Abstract:
Previous drilling in New Jersey at Island Beach, Atlantic City, and Cape May (ODP Leg 150X) provided ages of early-middle Miocene sequences, documenting that sequence boundaries onshore correlate with sequences on the NJ shelf-slope, Florida, and Bahamas. These comparisons indicate that Miocene sequences fulfill our first expectation of a global process such as eustasy: they correlate within the requisite resolution (0.5 m.y.) both regionally and interregionally. Correlation of the sequence boundaries with global oxygen isotopic increases suggests causal connection between early-middle Miocene glacioeustasy and margin erosion. Drilling at Ocean View, NJ (Fall 1999) targeted upper Miocene through middle Eocene sequences to verify ages and significance of several sequences that were sampled only at one previous borehole, to evaluate tectonic effects on sediments, and to test models of sequence progradation. At Ocean View, the chronology of lower Miocene sequences Kw0, Kw1a, Kw1b, Kw2a and middle Miocene sequence Kw2b are remarkably well validated by detailed Sr-isotopic stratigraphy. The Kw1a sequence (21.3-20.2 Ma) is unusually thick and well resolved at Ocean View (882-739 ft). This sequence can be split into 3 higher-order stratal packages that appear to be distinct sequences (Kw1a', 21.3-20.4 Ma, Kw1a', 20.4-20.3 Ma, and K1a", 20.3-20.2 Ma). Similarly, the Kw2a sequence (17.8-16.9 Ma) is unusually thick (636-465 ft) and can be split into a Kw2a' (17.8-17.2 ma) and Kw2a' (17.2-16.9 Ma) sequence. Both the Kw1c and Kw2c sequence are absent at Ocean View, but are present at Cape May due to greater downbasin accomodation and shifting sediment supply. A major drop in sea-level in the late middle Miocene progressively beveled off the upper middle Miocene Kw2b and Kw2c sequences updip from Cape May (e g., Kw2c is missing at Ocean View; Kw2b is missing at Island Beach). Ages and regional significance of upper middle to upper Miocene sequences (Kw3, Kw-Ch1, and ?Ch3-Ch6) are still poorly constrained due to uncertainties in Sr- age calibrations between 12 and 8 Ma, and lack of datable material. Drilling at Bethany Beach, Delaware (May-June 2000) should provide a clearer record of late middle to late Miocene sequences in this region.