MODERN PHYTOLITH ASSEMBLAGES FROM THE NORTH-AMERICAN GREAT-PLAINS

The analysis of fifty modern phytolith assemblages demonstrates the practicality of opal-phytolith analysis as a surrogate for pollen analysis in the North American Great Plains. The fifteen native grassland sites used in the study span both the east-west moisture and north-south temperature gradients of the central North American grasslands. Multiple soil samples analysed from each grassland site measure within-site variability and provide evidence of how assemblages are formed. Soil assemblages strongly reflect regional grassland composition rather than local vegetation. Five factors contribute to assemblage formation: decay-in-place, fire, eolian transport, herbivory and fluvial/colluvial deposition. Soil assemblages should be interpreted as the end result of these processes integrated over long time periods. The correspondence of assemblages to local conditions controlled by landscape position (e.g. upland v. lowland) is less important than the regional correspondence but is detectable and predictable. Data presented here will provide a basis for interpretation of fossil assemblages from late Quaternary paleosols in the North American Great Plains.