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OK I Tephra Yanagisawa et al., 1985

Abbr.: OK I

• Type locality: Tagawa river, Tokamachi city, Niigata prefecture
• Tephra
• Pleistocene

• Lithofacies: Rhyolite vitreous volcanic ash
• Sedimentary structures (Upper): Cross stratification, Graded bedding
• Sedimentary structures (Lower): Parallel stratification

• Host: Uonuma Formation
• Thickness: 54 cm

• Distribution: Tagawa river - Tobitari river, Tokamachi city, Niigata pref.; Koimo river, Uonuma city, Niigata pref.

• 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.)