Paper No. 4
Presentation Time: 2:20 PM
CEPHALOPODS FROM THE CRETACEOUS/TERTIARY BOUNDARY INTERVAL IN THE MANASQUAN RIVER BASIN, MONMOUTH COUNTY, NEW JERSEY
Geological investigations in the upper Manasquan River Basin, central Monmouth County, New Jersey, reveal a Cretaceous/Tertiary succession consisting of approximately 2 m of the Tinton Formation overlain by 2 m of the Hornerstown Formation. The top of the Tinton Formation consists of a very fossiliferous unit (the Pinna Layer), which is truncated at the top by an unconformity and overlain by the Hornerstown Formation. The base of the Hornerstown Formation is marked by a concentration of siderite nodules containing reworked fossils. The Pinna Layer contains approximately 110 species consisting of bivalves, gastropods, cephalopods, echinoids, sponges, annelids, crustaceans, and dinoflagellates. The ammonites and dinoflagellates are indicative of the uppermost Maastrichtian, corresponding to the upper part of calcareous nannofossil Subzone CC26b. The mode of occurrence of the fossils in the Pinna Layer suggests an autochthonous accumulation with little or no post-mortem transport. Specimens of Pinna laqueata Conrad are in life position and monospecific clusters of echinoids, oysters, baculites, and scaphites are common. Scaphite jaws are also present, which represent the first reports of these structures in the Upper Cretaceous of the Atlantic Coastal Plain. Iridium analyses reveal an elevated concentration of iridium at the base of the Pinna Layer. If this enriched concentration of iridium marks the bolide impact, it implies that the Pinna community was living at the moment of impact and may even have persisted for some time afterward. The community was buried by a rapid pulse of sedimentation, probably related to enhanced riverine discharge following the impact. Subsequently, the sea floor experienced an extended period of erosion and reworking, probably associated with a transgression in the early Danian, producing a concentrated lag of siderite nodules in the basal part of the Hornerstown Formation. This lag deposit is equivalent to the Main Fossiliferous Layer elsewhere in New Jersey. The marine community in the early Danian was greatly reduced in diversity, with most of the Cretaceous species missing.