SUBSURFACE DISTRIBUTION OF PALEOCENE TO EOCENE LITHOSTRATIGRAPHIC AND SEQUENCE STRATIGRAPHIC UNITS AND BENTHIC FORAMINIFERAL BIOFACIES OF THE NEW JERSEY COASTAL PLAIN

Deposition and accommodation on the New Jersey coastal plain (NJCP), a passive continental margin, was dominated over the last 100 million years by changes in global mean sea level and thermal, flexural, and compaction subsidence, modulated by changes in mantle dynamic topography (MDT). The New Jersey margin was a ramp setting in the Paleocene through early Eocene but transitioned to a margin dominated by prograding clinothems in the Middle to Upper Eocene. Paleocene to Middle Eocene sequences are generally thin and widespread, and they thicken regularly with distance from the beach, except for the Marlboro Clay (deposited during the Paleocene-Eocene thermal maximum) that has no basal unconformity and was deposited in prograding lobes. Upper Eocene sediments were deposited in four sequences containing three different facies: a coarse clastic facies (nearshore), a muddy quartz sand and glauconite facies (inner to middle shelf) and a deeper water clay facies (middle to outer shelf). The four sequences show distinct progradation through time. The shift from a ramp setting to one with prograding clinothems takes place at the end of the Middle Eocene.

We use benthic foraminiferal biofacies to interpret water depth changes. Foraminiferal biofacies indicate regularly deepening water depths from inner (<30 m) to outer neritic (100-200 m) environments, with deepest water depths in the Early Eocene (~150 m). Our foraminiferal paleodepths yield unusually high backstripped relative sea level estimates compared to δ¹⁸O-Mg/Ca based estimates. We considered the possibility that foraminiferal overestimates of Early Eocene water depth were incorrect, but we reject this hypothesis noting that Lower to Middle Eocene sediments in New Jersey (Manasquan and Shark River Formations) are relatively deeper water than coeval along-basin strata in Virginia (Nanjemoy Formation): they are finer grained, contain greater percentages of planktonic foraminifera, and have a distinctly different deeper water fauna. We attribute ~50-75 m of additional Early Eocene sea level recorded by the NJ margin backstripping studies to contributions from MDT effects.