群馬県西部霧積(きりづみ)川東方の地質

概要

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The Kirizumi Formation of the Neogene System is distributed along the River Kirizumi in the western part of Gunma Prefecture, Central Japan. The eastern part of the River Kirizumi is adjacent to the area of the northern part of Annaka City, where the Akima Formation is developed. Geological characters of the Kirizumi Formation are as follows. 1) The Kirizumi Formation consists mainly of pyroclastic rocks, lava flows and several andesite dykes, and is divided into four members. Their stratigraphic succession and the relations to the superjacent and subjacent formations are shown in the following table. [Table] 2) Altered green tuffs are found in the Kirizumi Formation in several parts of the Kirizumi-gawa valley. 3) The Kirizumi and the Akima Formations are heterotopic but contemporaneous sediments. 4) The Kirizumi Formation contains partially lake deposits at several horizons, and has many lava flows. 5) The Kirizumi Formation overlies unconformably the Itahana Formation of marine and brackish sediments.
日本地質学会の論文
1976-12-30