Ammonites from the Saratoga Chalk (Upper Cretaceous), Arkansas

Abstract

The Saratoga Chalk of Arkansas yields a rich ammonite fauna of 17 species, referred to the Nostoceras (N.) hyatti zone. Recognition that the northwest European N. (N.) pozaryskii Blaszkiewicz, 1980, is a synonym of N. (N.) hyatti Stephenson, 1941, and N. (N.) helicinum (Shumard, 1861) dates the zone as latest Campanian on the basis of co-occurrence with Belemnitella langei Jeletzky, 1948, in Poland. Most previous estimates of the Campanian–Maastrichtian boundary in the Gulf Coast have been drawn at too low a level, at least in terms of ammonite faunas. Elements of the N. (N.) hyatti zone fauna occur in the United States Western Interior, and show the base of the Maastrichtian there to lie above the Baculites jenseni zone.