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Hiraiga Formation (Yabe and Yehara, 1913) Shimazu et al., 1970
Invalid synonym: Hiraiga Sandstone
- Type locality: Hideshima island, Miyako city, Iwate prefecture
- Coherent formation
- Ezo forearc basin
- Early Cretaceous, Aptian (Ammonoids)
- Sedimentary facies: Marine
- Sedimentary facies: Lower shoreface - Inner shelf or Outer shelf
- Lithofacies: Interbedded sandstone and mudstone, Sandstone
- Sedimentary structures: Trough cross-stratification, Hummocky cross-stratification, Current ripples, Slump structures
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Hideshima island, Miyako city, Iwate pref.; Heipe seashore - Raga seashore, Tanohata city, Shimohei county, Iwate pref.
- Fossils: Belemnoids (Neohibolites miyakoensis), Brachiopods(Terebratulina? sp.), Gastropods (Solarium incrassatum, Turritella yaegashii), Scaphopods (Dentalium sp.), Echinoids(Epiaster sp., Holectypus (Coenholectypus) perioneus), Crinoids(Isocrinus sp.), Foraminifera (Orbitolina sp.), Sponges (Eusiphonella? japonica), Calcareous algae (Pterophyton miyakoense), Plants (Cladophlebis exiliformis), Wood fragments
- Fossils (Ammonoids): Diadochoceras nodosocostatiforme, Hamites? sp., Miyakoeceras tanohatense, Sanmarinoceras (Sanmarinoceras) sp.
- Fossils (Bivalves): Amphidonte (Ceratostreon) yabei, Astarte (Astarte) semicostata, Astarte (Nicaniella) minor, Glycimeris (Hanaia) denselineata, Lucinoma? kotoi, Mesosacella insignis, Nanonavis (Nanonavis) yokoyamai, Neithea (Neithea) ficalhoi, Nipponitrigonia kikuchiana, Ostrea, Parallelodon nipponicus, Pinna sp., Plicatula? sp., Protocardia hiraigensis?, Pterotrigonia hokkaidoana?, Spondylus decortus
- Fossils (Corals): Amphiastrea yabei, Astrocoenia japonica, Heterocoenia tetraseptata, Montilivaltia? todanaensis, Nefocoenia cf. favosites
- Urakawa et al. (2017) Jour. Geol. Soc. Japan, vol.123, no.3, pp.121-130 DOI
- Umetsu et al. (2013) Jour. Geol. Soc. Japan, vol.119, Supplement, pp.82-95 DOI
- Shimazu et al. (1970) Geology of the Taro District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 54p. (in Japanese with English abstract 6p.)