Preliminary age assignments were based on biostratigraphic analyses of calcareous nannofossils, planktonic foraminifers, radiolarians, and palynomorphs. Paleodepth interpretations were based on benthic foraminifers. All core catcher samples were analyzed for calcareous nannofossils, planktonic foraminifers, benthic foraminifers, and radiolarians, and select core catcher samples were analyzed for palynomorphs. Additional samples were examined for calcareous nannofossils and planktonic foraminifers, including thin sections for the latter group, in order to refine the biostratigraphy where appropriate and to focus on 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 (see Table T7 in the "Site 1276" chapter). The timescale of Berggren et al. (1995b) is applied in the Cenozoic, and timescales of Gradstein et al. (1995) and Channell et al. (1995) are used for the Cretaceous (Figs. F10, F11).
Ages of Cenozoic calcareous nannofossil and planktonic foraminifer first occurrence (FO or datum base) and last occurrence (LO 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), Premoli Silva and Sliter (1999), and Gardin et al. (2001). 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) is used for Cenozoic calcareous nannofossil biostratigraphy (Table T1). The zonal schemes of Sissingh (1977; CC zones), as modified by Perch-Nielsen (1985), Applegate and Bergen (1988; Lower Cretaceous subzones), and Burnett (1999; 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 (Table T3). The zonal scheme of Bralower et al. (1989; NK and NJK zones) is 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 F10 and F11. Cenozoic and Cretaceous nannofossil taxonomy is in accordance with that cited in Perch-Nielsen (1985), Firth and Wise (1992), and Bown (1998), 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 Premoli Silva and Sliter (1994, 1999) (Table T4; Fig. F10). 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 and Caron (1979), Leckie (1984), Robaszynski et al. (1984), Caron (1985), Nederbragt (1990, 1991), Coccioni and Premoli Silva (1994), and Petrizzo (2000, 2001).
At suprageneric levels, the classification scheme of Loeblich and Tappan (1988) is followed. Cenozoic (Paleogene) benthic foraminiferal taxonomic concepts are 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 Kuhnt and Urquhart (2001).
Cenozoic 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 Nyong and Olsson (1984), Holbourn et al. (2001), and backtracked paleodepth curves from Deep Sea Drilling Project (DSDP) and ODP data of Kaiho (1999). The following paleodepth terminology is applied (after van Morkhoven et al., 1986):
Radiolarian biostratigraphy studied during Leg 210 is based largely on the radiolarian zonation and code numbers tied to the global polarity timescale of Cande and Kent (1995) and documented by Sanfilippo and Nigrini (1998). Supplemental markers, also derived from Sanfilippo and Nigrini (1998), are used whenever possible and correlate with the data supplied by calcareous nannofossils and planktonic foraminifers.
The taxonomy of Early Cretaceous radiolarians is based on Baumgartner et al. (1995b). Eleven radiolarian Unitary Association Zones (UAZ) characterize the uppermost Jurassic and Lower Cretaceous and can be used for biostratigraphic correlation (Baumgartner et al., 1995a). A Unitary Association is a "maximal set of mutually compatible taxa" (Baumgartner et al., 1995a, p. 1014). The age correlation of radiolarian UAZs in the upper Barremian–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).
Leg 210 palynomorph biostratigraphy is based largely on the work of Powell (1992) and Williams et al. (unpubl. data [N1]) for the Paleogene and Stover et al. (1996), Duxbury (2001), and Williams et al. (unpubl. data [N1]) for the Cretaceous. Absolute ages for FO and LO datums of selected taxa are after Williams et al. (unpubl. data [N1]) (Table T5). Dinoflagellate cyst taxonomy is in accordance with that cited in Williams et al. (1998).
Calcareous nannofossils were examined in smear slides using standard light-microscope techniques, under cross-polarized, transmitted, and phase-contrast light at 1250x. The following abbreviations are used to describe nannofossil preservation:
Five calcareous nannofossil relative abundance levels are recorded as follows:
Unlithified sediment was soaked in a 3% solution of hydrogen peroxide (H2O2) with a small amount of Calgon added, warmed on a hot plate, and then washed with tap water over a 63-µm or 45-µm sieve (Lower Cretaceous interval). H2O2 was used in the interest of time efficiency and to keep pace with drilling operations. As a consequence, some of the agglutinated foraminiferal taxa, which incorporate organic cement into their tests, may have been eliminated from the processed residues.
