ARCHAEOLOGICAL SITES IN ALLUVIAL SETTINGS AS PALEOCLIMATIC AND PALEOENVIRONMENTAL ARCHIVES: EXAMPLES FROM THE CENTRAL PLAINS, USA

Multi-proxy data obtained from archaeological sites in alluvial settings of the Central Plains provide new evidence for regional climatic and environmental change during the late Quaternary. Geoarchaeological studies at Kanorado in NW Kansas, the Claussen and Coffey sites in NE Kansas, and the Eastep site in SE Kansas included phytolith, gastropod, and/or δ¹³C analysis of soil organic matter (SOM). Kanorado is a cluster of Paleoindian and Early Archaic campsites buried in alluvium along a draw cut into the High Plains surface. At Claussen, stratified Paleoindian cultural deposits occur in an alluvial paleosol 9-11 m below the surface of a terrace of Mill Creek. Alluvium at the Coffey and Eastep sites, both in large river valleys, harbors Early Paleoindian through Late Archaic and Late Archaic through Late Prehistoric records, respectively.

Based on the gastropod record at Kanorado, from ca. 12.4 to 11 ka shallow standing water was present in draws on the High Plains of western Kansas. Soon after ca. 11 ka and continuing until 9 ka, the landscape became drier, with aquatic snails quickly disappearing. The phytolith record for Kanorado suggests that at ca. 12.4 ka there was open parkland that included pooids and conifers. By 11 ka and continuing through the Younger Dryas, pooids declined in favor of chloridoids, and conifers disappear by 10 ka. The warming/drying trend continued into the early Holocene and intensified during the middle Holocene, a pattern supported by the δ¹³C record.

Trends in the data for Claussen and Coffey are similar to those for Kanorado. At Claussen, terrestrial snails indicate a moist woodland setting around 11 ka, but from ca. 11 to 10.5 ka there was a shift towards drier woodland, and by ca. 9 ka an open prairie was in place. The phytolith data support this interpretation, as does the δ¹³C record at Coffey.

Based on δ¹³C data for Eastep, since 2.8 ka a mixed C₃/C₄ vegetation community has been in place in SE Kansas. However, a shift towards higher δ¹³C values soon after ca. 1.3 ka may reflect an increase in contributions of SOM from C₄plants in response to the Medieval Warm Period.

In sum, multi-proxy data gleaned from archaeological sites in alluvial settings provide a history of climatic and environmental change in the Central Plains. This history is crucial to understanding human adaptations to bioclimatic change.