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Usuizawa Formation Hirayama and Sumi, 1963

• Type locality: Terazawa - Fujikoto river - Usuizawa, Kasuge, Fujisato city, Yamamoto county, Akita prefecture
• Coherent formation
• Pliocene

• Sedimentary facies: Marine
• Water temperature: Cold ocean current
• Lithofacies: Sandstone
• Lithofacies (Minor): Interbedded siltstone and sandstone, Conglomerate, Dacitic pumice tuff

• Thickness: 400 m or thicker
• Lower limit: Transitional (Kobinaizawa Formation)

• Distribution: Terazawa - Fujikoto river - Usuizawa, Kasuge, Fujisato city, Yamamoto county, Akita pref.
• Fossils (Omma-Manganji fauna): Acila cf. insignis, Anadara cf. amicula, Callista? sp., Chlamys sp., Diplodonta sp., Dosinia cf. angulosa, Dosinia japonica, Glycymeris yamasakii, Kaneharaia cf. kaneharai, Lucinoma acutilineata, Macoma cf. oinomikadoi, Macoma cf. praetexta, Mercenaria chitaniana, Mercenaria cf. yokoyamai, Mya cuneiformis, Patinopecten sp., Peronidia venulosa, Pitar sp., Protothaca adamsi, Saxidomus? sp., Serripes laperousi, Thracia kakumana, Thracia kamayashikiensis, Turritella cf. saishuensis motizukii, Vasticardium shiobarense, Venericardia sp., Yoldia notabilis

• Hirayama and Sumi (1963) Takanosu, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 90p. (in Japanese with English abstract 7p.)