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Koyamada Formation Masatani, 1950

• Type locality: western Koyamada, Kashima ward, Minamisoma city, Fukushima prefecture
• Coherent formation
• Early Cretaceous, Berriasian - Valanginian (Ammonoids, Radiolarians)
• Correlation: Futawatashi Shale Member, Isokusa Formation

• Sedimentary facies: Marine
• Lithofacies (Top): Sandstone
• Lithofacies (Upper): Shale
• Lithofacies (Upper, Minor): Siliceous shale, Acidic tuff
• Lithofacies (Lower): Sandstone
• Lithofacies (Lower, Minor): Tuffaceous sandstone, Shale, Dacitic tuff

• Thickness: 70 - 650 m
• Upper limit: Unconformity (Neogene)
• Lower limit: Bottom of tuffaceous sandstone bed or shale bed
• Lower limit: Transitional (Tomizawa Formation)

• Distribution: Koyamada - Oyama - Koike - Tochikubo, Kashima ward, Minamisoma city, Fukushima pref.; Ohara - Baba, Haramachi ward, Minamisoma city, Fukushima pref.
• Fossils: Nautiloids, Belemnites (Hibolithes sp.), Gastropods
• Fossils (Ammonoids): Berriasella sp., Dalmasiceras muneoi, Kiliamella umazawensis, Kilianella sp., Kilianiceras sp., Neocosmoceras akiyamae, Paraboliceras cf. fascicostatus, Parakilianella umazawensis, Thurmanniceras isokusense, Virgatosphinctes cf. rotundicus
• Fossils (Bivalves): Grammatodon takiensis, Parallelodon aff. inflatus, Astarte kambarensis, Neocrassina cf. subdepressa, Protocardia tosensis, Myophorella orientalis�AEntolium kimurai, Corbula? globosa, Myophorella sp.
• Fossils (Radiolarians): Acaeniotyle umbilicata, Alievium regulare, Archaeodictyomitra sp., Cecrops cf. septemporatus, Cryptamphorella dumitricai, Dicerosaturnalis dicranacanthos, Hemicryptocapsa capita, Holocryptocanium barbui, Obesacapsula verbana, Pantanellium squinaboli, Pseudodictyomitra carpatica, Sethocapsa aff. kaminogoensis, Sethocapsa utrbulus, Sethocapsa? zweilii, Svinitzium depressum, Svinitzium pseudopuga, Tethysetta boesii, Xitus cf. spicularius, Zhamoidellum sp.

• Sano et al. (2015) Jour. Geol. Soc. Japan, vol.121, no.2, pp.71-79 DOI
• Taketani and Osozawa (2013) Jour. Geol. Soc. Japan, vol.119, Supplement, pp.68-81 DOI
• Yanagisawa et al. (1996) Geology of the Somanakamura District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 114p. (in Japanese with English abstract 9p.)
• Kubo et al. (1990) Geology of the Haramachi and Omika District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 138p. (in Japanese with English abstract 7p.)
• Fujita et al. (1988) Geology of the Kakuda District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 99p. (in Japanese with English abstract 9p.)