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Yotsuyaku Formation Otuka, 1934

• Type locality: Shiratori river, Yotsuyaku, Shiratori, Ninohe city, Iwate prefecture
• Coherent formation
• early Miocene (18 - 16.5 Ma)

• Sedimentary facies: Terrestrial

• Thickness: 100 - 600 m or thicker
• Upper limit: Conformity (Kadonosawa Formation, Suenomatuyama Formation, Mainosawa Formation), Onlap unconformity (Sikonai Siltstone Member), , Unconformity (Kusagi Terrace Deposit)
• Lower limit: Unconformity (North Kitakami Belt, Cretaceous strata, Nisatai Formation)

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

• Distribution: Shiratori river, Yotsuyaku, Shiratori, Ninohe city, Iwate pref.; Kotoge, Shiratori, Ninohe city, Iwate pref.; Tate, Kintaichi, Ninohe city, Iwate pref.; Nisatai, Ninohe city, Iwate pref.; Ichinohe city, Ninohe county, Iwate pref.; Kuzumaki city, Iwate county, Iwate pref.

• Tuzino et al. (2018) Geology of the Ichinohe District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 161p. (in Japanese with English abstract 4p.)
• Yamanoi et al. (2010) Jour. Geol. Soc. Japan, vol.116, no.2, pp.114-117 DOI