Krypton‐81 Dating Constrains Timing of Deep Groundwater Flow Activation

Krypton-81 dating provides new insights into the timing, mechanisms, and extent of meteoric flushing versus retention saline fluids in subsurface response to changes geologic and/or climatic forcings over 50 ka 1.2 Ma year timescales. Remnant Paleozoic seawater-derived brines associated with evaporites Paradox Basin, Colorado Plateau, are beyond 81Kr range (>1.2 Ma) have likely been preserved due negative fluid buoyancy low permeability. formation waters above indicates topographically-driven recharge salt dissolution since Late Pleistocene (0.03–0.8 Ma). Formation below (up 3 km depth), basal aquifers, contain relatively young water components (0.4–1.1 based on 81Kr) that partially flushed remnant dissolved evaporites. We demonstrate recent, rapid denudation Plateau (<4–10 activated deep, basinal-scale flow systems as recorded groundwater age distributions.