抄録
The Akima and upper part of Itahana formations of the Neogene system are distributed between Usui- and Karasu-gawa which are tributaries of Tone-gawa. 1) The Akima formation consists most of tuff breccia and it is divided by lithofacies into six members and one welded tuff bed. The stratigraphic succession is as follows. Jizotoge tuff breccia member Chojakubo tuff breccia member Aiyoshi tuff breccia member Chausuyama welded tuff bed Odogai conglomerate, tuff breccia member Nagaiwa tuff breccia member Morikuma tuff breccia member (Akima formation) Kakihira conglomerate member (Itahana formation) 2) Lavas, dykes and sheet in the Akima formation are distributed only in the western part of this area. Likewise, the Akima formation in the west is larger in the thickness and richer in the lithofacies than in the east. 3) The Akima formation overlies unconformably the Itahana formation. 4) The upper part of Itahana formation which mainly consists of conglomerate is intercalated with four key beds consisting of tuff. 5) The beds in this Neogene system are generally inclined northward monoclinally and there are some faults and folds.
