STRATIGRAPHIC IMPLICATIONS OF THE DISTRIBUTION OF LATE CRETACEOUS AMMONITES ON THE NORTH ATLANTIC COASTAL PLAIN

Ammonites and lithology for thirty stratigraphic sections of Late Cretaceous age were analyzed from Atlantic Highlands in Northeastern New Jersey to the C&D Canal in Delaware. Six distinct facies were identified in the study section: 1) mottled to laminated, muddy very fine micaceous quartz sand; 2) Well sorted massive to crossbedded fine micaceous quartz sand; 3) Moderate to pebbly poorly sorted quartz sand (all included in the Wenonah Formation); 4) Glauconitic quartz sand (Mt Laurel Formation); and two facies of the Navesink Formation; 5) Pebbly glauconitic quartz sand at the base followed by 6) a glauconitic marl to sand above. Each facies was correlated paying particular attention to ammonite and exogyra occurrences within the sequence. Seven separate ammonite assemblages were constructed from occurrences throughout the Wenonah, Mount Laurel and Navesink Formations. Correlation with ammonite occurrences of the Western Interior and Gulf Coast yields information on temporal distribution of the facies. Most recent workers interpret the micaceous bedded sands and mud found in northeastern NJ as a facies change from the glauconitic quartz sand that represents the classic Mount Laurel Formation from Crosswicks Creek south to the C&D Canal in Delaware. However, the Mount Laurel is associated with the appearance of belemnites and E. cancellata along with ammonite assemblages including Didymoceras cheyennense and Didymoceras stevensoni which can be correlated to the Western Interior revealing a Late Campanian age. These faunal elements are not represented northeastern NJ. Instead the typical Wenonah Formation small bivalve fauna including the ammonites Placenticeras minor, Didymoceras binodosum and Baculites texanus (Middle Campanian) occur just below the Navesink Formation. This implies that the Mount Laurel was most likely not deposited or eroded away north of the Crosswicks basin. At Big Brook, near Marlboro NJ, sandy concretions occur in a basal lag in the Navesink Formation with Mount Laurel lithology. This possibly represents the remnants of the Mount Laurel Formation reworked during the transgression at the beginning of the Navesink Sequence.