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Kusanagi Formation Iizuka, 1924

• Type locality: Mogami river, Kusanagi, Tozawa city, Mogami county, Yamagata prefecture
• Coherent formation
• middle Miocene (Radiolarians, Diatoms)
• Contemporaneous heterotopic facies: Onnagawa Formation
• Correlation: Otaki Formation
• Intruded by: Andesite, Rhyolite, Dolerite

• Sedimentary facies: Marine
• Sedimentary facies: Inland sea
• Sedimentary facies: Reductive, Stagnant water
• Water temperature: Cold ocean current
• Lithofacies: Siliceous mudstone
• Lithofacies (Minor): Acidic tuff, Andesite pyroclastic rocks, Sandstone

• Thickness: 500 - 900 m
• Upper limit: Transitional (Kitamata Formation), Conformity (Furukuchi Formation), Unconformity (Owarabi Debris Avalanche Deposit)
• Lower limit: Transitional (Okawa Formation, Ishifutagarisawa Mudstone Member), Conformity (Aosawa Formation, Oyama Formation)

------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown

• Distribution: Mogami river, Kusanagi, Tozawa city, Mogami county, Yamagata pref.; Nikko river - Matsumine - Kitaaosawa - Ennoji - Sakamoto, Sakata city, Yamagata pref.; Osawa river - Myojin creek - Takasaka - Mansuke river - Oguni river, Mamurogawa city, Mogami county, Yamagata pref.; Oashi creek, Sakegawa city, Mogami county, Yamagata pref.; Karikawa - Mount Haguro - Yamazaki, Shonai city, Higashitagawa county, Yamagata pref.; Soegawa - Toge, Tsuruoka city, Yamagata pref.
• Fossils: Fish scales, Sponges (Makiyama chitanii)
• Fossils (Foraminifera): Bathysiphon sp., Cribrostomoides renzi, Cribrostomoides subglobosum, Cyclammina cancellata, Cyclammina japonica, Cyclammina pusilla, Globigerina bulloides, Globigerina falconensis, Globigerinita glulinata, Goesella schencki, Hormorsina sp., Martinottiella communis, Orbulina universa, Praeglobobulimina pupoides, Pyrgo sp., Quinquetoculina seminulum, Sphaeroidinellopsis seminulina, Sphaeroidinellopsis subdehiscens, Spirosigmoilinella compressa, Uvigerina sp., Valoulineria sadonica
• Fossils (Radiolarians): Cromydruppa concentrica, Cycladophora sp., Cyrtocapsella japonica, Cyrtocapsella tetrapera, Diartus sp., Didymocyrtis spp., Druppatractus irregularis, Eucyrtidium inflatum, Hexacontium sp., Larcospira spp., Lithocarpium spp., Porodiscus spp., Rhopalodictyum spp., Sethocyrtis japonica, Spongodiscus spp., Spongoplegma variabilis, Stichocorys delmontensis, Theocorys japonica, Theocyrtis redondoensis
• Fossils (Nannofossils): Braarudosphaera bigelowii, Calcidiscus leptoporus, Calcidiscus macintyrei, Coccolithus pelagicus, Dictyococcites perplexus, Dictyococcites productus, Discoaster bergrenii, Discoaster intercalaris, Discoaster pentaradiatus, Discoaster quinqueramus, Discoaster variabilis, Helicosphaera carteri, Pyrocyclus innersus, Reticulofenestra gelida, Reticulofenestra haqii, Reticulofenestra minuta, Reticulofenestra minutula, Reticulofenestra pseudoumbilica, Sphenolithus obies, Sphenolithus compactus, Sphenolithus cf. moriformis, Sphenolithus cf. verensis

• Moriya et al. (2008) Jour. Geol. Soc. Japan, vol.114, no.8, pp.389-404 DOI
• Moriya et al. (2008) Jour. Geol. Soc. Japan, vol.114, no.1, pp.1-15 DOI
• Nakano and Tsuchiya (1992) Geology of the Chokaisan and Fukura District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 138p. (in Japanese with English abstract 7p.)
• Tsuchiya (1989) Geology of the Osawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 85p. (in Japanese with English abstract 6p.)
• Tsuchiya et al. (1984) Geology of the Tsuruoka District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 77p. (in Japanese with English abstract 5p.)
• Ikebe et al. (1979) Geology of the Sakata District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 42p. (in Japanese with English abstract 3p.)