23. GLOBAL SIGNIFICANCE OF AN ISOTOPIC RECORD FROM THE NEW JERSEY COASTAL PLAIN: LINKAGE BETWEEN THE SHELF AND DEEP SEA IN THE LATE PALEOCENE TO EARLY EOCENE1Dorothy Pak,2,3 Kenneth Miller,2,4 and James Browning4 |
ABSTRACTStratigraphic correlation between shallow-water and deep-sea sections has proven notoriously difficult because of hiatuses, diachrony of marker species, and diagenesis on the shelf. Isotope stratigraphy, biostratigraphy, and magnetostratigraphy reveal that sedimentation on the New Jersey Margin (Island Beach borehole) was relatively continuous during the late Paleocene and early Eocene (~58-52.5 Ma). All planktonic foraminiferal and calcareous nannofossil zones are represented at Island Beach. However, two disconformities are recognized in the upper Paleocene to lower Eocene section: a physical surface (lithologic change) at the Vincentown/Manasquan contact (uppermost Paleocene), which has a hiatus of ~0.3 m.y., and a ~0.4-m.y. gap associated with a paraconformity in the lower Eocene section. Stable isotopic data from the New Jersey Margin indicate that this neritic section can be successfully correlated to the deep sea using delta13C and delta18O of benthic foraminiferal calcite. Comparison between the Island Beach and global isotopic records (as represented by deep Pacific Site 577) shows that Island Beach parallels the global trend in both delta18O and delta13C. All major features of the late Paleocene to early Eocene global isotopic record are preserved, including general delta18O decrease, step-like delta13C decrease, and the well-known latest Paleocene delta13C excursion. We recognize three 1- to 1.5-m.y. delta13C steps over our interval of study at both Island Beach and the deep Pacific (~56.6-55.8 Ma; ~55.5-54 Ma; ~53.6-52.6 Ma). These steps are correlative with intervals of increased paleodepth, as indicated by benthic foraminiferal biofacies studies, and decreased delta18O values. We suggest a link between increased temperature and sea level, and reduced organic carbon burial in the deep sea. Previous workers identified a latest Paleocene benthic foraminiferal faunal change on the New Jersey Margin (Clayton borehole). They suggested that this faunal turnover was the neritic correlative of the well-known latest Paleocene benthic extinction event. Our data indicate that at Island Beach, uppermost Paleocene delta13C and delta18O excursions occur above the disconformity and the associated shallow-water benthic foraminiferal faunal change. This isotopic excursion may be synchronous with the deep-sea extinction event or with a younger delta13C decrease. We suggest that the benthic foraminiferal event on the New Jersey Margin was the result of a dramatic water-depth increase on the shelf and was unrelated to the deep-sea extinction. |
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