Core drilling in poorly exposed Lower and Middle Pennsylvanian strata of the Pottsville and Allegheny Groups in northeastern Ohio has led to a better understanding of the character and distribution of key Pennsylvanian marine units. Two unknown and three previously known marine and marine-influenced units are identified in strata of this area in the Pottsville Group. Distribution and facies maps of these marine units in northeastern Ohio suggest pre-Pennsylvanian erosional paleotopography and periodic movement on subsurface faults locally influenced depositional patterns. Additionally, the traditional placements of the Lowellville marine unit and the Quakertown coal in the stratigraphic column for Ohio appear to be in error. The new data suggest the need for an extensive revision of the geologic column for the Lower and Middle Pennsylvanian rocks in Ohio and the need to develop a more representative stratigraphic nomenclature and framework for these rocks. Core drilling referenced in this investigation was done as part of the recent statewide mapping and core-drilling program conducted by the Ohio Geological Survey.