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Yamatsuda Formation Hayakawa and Kitamura, 1953
Invalid synonym: Arasawa Formation
- Type locality: Akabuchi, Omyojin, Shizukuishi city, Iwate county, Iwate prefecture
- Coherent formation
- Fore-arc basin sediments
- Miocene (10 - 8 Ma)
- Correlation: Kitamatagawa Formation
- Sedimentary facies: Marine, Brackish
- Sedimentary facies: Inner bay, Open sea (Shellfishes)
- Sedimentary facies: Upper - middle sublittoral, Tidal (Shellfishes)
- Lithofacies: Tuff, Interbedded sandstone, siltstone and tuff
- Lithofacies (Minor): Accretionary lapilli tuff, Lignite
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Akabuchi, Omyojin, Shizukuishi city, Iwate county, Iwate pref.; Azumai creek - Sakamoto river - Koshitomaezawa creek, Shizukuishi city, Iwate county, Iwate pref.; Kakkonda river - Sendachi river - Akakura creek, Shizukuishi city, Iwate county, Iwate pref.
- Fossils (Shiobara fauna): Anadara (Anadara) arasawaensis, Anadara (Anadara) cf. ogawai, Balanus sp., Cancellaria hukusimana, Cancellaria rara, family Cardiidae, Chione (Ploacamen?) sp., Clinocardium (Ciliatocadium) cf. ciliatum, Clinocardium (Clinocardium) decoratum, Crassostrea gigas, Dinocardium shiobarense, Dosinia (Phacosoma) ettyuensis, Dosinia (Kaneharaia) kaneharai kaneharai, Dinocardium shiobarense, Lucinoma annulata, Macoma (Macoma) tokyoensis, Mizuhopecten togeshitensis, Mya (Mya) cuneiformis, Mya? sp., family Naticidae, Neverita (Glossaurax) kiritaniana, Olivella sp., Panope japonica, Periploma sp., Phos cf. iwakianus, Pitar sp., Pseudoamiantis aff. tauyensis, Serripes groenlandicus, Venericardia? sp.
- Nakaya et al. (2013) Jour. Geol. Soc. Japan, vol.119, no.7, pp.457-473 DOI
- Suto and Ishii (1987) Geology of the Shizukuishi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 142p. (in Japanese with English abstract 5p.)