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Nuibetsu Formation
- Coherent formation
- early Oligocene (32.6 Ma, K-Ar)
- Sedimentary facies: Marine
- Sedimentary facies (Limestone): Authigenic methane-seep
- Depth of water: Deeper than continental shelf edge (150 m or deeper)
- Lithofacies (Top): Glauconite-bearing grayish white limestone (Key bed)
- Lithofacies (Main): Siltstone intercalating sandstone
- Thickness: 100 - 250 m
- Upper limit: Unconformity
- Lower limit: Conformity
- Onbetsu Group
- [ Upper ] Chokubetsu Formation
- ~~~~~~~~~~~~~~
- Nuibetsu Formation
- --------------
- Charo Formation
- ?--?--?--?--?-
- [ Lower ]
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Atsunai river, Urahoro city, Hokkaido
- Fossils: Diatoms, Bivalves (Conchocele bisecta (Conrad), Bathymodiolus sp.)
- Shimada et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.2, pp.81-85, DOI