a Member

[ Top ] [ Japanese ]

a Member

Synonym: U-IIa

Coherent formation
Late Cretaceous, middle Campanian (Bivalves)

Sedimentary facies: Marine
Sedimentary facies: Offshore shallower than the fair-weather wave base, Inner shelf, Outer shelf
Lithofacies: Sandstone, Interbedded sandstone and mudstone, Mudstone
Sedimentary structures: Large cross-stratification, Trough cross-stratification, Hummocky cross-stratification, Bioturbation

Thickness: 230 m or thicker
Upper limit: Conformity
Lower limit: Conformity

U-II Formation
[ Upper ]
--------------
b Member
--------------
a Member
--------------
[ Lower ]

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

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

Distribution: Mount Yohagimaru, Shimokoshikijima island, Koshikijima islands, Satsumasendai city, Kagoshima pref.
Fossils: Echinoids, Foraminifera
Fossils (Bivalves): Loxo japonica, Apiotrigonia sp., Yaadia japonica, Crassostrea sp., Inoceramus sp.

Komatsu et al. (2014) Jour. Geol. Soc. Japan, vol.120, Supplement, pp.19-39 DOI
Tonai et al. (2008) Jour. Geol. Soc. Japan, vol.114, no.11, pp.547-559 DOI