scholarly journals Calcareous nannofossil biostratigraphy and geologic age of the Kiyosumi Formation of the Awa Group, Boso Peninsula, central Japan: Age determination based on size variations of Reticulofenestra specimens

2010 ◽  
Vol 116 (10) ◽  
pp. 563-574 ◽  
Author(s):  
Koji Kameo ◽  
Ryota Shindo ◽  
Toshiaki Takayama
Keyword(s):  
Age Determination ◽  
Calcareous Nannofossil ◽  
Central Japan ◽  
Boso Peninsula ◽  
Calcareous Nannofossil Biostratigraphy

Oxygen isotope stratigraphy and calcareous nannofossil biostratigraphy of the Lower Pleistocene in the Boso Peninsula, central Japan

Stratigraphy ◽  
2021 ◽  
Vol 18 (2) ◽  
Author(s):  
Daisuke Kuwano ◽  
Yoshimi Kubota ◽  
Kanako Mantoku ◽  
Koji Kameo
Keyword(s):  
Oxygen Isotope ◽  
Northwestern Pacific ◽  
Calcareous Nannofossil ◽  
Boso Peninsula ◽  
Oxygen Isotope Stratigraphy ◽  
Age Model ◽  
Calcareous Nannofossil Biostratigraphy ◽  
Isotope Stratigraphy ◽  
Pacific Coast Of Japan ◽  
Cyclic Changes

ABSTRACT: Oxygen isotope stratigraphy and calcareous nannofossil biostratigraphy in the upper part of the Kiwada Formation, which is part of the Kazusa 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 micrometers) and Helicosphaera sellii,were recorded in the examined section. The LO of large Gephyrocapsa spp. coincides with the MIS 37/38 boundary which is 1241.2 plus or minus 0.4 ka. The LO of H. sellii is located in late MIS 40 and has a calculated age of 1291.4 plus or minus 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.

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