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doi:10.2204/iodp.proc.338.205.2016

Results

With the exception of several barren intervals, 36 taxa belonging to 15 genera of planktonic foraminifers were recognized in Holes C0002K and C0002L (Table T1). Fossil preservation is generally moderate to poor. In particular, sediment below ~300 m CSF-A have sparse occurrences of planktonic foraminifers with poor preservation and barren intervals (Table T1; Fig. F2). Most of these barren intervals contain only thick-walled benthic foraminifers with surfaces disfigured by dissolution.

Six age-diagnostic species were recognized in this study (Table T1). Globorotalia tosaensis sporadically occurs at 12 horizons between Samples 338-C0002L-21X-6, 45.0–47.5 cm (472.89 m CSF-A), and 338-C0002K-1H-5, 21.0–24.0 cm (203.57 m CSF-A). Globorotalia truncatulinoides was observed sporadically at 12 horizons between the same samples. Rare or few occurrences of Globoturborotalita obliquus were observed from only four samples (338-C0002K-7X-CC, 6.0–8.0 cm, and 338-C0002L-14X-8, 58.0–60.5 cm; 15X-1, 51.0–53.5 cm; and 19X-1, 43.0–45.5 cm). Among them, the uppermost occurrence in Sample 338-C0002K-7X-CC, 6.0–8.0 cm, might be reworked because the surface was brown and the test was filled by silty material (Plate P1; figs. 7a, 7b). Therefore, the top occurrence datum of this species (1.30 Ma; Wade et al., 2011) is suggested between Samples 338-C0002L-14X-8, 58.0–60.5 cm (409.25 m CSF-A), and 14X-5, 81.0–83.5 cm (405.44 m CSF-A) (Table T2). A few specimens of Neogloboquadrina inglei were obtained from 18 samples between Samples 338-C0002L-21X-6, 45.0–47.5 cm (472.89 m CSF-A), and 338-C0002K-1H-5, 21.0–24.0 cm (203.57 m CSF-A). This species was reported from the deeper interval drilled in Hole C0002B (Expedition 315 Scientists, 2009). Thus, the base occurrence datum of this species should be located below Sample 338-C0002L-21X-6, 45.0–47.5 cm (472.89 m CSF-A) (Table T2). Pulleniatina obliquiloculata was found in 19 samples, and its coiling direction is exclusively dextral throughout the section. Pulleniatina finalis was detected at only four horizons in Hole C0002L (Samples 338-C0002L-5X-1, 20.0–22.5 cm; 13X-7, 7.0–9.5 cm; 14X-5, 81.0–83.5 cm, and 15X-1, 51.0–53.5 cm). This species was detected from only one sample in deeper interval obtained from Hole C0002B (Expedition 315 Scientists, 2009). The base occurrence datum of this species (2.04 Ma; Wade et al., 2011) is hard to recognize because of its sparse occurrence.

The first occurrence of G. truncatulinoides is at 1.98 Ma (Wade et al., 2011) and defines the base of Zone N22 of Blow (1969). This biohorizon was previously recognized at deeper depths (753.86–767.20 m CSF-A) in Hole C0002B during Expedition 315. In addition, the last occurrence of G. tosaensis is at 0.61 Ma (Wade et al., 2011). Therefore, the interval below the top occurrence of G. tosaensis (Sample 338-C0002K-1H-5, 21.0–24.0 cm; 203.57 m CSF-A) (Table T2) should be restricted to within the lower part of Zone N22. This correlation is consistent with onboard calcareous nannofossil and paleomagnetic data (see the “Site C0002” chapter [Strasser et al., 2014c]) (Fig. F2).

Planktonic foraminiferal assemblages in the study interval are characterized by dominant occurrences of mixed-water and cosmopolitan species such as Neogloboquadrina incompta, Neogloboquadrina pachyderma (dextral), Globigerinita glutinata, Globigerina bulloides, and Globigerina falconensis associated with tropical to subtropical taxa including Globoconella inflata, Neogloboquadrina dutertrei, and Globigerinoides ruber (Table T1; Fig. F2). Currently, the study area lies beneath mixed water caused by the upwelling of cold water near the Kuroshio Current. Therefore, the foraminiferal composition of the studied interval is generally consistent with present-day oceanographic conditions.

The most noteworthy feature of the planktonic foraminiferal assemblages is cyclic changes of relative abundance in cold versus cosmopolitan components (Fig. F2). We can observe five 40–60 m thick cycles throughout the study interval. The precise correlation of the cycles with global events requires further studies including stable isotope analyses.

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