Fig. 8 in Cephalopods from the Cretaceous/Tertiary Boundary Interval on the Atlantic Coastal Plain, with a Description of the Highest Ammonite Zones in North America. Part 1. Maryland and North Carolina

Fig. 8. Proposed ammonite zonation of the upper Maastrichtian on the Gulf and Atlantic Coastal Plain and the corresponding zones in the U.S. Western Interior. The base of each zone is defined by the lowest occurrence of the index ammonite. The ammonite zones are correlated with the established calcareous nannofossil zonation based on the biostratigraphic distribution of the dinoflagellates and nannofossils associated with the ammonites in Maryland and North Carolina. The D. minardi Zone has not yet been recognized in the Gulf Coastal Plain. Correlation with the ammonite zones in the Western Interior is based on the presence of Discoscaphites conradi and Isabelidinium cooksoniae.