RADIOCARBON DATING OF PALEOSOLS TO CONSTRAIN TIMING OF HOLOCENE LAND SURFACES, BADLANDS NATIONAL PARK, SD

Paleosols found within sod tables in Badlands National Park, SD have been radiocarbon dated to constrain the timing of late Holocene alluvial-colluvial paleofans. The study area surrounds Key Hole Table (KHT), which lies adjacent and west of the Old Northeast Road, north of the junction with the Badlands Loop Road, SD 240. Sod tables are mesa-like landforms ranging from 0.5-9 meters in relief. The tables are remnants of ancient alluvial-colluvial fans sourced from Tertiary ‘castles.’ Episodes of fan aggradation were separated by periods of surface stability, allowing pedogenesis to produce distinct A-C and A-B-C soil profiles in the study area. This process was repeated several times, burying the previously deposited sediment under fresh alluvium. These graded surfaces are presently cut-off from their source areas, and have become dissected into sod tables through lateral and vertical stream erosion, exposing the stratigraphy of the fans. Soil profiles from 15 sod tables containing Ab and Bb horizons (paleosols) were described and sampled. Radiocarbon dates obtained from the paleosols are intended to constrain potential marker beds. Correlation of the marker beds among adjacent sod tables will assist in the reconstruction of paleo alluvial-colluvial fans. Three radiocarbon dates are completed and many others are pending. KHT 1-1 contained an Ab-horizon (44-63.5 cm) dated 2160 +/- 60 RCYBP. KHT 2-1 contained an Ab-horizon (38-40 cm) dated 1991 +/- 60 RCYBP. KHT 3-1 contained an A2b-horizon (72-90 cm) dated 2710 +/- 150 RCYBP. Charcoal found within the sod tables will also be dated using AMS 14C techniques. Magnetic susceptibility has been used to validate the presence of paleosols by detecting high concentrations of iron. Radiocarbon dating to constrain the timing of paleo-land surfaces in Badlands National Park will be instrumental in placing the evolution of the landscape into the context of the paleoclimatic record for the High Plains.