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Shirasaka Formation (Nakamura, 1913) Tokunaga, 1927

• Type locality: Shirasaka, Jobanyumoto town, Iwaki city, Fukushima prefecture
• Coherent formation
• southern Yezo Forearc basin (Jobanoki basin)
• early Oligocene (33 - 32 Ma, Diatom)

• Sedimentary facies: Marine
• Sedimentary facies: Outer shelf - Upper continental slope (Shellfishes)
• Climate: Temperate - Cool temperate (Pollen)
• Lithofacies: Siltstone
• Lithofacies (Minor): Tuff

• Thickness: 40 - 240 m
• Upper limit: Unconformity (Kunugidaira Formation, Goyasu Formation)
• Lower limit: Bottom of mudstone bed trantionally overlying sandstone bed
• Lower limit: Transitional (Asagai Formation)

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

• Distribution: Shirasaka, Jobanyumoto town, Iwaki city, Fukushima pref.; Suetsugi, Hisanohama town, Iwaki city, Fukushima pref.; Akagi - Hanyasawa, Tomioka city, Futaba county, Fukushima pref.
• Fossils (Shellfishes): Cyclocardia laxata, Periploma besshoense
• Fossils (Diatoms): Rhizosolenia oligocaenica, Rouxia obesa, Sceptroneis pesplanus, Thalassiosira mediaconvexa
• Fossils (Dinoflagelates): Dictyocha deflanbderei, Mesocena apiculata, Naviculopsis biapiculata, Trinovantedinium boreale

• 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.)