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Imaizumigawa Formation Tanaka et al., 2002

Invalid synonym: Yatsushiro Formation?, Tomochi Formation?, Hinagu Formation?, Miyaji Formation?

• Type locality: Imaizumi river, Imaizumi, Sakamoto village, Yatsushiro city, Kumamoto prefecture
• Coherent formation
• Deposition (Upper): Early Cretaceous, Albian
• Deposition (Lower): Early Cretaceous, late Aptian
• Deposition (Bottom): Early Cretaceous, late Aptian
• Correlation (Lower): Gumizaki Formation

• Sedimentary facies: Marine
• Lithofacies (Upper): Mudstone, Sandy mudstone
• Lithofacies (Lower): Interbedded sandstone and mudstone
• Lithofacies (Bottom): Conglomerate, Sandstone

• Thickness: 900 m or thicker
• Thickness (Upper): 220 m or thicker
• Thickness (Lower): 280 - 400 m
• Thickness (Bottom): 40 - 100 m
• Lower limit: Disconformity (Hachiryuzan Formation), Angular unconformity (Kesado Formation)

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

• Distribution: Imaizumi river, Imaizumi, Sakamoto village, Yatsushiro city, Kumamoto pref.
• Fossils (Upper): Echinoids
• Fossils (Upper, Bivalves): Lopha (Actinostreon) nagaoi, Astarte sp., Eotetragonites sp., Anagaudryceras sp., Pachydesmoceras ps., Eotetragonites sp. cf. E. gainesei
• Fossils (Lower): Radiolarians
• Fossils (Lower, Bivalves): Plicatula takahashii, Pterotrigonia n. sp.
• Fossils (Lower, Ammonoids): Cheloniceras (Epicheloniceras) sp., Diadochoceras sp., Gargasiceras ps., Cheloniceras (Epicheloniceras) sp. aff. C. (E.) sellindgense, Pseudohaploceras sp., Dufrenoyia sp.
• Fossils (Bottom, Bivalves): Costocyrena sp. aff. C. matsumotoi
• Fossils (Yatsushiro Formation, Ammonoids): Brewericeras enorme
• Fossils (Yatsushiro Formation, Bivalves): Neithea matsumotoi, Nemocardium yatsushiroense, Yabea akatsui, Pholadomya sp., Nanonavis yokoyamai (= aff. pseudocarinata), Astarte yatsushiroensis (Astarte subsenecta�����), Pterotrigonia hokkaidoana

• Miyake et al. (2015) Jour. Geol. Soc. Japan, vol.121, no.12, pp.447-462, DOI
• Terabe and Matsuoka (2009) Jour. Geol. Soc. Japan, vol.115, no.3, pp.130-140 DOI