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Inai Group (Otsuki, 1901) Ichikawa, 1951

Inai is named after Inai, Ishinomaki city, Miyagi pref.

There are opinions to include Rifu Formation as a top member.

• Coherent formation
• Early Triassic, Olenekian - Middle Triassic, Anisian
• Intruded by: Orikabe-1a type

• Sedimentary facies: Shallow marine
• Sedimentary facies: Continental shelf
• Sedimentary facies (Minor): Terrestrial
• Lithofacies: Sandy shale

• Thickness: 1,000 - 2,350 m
• Distribution (East-West): ca. 25 km
• Distribution (South-North): ca. 55 km
• Upper limit: Unconformity (Saragai Group, Shizukawa Group (Uchinohara Formation), Hashiura Group, Kosaba Formation, Kakeyama Conglomerate Member, Ojika Group)
• Lower limit: Unconformity (Toyoma Formation)

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

• Distribution: Minamisanriku city, Motoyoshi county - Kesennuma city, Miyagi pref.
• Fossils: Ammonoids (Hollandites sp.), Bivalves, Gastropods, Brachiopods, Crinoids, Plants

• Ehiro and Morikiyo (2013) Jour. Geol. Soc. Japan, vol.119, Supplement, pp.47-67 DOI
• Takeuchi and Mikoshiba (2002) Geology of the Senmaya District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 76p. (in Japanese with English abstract 3p.)
• Takeuchi and Kaneko (1996) Geology of the Shizugawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 93p. (in Japanese with English abstract 5p.)
• Kamada (1993) Geology of the Tsuya District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 70p. (in Japanese with English abstract 6p.)
• Kamada and Takizawa (1992) Geology of the Osu District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 69p. (in Japanese with English abstract 4p.)
• 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.)
• Takizawa et al. (1987) Geology of the Yoriiso District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 74p. (in Japanese with English abstract 5p.)
• Takizawa et al. (1984) Geology of the Ishinomaki District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 103p. (in Japanese with English abstract 7p.)
• Kambe and Shimazu (1961) Kesennuma, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 73p. (in Japanese with English abstract 16p.)