The Rise and Fall of Laramide Topography and the Sediment Evacuation From Wyoming

The modern topography within the Laramide region consists of high-relief ranges and high-elevation low-relief (HELR) surfaces separated by intraforeland basins. However, the timing and development of this topography within the type-locality of the Wyoming Laramide province is poorly understood. Previous models suggest that the modern topography is a young feature that was acquired after Laramide tectonism, post-Laramide burial, and basin evacuation; however, evidence of such a progression is sparse. We present low-temperature-thermochronological data from two Laramide uplifts in Wyoming, the Wind River and Bighorn Ranges, which document an early record of Laramide exhumation, subsequent reheating, and significant cooling after 10 Ma. Our results indicate that the Laramide ranges were buried by post-Laramide Cenozoic basin fill, creating a low-relief topography by the early Miocene that was reduced due to late Miocene regional incision and basin evacuation. We suggest that HELR surfaces experienced further relief reduction from Pleistocene glaciation.