SUBSURFACE FACIES ANALYSIS OF THE MISSISSIPPIAN BEREA SANDSTONE IN SOUTHEASTERN OHIO

The Mississippian Berea Sandstone is an internally complex heterogeneous unit that appears prominently both in outcrop and subsurface in Ohio. While the unit is clearly deltaic in outcrops in northeastern Ohio, its depositional setting is more problematic in southeastern Ohio where it is only in subsurface. The goal of this project is to assess alternative interpretations (i.e. distal delta front versus barrier/inlet channel) of the Berea Sandstone in southeastern Ohio. This project involved looking at cores and geophysical logs from five wells and geophysical logs from ten additional wells. Core descriptions involved hand specimen and thin section descriptions and core photography to enhance microstructures. The Berea Sandstone mostly consists of fine- grained quartz sandstone. A total of 17 different lithofacies were identified from the five cores analyzed indicating a dynamic depositional environment. Strong evidence for tidal processes is seen from prominent tidal rhythmites that include wavy, flaser, and lenticular bedding. Evidence for shallow-water wave processes include trough cross-bedding, planar tabular cross-bedding, wave ripples, and intraclasts. Planar laminated mudstones indicate evidence for mud flats. Evidence for rapid sedimentation includes massive sandstones without bioturbation, massive coarse gravel lithofacies, the rarity of fossils and trace fossils, soft-sediment deformation, and climbing ripple lamination. Evidence for a prograding shoreline includes basal lithology changes from sandstone to siltstone and mudstone. In southeastern Ohio, the Berea Sandstone is consistent with shallow shelf and nearshore environments.