Offshore freshened groundwater emplacement in an evolving siliciclastic margin (Canterbury Bight, New Zealand): A 3D modeling approach

Offshore freshened groundwater (OFG) represents a globally distributed subsurface resource with potential applications in water management, oil recovery, and environmental studies. Despite growing interest, the understanding of OFG systems, including their geometry, distribution, and emplacement dynamics, remains limited. In this study, we address these gaps by employing a novel 3D geostatistical modeling approach, focusing on the Canterbury Bight, a passive siliciclastic margin with proven OFG resources. Our methodology integrates high-resolution 2D seismic lines and borehole data, allowing us to capture the geological heterogeneity of the passive margin. Unlike traditional static models, our 3D approach considers the evolving stratigraphic architecture over multiple sea-level cycles, offering a more comprehensive understanding of OFG systems. Key findings include the successful incorporation of isostatic shifts and decompaction into our model, resulting in OFG distributions closely resembling those observed in the Canterbury Bight. We emphasize the importance of infilled buried channels and paleo-topographic highs in promoting OFG emplacement, shedding light on distribution patterns not easily explained by current seafloor topography or hydraulic heads. Our study advances the field by demonstrating how a 3D consideration of continental margin evolution significantly influences numerical estimations and improves the characterization of OFG resources. These findings contribute to a better understanding of OFG systems and provide valuable insights for future research and resource management.