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Oyama Formation (Tanai, 1951) Nishida and Chihara, 1966
Formerly defined as Kamigo Formation together with Zenpoji Formation.
- Type locality: Sakashita, Oyama, Tsuruoka city, Yamagata prefecture
- Coherent formation
- Miocene
- Lithofacies (Upper): Acidic - medium lapilli tuff, Tuff breccia
- Lithofacies (Upper, Minor): Tuffaceous sandstone, Mudstone
- Lithofacies (Middle): Acidic - medium tuffaceous sandstone, Mudstone
- Lithofacies (Middle, Minor): Lapilli tuff
- Lithofacies (Lower): Conglomerate, Tuffaceous sandstone
- Tsuruoka, Yamagata pref.
- [ Upper ]
- --------------
- Oyama Formation
- --------------
- Zempoji Formation
- ~~~~~~~~~~~~~~
- [ Lower ]
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Sakashita, Oyama - Shimoshimizu - Nakashimizu - Ioka - Futatsuya - Yudagawa - Takasaka, Tsuruoka city, Yamagata pref.
- Fossils (Yatsuo-Kadonosawa fauna): Anadara kamimachiensis, Angulus (Fabulina?) sp., Angulus (Moerella) aff. donacinus, Angulus (Moerella) kagayamensis, Angulus (Tellinides) timorensis, Apolymetis (Leporimetis) nipponica, Arca sp., Chicoreus (Rhizophorimurex) tiganonranus, Clementia papyracea, Cultellus otukai, Cultellus oyamaensis, Cyclina mitsuchii, Geloina yamanei, Joannisiella takeyamai, Sanguinolaria (Soletellina) sp., Striarca (Estellacar) uetsukiensis, Tellina (Scissulina) cfr. disper, Vicarya yokoyamai
- Tsuchiya et al. (1984) Geology of the Tsuruoka District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 77p. (in Japanese with English abstract 5p.)