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Hibara Formation (Suzuki et al., 1964) Furukawa et al., 2018

Invalid synonym: Gomaizawa Formation (Upper volcaniclastic rocks)

• Type locality: Hibara - Araragi pass, Kitashiobara city, Yama county, Fukushima prefecture
• Coherent formation
• middle Miocene
• Correlation (Lower): Myozawabashi Formation
• Correlation: Higashiomata Formation
• Intruded by: Andesite, Rhyolite, Basalt

• Sedimentary facies: Marine
• Sedimentary facies (Minor): Terrestrial
• Sedimentary facies (Lower, Minor): Braided river
• Lithofacies (Upper): Rhyolite lapilli tuff, Tuff breccia, Tuff, Volcanic sands
• Lithofacies (Lower): Conglomerate, Sandstone
• Lithofacies (Lower, Minor): Siltstone, Basalt scoriaceous volcanic conglomerate
• Sedimentary structures: Parallel stratification, Low-angle cross-stratification

• Thickness (Upper): ca. 300 m
• Thickness (Lower): ca. 500 m
• Upper limit: Conformity (Ninosawa Formation), Unconformity (Otoge Formation)
• Lower limit: Conformity (Meganebashi Formation)

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

• Distribution: Lake Hibara - Hibara - Araragi pass - Oshio, Kitashiobara city, Yama county, Fukushima pref.

• 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.)
• Hasegawa et al. (2011) Jour. Geol. Soc. Japan, vol.117, Supplement, pp.33-48 DOI