EARLY TO MIDDLE HOLOCENE CARBON ISOTOPE AND PHYTOLITH RECORDS FROM SOUTHWEST MISSOURI

New pedologic, carbon isotope and phytolith analyses along with stratigraphic correlations to nearby archaeological sites record the spatial and temporal distribution of past vegetation patterns in the Sac Valley Archaeological District of southwest Missouri. Radiocarbon ages obtained from a soil core along Bear Creek, CB5, are related to those from Hajic et al. (1998, 2000) indicating that the CB5 location contains correlative middle Rodgers Shelter submember deposits. This relationship also indicates that sedimentation was approximately two times greater than at the Big Eddy (23CE426) archaeological site providing much higher temporal resolution for the alluvial history and associated vegetation proxies during the early to middle Holocene. A new core, DDY-KR2, was obtained from the Big Eddy (23CE426) archaeological site and a finer resolution of δ¹³C values at Big Eddy increased the detail about alluvial activity. The vegetation types suggested by the δ¹³C values for DDY-KR2 are reflected in the phytolith assemblages. This indicates that in the absence of pollen or macrofossils, phytolith assemblages are useful for reconstructing local vegetation in concert with the study of pedogenesis and sedimentation history.

Most midcontinent climate proxy records include indications of an early Holocene warm period when prairie replaced forests, then a cooler period in which trees dominated the landscape, followed by a warmer middle Holocene period when prairie vegetation was dominant. However, the CB5 δ¹³C profile of mixed C₃/C₄ vegetation indicates either that the vegetation in this location was not as sensitive to climate change or that this location was buffered from other influences, e.g. fire, which were critical to the expansion of prairie vegetation. On the other hand, the phytolith assemblages at CB5 indicate that there were periods with abundant C₄ grasses even though the δ¹³C values indicate a dominance of C₃ vegetation. This indicates that in the mixed forest/prairie ecotone interpretations of past vegetation from either carbon isotopes or phytolith assemblages alone may not accurately reflect regional patterns of vegetation.