Vincentown Formation

Vincentown Formation - Upper part, sand, glauconite (35-40 percent) and quartz (60-65 percent), fine- to very fine grained, very clayey and silty, massive, dark-gray, bioturbated, very micaceous. Lower part, sand, massive, less micaceous and clayey, dark-gray-green. The lower 4.5 m (15 ft) of the formation is a fine- to medium-grained, clayey glauconite sand. Locally, there is an accumulation of disarticulated calcareous shells along the contact with the underlying Hornerstown Formation. These shells are commonly the brachiopod Oleneothyris harlani or the mollusk Gryphaea dissimilaris. Where the shell bed is absent it is difficult to separate glauconite sand of the basal part of the Vincentown from the underlying Hornerstown Formation, which also is a glauconite sand. Gamma logs through this interval show that there is a small gamma spike along the contact between the glauconite sands. The grain size decreases and the formation is significantly more clayey downdip. At Allaire State Park, Monmouth County (drillhole Allaire-C), for example, the bulk of the Vincentown is a clayey, very micaceous, dark-gray, slightly feldspathic quartz sand. Large fossils, which are abundant in the near-surface beds, are absent. In addition, the basal glauconite beds tend to thicken somewhat downdip. Farther basinward, the bulk of the formation is an unfossiliferous, gray-green to locally tan clayey silt or silty clay. Locally, a thin- to thick-bedded glauconite sand occurs at the base. In the thickest downdip section penetrated at Island Beach, the Vincentown is mostly a pale-gray to dark-gray clay-silt. No megafossils were observed in the Island Beach core. On the basis of geophysical log interpretations in the deepest subsurface, this unit has a maximum thickness of about 38 m (125 ft). The age of the Vincentown is best indicated by calcareous nannofossils, which indicate Zones NP 5 to NP 9 (Bybell, 1992). Common nannofossils from Zone NP 5 are Chiasmolithus bidens, Ellipsolithus distichus, Fasciculithus tympaniformis, Scapholithus fossilis, and Toweius eminens. Common nannofossils in Zone NP 9 are Biantholithus astralis, Chiasmolithus bidens, Discoaster multiradiatus, D. salisburgensis, Fasciculithus involutus, F. schaubii, F. thomasii, and Lophodolithus nascens. The upper part of the Vincentown falls within the upper part of Zone NP 9 and therefore is late Paleocene (Selandian) in age.