a Member

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a Member

Synonym: U-IVa

Invalid synonym: E1, E2

Coherent formation
Late Cretaceous

Sedimentary facies: Marine
Lithofacies: Mudstone
Lithofacies (Minor): Sandstone, Interbedded sandstone and mudstone
Sedimentary structures: Hummocky cross-stratification, Paralle stratification, Wave-formed ripples

Thickness: 500 m or thicker
Upper limit: Conformity
Lower limit: Conformity

U-IV Formation
[ Upper ]
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c Member
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b Member
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a Member
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[ Lower ]

Himenoura Group (Koshikijima islands)
[ Upper ]
~~~~~~~~~~~~~~
U-IV Formation
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U-III Formation
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U-II Formation
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U-I Formation
?--?--?--?--?-
[ Lower ]

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

Distribution: Nakakoshikijima island, Koshikijima islands, Satsumasendai city, Kagoshima pref.
Fossils: Echinoids, Radiolarians, Foraminifera, Turtles
Fossils (Shellfishes): Inoceramus sp., Glycymeris amakusensis, Corbula ushibukensis, Nanonavis sp., Miltha sp., Crassostrea sp.
Fossils (Traces): Thalassinoides isp., Ophiomorpha isp.

Aramaki et al. (2013) Jour. Geol. Soc. Japan, vol.119, no.1, pp.45-50 DOI
Tonai et al. (2008) Jour. Geol. Soc. Japan, vol.114, no.11, pp.547-559 DOI