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Nakahara Formation Mori, 1947
- Type locality: Okinagura, Kitakami town, Ishinomaki city, Miyagi prefecture
- Type locality (Sub): Mitobe river, Shizukawa, Minamisanriku city, Motoyoshi county, Miyagi prefecture
- Type locality (Original): Nakahara, Kitakami town, Ishinomaki city, Miyagi prefecture
- Coherent formation
- Middle Jurassic, Bajocian
- Correlation: Aratozaki Formation, lower Arato Formation
- Intruded by: Okayazawa Mass
- Sedimentary facies: Marine
- Lithofacies: Sandy shale
- Lithofacies (Minor): Sandstone, Shale
- Lithofacies (Basal): Conglomerate, Sandstone
- Sedimentary structures: Cross stratification
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Okinagura - Honji, Kitakami town, Ishinomaki city, Miyagi pref.; Mitobe river, Minamisanriku city, Motoyoshi county, Miyagi pref.; Nakahara, Kitakami town, Ishinomaki city, Miyagi pref.; Nojiri, Tsuyama town, Tome city, Miyagi pref.
- Fossils: Ammonoids (Holophylloceras sp., Seymourites sp.), Nautiloids, Belemnoids (Belemnopsis sp.), Crabs (Anaptychus sp.), Gastropods, Plants
- Fossils (Bivalves): Biplices sp., Chlamys sp., Inoceramus aff. galoi, Inoceramus cf. haasti, Inoceramus hashiurensis, Oppelia sp., Plagiostoma sp., Retroceramus sp., Vaugonia sp.
- Takizawa et al. (1990) Geology of the Toyoma District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 126p. (in Japanese with English abstract 8p.)