Sedimentology, Ichnology, and Paleoenvironments of the Upper Cretaceous Wenonah and Mt. Laurel Formations, New Jersey

ABSTRACT The Wenonah and Mt. Laurel Formations of the New Jersey Coastal Plain comprise a shallow subtidal, coarsening-upward, regressive sequence that accumulated along a wave-dominated coast in Late Cretaceous (Maestrichtian) time. The highly bioturbated, muddy, very fine to fine quartz sands of the Wenonah Formation were deposited mainly in the offshore zone of an inner shelf, below storm wave base. Distinctive trace fossils include Rosselia socialis and a planar form of Zoophycos. The Mt. Laurel Formation consists of two lithofacies. In the northern New Jersey Coastal Plain, the formation is characterized by burrowed, clean quartz sands that are thinly interbedded with muddy sand and mud. Characteristic trace fossils include Ophiomorpha nodosa, Rosselia socialis, two forms of Skolithos, and a delicate branching burrow. Deposition occurred mainly in the offshore-shoreface transition zone between fair weather and storm wave base. Storm deposits include burrowed sands displaying trough cross-stratification, hummocky cross-stratification, lenticular and wavy ripple-bedding, and parallel lamination. Fair weather deposits consist of thoroughly bioturbated, muddy sand and thin-bedded mud. At updip exposures, shoreface deposits include trough cross-strati ied, burrowed, fine to medium sands. Paleocurrents were bipolar, with a predominant northwest (onshore) mode. A massive sand lithofacies characterizes the Mt. Laurel Formation in the central and southern New Jersey Coastal Plain and is characterized by highly bioturbated, medium to coarse sand. Rare cross-stratification indicates a polymodal paleocurrent pattern with predominantly northwest transport. Distinctive trace fossils include Ophiomorpha nodosa and Skolithos linearis. This lithofacies accumulated mainly as shoals or bars in the transition and offshore zones of the inner shelf. A shoreface ebb tidal delta facies was locally developed. The Marshalltown, Wenonah, and Mt. Laurel Formations comprise a depositional sequence (in the sense of Haq et al. 1987) that accumulated during a third order, eustatic sea level cycle (UZA-4.4). The Wenonah-Mt. Laurel regression occurred during a sea level high-stand as sediments began to overflow estuaries created during the Marshalltown transgression. Subsequent falling sea level intensified the regression, and ultimately led to erosional truncation of the Mt. Laurel sediments. Then eustatic rise in sea level during the Late Maestrichtian (UZA-4.5) led to ravinement. During this ravinement event, a fossiliferous and pebbly, glauconitic quartz sand lithofacies was deposited as a transgressive lag in the transition and offshore zones of the inner shelf. These transgressive sheet sand ediments comprise the lower part of the Navesink Formation. The depositional model developed herein for the Wenonah-Mt. Laurel regressive interval integrates both sedimentologic and ichnologic data. This model is compared with the well-known Gallup and Blackhawk Cretaceous regressive sequences of the North American Western Interior. It should be applicable in the evaluation of other regressive sequences in Cretaceous strata of the U.S. Atlantic Coastal Plain and Western Interior, as well as epeiric sea cycles from other similar settings around the world.