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Koani Formation Saito and Ozawa, 1956

• Type locality: Kamikoani city, Kitaakita county, Akita prefecture
• Coherent formation
• Miocene
• Contemporaneous heterotopic facies: Koyanotani Formation, Aniai Formation

• Lithofacies: Shale, Basalt sill
• Lithofacies (Minor): Spilitic basalt lava, Pyroclastic rocks

• Upper limit: Conformity (Onnagawa Formation)

• Distribution: Kamikoani city, Kitaakita county, Akita pref.; upper reaches of Babame river, Gojome city, Minamiakita county, Akita pref.
• Fossils (Foraminifera): Cyclammina sp.

• Hase and Hirayama (1970) Geology of the Gojome District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 46p. (in Japanese with English abstract 6p.)