MAPPING BEDROCK TOPOGRAPHY AND QUATERNARY GEOLOGY IN MADISON COUNTY, OHIO

New bedrock topography and Quaternary geology maps of Madison County, Ohio depict our updated understanding of the bedrock surface and glacial history. The buried bedrock surface in the county contains the deeply incised valley formed by the Teays River that once flowed northwestward through Ohio but was dammed during a pre-Illinoian glaciation. Subsequent glaciations buried the valley, leaving no evidence of the ancient river on the land surface in the county. The valley’s location is uncertain because of sparse control on the depth to bedrock. Wisconsinan glacial materials make up most of the county’s surficial deposits. The ground surface is dominantly low-relief till plains containing mostly ground moraines, end moraines, and outwash that represent the complex ice movement of the Scioto Sublobe.

These maps detail the buried Teays Valley and surficial Quaternary features. The bedrock surface model was improved through Horizontal-to-Vertical Spectral Ratio (HVSR) geophysical surveys, resulting in over 600 stations. About 60 HVSR stations were used to create calibration equations to characterize shear wave velocities for various depths and geologic materials. HVSR data and borehole logs support a different Teays paleochannel location and morphology than previously interpreted. Additionally, the surficial geology was remapped by analyzing over 70 field observations, hand-auger holes, and outcrop descriptions. New geomorphologic interpretations were made from a 2.5-ft x 2.5-ft–resolution DEM. Several mapped moraines with a Caesar Till core likely were formed before 24k cal yr BP but became palimpsest upon being overridden by an ice advance around 22k cal yr BP. This readvance is determined from the deposition of Darby Till, which has different characteristics and composes younger recessional moraines. The timing of glacial events is supported by recent mapping elsewhere in the Scioto Sublobe. Future work will focus on remapping the Quaternary geology of the Scioto and Miami Sublobes in Ohio, and refining bedrock topography datasets that contain the Teays Valley system. Results from these USGS Great Lakes Geologic Mapping Coalition funded projects identify groundwater supplies, improve infrastructure projects, and develop the region’s glacial and preglacial history.