Cenozoic

Cretaceous

Jurassic

Triassic

Permian

Select Region(s) to search
Hold Ctrl (Windows/Linux) or Command (Mac) to select multiple

Osawa Formation

Osawa Fm

Period:

Triassic

Age Interval:

Early-Middle Triassic (Olenekian), (8e, 8f, 8g, 8h)

Province:
South Kitakami Belt-Central Sub-belt, South Kitakami Belt-Western Sub-belt

Type Locality and Naming

the Karakuwa-Oshika Sub-belt, the Shizugawa (Shizukawa)-Hashiura Sub-belt; Mizunuma area, the Shizugawa (Shizukawa)-Hashiura Sub-belt; Hashiura area, the Shizugawa (Shizukawa)-Hashiura Sub-belt; Shizugawa area

Synonym:

Lithology and Thickness

It consists mainly of calcareous laminated or massive mudstone, but sometimes contains lenticular slump beds of sandstones and conglomerates in the middle part. (e.g., Kamada 1980, 1983).

Lithology Pattern:

Claystone

Relationships and Distribution

Lower contact

Regionally, the schematic strat column indicates the next older unit as Hiraiso Fm

Upper contact

Regionally, the schematic strat column indicates the next younger unit as Fukkoshi Fm

Regional extent

GeoJSON

null

Fossils

The Osawa Formation has yielded the Ichthyosaurian fossil Utatsusaurus hataii in association with abundant ammonoids belonging to the Columbites-Subcolumbites fauna (Bando & Shimoyama1974; Bando& Ehiro I982).

Age

It is dated as late Olenekian (Spathian) (Bando & Shimoyama1974; Bando& Ehiro I982).

Age Span:

Beginning stage:

Olenekian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

249.88

Ending stage:

Olenekian

Fraction up in the ending stage:

1.0

Ending date (Ma):

246.70

Depositional setting

Depositional pattern:

Additional Information

Compiler:

Moreno, T., WALLIS, S., Kojima, T. & Gibbons, W. (Eds) 2016. The Geology of Japan. Geological Society. London. 1-24.