SOM- AND BONE-DERIVED ISOTOPIC SIGNALS AS PROXIES OF LATE PLEISTOCENE AND HOLOCENE CLIMATIC CONDITIONS IN THE CENTRAL GREAT PLAINS, U.S.A

In recent years, a record of climatic prehistory for the central Great Plains (Kansas, Nebraska, eastern Colorado) has begun to emerge. Stable isotope ratio analysis (SIRA) of carbon has proven to be particularly useful in determining the flora and fauna, and hence climate for the Late Pleistocene and Holocene. SIRA was conducted on (1) soil organic matter (SOM) of modern and buried soils, and (2) bone of modern and prehistoric prairie dogs (Cynomys sp.) and ground squirrel (Spermophilus sp.). SIRA of carbon on modern soil and bone material provides the necessary baseline data for contemporary climatic patterns and reflects the regional westward decrease in moisture and attendant change in grass carbon pathways (C3-C4 shift). To appreciate the local/topographic variability inherent in isotopic values from modern soils, a 0.6km grid was sampled in near-pristine prairie at the Konza Prairie, a Long Term Ecological Research Area. The prehistoric record was extracted from two major soils developed and preserved throughout the region, the Gilman Canyon Formation soil (c. 35-20 ka) and the Brady soil (c. 11-9 ka), as well as from the associated Peoria and Bignell loesses. The prehistoric isotopic sequences reveal periods of both gradual and abrupt environmental change, and highlight the nature of the Pleistocene-Holocene boundary.