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Umegase Formation Ueda, 1930

Invalid synonym: Iwasaka Formation, Hasumi Formation

• Type locality: Umegase valley, Asobara, Ichihara city, Chiba prefecture
• Coherent formation
• Fore-arc basin sediments (Kazusa trough)
• Pleistocene
• Correlation: Bushi Formation, Koshiba Formation, Kamo Formation
• Correlation (Upper): upper Higashihigasa Formation
• Correlation (Lower): lower Higashihigasa Formation

• Sedimentary facies: upper - middle Submarine fan
• Water temperature (Middle): Cold ocean current
• Water temperature (Lower): Warm ocean current
• Depth of water (Upper): lower Continental shelf
• Depth of water (Lower): upper - middle Continental slope
• Depth of water: ca. 800 m (Foraminifera)
• Lithofacies: Turbidite
• Lithofacies: Sandstone-dominant interbedded sandstone and mudstone, Mudstone-dominant interbedded sandstone and mudstone
• Sedimentary structures: Slump structure, Channel structure

• Thickness: 123 - 600 m
• Upper limit: Bottom of Ku6E
• Upper limit: Conformity (Kokumoto Formation), Unconformity (Nagahama Sand and Gravel Member, Ichijiku Formation)
• Lower limit: Bottom of sandstone-dominant interbedded sandstone and mudstone, Top of O1
Lower limit: Conformity (Otadai Formation)

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

• Distribution: Umegase valley, Asobara, Ichihara city, Chiba pref.; Mutsuzawa city - Ichinomiya city, Chosei county, Chiba pref.; Takamizo - Morokuzure - Saurai - Iwasaka - Minato, Futtsu city, Chiba pref.; Funazuka - Higashiawakura - Kujukutani, Kimitsu city, Chiba pref.; Otaki city, Isumi county, Chiba pref.
• Fossils: Whale (Pseudorca sp. (Teeth))
• Fossils (Shellfishes): Amalthea conica, Ancistrolepis trochoideus, Gibberulina cotamago, Homalopoma granuliferum, Homalopoma sangarense, Kogomea novemprovincialis, Limopsis uwadokoi, Portlandia lischkei, Ringuhdrillia mediocarinata, Suavodrillia engonia, Solidula clathrata, Stenotis smithi, Yoldia lischkei
• Fossils (Foraminifera): Globorotalia inflata, Globorotalia tosaensis, Globorotalia truncotulinoides, Neoglogoquadrina incompta, Neoglogoquadrina pachyderma
• Fossils (Diatoms): Nitzschia fossilis, Rhizosolenia matuyamai
• Fossils (Calcareous nannofossils): Reticulofenestra sanoi
• Fossils (Pollen): Cryptomeria sp., Fagus sp., Keteleeria sp., Liquidambar sp., Metasequoia sp., Picea sp., Pseudolarix sp., Quercus sp., Sequoia sp.
• Tephra: U1, U2A, U2A', U2B, U3A, U3B, U4, U4.5, U5, U6A, U6B, U6C, U6D, U7, U7.5, U7.6B, Sr-Kc-U8, U9, U9.2, U10A, U10B, U11, U12, O1

• Utsunomiya and Ooi (2019) Geology of the Kazusa-Ohara District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 127p. (in Japanese with English abstract 4p.)
• Tamura et al. (2019) Jour. Geol. Soc. Japan, vol.125, no.1, pp.23-39 DOI
• GSSP proposal group (2019) Jour. Geol. Soc. Japan, vol.125, no.1, pp.5-22 DOI
• Nanayama et al. (2016) Geology of the Mobara District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 101p. (in Japanese with English abstract 4p.)
• Suzuki and Murata (2011) Jour. Geol. Soc. Japan, vol.117, no.7, pp.379-397 DOI
• Nakajima and Watanabe (2005) Geology of the Futtsu District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 102p. (in Japanese with English abstract 8p.)