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Nadachi Formation Fujimoto et al., 1951

• Type locality: Senno, Itoigawa city, Niigata prefecture
• Coherent formation
• Rift basin sediments
• late Pliocene - early Pleistocene (ca. 3.5 - 2.5 Ma, Diatoms)
• Contemporaneous heterotopic facies: Tanne Formation
• Contemporaneous heterotopic facies (Lower): Kawazume Formation, Umikawa Formation
• Correlation: middle Nishiyama Formation

• Sedimentary facies: Marine
• Depth of water: Inner shelf, Outer shelf
• Depth of water: Lower sublittoral
• Lithofacies: Sandy mudstone
• Lithofacies (Minor): Interbedded sandstone and mudstone, Conglomerate, Sandstone, Acidic tuff, Tuffaceous mudstone, Tuffaceous sandstone
• Sedimentary structures: Slump structure

• Thickness: 300 - 500 m
• Upper limit: Tanihama Unconformity (Osuga Tuff Member), Unconformity (Eboshiyama Formation, Arimagawa Mudstone Member, Kajiyashiki Formation)
• Lower limit (Nechi Formation): Bottom of sandstone and tuffaceous sandstone-bearing horizon
• Lower limit: Conformity (Tsutsuishi Alternation of Sandstone and Mudstone Member, Nechi Formation)

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

• Distribution: Senno - Kyogamine - Nishiyachi - Terayama, Itoigawa city, Niigata pref.; Shimotsunako - Kuwatori river - Nadachi river, Joetsu city, Niigata pref.
• Fossils: Diatoms, Trace fossils
• Fossils (Shellfishes): Acila insignis, Anadara sp., Arca cf. boucardi, Astarte alaskensis, Brachidontes sp., Buccinum sp., Cardium fastasum, Chlamys swifti, Dentalium sp., Glycymeris yessoensis, Limopsis sp., Lucinoma actilineata, Macoma sp., Mercenaria yokoyamai, Natica sp., Nuculana onoyamai, Ophiodermella miyatensis, Ophiodermella ogurana, Ostrea sp., Palliolum peckhami, Patinopecten kurosawaensis, Shiphomalia sp., Siphonodentalium sp., Tetonatica janthostomoides, Thyasira bisecta, Turritella sanshuensis saishuensis, Umbonium (Suchium) akitanum, Yoldia cf. tokunagai

• Nagamori et al. (2018) Geology of the Itoigawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 75p. (in Japanese with English abstract 3p.)
• Takano (2011) Jour. Geol. Soc. Japan, vol.117, no.4, pp.238-258 DOI
• Akahane and Kato (1989) Geology of the Takada-Seibu District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 89p. (in Japanese with English abstract 3p.)