Geochronology and sediment provenance of the Precipice Sandstone and Evergreen Formation in the Surat Basin, Australia: implications for the palaeogeography of eastern Gondwana - Geochronology data

A new view of the palaeogeography and tectonic evolution of eastern Gondwana during the late Mesozoic is emerging, driven largely by the detrital zircon record of sedimentary basins comprising the Great Australian Superbasin (GAS). The updated model suggests that a long-lived magmatic arc was present on the eastern margin of Australia, which is in stark contrast to some previous views that eastern Australia was situated well-inland of a plate boundary. However, the active magmatic arc model is derived from Late Jurassic-Cretaceous strata, with tectonic processes and sediment pathways operating in the Early Jurassic still poorly understood. The Lower Jurassic Precipice Sandstone in the Surat Basin – an important stratigraphic component of the GAS – affords an opportunity to fill such a knowledge gap. The Precipice Sandstone is also economically important due to its aquifer capacity and prospectivity for CO2 sequestration. Previous work has hypothesized that the formation contains deposits sourced from multiple terranes, yet this has not been rigorously tested.

This geochronology dataset comprises two parts: detrital zircon LA-ICP-MS data and CA-TIMS ages from tuff samples. These radiometric dating methods were used to 1) constrain depositional ages and add resolution to the stratigraphic framework for the lower part of the Surat Basin succession, and 2) characterise the sedimentary provenance of the Precipice Sandstone and the overlying Evergreen Formation. The new U-Pb zircon dates provide some of the first radiometric depositional age constraints for the Lower Jurassic part of the GAS succession, thus far based on palynology and lithostratigraphy. Our analysis revealed mixed provenance with multiple source terranes within the broader Tasmanides region. The dataset is dominated by Grenvillian (~900-1200 Ma), Pacific-Gondwanan (~500-650 Ma) and Permian-Triassic (240-266 Ma) age populations. Smaller proportions of other Palaeozoic and Proterozoic ages, as well as a small but prominent syn-depositional Early Jurassic population, are also present. This age profile indicates that the bulk of sediment was derived from the Thomson Orogen, with a lesser contribution from the New England Orogen. We found no evidence for sediment derived from the Lachlan Orogen, despite a distinct northward palaeocurrent component. Syn-depositional volcanic material within the succession corroborates the notion of continued arc magmatism along the eastern Gondwana margin, which contributed sediment to the GAS throughout the Early Jurassic. Radiometric ages place the Precipice Sandstone in the Lower Jurassic Sinemurian-Pliensbachian and the Evergreen Formation in the middle Pliensbachian-topmost Toarcian, and suggest diachronous deposition across the basin. Despite pronounced variations in formation thickness, the Precipice Sandstone shows relatively uniform provenance across the basin, showing little evidence for multiple depocenters.