GEOLOGIC, LITHOSTRATIGRAPHIC, AND HYDROSTRATIGRAPHIC CLASSIFICATION OF SALT FLATS: IMPLICATIONS FOR RESOURCES AND ENVIRONMENT

Salt flats (“salars”) are an accessible mining medium via groundwater extraction for mineral resources including . Developing frameworks for assessing resource potential of salars is vital for the sustainability of renewable energy sources. Current frameworks for characterizing salt flats are limited to their spatial extent and depth without consideration of either the architecture or variation in the hydrogeologic properties. Additionally, the sequences of evaporites, volcanic, and clastic deposits are further complicated by faults which can create unique hydrogeologic conditions that either favor or inhibit brine extraction from a resource and reserve standpoint. These hydrogeologic features also exert important controls on the distribution of surface water bodies. We therefore assess the architecture of salt flat stratigraphy coupled with hydraulic properties to define a hydrostratigraphic framework for a range of salars with varying degrees of inflow chemistry, age, thickness, geologic heterogeneity, and sedimentationWe find that halite-dominated evaporite sequences with high hydraulic conductivity encourage advective flow (100-0.1 m⸳d^-1) between 0-60 meters below the surface. While data indicate that below 60 meters these sequences decline in conductivity thereby favoring diffusive flow (≤0.01 m⸳d^-1), between 45-80of evaporite sequences maintain advection-driven flow up to 100 meters depth. Results also indicate that alluvial, non-evaporite lacustrine, and clastic sediments are common in salars. Non-evaporite sediments are valuable for characterizing the hydraulic properties of an aquifer as a potential reserve as they are more likely to retain hydraulic properties at depth than evaporite sequences, thus increasing resource and reserve potential. Observations further indicate that the potential for resource development is sensitive to the depth and physical distribution of lithostratigraphy. This study provides the first global-scale analysis of coupling hydraulics and stratigraphy to characterize both resource and reserve potential available in aquifers underlying salars. Findings also have implications for the time-sensitive dynamics of these systems as modern climate-driven change in the hydrologic budgets of these systems gains eminence.