Preliminary age assignments were primarily based on biostratigraphic analyses of calcareous nannofossils and planktonic foraminifers. Paleodepth interpretations were based on benthic foraminifers. Calcareous nannofossil and planktonic foraminiferal datums were determined by examining core catcher samples. Additional samples were examined in order to refine the biostratigraphy of both groups where appropriate and to discern unconformities and other critical intervals. The preservation, abundance, and zonal assignment for each sample and for each microfossil group were recorded in the stratigraphic site summary sheets and entered into the Janus database. The timescale of Berggren et al. (1995b) was applied for the Cenozoic and those of Gradstein et al. (1995) and Channell et al. (1995) for the Cretaceous (Figs. F4, F5).
Ages of Cenozoic calcareous nannofossil and planktonic foraminiferal first and last occurrences (FO = first occurrence or datum base, LO = last occurrence or datum top) older than 14 Ma follow Berggren et al. (1995b); younger datums are astrochronologically tuned ages from several sources (Shackleton et al., 1995; Backman and Raffi, 1997; Chaisson and Pearson, 1997). Ages for Cenozoic datums are presented in Tables T1 and T2. Age estimates for Cretaceous calcareous nannofossil and planktonic foraminiferal datums are from Erba et al. (1995), Bralower et al. (1997), and Premoli Silva and Sliter (1999). Cretaceous datums are presented in Tables T3 and T4.
The zonal scheme of Bukry (1973, 1975; zonal code numbers CN and CP added and modified by Okada and Bukry, 1980) was used for Cenozoic calcareous nannofossil biostratigraphy (Table T1). The zonal schemes of Sissingh (1977; CC zones), as modified by Perch-Nielsen (1985), and Burnett (1999; UC zones) were used for the Late Cretaceous, and those of Roth (1978, 1983; NC zones) with subdivisions by Bralower et al. (1993) were used for the Early Cretaceous (Table T3). The zonal scheme of Bralower et al. (1989; NK and NJK zones) was applied for the Jurassic/Cretaceous boundary interval. All of these zonations represent a general framework for the biostratigraphic classification of mid- to low-latitude nannofloral assemblages and are presented in Figures F4 and F5. Nannofossil taxonomy follows that used in Bown (1999), where full taxonomic lists can be found.
The tropical planktonic foraminiferal zonal scheme (N and P zones) used for the Cenozoic follows Berggren et al. (1995b; Table T2). 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, 1995, 1997) and by Premoli Silva and Sliter (1994, 1999) (Figs. F4, F5). Age estimates for planktonic foraminiferal datum markers were obtained from Erba et al. (1995), Bralower et al. (1997), and Premoli Silva and Sliter (1999; Table T4).
Cenozoic taxonomic concepts follow Postuma (1971), Kennett and Srinivasan (1983), Bolli and Saunders (1985), Toumarkine and Luterbacher (1985), Spezzaferri and Premoli Silva (1991), Chaisson and Leckie (1993), Leckie et al. (1993), Spezzaferri (1994), Pearson (1995), Berggren and Norris (1997), Chaisson and Pearson (1997), Pearson and Chaisson (1997), Norris (1998), and Olsson et al. (1999). Genus-species combinations generally follow those used by Berggren et al. (1995b) with few modifications. Cretaceous taxonomic concepts are based on Longoria (1974), Robaszynski et al. (1979, 1984), Leckie (1984), Caron (1985), Nederbragt (1990, 1991), and Petrizzo (2000).
At suprageneric levels, the classification scheme of Loeblich and Tappan (1988) is followed here, with the exception of trochospirally coiled calcareous taxa, which are classified according to the scheme of Kaiho (1998). Cenozoic benthic foraminiferal taxonomic concepts were mainly based on Tjalsma and Lohmann (1983), van Morkhoven et al. (1986), Kaiho (1992), and Bolli et al. (1994). Cretaceous taxonomic concepts follow Luterbacher (1973), Sliter (1977, 1980), Gradstein (1978), Bolli et al. (1994), Holbourn and Kaminski (1997), and Kaiho (1998).
Neogene paleodepth estimates are based on the work of Pflum and Frerichs (1976), Woodruff (1985), and van Morkhoven et al. (1986). For the Cretaceous section, estimates are mainly based on the studies of Sliter (1977, 1980) Nyong and Olsson (1984), Kaiho (1998), Holbourn et al. (2001), and a backtracked paleodepth curve from Deep Sea Drilling Project (DSDP) and ODP data of Kaiho (1999). The following terminology was applied:
The taxonomy of Early Cretaceous radiolarians is based on Baumgartner et al. (1995b). Eleven radiolarian Unitary Association Zones (UAZs) characterize the uppermost Jurassic and Lower Cretaceous interval and can be used for biostratigraphic correlation (Baumgartner et al., 1995a). A UAZ is a "maximal set of mutually compatible taxa" (Baumgartner et al., 1995a, p. 1014). The age correlation of radiolarian UAZs in the upper Barremian to Aptian interval follows Erba et al. (1999), and the uppermost Jurassic-lower Barremian interval is correlated to the Mesozoic polarity chronozones (Gradstein et al., 1995) by Baumgartner et al. (1995a).
Calcareous nannofossils were examined in smear slides using standard light microscope techniques, under crossed polarized light, transmitted light and phase contrast at 1000x magnification. The following abbreviations were used to describe nannofossil preservation:
Six calcareous nannofossil abundance levels are recorded as follows:
Foraminifers from unlithified ooze were soaked in a 3% solution of hydrogen peroxide with a small amount of Calgon added and then washed with tap water over a 63-µm sieve (Quarternary-lower Eocene interval) or a 45-µm sieve (basal Eocene-Upper Cretaceous interval). Semilithified ooze and chalk were first partially fragmented by hand and then soaked in hydrogen peroxide and Calgon before washing. After every use, the sieve was dipped in a dilute solution of methyl blue dye to identify contaminants from previous samples. After washing, all samples were collected on filter paper and then dried on a hot plate at ~50°C.
Species identification for planktonic foraminifers were generally made on the >250-µm and >150-µm size fractions. Two picking trays per sample from >250-µm size fraction (Neogene) or the >125-µm fraction (Paleogene-mid-Cretaceous) were examined for identification and abundance estimation of benthic foraminifers. Samples within 0.5 m above the Cretaceous/Tertiary (K/T) boundary and the Lower Cretaceous were treated the same as other unlithified ooze samples except that a 38-µm sieve was used to isolate the dwarfed microfossil assemblages.
The following abundance categories were estimated from visual examination of the dried sample for planktonic foraminifers:
The following abundance categories were used for benthic foraminiferal abundance (as a group) based on the number of benthic foraminifers encountered in two picking trays:
The preservation of the planktonic and benthic foraminifers was estimated as follows:
Radiolarians were extracted from claystone, chalk, and porcellanite by applying the same preparation method used for foraminifers, and they were studied in the stereomicroscope.