GAB | Connectivity between Australia's Great Artesian Basin, underlying basins, and the Cenozoic cover

• Bruce Radke
• Tim Ransley

A defined hydrogeological basin is convenient for understanding and classifying groundwater systems. However, groundwater flow results generally from pressure and density gradients and may pass through boundaries defined by hydrostratigraphy. Earlier conceptual models of Australia’s Great Artesian Basin (GAB) ascribed all artesian water in the region to the GAB. Although this may have facilitated regulation and control of groundwater usage, it created an unwieldy and unpredictable boundary definition for the GAB. As the understanding of hydrodynamics in the GAB steadily grows, so does the appreciation of interconnectedness of this Jurassic-Cretaceous system with underlying sedimentary basins and overlying cover. In 2012, the definition of the GAB as a hydrogeological basin was modified to align with the Eromanga, Surat and Carpentaria geological basins to simplify this issue for the GAB Water Resource Assessment (GABWRA). This revised definition has since been broadly adopted and remains in use; however, this definition has necessitated a more consistent regional understanding of connectivity with deeper basins that have been of increasing interest and importance for the exploitation of petroleum and gas reserves. Extraction commonly produces groundwater as a by-product, modifying pressure in the host reservoir and potentially in adjoining aquifers, as well as causing possible contamination through fluid transfer. Twenty-seven sedimentary basins are currently known to underlie the GAB and this number is steadily growing through regional seismic studies and exploration.