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Isomatsu Formation Igakura, 1931
- Type locality: Isomatsu river, Goshogawara city (Shiura city), Aomori prefecture
- Coherent formation
- early Miocene (17.7 - 15.3 Ma, FT, U-Pb: 20 Ma, Sr)
- Sedimentary facies (Upper): Marine
- Sedimentary facies (Middle): Marine
- Sedimentary facies (Lower): Terrestrial
- Lithofacies (Upper): Tuffaceous sandstone
- Lithofacies (Upper, Minor): Conglomerate, Mudstone
- Lithofacies (Middle): Tuff, Interbedded sandstone and shale
- Lithofacies (Lower): Conglomerate, Dacitic pyroclastic flow deposit
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Kayobe, Kodomari, Nakadomari city, Kitatsugaru county, Aomori pref.; Koyobi creek - Katakariishi creek, Kodomari, Nakadomari city, Kitatsugaru county, Aomori pref.; Isomatsu river - Katsura river - Yotsudakizawa river - Nagane creek, Goshogawara city, Aomori pref.
- Fossils (Kadonosawa fauna): Mytilus ksakurai, Nanaochlamys kitamurai, Nanochlamys notoensis, Neogenella sp., Dosinia sp., Dosinia nomurai, Batillaria yamanarii, Chicoreus sp., Ostrea sp., Littorina (Littorivaga) sp., Sericominolia sp., Protorotella yuantaniensis, Turritella sp., Sinum cfr. planulatum, Cerithidea cfr. sugaii, Cerithidea? sp., Vicaryella? otukai, Searlesia cfr. kurodai, Nassarius iwakianus, Chlamys? sp., Pillucina? sp., Felaniella sp., Cardium sp., Callista sp., Pitar itoi, Katelysia nakamurai, Tapes? sp., Clinocardium shinjiense, Mercenaria chitaniana, Protothaca tateiwai, Volsella tugaruana, Patinopecten kobiyamai
- Hoshi et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.4, pp.163-170, DOI
- Kamikuri et al. (2010) Jour. Geol. Soc. Japan, vol.116, no.8, pp.403-411 DOI
- Tsushima and Uemura (1959) Kodomari, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 45p. (in Japanese with English abstract 5p.)
- Ota et al. (1957) Mimmaya, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 30p. (in Japanese with English abstract 5p.)