妙高火山群テフラ地域南部の最新世テフラ層--示標テフラ層の記載とそれに関係した2・3の問題

概要

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The eastern region of the Myoko volcano group, Central Japan, is covered with thick tephra formations, and is called the"tephra region of Myoko volcano group". A catalogue of Pleistocene tephra layers in this tephra region was presented by HAYATSU and ARAI (1980). This paper presents the additional descriptions about some marker tephra layers distributed especially at the southern half part of this tephra region. Petrographic characteristics of six marker tephra layers such as pumice, scoria and ash layers are described in detail.In addition, the stratigraphic relations between marker tephras and non-volcanic sediments at the foot of volcanoes are shown. Some lake deposits (Sasagamine, Furuma, Mure and Nojiri lake deposits) are formed during the nearly same period respectively. Some of marker tephra, layers have their source in the volcanoes far away from the Myoko volcano group. They are usually found as very thin layers in the tephra formations, being well preserved only at the limited locations where settling of tephra proceeded rather rapidly.
日本第四紀学会の論文