THE HOLOCENE PHYTOLITH RECORD FROM MORGAN PLAYA IN THE ROLLING PLAINSOF TEXAS

Phytolith analyses of playa-fill sediments from Morgan Playa yield str ong evidence for Holocene vegetation and climate change. Morgan Playa is located in the Rolling Plains of Garza County, north-central Texas. Backhoe excavation of the small (about 3.2 hectares) basin exposed 25 0 cm of Holocene age sediments. A strongly developed Early Holocene pa leosol occurs at the base (205-250 cm) of the profile. Dark gray-brown , clayey playa sediments compose the upper 205 cm. A single bulk radio carbon sample from 170-180 cm dating to 6840+/-140 yrs BP (Beta-48207) provides limited chronological control. Compositional changes in gras s phytolith assemblages are used to define four bio-stratigraphic zone s. Phytolith assemblages from the lowest zone, correlated with a paleo sol, represent a mired grass prairie. Climatic estimates derived from this zone suggest an annual temperature near present levels but signif icantly greater (+100 mm) annual precipitation than today. A transitio nal zone (145-205 cm) shows increase in warm-season short grasses (gra ma and buffalo grasses) and Aristida (three-awn). This change is assoc iated with increasing aridity during the Middle Holocene. Warm-season short-grass phytoliths dominate the bulk of the profile (15-145 cm). C limatic estimates for this zone include both lower annual precipitatio n (-50 mm) and significantly higher (+3 degrees C) annual temperatures than today. Reduction in short-grass phytolith percentages and an inc rease in phytolith percentages from cool-season grasses characterize t he upper 15 cm of deposit. It is unclear whether this upper zone is th e result of climate change or historic land use. The Morgan Playa reco rd demonstrates the utility of phytolith analysis for inferring paleoc limatic change in a region where pollen analysis is unfruitful and unr eliable.