Correlation of the late Pliocene Tzw-Smg-Tnkw-Jic Tephra Beds in the Niigata region, northeast Japan

概要

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The late Pliocene Tzw Tephra Bed is intercalated in the middle Nishiyama Formation 10m above the Ftj-UN Tephra Bed in the Chuo Oil Field. The Tzw was correlated to the Smg Tephra Bed in the Nishiyama Oil Field and also to the Tnkw Tephra Bed in the Kuwae Formation along the Tainai River, northern Niigata region by means of their horizon, field occurrences, petrography and chemical composition of glass shards. The Smg Tephra Bed was so far correlated to the Jic Tephra Bed in the Kawauchi Formation in Sado Island. Thus, the Tzw-Smg-Tnkw-Jic Tephra Bed was revealed to be one of the widespread fallout tephra beds of late Pliocene in the Niigata region, distributed in the area of more than 100x60km^2. This Tephra Bed is possibly situated between the two geologically important marker horizons; that is above the boundary of the fossil diatom zones of the Neodenticula koizumii - N. kamtschatica Zone and the Neodenticula koizumii Zone, and also just below the boundary of the Gauss and Matuyama Chrons in magnetostratigraphy. The age of the Tzw Tephra Bed as the general name is assumed to be around 2.6Ma.
新潟大学の論文
2004-02-27