Abstract

Six localities of mid-Pleistocene tephra-the Muddy Ridge, Red Creek, Lander, Kinnear, Morton and Yellow Calf ashes-are now known in the western Wind River Basin. Geochronologic studies confirm the Muddy Ridge, Red Creek and Kinnear ashes as the 620-650 ka Lava Creek tephra from the Yellowstone National Park region (Izett et al. 1992; Izett and Wilcox, 1982). Geochemical data, shard morphology and field evidence indicate that the Lava Creek A component of the 620-650 ka eruption is more likely to be preserved along major tributaries (Popo Agie, Little Wind River and Muddy Creek) of the Wind River. Only Lava Creek Bash beds are identified along the paleo-Wind River. Interbedded fluvial gravels and tephra from the middle Pleistocene (620-650 ka) eruption of the Yellowstone caldera allow a glimpse of the Wind River fluvial system at an instant of geologic time. Comparison of the fluvial sediments and volcanic ash along major tributaries (Lander, Muddy Ridge and Yellow Calf localities) with those along the paleo-Wind River (Kinnear, Morton, and Red Creek localities) indicate a difference in discharge and competence between the Wind River and its major tributaries (Little Wind River, Popo Agie and Muddy Creek) during the glaciation associated with oxygen-isotope stage 16. The pumice-bearing fluvial sediments at the Morton locality have significant implications for the correlation of Quaternary glacial and fluvial deposits along the Wind River Range. Localities of tephra enable calculation of average rates of local incision in the western Wind River Basin. The spatial variation in the average rates of local incision (0.07-0.23 m / kyrs) reflects fluvial differences between the Wind River and its major tributaries and possible tectonic influences associated with the migration of the Yellowstone hotspot.