Sr-isotopic age estimates were obtained from mollusk shells (~4-6 mg) at the Ocean View borehole (Table T1; Figs. F2, F3, F4, F5, F6, F8, F9). Shells and foraminiferal tests were cleaned ultrasonically and dissolved in 1.5-N HCl. Sr was separated using standard ion-exchange techniques (Hart and Brooks, 1974) and analyzed on a VG Sector mass spectrometer at Rutgers University. Internal precision on the Sector for the data set averaged 0.000007; external precision is approximately ±0.000020 (Oslick et al., 1994). National Bureau of Standards Reference Material 987 is measured routinely at Rutgers at 0.710255 normalized to 88Sr/86Sr of 0.1194 (Oslick et al., 1994). Sr-isotopic ages were assigned using the Cande and Kent (1992) time scale (Table T5) using the early Miocene and middle Miocene regressions of Oslick et al. (1994) with age errors of ±0.61 and ±1.17 m.y. at the 95% confidence interval for one analysis, respectively. The Oligocene-Miocene portion of the Cande and Kent (1992) scale is identical to the Berggren et al. (1995) time scale, which is used to assign calcareous and planktonic foraminiferal ages. The regressions of Martin et al. (1999) were also computed for the middle to late Miocene. A significant age discrepancy exists between ages derived using the regressions of Oslick et al. (1994) vs. Martin et al. (1999) that must be resolved in future work.
The Miocene section drilled at Ocean View contained more shells than previous Leg 150X and 174AX boreholes, thereby allowing a detailed Sr-isotope age chronology. No shells were found above 293 ft (89.33 m). Six shell beds between 293.3 and 327 ft (89.42 and 99.69 m) (Fig. F3) within the Kw-Cohansey sequence yielded ages ranging from 12.4 to 14.0 Ma (regression of Oslick et al., 1994) or 10.0 to 11.8 Ma (regression of Martin et al., 1999). The variable and stratigraphically inverted ages obtained for this sequence vs. the underlying sequence (Fig. F8) suggest reworking of older shell material upsection or diagenetic alternation or original Sr-isotopic ratios. As a result, the Sr-isotopic ages for this sequence do not reflect the true ages, though the youngest ages obtained (12.4 Ma using Oslick et al.  at 309.4 ft [94.31 m]) may provide a maximum age for the Kw-Cohansey sequence at Ocean View (i.e., at Cape May, the Kw-Cohansey sequence is dated as 12.1-11.5 Ma) (Miller et al., 1997).
Five Sr-isotope age estimates obtained between 335.8 and 397.12 ft (102.4 and 121.04 m) (Fig. F3) range from 12.4 to 14.1 Ma (regression of Oslick et al., 1994) or 10.1 to 12.3 Ma (regression of Martin et al., 1999) and show a more continuous age progression than the sequence above. These ages suggest correlation of the sequence between 327.1 and 410.05 ft (99.70 and 124.98m) with the Kw3 sequence of Sugarman et al. (1993, 1997) and Miller et al. (1997). A definitive age break of 1.8 m.y. occurs between the Kw3 sequence and the underlying sequence (Fig. F3).
The section from 427.1 to 460.65 ft (130.18 to 140.41 m) records ages of 15.6-16.0 Ma (Fig. F4). This correlates the sequence from 410.05 to 464.5 ft (124.98 to 141.58 m) to the Kw2b sequence of Sugarman et al. (1993, 1997) and Miller et al. (1997).
The Kw2a sequence (464.5-640.4 ft; 141.43-195.19 m) contains 18 Sr-isotopic age estimates from different shell-bearing horizons (Fig. F4). Sr-isotopic age estimates clearly separate Sequence Kw2a from Sequence Kw2b with a 16.0- to 16.9-Ma age break between 460.65 and 465.1 ft (140.41 and 141.76 m), although there is one younger age of 16.4 Ma at 475 ft (144.78 m) (Fig. F4).
A detailed lithostratigraphic and sequence stratigraphic analysis of the thick Kw2a sequence (see "Lithostratigraphy") allows subdivision of this thick sequence into three higher-order sequences (Fig. F4). The age differences among the three higher-order sequences, Kw2a3, Kw2a2, and Kw2a1, are distinguishable by Sr-isotopic age constraints, although hiatuses between the sequences are within the errors.
The Kw1b sequence (640.4-718.4 ft; 195.19-218.97 m) underlies the Kw2 sequence complex (Fig. F5). Seven Sr-isotopic age estimates obtained between 651.5 and 717.13 ft (198.58 and 218.58 m) range from 19.9 to 20.6 Ma. These ages correlate the sequence (640.4-718.4 ft; 195.19-218.97 m) with the Kw1b sequence of Sugarman et al. (1993) and Miller et al. (1997) and establish an ~2-m.y. age break separating it from the younger Kw2a sequences.
Nine different Sr-isotopic age estimates ranging from 19.6 to 21.3 Ma correlate the sequence from 718.4 to 891.65 ft (218.97 to 271.88 m) with the Kw1a sequence of Sugarman et al. (1993, 1997) and Miller et al. (1997) (Fig. F5). The best estimate for the ages of this sequence is 20.4 to either 20.5 or 21.5 Ma (Fig. F8).
Like Sequence Kw2a, Sequence Kw1a can be further subdivided into three higher-order sequences termed, youngest to oldest, Sequences Kw1a3, Kw1a2, and Kw1a1 (Fig. F5). Sr-isotopic age estimates have only been found from shell-bearing beds in Sequences Kw1a3 and Kw1a1; the thick sand beds of Sequence Kw1a2 have yet to yield any dateable material. Two different shell-bearing units (735.5 and 737.35 ft; 224.09 and 224.74 m) within the Kw1a3 sequence yielded ages from 20.3 to 20.6 Ma (Fig. F5) (an age of 19.6 Ma at 825.25 ft [252.54 m] is considered an outlier, as indicated by a duplicate age of 20.5 Ma at this level). Seven Sr-isotopic age estimates from within the Kw1a1 sequence (825.25-890 ft; 251.54-271.27 m) yielded ages between 20.4 and 21.3 Ma (Fig. F5).
The oldest Miocene sequence, Kw0, encountered along the New Jersey margin occurs at Ocean View between 891.65 and 895.55 ft (271.77 and 272.96 m) (Fig. F5). Four shells within this sequence yielded Sr-isotopic age estimates from 21.3 to 23.8 Ma (Fig. F5). Just beneath the Kw0 sequence boundary identified by lithostratigraphic data, a shell bed at 897 ft (273.41 m) gave an Sr-isotopic age estimate of 25.0 Ma (Fig. F5).
Sr-isotopic age estimates provided the chronostratigraphic framework for correlating the Oligocene strata at Ocean View to Oligocene sequences previously defined in New Jersey (Pekar et al., 1997a, 2000).
The Ocean View borehole contains an exceptional record of Oligocene stratigraphy. For example, Ocean View contains the thickest Oligocene section recovered in New Jersey (275.95 ft; 84.13 m) and the best representation of Oligocene sequences (only Sequence O4 is not definitively recognized at this site).