Post-Pleistocene Depositional Change at Rodgers Shelter, Missouri

Abstract

Investigations of the deposits in Rodgers Shelter (23BE 125), on the western periphery of the Ozark Highlands, delineated major depositional patterns at the site and determined the chronological relationship of these patterns to human activities. Twenty-five sediment samples representing a stratigraphic sequence through the 11,000 year old accumulation were subjected to 2 types of analysis: 1) particle size determinations made by a combination of the hydrometer method and wet sieving, and 2) determination of mineral and rock composition of gravel and coarse sand by visual examinationPrincipal components factor analysis applied to particle size and composition data yielded 3 factors representing changing upland and hillslope erosional patterns, shifting location of the nearby Pomme de Terre River channel, and variations in vertical accretion by the Pomme de Terre River.Weighted average cluster analysis of factor scores on the 3 depositional variables delimited 7 major groups of samples, each representing distinctly different depositional conditions. Viewed stratigraphically, 10 depositional units were defined. The depositional environment of each was determined by mean factor scores. These stratigraphic units provide a more refined picture of site stratigraphy than is available from field observations alone.Viewed chronologically, the cluster analysis provides a model of the post-Pleistocene depositional history of the site: progressing from a period of intense upland erosion and aggradation by the Pomme de Terre, to a period of severe local hillslope erosion and valley degradation, and finally to a period of combined alluvial and colluvial deposition on the T-lb terrace. When the depositional history and cultural history of the site are compared, every major hypothesized change in human adaptive strategy coincides with a major change in depositional patterns, providing a convincing example of the close interrelationship between human behavior and surrounding environmental conditions