METHODS

Revised zonal schemes of Martini (1971; with modifications by Martini and Müller, 1986) and Bukry (1973, 1975; zonal code numbers added and modified by Okada and Bukry, 1980) were used to age-date the Cenozoic calcareous nannofossil sequences (Table T1).

Standard smear slides were prepared for samples from both sites at an interval of one sample every other section (or every 3 m). Calcareous nannofossils were examined using standard light-microscope techniques under crossed polarizers, transmitted light, and phase contrast at 1250x magnification. The scanning electron microscope was deployed to distinguish Emiliania huxleyi from small-sized Gephyrocapsa species and to define the Zone CN15/CN14b boundary.

Following the methodology of Sato et al. (1998), the abundance of C. pelagicus was investigated for sediments younger than 3.83 Ma (last occurrence [LO] of Reticulofenestra pseudoumbilicus) in both Holes 1150A and 1151A. For Hole 1150A, the first 200 specimens from each slide were counted to obtain the relative abundance of selected calcareous nannofossils. This procedure followed the example of Sato et al. (1998) for ODP Hole 883C. Next, 300 additional specimens were counted for each slide to determine the ratio of C. pelagicus in the total count of 500 specimens. For Hole 1151A, only the number of C. pelagicus specimens in a total of 500 nannofossils was counted for selected samples.

Preservation and abundance of calcareous nannofossil species may vary significantly because of etching, dissolution, or calcite overgrowth. A simple code system to characterize preservation is listed below:

VG = very good (no evidence of dissolution and/or overgrowth; no alteration of primary morphological characteristics and specimens appear diaphanous; specimens are identifiable to the species level).

G = good (little or no evidence of dissolution and/or overgrowth; primary morphological characteristics only slightly altered; specimens are identifiable to the species level).

M = moderate (specimens exhibit some etching and/or overgrowth; primary morphological characteristics somewhat altered; however, most specimens are identifiable to the species level).

P = poor (specimens are severely etched or exhibit overgrowth; primary morphological characteristics largely destroyed; fragmentation has occurred; specimens cannot be identified at the species and/or generic level).

Six calcareous nannofossil abundance levels are recorded as follows:

V = very abundant (>10-100 specimens per field of view).

A = abundant (1-10 specimens per field of view).

C = common (1 specimens per 2-10 fields of view).

F = few (1 specimens per 11-100 fields of view).

R = rare (1 specimens per >101-1000 fields of view).

B = barren.

ODP core identifiers indicate core type. The following abbreviations are used:

H = hydraulic piston core (HPC; also referred to as APC, or advanced hydraulic piston core).

X = extended core barrel (XCB).

R = rotary core barrel (RCB).