Middle Jurassic–Lower Cretaceous stratigraphy of the northern Great Australian Superbasin: insights from maximum depositional age constraints from the U–Pb detrital zircon record

Abstract

The Great Australian Superbasin, incorporating the Great Artesian Basin, is host to one of the largest artesian groundwater systems on Earth. However, despite the crucial nature of this resource to Australian agriculture, industry and rural communities, key aquifer units remain poorly studied, apart from the exposed eastern/southeastern portions of the superbasin. In this study, maximum depositional age (MDA) estimations for stratigraphic units, derived from detrital zircon U–Pb geochronology, were undertaken across the Carpentaria and northern Eromanga basins, representing the northern Queensland sector of the Great Australian Superbasin. The objective was to better constrain the ages of key aquifer and aquitard units, thereby facilitating improved stratigraphic correlations and future hydrogeological modelling. Age dating of detrital zircon significantly enhances the confidence, accuracy and precision of age assignments based solely on palynology, especially in continental facies. Furthermore, the provision of MDA estimates permits confident correlation of endemic Australian spore-pollen zonations (used to date continental strata), and dinocyst zonations (used to date marine strata) to the international time-scale. Results indicate that calculated MDAs are commonly either equivalent to, or appreciably younger than, stratigraphic age estimates based on palynostratigraphy. Therefore, several of the most economically strategic aquifer units in the superbasin have been revised upwards in geological time. Similar geochronological campaigns are required in the central, western and southern superbasin to facilitate both high-resolution correlation of key aquifer units across the superbasin and the detailed tracking of the Jurassic to Early Cretaceous paleogeographic evolution of eastern Australia. Key points U–Pb detrital zircon maximum depositional age (MDA) constraints generated are applied to the Jurassic–Cretaceous stratigraphy of the northern Great Australian Superbasin. MDA estimates facilitate robust correlation of endemic Australian palynostratigraphic zones to the international time-scale, reducing chronostratigraphic uncertainty. Several of the key aquifer units across the northern superbasin (e.g. Hooray Sandstone) yield MDA estimates younger than age assignments based on palynostratigraphy and have been revised upwards in geological time. Several units yield divergent MDA estimates, suggesting either unit diachroneity or miscorrelation, indicating that the chronostratigraphic framework of the northern superbasin (and the superbasin at large) warrants further examination.