CONODONT-BASED CORRELATION OF LOWER CONEMAUGH MARINE UNITS (LATE PENNSYLVANIAN) IN NORTHERN APPALACHIAN BASIN

Most Pennsylvanian marine units in the Appalachian Basin were named during early stratigraphic focus on identification and distribution of mineable coal beds. Although the state geological surveys introduced local names for these units in their states, they used some names from adjacent states for which correlation was accepted, based on lithology and general position. This led to stratigraphic successions for adjacent states that include a combination of local and more basin-wide names that implied direct correlation. Marine units in the lower Conemaugh Group of the northern Appalachian Basin contain conodont faunas that are similar to those described from the more marine succession in central US. Updated descriptions of these Appalachian faunas now allow direct correlation of these Appalachian marine units with the major marine cyclothems in the Midcontinent and Illinois basins. These faunas also clarify the correlation of named units among the states of the northern Appalachian Basin, and thus correct a long-standing miscorrelation of the Pine Creek Limestone of Pennsylvania with the Cambridge Limestone of Ohio. At the base of the succession, the Brush Creek Limestone of Pennsylvania contains a distinctive conodont fauna characterized by Idiognathodus cancellosus and related endemic forms that indicate its correlation with only the Lower Brush Creek Limestone of Ohio. The overlying Pine Creek Limestone contains a distinctive conodont fauna characterized by Idiognathodus confragus and related endemic forms that indicate its correlation with the Upper Brush Creek Limestone of Ohio. In contrast, the Cambridge Limestone of Ohio contains a younger fauna dominated by Streptognathodus excelsus and related species that allow its correlation with the Nadine Limestone of Pennsylvania. Both the overlying Portersville Shale of Ohio and the overlying Woods Run Limestone of Pennsylvania also contain a similar fauna dominated by these species of Streptognathodus, and they are correlated by their positions above the Cambridge and Nadine limestones respectively. Part of the reason why the Cambridge-Pine Creek miscorrelation stood for so long is that the Nadine is so lenticular over much of Pennsylvania that it typically was not intersected in cores, hence was easily overlooked in subsurface studies.