Abstract
Deep confined aquifers within Australia's Great Artesian Basin (GAB) represent vital groundwater resources supporting ecological, agricultural, and industrial systems across arid regions. However, the exact recharge pathways, residence times, and sub-surface mixing dynamics in the deeper Jurassic-Cretaceous sandstones remain subject to significant uncertainty. In this study, we integrate environmental radium isotopes (226Ra and 228Ra) with noble gas signatures (4He accumulation and noble gas recharge temperatures) across a 600-kilometer transect in the Eromanga Sub-basin. Our findings reveal dual recharge mechanisms: slow, diffuse matrix infiltration across Eastern Margin intake beds, complemented by localized, rapid preferential flow along deep-seated structural fault corridors. Calculated noble gas recharge temperatures range from 16.2°C to 21.5°C, recording cooler late Pleistocene surface temperatures during major recharge pulses. Radiogenic 4He accumulation kinetics indicate groundwater residence times exceeding 450,000 years in the central basin interior, where flow velocities drop to less than 0.8 m/yr. Furthermore, elevated 226Ra/228Ra activity ratios along specific flow paths reflect intense water-rock interaction within alpha-recoil-dominated alpha-emitting grain matrices, decoupled from bulk salinity trends. These results provide an updated hydrodynamic framework for the GAB, demonstrating that deep aquifer replenishment is strongly controlled by structural permeability and paleoclimate variations, with major implications for long-term water allocation and aquifer management under future climate projections.
