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Tsunaki Formation

Invalid synonym: Hayama Tuff Member

• Type locality: Tsunaki, Sendai city, Miyagi prefecture
• Coherent formation
• late Miocene (10 - 8.3 Ma, FT)
• Correlation: Bangamoriyama Formation, Aoso Formation, Nanakita Formation, Omatsuzawa Formation, Yamairi Formation

• Sedimentary facies: Shallow marine
• Sedimentary facies: Continental shelf (Foraminifera)
• Sedimentary facies (Middle): Submarine debris flow
• Lithofacies (Upper, Oso-67): Interbedded siltstone, tuffaceous sandstone and lapilli tuff, Interbedded breccia, tuffaceous sandstone and pumice tuff
• Lithofacies (Middle, Oso-57-Oso-67): Conglomerate, Interbedded conglomerate, sandstone and pumice tuff, Tuffaceous sandstone
• Lithofacies (Lower, Oso-32-Oso-57): Tuffaceous sandstone
• Lithofacies (Lower, Minor): Pumice tuff, Tuff, Lapilli tuff
• Sedimentary structures (Middle): Parallel-stratification, Cross-stratification
• Sedimentary structures (Lower): Cross-stratification

• Thickness (Overall): 350 m or thicker
• Thickness (Upper): ca. 100 m
• Thickness (Middle): 90 - 100 m
• Thickness (Lower): ca. 155 cm
• Upper limit: Uncomformity (Nashino Formation, Mitaki Formation, Yumoto Formation, Kameoka Formation, Yumoto Formation)
• Lower limit: Bottom of a set of 3 andesitic tuff breccia beds with ca. 60 cm thick.
• Lower limit: Conformity, partly unconformity (Hatatate Formation)

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

• Distribution: Tsunaki - Kagitori - Mount Naraibanzan - Hiyori-danchi - Hirose river, Kunimi, Sendai city, Miyagi pref.
• Fossils: Trace fossils
• Fossils (Bivalves): Chlamys miyatokoensis, Solen spp., Lucinoma annulata, Serripes spp., Clinocardium spp., Kaneharaia kaneharai, Glycymeris sp., Umbonium sp.
• Fossils (Foraminifera): Buccella cf. tanaii, Cibicides lobatulus, Cibicides malloryi, Cibicides cf. refulgens, Cibicides tani, Discorbinella convexa, Epistominella pulchella, Fissurina sp., Gavelinopsis sp., Globocassidulina sp., Hanzawaia nipponica, Islandiella cf. yabei, Melonis cf. affinis, Melonis pompilioides, Paracassidulina sp., Pseudoparrella naraensis, Pullenia bulloides, Rosalina sp., Sigmomorphina sp., Trifarina hughesi
• Fossils (Diatoms): Fragilaria sp. Pinilaria sp.
• Tephra (Key bed): Oso-32 - Oso-70

• Miyamoto et al. (2013) Jour. Geol. Soc. Japan, vol.119, Supplement, pp.27-46 DOI
• Fujiwara et al. (2013) Jour. Geol. Soc. Japan, vol.119, Supplement, pp.96-119 DOI
• Kitamura et al. (1986) Geology of the Sendai District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 134p. (in Japanese with English abstract 9p.)