MATERIALS AND METHODS

Hole 1237B was cored by double advanced piston coring to a depth of nearly 360 meters composite depth (mcd), reaching sediments of early Oligocene age. Paleomagnetic inclination data (25-mT demagnetization on the shipboard pass-through magnetometer) reveal detailed records of late Oligocene Chrons 7Ar to 9n in Core 202-1237B-31H (Shipboard Scientific Party, 2003). In particular, three reversals are recorded in this core, which span 281.0–290.5 meters below seafloor and 316.41–327.07 mcd (Fig. F4). Interpretation of these paleomagnetic chrons is supported by biostratigraphic data. The late Oligocene calcareous nannofossil zonal boundary NP24/NP25 (27.3 Ma) lies near the base of this core, and the planktonic foraminifer zonal boundary P21/P22 (26.8 Ma) lies within the core (Shipboard Scientific Party, 2003). These ages are obtained by magnetobiostratigraphic correlations (Berggren et al., 1995) updated to the GTS 2004 (Gradstein et al., 2004).

Samples of 20 cm³ were taken at 5-cm intervals from Core 202-1237B-31H, freeze-dried, weighed, washed over a 63-µm sieve, oven-dried at <50°C, and picked for C. mundulus from the >150-µm size fraction. Where possible, four to eight C. mundulus specimens (40–100 µg) were used for stable isotope analysis. Oxygen and carbon isotope data were generated using a ThermoFinnigan MAT Delta Plus XL stable isotope ratio mass spectrometer (SIRMS) equipped with a Kiel III automated carbonate preparation device. External precision, based on >1000 National Institute of Standards and Technology (NBS)-19 standards run since July 2000, is better than ±0.08 for ¹⁸O and ±0.04 for ¹³C. Estimated precision based on replicate analyses is ±0.15 for ¹⁸O and ±0.07 for ¹³C (n = 6). Data are reported relative to the Vienna Peedee belemnite carbonate standard. Coarse fraction data are calculated as weight of the >63-µm size fraction divided by dry bulk weight and expressed as percentage. Planktonic foraminifers were also studied in selected samples to refine the biostratigraphy. Supporting data are available electronically in the Janus database (www-odp.tamu.edu/database/) and in the CHRONOS Data Repository (www.chronos.org).