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Tobishima Formation Jimbo et al., 1972

• Type locality: Sainokawara - Cape Hachiman, Tobishima island, Sakata city, Yamagata prefecture
• Coherent formation
• Miocene
• Correlation: Nishikurosawa Formation

• Lithofacies (Upper): Basaltic tuff breccia, Lapilli tuff, Volcanic breccia, Tuff
• Lithofacies (Upper, Minor): Sandstone, Conglomerate
• Lithofacies (Lower): Acidic tuff, Lapilli tuff, tuff breccia, Pyroxene andesite tuff, Lapilli tuff, Tuff breccia
• Lithofacies (Lower, Minor): Rhyolite lava, Pyroxene andesite lava, Pyroxene-bearing dacite lava, Sandstone, Mudstone, Lignite

• Thickness: 400 - 500 m
• Thickness (Upper): 220 - 280 m
• Thickness (Lower): 200 - 240 m
• Upper limit: Unconformity (Terrace deposits)

• Distribution: Tobishima island - Ojaku island - Eboshi islands, Sakata city, Yamagata pref.
• Fossils: Silicified woods
• Fossils (Plants): Elaeagnus cfr. semiannuliporosa, Hovenia cfr. dulcis, Tsuga? sp., Ulmus crystallophora

• Ozawa et al. (1982) Geology of the Kisakata District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 73p. (in Japanese with English abstract 4p.)