CONODONTS FROM THE MARCELLUS SHALE INTERVAL IN THE CENTRAL APPALACHIANS

New conodont investigations in the Middle Devonian in northwestern Virginia and eastern West Virginia show that conodonts should allow refinements and/or constraints in the biostratigraphy of this complex sedimentological interval. The succession above the Oriskany Sandstone upward to the Tully Limestone (or its equivalents) in this area comprises a complex of sandstones, siltstones, gray to black shales and mudstones, and minor silty and muddy carbonate rocks. The lithostratigraphic units are difficult to correlate regionally because of significant lateral facies changes over short distances, the small number of well-exposed surface sections, and sparseness of index fossils. Large (5 to 10 kg) samples of some of the carbonates within the Needmore, Millboro, Mahantango, and Marcellus Formations have yielded small numbers of conodont elements; however, some of the contained species allow us to make some preliminary interpretations of biofacies and age. Within the Millboro/Marcellus interval in the study area, species of Icriodus are present in the eastern sections, but are rare to absent in the western ones, where species of Polygnathus dominate. Species of the P. linguiformis group are the most common of the polygnathids throughout the study area, but species of the P. pseudofoliatus group have been found as well. Importantly, within the latter are members of the P. hemiansatus lineage, indicating that the Eifelian/Givetian boundary is contained within this succession in this area, although more work is necessary before confident placement of this boundary can be accomplished.