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Oarasawa Formation Ijiri, 1941
Invalid synonym: Isawagawa Formation (Iwate pref. side), Kuwanokizawa Formation (Akita pref. side)
- Type locality: Waga river, Oarasawa, Nishiwaga city, Iwate prefecture (Submerged)
- Type locality: Oarasawa, Suginahata, Nishiwaga city, Iwate prefecture (Redefined, 2013)
- Volcanic rocks
- Half-graben associated with rifting of the back-arc basin (Japan sea)
- Miocene (20.0 - 18.0 Ma; 20 - 18 Ma, FT; 30 Ma, U-Pb)
- Correlation: Yamauchi Formation, Yunosawagawa Formation, Nozoki Formation
- Sedimentary facies: Marine (Bivalve fossils)
- Sedimentary facies: Submarine volcano
- Lithofacies: Andesite lava (Hyaloclastite), Agglomerate, Tuff breccia, Lapilli tuff, Debrite, Turbidite
- Lithofacies (Lower): Basal conglomerate, Sandstone
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Oarasawa - Suginahata, Nishiwaga city, Iwate pref.; Upper reaches of Isawa river - upper reaches of Shitomae river, Oshu city, Iwate pref.; Mount Kamihachi - Mount Shimohachi - Mount Oazami, Higashinaruse city, Ogachi county, Akita pref.; Shinyu hot spring, Genbi town, Ichinoseki city, Iwate pref.
- Fossils: Bivalves
- Fossils: Daijima flora
- Hosoi et al. (2018) Jour. Geol. Soc. Japan, vol.124, no.10, pp.819-835 DOI
- Hosoi and Amano (2013) Jour. Geol. Soc. Japan, vol.119, no.9, pp.630-646 DOI
- Hosoi and Amano (2012) Jour. Geol. Soc. Japan, vol.118, no.8, pp.493-498 DOI
- Ozawa et al. (1971) Geology of the Kawashiri District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 40p. (in Japanese with English abstract 5p.)
- Kitamura (1965) Yakeishi-dake, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 40p. (in Japanese with English abstract 8p.)