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Shibikawa Formation (Ohashi ex Toyama, 1925) Chitani, 1930

• Type locality: Anden seashore, Iriai, Oga city, Akita prefecture
• Coherent formation
• Pleistocene (ca. 455 - 150 ka)
• Correlation: Maeyamagawa Formation, Tatematazawa Formation, Takaoka Formation, Nishime Formation, Shonai Group, Mamurogawa Formation

• Sedimentary facies: Marine
• Sedimentary facies: 5 transgression - regression cycles
• Sedimentary facies (Upper part of a cycle): Inner bay - Tidal flat
• Sedimentary facies (Lower part of a cycle): Flood plain - Salt marsh
• Lithofacies: Sandstone, Conglomerate
• Lithofacies (Minor): Liginite, Pumice lapilli tuff, Tuff
• Lithofacies (Upper part of a cycle): Sand
• Lithofacies (Lower part of a cycle): Silt, Clay
• Sedimentary structures: Cross stratification

• Thickness: ca. 110 m
• Upper limit: Unconformity (Katanishi Formation)
• Lower limit: Boundary between sandy siltstone and overlying thick sandstone bed
• Lower limit: Transitional (Wakimoto Formation), Unconformity (Sasaoka Formation)

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

• Distribution: Wakimoto, Oga city, Akita pref.; Anden seashore, Iriai, Oga city, Akita pref.; Babame river - Yomoginaizawa, Gojome city, Minamiakita county, Akita pref.
• Fossils: Trapa sp., Pollen (family Taxodiaceae, Betula sp., Fagus sp.), Foraminifera, Stony corals, Crustaceans, Brachiopods, Echinoids (Lagnidae), Fishes, Sharks, Diatoms, Trace fossils
• Fossils (Mammalia): Eared seals, Sinomegaceros sp., Whales
• Fossils (Shellfishes): Corbicula sp., Glycymeris yessoensis, Mizuhopecten yessoensis, Corbicula sp., Turritella otukai
• Fossils (Trace): Macaronichnus isp.
• Tephra: Oga, Wkm, B-Og, Aso-1

• Kano et al. (2011) Geology of the Toga and Funakawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 127p. (in Japanese with English abstract 4p.)
• Shiraishi et al. (2008) Jour. Geol. Soc. Japan, vol.114, Supplement, pp.33-50 DOI
• Fujimoto et al. (2008) Jour. Geol. Soc. Japan, vol.114, Supplement, pp.51-74 DOI
• Hase and Hirayama (1970) Geology of the Gojome District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 46p. (in Japanese with English abstract 6p.)