MATERIALS AND METHODS

A total of 291 samples were taken aboard JOIDES Resolution at 2 per section (at a sample spacing of 75 cm) for all cores from Hole 1256B, and smear slides were made for all samples. Preparation of smear slides followed standard techniques using Norland-61 optical adhesive as a mounting medium. Slides were examined using a Zeiss Axioskop II microscope under cross-polarized light, transmitted light, and phase-contrast light at 800x and 1250x magnification. A JEOL JSM 840 scanning electron microscope (SEM) was employed to take digital images for more precise species identification. Relative abundance of individual nannofossil species and overall preservation and abundance of the nannofossil assemblages were recorded in semiquantitative estimates under a magnification of 1000x for each sample. Letter codes for these estimates follow those of Arney and Wise (2003) as below.

Estimates of overall nannofossil abundance were given the following letter codes:

V = very abundant (>10 nannofossils per field of view).

A = abundant (1–10 nannofossils per field of view).

C = common (1 nannofossil per 2–10 fields of view).

F = few (1 nannofossil per >10–100 fields of view).

R = rare (1 nannofossil per >100 fields of view).

B = barren (no nannofossils per >500 fields of view).

The average state of preservation of the nannofossil assemblage in each sample is designated as follows with transitional conditions between them:

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 sometimes 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).

Relative individual species abundance estimations follow the procedure of Hay (1970) as below:

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

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

C = common (1 specimen per 2–10 fields of view).

F = few (1 specimen per 11–100 fields of view).

R = rare (1 specimen per 101–1000 fields of view).