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Irieno Formation

• Coherent formation
• Miocene (9.4 - ? Ma, K-Ar)

• Sedimentary facies: Marine
• Lithofacies: Muddy sandstone
• Lithofacies (Lower): Interbedded tuff and tuffaceous sandstone (Shimohanawa Tuffaceous Sandstone Member)

• Lower limit: Conformity (Tanokura Formation)

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

• Distribution: Tochigi pref.
• Fossils (Shiobara-Yama fauna): Cultellus izumoensis, Chlamys kaneharai, Mercenaria yokoyamai, Anadara cf. ninohensis, Cyclocardia cf. ochiaiensis, Lucinoma acutilineata, Mya cuneiformis

• Matsui et al. (2011) Jour. Geol. Soc. Japan, vol.117, Supplement, pp.89-102 DOI
• Hayashi et al. (2008) Jour. Geol. Soc. Japan, vol.114, no.3, pp.141-144 DOI