Semilithified claystone, mudstone, and shale were first partially fragmented by hand and then soaked in hydrogen peroxide and Calgon before washing; lithified samples were first crushed using a Carver laboratory press in order to facilitate disaggregation. After every use, the sieve was dipped in a dilute solution of methyl blue dye to identify contaminants from previous samples. All samples (residues >63 or 45 µm) were dried on filter paper placed on a hot plate at ~50°C.
Samples within 0.5 m above the Cretaceous/Tertiary boundary were treated the same as other unlithified sediment samples, except that a 38-µm sieve was used to catch the dwarf microfossil assemblages.
Species identifications for planktonic foraminifers were generally made on the >63-µm fraction, although the >250- and >150-µm size fractions were carefully scanned for larger age-diagnostic taxa and other constituents of the sand-sized residues. In addition to planktonic foraminiferal species, other biotic (e.g., radiolarians, sponge spicules, echinoid spines, fish bone/teeth, ostracodes, and inoceramid prisms) and mineral (glauconite, pyrite, and phosphate pellets) constituents were noted in each of the core catcher residues. Two picking trays per sample from the >63-µm fraction were examined to identify benthic foraminifers and estimate their abundance.
The following abundances of species (in relation to total foraminifers) were estimated from visual examination of dried samples of planktonic foraminifers:
The following abundance categories were used for relative benthic foraminiferal abundance based on the number of benthic foraminifers encountered in two picking trays:
The preservation status of the planktonic and benthic foraminifers was estimated as follows:
The presence/absence of radiolarians in core catcher samples was evaluated from the foraminiferal residue and in slides prepared for palynology.
Total radiolarian abundance was determined based on strewn-slide evaluation at 100x, using the following convention:
The abundance of individual radiolarian species was estimated as a fraction of the total assemblages as follows:
Radiolarian preservation was recorded as follows:
Up to 20 cm3 of sample was processed following standard palynological techniques (e.g., Pross, 2001). Samples composed of fine-grained, dark-colored detrital material were selected wherever possible. Briefly, the processing procedure included digestion by HCl and HF, with centrifuging and rinsing through a stainless steel 20-µm mesh after each step. If necessary, the recovered residue was then treated with nitric acid to partially oxidize the organic matter and with potassium hydroxide solution to remove humic acids. For some samples from quartz-rich sediments, heavy-liquid separation using a ZnCl2 solution was completed. Residues were partly stained with Safranine to improve palynomorph visibility. Finally, residues from each sample were strew mounted on glass slides using glycerine jelly. For biostratigraphic purposes, a minimum of two slides were prepared and evaluated.
Preservation was classified as one of the following:
To determine sedimentation rates, one must first generate an age-depth relationship. Paleomagnetic stratigraphy with unambiguously defined chrons can be a prime tool in this determination, but, unfortunately, a polarity-reversal history was not well resolved in Leg 210 holes. Instead, we had to rely on biostratigraphic data.
Where biostratigraphic datums are used, the chief uncertainty in determining sedimentation rates arises from the fact that with a limited amount of time for study, many datums are determined to lie between widely separated samples. During many ODP legs, it has been necessary to reconstruct sedimentation rates using datums determined only from core catcher samples (i.e., within 9.5 m). The amount of uncertainty in each sedimentation-rate estimate derived in this way is defined by the thickness of the interval over which the rate is averaged, divided by the combined age uncertainty in the top and bottom controls.
A second source of uncertainty is the accuracy with which datums can be picked in the cores. This depends on fossil abundance, preservation, and reworking, as well as the fossil assemblage (one or several groups) that is available for study. Finally, there is uncertainty in the absolute ages of the datums as defined by the timescale that is used.
Sedimentation rates (in meters per million years) were estimated from age-depth plots by drawing best-fit lines through all the biostratigraphic data over successive depth intervals (i.e., by drawing straight-line segments through discrete intervals of data). Sedimentation rates were calculated using midpoints in the observed range of uncertainty in sample age or datum depth.