1. Oxygen isotope stratigraphy and calcareous nannofossil biostratigraphy of the Lower Pleistocene in the Boso Peninsula, central Japan.
- Author
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Daisuke Kuwano, Yoshimi Kubota, Kanako Mantoku, and Koji Kameo
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PLEISTOCENE Epoch , *BIOSTRATIGRAPHY , *PENINSULAS , *CARBON isotopes , *NANNOFOSSILS , *OXYGEN isotopes ,KUROSHIO - Abstract
Oxygen isotope stratigraphy and calcareous nannofossil biostratigraphy in the upper part of the Kiwada Formation, which is part of theKazusa Group in the Boso Peninsula in the central part of the Pacific coast of Japan, were examined to establish a high-resolution age model and estimate the age of the lower part of Pleistocene nannofossil biohorizons in the northwestern Pacific region. The new age model indicates that the upper part of the Kiwada Formation corresponds to Marine Isotope Stage (MIS) 41 through MIS 36. Two nannofossil biohorizons, the last occurrences of large forms of Gephyrocapsa (>5.5 µm) and Helicosphaera sellii, were recorded in the examined section. The LOof large Gephyrocapsa spp. coincideswith theMIS 37/38 boundary which is 1241.2 ± 0.4 ka. The LOofH. sellii is located in late MIS 40 and has a calculated age of 1291.4 ± 1.4 ka. These biohorizons are traceable even though the LO of H. sellii is a diachronous event. Size variations of Gephyrocapsa from approximately 1250 ka are discussed and fluctuations of small size Gephyrocapsa could represent cyclic changes of the Kuroshio and Oyashio currents. [ABSTRACT FROM AUTHOR]
- Published
- 2021
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