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Umikawa Formation (Shimazu et al., 1976) Nagamori et al., 2010

Invalid synonym: Umikawa Volcanic Rocks, Awakura Agglomerate

• Type locality: Umikawadaini power plant - Ebikura, Umikawa river, Itoigawa city, Niigata prefecture
• Andesite submarine volcano
• Volcanic rocks
• Pliocene (3.92 - 3.16 Ma, K-Ar)
• Contemporaneous heterotopic facies: lower Nadachi Formation, upper Nechi Formation
• Intruded by: Basalt dikes, Rhyolite - Dacite dikes

• Sedimentary facies: Subaqueous
• Lithofacies: Andesite - Basalt lava, Volcanic breccia, Tuff breccia
• Lithofacies (Minor): Rhyolite -Dacite lava, Volcanic breccia, Lapilli tuff, Sediments

• Thickness: ca. 100 - 800 m or thicker
• Upper limit: Unconformity (Tanne Formation)
• Lower limit: Unconformity (Nechi Formation)

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

• Distribution: Umikawa river - Tannegawa river, Itoigawa city, Niigata city, Niigata pref.

• 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.)
• Nagamori et al. (2010) Geology of the Kotaki District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 130p. (in Japanese with English abstract 4p.)
• Takeuchi et al. (2010) Jour. Geol. Soc. Japan, vol.116, Supplement, pp.123-142 DOI