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Ishizaka Formation (Tomizawa and Kitahara, 1967) Nagamori et al., 2010

Invalid synonym: Ishizaka Tuff, Ishizaka Rhyolite, Ishizaka rhyolitic lava

• Type locality: Ishizaka, Nakaotari, Otari city, Kitaazumi county, Nagano prefecture
• Volcanic rocks
• Cretaceous - Eocene (60.9 - 54.7 Ma, FT; 58.0 Ma, K-Ar)
• Correlation: Eboshiyama Formation, Futomiyama Group
• Intruded by: Basalt dykes, Andesite dykes

• Sedimentary facies: Terrestrial
• Lithofacies: Rhyolitic welded lapilli tuff
• Lithofacies (Minor): Rhyolitic lava
• Lithofacies (Basal): Conglomerate, Charcoal

• Thickness: ca. 250 - 500 m
• Lower limit: Unconformity (Sennozawa Formation, Tokurayama Formation), Abut unconformity (Atosugiyama Formation)
• Lower limit: Unconformity (Oeyama Ophiolite, Ipponmatsuyama Formation, Himekawa Complex, Kuruma Group, Omi Limestone)

• Distribution: Kotaki - Azakiri creek - Mount Gongenyama - Mount Senjomine - Mount Kurohimeyama, Itoigawa city, Niigata pref.; Ishizaka - Kitaotari - Ikehara, 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.)
• Machi and Ishiwatari (2010) Jour. Geol. Soc. Japan, vol.116, no.6, pp.293-308 DOI
• Takeuchi et al. (2010) Jour. Geol. Soc. Japan, vol.116, Supplement, pp.123-142 DOI
• Nakano et al. (2002) Geology of the Shiroumadake District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 105p. (in Japanese with English abstract 5p.)