A LATE CRETACEOUS FAUNAL ASSEMBLAGE AT RANCOCAS, NEW JERSEY: BIOSTRATIGRAPHIC IMPLICATIONS

The Navesink Formation outcrops throughout the New Jersey Costal Plain. It is characterized by a coarse, fossiliferous, glauconitic quartz sand at the base, which grades into a glauconitic mud and sand at the top of the sequence. This study focuses on outcrops exposed at three sites: the Rancocas River, Crosswicks Creek, and Atlantic Highlands, Monmouth County, New Jersey. The Rancocas site is new and contains a diverse fauna including Eubaculites sp.. At these localities, the basal Navesink Formation is represented as a transgressive, time-averaged lag deposit. It is possible that the Campanian-Maastrichtian boundary occurs within this lag. The lag deposit consists of faunal elements which can be grouped into various paleocommunities, each representing specific marine facies. This mixed assemblage includes species of Mytilus, Lithophaga and Spondylus as examples of a shoreline to shallow shelf, high energy environment; species of Exogyra, Pecten and Lima are part of a deep shelf, low energy environment. This may indicate a succession of paleo-communities. However, it is difficult to decipher the temporal succession within the lag deposit. The base of Navesink is time transgressive and is probably younger towards the southwest as indicated by the presence of Eubaculites sp. at the Rancocas site.