Abstract
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 (2-2.5 km depth) associated with evaporites in the Paradox Basin,
Colorado Plateau, are beyond the 81Kr dating range
(>1.2 Ma) and have likely been preserved due to negative
fluid buoyancy and low permeability. 81Kr dating of
formation waters above the evaporites indicates topographically-driven
meteoric recharge (0.03-0.8 Ma) and salt dissolution since the Late
Pleistocene. Formation waters below the evaporites, in basal aquifers,
contain relatively young meteoric water components (0.4-1.1 Ma based on
81Kr) 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 81Kr groundwater age
distributions.