MAPPING PREGLACIAL FLUVIAL LANDFORMS AND DEPOSITS IN NORTHERN KENTUCKY — PRELIMINARY RESULTS

An abandoned, meandering, high-level fluvial valley extends from the Kentucky River near Carrolton, Ky., northeastward to Lawrenceburg, Ind. Previous investigations interpreted this valley as the trace of the preglacial Kentucky River. Another meandering, north-trending, high-level fluvial valley, tributary to the preglacial Kentucky River near Warsaw, Ky., has also been identified as the preglacial Eagle Creek Tributary. Current surficial mapping in northern Kentucky using LiDAR-derived base maps has resulted in modifications to the original bedrock-focused geologic maps.

Easily identifiable surficial features such as alluvium, areas of development (artificial fill), and landforms were digitized using LiDAR-derived base maps early in the current mapping process in order to identify topographic anomalies. LiDAR-derived base maps include hillshade, slopeshade, slope, and contour maps. Soil samples were obtained for grain-size analysis for the high-level fluvial deposits by using a T-probe. A truck-mounted Geoprobe was used to obtain continuous core samples for grain-size analysis, lithologic description, and determining depth to bedrock.

The preglacial Kentucky River deposits are deeply weathered and consist of clayey silt, sand, and gravel. Scattered pebbles, cobbles, and boulders consisting of quartz, chert, geodes, and sandstone have been observed in drainages adjacent to the high-level fluvial deposits. Core samples taken from the high-level fluvial deposits show a sequence of fluvial deposition capped with thin loess. Depth to bedrock for the high-level deposits ranges from 20 to 30 feet.

The preglacial Eagle Creek deposits are also deeply weathered, and consist of clayey silt with sparse sand and gravel. Sparse fluvial pebbles occur in adjacent drainages. Core samples revealed thin loess deposition on fine-grained fluvial deposits; one core has a thin sand and gravel interval. Depth to bedrock for the preglacial Eagle Creek deposits is less than 10 feet.