A LITHOSTRATIGRAPHIC, BIOSTRATIGRAPHIC, AND PETROGRAPHIC ANALYSIS OF THE MIDDLE AND UPPER ORDOVICIAN STRATA IN GAP MILLS, WEST VIRGINIA TO BETTER UNDERSTAND THE STRATIGRAPHY AND NOMENCLATURE IN A STRUCTURALLY COMPLEX REGION

The Middle and Upper Ordovician stratigraphic framework in the region where the central and southern Appalachians meet is complex, and the resulting nomenclature has created confusion for over a century. A better understanding of the depositional environments and facies changes in this mostly carbonate rock sequence is leading to a more precisely defined local and regional lithostratigraphic framework. This presentation focuses on the Hanging Rock section, located in the Gap Mills 7.5 minute quadrangle of Monroe County, West Virginia, which is being mapped as part of a county-wide bedrock mapping effort. Detailed measurements of the Hanging Rock and other sections have been made throughout this region by previous workers including H.P. Woodward and G.M. Kay, and those measurements and descriptions are compared with our work at the Hanging Rock section. Our decimeter-scale measurements and lithologic descriptions through >400 m of section in 2018-2019, with samples being collected from zones of major lithologic change, and at formational contacts. These samples have facilitated detailed petrographic characterization of framework grains, matrix, cement, and porosity, characterization of microfacies, and for processing for conodonts. The recovery of conodont elements has allowed for detailed conodont biostratigraphy of the Hanging Rock section for the first time, thus aiding in correlation of various microfacies and formational contacts throughout the region both along and across strike. A comparison of measured sections shows that issues of nomenclature which predate the North American Stratigraphic Code have persisted into the present time. Our work at the Hanging Rock section includes a multi-faceted analysis of the best exposed stratigraphic section of Middle and Upper Ordovician carbonates, and it provides a model for use going forward that can be applied to efforts involving the reconciliation of stratigraphic and nomenclature issues throughout this and other areas of the Valley and Ridge province.