On the Nize Tuff in Akita Oil Field

Abstract

Abstract: In 1936, the igneous rocks which are developed at Nize pass and the upper course of Babanome river, east of Gojome in Akita prefecture, are called "Nize Tuff" by Omura and he considered that these rocks consist mainely of basaltic and intrusive rocks of the pre-Onnagawa stage.
According to the recent studies of the writers, the Nize tuff is not so simple as Omura considered, it is pyroclastic compound of Sunakobuchi formation, Onnagawa formation, dolerites, basaltic andesite and Manaitayama volcanic rocks. Excepting the Sunakobuchi formation, others are developed at the Nize pass, the type locality of the Nize tuff. They are effusive and intrusive products of the Onnagawa or the post-Onnagawa stage, and are clearly younger than the Nize tuff which Omura defined. The Sunakobuchi formation, which consists mainly of spilitic basalt and is older than the Onnagawa formation, does not expose at environs of the Nize pass, though it is widely distributed at eastern border of Akita oil field.
The name of Nize tuff must be abolished or redefined, though it has been used by many oil geologist for long time.