Koiwai Mudstone Member

Koiwai Mudstone Member (Otuka, 1934) Tuzino et al., 2018

Invalid synonym: Koiwai Shell Beds, Koiwai Mudstone, Sandstone and Conglomerate Member

Type locality: Shiratori river, Tsunagi - Matsukura, Shiratori, Ninohe city, Iwate prefecture
Type locality (Sub): Tsunagi - Koiwai, Shiratori, Ninohe city, Iwate prefecture
Coherent formation
early Miocene (21 - 17 Ma)

Sedimentary facies: Shallow marine
Climate: Warm (Shellfishes)
Lithofacies: Mudstone, Sandstone
Lithofacies (Minor): Conglomerate

Thickness: ca. 100 m
Upper limit: Conformity
Lower limit: Interfingered (Matsukura Siliciclastic Rock Member), Unconformity (North Kitakami Belt)

Yotsuyaku Formation
[ Upper ]
--------------
Sukohata Siliciclastic Rock Member
-------''''/,,,
Keiseitoge Volcanic Rock Member
-------''''/,,,
Koiwai Mudstone Member
-------''''/,,,
Matsukura Siliciclastic Rock Member
~~~~~~~~~~~~~~
[ Lower ]

Shiratorigawa Group
[ Upper ]
~~~~~~~~~~~~~~
Suenomatuyama Formation
--------------
Kadonosawa Formation
--------------
Yotsuyaku Formation
~~~~~~~~~~~~~~
[ Lower ]

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

Distribution: Matsukura - Tsunagi, Shiratori - Koiwai - Makaja - Ishikura, ninohe city, Iwate pref.; Keisei pass, Ichinohe city, Ninohe county, Iwate pref.; Kogura pass, Kunohe city, Kunohe county, Iwate pref.
Fossils (Akeyo-Kunugidaira fauna): Vicarya yokoyamai

Tuzino et al. (2018) Geology of the Ichinohe District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 161p. (in Japanese with English abstract 4p.)