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Ishido Formation Yabe et al., 1926

• Coherent formation
• late Early Cretaceous, Hauterivian - early Barremina (- early Aptian?) (Ammonoids, Radiolarians)

• Sedimentary facies: Marine
• Lithofacies: Sandy shale
• Lithofacies (Basal): Conglomerate

• Thickness: 100 - 450 m
• Upper limit: Conformity (Sebayashi Formation)
• Lower limit: Lithofacies boundary

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

• Distribution: Myokezawa creek - Mamonozawa creek, Nakazato, Kanna city, Tano county, Gunma pref.; Saitama pref.; Otomo - Mount Azumayasan, Ogano city, Chichibu county, Saitama pref.
• Distribution (?): Kawakubo, Sakuho city, Minamisaku county, Nagano pref.
• Fossils: Northern Tethyan
• Fossils: Hoplitids, Belemnoids, Brachiopods?, Echinoids (Enallaster yuasensis, Washitaster macroholcus), Foraminifera (Orbitolina sp.), Plants (Zamiophyllum sp., Plant fragments), Archaeolithothamnium sp., Lithothamnium sp., Parachaetetes? sp.
• Fossils (Ammonoids): Barremites otsukai (corrected from Barremites strettostoma, Barremites difficilis), Hamultina? sp., Lytoceratids, Nipponophycus sp., Pentacrinus sp., Phylloceras? sp., Pseudohaploceras japonicum, Shasticroceras sp., Stenoporidium sp., Toxoceras? sp.
• Fossils (Bivalves): Astarte shinanoensis, Astarte subsenecta, Bakevellia haradae, Capulus? annulatus, Cerithium sanchuensis, Corbicula sanchuensis, Cyprina? sp., Entolium sanchuensis, Exogyra sp., Gastropods, Gervilla aff. forbesiana, Goniomya? sp., Lopha diluviana, Lucina? sp., Monia cfr. aptiana, Monia pseudotruncata, Nanonavis yokoyamai, Neithea cfr. atavus, Nipponitrigonia kikuchiana, Nucula ishidoensis, Nuculana sanchuensis, Panopea aff. gurgites, Pecten sp., Perna? sanchuensis, Pholadomya? sp., Pleuromya? sp., Polymesoda shiroiensis, Propeamussium? sp., Pterotrigonia hokkaidoana, Pterotrigonia pocilliformis, Ptychomya densicostata, Rudistid, Rutitrigonia sanchuensis, Spondylus sp., Surcura? sp., Tellina? sp., Trigonia sp.
• Fossils (Limestone): Hexacorals, Neoschwagerina simplex, Pseudofusulina sp.
• Fossils (Trace fossils): Creeping marks

• Matsui et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.6, pp.261-266, DOI
• Hara et al. (2010) Geology of the Mitsumine District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 110p. (in Japanese with English abstract 4p.)
• Terabe and Matsuoka (2009) Jour. Geol. Soc. Japan, vol.115, no.3, pp.130-140 DOI
• Kawachi (1974) Geology of the Tateshinayama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 114p. (in Japanese with English abstract 5p.)
• Okubo and Horiguchi (1969) Geology of the Mamba District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 65p. (in Japanese with English abstract 5p.)