Revised Jurassic and Cretaceous correlations across the Great Artesian Basin: improving hydrogeological conceptualisations

The Great Artesian Basin (GAB) is the largest groundwater basin in Australia, underlying approximately one fifth of the continent, including parts of Queensland, New South Wales, South Australia and the Northern Territory. The GAB consists of three hydraulically-connected geological basins – Eromanga, Surat and Carpentaria, which contain a sedimentary assemblage deposited almost continuously from Early Jurassic to Late Cretaceous. Groundwater from the GAB is a vital resource for agricultural and extractive industries, community water supplies. It supports cultural values and sustains groundwater-dependent ecosystems such as springs and wetlands. Knowledge of sedimentary depositional systems and stratigraphic correlations varies considerably across the GAB. Groundwater resources are continuous across the GAB and need to be mapped consistently to better assess the complex interconnected pathways across jurisdictions. The hydrogeological conceptualisations that underpin groundwater resource management approaches can be based on diverse and sometimes incompatible historic nomenclature across state and territory borders. Recent studies have shown significant spatial lithological variability within hydrostratigraphic units. Consistent and higher resolution mapping of the geological complexity at a basin-wide scale will provide an improved hydrogeological framework to underpin effective long-term management of GAB water resources. We have compiled and standardised existing and newly interpreted biostratigraphic data, well formation picks, 2D seismic and airborne electromagnetic data in a consistent chronostratigraphic framework to better correlate geological and hydrostratigraphic units across the GAB. Correlating the chronostratigraphy across the GAB reveals age-equivalent sediments deposited in different environments during alternating transgressive and regressive events. Comprehensive biostratigraphic control applying a unified zonation scheme helps to constrain lithological correlations. The distribution of sand/shale ratio in key wells across the GAB improves mapping of aquifer hydrogeological variability. This novel approach generates a consistent mapping of the regional distribution and properties of aquifers and aquitards across the GAB. The refined correlation of Jurassic and Cretaceous rock units between the Surat, Eromanga and Carpentaria basins improves our understanding of hydrogeological unit geometry, lithological variation, and potential groundwater connectivity above, below and within the GAB aquifers. The 3D hydrogeological architecture provides a model for refining hydraulic relationships between aquifers within the GAB, and enables development of more accurate system conceptualisations. This represents an important step towards the future goal of quantifying hydraulic properties and aquifer inter-connectivity to underpin more robust basin water balance estimates. This Abstract was submitted/presented to the 2022 Central Australian Basins Symposium IV 29-30 August (https://agentur.eventsair.com/cabsiv/).