男鹿半島北浦層のKm2テフラ層と新潟地域のSK100テフラ層の対比

概要

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The early Pleistocene Km2 Tephra Bed in the Kitaura Formation in the Oga Peninsula, Akita region of northeast Japan was correlated to the SK100 Tephra Bed in the Uonuma and Taira Formations in the Niigata region, central Japan. The Km2 and SK100 Tephras are mainly composed of micropumice type glass shards, accompaning 10-38% plagioclase crystals. Biotite crystals are dominant in mafic minerals, accompaning small amount of allanite in common. Chemical composition of the glass shards are also coincident. Basal units of both Tephra Bed are similar in lithlogy. The SK100 Tephra had been revealed as a subaqueous gravity flow deposit of about 1.6Ma in the Niigata region. The continuity of this gravity flow to the Akita region, which is about 450km apart from the possible on-land volcanic source, was suggestively discussed.
2004-09-25