Sr isotopic age estimates were obtained from mollusk shells. Approximately 4–6 mg of shells was cleaned in an ultrasonic bath and HCl and then dissolved in 1.5 N HCl. Sr was separated using standard ion exchange techniques (Hart and Brooks, 1974). The samples were analyzed on an Isoprobe T Multicollector thermal ionization mass spectrometer (TIM). Internal precision on the Isoprobe for the data set averaged 0.000007, and the external precision is approximately on replicate analyses of standards). National Bureau of Standards (NBS) 987 is measured for these analysis at 0.710241 normalized to 86Sr/88Sr of 0.1194.
Carbonate shells were first encountered in the Double Trouble corehole at 461 ft (140.5 m). Two Sr isotopic ages were attempted at 461.0 and 467.8 ft (140.5 and 142.6 m). Strontium ratios for both of these samples (Table T6) indicate Eocene ages older than 37 Ma. More precise ages are not obtainable because of the low rate of change of Sr isotopes older that ~35 Ma.
Cretaceous ages were assigned (Table T6) using linear regressions developed for upper Coniacian through Maastrichtian sections by Miller et al. (2004). Using a similar late Campanian–Maastrichtian regression, Sugarman et al. (1995) conservatively estimated age errors of at the 95% confidence interval for one Sr isotopic analysis; age errors for the coeval and older sections are purportedly one order of magnitude better according to Howarth and McArthur (1997). We estimate that the maximum Sr isotopic age resolution for this interval is of the regressions of ~0.000020/m.y.). For comparison, Table T6 also shows ages derived from the look-up tables of McArthur et al. (2001).
Four Sr isotopic ages were obtained on shell material in the Navesink Formation. The sample at 845.6 ft (257.7 m) obtained an age of 61.4 Ma, which is too young for the Maastrichtian Navesink and is assumed to have been affected by diagenesis. The other three samples (246.1, 855, and 856 ft; 257.9, 260.6, and 260.9 m) gave ages between 64.5 and 65.9 Ma, consistent with the Navesink II sequence of Miller et al. (2004).
Eight bulk oxygen and carbon isotopic measurements were made on the sequence from 706.5 to 741.9 ft (215.3 to 226.1 m) to aid in correlation of this section. In particular, we were interested to determine if this sequence postdated the global CIE (Kennett and Stott, 1991), as suggested by nannofossil biostratigraphy (see "Calcareous Nannofossils"), or predated the CIE (i.e., Paleocene age), as suggested by the presence of the planktonic foraminifer Globanomalina pseudomenardii (see "Planktonic Foraminifers"). Small "chip" samples were obtained, dried, ground, and analyzed on a Fisions Optima mass spectrometer at Rutgers University supervised by J.D. Wright. Carbon isotopic values obtained (~0.0
–0.5) (Fig. F6) are consistent with post-CIE values in other New Jersey coastal plain coreholes (e.g., Cramer et al., 1999). This implies reworking of Paleocene planktonic foraminiferal specimens in the sequence from 706.5 to 741.9 ft (215.3 to 226.1 m) to explain the Zone 9b assignment.
