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Amatsu Formation Otsuka, 1936

Invalid synonym: Amatsu Mudstone Formation

• Type locality: Amatsu, Kamogawa city, Chiba prefecture
• Coherent formation
• Forearc basin sediments
• Miocene (13 - 5 Ma, FT, Calcareous nannofossils)
• Correlation (Upper): Zushi Formation
• Correlation: Misaki Formation, Ishido Formation, Nishizaki Formation

• Sedimentary facies: Marine
• Sedimentary facies: Hemipelagic
• Sedimentary facies: Continental shelf (Shellfishes)
• Sedimentary facies (Minor): Turbidite
• Lithofacies: Siltstone
• Lithofacies (Minor): Sandy mudstone, Muddy sandstone, Sandstone, Conglomerate, Tuff, Scoria
• Sedimentary structures: Slump structures, Cross stratification

• Thickness: 225 - 1,025 m
• Upper limit: Top of Am98
• Upper limit: Conformity (Kiyosumi Formation)
• Lower limit: Bottom of Am1 (12 Ma)
• Lower limit: Transitional (Kinone Formation)

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

• Distribution: Mihara river, Surusumori, Wada village, Minamiboso city, Chiba pref.; Aikawa - Takeoka - Toyooka - Nashizawa, Futtsu city, Chiba pref.; Koito river, Toyofusa, Kimitsu city, Chiba pref.; Amatsu - Kawadani - Kanigawa - Mount Kiyosumiyama - Kominato - Taenoura - Okitsu, Kamogawa city, Chiba pref.; Motona - Okatabira - Iwaibukuro, Kyonan city, Awa county, Chiba pref.
• Fossils: Sponges (Makiyama sp.)
• Fossils (Shellfishes): Buccinum sp., Calyptogena koikei, Conchocele bisecta, Dentalium sp., Lucina acutilineata, Lucina kamenoensis, Lucina spectabilis, Niso amatuensis, Palliolum (Delectopecten) peckhami, Solemya tokumagai
• Fossils (Radiolarians): Lychnocanoma magnacomuta, Cyrtocapsella japonica, Stichocorys delmontensis, Stichocorys peregnina, Didymocyrtis laticonus, Didymocyrtis antepenultima, Didymocyrtis penultima, Cannartus sp., Diartus petterssoni, Diartus hughesi, Lithopera thornburgi, Lithopera neotera, Lithopera bacca, Eucyrtidium inflatum, Eucyrtidium yatsuoense, Phormostichoartus corbula, Phormostichoartus doliolum
• Fossils (Siliflagellata): Dictyocha fibula, Distephanus crux, Distephanus speculum, Distephanus speculum var. connopiloides, Distephanus speculum var. pentagonusMesocena circulus, Mesocena diodon, Mesocena quadrangula
• Tephra: Am1, Am4, Am19, Am28, Am40, Am56, Am61, Am78, Am94, Am98

• Yamamoto et al. (2016) Jour. Geol. Soc. Japan, vol.123, no.1, pp.41-55, DOI
• Takahashi et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.8, pp.375-395, DOI
• Kokado et al. (2015) Jour. Geol. Soc. Japan, vol.121, no.10, pp.359-372, DOI
• Sawada et al. (2009) Jour. Geol. Soc. Japan, vol.115, no.5, pp.206-222 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.)
• 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.)
• Nakajima et al. (1981) Geology of the Kamogawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 107p. (in Japanese with English abstract 7p.)