Marine to nonmarine facies transition in Permian evaporites of the Palo Duro Basin, Texas; geochemical response

The late Paleozoic Palo Duro Basin evolved from a marine to nonmarine environment as it was infilled. The evaporitic part of the sequence (Leonardian through Ochoan) is composed of regressive carbonate-anhydrite-halite cycles that displaced open-marine environments toward the south during basin filling. Systematic vertical changes in evaporite geochemistry through the evaporite section include increasing (super 87) Sr/ (super 86) Sr ratios and decreasing (altered from marine) delta (super 34) S in anhydrite, decreasing (recycled) bromide content of the halite, and increasing meteoric influence on the stable isotopic composition of fluid inclusions in halite. Geochemical changes correspond to changes in evaporite sedimentology and document the evolution from marine-dominated to partly nonmarine evaporites. Geochemical tracers, when used with sedimentological and facies analysis, provide reliable indicators of the sources of water and solutes in an anhydrite-halite facies tract. Perennial, intermittently stratified, and ephemeral brine-pool conditions affect the amount of synsedimentary recycling. Variable rates of reflux and marine recharge control residence times of brines in the depositional environment. These are two key processes in relating evaporite geochemistry to depositional environment.