Beagle Sub-basin and the Exmouth Plateau, and a small depocentre located within the Rowley Sub-basin. Thermal subsidence prevailed but syn-depositional extension is especially evident in the NE Barcoo Sub-basin. Sources of sediment delivery to the region included two re-entrants that extended into the Canning Basin. During time Interval 1 (Induan-mid Anisian) a basal marine mudstone transgressed the region and fluvio-deltaic systems were confined inboard. Local deep incision at the start of Interval 2 (mid Anisian-mid-Landinian) was followed by extensive fluvio-deltaic deposition. During Intervals 3 (mid-Ladinian-early Rhaetian) and 4 (Rhaetian), the fluvio-deltaic system progressively back-stepped and was replaced in outboard areas by deposition of carbonate-rich platform sediments. The discrete Rowley Sub-basin depocentre and associated Steel Dragon Structure may be igneous complexes generated by rifting processes on the adjacent Argo landmass. Palaeogeographic maps that track the evolution of the CNWS inform aspects of Triassic prospectivity, such as the geographic extent of the new fluvio-deltaic petroleum system in the Bedout Sub-basin, the distribution of a carbonate build-up play, and the significance of syn-depositional extension for source rock accumulation.