THE QUATERNARY GEOLOGY OF FAYETTE COUNTY, OHIO: PALIMPSEST MORAINES AND THE TIMING AND RETREAT OF THE SCIOTO SUBLOBE

Fayette County, Ohio, contains a host of unique geologic features. In 2022, the Quaternary geology of the county was mapped through the interpretation of a LiDAR-based digital elevation model, field observations, and two 15.5-meter-deep boreholes. Much of the county is characterized by low, hummocky ground moraine with several broad recessional moraines formed by the Scioto Sublobe. Notable moraines in the county include the Reesville, Glendon, Jeffersonville, Jonesboro (formerly known as the “Esboro”), and Bloomingburg moraines. The Scioto Sublobe reached its terminal position approximately 27,000 years ago at the Cuba Moraine, southwest of the county. After construction of the Cuba Moraine, ice began to retreat northward leaving a series of moraines the loess-capped, dark-gray Caesar Till. After this short period of retreat, a second advance of the Scioto Sublobe occurred and covered most of Fayette County; but it stalled ten miles short of the Cuba Moraine, where it constructed the Reesville Moraine and deposited the associated dark-gray Darby Till. The Darby Till is notably different from the Caesar because of its lack of a loess cap. This readvance and subsequent retreat from the Reesville Moraine did not destroy the pre-existing moraines that formed during retreat from the Cuba Moraine. Instead, Darby Till was draped over the existing landscape, preserving the imprint of palimpsest features. Evidence of palimpsest geomorphology within Fayette County includes the overtopping of the Glendon Moraine by the Jeffersonville Moraine, the uncoupling of the Bloomingburg Moraine from the Marcy Moraine, and the crosscutting of the Jonesboro Moraine by the Washington Esker. An OSL age of 23.5 ± 2.2 ka was collected on a small fan at the mouth of the Washington Esker and provides a maximum age for the Reesville Advance. Although no obvious contact between the Caesar Till and the Darby Till was found during coring of two boreholes, plant material collected from a depth of 13.8 m (45.3 ft) within the Jonesboro Moraine has a radiocarbon age of 18,600 ± 150 ¹⁴C (BP; 22,604 ± 323 cal. years) further corroborating the timing of the Reesville Advance. Additional OSL ages from an outwash fan on the Bloomingburg Moraine (23.8 ± 2.8 ka) and outwash terrace along Paint Creek (25.4 ± 2.1 ka) reinforce this age signal.