BEDROCK TOPOGRAPHY OF THE FOUR-MILE CREEK BURIED VALLEY NEAR OXFORD, OHIO: IMPLICATIONS FOR GROUNDWATER RESOURCES AND LATE WISCONSINAN LANDSCAPE EVOLUTION

In a collaboration between Miami University and the Ohio Department of Natural Resources (ODNR), Division of Ohio Geological Survey, a detailed study has been conducted in order to delineate the bedrock topography of the Four-Mile Creek valley near Oxford, Ohio. This area of southwestern Ohio was last glaciated ~20,000 years ago by the southern portion of the Miami sub-lobe of the Laurentide Ice sheet. Glacial till, outwash, and lacustrine deposits overlie Ordovician bedrock, which consists primarily of interbedded limestone and shale.

Data used to define the bedrock-topographic surface was collected from local water-well drilling records from the ODNR and City of Oxford, and borehole logs from the Ohio Department of Transportation and Miami University. The study also incorporated field mapping of exposures of the Quaternary-Paleozoic contact as well as horizontal-to-vertical spectral ratio (HVSR) passive seismic analysis. HVSR data were calibrated at recording stations adjacent to wells with bedrock penetrations. Calibrated wells were used to calculate a power-law relationship that relates recorded primary shear-wave resonance frequency with depth and applied to localities from both filled-valley and glaciated-upland localities.

Study results generated over 180 individual elevation points of the Quaternary-Paleozoic contact within the study area. The resulting bedrock topography contour map indicates valley-fill deposits are ~50 feet thicker than previously mapped. As these deposits serve as on the primary municipal aquifer in the study area, these findings may have important implications for the future development and utilization of local groundwater resources. In addition, the study identified a narrow and now deeply buried (~300 ft) valley segment in the southeastern part of the study area that was likely abandoned following the penultimate late Wisconsinan glacial advance. The subsequent diversion of the Four-Mile Creek drainage resulted in the erosion of an ~100 ft deep incised meander belt cut into Quaternary/Paleozoic deposits outside the pre-existing valley margin. Potential ponding of the drainage prior to downcutting may have contributed to deposition of relatively extensive lacustrine valley-fill deposits identified upstream of the diversion.