Shark River Formation

Shark River Formation - Consists of three lithofacies, a basal clayey, greenish-gray glauconite sand; a middle dark-green to gray-green silty clay or clayey silt; and an upper medium-gray to gray-green, silty quartz sand. Updip beds are cyclic with a fine- to medium-grained, somewhat clayey, fossiliferous, dark-green, glauconite-quartz (25 percent) sand at the base. The basal lithofacies is about 12 m (39 ft) thick in the southern sheet and 3 m (10 ft) thick in the central sheet. There is a general increase in quartz sand upward and a change in color to dark gray or brownish gray. Locally, some of the beds are more clayey and have more calcareous shell fragments. The middle clay and silt facies is typically the thickest lithofacies in most Shark River sections (as much as 38 m (125 ft) thick) and is massive to thick bedded. The thick-bedded parts typically consist of intercalated silty and clayey beds that are extensively bioturbated. Macro- and microfossils are abundant in this facies. Most of the macrofossils are thin-walled pelecypods. This facies is gradational into the upper quartz-sand facies. The quartz sand is well developed in the Toms River Chemical Plant drillhole, Toms River, Ocean County (sheet 1). This facies apparently was beveled off in the updip areas during erosion prior to deposition of the Kirkwood Formation. The Shark River Formation in the updip area near Bridgeton, Cumberland County (sheet 2), is about 52 m (171 ft) thick. All of the Shark River lithologies in the downdip area are extensively bioturbated. The Shark River is thickest (more than 60 m (197 ft)) in a trough that lies near the middle of the southern sheet. The contact between the Shark River and the underlying Manasquan Formation is sharp and contains a thin zone of reworked glauconite sand, granules of quartz, and phosphatic debris. On most gamma-ray logs through this contact, there is a sharp gamma high reflecting the concentration of phosphatic sediment. The vertical arrangement of facies in this formation is from a transgressive (mostly clay) facies at the base to a regressive (mostly sand) facies at the top. Calcareous nannofossils and foraminifera were used to date this unit. Where the unit is thickest, the nannofossils range from the upper part of Zone NP 14 (Rhabdosphaera inflata) to the lower part of Zone NP 18 (Chiasmolithus oamaruensis). The entire sequence of Zones NP 14 through NP 18 was observed only in the ACGS-4 corehole near Mays Landing. The planktic foraminifera zones range from the Turborotalia frontosa Zone at the base to the Turborotalia pomeroli/Turborotalia cerroazulensis Zone at the top. A middle to early late Eocene age for the Shark River is indicated by these zones (Poore and Bybell, 1988).