Atokura Formation

Atokura Formation Watabe et al., 1950

Invalid synonym: Tochiya Formation (Local name in Ogawa - Yorii area, Saitama pref.), Kazo Formation, Takeyama Formation

Coherent formation
Late Cretaceous (129.0 - 127.0 Ma, Ammonoids; 86.0 - 84.0 Ma, Ammonoids, Inoceramus)

Sedimentary facies: Marine
Metamorphic facies: Pumpellyite-Actinolite
Lithofacies (Upper): Turbidite
Lithofacies (Upper): Interbedded sandstone and mudstone
Lithofacies (Middle): Sandstone
Lithofacies (Lower): Conglomerate
Sedimentary structures: Graded bedding, Sole marks
Paleocurrent: East-southeast to West-northwest

Thickness: 1,650 m or thicker
Thickness (Interbedded sandstone and mudstone): 350 - 600 m
Thickness (Conglomerate, Sandstone): 250 - 400 m
Upper limit: Unknown
Lower limit: Unconformity (Hornfels associated with Kinshozan Quartz Diorite)

Atokura Formation
[ Upper ]
?--?--?--?--?-
Shimokanoya Mudstone Member
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Nakanokaya Conglomerate Member
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Miyamuro Sandstone and Mudstone Member
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Okuwahara Sandstone Member
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Atokura Conglomerate Member
~~~~~~~~~~~~~~
[ Lower ]

Atokura Nappe (Saitama pref.)
[ Upper ]
/--/--/--/--/-
Yorii Welded Tuff, Paleocene
/--/--/--/--/-
Yorii Formation, Late Cretaceous - Paleocene
/--/--/--/--/-
Atokura Formation, Late Cretaceous
/--/--/--/--/-
Kinshozan Quartz Diorite, Permian
/--/--/--/--/-
[ Lower ]

Atokura Nappe (Gunma pref.)
[ Upper ]
/--/--/--/--/-
Kotsutateyama Tuff, Paleocene
/--/--/--/--/-
Atokura Formation, Late Cretaceous
/--/--/--/--/-
Yotsumatayama Quartz Diorite, Early Cretaceous
/--/--/--/--/-
Kawaiyama Quartz Diorite, Permian
/--/--/--/--/-
[ Lower ]

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

Distribution: Mount Ogui - Mount Ontakeyama - Okitano, Shimonita city, Kanra county, Gunma pref.; Tochiya - Ouchizawa - Yatsu - Murei, Yorii city, Osato county, Saitama pref.; Ogawa city, Hiki county, Saitama pref.; Hirasawa, Ranzan city, Hiki county, Saitama pref.; Kanezawa - Mount Odake, Minano city, Chichibu county, Saitama pref.; Mount Kamiyama, Kamikawa city, Kodama county, Saitama pref.
Fossils: Ammonoids (Diplomoceratid), Foraminifera, Pollen, Plant fragments
Fossils (Bivalves): Astarte? sp., Inoceramus sp., Nucula sp., Propeamussium sp.
Fossils (Radiolarians): Amphipyndax? sp., Archaeodictyomitra sp., Archaeospongoprunum? sp., Dictyomitra sp., Holocryptocanium cf. burbi, Praeconocaryomma sp., Stichomitra sp.

Takagi et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.7, pp.305-324, DOI
Makimoto and Takeuchi (1992) Geology of the Yorii District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 136p. (in Japanese with English abstract 6p.)