SURVEY OF ALLUVIAL PHYTOLITH ASSEMBLAGES IN THE SAC VALLEY ARCHAEOLOGICAL DISTRICT, SOUTHWEST MISSOURI

During the late Pleistocene to early Holocene, the ecology of southwest Missouri was mixed forest/prairie, a transition zone between the Eastern Woodlands and the Tallgrass Prairie just to the west. This transition zone is particularly sensitive to small paleoenvironmental changes that can be quantitatively measured by phytolith analysis to map the spatial and temporal distribution of past vegetation patterns. Studying changes in the distribution of vegetation across the landscape through time can be used to reconstruct past climate and environmental conditions because the dominant plant type in a community is strongly correlated with environmental parameters such as temperature and moisture. These parameters also influence erosion, fire incidence, and different human adaptations and land-use patterns, all of which have a direct impact on the deposition and preservation of phytolith assemblages.

While phytoliths are most commonly deposited in soil and sediment where they grow, in open landscapes or where humans are manipulating vegetation, phytoliths may be transported before being deposited. For example, wind, fire, and water can carry phytoliths great distances from their original environment. In addition, differential preservation of phytoliths has been demonstrated to depend on the type of phytolith and the characteristics of the depositional environment. Based on previous analysis of pollen and plant macrofossils, the Sac Valley Archaeological District contains numerous phytolith producers. However, alluvial settings are complex, producing differential patterns of deposition, and this area has been and continues to be subjected to modern land and stream management practices, which may further impact the preservation of phytolith assemblages. On floodplains, for example, sedimentation processes strongly influence the distribution of soils. In some settings, periodic additions of sediment inhibit soil formation or produce buried soils that can preserve cultural as well as ecological artifacts. To better understand the paleoenvironment of this archaeological district, this work presents new pedologic and phytolith analyses and stratigraphic correlation to nearby archaeological sites to evaluate sources of potential local variation in phytolith deposition and preservation.