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Barrier vs. Conduit Behavior of Faults Near Salt: Examples From the Gypsum Valley Salt Wall, Paradox Basin, Colorado


Rising salt bodies create unique deformation patterns and faulting associated with salt tectonics. These fracture networks can influence the hydrological behavior of rocks near salt bodies by acting as barriers or conduits for the movement of fluids like sedimentary brine, meteoric water, hydrocarbons and various ore-forming fluids. Studying the field characteristics of brittle deformation near salt can help identify and rank the significance of variables associated with the compartmentalization of subsurface fluids by faults adjacent to salt. In the southwestern portion of the Paradox Basin, in southwestern Colorado, the southern end of the Gypsum Valley salt wall features a NW-trending counter-regional fault and two SW-trending radial faults. We combined field and laboratory analyses to investigate the paleohydrological behavior of these faults. Field observations suggest radial fractures formed first and are enhanced by the two radial faults, while concentric fractures formed later. Fracture intensity generally decreases with distance from the radial faults suggesting that some fractures were induced by faulting. Microtextures in calcite veins suggest mineralization was primarily postkinematic. Stable isotopes of carbon and oxygen in calcite show the presence of two paleofluid types: meteoric water or sedimentary brines. Both are found along the radial faults, while one type is found along the counter-regional fault suggesting the faults in this area served as conduits to flow, but that different fluids may have moved along each type of fault. There is no partitioning of paleofluid types across the faults, indicating that they did not compartmentalize the regional, kilometer-scale fluid system.