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Masuma Formation Suzuki et al., 1979

• Type locality: Masuma dam, Masuma, Minamiboso city, Chiba prefecture
• Accretionary complex
• middle Miocene
• Correlation: Furubo Formation, Takazuru Formation, Nabuto Formation, Emi Formation

• Sedimentary facies: Marine
• Lithofacies: Interbedded sandstone and mudstone, Interbedded tuff and mudstone, Mudstone

• Thickness: ca. 3,000 m
• Upper limit: Top of the sandstone and tuff-rich horizon
• Upper limit: Transitional (Aokiyama Formation)

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

• Distribution: Masuma dam, Masuma, Minamiboso city, Chiba pref.; Haraoka, Tomiura town, Minamiboso city, Chiba pref.; Iwai - Kujiraoka - Shioido - Miyashita, Minamiboso city, Chiba pref.; Kamegasaki, Kyonan city, Awa county, Chiba pref.
• Fossils (Silicoflagellates): Corbisema triacantha

• Takahashi et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.8, pp.375-395, DOI
• Suzuki et al. (1990) Geology of the Nago District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 48p. (in Japanese with English abstract 3p.)