Subsurface Facies Analysis of the Devonian Berea Sandstone in Southeastern Ohio

James Evans, AdvisorThe Devonian 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 found in the subsurface. The goal of this project was to search for evidence of a barrier island/inlet channel depositional environment for the Berea Sandstone to assess whether the Berea Sandstone was deposited under conditions in southeastern Ohio unique from northeastern Ohio. This project involved looking at cores from 5 wells: 3426 (Athens Co.), 3425 (Meigs Co.), 3253 (Athens Co.), 3252 (Athens Co.), and 3251 (Athens Co.) In cores, the Berea Sandstone ranges from 2 to 10 m (8-32 ft) thick, with an average thickness of 6.3 m (20.7 ft). Core descriptions involved hand specimens, thin section descriptions, and core photography. In addition to these 5 wells, the gamma ray logs from 13 wells were used to interpret the architecture and lithologies of the Berea Sandstone in Athens Co. and Meigs Co. as well as surrounding Vinton, Washington, and Morgan counties. Analysis from this study shows evidence of deltaic lobe progradation, abandonment, and re-working. Evidence of interdistributary bays with shallow sub-tidal environments, as well as large sand bodies, is also present. A prominent sequence of climbing ripples = 6 cm give evidence for distributary mouth bars. Frequently appearing massive bedding, sparse bioturbation, and a sequence of massive bedding to planar lamination overlying convoluted bedding provides evidence that high sedimentation rates were common during the deposition of the Berea Sandstone. Turbulent debris flows are interpreted based on the presence of a 10 cm incomplete turbidite lithofacies assemblage. Tidal processes can be inferred from tidal rhythmite sequences approximately 5 m thick, and clear storm activity is apparent from the presence of a 16 cm tempestite lithofacies assemblage. Geophysical log analysis allowed for the interpretation of the subsurface architecture of the formation. Combined, these features provide strong evidence for the interpretation that, in southeastern Ohio, the Berea Sandstone was deposited in a tidally-influenced, deltaic environment.