Shiroyama Formation

Invalid synonym: Shiroyama Conglomerate, Tsubasayama Sandstone, Minami Conglomerate and Sandstone, Korobishi Formation, Korobishi Conglomerate and Sandstone

Type locality: Shiroyama, Higashikagawa city, Kagawa prefecture
Coherent formation
Izumi sedimentary basin
Forearc basin associated with strike-slip fault related to Median Tectonic Line
Late Cretaceous, Campanian (Ammonoids, Paleomagnetism)
Interfingered: Takikubo Formation
Correlation: Bodaiyama Conglomerate

Sedimentary facies: Northern margin of the sedimentary basin
Sedimentary facies: non-Turbidite
Sedimentary facies: Fluvial - Brackish - Shallow marine
Sedimentary facies (Upper): Upper shoreface
Sedimentary facies (Middle): Estuary (Muddy tidal flat)
Sedimentary facies (Middle): Estuary (Sandy tidal flat)
Sedimentary facies (Lower): Fluvial
Lithofacies: Sandstone, Conglomerate
Lithofacies (Minor): Interbedded sandstone and mudstone, Felsic tuff

Thickness: 600 - 1,100 m
Upper limit: Conformity or Interfingered (Hiketa Formation), Unconformity (Koda Formation, Yakeo Formation)
Lower limit: Unconformity (Ryoke Granitoids, Kan-onji Granite)

Northern marginal facies (Asan mountains, Kagawa pref.)
[ Upper ]
~~~~~~~~~~~~~~
Hiketa Formation
--------------
Shiroyama Formation
~~~~~~~~~~~~~~
[ Lower ]

Izumi Group
[ North ]
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Northern marginal facies
~~~~~~~~~~~~~~
Main facies
~~~~~~~~~~~~~~
Southern facies
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[ South ]

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

Distribution: Dokigawa river - Shioiri - Soda - Nakatojigengyo - Noguchi dam, Manno city, Nakatado county, Kagawa pref.; Kanewari, Sanuki city, Kagawa pref.; Shiroyama, Higashikagawa city, Kagawa pref.; Marui - Takenari - Lake Iwanabeike, Kanonji city, Kagawa pref.; Tsuji - Kochi - Saitanaka - Yamawaki - Shichika - Togawa dam, Mitoyo city, Kagawa pref.; Kashiwabara - Sogisho, Ayagawa city, Ayauta county, Kagawa pref.; Kanewari, Sanuki city, Kagawa pref.
Fossils: Brachidontes nankoi, Crassostrea sp., Eriphyla sp., Loxo japonica, Ostrea sp., Periplomya sp., Pitaria sp., Placunopsis? sp., Portlandia sp., Thyasira sp., Yoldia japonica

Noda et al. (2021) Geology of the Ikeda District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 150p. (in Japanese with English abstract 5p.)
Noda et al. (2017) Geology of the Kan-onji District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 96p. (in Japanese with English abstract 4p.)
Yoshikawa et al. (2011) Jour. Geol. Soc. Japan, vol.117, no.9, pp.523-537 DOI