METHODS

The nannofossil biostratigraphy presented here is based on examination of smear slides prepared from unprocessed sediments and viewed using phase contrast and cross-polarized light microscopy at a magnification of 1550x. The biostratigraphic zonation scheme used for the Paleocene (Fig. F4) is that of Martini (1971) and Okada and Bukry (1980). The Martini zonation is widely used for Cenozoic, low-latitude, open-marine sediments, whereas the Okada and Bukry zonation is widely used for low- to mid-latitude, open-marine sections. Biostratigraphic zonation of Cretaceous sediments follows Sissingh (1977) as modified and illustrated in Perch-Nielsen (1985) (Fig. F5).

Abundances of individual taxa are represented by letter codes and were recorded according to the following definitions:

S = single, 1 specimen observed.

R = rare, 1 specimen per 101-1000 fields of view.

F = few, 1 specimen per 11-100 fields of view.

C = common, 1 specimen per 2-10 fields of view.

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

V = very abundant, 10-100 specimens per field of view.

The same definitions were used for estimates of total abundance in each sample, with an added definition: B (barren of nannofossils).

The preservation of nannofossils can vary significantly because of etching, dissolution, or calcite overgrowth. Finding pristine specimens in the same sample as specimens that are severely overgrown or etched is not uncommon. The state of preservation of the nannofossil assemblages in this paper was recorded as follows:

G = good preservation, little or no evidence of dissolution and/or overgrowth, primary diagnostic features preserved, specimens are identifiable to the species level.

M = moderate preservation, specimens exhibit some etching and/or overgrowth, primary diagnostic features somewhat altered but most specimens are identifiable to the species level.

P = poor preservation, specimens are severely etched or exhibit overgrowth, primary diagnostic features largely destroyed, fragmentation has occurred, many specimens cannot be identified to the species and/or generic level.

Sedimentation rates were calculated using the nannofossil datums only. Ages for the nannofossil datums in the Cenozoic were obtained from Berggren et al. (1995); ages for the nannofossil datums in the Cretaceous were obtained from Gradstein et al. (1995) and Erba et al. (1995).

Mass accumulation rates were calculated using the following equation from Davies et al. (1995):

MAR = {T x [BD - (P x WD)]}/t,

where BD is wet bulk density (in grams per cubic centimeter), P is porosity (in weight percent), WD is seawater density (1.025 g/cm³), and T is the thickness of sediment accumulated at time t (10³ yr). Limited numbers of multisensor track data were available from shipboard measurements and can be found in the Leg 173 Initial Reports volume in the appropriate chapters (Whitmarsh, Beslier, Wallace, et al., 1998).