THE DISTRIBUTION OF BRINES IN A FORELAND BASIN EAST OF THE ROCKY MOUNTAINS

Aquifer systems in the foreland basin underlying the Central United States east of the Rocky Mountains contain water with dissolved-solids concentrations ranging from 1,000 to greater than 300,000 milligrams per liter. Knowledge of the distribution of brines should provide clues to long-term, large-scale fluid flow in the basin. Whereas salinity has been found to increase when plotted in one dimension as a function of depth for most sedimentary basins, such a trend is not evident in this basin and no two dimensional cross-section showing salinity distribution has been published. We plotted salinity along a geological cross-section from eastern Colorado through Kansas to western Missouri using geochemical datasets from the Kansas Geological Survey, the United States Geological Survey, and several other published and unpublished sources. The results show that high salinity is spatially associated with thick Permian-age halite evaporite deposits. This pattern supports previous geochemical studies done on brines discharging from the Western Interior Plains aquifer system in southeastern Missouri that have suggested the high salinity is due to dissolution of halite from water of a far-traveled meteoric origin. This is significantly different than brines located in geologically similar basins east of the Rocky Mountains that have generally been interpreted to be ancient evaporatively concentrated seawater. The distribution and chemical composition of the brines will be used to constrain a finite element numerical model simulating variable-density fluid flow, heat transport, and solute transport. Local variable-density related effects on the regional topographically driven flow system are anticipated in areas of high salinity. A steady-state distribution and short residence time is predicted for the brines.