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Oganomachi Formation (Arai, 1960) Makimoto and Takeuchi, 1992

Invalid synonym: Oganomachi Group, Futtono Formation, Kurokaido Formation, Yoshida Formation, Iida Formation, Miyato Formation

• Type locality: Akahira river, Tomita, Chichibu city - Nagura, Ogano city, Chichibu county, Saitama prefecture
• Coherent formation
• Half graben-fill deposit
• middle Miocene (15.6 Ma, FT)
• Correlation: Arakawa Formation, Obata Formation

• Sedimentary facies: Marine
• Sedimentary facies: Lower submarine fan - Bottom of sedimentary basin
• Depth of water: Middle bathyal
• Lithofacies: Turbidite
• Lithofacies (Top): Mudstone
• Lithofacies (Upper): Sandstone-dominant interbedded sandstone and siltstone
• Lithofacies (Upper, Minor): Congomerate
• Lithofacies (Lower): Mudstone-dominant interbedded sandstone and siltstone
• Sedimentary structures: Slump structures, Graded bedding, Sole marks (Flute cast, Groove cast)
• Paleocurrent: South to North

• Thickness: 950 - 2,000 m
• Thickness (Top): 5 - 30 m
• Thickness (Upper): 400 - 1,000 m or thicker
• Thickness (Lower): 500 - 1,200 m or thicker
• Upper limit: Conformity (Chichibumachi Formation)
• Upper limit: Top of the turbidite facies horizon
• Lower limit: Conformity (Nenokami Formation, Tomita Formation)

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

• Distribution: Akahira river, Tomita, Chichibu city - Nagura, Ogano city, Chichibu county, Saitama pref.; Susuki river - Kawarazawa river - Kuriozawa creek - Izusawa, Ogano city, Chichibu county, Saitama pref.
• Fossils: Calcareous nannofossils, Plant fragments, Trace fossils
• Fossils (Foraminifera): Lepidocyclina sp., Miogypsina sp.

• Matsui et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.6, pp.261-266, DOI
• Hara et al. (2010) Geology of the Mitsumine District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 110p. (in Japanese with English abstract 4p.)
• Takahashi and Yanagisawa (2004) Jour. Geol. Soc. Japan, vol.122, no.12, pp.625-635.
• Makimoto and Takeuchi (1992) Geology of the Yorii District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 136p. (in Japanese with English abstract 6p.)
• Okubo and Horiguchi (1969) Geology of the Mamba District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 65p. (in Japanese with English abstract 5p.)