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Hachiwari Formation Hosoi et al., 2019

Invalid synonym: Sunakobuchi Formation (Baslat - basaltic andesite), Uyashinai Formation (Dacite - rhyolite), Uyashinai Mudstone Member

• Type locality: Osawa, Hachiawari, Kakunodate town, Senboku city, Akita prefecture
• Volcanic rocks
• middle Miocene (ca. 16 - 12 Ma; 12.7 - 11.9 Ma, K-Ar)

• Lithofacies: Basalt, Basaltic andesite, Dolerite, Dacite, Rhyolite
• Lithofacies: Lava, Intrusive rocks, Volcaniclastic rocks
• Lithofacies (Lower): Interbedded siliceous stone and sandstone
• Lithofacies (Minor): Mudstone, Siliceous mudstone
• Sedimentary structures: Graded bedding, Parallel stratification, Trough cross-stratification, Hummocky cross-stratification

• Thickness: ca. 1,200 m or thinner
• Upper limit: Conformity (Onnagawa Formation, Manaitayama Volcanic Rocks)
• Lower limit: Interfingered (Shiotezawa Formation), Unconformity (Katsurabuchi Formation)

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

• Distribution: Osawa, Hachiawari, Kakunodate town, Senboku city, Akita pref.
• Fossils (Foraminifera): Globigerina praebulloides, Globigerina woodi, Cibicides malloryi, Gyroidina orbicularis, Melonis pompilioides, Bathysiphon sp., Martinottiella communis
• Fossils (Diatoms): Actinocyclus ingens, Actinocyclus tsugaruensis, Thalassionema hirosakiensis
• Fossils: Calcareous nannofossils

• Hosoi et al. (2019) Jour. Geol. Soc. Japan, vol.125, no.4, pp.279-295 DOI