Shiramazu Formation

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Shiramazu Formation Kotake, 1988

Type locality: Shiramazu fishing harbour, Chikura town, Minamiboso city, Chiba prefecture
Coherent formation
Trench fill sediments, Landward slope basin of trench
late Pliocene (3.68 - 3.31 Ma)
Correlation: Anno Formation

Sedimentary facies: Marine
Sedimentary facies (Upper): Turbidite
Sedimentary facies (Lower): Debris flow deposit
Lithofacies: Sandstone-dominant interbedded sandstone and tuffaceous siltstone
Sedimentary structures: Slump structures, Cross stratification
Paleocurrent: South to North

Thickness: 200 - 400 m
Upper limit: Transitional (Mera Formation, Hata Formation)
Lower limit: Conformity (Shirahama Formation)

Chikura Group (Northern part)
[ Upper ]
?--?--?--?--?-
Negata Formation
--------------
Sagashi Formation
?--?--?--?--?-
[ Lower ]

Chikura Group
[ Upper ]
?--?--?--?--?-
Hata Formation
-------'''/,,,
Mera Formation
--------------
Shiramazu Formation
--------------
Shirahama Formation
?--?--?--?--?-
[ Lower ]

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

Distribution: Shiramazu fishing harbour, Chikura town, Minamiboso city, Chiba pref.; Shirahama town, Minamiboso city, Chiba pref.; Mera, Tateyama city, Chiba pref.
Fossils: Calyptogena sp., Foraminifera, Radiolarians, Diatoms, Calcareous nannofossils, Trace fossils
Tephra: GP, HI

Utagawa et al. (2017) Jour. Geol. Soc. Japan, vol.123, no.11, pp.969-976 DOI
Okada et al. (2012) Jour. Geol. Soc. Japan, vol.118, no.2, pp.97-108 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.)