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Otoge Formation (Suzuki et al., 1964) Yamamoto, 1994

Invalid synonym: Otoge Tuff, Yatani Formation, Heihachizawabashi Formation, Fudozawa Formation, Mayoizawa Mudstone

• Type locality: Kotaru river - Otoge pass, Yonezawa city, Yamagata prefecture
• Volcanic rocks
• early Pliocene
• Contemporaneous heterotopic facies: Hachimoriyama Formation, Takamine Formation, Fujitoge Formation

• Sedimentary facies (Lower): Debris avalanche deposit
• Lithofacies (Lower): Breccia

• Thickness (Lower): ca. 700 m
• Lower limit: Unconformity (Hibara Formation, Meganebashi Formation)

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

• Distribution: Kotaru river, Yonezawa city, Yamagata pref.; Otoge pass, Yamagata pref. - Fukushima pref.
• Deposit: Yatani Mine, Otoge Kaoline-Pyrophyllite deposit

• Furukawa et al. (2018) Geology of the Azuma Yama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 74p. (in Japanese with English abstract 3p.)