THE STRATIGRAPHIC, PEDOLOGIC AND PALEOENVIRONMENTAL FRAMEWORK OF A PALEOINDIAN SITE IN THE PRAIRIE-FOREST ECOTONE

The Montgomery archaeological site is located in southwestern Missouri along the western margin of the Ozark Plateau, within the prairie-forest ecotone. The sensitive location of the Montgomery site provides a unique opportunity to examine climate-driven vegetation changes between grassland and deciduous forest during the Holocene. Environmental fluctuations from the last 12,000 years are recorded in deep alluvial deposits at the site. Twenty-four cores record pedologic and lithologic variations in these sediments. Two stable carbon isotope profiles provide a proxy for vegetation changes in the Sac River Valley since the last glacial maximum.

Early Holocene sediments exhibit relatively light d¹³C values, indicating a high percentage of C₃ forest vegetation. d¹³C values are heavier in middle Holocene sediments due to increased C₄ prairie vegetation. The late Holocene begins with dominant C₃ vegetation assemblages, but a prairie interval interrupts deciduous forest and has been recorded at other sites in the region.

Several periods of landscape stability were identified based on pedologic and sedimentologic features commonly associated with buried soil horizons. Significant floodplain stability and soil formation occurred at the beginning and end of the middle Holocene (between 8,500 and 8,100 years BP and again between 4,500 and 4,000 years BP). Soil formation at the Montgomery site is limited to periods of increased prairie vegetation (heavier d¹³C values and increased C₄ plants). A cumulative soil was identified at an average depth of 290cm and is associated with a previously identified Dalton cultural horizon. Based on regional cultural information, as well as comparisons with other regional d¹³C profiles, this soil was likely formed between 10,100 and 9,400 years BP.