Southeastern Section–55th Annual Meeting (23–24 March 2006)

Paper No. 5
Presentation Time: 8:00 AM-12:00 PM


THOMPSON, Mark F.1, ANDREWS Jr, William M.2, COUNTS, Ronald C.3, MARTIN, Steven L.1 and MURPHY, Michael1, (1)Kentucky Geol Survey, 228 MMRB, UK, Lexington, KY 40506, (2)Kentucky Geological Survey, Univ of Kentucky, 228 MMRB, UK, Lexington, KY 40506-0107, (3)Kentucky Geological Survey, 1401 Corporate Court, Henderson, KY 42420,

New Quaternary geologic mapping performed by the Kentucky Geological Survey in and adjacent to the alluviated valley of the Ohio River in western Kentucky has enabled Quaternary facies models for this region to be updated. Accurate facies models are essential for accurately predicting subsurface lithologic variations for a variety of applications.

Our study area lies south of the known limits of continental glaciation, but served as a drainageway for glacial meltwater and debris. Prior to continental glaciations, the paleo-Ohio River flowed within a deeply incised bedrock valley with a relatively flat valley bottom and bedrock terraces approximately 125 feet below the normal bed of the present-day river. Previously published bedrock topography maps suggested a more V-shaped bedrock valley and proved to be unreliable in planning well construction in the area.

During the late Pleistocene, the paleo-Ohio River channel and valley were subsequently buried beneath as much as 200 feet of complex fluvial/outwash valley deposits capped with high terrace/lake deposits at the maximum filling stage, which ceased approximately 18,000 to 20,000 years ago, based on new and previously published radiocarbon and luminescence dating. Multiple intermediate sand-and-gravel terraces have been identified between the high outwash terrace and the modern floodplain level; further investigation is needed to interpret a mechanism for these terraces. Abandoned Green River paleochannels record significant channel migration of that stream during the late Pleistocene and early Holocene. Benched upland topography adjacent to lacustrine deposits may represent areas periodically inundated with lake waters or related spillways and paleochannels. Loess deposition, which extended into the Holocene, mantles the high terrace, lake deposits, and much of the adjacent bedrock uplands.

The current results are preliminary; additional mapping will provide pertinent information critical to improving Quaternary facies models for this area.