Joyama Mudstone Member

Coherent formation
early - late Miocene
Contemporaneous heterotopic facies: Shiotani Sandstone Member

Sedimentary facies: Marine
Sedimentary facies: Coastal
Sedimentary facies (Minor): Shallow marine
Lithofacies: Tuffaceous mudstone
Lithofacies (Minor): Sandstone

Thickness: ca. 300 - 550 m
Upper limit: Conformity (Mitani Mudstone Member), Unconformity (Jono Sandstone and Conglomerate Member, Hirabayashi Sandstone Member, Aoidani Mudstone Member)
Lower limit: Transitional (Monmyoji Alternation of Sandstone and Mudstone Member), Conformity (Kurosedani Formation)

Yatsuo Group (Higashitonami, Toyama pref.)
[ Upper ]
~~~~~~~~~~~~~~
Mitani Mudstone Member
--------------
Joyama Mudstone Member / Shiotani Sandstone Member
--------------
Kurosedani Formation
--------------
Iozen Formation
--------------
Iwaine Formation
~~~~~~~~~~~~~~
[ Lower ]

Yatsuo Group (Yatsuo, Toyama pref.)
[ Upper ]
~~~~~~~~~~~~~~
Joyama Mudstone Member
--------------
Monmyoji Alternation of Sandstone and Mudstone Member
--------------
Kurosedani Formation
--------------
Muromaki Conglomerate Member
~~~~~~~~~~~~~~
Iozen Formation
--------------
Iwaine Formation
~~~~~~~~~~~~~~
[ Lower ]

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

Distribution: Yamadagawa river - Kashio, Toyama city, Toyama pref.; Ikuridani, Tonami city, Toyama pref.
Fossils: Echinoids, Balanus sp., Sponges (Makiyama sp.), Foraminifera, Radiolarians
Fossils (Shellfishes): Acila submirobilis, Amussium sp., Chlamys sp., Dentalium sp., Limopsis sp., Lucina sp., Lucinoma sp., Macoma sp., Natica sp., Nucula sp., Palliorum sp., Pecten sp., Phaxus sp., Portlandia thraciaeformis, Propeamussium tateiwai, Solemya sp., Teredo sp.

Sakamoto and Nozawa (1960) Yatsuo, Explanatory Text of the Geological Map of Japan, Scale 1:50,000, Geological Survey of Japan, 69p. (in Japanese with English abstract 8p.)