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Omori Formation (Tomita and Sakai, 1937) Kano et al., 1991

Invalid synonym: Kimachi Formation, Kiyomizudera Andesite, Kiyomizu Andesite, Ijiri Andesite, Hane Andesite, Kinuya Dacite, Shuno Dacite

• Type locality: Omori, Kimachi, Matsue city, Shimane prefecture
• Coherent formation
• middle Miocene (17.1 - 13.7 Ma, K-Ar; 17.1 Ma, FT)
• Correlation: Ushikiri Formation
• Intruded by: Andesite dikes

• Sedimentary facies (Upper): Shallow marine
• Sedimentary facies (Lower): Terrestrial, Shallow marine
• Sedimentary facies (Upper): Alluvial fan, Delta
• Sedimentary facies (Lower, Minor): Surge deposits, Lava dome
• Depth of water: 50 m or shallower
• Lithofacies (Andesite, Mafic dacite): Tholeiite
• Lithofacies (Felsic dacite): Calc-alkaline
• Lithofacies: Conglomerate, Sandstone, Andesite - Dacite lava, Rhyolite pumice tuff
• Lithofacies (Minor): Silicified woods, Volcanic breccia
• Lithofacies (Bottom): Conglomerate
• Lithofacies (Minor): Basalt - andesite - dolerite - porphyrite dikes
• Sedimentary structures (Upper): Graded bedding, Reversed graded bedding, Trough cross-stratification, Planar cross-stratification, Hummocky cross-stratification
• Sedimentary structures (Lower): Platy joints, Columnar joints
• Sedimentary structures (Lower, Minor): Large-scale low angle cross-stratification, Bomb sag structure

• Mode of eruption (Lower, Minor): Phreatomagmatic
• Thickness: ca. 80 - 1,500 m
• Thickness (Lower, Minor): 100 m or thicker
• Upper limit: Conformity (Fujina Formation), Unconformity (a href="74izumoFOe.htm">Older Fan Deposits, Noro Basalt, Tsunozu Formation)
• Lower limit: Unconformity (Kuri Formation, Kawai Formation, Karakuri Dacite, Hata Formation, Uzuki Gabbro, Fube Granite, Hosekidani Body)

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

• Distribution: Gotsu city, Shimane pref.; Omori - Mount Kasenzan - Mount Wanoyama - Sakusa town - Okusa town - Adakae - Higashiinbe town - Noshira town - Kimachi - Iwayamae, Matsue city, Shimane pref.; Hijira town - Uzukigawa river - Fukutomigawa river - Hoshojigawa river - Mount Kiyomizusan - Mount Dakesan - Cape Yahirobana - Kayashima island - Mori - Ijiri - Kirikui, Yasugi city, Shimane pref.; Sannoji - Suga - Takakubo - Mount Manjuyama - Fukuda, Unnan city, Shimane pref.; Unate town - Koshi town - Mimiku town, Izumo city, Shimane pref.; Nima - Takase - Kumagai - Takuno, Oda city, Shimane pref.; Fukuyori - Takahime - Munakata, Nanbu city, Saihaku county, Tottori pref.
• Fossils: Dicrocerus aff. furcatus, Paleoparadoxia tabatai, Sharks (Carcharodon megalodon), Crabs (Mursia takahashii), Foraminifera, Trace fossils, Silicified woods
• Fossils (Shellfishes): Anadara sp., Calliostoma simane, Clementia papyracea, Clinocardium shinjiense, Conchocele sp., Euspira sp., Fissidentalium yokoyamai, Glycymeris cisshuensis, Laevicardium shiobarense, Macoma sp., Mercenaria yokoyamai, Phacosoma hataii, Sinum yabei, Vasticardium sp.

• Kano et al. (2025) Geology of the Yonago District (2nd Ed.), Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 84p. (in Japanese with English abstract 4p.)
• Kano (2018) Jour. Geol. Soc. Japan, vol.124, no.10, pp.781-803 DOI
• Sawada et al. (2013) Jour. Geol. Soc. Japan, vol.119, no.4, pp.267-284 DOI
• Hayashi et al. (2013) Jour. Geol. Soc. Japan, vol.119, no.4, pp.300-311 DOI
• Sato et al. (2011) Jour. Geol. Soc. Japan, vol.117, no.8, pp.439-450 DOI
• Utada (2007) Jour. Geol. Soc. Japan, vol.113, no.8, pp.438-453 DOI
• Matsuura et al. (2005) Geology of the Kisuki District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 72p. (in Japanese with English abstract 5p.)
• Kano et al. (2001) Geology of the Yunotsu and Gotsu District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 129p. (in Japanese with English abstract 5p.)
• Kano et al. (1998) Geology of the Iwami-Oda and Oura District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 118p. (in Japanese with English abstract 5p.)
• Kano et al. (1998) Geology of the Taisha District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 58p. (in Japanese with English abstract 3p.)
• Kano et al. (1994) Geology of the Matsue District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 126p. (in Japanese with English abstract 5p.)
• Kano et al. (1991) Geology of the Imaichi District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 79p. (in Japanese with English abstract 5p.)
• Hattori et al. (1983) Geology of the Sambesan District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 168p. (in Japanese with English abstract 7p.)