THE CARBON AND OXYGEN ISOTOPE RECORDS OF A LATE HOLOCENE ALLUVIAL SEQUENCE AT EUREKA, KANSAS

A recently discovered, deeply buried stratified archaeological site in Eureka, Kansas offers extensive cultural and paleoclimatic information spanning the past 4000 years. The site's stratigraphic sequence shows alternating paleosol horizons and fine-grained deposits, underlain by a reduced organic-rich alluvial layer. The site contains seven distinct cultural zones; within these zones, cultural remains include archeological mussel midden, mussel shells, charcoal, burned rock fragments, and burned rock features. A series of radiocarbon ages on wood at the base of the section and on wood charcoal in selected midden deposits have been obtained by the Kansas Geological Survey. The goal of this project is to determine the carbon and oxygen isotope records at the Eureka site. The carbon isotope record provides rich paleoenvironmental information, delineating dominant vegetation type and implying correlative climatic conditions. Initial geochemical research shows a biotic transition from C4 to C3 plants within the stratigraphic section's upper 120 cm. Eureka's geographic location positions the site at the western margin of the southern forest-prairie ecotone, a transitional zone between the eastern deciduous forest and mid-western tallgrass prairie; thus, this site's carbon isotope data will elucidate transitional ecotone dynamics. The oxygen isotope signature, recorded in shell remains from the site, will provide submillennial-scale data on variations in stream productivity that will be related to vegetation change and flood dynamics.