[BPT06-P10] Lower Pleistocene calcareous nannofossil biostratigraphy in the Boso Peninsula and the Choshi district and estimated sea surface environments
Keywords:Calcareous nannofossils, Quaternary, Kazusa Group, Paleoceanography
Calcareous nannofossil assemblages in both Groups were characterized by abundant occurrences of Gephyrocapsa, Reticulofenestra, and Pseudoemiliania. Because Coccolithus pelagicus, an Oyashio water index, and Umbilicosphaera sibogae, a Kuroshio water index (Tanaka, 1991), were very few, this study examined the number of these specimens in a gram of dry sediment. The number of U. sibogae was much larger than those of C. pelagicus in all samples, and thus, the Kuroshio current dominated during the investigated interval. In particular, the sudden increases of this species near 0.87Ma clearly demonstrates temporary intensification of the Kuroshio current. The intensity of Kuroshio current was estimated to strengthen and weaken repeatedly in this region during the early Pleistocene, because stratigraphic changes of this species show similar patterns through the studied interval.
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