Abstract
Key tephra bed 'Kd38' occurs near the boundary between Tertiary and Quaternary. The tephra, characterized by the presence of Fe-rich orthopyroxene, had been confirmed at many localities in central Boso Peninsula and Choshi area. In this study, we confirmed the tephra at one or two study routes in the Chikura Group, southern part of the Boso Peninsula mainly based on chemical composition of orthopyroxene in the tephras, referring to the results of microfossil and paleomagnetism studies.
In the Hata path, 'HT08B' and 'HT07' tephras are correlated to the key tephra beds 'Kd38' and 'Kd39' in the central Boso Peninsula, respectively. In the Yamakura path, 'YK03' tephra corresponds to the key tephra bed 'Kd39', and it seems that 'YK04C' tephra can be correlated to the key tephra bed 'Kd38'.
Both the key tephra beds 'Kd38' and 'Kd39' were confirmed to occur at the Yokohama area from Miura Peninsula. 'YH10' and 'YH02' tephras in the Hitorizawa route are correlated to 'Kd38' and 'Kd39', respectively. 'Tzc' tephra from Niigata Prefecture is one of famous tephra beds corresponding to the key tephra bed 'Kd38'. It was reconfirmed by the compositional variations of orthopyroxenes in this study.
