PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024 Number 3454, 64 pp., 22 ®gures, 2 tables August 23, 2004 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 NEIL H. LANDMAN,1 RALPH O. JOHNSON,2 AND LUCY E. EDWARDS3 ABSTRACT The sedimentary deposits on the Atlantic Coastal Plain in New Jersey, Delaware, Maryland, North Carolina, South Carolina, and Georgia span the Cretaceous/Tertiary boundary. We in- vestigate the ammonites of the Severn Formation on the western and eastern shore of Ches- apeake Bay, Maryland, and the Peedee Formation, North Carolina. We describe three am- monite assemblages from the Severn Formation and their associated dino¯agellates, de®ning three successive ammonite zones in the upper Maastrichtian. The lowest ammonite zone is the Discoscaphites conradi Assemblage Zone. It occurs near the top of the Severn Formation in Prince Georges County, Maryland, just below the Paleocene Brightseat Formation. The ammonite fauna consists of Sphenodiscus pleurisepta (Conrad, 1857), Sphenodiscus lobatus (Tuomey, 1856), Discoscaphites conradi (Morton, 1834), Discoscaphites gulosus (Morton, 1834), Jeletzkytes nebrascensis (Owen, 1852), Glyptoxoceras rugatum (Forbes, 1846), Bacu- lites vertebralis Lamarck, 1801, and Eubaculites latecarinatus (Brunnschweiler, 1966). Di- no¯agellates from a sample of matrix include Isabelidinium aff. I. cooksoniae (Alberti, 1959) Lentin & Williams, 1977, which correlates with calcareous nannofossil Zone CC25b, indicat- ing the lower part of the upper Maastrichtian (68.2±67.4 MaBP). The D. conradi Zone is also present in parts of the Corsicana Formation, Texas, the Prairie Bluff Chalk, Alabama and 1 Division of Paleontology (Invertebrates), American Museum of Natural History (
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