PETE BIRKELAND, THE TIME FACTOR, AND GEOARCHAEOLOGY

Pete Birkeland’s approach to using soils to reconstruct the geologic past had a profound impact in a variety of subdisciplines of the Quaternary geosciences. Recognizing the Time Factor in pedogenesis has proven useful in understanding how landscapes evolve. Soils buried in stratigraphic sequences further inform us regarding episodic instability (sedimentation or erosion) and stability (and soil formation) in geomorphic systems. Soils as time indicators and as indicators of geomorphic context are particularly invaluable in geoarchaeological research. These concepts aid in predicting presence/absence of archaeological sites and site age (e.g., old sites will not be on young, unburied soils), in reconstructing occupation history (e.g., multiple occupations may form a palimpsest on old landscapes, whereas multiple, youthful, buried soils could contain multiple, discrete occupation zones), and in reconstructing post-burial physical and chemical alterations of sites and artifacts.

Such insights are useful in understanding how the earliest (Paleoindian) settlers of New Mexico, Arizona, and Sonora used terminal Pleistocene landscapes. Most reported Paleoindian sites are on these old, exposed surfaces rather than in buried, stratified contexts. These landscapes are characterized by well-expressed soils (Bt or Bt-Bk horizonation) and therefore provide a means of predicting site locations on old, unburied surfaces. Most Paleoindian sites are on alluvial fans, providing access to freshwater, or on sand sheets and sand dunes on basin floors, in proximity to resources in playas or paleo-lakes. Most sites include palimpsests of younger artifacts. Changes in local depositional environments on the old landscape are useful in understanding regional environmental changes such as slope instability or rising water tables.