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Tsuma Formation (Tomita, 1936) Kakudate, 1988

• Type locality: Kamaya seashore - Nakazato, Tsuma, Okinoshima city, Oki county, Shimane prefecture
• Coherent formation
• late Miocene (6.6 Ma, FT)
• Contemporaneous heterotopic facies (Upper): lower Omosu Formation
• Correlation: Ama Formation
• Correlation (Nakazato Member): Shimazushima Formation
• Correlation (Kamaya Member): Ichibu Formation

• Sedimentary facies: Marine
• Sedimentary facies (Lower): Shallow marine subjected to the influence of the open sea
• Water temperature: Cold ocean current
• Lithofacies (Upper): Tuffaceous sandstone, Rhyolitic pyroclastic rocks, Tuffaceous conglomerate
• Lithofacies (Upper, Minor): Diatomaceous mudstone, Tuffaceous mudstone
• Lithofacies (Lower): Sandstone

• Thickness: ca. 120 - 270 m or thicker
• Thickness: ca. 90 m
• Thickness: ca. 180 m
• Upper limit: Conformity (Omosu Formation)
• Lower limit: Unconformity (Kumi Formation)

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

• Distribution: Tsuma - Kamaya seashore - Nakazato - Tsudo Island Park - Senjigawa river - Takugi - Mount Iinoyama - Fukuura - Nagaoda, Okinoshima city, Oki county, Shimane pref.
• Fossils (Lower): Whales, Sharks (Carcharodon sp.), Echinoid (Linthia nipponica), Brachiopods (Terebratulina sp.), Foraminifera, Sponges, Pipe rocks
• Fossils (Lower, Shiobara-Yama fauna, Omma-Manganji fauna): Anadara (Anadara) amicula, Chlamys cosibensis heteroglypta, Clinocardium ciliatum, Clinocardium fastosum, Coptothyris grayi miyagiensis, Felaniella aff. usta, Glycymeris sp., Limatula kurodai, Lucinoma acutilineatum, Lucinoma annulata, Lutraria (Psammophila) sieboldii, Macoma nipponica, Mactra (Mactra) sp., Megacrenaella aff. collumbiana, Miyagipecten matsumoriensis, Mizuhopecten matsumoriensis, Mizuhopecten paraolebejus murataensis, Mizuhopecten cf. trybrium, Mya (Arenomya) japonica, Nanaochlamys notoensis otutumiensis, Natica sp., Panope japonica, Panomya simotomensis, Panope japonica, Pitar itoi, Serripes groenlandicus, Spisula (Mactromeris) ff. voyi, Swiftopecten swiftii, Teredo sp., Thracia kakumana, Thracia kamayashikiensis, Thyasira tokunagai, Tonna sp., Turritella (Idaella) tanaguraensis, Venericardia sp., Yoldia (Cnesterium) notabilis
• Fossils (Diatoms): Actinocyclus ehrenbergii, Actinocyclus ingens, Actinoptychus senarius, Arachnoidiscus ehrenbergii, Aulacosira granulata, Cocconeis curvirotunda, Coscinodiscus aymbolophorua, Coscinodiscus endoi, Coscinodiscus marginatus, Coscinodiscus radiatus, Cymbella sp., Denticulopsis hustedtii, Denticulopsis punetata, Diploneia sp., Fragilaria captina, Grammatophora sp., Ikebea sp., Navicula sp., Nitzschia sp., Paralia sulcata, Rhizosolenia sp., Stephanogonia hanzawae, Stephanopyxia sp., Thalassionema cf. hirosakiensis, Thalassionema nitzschioides, Thalassiosira cf. yabei, Triceratium condecorum

• Yamauchi et al. (2009) Geology of the Saigo District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 118p. (in Japanese with English abstract 3p.)
• Chiba et al. (2000) Geology of the Urago District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 74p. (in Japanese with English abstract 3p.)