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Chonan Formation (Mitsuchi, 1933) Tokuhashi and Endo, 1984

• Type locality: Chonan, Chonan city, Chosei county, Chiba prefecture
• Coherent formation
• Fore-arc basin sediments (Kazusa trough)
• Pleistocene (MIS 16)
• Correlation: Hama Formation, Higashinagata Formation, Takigawa Formation

• Sedimentary facies: Marine
• Sedimentary facies: Open bay
• Sedimentary facies: Continental shelf subjected to storm waves
• Sedimentary facies (Middle): Turbidite
• Sedimentary facies (Lower): Proximal turbidite
• Climate: Cold (Pollen)
• Water temperature: Cold ocean current (Shellfishes, Foraminifera)
• Depth of water: 100 - 200 m (Shellfishes)
• Lithofacies (Upper): Sandstone-dominant interbedded sandstone and mudstone
• Lithofacies (Middle): Mudstone-dominant interbedded sandstone and mudstone
• Lithofacies (Lower): Siltstone
• Lithofacies (Lower, Minor): Sandstone
• Sedimentary structures (Upper): Convolute foliation, Slump structure
• Sedimentary structures (Middle): Slump structure
• Sedimentary structures (Lower): Convolute foliation, Cross stratification

• Thickness: 150 - 175 m
• Thickness (Upper): 70 - 125 m
• Thickness (Middle): 20 - 25 m
• Thickness (Lower): 7 - 50 m
• Upper limit: Top of interbedded sands and mud
• Upper limit: Transitional (Kasamori Formation), Unconformity (Nagahama Sand and Gravel Member)
• Lower limit: Conformity (Kakinokidai Formation, Ichijiku Formation)

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

• Distribution: Chonan, Chonan city, Chosei county, Chiba pref.; Ishigami - Mobara park, Mobara city, Chiba pref.; Mount Kanozan - Manobori - Fukuoka - Oido, Kimitsu city, Chiba pref.
• Fossils (Shellfishes): Buccinum sp., Limopsis uwadokoi, Lucinoma aokii, Macoma calcarea, Nuculana ikebei, Nuculana yokoyamai, Portlandia (Portlandella) lischkei, Raeta yokohamensis, Serripes sp., Turritella nipponica
• Fossils (Foraminifera): Cassidulina subglobosa, Elphidium clavatum, Globigerina pachyderma, Globigerina quinqueloba, Globigerinita uvula, Globorotalia tosaensis, Globorotalia truncatulinoides, Lagenonodosaria scalaris, Pseudononion japonicum
• Fossils (Pollen): Abies sp., Larix sp., Menyanthes sp., Picea sp., Tsuga sp.
• Tephra: Ch1, Ch2 (Se-Tg), Ch3

• 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.)
• Tokuhashi and Endo (1984) Geology of the Anesaki District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 136p. (in Japanese with English abstract 6p.)