BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 70 , Issue 6
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  • Masayuki Utsunomiya, Kiyohide Mizuno, Itoko Tamura
    2019 Volume 70 Issue 6 Pages 373-441
    Published: December 26, 2019
    Released: January 11, 2020
    JOURNALS FREE ACCESS

    The lower to middle Pleistocene Kazusa Group on central Japan is known as one of the stratotype sections of the NW Pacific region, owing to the abundant tephra beds which enable precise correlation. A robust chronological framework obtained with helps of biostratigraphy and magnetostratigraphy provide highly resolved depositional age of the tephra beds and temporal variation of the volcanic activities around this region (i.e., the Honshu and Izu-Bonin arcs). The lower Pleistocene Kiwada Formation in the Kazusa Group is a deep-marine, siltstone-dominated strata (720 m in total thickness) in which many (>200) well-preserved tephra beds are intercalated. However, there have been some confusions in the stratigraphic relation among the tephra beds.

    This paper reports stratigraphic positions, outcrop occurrences, petrographic characteristics, accompanied with major and trace element composition of volcanic glass of the selected marker tephra beds and previously undescribed tephra beds. The undescribed tephra beds were numbered in descending stratigraphic order and prefixed withKd, following notation of the previous studies. The continuous tephrostratigraphy and chemical characteristics of the tephra beds in the Kiwada Formation would contribute further investigation for regional correlation of Japanese Quaternary sections and volcanic activities around NW Pacific region.

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