[BPT05-P03] Calcareous nannofossil biostratigraphy and oxygen isotope stratigraphy of the lower part of the Pleistocene formation distributed in the central part of the Pacific side of Japan
Keywords:Calcareous nannofossil, Biohorizon, Quaternary, Oxygen isotope stratigraphy
An oxygen isotope curve obtained from 44 samples was correlated with the LR04 stack curve (Lisiecki and Raymo, 2005) and Marine Isotope Stages (MIS) 40 to 36 were recognized in the formation. Two calcareous nannofossil biohorizons, the last occurrences (LO) of large forms of Gephyrocapsa (>5.5 μm) and Helicosphaera sellii coincide with MIS 37/38 boundary and MIS 40, respectively. The LO of large forms of Gephyrocapsa is slightly older than those in other areas because this biohorizon is mostly situated in the early part of MIS 37 (Raffi et al., 2006). On the other hand, the LO of Helicosphaera sellii is found in MIS 38 in the northeastern Atlantic (Sato et al., 2009) and MIS 42 in the eastern equatorial Pacific (Wei, 1993). This biohorizon is possibly diachronous bioevent due to sporadic occurrences of this species.
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