THE GREAT DIVIDE BASIN: A TRANSIENT SPLIT ON THE NORTH AMERICAN CONTINENTAL DIVIDE

In most settings, closed basins are thought to be the result of tectonic activity where subsidence rates outpace basin filling. Examples include Death Valley in the extensional setting of the southwestern United States and the Qaidam basin in the contractional setting of western China. These basins are characterized by stable interiors with little deformation, extremely low precipitation rates, and often long continuous histories of internal drainage and the accumulation of nonmarine sediments. The Great Divide Basin of south-central Wyoming is a large, closed basin encircled by the North American continental divide. To first-order, it resembles most other closed basins. It exhibits extremely low internal relief, varying less than 200 meters on average, and is confined by walls of uplifted Laramide ranges that impound fluvial, lacustrine and eolian sediments. However, the Great Divide Basin's internal drainage has nothing to do with tectonic subsidence. We evaluate the timing and cause of the closure of the Great Divide Basin by mapping the distribution and elevation of eolian deposits with respect to the spillover points along the divide. Divide elevations and sand dune thicknesses are such that the basin outlets are apparently sealed with sand dune deposits that developed in the Holocene. Our results indicate that the internal drainage of the Great Divide Basin is a transient feature. If not for a lack of precipitation, relatively low elevations of surrounding ranges, the presence of strong prevailing easterly winds, and a few strategically formed ~40 meter thick sand deposits, the basin would drain to the North Platte River to the east. These results have important implications for the history of the migration of the North American continental divide over time and for interpretations of tectonic subsidence related to post-Laramide tectonism in the Rocky Mountains.