During Leg 191, calcareous nannofossils, foraminifers, palynomorphs, and radiolarians were studied in order to assess biostratigraphic constraints on the sedimentary section at Site 1179. The reference time scale adopted for Leg 191 follows Gradstein et al. (1994, 1995) for the Cretaceous and Berggren et al. (1995a) for the Cenozoic. Specific biozonations for each fossil group are discussed below in more detail.
We referred primarily to the zonations of Okada and Bukry (1980) and Martini (1971) for Cenozoic sediments and Perch-Nielsen (1983) for Cretaceous sediments. To facilitate comparison with other studies, numerical ages used are those compiled by Berggren et al. (1995a). Calcareous nannofossil assemblages were described from smear slides prepared for each core-catcher sample and for as many additional core samples as time permitted. Standard preparation techniques were used throughout. Examination was performed exclusively with a light microscope, using whatever optical configuration yielded useful results. In all cases, a magnification of 1000× was used to make semiquantitative estimates of abundances. Abundances of individual species were estimated for each sample. Five levels of individual species abundance were recorded, with the following approximate definitions:
Total abundance of calcareous nannofossils for each sample was estimated as follows:
The qualitative evaluation of the preservation of calcareous nannofossils was recorded as poor, moderate, or good. These categories represent subjective impressions according to the following definitions:
No widely accepted dinocyst zonation exists for the Neogene to Holocene, but ages for these sediments are based mainly on the dinocyst biozonations of Powell (1992) and Harland (1992), which are derived largely from western Europe. The work of Matsuoka (1983) on late Cenozoic dinoflagellates and acritarchs in central Japan proved to be extremely useful at this western North Pacific site. Our Pleistocene biostratigraphy is supplemented by the zonation developed for the midlatitude North Atlantic by McCarthy et al. (2000). The Northern Hemisphere composite range estimates for Mesozoic-Cenozoic strata of Williams et al. (1993) and dinocyst datums established in various Deep Sea Drilling Project (DSDP) and ODP holes (e.g., de Verteuil, 1996; McCarthy and Mudie, 1996; Mudie, 1987) were also used to determine ages.
As many 20-cm3 core-catcher samples were examined as time permitted. Additional 20-cm3 samples were examined from intervals of particular stratigraphic interest. Processing consisted of heating the sample in a 1% Calgon solution until clays were disaggregated followed by sieving through a 10-µm Nitex nylon sieve. Residues were then digested in hot 10% hydrochloric acid and washed with distilled water. Because of high silica content, samples were digested for ~1 hr in hot concentrated hydrofluoric acid and again washed with water. This was followed by a second sieving through a 10-µm Nitex nylon sieve. Swirling the organic residues in a large watchglass removed residual coarse silicates, sulfides, and detrital minerals when they were present. Residues were strew mounted in glycerine jelly on glass slides and examined in bright field transmitted light at 250-400× magnification. Absolute abundances (or concentrations) of dinocysts and terrestrial palynomorphs (pollen and spores) were estimated and are reported as cysts per cubic centimeter of sediment. Samples were spiked with a tablet containing a known quantity of Lycopodium clavatum spores following the method of Stockmarr (1971) to determine absolute palynomorph concentrations. Relative species abundances are reported as follows:
Qualitative evaluation of the preservation of dinocysts only is recorded as poor, moderate, or good. These categories represent subjective impressions with approximately the following meaning:
All assemblages recovered are thermally immature, and therefore, thermal alteration is not a relevant factor in fragmentation or color alteration of palynomorphs.
Samples of ~25 mL were soaked in a Calgon solution, washed through a 63-µm sieve, and dried under a heat lamp.
Benthic and planktonic foraminifers were examined from the >150-µm size fraction. Species abundance relative to the total foraminifer fauna was estimated as follows:
Preservation characteristics were divided into four categories:
The foraminifers were used primarily as carbonate preservation indicators. For identification, Loeblich and Tappan (1988) was used.
To obtain radiolarians from CC samples, ~10 cm3 of sediment was disaggregated and boiled using 10% H2O2, 10% HCl, and ~1% Calgon solutions. Brief treatment of samples in an ultrasonic bath was followed by washing on a 63-µm mesh sieve. The residue was moved into a beaker, and a strewn slide was made using a pipette. Canada balsam was used as a mounting medium. Additional random strewn slides will be prepared onshore to locate biostratigraphic events more accurately within cores. Overall radiolarian abundance was determined based on strewn-slide evaluation at 100× using the following conventions:
The abundance of individual species was recorded relative to the fraction of the total assemblage as follows:
Preservation was recorded as follows: