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Timing of Source Rock Formation and Hydrocarbon Generation Based on Re-Os Geochronology in the Georgina Basin, Australia

Abstract

The Neoproterozoic to Devonian Georgina Basin is a shale gas and shale oil bearing sedimentary basin in Queensland and Northern Territory, Australia. The primary oil prone shale in the basin, the middle Cambrian Arthur Creek Formation (∼505 Ma), unconformably overlies the oil and gas prone secondary target, the Hay River Formation (∼510 Ma). The stratigraphy has previously been characterized based on the Central Australian Trilobite Zonation and well bores, but the basin is almost 300,000 km2 and less than 30 well bores penetrate these two source rocks. Recent re-evaluation of the faunal assemblages in the Arthur Creek and Hay River Formations indicates that temporal relationships across the basin are diachronous. Basin modelling also suggests multiple hydrocarbon generation events. Our work will help to characterize the temporal relationships between the Arthur Creek and Hay River formations. We have used rhenium (Re) - osmium (Os) geochronology in multiple core samples from across the basin to establish the temporal continuity of the Arthur Creek Formation and Hay River Formations. We will use Re-Os geochronology to establish time frames for oil generation from the Arthur Creek Formation and model migration pathways based on isotopic tracers. Additionally, the Re-Os isotopic abundances will be compared to organic geochemical analysis to help identify depositional environment conditions. The initial data suggests that both the Arthur Creek Formation and the Hay River Formation are younger than previous interpretations, with initial ages ca. 480 Ma. Re-Os geochronology suggests that the isotopic ages fall within the Early Ordovician. The reasons for the age discrepancy between isotopic and fossil evidence will be discussed.