BIOSTRATIGRAPHY

Initial biostratigraphic determinations for calcareous nannofossils were performed on core catcher samples. Additional samples were subsequently investigated from selected core sections to refine the biostratigraphic zonal assignments. Slides for nannofossil investigations were prepared by smearing sediment across a glass slide and attaching a cover glass. Taxa identifications were made under plane-polarized and cross-polarized light using a Zeiss Axioscope microscope.

Relative abundance estimates for individual nannofossil species were made using a magnification of 1000x; abundances were estimated as follows:

D = dominant (>100 specimens of a species per field of view).

A = abundant (>10-100 specimens of a species per field of view).

C = common (>1-10 specimens per field of view).

F = few (1 specimen per 10 fields of view).

R = rare (<1 specimen per 10 fields of view).

B = barren (no nannofossils found).

Preservation of nannofossil specimens was characterized as follows:

VG = very good (no dissolution or secondary overgrowths of calcite). All specimens can be identified with certainty.

G = good (little dissolution or secondary overgrowths). Essentially all specimens can be identified at the species level.

M = moderate (slight to moderate dissolution and/or overgrowths). Identification of some species is impaired, but most species can still be identified.

P = poor (severe dissolution, breakage, or secondary overgrowths have largely destroyed the primary morphological features). Many specimens cannot be identified at the species level; some cannot be identified at the generic level.

Calcareous nannofossil zonation schemes used during Leg 197 were those of Martini (1971) for the Tertiary and Sissingh (1977) for the Cretaceous (Fig. F10). The other widely used Cenozoic zonation, that of Okada and Bukry (1980), is included in Figure F10 for comparison. Positions of well-dated nannofossil events are shown in Figure F10, and datum ages are given in Table T1.

Figure F10 also shows the correlation of geochronological units, nannofossil zones, and the magnetic polarity timescale. This figure is modified from the correlation scheme used during ODP Leg 165 by the Shipboard Scientific Party (1997b). The Shipboard Scientific Party (1997b) used data sources for the original figure as follows. The Cande and Kent (1995) polarity timescale was used. Correlation of zonations to the polarity timescale was based on Berggren et al. (1995) for the Tertiary and Shipboard Scientific Party (1997b) for the Cretaceous. Age estimates of nannofossil datums occurring between 14 and 65 Ma were taken from Berggren et al. (1995) and Shipboard Scientific Party (1995, 1997b). Age estimates for Late Cretaceous datums were taken from Erba et al. (1995), Bralower et al. (1995), and Shipboard Scientific Party (1997b). All age estimates of biostratigraphic data were calibrated to the magnetic polarity timescale of Cande and Kent (1995) (Shipboard Scientific Party, 1997b).

Abundance, preservation, and zonal data for each sample investigated during Leg 197 were recorded in the ODP PAL paleontology database.