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Namihana Formation Koike, 1949
- Type locality: Ohara, Isumi city, Chiba prefecture
- Coherent formation
- Fore-arc basin sediments (Kazusa trough)
- Contemporaneous heterotopic facies: Kurotaki Formation
- Sedimentary facies: Abyssal plain, lower Submarine fan, slope base of Submarine fan
- Lithofacies: Mudstone, Mudstone-dominant interbedded sandstone and mudstone
- Sedimentary structures (Bottom): Slump structures
- Thickness: ca. 200 - 210 m
- Upper limit: Bottom of sandstone-dominant interbedded sandstone and mudstone
- Upper limit: Conformity (Ohara Formation)
- Lower limit: Bottom of the slump structure above Kr1
- Lower limit: Conformity (Katsuura Formation)
------ Conformity, ~~~~~~ Unconformity, ~~~--- Local unconformity, '''/,, Interfingered, :::::: Fault, /--/-- Thrust, +__+__ Ground surface, ?--?-- Unknown
- Distribution: Ohara, Isumi city, Chiba pref.; Onjuku city, Isumi county, Chiba pref.; Hirata - Matsubeyamada - Arakawa, Katsuura city, Chiba pref.
- Fossils (Shellfishes): Cavolinia tridentata, Clio pyramidata, Diacria trispinosa, Nuculana sagamiensis
- Fossils (Foraminifera): Globorotalia tosaensis, Pulleniatina sp.
- Fossils (Calcareous nannofossils): Discoaster brouweri
- Fossils (Trace fossils): Chondrites isp., Palaeophycus isp., Phycosiphon isp., Zoophycos isp.
- Tephra: Nm1, Nm2, Nm3, Nm4, Nm5, Nm6, Nm7, Nm8, Nm9, Nm10, Nm11, OFN3, Nm13, OFN2, OFN1, Nm16, Nm17, Nm18, Nm19, Nm20, MY, IW2
- Utsunomiya and Ooi (2019) Geology of the Kazusa-Ohara District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 127p. (in Japanese with English abstract 4p.)
- Tamura et al. (2019) Jour. Geol. Soc. Japan, vol.125, no.1, pp.23-39 DOI
- GSSP proposal group (2019) Jour. Geol. Soc. Japan, vol.125, no.1, pp.5-22 DOI
- Suzuki and Murata (2011) Jour. Geol. Soc. Japan, vol.117, no.7, pp.379-397 DOI