LATE QUATERNARY EVOLUTION OF THE CENTRAL OHIO RIVER VALLEY

Prior to Pleistocene glaciation, the central Ohio Valley region was dominated by portions of two watersheds, the Teays River and the ancestral, lower Ohio River systems, draining to the northeast and southwest, respectively, away from a bedrock divide near Madison, Indiana. Likely, it was not until continental ice sheets overrode the Teays basin, ponding its headwaters in Kentucky and West Virginia and forcing a flow reversal to the southwest across the Madison divide, that the central and eastern portions of the Ohio River system formed. The timing and/or number of events required for permanent establishment of the modern Ohio is poorly constrained.

This preliminary investigation was undertaken to assess and refine the accuracy of this scenario. We described and mapped Quaternary deposits and landforms within the central Ohio River valley from topographic maps, soil surveys, well logs, and field reconnaissance; and estimated their relative ages using geomorphic and stratigraphic relationships and soil profile development. We developed several morphostratigraphic units representing soil-landform-sediment associations, and generated fifteen 7.5 minute geologic maps in the study area that were then transferred to a GIS database.

We inferred several significant geomorphic events in the Ohio River valley's evolution from our data analysis. The main phase of valley entrenchment resulted from one or more pre-Illinoian ice sheet advances. The Illinoian ice sheet advanced into an already extant modern Ohio River drainage, obliterating all evidence of formerly developed features and depositing till and outwash preserved as isolated, hummocky benches in the main valley about 100 feet above the modern floodplain. The Wisconsinan ice sheet advanced into the northern margin of the Ohio's watershed, its meltwater removing much of the former Illinoian features while depositing an extensive outwash terrace capped by eolian sediments in the main valley about 40 feet above the modern floodplain, lacustrine silts in several tributaries graded to that terrace, and strath terraces cut and backfilled into the main valley terrace. Holocene modification of previously developed features includes extensive weathering, gullying, and/or deposition of colluvial wedges and alluvial fans.