BULLETIN OF THE GEOLOGICAL SURVEY OF JAPAN
Online ISSN : 2186-490X
Print ISSN : 1346-4272
ISSN-L : 1346-4272
Volume 65 , Issue 1-2
Bulletin of the Geological Survey of Japan
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  • Tadashi Maruyama, Masaru Saito
    2014 Volume 65 Issue 1-2 Pages 1-9
    Published: March 31, 2014
    Released: January 29, 2015
    JOURNALS FREE ACCESS
    We report occurrence and petrological characteristics of the Daisen-Kurayoshi tephra (DKP; ≥55 ka), a late Pleistocene widespread tephra in Japan, identified from borehole cores at Horinji, Nanto City, Toyama Prefecture, drilled for defining shallow subsurface geometry of the Horinji fault. DKP found from the cores contains abundant volcanic glasses compared with the heavy minerals such as orthopyroxene and hornblende, whose occurrence is very rare because the glasses are commonly altered into clay minerals. Range of refractive index of the volcanic glass, reported for the first time in and around Hokuriku region including Toyama, as well as that of orthopyroxene and hornblende, is similar to that of the source area. Result of pollen analysis of organic silt just below DKP suggests that the silt was accumulated under cool climatic condition correlated with the period of marine oxygen isotope stage (MIS) 3. Identification of intact DKP from downthrown side of the Horinji fault implies that the precise correlation of the strata or terrace surfaces of MIS 3 separated by faulting might be possible through detailed examination of the strata with tephra and pollen analyses, which provides basis for determining more reliable long-term slip rate of active faults in the Hokuriku region.
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