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

Automated summary

Krypton-81 dating provides new insights into the timing, mechanisms, and extent of meteoric flushing versus retention of saline fluids in the subsurface. The study demonstrates that the preservation of Paleozoic seawater-derived brines in the Paradox Basin is attributed to negative fluid buoyancy and low permeability. The dating results also reveal topographically-driven meteoric recharge and salt dissolution since the Late Pleistocene and the flushing of remnant brines and dissolved evaporites by relatively young meteoric water components in basal aquifers. The study further illustrates the activation of deep, basinal-scale flow systems in the Colorado Plateau due to rapid denudation in recent times.