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Nishitajiri Formation Chihara et al., 1981

Invalid synonym: Hitomurao Formation, Shonomata Formation

• Type locality: Nishitajiri, Tokamachi city, Niigata prefecture
• Volcanic rocks
• late Miocene (6.2 Ma, K-Ar; Diatoms)
• Middle: late Miocene (6.3 Ma, K-Ar)
• Lower: late Miocene (6.8 Ma, K-Ar)
• Intruded by: Quartz-bearing augite andesite sills, Dolerite sills
• Correlation: Shiiya Formation

• Sedimentary facies: Marine
• Sedimentary facies: Submarine volcano
• Lithofacies: Low alkaline tholeiite
• Lithofacies (Upper): Lapilli tuff, Volcanic breccia
• Lithofacies (Upper, Minor): Andesite lava, Siltstone, Tuff
• Lithofacies (Middle): Basalt - Andesite lava, Volcaniclastic rocks, Basalt pillow lava
• Lithofacies (Middle, Minor): Interbedded tuff breccia and Volcanic sandstone/Mudstone
• Lithofacies (Lower): Pumice tuff, Andesite tuff brecccia, Andesite lava

• Thickness: ca. 30 - 1,000 m
• Upper limit: Conformity (Iwanosawa Formation, Minagawa Formation), Unconformity (Shitoka Formation, Furuto Formation, Uonuma Formation, 2nd stage products, Shikumigawa Formation)
• Lower limit: Conformity (Mugurazawa Formation), Unconformity (Nishimyo Formation, Ketto Formation)

• Distribution: Nishitajiri - Kakuma - Kiyotsu river - Kama river - Kurotaki river - Kurashita - Miyanoshita, Tokamachi city, Niigata pref.; Kamakurazawa river - Hitomurao - Aoshima - Urasa - Nagisawa - Kimigaeri, Minamiuonuma city, Niigata pref.; Anafuji, Tsunan city, Nakauonuma county, Niigata pref.; Kama river, Sakae city, Shimominochi county, Nagano pref.
• Fossils: Sponges (Makiyama chitanii)
• Fossils (Diatoms): Neodenticula kamtschatica, Thalassiosira antiqua, Thalassiosira temperei

• Amano et al., (2009) Jour. Geol. Soc. Japan, vol.115, no.11, pp.597-609 DOI
• Takeuchi et al. (2000) Geology of the Matsunoyama Onsen District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 76p. (in Japanese with English abstract 5p.)
• Shimazu and Tateishi (1993) Geology of the Naebasan District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 90p. (in Japanese with English abstract 5p.)
• Yanagisawa et al. (1986) Geology of the Ojiya District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 177p. (in Japanese with English abstract 6p.)
• 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.)
• Chihara et al. (1981) Geology of the Echigo-Yuzawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 108p. (in Japanese with English abstract 8p.)