房総半島中部の大釜戸背斜の形成機構  [in Japanese] The formation of the Ookamado anticline in the middle part of the Boso Peninsula  [in Japanese]

The Miura Group composed of Miocene clastic sediments are distributed in many E-W trending folds at the middle part of the Boso peninsula. The formations are subdivided in to the Senhata Formation, Inakozawa Formation and the Hagiu Formation in ascending order. These formations are made up largly of alternating beds of sandstone and siltstone and contain much intercalated key tuff beds. The stratigraphical anylysis lead some results as follows. (1) the thickness and facies of these formations change near the axis of the Ookamado anticline. These changing shows that the Furuyashiki syncline was initiated during the stage of deposition of the Hagiu Formation, whereas north wing of the Ookamado anticline was not formed. It is possible to consider that the north wing of the Ookamado anticline was formed during the stage of initiating of the Higashihigasa channel structure (Middle part of the Kazusa Group) situated in the northern part of this anticline. (2) Unconformable contact by channel between the Hagiu Formation and the Inakozawa Formation was revealed at near the axis of the Furuyashiki syncline. This channel structure was formed by the rapidly northern shifting of deposition center of the Hagiu Formation. Moreover the analysis of both the Ookamado anticline and the Furuyashiki syncline by using tectonic simulation (KODAMA, et al., 1985) suggest that these folds were formed by the different stage ofmovement of basal block. It appear from the above to the closely relationship between formation of fold and northward shifting of deposition center.