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Iriai Formation Shiraishi, 2000

• Type locality: Anden seashore, Iriai, Oga city, Akita prefecture
• Coherent formation
• Pleistocene
• Correlation: Aikawa and Kotokawa Terrace Deposit, Kamayachi Formation

• Sedimentary facies (Upper): Marine
• Sedimentary facies (Middle): Inner bay, Tidal flat
• Sedimentary facies (Lower): Fluvial
• Climate: Warm (Pollen)
• Lithofacies: Sands, Silt, Lignite, Silty sands
• Lithofacies (Minor): Peat
• Sedimentary structures: Trough cross-stratification

• Thickness: ca. 10 m
• Lower limit: Unconformity (Katanishi Formation)

• Distribution: Kotokawa and Aikawa terrace
• Distribution: Makino terrace - Kotooka terrace, Oga city, Akita pref.; Anden seashore, Iriai, Oga city, Akita pref., Hamamaguchi, Oganaka, Oga city, Akita pref.
• Fossils: Shellfishes (Corbicula sp., ca. 50 species), Trace fossils

• Kano et al. (2011) Geology of the Toga and Funakawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 127p. (in Japanese with English abstract 4p.)
• Shiraishi et al. (2008) Jour. Geol. Soc. Japan, vol.114, Supplement, pp.33-50 DOI