Refining Early-Middle Holocene Soil-Geomorphic Associations In the Lower Ohio River Valley

Previous soil-geomorphic modeling in the Indiana/Kentucky border area of the lower Ohio River valley discriminated between early Holocene and late Holocene alluvial landforms by examining soil weathering properties. Alfisols tend to be associated with early Holocene geomorphic surfaces and underlying alluvium, while Mollisols are correlated with late Holocene Ohio River units (Stafford 2004). Geoarchaeological studies at the Caesars Archaeological Project (CAP) near Louisville, Kentucky sampled poorly known prehistoric periods dating to the Late Wisconsin/Holocene transition and the middle Holocene. In this alluvial sequence Early Archaic occupations are stratified in overbank/bar deposits underlying an early Holocene terrace dating from 10k to 8k rcybp. Middle Archaic occupations are buried in Late Holocene alluvium dating from 7.5k to 2k rcybp. There is a 500 year gap in the alluvial sequence at CAP. Other locations in the valley suggest that what have been generically categorized as early Holocene landforms formed in the middle Holocene and therefore span the gap at CAP.

The purpose of this study is to identify and initially examine locations in the Indiana/Kentucky border area where soil-geomorphic associations and archaeological data suggest that alluvial units that began aggrading during the early Holocene continued into the middle Holocene (10k to 6k rcybp) through lateral prograding of bank-side bars. One of the locations examined is the confluence of Indian Creek and the Ohio River in Harrison County, Indiana. Archaeological and soil-geomorphic analyses indicate a series of landforms that span the early to middle Holocene period and may include the part of the alluvial sequence not present at CAP. The stratigraphic sequence and soil-geomorphic relationships are discussed, as well as implications for detecting Archaic occupations that date from 8k to 7.5k rcybp and the possible timing of shifts in the early Holocene Ohio River channel.