著者

中条 武司 中西 健史 前島 渉

出版者

地学団体研究会

雑誌

地球科学 (ISSN:03666611)

巻号頁・発行日

vol.47, no.6, pp.473-484, 1993-11-25 (Released:2017-06-06)

被引用文献数

3

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The early Middle Miocene Togane Formation is one of the Miocene basin-fills in the Setouchi Province of Southwest Japan. Togane sedimentation took place during eustatic sea-level rise in the Early to Middle Miocene. The Togane Formation unconformably overlies the Paleogene Kokufu Volcanic Rocks. The formation is 200m thick, and is lithostratigraphically subdivided into four members in ascending order: the Toganegawa Mudstone, Anegahama Sandstone, Kanaso Conglomerate and Sandstone, and Tatamigaura Sandstone Members. The Toganegawa Mudstone Member (up to 70m thick) is dominated by massive mudstone with a conglomerate unit at the base. The Anegahama Sandstone Member (65m thick) is mainly composed of fine- to medium-grained sandstone with subordinate muddy sandstone and conglomerate. The Kanaso Conglomerate and Sandstone Member (20 to 30m thick) shows a remarkable N-S facies change. In the south, the member is characterized by a thick succession of conglomerates, which interfinger with coarse-grained, pebbly sandstones to the north. The Tatamigaura Sandstone Member (more than 40m thick) consists of fine- to medium-grained sandstone and muddy sandstone. The Togane Formation appears to infill a N-S oriented depression in the basement rocks, with the basin configuration controlled by the preexisting topography. The Togane basin developed due to regional downwarping in the Setouchi Province.