Kohama Formation

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Kohama Formation Kawakami and Shishikura, 2006

Invalid synonym: Namuya Formation

Type locality: Namuya - Kohama, Tomiura town, Minamiboso city, Chiba prefecture
Coherent formation
late Miocene
Correlation: Kinone Formation, Emi Formation, Nishizaki Formation

Sedimentary facies: Marine
Lithofacies: Interbedded sandstone and siltstone
Sedimentary structures: Slump structures

Thickness: 300 m
Upper limit: Conformity (Koura Formation)
Lower limit: Conformity (Hota Group)

Minamiboso Group
[ Upper ]
~~~~~~~~~~~~~~
Kagamigaura Formation
--------------
Hedate Formation
--------------
Koura Formation
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Kohama Formation
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Haraoka Formation
--------------
Ishido Formation
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Azuma Formation
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Iwaibukuro Formation
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[ Lower ]

Mineoka Belt (Boso peninsula)
[ Upper ]
~~~~~~~~~~~~~~
Awa Group / Minamiboso Group
~~~~~~~~~~~~~~
Hota Group
::::::::::::::
Mineoka Group
?--?--?--?--?-
[ Lower ]

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

Distribution: Namuya - Kohama, Tomiyama town, Minamiboso city, Chiba pref.; Heguri, Minamiboso city, Chiba pref.
Fossils: Radiolarians, Calcareous nannofossils

Takahashi et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.8, pp.375-395, DOI
Kawakami and Shishikura (2006) Geology of the Tateyama District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 82p. (in Japanese with English abstract 5p.)
Suzuki et al. (1990) Geology of the Nago District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 48p. (in Japanese with English abstract 3p.)