PALEOCENE TO EOCENE POWDER RIVER BASIN PROVENANCE BASED ON DETRITAL GARNET AND APATITE GEOCHEMISTRY

The relative timing of exhumation of the Laramide uplifts adjacent to the Powder River Basin, and which were its primary sediment sources during their coeval formation, is unclear. Previous provenance work in the region has focused on the bulk heavy mineral content of the Paleocene-Eocene Fort Union and Wasatch formations. During deposition of these units, the environments in the basin transitioned from fluvial to fluvio-deltaic and lacustrine and back to fluvial, due largely to tectonic activity, with paleocurrent data suggesting drainage from south to north along primary and secondary basin axes. We will be using detrital garnet major element and apatite trace element compositions from the Lebo Shale and Tongue River members of the Fort Union Formation and the Wasatch Formation to determine the sediment sources to the basin. These data will allow us to discriminate among the metamorphic facies and types of igneous rocks contributing sediment to the basin. Our results will be compared to the same data recently collected from modern rivers that are draining the uplifts adjacent to the Powder River Basin. Establishing the timing of the uplifts in the region will help us to better understand the tectonic evolution of the Laramide Province near the eastern extent of the orogen, with economic implications for critical mineral and hydrocarbon exploration and recovery.