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Osawa Formation Chihara et al., 1981

• Type locality: Mount Osawa, Shiozawa, Minamiuonuma city, Niigata prefecture
• Coherent formation
• Miocene
• Correlation: Teradomari Formation
• Intruded by: Kiyotsukyo Quartz diorite porphyry
• Intruded by (Sills): Augite hypersthene andesite, Pyroxene andesite

• Lithofacies (Upper): Interbedded glauconite-bearing sandstone and shale
• Lithofacies (Upper, Minor): Tuff, Conglomerate
• Lithofacies (Lower): Andesite tuff, Volcanic sandstone, Shale
• Lithofacies (Lower, Minor): Andesite breccia
• Sedimentary structures (Lower): Slump structures, Parallel stratification

• Thickness: ca. 150 - 700 m
• Upper limit: Conformity (Mugurazawa Formation), Unconformity (Uonuma Formation)
• Lower limit: Conformity (Uwano Formation)

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

• Distribution: Mount Osawa, Shiozawa, Minamiuonuma city, Niigata pref.; Junitoge pass, Minamiuonuma city, Niigata pref.; Kiyotsu river - Shibakura river - Mount Mitako, Tokamachi city, Niigata pref.
• Fossils: Plants (Paliurus cfr. protonipponicus), Foraminifera

• Shimazu and Tateishi (1993) Geology of the Naebasan District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 90p. (in Japanese with English abstract 5p.)
• Yanagisawa et al. (1985) Geology of the Tokamachi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 104p. (in Japanese with English abstract 6p.)
• Chihara et al. (1981) Geology of the Echigo-Yuzawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 108p. (in Japanese with English abstract 8p.)