著者

宮坂 省吾 山崎 茜 岡村 聡 英 弘 石井 正之 小板橋 重一

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.113, no.Supplement, pp.S19-S28, 2007 (Released:2009-01-27)

参考文献数

30

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札幌市の西に広がる後志火山性台地は,中新世後半から更新世にかけて形成された溶岩台地で,平坦面溶岩が広く分布しその火山原面が残されている.また,活発な火山活動は変質作用を伴い,多くの金属資源が開発されてきた.これらの地質要因を背景とする大規模地すべりを含む地すべり地形が広く分布し,時には自然災害としてあるいは開発行為を契機に地すべり活動が発生している.この見学コースでは,地質時代に発生した山体崩壊と岩屑なだれ堆積物,周氷河斜面堆積物を母材とした地すべりを観察する.

著者

保柳 康一 三戸 望 吉岡 正俊 宮坂 省吾 渡辺 寧 松井 愈

出版者

地学団体研究会

雑誌

地球科學 (ISSN:03666611)

巻号頁・発行日

vol.39, no.6, pp.393-405, 1985-11-25

被引用文献数

6

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Thick Miocene sediments are distributed in the Ishikari-Teshio Belt along the western side of the Kitami mountain range in the north and the Hidaka mountain range in the south. In the southern part of this belt, the Miocene sequences are divided into the Furanui, Ukekoi, and Motokanbe Formations, in ascending order. The Furanui Formation (early Middle Miocene) consists mainly of greenish gray sandstones and mudstones The Ukekoi Formation (Middle Miocene) composed mainly of alternating beds of sandstone and mudstone and conglomerates, attains a maximum thickness of about 2,100 meters, which is correlated with the Kawabata Formation in the Ishikari district and the Kotanbetsu Formation in the Haboro district. The Motokanbe Formation (Late Miocene) consists mainly of hard shales and subordinate intercalated conglomerates. The Ukekoi Formation is subdivided lithologically into the U_1, U_2, and U_3 members in ascending order. The U_1 and U_3 are composed mainly of alternating beds of sandstone and mudstone with Bouma sequences, and the U_2 member consists of coarse clastic sediments with grading and imbrication structures developed well in the conglomerates. These facies are of turbidites and their related sediments. In the southern part of the studied area, these three members change laterally into the U4 member composed of alternating beds of sandstone and mudstone. The distribution pattern of these members can be assingned to the submarine fau environmental models of WALKER and MUTTI (1973) or WALKER (1978). The U_2 member is of the upper fan channel-fill deposits in the northern part of this area and of mid-fan deposits in the central part. The U_4 member in the southern part corresponds to the lower fan depoosits. The upper fan main channnel contains numerous smaller channels 10 meters or more deep and some 100 meters wide. These channels are filled with coarse clastic sediments transported from the north. On the basis of the above-mentioned discussion with the examination of the conglomerates, it is concluded that the Middle Miocene Ukekoi Formation is of submarine fan deposits transported far from the northern part of the Hidaka and Kamuikotan Belts, e. g. the Uenshiri Horst, while the Upper Miocene Motokanbe Formathionis of fan delta deposits derived from the eastern adjacent hinterland of the Hidaka Metamorphic Belt.