<国立科博専報>秋田県西部の下部グリン・タフ層序

概要

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The lower Neogene volcanogenic rock sequences, so-called green tuff, in the Dewa Mountains of Akita Prefecture were divided into the following five formations; the Yuno-sawagawa, Okachigawa, Iizawa-Saragawa, Daisenyama-Hatamura, and the Sugota For-mations in ascending order. Although the Nozoki and Yokonetoge Formations were used formerly for the volcanic rocks of Palaeogene to early Middle Miocene in Akita Prefecture, they are subdivided into the formations mentioned above (except the Sugota Formation) in this paper. The volcanogenic rocks of the Late Cretaceous to the early Middle Miocene in the Akita-Yamagata area were divided into five groups (I-V) based on their correlation. The group I (Late Cretaceous), II (Palaeognee) and III (Early Miocene) are terrestrial acid pyroclastic rocks occurring exclusively in the coastal and mountain areas along the Japan Sea. They have not been found in the Ou Backbone Range. The group IV (Early Miocene) and V (early Middle Miocene) consist mainly of andesitic to basaltic rocks with similar lithofacies and occur widely in the Akita-Yamagata area. Judging from the mode of occurrence of volcanic rocks, the volcanisms seem to have been terrestrial from Late Cretaceous to Early Miocone and subsequemly shifted into the subaqueous ones at the later stage of Early Miocene. The marine transgression in the early stage of Middle Miocene submerged many parts of the area.
国立科学博物館の論文
1983-12-01