Preliminary age determinations were based on shipboard analysis of planktonic foraminifers from core-catcher samples, in conjunction with other microfossil biostratigraphy and magnetostratigraphy (Shipboard Scientific Party, 1996a). Additional samples were then used to refine the planktonic foraminifer biostratigraphy. Abundance and preservation data were recorded throughout the study to assess surface-water environments and sediment dissolution. Biostratigraphic zonal assignments are correlated with the geomagnetic polarity time scale (GPTS) directly where possible (see Channell and Lehman, Chap. 8, this volume) or correlated indirectly based on calcareous nannofossil data (Jansen, Raymo, Blum, et al., 1996). Placement of epoch boundaries relative to paleomagnetic chrons and biostratigraphic zones followed Berggren et al. (1985, 1995). Age assignments of individual planktonic foraminifer datum levels are from Weaver and Clement (1986), Raymo et al. (1989), and Berggren et al. (1985, 1995), updated to the Cande and Kent (1995) time scale.
Planktonic foraminifers were obtained by disaggregating a 10-cm3 sample and washing it over a 63-µm sieve. Disaggregation methods for well-indurated sediments included ultrasonic treatment and sodium hexametaphosphate solution. Between samples, sieves were soaked in methylene blue carbonate stain to identify potential contamination. The samples were dried and examined under a binocular microscope, and planktonic foraminifers from the >150-µm fraction were identified to species level where possible. Planktonic foraminifer relative abundance (based on ~200 specimens) was recorded as follows:
- D (dominant) = >60%,
- A (abundant) = >30%-60%,
- C (common) = >10%-30%,
- F (few) = >5%-10%,
- R (rare) = >1%-5%,
- T (trace) = <1%, and
- B (barren) = no specimens observed.
Preservation (absence of dissolution and/or calcite overgrowth) was recorded as G (good), M (moderate), and P (poor).