MATERIALS AND METHODS

Calcareous nannofossils were examined in strewn slides using standard light microscope techniques under cross-polarized and phase-contrast light at 625x magnification on a Zeiss Axiophot. Settled strewn slides were prepared by mixing a small amount of sediment with 1–2 mL of buffered, distilled water, which was then thoroughly mixed with a plastic pipette. The mixture was distributed on a 22 mm x 40 mm glass coverslip, which was then dried on a slide warmer until all of the water had evaporated. The dried coverslip was then adhered to the slide with three drops of Norland-61 optical adhesive, and the adhesive was cured under ultraviolet light.

The following abbreviations are used to describe nannofossil preservation:

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

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

P = poor preservation (specimens were severely etched or overgrown; primary morphological characteristics largely destroyed; fragmentation has occurred; specimens often could not be identified at the species and/or generic level).

Five calcareous nannofossil abundance levels are recorded as follows:

V = very abundant; 11–100 specimens/field of view (FOV).

A = abundant; 1–10 specimens/FOV.

C = common; 1 specimen/2–10 FOV.

F = few; 1 specimen/11–100 FOV.

R = rare; 1 specimen/101+ FOV.

The same definitions are used for estimations of total abundance of each sample, with the additional definition of "B" (B = barren of nannofossils). This abundance scheme allows comparison of Site 1276 results with those obtained on the conjugate Iberian margin at Deep Sea Drilling Project (DSDP) Site 398 and ODP Sites 1067 through 1069 (Blechschmidt, 1979; McGonigal and Wise, 2001).

The zonal scheme of Bukry (1973, 1975; zonal code numbers CN and CP added and modified by Okada and Bukry, 1980) is used for Cenozoic calcareous nannofossil biostratigraphy. The zonal schemes of Sissingh (1977; CC zones), as modified by Perch-Nielsen (1985), Applegate and Bergen (1988; Lower Cretaceous subzones), and Burnett (1998; UC zones) are used for the Late Cretaceous, and those of Roth (1973, 1983; NC zones), with subdivisions by Bralower et al. (1993), are used for the Early Cretaceous. Age estimates for calcareous nannofossil first and last occurrences are summarized in Tucholke, Sibuet, Klaus, et al. (2004).

Unlithified sediments were soaked in a 3% solution of hydrogen peroxide (H₂O₂), warmed on a hot plate (~50°C) for 20 min, and then washed with tap water over a 63-µm sieve. Samples within 0.5 m above the Cretaceous/Tertiary boundary were washed over a 38-µm sieve to catch the dwarf microfossil assemblages, and samples from the Lower Cretaceous interval were washed over a 45-µm sieve. Lithified sediments were first mechanically crushed into <1 cm fragments and then treated in the same manner. All samples (residues >63, 45, or 38 µm) were dried on filter paper on a hotplate at ~50°C and then sieved through a sieve tower of 125-, 250-, and 500-µm meshes. Samples were examined for age-diagnostic species of planktonic foraminifers on the >250-µm, 125- to 250-µm, and 63- to 125-µm size fractions. In addition, all size fractions were carefully scanned for other biotic (e.g., radiolarians, sponge spicules, echinoid spines, fish bone/teeth, ostracodes, and inoceramid prisms) and mineral (glauconite, pyrite, and phosphate pellets) constituents of the sand-sized residues.

The following abundance categories used in the text were estimated from visual examination of the dried sample for biotic constituents and for mineral grains >63 µm:

D = dominant (>30%).

A = abundant (10%–30%).

F = few (5%–10%).

R = rare (1%–5%).

P = present (<1%).

The preservation status of the recovered microfossils >63 µm is estimated as follows:

VG = very good; no evidence of overgrowth, dissolution, or abrasion.

G = good; little evidence of overgrowth, dissolution, or abrasion.

M = moderate; calcite overgrowth, dissolution, or abrasion are common, but minor.

P = poor; substantial overgrowth, dissolution, or fragmentation.

The tropical Paleogene planktonic foraminiferal zonal scheme (P zones) follows Berggren et al. (1995). The zonation used for Cretaceous planktonic foraminifers is based on the tropical zonal schemes of Caron (1985) and Sliter (1989; KS zones), with modifications by Bralower et al. (1993, 1995a, 1997) and Premoli Silva and Sliter (1994, 1999). Age estimates for planktonic foraminifer first and last occurrences are summarized in Tucholke, Sibuet, Klaus, et al. (2004).