PLEISTOCENE FLUVIAL INCISION, AGGRADATION, AND SLACKWATER DEPOSITION ASSOCIATED WITH THE LICKING RIVER IN NORTHERN KENTUCKY

The Licking River, a tributary of the Ohio River and former Teays-Mahomet River system, has been a major drainage for central and northern Kentucky throughout the Quaternary. Previous work has addressed the broader characteristics of the Licking River, with timing constraints based only on qualitative observations. New surficial mapping in northern Kentucky is providing an opportunity to address more detailed aspects and apply new techniques to test longstanding hypotheses. In the DeMossville and Butler quadrangles, a succession of fluvial incision and aggradation, and slackwater depositional environments, have been identified that span more than 250 ft of topographic relief. LiDAR elevation data show the trace of a paleochannel at 650–750 ft elevation. The paleochannel is composed of a (1) lower alluvial silt, sand, and gravel unit, overlain by (2) a middle lacustrine clay and silt unit, which is overlain and partially interfingered with (3) an upper sand, silt, and gravel alluvial/deltaic deposit. The middle lacustrine deposit (unit 2) has been interpreted to represent pre-Illinoian glacial damming of the Licking River (unit 1), which is currently being evaluated with optically stimulated luminescence (OSL) and Be-Al cosmogenic radionuclide geochronology. The modern Licking River has partially dissected the upland paleochannel. LiDAR and field mapping reveal four regional terrace generations at ~510 ft (Qat1), ~530 ft (Qat2), ~570 ft (Qat3), and ~600 (Qat4) ft. Qat3 and Qat4 are alluvial deposits composed of orange-brown silt, sand, and minor quartz gravels. OSL analyses of quartz sand from Qat3 indicate a depositional age of 76 ka. Qat2 is the most expansive deposit in the Licking River Valley, and is tentatively interpreted as a younger lacustrine slackwater deposit, probably correlative with Wisconsin outwash at the mouth of the Licking River. Qat1 is relatively narrow and inconsistently developed compared to the other terraces, and the modern river channel feeds into the Ohio River near Covington, Ky. The repeated cycles of deposition of sediments from fluvial processes and lacustrine environments directly correlates with the retreats and maximum advances of the Quaternary ice sheets. This is an active project, and details regarding mapping and new age constraints will be disseminated as they are obtained.