房総半島中部西岸・浦賀水道地域の第三系の地質構造  [in Japanese] Geological structure of the Tertiary formations in the western part of the middle Boso Peninsula and the Uraga Strait, Kanto district, Japan  [in Japanese]

房総半島西岸の三浦層群上部には, 褶曲構造が多数存在する。この三浦層群は, 下位より佐久間層, 木ノ根層, 天津層, 稲子沢層, 萩生層に区分される。鍵層にもとづいた詳細な調査から褶曲構造とその層厚の変化を明らかにした。その結果, 各層の層厚部が異なった位置に存在することから, 鋸山向斜の基本的な形態は天津層の堆積期においてほぼ形成され, また, 金谷向斜および古屋敷向斜の基本的な形態は稲子沢層上部の堆積期に形成されると推定される。沈降の中心を示すと考えられる層厚部の移動をもたらした運動は稲子沢層上部堆積時においてチャネル構造(白狐チャネル)を形成し, またこれは三浦層群の堆積盆の移動に関連すると考えられる。さらに, 浦賀水道域の音響断面の再検討し三梨・矢崎(1968)による三浦半島の層序断面図から房総・三浦両半島の三浦層群の概念的層序断面図を作成し, そこに発達する部分不整合の形態と構造的位置の相違を示した。

In the western part of the middle Boso Peninsula, many folds are developed in the Mio-Pliocene Miura Group which is subdivided in to the Sakuma, Kinone. Amatsu, Inakozawa and the Hagiu Formation in ascending order. The variation of thickness of each formation is investigated in detail on the basis of precisely correlating by the pyroclastic maker-beds. The results show that the partially thickening part of the each formation which is though to correspond to one of depocenter have the different location from each other. It is inferred that the basic form of the Nokogiriyama syncline was mostly produced during the deposition of the Amatsu Formation, though the Kanaya and the Furuyashiki synclines have began to be formd during the deposition of the upper Inakozawa Formation. The large-scale channel about 100 min depth which is found in the upper lnakozawa Formation and named the Byakko Channel in this paper, seems to be closely corrected to the tectonic movement causing the migration of depocenter of the Miura Group. By means of reexamining the seismic profiles in the Uraga Strait on the westpart of the study area, the stratigrafical profile of the study area is connected to ones of the Miura Peninsula (MITSUNASHI and YAZAKI, 1968). The schematic stratigrafical profile between the Boso and Miura Peninsula (Fig. 15) shows the morphlogy and the tectonic significance of the local unconformity in the Miura Group.