GEOLOGIC MAPPING STUDIES IN THE GREATER PLATTE RIVER BASINS (CENTRAL GREAT PLAINS) IN SUPPORT OF ECOSYSTEM AND CLIMATE CHANGE RESEARCH

Geologic mapping studies are underway to help define the geologic framework of ecosystems and support climate change research in the Greater Platte River basins, an ecoregion being considered as a potential target of concentrated collaborative observation and research by the Climate Effects Network of the USGS Global Change Program. Geologic mapping and associated geochronological research provide information about physical and chemical properties, distribution, age, origin, and stratigraphic relations of surficial geologic deposits for reconstructing geologic history and recognizing geomorphic response to climate change recorded in the geologic record. Mapping and research primarily focus on three areas: 1) the South Platte River on the drought-prone eastern plains of Colorado, a semiarid environment where geomorphic systems tend to be highly sensitive to climate change; 2) the Niobrara National Scenic River in northern Nebraska, situated at the crossroads of six ecosystems, where many plant and animal species are near their range limits, and geomorphic systems may be near threshold limits; and 3) the Crescent Lake Wildlife Refuge area, in the western Nebraska Sand Hills, where dune migration during past episodes of eolian sand activity blocked drainages and created numerous lakes. In each of these areas, the geologic records of fluvial and eolian systems are intimately interrelated and reflective of past changes in climate. Large-scale geologic mapping with emphasis primarily on river floodplain and terrace deposits, sand dune, interdune, and dune-dammed lake deposits, wind-blown silt deposits, and relations among these different types of surficial deposits will complement ongoing studies by other researchers. In addition, the three areas roughly fall along northern (Niobrara River area) and southern (Crescent Lake and South Platte River areas) east-to-west ecological-condition gradients that have been proposed for the Greater Platte River basins, and therefore will contribute fundamental data for understanding the geologic framework and the impacts of past climates on ecosystems along those gradients.