LATE CRETACEOUS SEQUENCES IN THE NEW JERSEY COASTAL PLAIN

Cretaceous cycles in the NJ Coastal Plain are sequences bounded by unconformities associated with baselevel lowerings. Continuous coring by the NJ Coastal Plain Drilling Project (ODP Legs 150X and 174A) recovered 8-9 Upper Cretaceous Cenomanian-Maastrichtian sequences at Bass River and Ancora that are thick, downdip equivalents of sequences observed discontinuously in outcrops and wells. Facies changes within Upper Cretaceous sequences are pronounced and generally follow a predictable pattern of basal glauconite shelf sands (TST), medial prodelta silts (lower HST), and upper quartz sands (upper HST). Though facies changes are distinct, benthic foraminiferal biofacies studies suggest minimal water depth variations within the 4 sequences examined; the other 4 are poorly fossiliferous. A relatively precise chronology was obtained for Ancora, providing the first independent means of verifying biostratigraphic correlations and resolving discrepancies. The Ancora borehole indicates minimal hiatuses (<<1 m.y.) associated with the basal Merchantville II/I, Englishtown, and Marshalltown sequence boundaries and long hiatuses (>1 m.y.) associated with other sequence boundaries. Several sequence boundaries correlate well with those of Haq et al. (1987), suggesting that they are global, though several do not agree between studies. We attribute minimal water depth variations within Late Cretaceous sequences to minimal sea-level variations (10-m scale), though sequence boundaries certainly reflect larger (10’s of m) lowerings. The basal Navesink sequence boundary (ca. 71.5) can be tied to a global oxygen isotopic increase interpreted as a glacioeustatic lowering. Santonian-Campanian sequence boundaries cannot be readily related to oxygen isotopic variations due to poor global records. Though difficult to ascribe Upper Cretaceous sequence boundaries to ice volume increases, we conclude that further study evaluating such links is warranted.