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Omma Formation, Onma Formation

Invalid synonym: Omma Sandstone Formation, Onma Sandstone Formation

• Type locality: Okuwa, Kanazawa city, Ishikawa prefecture
• "Omma" is the old name of Okuwa
• Coherent formation
• early Pleistocene (2.02 - 0.99 Ma)
• Correlation: Chokeiji Sand Member, Anyobo Sandstone and Mudstone Alternation Member

• Sedimentary facies: Marine
• Climate: Cold
• Depth of water (Upper): Upper sublittoral zone (20 -100m, Nannofossils)
• Depth of water (Lower): Lower sublittoral zone (35 -100m, Nannofossils)
• Lithofacies (Upper, Main): Fine - coarse sandstone
• Lithofacies (Upper, Minor): Siltstone, Conglomerate
• Lithofacies (Lower, Main): Fine sandstone, Siltstone

• Thickness: ca. 210 m

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

• Distribution: Southern Kanazawa city, Ishikawa pref.; Tagawa - Hachibuse, Oyabe city, Toyama pref.
• Fossils: Omma-Manganji fauna
• Fossils: Calcareous nannofossils, Bivalves, Gastropods, Echinarachnius sp. (Upper)
• Tephra: Tagawa tuffaceous tuff (21 m thick), O2 tuff

• Kaneko et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.5, pp.193-206, DOI
• Tamura et al. (2010) Jour. Geol. Soc. Japan, vol.116, Supplement, pp.1-20 DOI