THE MIDDLE DEVONIAN (GIVETIAN) AMMONOID PHARCICERAS FROM THE NEW ALBANY SHALE, KENTUCKY

PHARCICERAS Hyatt, 1884 is the diagnostic ammonoid of the late middle Givetian Stage of the Middle Devonian Series. It occurs in the Rhenish Massif in Germany, the Montagne Noire in southern France, and in equivalent strata in the Anti-Atlas in southern Morocco. Verified North American occurrences of Pharciceras are confined to the New York succession, where the appearance of the ancestral species P. amplexum (Hall, 1886) in the Upper Tully Limestone represents an important and well-established biostratigraphic datum within the Taghanic onlap interval (see Aboussalam and Becker, 2001 for discussion). In this note we describe a second, distinctly younger, North American species, Pharciceras barnetti n. sp., from the New Albany Shale in east-central Kentucky that provides new evidence on the Taghanic onlap interval (Upper Tully/Geneseo Sequence of Baird and Brett, 2003) in the central Appalachian Basin. This occurrence is particularly significant because of its association with conodonts that provide a basis for refined correlations between the central Appalachian Basin and the Taghanic onlap succession in New York. Representatives of Pharciceras barnetti n. sp. were recovered from the Trousdale Member of the New Albany Shale at the J. K. Smith Power Plant, 3.7 km (2.3 mi) west of Trapp, Clark County, Kentucky. Here, the Trousdale sequence consists of 2.4 m of massive, platy black shale that disconformably overlies thinly interbedded argillaceous dololutites and black dolomitic shales of the Portwood Member of the New Albany Shale and is unconformably overlain by interbedded black and greenish gray shales of the Camp Run Member of the New Albany Shale (see Brett et al., 2004 for a sequence stratigraphic analysis of the Portwood and Trousdale members in central Kentucky). Ammonoids occur singly and in thin, 1–3 cm thick, pyritic chert lenses in the lower half of the Trousdale, 1.4–1.9 m above the top …