前進するファンデルタシステムの堆積相
北部フォッサマグナ犀川背斜地域の上部中新統と鮮新統
1993 年 39 巻 39 号 p. 15-25
詳細
1993 年 39 巻 39 号 p. 15-25
The study area is situated at the southern part of the Northern Fossa Magna region and is underlain by Miocene to Early Pliocene sedimentary rocks. The Miocene rocks are divided into the Aoki and Ogawa Formations. Lower Pliocene is newly named the Ashinojiri Formation. Aoki Formation is mainly composed of mudstone and sandstone. Ogawa and Ashinojiri Formations are mainly composed of sandstone and conglomerate. Ogawa Formation interbedded with acidic tuff layer (Koso Tuff) which can make a useful key bed of this area.
These formations are divided into ten sedimentary facies. On the basis of the facies analysis, they were deposited at the slope, shelf and nearshore environments, and also they formed a fan delta system. The fan delta system consists of the progradational stage and aggradational stage. The fan delta prograded to the basin and coarse materials were deposited on the slope in the progradational stage. While in the aggradational stage, the coarse materials were deposited on the shelf. The slope prograded during the progradational stage, and the shelf was filled up by aggradation of sediments.
