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Koshiba Formation Otsuka, 1937

• Type locality: Koshiba seashore, Shiba town, Kanazawa ward, Yokohama city, Kanagawa prefecture
• Coherent formation
• Fore-arc basin sediments (Kazusa trough)
• Pleistocene
• Interfingered: lower Nakazato Formation
• Contemporaneous heterotopic facies (Lower): Kamihoshikawa Formation
• Correlation: Kakinokidai Formation, Kokumoto Formation, Umegase Formation

• Sedimentary facies: Marine
• Sedimentary facies: Tidal zone, Shallow marine, Lower sublittoral
• Water temperature: Warm ocean current
• Lithofacies: Tuffaceous sandstone, Sandstone
• Sedimentary structures: Cross stratification

• Thickness: 90 m
• Upper limit: Transitional (Nakazato Formation)
• Lower limit: Conformity (Lithofacies boundary between lower massive mudstone and sandy mudstone)
• Lower limit: Transitional (Ofuna Formation)

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

• Distribution: Shiba town - Nishishiba, Kanazawa ward, Yokohama city, Kanagawa pref.; Hitorizawa town - Mount Enkaizan, Isogo ward, Yokohama city, Kanagawa pref.; Nakano town - Kosugaya town - Iijima, Sakae ward, Yokohama city, Kanagawa pref.
• Fossils (Shellfishes): Acar sp., Acila sp., Acmaea pallida, Alvania sp., Ancilla sp., Anisocorbula venusta, Arca miyatensis, Astarte hakodatensis, Ataxocerithium sp., Atlanta? sp., Barbatia sp., Barleeia? angustata, Benthovoluta hilgendorfi, Bittium sp., Borsonia? sp., Cadella? kesenensis, Calliostoma? sp., Cancellaria spengleriana, Cardita leana, Cardium californiensis, Cavolina sp., Ceratostoma aduncum, Chama fragum, Chlamys cosibensis, Chlamys jousseaumei, Chlamys nipponensis, Chlamys vesiculosa, Clingulina sp., Clio sp., Collisella cf. grata, Collisella heroldi, Conotalopia sp., Conus tuberculatus, Crassatellites oblongatus, Crenella sp., Cymatium sp., Cymatosyrinx spp., Dentalium yokoyamai, Diacria trispinosa, Diala? sp., Diodra sp., Emarginula sp., Eocylichna musashiensis, Eumeta? sp., Fasciolaria (Pleuroploca) sp., Fossarina sp., Fulgoraria prevostiana kamakurensis, Fulgoraria prevostiana kosibensis, Fusinus sp., Fusitriton oregonens, Galactella symmetrica, Gemmulofusus musashinoensis, Glycymeris nipponica, Glycymeris pilsbryi, Glycymeris rotunda, Heliacus sp., Lacuna sp., Latiaxis sp., Leptothyra granuliferum, Lima goliath, Lima quantoensis, Limatula japonica, Limatula kurodai, Limposis azumana, Limopsis crenata, Limopsis tokaiensis, Lora dissoluta, Lucina? sp., Lunatica sp., Mangelia nagasakiensis, Mitra fusiformis, Mitrella varianus, Monia radiata, Myadora japonica, Nemocardium samarangae, Neptunea yokoyamai, Notoaemea cf. fuscoviridis, Notostrea musashiensis, Nuculana yokoyamai, Odostomia sp., Paradrillia hivalioides, Pecten tokyoensis, Pecten yessoensis, Pectinodonta? kuragiensis, Peristernia? sp., Polynemamussium intuscostalum, Proterato callosa, Protothaca sp., Pseudogrammatodon obliquatus, Puncturella fastigiata, Putilla mundana, Putilla (Pseudosetia) sp., Rissoina (Zebinella) sp., Samacar sp., Seila sp., Septifer keeni, Serpulorbis cf. medusae, Siphonalia sp., Solen cf. gouldi, Solen grandis, Spisula bernardi, Syrnola spp., Tectonatica clausiformis, Tectonatica janthostomoides, Trichotropis sp., Triphora sp., Tritia acutidentata, Trophon echinus, Trophon xestra, Turbonilla sp., Turcicula crumpii, Turritella nipponica, Velutina? sp., Venericardia ferruginea, Vermetus sp., Volsella sp., Zafra sp., Zebina sp.
• Fossils (Brachioopods): Laqueus rubellus, Terebratalia gouldi, Terebratulina crossei, Terebratulina miurensis
• Tephra: Ku2A, MT, H1, H2, U6A, Ka2.3, Ka2.4A, Ob4c-Kd24 (= Sg1, H-7)

• Suzuki and Murata (2011) Jour. Geol. Soc. Japan, vol.117, no.7, pp.379-397 DOI
• Mitsunashi and Kikuchi (1982) Geology of the Yokohama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 105p. (in Japanese with English abstract 4p.)