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Iwaki Formation Tokunaga, 1927
- Type locality: Jobanyumoto town, Iwaki city, Fukushima prefecture
- Coherent formation
- southern Yezo Forearc basin (Jobanoki basin)
- late Eocene - early Oligocene (41.2 - 39.1 Ma, Sr)
- Sedimentary facies: Marine, Fluvial
- Sedimentary facies (North): Gravelly alluvial fan, Sandy braided river
- Sedimentary facies (South, Upper): Marsh-dominant estuary, Inner bay
- Sedimentary facies (South, Middle): Gravelly alluvial fan, Sandy braided river
- Sedimentary facies (South, Lower): Marsh-dominant estuary, Inner bay
- Climate: Warm (Pollen)
- Lithofacies (North): Sandstone, Conglomerate
- Lithofacies (South, Upper): Sandstone, Conglomerate
- Lithofacies (South, Middle): Mudstone, Coal
- Lithofacies (South, Lower): Sandstone, Conglomerate
- Lithofacies (Minor): Coal
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Kitazawa - Kamagasaki, Hirono city, Futaba county, Fukushima pref.; Itagizawa - Yamanota - Ohisa river, Ohisa town, Iwaki city, Fukushima pref.; Jobanyumoto town, Iwaki city, Fukushima pref.; Akagi - Hanyasawa, Tomioka city, Futaba county, Fukushima pref.
- Fossils: Mammalia (Entelodon cf. orientalis <= Anthracothema tsuchiyai), Birds (Plotopteridae), Reptiles
- Fossils (Shellfishes): Acila (Truncacila) oyamadensis, Ancistrolepis (Ancistrolepis) iwakiensis (<= Neptunea sp.), Clinocardium asagaiensis, Cyclocardia laxata, Cyclocardia tokunagai, Liocyma furtiva, Macoma sejugata, Mya (Arenomya) grewingki, Nemocardium iwakiense, Neverita asagaiensis, Papyridea harrimani, Profulvia harrimani, Thracia kidoensis, Turritella tokunagai
- Fossils (Plants): Acer arcticum, Acer trilobatum, Betul aprisca, Comptonia yanagisawae, Corylus macquarrii, Diospyros brachysepala, Equisetum arcticum, Glyptostrobus europaeus, Juglans acuminata
- Fossils (Pollen): Alnus sp., Carya sp., Ilex xp., Liquidamber sp., Nyssa sp., Pinaceae, Quercus sp., Rhus sp., Taxodiaceae
- Ando et al. (2011) Jour. Geol. Soc. Japan, vol.117, Supplement, pp.49-67 DOI
- Kubo et al. (2002) Geology of the Kawamae and Ide District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 136p. (in Japanese with English abstract 6p.)
- Kubo et al. (1994) Geology of the Namie and Iwaki-Tomioka District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 104p. (in Japanese with English abstract 7p.)
- Iwao and Matsui (1961) Taira and Kawamae, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 103p. (in Japanese with English abstract 17p.)