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doi:10.2204/iodp.proc.322.102.2010 BiostratigraphyPreliminary ages were assigned to sedimentary strata primarily based on core catcher samples. Samples from within the cores were examined when a more refined age determination was necessary. Ages for calcareous nannofossil and foraminiferal events from the early Miocene through the Quaternary were estimated by correlation to the geomagnetic polarity timescale (GPTS) of Lourens et al. (2004). The biostratigraphic events, zones, and subzones for nannofossils and planktonic foraminifers are summarized in Figure F15. The Pliocene/Pleistocene boundary has been formally located just above the top of the Olduvai (C2n) magnetic polarity subchronozone (Aguirre and Pasini, 1985) and just below the lowest occurrence of medium Gephyrocapsa caribbeanica (≥3.5 but <5.5 µm) (Takayama and Sato, 1993–1995; Raffi et al., 2006). We used the lowest occurrence of medium G. caribbeanica (≥3.5 but <5.5 µm) to mark the Pliocene/Pleistocene boundary. The Miocene/Pliocene boundary has not been formally defined yet. We tentatively used the last occurrence (LO) horizon of Discoaster quinqueramus for the boundary. The first occurrence (FO) of Globorotalia tumida (planktonic foraminifer) also marks the approximate position of the stage boundary. Details of the shipboard methods are described below for each microfossil group. Calcareous nannofossilsThe calcareous nannofossil zonal scheme established by Martini (1971) and Okada and Bukry (1980) and modified by Young (1998) was used for lower Miocene–Quaternary sequences during Expedition 322. The calcareous nannofossil biostratigraphic classification of sedimentary sequences follows the recent review by Raffi et al. (2006). In addition, the upper Pliocene–Quaternary biohorizons originally defined by Sato and Takayama (1992) and modified by Raffi et al. (2006) were used for more detailed correlations. Astronomically tuned age estimates for the lower Miocene–Quaternary rely on the geological timescale developed by the International Commission on Stratigraphy (ICS) in 2004 (Lourens et al., 2004). A size-defined species of the genera Reticulofenestra was placed into size categories as proposed by Young (1998). For the gephyrocapsids, we adopted the concept of Raffi et al. (2006), and morphological terminology used here is summarized in Perch-Nielsen (1985) and Takayama and Sato (1987). Accordingly, Gephyrocapsa is divided into four major groups by maximum coccolith length: small Gephyrocapsa (<3.5 µm), medium Gephyrocapsa (G. caribbeanica and Gephyrocapsa oceanica; ≥3.5 but <5.5 µm), Gephyrocapsa sp. 3 (Gephyrocapsa parallela; ≥4 but <5.5 µm), and large Gephyrocapsa (G. caribbeanica and G. oceanica; ≥5.5 µm). The zonal scheme and nannofossil biohorizons are shown in Figure F15 and Table T9. MethodFor nannofossil analyses, the core catcher sections of each core were sampled. Samples from other sections were sometimes included where nannofossils were not abundant in core catcher material, and many such samples were targeted specifically in burrows. Standard smear slide methods were utilized for all samples using optical adhesive as a mounting medium. Calcareous nannofossils were examined under a light polarizing microscope at 1250× magnification. Abundance, preservation, and zonal data for each sample investigated were recorded in the J-CORES database. We followed the taxonomic concepts summarized in Takayama and Sato (1987) (Deep Sea Drilling Project Leg 94). Calcareous nannofossil preservation was based on the following:
Total abundance of calcareous nannofossils for each sample was estimated as
Nannofossil abundances of individual species were recorded as
As a way to check these abundances, we compared these abundances with carbonate content and relative percentages of calcite from bulk XRD. Planktonic foraminifersThe planktonic foraminifer zonation of Blow (1969) and astronomically calibrated biohorizons of Neogene planktonic foraminifers compiled by the ICS in 2004 (Lourens et al., 2004) were applied for this expedition. The LO of Globigerinoides ruber rosa has been located at 0.12 Ma in the Indian and Pacific Oceans (Thompson et al., 1979) and confirmed by others (i.e., Li et al., 2005, at ODP Site 1143, South China Sea). The LOs of Neogloboquadrina asanoi and Globoquadrina dehiscens and the FO of Globoconella inflata modern form were correlated to geomagnetic polarities at ODP Sites 1150 and 1151 off northeast Japan (Motoyama et al., 2004). These foraminifer zonations and biohorizons are shown in Figure F15 and Table T10. MethodAbout 10 cm3 of sediment from core catcher sections was collected for foraminifer analyses. Soft-sediment samples were disaggregated using a hydrogen peroxide solution. Firm mudstone or hard rock samples were treated by the sodium tetraphenylborate method (Hanken, 1979). After samples became macerated, each sample was wet-sieved through a screen (63 µm opening). Planktonic foraminifer specimens >125 µm were taken from the dried residues. Semiquantitative estimates of the relative abundance of species were made as follows:
Preservation of each sample was recorded by the following criteria:
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