--> Middle Cambrian Chemostratigraphy and Biostratigraphy in the Southern Georgina Basin: Correlating the Arthur Creek “Hot Shale”

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Middle Cambrian Chemostratigraphy and Biostratigraphy in the Southern Georgina Basin: Correlating the Arthur Creek “Hot Shale”

Abstract

The Georgina Basin is a Neoproterozoic to Lower Devonian sedimentary basin covering 325,000 km2 of western Queensland and the Northern Territory. It is a northwest-southeast-trending extensional basin, with prospective conventional and unconventional hydrocarbon targets within Cambrian and Ordovician carbonate and siliciclastic rock units in the southern depocentres. Recent biostratigraphic work has highlighted an age discrepancy in the prospective organic-rich ‘hot shale’ in the base of the middle Cambrian Arthur Creek Formation. This unit is present in the two major southern depocentres, the Dulcie and Toko synclines, where it has previously been considered as correlative. Recent results, however, suggest that the basal ‘hot shale’ is either significantly younger in the Toko Syncline than in the Dulcie Syncline, or represents a very condensed section in the former. Middle Cambrian carbon isotope excursions have been correlated across a number of Australian basins and can be used to test correlative models across the Georgina depocentres. In the current study, high resolution sampling across this middle Cambrian section has been carried out in a number of wells in the Dulcie Syncline and in the Undilla Sub-basin, where the age equivalent Inca Shale is penetrated. Carbon isotopes from organic carbon (kerogen) as well as carbon and oxygen isotope ratios of four carbonate mineral phases (calcite, ankerite, dolomite and siderite) were analysed. These new data are compared with the existing carbon isotope stratigraphy from the Dulcie and Toko synclines. Initial results corroborate the new biostratigraphic interpretation. This work provides a detailed understanding of middle Cambrian isotope signatures and correlates this prospective unit across the southern Georgina Basin.