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Yokonuma Formation (Shiida, 1940) Onuki, 1969
Invalid synonym: Oshima Formation
- Type locality: Yokonuma, Kesennuma city, Miyagi prefecture
- Coherent formation
- Early Cretaceous, Hauterivian - Barremian (Ammonoids)
- Sedimentary facies: Marine
- Sedimentary facies (Lower): non-Marine
- Lithofacies: Interbedded slate and sandstone
- Lithofacies (Minor): Calcareous sandstone, Tuffaceous sandstone, Conglomerate, Limestone
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Yokonuma - Yogai, Kesennuma city, Miyagi pref.
- Fossils (Ammonoids): Crioceratites ishiwarai, Paracrioceras ishiwarai
- Fossils (Shellfishes): Alectryonia diluviana, Corbicula sp., Gervillia haradai, Nerinea cf. ridiga, Perna sp., Spondylus sp., Trigonia hokkaidoana, Trigonia pociliformis, Trisonia hokkaidoana, Turritella sp.
- Fossils (Corals): Centrastrea japonica, Enallkelia nipponica, Eohydnophora cf. picteti, Eugyra oshimaensis, Mastophyllia japonica, Meandrarea mabutii, Meandrarea nipponica, Microsolena japonica, Microsolena subexcavata, Rhabdophyllia osimaensis, Stylina japonica, Thamnasteria cycloides, Thamnasteria komagataensis, Thamnasteria? maxima, Thamnasteria protosericides, Thamnasteria rikuzenica, Trochosmilia? orientalis
- Kamada (1993) Geology of the Tsuya District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 70p. (in Japanese with English abstract 6p.)
- 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.)