北部フォッサマグナ高府向斜地域に分布する前期鮮新世下部柵層の堆積相と堆積環境
1996 年 43 巻 43 号 p. 47-58
詳細
1996 年 43 巻 43 号 p. 47-58
The early Pliocene Lower Shigarami Formation is well developed in the Takafu syncline of the northern Fossa Magna region. This formation is divided into the Gonda conglomerate and sandstone member in the southern part of this district and the Takafu mudstone member in the north. The both members show interfingering relationship each other. It has been stated that the former member deposited at fan delta environment and the latter at off-shore. In this study details of the depositional conditions in the two members were clarified as follows.
1. The Lower Shigarami Formation is composed of 11 sedimentary facies, which were formed under a fan delta system on the shelf and a channel system on the continental slope.
2. These sedimentary systems are descriminated as two stages; namely, Stage 1 and Stage 2. At the Stage 1, a fan delta prograded from the southeast and turbidites in the north of this district was supplied from a fan delta on the east. And at the last of Stage 1, outer shelf environment extended to all over this area. At the Stage 2, the sedimentary environment in the south changed from outer shelf to delta front due to fan delta progradation at the early, and delta plane extended to the north at the later.
