18O
records.The Ocean View Site (September and October 1999) was the sixth continuously cored borehole drilled as part of the New Jersey Coastal Plain Drilling Project and the third site drilled as part of Ocean Drilling Program (ODP) Leg 174AX, complementing shelf drilling during Leg 174A. Located between the Leg 150X Atlantic City and Cape May Sites, drilling at Ocean View (39°10´43.826''N, 74°43´31.643''W; elevation = 9.4 ft [2.87 m]; Sea Isle City, United States Geological Survey [USGS] 7.5-min quadrangle; Dennis Township, Cape May County, New Jersey) targeted upper Miocene through middle Eocene sequences. Recovery was very good (mean recovery = 81%), ending at a total depth (TD) of 1575 ft (480.06 m) in lowermost middle Eocene sediments. A full suite of slimline logs was obtained to 1123 ft (342.29 m), and a gamma-ray log was obtained to 1560 ft (475.49 m). The scientific team provided descriptions of sedimentary textures, structures, colors, and fossil content and identified lithostratigraphic units, lithologic contacts, and sequences (unconformity-bounded units). Sr-isotopic analyses of the numerous shell beds found at Ocean View provide excellent age control, supplemented by biostratigraphic (planktonic foraminiferal, nannofossil, and dinocyst) studies.
The Cape May Formation (5-107.5 ft; 1.5-32.8 m; ?middle-late Pleistocene-Holocene) consists primarily of sands and subordinate gravels and clays that represent nearshore environments. Gravels (0-16.1 ft [0.00-4.91 m]) comprise the terrace that has been dated at Cape May as oxygen isotope Stage 5e. Below this (to 107.5 ft; 32.8 m), the Cape May Formation consists primarily of very fine to medium occasionally gravelly quartz sands, deposited in nearshore barrier complex environments. Sands assigned provisionally (107.5-166.7 ft; 32.8-50.81 m) and definitively (166.7-220.55 ft; 50.81-67.2 m) to the Cohansey Formation represent three or four sequences that either were not represented in previous New Jersey boreholes or were very poorly defined in estuarine sediments at Cape May. At Ocean View, these sands were deposited in nearshore and estuarine environments. Dinocysts indicate that they can be assigned to either Zone DN8 (upper middle Miocene) or DN6 (upper Miocene). These sequences should complement the fully marine upper middle to upper Miocene sequences sampled by the Leg 174AX Bethany Beach, Delaware, borehole.
The Kirkwood Formation (220.55-1002.8 ft; 67.22-305.65 m) at Ocean View is comprised of three middle Miocene (Kw/Co, Kw3, Kw2b) and four lower Miocene (Kw2a, Kw1b, Kw1a, and Kw0) sequences. Sequences Kw2c and Kw1c are not represented at Ocean View but are truncated between this site and Cape May. Sequences Kw2 and Kw1a are each provisionally subdivided into three higher-order sequences (Kw2a1, Kw2a2, and Kw2a3; Kw1a1, Kw1a2, and Kw1a3, respectively). The preservation of higher-order lower-middle Miocene sequences can be explained by higher sediment supply and accommodation space provided by loading; alternatively, the great thickness of the section is consistent with an autocyclical cause (lobe switching) for these apparent sequences. Analyses of nearshore seismic profiles recently collected near Ocean View should reveal if the higher-order cyclicity is due to base level lowering, and hence, if these are true sequences or due to autocyclical processes. Possible lowstand deposits are identified for the first time in the Kirkwood Formation in both Sequences Kw2a and Kw1a.
The Kirkwood sequences
have many more shell beds than were previously found at other onshore New Jersey
boreholes; these shells provided Sr-isotopic age estimates that are critical in
dating sequences, sequence boundaries, and their relationship to glacioeustasy.
The relatively complete lower to middle Miocene section at Ocean View will allow
(1) comparison with those to the north (Atlantic City and Island Beach) and to
the south (Cape May and Bethany Beach, Delaware, boreholes) to evaluate the
effects of regional tectonics on the preservation and architecture of sequences
and (2) evaluation of the stratigraphic response to eustasy estimated from both
backstripped and global 18O
records.
The thick Oligocene
section (895.55-1171.5 ft; 272.96-357.07 m) at Ocean View consists of six to
eight sequences. Numerous shell beds in the Oligocene section provide detailed
Sr-isotopic age estimates. Integration of Sr-isotopic ages with
lithostratigraphy suggests correlation with Sequences O6, O5, possibly O4, O3,
O2b, O2a, O1, and possibly ML of Pekar et al. (1997a), indicating that the Ocean
View borehole provides the most complete record of Oligocene deposition in New
Jersey. Further analysis of the Oligocene section will (1) test a model that
explains the patchy distribution of onshore Oligocene strata by clinoform
progradation, (2) develop a more detailed Oligocene eustatic estimate using
two-dimensional backstripping, and (3) evaluate the stratigraphic response to
eustasy estimated from both the backstripped and global 18O
records.
The upper Eocene section at Ocean View (1171.5-1434.4 ft; 357.07-437.21 m) is the thickest cored in New Jersey. At least two sequences were identified, correlating with Sequences E11 and E10 of Browning et al. (1997a), both of which are assigned to the Absecon Inlet Formation. This section is significant because it is quite fossiliferous, exhibits minimal diagenetic alteration, and was deposited in the deepest paleodepth of any upper Eocene section in New Jersey. This upper Eocene section provides an excellent opportunity to develop a stable isotopic stratigraphy and a eustatic record, allowing us to test a first-order link between glacio-eustatic change and unconformities for this interval. Whereas these goals have been achieved for the Oligocene and younger record, is it unclear if glacioeustasy, in fact, controlled the development of late Eocene sequences. The lithologic assignment of the upper Eocene section between 1374.4 and 1402.9 ft (418.92 and 427.60 m) is equivocal, though we provisionally identify it as the Absecon Inlet Formation and a newly recognized sequence, E10a. Intercalations of nannofossil Zones N19/N20 and NP18 in this sequence suggest reworking, possibly associated with the Chesapeake Bay impact event. However, the underlying sequence (1402.9-1434.4 ft; 427.60-437.21 m) contains upper Eocene nannofossils (Zone NP18) mixed with middle Eocene acarininids and is correlated with Sequence E9; this sequence elsewhere in New Jersey has been correlated with the impact event. Further evaluation of the regional and global correlations of this event in New Jersey are needed, especially considering that previous studies have failed to find the correlative microtektites in New Jersey that are predicted for this event.
We recovered a relatively complete middle Eocene section (1434.4-1575 ft; 437.21-480.06 m) with the borehole TD in the lowermost middle Eocene. At least four sequences were recognized, and three were correlated with Sequences E8, E7, and E6 of Browning et al. (1997b). The middle Eocene section is significant because it was deposited further downdip than any previously cored middle Eocene section in New Jersey, providing a record of the full range of water depth variations for this interval. The section from 1521 ft (463.60 m) and below contains an interesting mix of lower Eocene planktonic foraminifers (Zones P6b/P7; Morozovella formosa, Morozovella gracilis, and various acarininids) and middle Eocene nannofossils (Zone NP15) and planktonic foraminifers (Zone P10 or younger). Such pervasive reworking is generally uncommon in New Jersey Coastal Plain subsurface boreholes and may point to a slumping event. Although much of the section below 1480 ft (451.10 m) suffers from silica diagenesis that may preclude stable isotopic studies, the section above appears to be suitable for isotopic studies that will evaluate the link between glacio-eustatic change and sequences for the middle Eocene.
The Ocean View borehole was a tremendous success in meeting scientific goals. We obtained the following:
