Osawa Formation

Osawa Formation Mikami, 1955

Invalid synonym: Osawa Tuff

Type locality: Osawa, Atsugi city, Kanagawa prefecture
Volcanic rocks
Oceanic arc of Paleo-Izu-Bonin arc
Mountain flank deposits of submarine volcanos and volcanic islands on Tanzawa mass
Middle Miocene (12.0 - 11.5 Ma)

Sedimentary facies: Marine
Metamorphic facies: Prehnite-Pumpellyite
Lithofacies: Subaqueous volcaniclastics, Subaqueous lavas
Lithofacies: Epiclastic turbidite, Pumiceous turbidite
Lithofacies: Dacite lapilli tuff, Andesite - Basalt tuff breccia, Lapilli tuff, Tuff
Lithofacies (Minor): Tuffaceous sandstone, Shale, Tuff breccia

Thickness: 250 - 1,000 m
Upper limit: Bottom of the horizon intercalating mudstone and fine-grained tuff
Upper limit: Conformity (Yataro Formation)
Lower limit: Conformity

Susugaya Subgroup
[ Upper ]
~~~~~~~-------
Yataro Formation
--------------
Osawa Formation
--------------
Fudojiri Formation
--------------
[ Lower ]

Tanzawa Group
[ Upper ]
--------------
Susugaya Subgroup
--------------
Oyama Subgroup
--------------
Togatake Subgroup
--------------
[ Lower ]

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

Distribution: Osawa, Atsugi city, Kanagawa pref.; Shijuhasse river, Hadano city, Kanagawa pref.; Yataro river - Toriyamachi creek, Kiyokawa city, Aiko county, Kanagawa pref.
Fossils: Chlamys kaneharai, Plant fragments

Ishikawa et al. (2016) Jour. Geol. Soc. Japan, vol.122, no.7, pp.291-304, DOI
Ueki et al. (2013) Geology of the Hachioji District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, AIST, 137p. (in Japanese with English abstract 6p.)
Matsubara and Amano (2010) Jour. Geol. Soc. Japan, vol.116, no.3, pp.134-150 DOI
Oka et al. (1979) Geology of the Fujisawa District, Quadrangle Series, Scale 1:50,000, Geological Survey of Japan, 111p. (in Japanese with English abstract 5p.)