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Shirasawa Formation Iwai, 1949

Invalid synonym: Shirasawa Group, Baba-Shirasawa Group, Ohori Formation, Kitane Formation

• Type locality: Shirasawa, Aoba ward, Sendai city, Miyagi prefecture
• Coherent formation
• late Miocene (10, 8 Ma, K-Ar; 11.3, 10.9, 9.4 Ma, FT)
• Contemporaneous heterotopic facies: Mitaki Formation

• Sedimentary facies: Lacustrine
• Lithofacies: Acidic pumice tuff, Tuff, Tuffaceous siltstone (Nashino Formation origin)
• Lithofacies (Minor): Tuffaceous sandstone, Lapilli tuff

• Thickness: 150 - 300 m or thicker
• Upper limit: Unconformity (Kameoka Formation, Arakawa Pyroclastic Rocks)
• Lower limit (Nanakita Formation): Bottom of the tuff-dominant horizon
• Lower limit: Conformity (Nanakita Formation, Nashino Formation)

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

• Distribution: Shirasawa - Yoshinari - Mount Naribanzan, Aoba ward, Sendai city, Miyagi city, Miyagi pref.; Nanakita river - Neshiroishi - Fukuoka - Hozawa - Sanezawa - Kamiyagari, Izumi ward, Sendai city, Miyagi pref.
• Fossils: Insects (Wings)
• Fossils (Upper Neshiroishi flora, Lower Neshiroishi flora): Acer miorufinerve, Alnus miomaximowiczii, Betula miomaximowicziana, Fagus paleocrenata, Liriodendron honsyuensis, Sassafras yabei, Sassafras oishii
• Fossils (Freshwater diatoms): Achnanthes lanceolata var. elliptica, Epithemia sorex, Fragilaria construens, Melosira granulata, Opephora martyi

• Miyamoto et al. (2013) Jour. Geol. Soc. Japan, vol.119, Supplement, pp.27-46 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.)
• Kitamura et al. (1983) Geology of the Yoshioka District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 50p. (in Japanese with English abstract 5p.)