長野県犀川下流域の新第三系

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1) The Neogene formations are widely distributed in this area, with following lithostratigraphic succession in ascending order; Asakawa mudstone member, Lower Susobana tuff member, Upper Susobana tuff member, Sakainomiya sandstone and mudstone member, Funakubo mudstone member, Imori sandstone member, Sewaki mudstone member, Takafu mudstone member, Ichinose sandstone member, Gonda conglomerate and sandstone member, Joshita sandstone and conglomerate member, Arakurayama pyroclastics member and Hirose mudstone member. 2) The Susobana tuff member is covered with partial unconformity by Imori sandstone member. 3) The folded system of the area is divided into three groups. The Sumeragi anticline, Saikawa anticline and Joshita syncline, all developed in the western part of the area, are asymmetric folds, and their axial planes dip to the northwest. The Odagiri anticline, Naniai syncline, Jinda anticline and the folds within the Susobana tuff member are found in the eastern part of the area, and they are symmetric folds with vertical axial planes and southwest plunges. In the northern part of the area the geologic structure is monoclinic, 4) The Sumeragi anticline shows a north-south trend in its southern part, a northeast-southwest trend in its central part and an east-west trend in its northeastern part. It plunges southward, while it disappears in the northeast where it is intersected by the Joshita syncline. 5) The Asakawa mudstone member, correlated to the Aoki formation, is characterized by a gentle geologic structure, and is thin compared with the Aoki formation in the Takafu synclinal area. These characters suggest a marginal area of a basin, and are similar to those of the formations on the Central Upheaval Zone of the Northern Fossa Magna, The area of the Asakawa mudstone member is situated in the western marginal area of the Central Upheaval Zone.
日本地質学会の論文
1976-12-30

長野県犀川下流域の新第三系

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