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Yuasa Formation

• Type locality: Itogatoge pass, Arita city - Yuasa city, Wakayama prefecture
• Coherent formation
• Yuasa - Aridagawa basin
• Early Cretaceous, Hauterivian
• Correlation: Kitadani Formation

• Sedimentary facies (Upper): Brackish, Terrestrial
• Sedimentary facies (Lower): Terrestrial
• Sedimentary facies (Upper): Fan delta, Fan
• Sedimentary facies (Lower): Fan
• Lithofacies: Sandstone, Shale
• Lithofacies (Minor): Conglomerate, Coal
• Lithofacies (Basal): Conglomerate
• Paleocurrent: North to South

• Thickness (North): ca. 30 - 100 m
• Thickness (South): 300 m or thicker
• Thickness (Basla): ca. 20 m
• Upper limit: Conformity (Arida Formation)
• Lower limit: Unconformity (Kurosegawa Belt, Northern Chichibu Belt)

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

• Distribution: Itogatoge pass, Arida city - Yuasa city, Wakayama pref.; Takada seashore, Arida city, Wakayama pref.; Ayame seashore, Yuasa city, Arida county, Wakayama pref.; Mount Tennoyama, Hirokawa city, Arida county, Wakayama pref.
• Fossils (Shellfishes): Anomia pseudotruncata, Barbatia shinanoensis, Exogyra spp., Glauconia? neumayri, Lopha sp., Modiola? ishidoensis, Ostrea (Crassostrea) cf. yoshimoensis, Ostrea cf. ryosekiensis, Polymesoda (Isodomella) otsukai, Polymesoda (Isodomella) shiroiensis, Polymesoda (Paracorbicula) sanchuensis
• Fossils (Plants): Cladophlebis exiliformis, Nilssonia schaumburgensis, Onychiopsis elongata, Ptilophyllum pecten, Sphenopteris? elegans, Zamiophyllum buchianum

• Yao (2012) Jour. Geol. Soc. Japan, vol.118, Supplement, pp.90-106 DOI
• Kase and Maejima (2010) Jour. Geol. Soc. Japan, vol.116, no.5, pp.287-290 DOI
• Hirayama and Tanaka (1956) Kainan, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 62p. (in Japanese with English abstract 12p.)