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Imai Formation (Yoshimura and Ishibashi, 1979) Nagamori et al., 2010

Invalid synonym: Shiraizawa Formation, Yokokawa Formation

• Type locality: Nakayachi - Iwaki, Itoigawa city (former Imai city), Niigata prefecture
• Volcanic rocks
• middle Miocene (17.6Ma, FT)
• Correlation (Shiraizawa Formation): Tokurayama Formation

• Sedimentary facies: Marine
• Lithofacies: Rhyolite lava, Pumiceous lapilli tuff, Tuff
• Lithofacies (Minor): Mudstone, Sandstone

• Thickness: 40 - 300 m or thicker
• Upper limit: Conformity (Nechi Formation), Unconformity (Sennozawa Formation)
• Lower limit: Unconformity (Yamamoto Formation, Mushikawa Formation)

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

• Distribution: Nakayachi - Iwaki - Nishinaka, Itoigawa city, Niigata pref.; Yokokawa river - Shiroisawa crrek - Nigorisawa creek, Otari city, Kitaazumi county, Nagano 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