A CHRONOSTRATIGRAPHIC RECORD OF MID-WISCONSINAN AGGRADATION IN THE LOWER OHIO RIVER VALLEY AND IMPLICATIONS FOR THE LAURENTIDE ICE SHEET (Invited Presentation)

The Quaternary evolution of the Ohio River was profoundly influenced by the Laurentide ice sheet. Early Pleistocene glacial-interglacial cycles resulted in the capture of the Teays River, transforming the Ohio River from a narrow bedrock stream in a relatively small watershed to a terraced fluvial landscape that drains a significant portion of the east-central United States. A chronostratigraphic framework for the lower Ohio River valley, developed from geologic and geomorphic mapping, sediment coring, geophysics, and from AMS radiocarbon and optically stimulated luminescence (OSL) dating reveals that the lower Ohio and Wabash River valleys experienced a significant phase of aggradation from ~45ka to 29ka. The timing of this aggradation corresponds to the deposition of the mid-Wisconsinan Roxana silt, which is ubiquitous in these valleys, and includes Heinrich events H5 through H3. This pulse of aggradation implies that the Laurentide ice sheet advanced into the Ohio River Basin during the mid-Wisconsinan, and meltwater was routed from an eastern to a southern outlet. There are many published radiocarbon ages for till and associated glacial deposits in the Great Lakes region that range from >30ka to finite (>48ka) and support a mid-Wisconsinan ice advance, but deposits of this age were frequently dismissed as old material reworked by late Wisconsinan ice and a mid-Wisconsinan advance is generally not recognized. The use of AMS radiocarbon and luminescence dating techniques is significantly advancing the state of knowledge for mid-Wisconsinan deposits that were previously not recognized because this time interval is near the limits of conventional radiocarbon dating. As more researchers utilize new dating methods such as luminescence and terrestrial cosmogenic nuclide dating and identify additional mid-Wisconsinan glaciofluvial deposits, new models for the position and chronology of the Laurentide ice sheet during mid-Wisconsinan time can be developed and tested.