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Tomikura Formation (Morishima, 1941) Yanagisawa et al., 2000

• Type locality: Matsuda river, Tomikura, Iiyama city, Nagano prefecture; Hiramaru river, Hiramaru, Myoko city, Niigata prefecture
• Coherent formation
• late Miocene - early Pliocene (7.6 - 3.5 Ma, Diatoms)
• Correlation: Sugawa Formation, Teradomari Formation, Shiiya Formation
• Contemporaneous heterotopic facies: lower Ichinose Formation
• Intruded by: Granodiorite porphyry

• Sedimentary facies: Marine
• Sedimentary facies: Basin floor, Continental slope
• Water temperature: Cold ocean current
• Depth of water: Lower sublittoral
• Lithofacies: Mudstone
• Lithofacies (Minor): Sandstone, Interbedded sandstone and mudstone

• Thickness: ca. 850 - 1,300 m
• Upper limit: Conformity, partly Interfingered (Ichinose Formation), Nagasawa Unconformity (Nigoriike Formation), Unconformity (Seguchi Formation, Konigori Formation)
• Lower limit: Conformity (Lower Teradomari Formation)

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

• Distribution: Matsuda river, Tomikura, Iiyama city, Nagano pref.; Hiramaru river, Hiramaru, Myoko city, Niigata pref.
• Fossils (Omma-Manganji fauna): Acila (Truncacila) insignis, Anadara cf. amicula, Ennucula nipponica, Pectinidae, Portlandia (Portlandella) toyamaensis, Robaia robai, Turritella saishuensis saishuensis
• Fossils (Diatoms): Actinocyclus cf. curvatulus, Actinocyclus octonarius, Actinocyclus tenerus, Actinoptychus senarius, Adoneis pacifica, Aulacoseira spp., Clavicula polymorpha, Cocconeis californica, Cocconeis costata, Cocconeis curviritunda, Cocconeis scutellum, Cocconeis vitrea, Coscinodiscus marginatus, Coscinodiscus perforatus, Coscinodiscus radiatus, Cyclotella striata, Delphineis surirella, Grammatophora spp., Hyalodiscus obsoletus, Hyalodiscus rodiatus, Koizumia tatsunokuchiensis, Neodenticula kamtschatica, Nitzschia rolandii, Paralia sulcata, Proboscia barboi, Rhizosolenia hebetata, Rhizosolenia styliformis, Stellarima microtrias, Stephanopyxis spp., Thalassionema nitzschioides, Thalassiosira antiqua, Thalassiosira jacksonii, Thalassiosira leptopus, Thalassiosira marujamica, Thalassiosira nidulus, Thalassiosira oestrupii, Thalassiosira praeoestrupii, Thalassiosira temperei, Thalassiosira trifulta, Thalassiothrix longissima, Trochosira concava
• Tephra: Kamikozawa Tuff, Shimotarumoto Tuff

• Yanagisawa et al. (2000) Geology of the Iiyama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 144p. (in Japanese with English abstract 6p.)