Okui Formation

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Okui Formation

Type locality: Chikuma river, Okui, Yamaura, Komoro city, Nagano prefecture
Coherent formation
Inland basin-fill deposit
Pliocene - Pleistocene

Lithofacies: Interbedded conglomerate, sandstone and mudstone
Lithofacies (Minor): Pumice tuff, Welded tuff, Hornblend-bearing hypersthene augite andesite tuff breccia
Sedimentary structures: Welded tuff

Thickness: 150 m
Upper limit: Conformity (Nunobiki Formation)
Lower limit: Bottom of Komoro Welded Tuff
Lower limit: Conformity (Nashidaira Formation)

Okui Formation
[ Upper ]
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Main part
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Komoro Welded Tuff
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[ Lower ]

Komoro Group
[ Upper ]
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Uryuzaka Formation
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Nunobiki Formation
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Okui Formation
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Nashidaira Formation
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[ Lower ]

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

Distribution: Chikuma river, Okui, Yamaura, Komoro city, Nagano pref.; Kamimaruko - Nunoshita, Ueda city, Nagano pref.
Fossils: Stegodon (Parstegodon) sp. (Molar), Gastropods
Fossils (Plants): Acer pictum, Buxus japonica, Carpinus japonica, Carpinus tschonoskii, Euryale akashiensis, Fagus ferruginea, Liquidambar formosa, Metasequoia japonica, Metasequoia disticha, Populus sp., Trapa sp.

Kawachi and Aramaki (1979) Geology of the Komoro District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 39p. (in Japanese with English abstract 2p.)