Monday, 6 October 2008: 9:15 AM
George R. Brown Convention Center, 350DEF
Lacustrine deposits occur adjacent to major late Pleistocene meltwater sluiceways within the Ohio River system. We delineated multiple lake basins along the Ohio River in southeastern Indiana. Stratigraphic and sedimentologic analyses from streambank profiles indicate a decrease in bedding thickness and grain size and an increase in sorting upbasin, with low organic matter and total carbonate throughout (except in the upper portions of profiles). Our faunal analyses identified several species of freshwater pelecypods and gastropods that we interpret to indicate relatively cool, clear water conditions with only moderate biological productivity. Shell fragments from several locations provide bracketing radiocarbon ages from 19,100 to 10,500 years BP for the lacustrine sediments. The oldest dates are from basal locations overlying bedrock and/or sediment containing Canadian-shield igneous intrusive clasts (which we interpret to be Illinoian till). The youngest dates are from locations near the lacustrine terrace surface, suggesting persistence of lakes beyond the end of glacial meltwater input. Our research confirms that lacustrine sediments accumulated in lake basins developed in the lower portion of tributaries to the Ohio during maximum late Wisconsinan ice advance into the northern portion of the Ohio's watershed. Glacial meltwater in the Ohio was associated with a broad, rapidly aggrading, braided stream system. Glacial outwash damned and ponded tributaries where lakes formed and gradually filled with sediment graded to the level of the adjacent outwash deposits. These lakes developed concurrently with the Ohio's braided-stream system, receiving periodic sediment-laden flood waters from that system, but were often feed by local streams with sufficient discharge to sustain them beyond termination of glacial meltwater input. Climatic change and lowering of local base level in the Ohio River valley during the latest Pleistocene and early Holocene resulted in reduced runoff and stream downcutting, both factors contributing to the eventual demise of these lakes.