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Kosho Mudstone Member Kanno and Arai, 1964 (Photo)
Invalid synonym: Kosho Formation, Higashiirino Formation
- Type locality: Akikawa river, Kosho, Akiruno city, Tokyo
- Coherent formation
- middle Miocene
- Lithofacies: Mudstone
- Lithofacies (Minor): Sandstone, Conglomerate, Tuff
- Sedimentary structures: Slump structures
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Akiruno river - Itsukaichi - Sannai river - Hirai river, Akiruno city, Tokyo; Kawaguchi river, Hachioji city, Tokyo; Shiozawa, Oguno, Hinode city, Tokyo
- Fossils: Crabs, Ophiuroids, Storomatolite
- Fossils (Shellfishes): Akebiconcha chitanii, Macoma optiva, Malletia (Neilo) inermis, Natica sp., Nuculana pennula, Portlandia (Hataiyoldia) tokunagai, Solemya (Acharax) tokunagai, Turritella itsukaichiensis, Venericardia (Cyclocardia) siogamensis
- Fossils (Foraminifera): Ammonia beccarii, Amphicaryna scalaris, Brizalina fujimotoi, Brizalina pisciformis, Buccella akahiraensis, Cassidulina sp., Cibicides asanoi, Cribroelphidium yabei, Cyclammina cf. incisa, Cyclammina pusilla, Dorothia sp., Epistominella naraensis, Globobulimina sp., Haplophragmoides sp., Lenticulina sp., Melonis pacificus, Nonionella miocenica, Trifarina kokozuraensis
- Ueki and Sakai (2007) Geology of the Ome District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 189p. (in Japanese with English abstract 5p.)
- Sakai (1987) Geology of the Itsukaichi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 75p. (in Japanese with English abstract 5p.)