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Iwanosawa Formation (Mizukami?, 1981) Yanagisawa et al., 1985

• Type locality: Iwanosawa river, Kakenoue, Minamiuonuma city, Niigata prefecture
• Coherent formation
• Pliocene
• Correlation: Hachioji Formation, Haizume Formation

• Lithofacies: Sandy siltstone
• Lithofacies (Minor): Sandstone, Conglomerate, Gravel-bearing mudstone

• Thickness: ca. 100 - 350 m
• Upper limit: Transitional (Furuto Formation)
• Lower limit: Unconformity (Nishitajiri Formation)

• Distribution: Kakenoue - Urasa - Kimigaeri, Minamiuonuma city, Niigata pref.
• Fossils: Sharks (Carcharhinidae, Teeth), Crabs (Claws)
• Fossils (Shellfishes): Anadara amicula, Chlamys cosibensis, Mercenaria yokoyamai, Patinopecten yessoensis, Turritella ikebei, Turritella kurosio, Turritella saishuensis, Turritella saishuensis etigoensis

• Yanagisawa et al. (1985) Geology of the Tokamachi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 104p. (in Japanese with English abstract 6p.)