DIFFERENTIATING PLEISTOCENE AND HOLOCENE SEDIMENTS IN THE PLATTE RIVER VALLEY USING OPTICALLY STIMULATED LUMINSECENCE DATING

Sediment cores were taken from the alluvial fill beneath the Platte River floodplain near Gothenburg, Nebraska some 50km southeast of the confluence of the North Platte and South Platte Rivers. At this site the Platte’s floodplain is approximately 1.5 to 2 km wide and the alluvial fills range from 12 to 23 m in depth. In the study area, the Platte alluvial fills are slightly calcareous (1-2% carbonate) medium to fine-grained silty sands with occasionally interspersed gravels that directly overly silt and siltstones of the Ogallala Group. Preliminary results from this and previous studies of the Platte fill indicate either no difference or minimal differences between the Holocene and Pleistocene aged alluvium. The similarity between units causes difficulty in interpretation of the Platte River’s evolutionary history of erosion and deposition through time. Optically Stimulated Luminescence dating was used to determine the burial age of these sediments, allowing differentiation between Pleistocene and Holocene units. Initial results from this study will improve our understanding of stratigraphic architecture and evolutionary history of the Platte River over the past ~40,000 years.