Lake Theo: Late Quaternary Paleoenvironmental Data and New Plainview (Paleoindian) Date

Abstract

Lake Theo (Briscoe County, Texas) is a well stratified archaeological site with Paleoindian (Folsom, Plainview) and Archaic occupations. It is located immediately east of the Southern High Plains (Llano Estacado). Preliminary field and laboratory investigations of site stratigraphy, soils, and microbiology were initiated in order to reconstruct late Quaternary paleoenvironments and date the Paleoindian occupations. The site contains a series of ten late Quaternary fluvial, and possible aeolian, deposits; and five soils (ranging from weakly to moderately well developed) formed therein. Radiocarbon ages of 9950 ± 110 years B.P. (SMU-866) and 9420 ± 85 years B.P. (SMU-856) were determined on humates from the bottom and top (respectively) of a thick, slowly aggrading, buried A horizon. The lower date is associated with a Plainview occupation and immediately overlies a Folsom occupation. Comparison of dates and associated stratigraphic and pedologic data with other sediments and soils in the section indicates that during the past 12,000 years, most sedimentation was relatively rapid and sporadic with intervening periods of soil formation of varying lengths. Citrate soluble phosphorous analysis of the soils did not show notable evidence of intense human occupation at any time. Invertebrates recovered indicate a progressive, local extirpation of terrestrial gastropods since Folsom times. The progression is a result of decreased effective precipitation. The most marked stage of extirpation occurred during deposition of Unit 7 (9000 to 8000 B.P.).