MODERN ANALOGS OF PLEISTOCENE LACUSTRINE SHORELINE DEPOSITS IN NORTHERN AND WESTERN KENTUCKY

Bathymetry and geomorphic study of modern lake shores and lake sediments using LiDAR and reconnaissance sonar demonstrate the modern lakes are useful analogs for Pleistocene lake deposits and landforms elsewhere in Kentucky. The Kentucky Geological Survey has an ongoing field mapping program for surficial geology in priority areas of the state. Much of this STATEMAP-supported work has been focused on areas that include Pleistocene lacustrine deposits associated with impoundment of Ohio River tributaries by rapidly aggraded Wisconsinan or Illinoian outwash.

In the lower Ohio River Valley near Owensboro and Henderson, extensive lacustrine deposits fill wide valley bottoms adjacent to the Ohio River. Along the upland margins of these deposits, an ambiguous loess-mantled mosaic of fluvial terraces, alluvial fans and deltas, colluvial deposits, and slope-wash is irregularly preserved. Delineating the boundaries of these component deposits under the loess cover has proven challenging. Subsequent mapping in the Louisville metropolitan area and in northern Kentucky has delineated a series of distinct depositional features and landforms along valley margins: alluvial fans, terraces, and colluvial toe slopes are common along many streams tributary to the Ohio River. Along many of these streams, terraces related to Pleistocene lacustrine deltas are locally preserved. The thinner or absent loess cover in these areas enables more confident delineation and facilitates the use of LiDAR-supported landform mapping of these deposits.

Modern Kentucky lakes (the oldest being considered is < 80 years old), most managed by the U.S. Army Corps of Engineers for flood control, are developed on similar bedrock lithologies as the ancient lakes in the field mapping areas. Local materials dominate the deposits being examined. Each lake has different characteristics of size, specific valley geomorphology, contributing drainage area, and patterns of seasonal and storm-response lake-level variation. Waves, groundwater changes, slope-stability processes, and fluvial sedimentation all contribute to the development of numerous near-shore landforms and deposits (deltas and fans, bank-collapse toe-slopes, gravel spits), which provide useful analogs for understanding the context of the ancient features.