Geoarchaeological variability among two central Iowa drainage basins; Geological Society of America, 1997 annual meeting

Detailed investigations of the alluvial stratigraphy, chronology and archaeology of two small tributaries of the South Skunk River in central Iowa indicate considerable variability among the records. Buchanan Drainage, located near the southern margin of the Late Wisconsinan Des Moines Lobe is a small, narrow, steep-sided tributary whose initial entrenchment and headward expansion occurred approximately 13,000 B. P. Holocene alluvial and colluvial deposits within the basin are stored along the valley margins beneath a single, low terrace. The archaeological record within the valley is dominated by Middle to Late Archaic deposits (7,000-2,500 B.P.). Late Paleoindian and Early Archaic (8,500-7,000 B.P.) artifacts are rare in extensive collections from the valley. Erickson Creek, located approximately 15 km southeast of the Buchanan Drainage is significantly wider and more open than the Buchanan Drainage, and contains several terraces and alluvial fans. Initial headward expansion of this drainage system occurred at about the same time as at Buchanan Drainage, but occurred within a pre-existing linked-depression system. In contrast to the archaeological record from the Buchanan Drainage, numerous Late Paleoindian and Early Archaic archaeological deposits are present, while Middle and Late Archaic deposits are less common. Variability in the archaeological record of these valleys is partially attributable to geologic factors such as erosion and deep burial. Early Holocene archaeological deposits may be present in deeply buried contexts within the lower reaches of the Buchanan Drainage, while deposits of this age are well exposed in the Erickson Creek basin. A late Holocene floodplain widening episode removed most of the middle Holocene archaeological deposits from the lower portion of the Erickson Creek valley, while floodplain aggradation in the lower portions of Buchanan Drainage buried and preserved these deposits. Geologic processes do not account for all variability in the archaeological record of these valleys. The presence of bison kill sites in the Erickson Creek basin and their apparent absence in the Buchanan Drainage suggests differing human land-use patterns.