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Osarubegawa Formation

• Volcanic rocks
• Miocene

• Sedimentary facies (Lower): Marine
• Sedimentary facies (Lower): Turbidite
• Water temperature: Warm ocean current, Cold ocean current
• Lithofacies (Upper): Pumice tuff, Shale
• Lithofacies (Upper, Minor): Basaltic lapilli tuff, Tuff
• Lithofacies (Lower): Acidic tuff breccia, Mudstone
• Lithofacies (Lower, Minor): Acidic tuff, Rhyolite lava, Sandstone, Conglomerate

• Thickness: 450 - 1,200 m or thicker
• Thickness (Upper): 250 - 500 m
• Thickness (Lower): 0 - 980 m
• Upper limit: Bottom of hard shale bed or fine tuff bed
• Upper limit: Conformity (Iwaya Formation), Unconformity (Yuguruma Formation)
• Lower limit: Akarimata Unconformity (Kirinai Formation, Makibuchi Formation, Omata Formation)

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

• Distribution: Osarube river, Kitaakita city, Akita pref.
• Fossils (Shellfishes): Arca sp., Barbatia sp., Brachiopoda sp., Cardilia uyemurai, Cellana sp., Chlamys kaneharai, Chlamys swifti, Clinocardium sp., Decatopecten sp., Glycymeris cfr. vestitoides, Lucinoma sp., Mya sp., Mytilus sp., Nemocardium sp., Ostrea sp., Ostrea (Crassostrea) sp., Paphia takadatensis, Patella sp., Patinopecten kimurai murayamai, Pinna sp., Polinices sp., Portlandia cfr. lischkei, Portlandia (Megayoldia) cfr. thraciaeformis, Terebratulina sp., Volsella sp.
• Fossils (Foraminifera): Ammobaculites sp., Bathysiphon sp., Cyclammina japonica, Globigerina sp., Gyroidina orbicularis, Haplophragmoides cf. evolutum, Haplophragmoides renzi, Haplophragmoides trullissatum, Martinottiella communis, Sphaeroidina sp., Spirosigmoilinella compressa

• Sumi and Moritani (1973) Geology of the Yonaizawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 46p. (in Japanese with English abstract 4p.)