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Izumi Group (Harada, 1890) Matsumoto and Maeda, 1951

• Coherent formation
• Izumi sedimentary basin
• Forearc basin associated with strike-slip fault related to Median Tectonic Line
• east Shikoku: Late Cretaceous, early - middle Campanian (Fossils, FT)
• west Shikoku: Late Cretaceous, late Campanian (Fossils)
• Osaka: Late Cretaceous, Maastrichtian (ca. 77 - 72 Ma, FT)
• Intruded by: Nabeyama Andesite, Rhyolite dikes

• Sedimentary facies: Marine
• Sedimentary facies: Turbidite
• Sedimentary facies (Northern margin, Southern): non-Turbidite
• Lithofacies: Interbedded sandstone and mudstone, Conglomerate, Sandstone, Mudstone
• Lithofacies (Minor): Felsic tuff
• Lithofacies (Basal): Conglomerate
• Lithofacies (Northern marginal): Mudstone
• Sedimentary structures: Flute marks, Groove marks
• Paleocurrent (Longitudinal): from East-northeast to West-southwest
• Paleocurrent (Lateral): from North to South, from Northwest to Southeast

• Thickness: 5,000 - 20,000 m or thicker
• Length: ca. 300 km
• Width: 5 - 15 km
• Upper limit: Unconformity (Sennan Formation, Kuma Group, Ishizuchi Group, Syuso Formation, Lower Terrace Deposits (Hannan), Oyodo Formation, Ryumon Formation, Denoto Formation, Higher and Lower Terrace Deposits, Lower Terrace Deposits (Mitoyo))
• Lower limit: Unconformity (Sennan Rhyolites, Takijiri Adamellite, Ryoke Metamorphic Rocks, Kogigawa Granite), Abut unconformity (Kan-onji Plutonic Rocks)
• Southern limit: Median Tectonic Line

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

• Distribution: Kii peninsula - Awaji island - Shikoku - Kyushu
• Distribution: Gojo city, Nara pref.
• Fossils: Ammonoids, Bivalves, Gastropods, Nautiloidea, Sharks (Teeth), Echinoids, Shrimps, Plants, Corals, Foraminifera, Radiolarians, Archaeozostera sp.

• Noda et al. (2021) Geology of the Ikeda District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 150p. (in Japanese with English abstract 5p.)
• Noda et al. (2017) Geology of the Kan-onji District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 96p. (in Japanese with English abstract 4p.)
• Ikeda et al. (2017) Jour. Geol. Soc. Japan, vol.123, no.7, pp.445-470 DOI
• Seike et al. (2013) Jour. Geol. Soc. Japan, vol.119, no.12, pp.759-775 DOI
• Kano and Takagi (2013) Jour. Geol. Soc. Japan, vol.119, no.12, pp.776-793 DOI
• Kikuchi and Kotake (2013) Jour. Geol. Soc. Japan, vol.119, no.9, pp.613-629 DOI
• Seike and Hirano (2013) Jour. Geol. Soc. Japan, vol.119, no.6, pp.397-409 DOI
• Miyata et al. (2012) Jour. Geol. Soc. Japan, vol.118, Supplement, pp.37-52 DOI
• Yoshikawa et al. (2011) Jour. Geol. Soc. Japan, vol.117, no.9, pp.523-537 DOI
• Noda et al. (2010) Jour. Geol. Soc. Japan, vol.116, no.2, pp.99-113 DOI
• Makimoto et al. (2004) Geology of the Kokawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 89p. (in Japanese with English abstract 4p.)
• Miyata et al. (1993) Geology of the Wakayama and Ozaki District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 68p. (in Japanese with English abstract 4p.)
• Takahashi et al. (1992) Geology of the Sumoto District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 107p. (in Japanese with English abstract 5p.)
• Itihara et al. (1986) Geology of the Kishiwada District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 148p. (in Japanese with English abstract 7p.)
• Hirayama and Kambe (1959) Koyasan, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 41p. (in Japanese with English abstract 7p.)
• Hirayama and Kishimoto (1957) Yoshinoyama, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 44p. (in Japanese with English abstract 8p.)