Abstract:
Three recently drilled boreholes at Island Beach, Atlantic City, and Cape May, New Jersey, recovered over 650 feet of Oligocene sediments. This allows an evaluation of the New Jersey Oligocene and its correlation to the global curve of Haq et al. (1987) and the delta (super 18) O proxy of glacioeustasy. Oligocene strata of New Jersey can be divided into sequences bounded by unconformities. Sequence boundaries were identified and dated by an integrated approach using changes in lithology, Sr-isotopic stratigraphy, biostratigraphy, magnetostratigraphy, and variations in benthic foraminiferal biofacies. Oligocene sequences consist of basal transgressive glauconite sands, medial glauconitic silts, and upper glauconitic quartz sands. Glauconite formed in situ during the transgressions, but was recycled during the regressions, masking the sequence stratigraphic succession. Paleodepths ranged from inner to outer neritic, as indicated by benthic biofacies and lithologic indicators. Oxygen isotope increases are associated with ice volume increases and eustatic lowerings during the Oligocene. A composite of the three boreholes shows excellent agreement with the delta (super 18) O record, with hiatuses associated with the delta (super 18) O increases and resumption of deposition associated with bases (= peak values) of the oxygen isotopic zones (Oi1, 35.8 Ma; Oi2, 32.2 Ma; Oi2b, 28 Ma; Mi1, 23.6 Ma; time scale of Berggren et al. (1985), BKF85). Smaller delta (super 18) O increases observed at 34.0 Ma, approximately 30.0 Ma, and at 26.0 Ma are correlated to unconformities observed in the N. J. Oligocene; implying that the unconformities are eustatically controlled and that the delta (super 18) O increases are due primarily to ice volume increases. The hiatuses also coincide with eustatic fails shown on the Haq et al.'s record for the Oligocene. By correlating these sections with the delta (super 18) O record and the Haq et al. (1987) eustatic curve, the stratigraphy of the N.J. Oligocene is interpreted to be controlled by eustatic changes. However, presence of a well-developed "middle" Oligocene sequence at Atlantic City and its absence at Cape May and at Island Beach indicate local tectonic changes.