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Rifu Formation Ichikawa, 1951

Some opinions defines Rifu Formation as a top member of Inai Group.

• Type locality: Hamada, Rifu city, Miyagi county, Miyagi prefecture
• Coherent formation
• Triassic, Anisican - Ladinian (Ammonoids)
• Intruded by: Hornblende porphyry, Plagioclase porphyry

• Sedimentary facies: Marine
• Lithofacies: Shale
• Lithofacies (Minor): Sandy shale, Sandstone

• Thickness: 500 - 700 m or thicker
• Upper limit: Unconformity (Shiogama Formation, Ajiri Formation, Hataya Formation, Tomegaya Formation, Toguhama Formation), Abut unconformity (Sauramachi Formation)

• Distribution: Hamada - Miyamae - Morigo, Rifu city, Miyagi county, Miyagi pref.; Mount Anetori, Matsushima city, Miyagi county, Miyagi pref.; Takasaki - Higashitanaka, Tagajo city, Miyagi pref.
• Fossils: Cephalopods (Atractites hataii), Fishes, Plants (Lepidodendron? sp.), Trace fossils (Rhizocorallium isp.)
• Fossils (Ammonoids): Anogymnites aff. acutus, Arpadites? sp., Beyrichites chitanii, Danubites sp., Epigymnites aff. jollyanus, Flexoptychites matsushimaensis, Gymnotoceras paucicostatus, Hollandites nipponicus, Hungarites nipponicus, Japonites cf. dieneri, Japonites aff. ugra, Kellnerites cf. bosnensis, Monophyllites sphaerophyllus, Monophyllites wengensis, Nevadites? angusticostatus, Nevadites? japonicus, Paraceratites cf. clarkei, Paraceratites orientalis, Paraceratites cf. trinodosus, Paraceratites cf. wardi, Protrachyceras reitzi, Ptychites aff. cognatus, Ptychites compressus, Ptychites compressus hamadaensis, Ptychites miyagiensis, Ptychites nipponicus, Ptychites rifunus, Ptychites cf. trocheaeformis, Ptychites yabei, Tropigastrites aff. halli
• Fossils (Nautiloids): Pleuronautilus (Holconautilus) yabei, Syringonautilus japonicus
• Fossils (Bivalves): Daonella densisulcata, Daonella kotoi, Megalodosus sp., Myoconcha hamadaensis, Nucula? sp., Pecten sp., Pedalion sp.
• Fossils (Gastropods): Coelostylina (Coelostylina?) aff. abbreviata, Lepodotrichus? hataii, Mellarium aff. nodulosum, Pleurotomaria (Eymarella?) aff. praebaucis
• Fossils (Brachiopods): Spiriferina kaneharai, Spiriferina cf. lilangensis

• Kamada (1993) Geology of the Tsuya District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 70p. (in Japanese with English abstract 6p.)
• Kitamura et al. (1986) Geology of the Sendai District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 134p. (in Japanese with English abstract 9p.)
• Kitamura et al. (1983) Geology of the Yoshioka District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 50p. (in Japanese with English abstract 5p.)
• Ishii et al. (1983) Geology of the Shiogama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 112p. (in Japanese with English abstract 6p.)
• Ishii et al. (1982) Geology of the Matsushima District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 121p. (in Japanese with English abstract 9p.)