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Ako Formation (Kishida and Wadatsumi, 1967) Sato et al., 2016
- Type locality: Mount Tomiyama, Aioi city, Hyogo prefecture
- Type locality (Welded tuff): Sogo, Bizen city, Okayama prefecture - Fukuura, Ako city, Hyogo prefecture
- Volcanic rocks
- Late Cretaceous (82.6 Ma, U-Pb; 73 Ma, K-Ar)
- Intruded by: Tenkadaiyama Rhyolite, Aioi Body, Osaki Body, Shioya Body
- Sedimentary facies: Caldera-fill deposits
- Sedimentary facies: Valles type caldera
- Lithofacies: Pyroclastic flow deposits
- Lithofacies (Upper): Dacite - Rhyolite welded crystalline tuff
- Lithofacies (Middle): Rhyolite welded lapilli tuff, Tuff
- Lithofacies (Middle, Minor): Breccia
- Lithofacies (Lower): Dacite crystalline tuff
- Lithofacies (Bottom, Minor): Tuffaceous siltstone, Sandstone
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Mount Tomiyama - Fukuura - Kariya - Misaki - Osaki, Ako city, Hyogo pref.; Aioi - Iwashihama, Aioi city, Hyogo pref.; Mitsu town, Tatsuno city, Hyogo pref.; Sogo, Bizen city, Okayama pref.
- Sato et al. (2016) Geology of the Banshu-Ako District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 68p. (in Japanese with English abstract 3p.)
- Igi and Wadatsumi (1980) Geology of the Kamigori District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 74p. (in Japanese with English abstract 4p.)