LATE QUATERNARY HISTORY AND GEOMORPHOLOGY OF AN UNDERFIT STREAM VALLEY IN SOUTHERN VANDERBURGH COUNTY, INDIANA

This research explores the Quaternary history of an underfit stream valley near the campus of the University of Southern Indiana. The study area is a plot of abandoned agricultural land situated in a north-south oriented valley flanked by loess-capped highlands to the east and west, underlain by glaciolacustrine sediments and Quaternary alluvium. A stream flows north to south through the valley, meandering, but generally hugging the western margin of the valley. The stream width averages 6.0 m ± 1.6, has steep ~2 m high incised banks, and drains a basin of 3.7 km². The valley, by contrast is 230 m wide on average, producing a stream width/ valley width ratio of 0.03, and categorizing it as underfit. The area lies 30 km south of the Illinoisan glacial maximum and 170 km south of the Wisconsoninan glacial limit.

Sediment cores and soil pits reveal sand to sandy silt at a depth of 3.26 to 3.35 m overlain by 0.82 to 2.25 m of sandy silt determined to be of locally derived fluvial origin. Overlying these sediments is a 30 cm to 1 m thick layer of silt to clayey silt probably derived from locally common loess-covered uplands and deposited as floodplain sediments. Wakeland series soils developed in the upper silt are poorly drained, with Ap/Bt/C profiles extending through the silt into the uppermost part of the silty alluvium. The subsoil sediments include cross-stratified sands, poorly sorted, non-imbricated siltstone and sandstone pebbles and granules interpreted as levee deposits, and silt and clay interpreted as floodplain deposits. The lack of laminar bedding in the fine sediments, as well as the presence of an acorn, a gastropod shell, and charcoal found in this layer support the floodplain interpretation rather than a lacustrine environment found elsewhere in tributaries to the Ohio River.

The sequences of sediment interpreted as fluvial and the small stream/valley width ratio support the hypothesis that the sediments in this valley are glacially derived and the products of a stream that was much larger in the past than it is now.