Cephalopods from the Cretaceous/Tertiary boundary interval on the Atlantic Coastal Plain, with a description of the highest ammonite zones in North America. Part 2, Northeastern Monmouth County, New Jersey

• Published in: Bulletin of the American Museum of Natural History p. 96
• Main Authors: Landman, Neil H, Johnson, Ralph O, Edwards, Lucy E
• Format: Journal Article
• Language: English
• Published: American Museum of Natural History 2004
• Subjects: Ammonoidea; Atlantic Coast (U.S.); Cephalopoda, Fossil; Cretaceous; Cretaceous-Paleogene boundary; Gulf Coast (U.S.); Mollusks, Fossil; Monmouth County; New Jersey; Paleontology; Stratigraphic correlation; United States
• ISSN: 1937-3546

The sedimentary deposits of the New Jersey Coastal Plain span the Cretaceous/Tertiary boundary and reveal a complex stratigraphy in the northeastern part of their outcrop belt. Newly discovered exposures of the New Egypt Formation in northeastern Monmouth County, New Jersey, indicate that a tongue of this formation, previously thought to be restricted in outcrop to southwestern Monmouth County, extends to the northeast. This formation is sandwiched between the Tinton Formation below and the Hornerstown Formation above. The upper contact is unconformable. Fossils occur in the upper part of the New Egypt Formation and the basal part of the Hornerstown Formation and are concentrated at the formational contact--this accumulation is known as the Main Fossiliferous Layer. The Discoscaphites minardi Assemblage Zone occurs in the New Egypt Formation approximately 2 m below the base of the Hornerstown Formation and contains Discoscaphites minardi Landman et al., 2004, Discoscaphites sp., Eubaculites carinatus (Morton, 1834), Eubaculites sp., and Eutrephoceras dekayi (Morton, 1834). Associated dinoflagellates include Deflandrea galatea (Lejeune-Carpentier, 1942) Lentin & Williams, 1973, and Thalassiphora pelagica (Eisenack, 1954) Eisenack & Gocht, 1960. The D. minardi Zone represents the middle part of the Upper Maastrichtian corresponding to the upper part of calcareous nannofossil Subzone CC26a and the lower part of Subzone CC26b. The Discoscaphites iris Assemblage Zone occurs at the top of the New Egypt Formation in an interval at least 20 cm thick and contains Discoscaphites iris (Conrad, 1858), Discoscaphites gulosus (Morton, 1834), D. minardi, Eubaculites latecarinatus (Brunnschweiler, 1966), E. carinatus, Sphenodiscus pleurisepta (Conrad, 1857), Sphenodiscus sp., and Eutrephoceras dekayi. Associated dinoflagellates include Palynodinium grallator Gocht, 1970, and T. pelagica. The D. iris Zone represents the uppermost Maastrichtian, corresponding to the upper part of calcareous nannofossil Zone CC26b. The basal beds of the Hornerstown Formation contain a mixed assemblage of Cretaceous and Paleocene fossils. Paleocene dinoflagellates include Carpatella cornuta Grigorovich, 1969, and Senoniasphaera inornata (Drugg, 1970) Stover & Evitt, 1978, and suggest that these beds correspond to planktonic foraminiferal zones PO-P[alpha]. There is no enrichment of iridium ([greater than or equal to]0.1 ppb) or layer of spherules at the formational contact but a dinoflagellate specimen with pockmarked damage consistent with melting is present in the top of the New Egypt Formation. The formational contact spans the Cretaceous/Tertiary boundary but probably contains a hiatus of approximately 100 k.y. All of the Cretaceous fossils in the Main Fossiliferous Layer are reworked from the upper New Egypt Formation and reflect a period of erosion and winnowing, perhaps related to changes in sea level as well as events associated with the bolide impact at the end of the Cretaceous. Subsequently and simultaneously, the sea floor experienced extensive bioturbation, which may have further reworked fossils. Elsewhere on the Gulf and Atlantic Coastal Plain, the D. iris Zone also occurs immediately below the K/T boundary and is truncated by an erosional unconformity, commonly with reworked material in the overlying beds. The geographic distribution of the D. iris Zone and cores spanning the K/T boundary on the Gulf and Atlantic Coastal Plains help approximate the coastline of North America at that time and indicate a broad Mississippi embayment. However, there is no firm evidence that the Western Interior Seaway persisted until the end of the Cretaceous.