GEOARCHAEOLOGY AND HOLOCENE BIOCLIMATIC CHANGE ON THE EDGE OF THE LLANO ESTACADO IN WEST TEXAS

Interdisciplinary research is being conducted along the north-south geomorphic boundary between the Southern High Plains and Rolling Plains, in west Texas. The study area contains abundant springs, lithic resources, shelter, and plant and animal food sources that attracted hunter-gatherer groups to the escarpment edge. A record of late Quaternary sediments and soils has captured the past dynamic history of cultural and environmental change in the region. The geoarchaeological potential for buried cultural material is assessed, and a high-resolution multi-proxy paleoenvironmental data set is used to interpret bioclimatic change across the caprock escarpment. Lithologic and pedologic descriptions, radiocarbon ages determined on soil organic matter, and stable carbon isotope and phytolith data are presented from multiple localities containing alluvial, lacustrine, and palustrine deposits. Results suggest that ephemeral low-order streams feeding the South Fork of the Double Mountain Fork of the Brazos River rapidly removed sediment and cultural material during the early to mid-Holocene, but a late Holocene pedocomplex is preserved. Early Holocene buried soils in alluvial, palustrine and lacustrine deposits in reentrant canyons have high potential for the early cultural record. One buried soil in a co-alluvial fan dates to the mid-Holocene. Ongoing stable carbon isotope and phytolith analyses of the deposits are providing information about changes in plant communities through the Holocene. Initial results indicate that a mixed C₃/C₄ plant community persisted through the early Holocene before gradually shifting to C₄ grassland. Phytolith results are compared to the stable carbon isotope record, and are used to determine the abundance of drought-resistant species, and to establish the types of plants that may have been used by hunter-gatherers.