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Yokoyama Formation Akutsu, 1953

• Type locality: Yokoyama town, Utsunomiya city, Tochigi prefecture
• Coherent formation
• Miocene

• Lithofacies: Conglomerate, Tuff
• Lithofacies (Upper): Tuffaceous siltstone
• Lithofacies (Lower): Interbedded tuffaceous sandstone and mudstone
• Lithofacies (Basal): Conglomerate
• Sedimentary structures (Upper): Onion structure, Slaking

• Thickness: ca. 50 m
• Thickness (Upper): ca. 40 m
• Thickness (Lower): ca. 20 m
• Thickness (Basal): 1- 5 m
• Upper limit: Conformity (Oya Formation)
• Lower limit: Unconformity (Kasamatsuyama Formation, Kazamiyamada Formation)

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

• Distribution: Yokoyama town, Utsunomiya city, Tochigi pref.
• Fossils: Shellfishes (Chlamys hatai), Plants

• Matsui et al. (2011) Jour. Geol. Soc. Japan, vol.117, Supplement, pp.89-102 DOI
• Yoshikawa et al. (2010) Geology of the Utsunomiya District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 79p. (in Japanese with English abstract 6p.)
• Hayashi et al. (2008) Jour. Geol. Soc. Japan, vol.114, no.3, pp.141-144 DOI