EXTENT OF SALT DISSOLUTION IN THE PARADOX BASIN AND CHLORIDE FLUXES TO THE COLORADO RIVER AND OTHER RIVERS WORLDWIDE

The Dolores River is a tributary to the Colorado River and is widely known for its high salt loads. The Dolores River transects the Paradox Valley, an anticlinal salt valley, underlain by a salt wall of the Pennsylvanian Hermosa Formation. Discharge of shallow brines (up to 43,300 tons per yr TDS prior to installation of brine extraction wells) from the alluvial aquifer into the Dolores River is responsible for the significant increase in the salinity load. Prior research concluded the dissolution of halite and anhydrite by topographically-driven meteoric recharge from the nearby La Sal mountains is the main contributor of salinity in the shallow aquifer and Dolores River. Using the dissolved salt flux, area of the basin, and estimated time since exhumation of the salt wall (~3 Ma) we estimated that ~400 meters of salt has been dissolved from the salt wall and discharged into the Dolores River and Colorado River downstream over the last 3 million years. River discharge rates and dissolved salt fluxes were assumed to be 3 times higher during the Pleistocene based on previous paleo-hydrology studies in the area. Four hundred meters of salt dissolution in the Paradox Valley is consistent with a similar thickness of salt dissolved in the Spanish Valley to the northwest, based on stratigraphic restorations. Results from this study will help further constrain mechanisms and timing of salt valley formation in the Colorado Plateau. In addition, by investigating other world rivers underlain by salt deposits, we can estimate global riverine chloride fluxes from geologic sources. Preliminary results indicate >4% of modern riverine chloride fluxes come dissolution of salt deposits.