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Akima Formation (Fujimoto and Kobayashi, 1938) Akima Collaborative Research Group, 1971

• Type locality: Akima river, Morikuma - Chojakubo, Nishikamiakima, Annaka city, Gunma prefecture
• Volcanic rocks
• late Miocene - early Pleistocene (ca. 6.6 - 0.9 Ma)
• Upper: early Pleistocene (ca. 2.4 - 0.9 Ma)
• Lower: late Miocene - Pliocene (ca. 6.6 - 4.1 Ma)
• Contemporaneous heterotopic facies: Ainokawa Formation

• Sedimentary facies: Volcanic-fan deposit, Fluvial
• Sedimentary facies: Pyroclastic flow deposit, Debris flow deposit, River bed deposit
• Lithofacies: Tholeiite, Calc-alkaline
• Lithofacies: Tuffaceous sandstone, Tuff breccia
• Paleocurrent: from West

• Source: Aimagawa Formation
• Thickness: ca. 1,000 m
• Thickness (Lower): ca. 550 m
• Upper limit: Unconformity (Older Haruna Volcanic Fan Depostis, Jizotoge Formation)
• Lower limit: Bottom of the horizon containing pyroxene andesite boulders
• Lower limit: Angular unconformity (Itahana Formation)

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

• Distribution: Akima river, Morikuma - Chojakubo, Nishikamiakima, Annaka city, Gunma pref.; Chimase - Annakaharuna station - Itahana, Annaka city, Gunma pref.

• Geshi and Takeuchi (2012) Geology of the Haruna San District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 79p. (in Japanese with English abstract 3p.)