The Lower Silurian clastic rocks of the northeastern Ohio subsurface represent a deltaic sequence of complexly intertonguing sandstones and shales. These rock units overlie Ordovician shales throughout the area. The complexity of sandstone and shale facies resulted from migration of distributary channels during the constructive phase of deltaic progradation. At the close of delta growth, a transgressive pattern of lithofacies occurred, culminating in the deposition of a carbonate unit, the “Packer Shell” (Brassfield) which serves as an overlying distinct marker bed for correlation. The overall thickness of the interval between the base of the Packer Shell and the underlying Ordovician shales is nearly constant, allowing these shales to be used as a lower bounding surface for mapping the sedimentary package of “Clinton” sandstones and shales.
Depositional trend maps were constructed using conventional subsurface techniques and compiled using the SYMAP computer contouring program. The total sandstone lithosome of the Clinton and sandstone quality (based on gamma-ray log deflection) are shown on isopach maps of the Clinton. A total of more than 2,600 wells were used in the study of several counties in northeastern Ohio after conventional stratigraphic work was completed.
The trends show dominant sandstone depositional environments in the deltaic sequence which prograded westward on a low slope across eastern and central Ohio. Cross sections delineate the three-dimensional aspects of sand bodies and show the complexity of the facies changes between distributary and interdistributary deposits. The cross sections also show the effect of the interfingering nature of the Clinton reservoirs over small distances on petroleum production. In addition, they illustrate that the threefold subsurface division of the Clinton into the “Stray,” “Red,” and “White” is not locally reliable; instead the interfingering sand and shale lithosomes should be mapped in this interval.