An updated stratigraphic framework for the Georgina Basin, NT and Queensland

Abstract

The Georgina Basin is a Neoproterozoic to Lower Devonian sedimentary basin covering 325,000 km2 of western Queensland and the NT. It is a northwest-southeast-trending extensional basin, with prospective conventional and unconventional hydrocarbon targets in Cambrian and Ordovician carbonate and siliciclastic rock units. The unconventional gas and oil potential of the basin has led to recent exploration interest, although the basin has been relatively less explored in the past. At the southern end of the basin, depocentres contain up to 2.2 km of Cambrian to Devonian sedimentary rocks, overlying Neoproterozoic sedimentary rocks more than 1.5 km thick. The basin succession thins toward the north, where Cambrian sediments overlie the McArthur Basin sediments in the Beetaloo Sub-basin. Biostratigraphic interpretations of the prospective southern, central and eastern regions of the basin have been revised to reflect the 2012 Geological Time Scale (Gradstein, Ogg, Schmitz, and Ogg, 2012), resulting in an updated chronostratigraphic framework for the basin. The revised biostratigraphic interpretations have implications for important hydrocarbon source rocks. For example, the limestone unit in the southern parts of the basin, generally regarded as the Thorntonia Limestone, is of a different age to the type section for this unit, located in the Undilla Sub-basin. Additionally, the basal hot shale of the Arthur Creek Formation is diachronous across the Dulcie and Toko synclines, which may have ramifications for hydrocarbon exploration. This revised chronostratigraphic framework (by Geoscience Australia) for the Georgina Basin provides a baseline for the first basin-wide assessment of the unconventional hydrocarbon potential of the basin.