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Iwaobashi Sandstone Member Akahane, 1975

• Type locality: Iwao bridge, Seto, Nadachi ward, Joetsu city, Niigata prefecture
• Coherent formation
• Rift basin sediments
• Pliocene
• Interfingered: Tsutsuishi Alternation of Sandstone and Mudstone Member, Tsunako Conglomerate Member, Doguchi Alternation of Sandstone and Mudstone Member

• Sedimentary facies: Marine
• Lithofacies: Tuffaceous sandstone
• Lithofacies (Minor): Gravelly sandstone, Conglomerate, Mudstone, Tuff
• Sedimentary structures: Graded bedding, Sole marks

• Thickness: ca. 50 - 80 m
• Upper limit: Conformity (Tsutsuishi Alternation of Sandstone and Mudstone Member)
• Lower limit: Conformity (Seto Tuff Member)

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

• Distribution: Iwao bridge, Seto, Nadachi ward, Joetsu city, Niigata pref.; Doguchi - Higashiyachi, Joetsu city, Niigata pref.; Kawazume, Itoigawa city, Niigata pref.

• 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.)