THE LATE CAMPANIAN (UPPER CRETACEOUS) CEPHALOPOD FAUNA OF THE COON CREEK TONGUE OF THE RIPLEY FORMATION AT ITS TYPE LOCALITY

There is an unusually rich, Upper Campanian (Late Cretaceous), molluscan fauna in the Coon Creek Tongue of the Ripley Formation at its type locality, 7 1/2 miles north of Adamsville, McNairy County, Tennessee. The ammonite fauna is a typical, Late Campanian Gulf Coast fauna, consisting almost entirely of aberrant ammonites, and only one tightly coiled, planispiral form. A few authors have published on the cephalopod fauna from this locality, most notably Wade (1926), and Cobban and Kennedy (1994a). The ammonite fauna consists of Pachydiscus (Pachydiscus) arkansanus (Stephenson), Baculites claviformis Stephenson, B. undatus Stephenson, Lewyites oronensis (Lewy), Parasolenoceras pulcher Cobban and Kennedy, Solenoceras reesidei Stephenson, S. texanum (Shumard), Cirroceras conradi (Morton), Didymoceras sp., Nostoceras (Nostoceras) approximans (Conrad), N. (N.) helicinum (Shumard), N. (N.) hyatti Stephenson, Jeletzkytes reesidei (Wade), Hoploscaphites sp. and Discoscaphites sp. The only nautiloid is Eutrephoceras planoventer Stephenson. This is the first reported occurrence for Pachydiscus arkansanus, Hoploscaphites and Discoscaphites from the site, and the earliest known occurrence for Discoscaphites. Except for Discoscaphites the ammonite fauna from this locality compares both at a species level, and stratigraphically with the fauna from the Nacatoch Sand in Kaufman and Navarro Counties of Texas (Stephenson, 1941). Some of this ammonite fauna also correlates to the fauna from the Baculites compressus through Baculites jenseni Zones of the Pierre and Bearpaw Shales of the Western Interior (Cobban and Kennedy, 1994a). The presence of Cirroceras conradi, Jeletzkytes reesidei, Solenoceras reesidei, and S. texanum, more precisely puts the age of the Coon Creek Tongue at the type locality, at the equivalent age of the lower Baculites reesidei Range Zone of the Western Interior.