Cenozoic

Cretaceous

Jurassic

Triassic

Permian

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Hiraiso Formation

Hiraiso Fm

Period:

Triassic

Age Interval:

Early-Middle Triassic (Induan), (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 of a basal conglomerate overlain by bedded calcareous sandstones followed by alternating beds of calcareous sandstone and mudstone in the upper part.

Lithology Pattern:

Aus conglomerate

Relationships and Distribution

Lower contact

The Hiraiso Fm rests unconformably on the various horizons on the Upper Permian (Wuchiapingian-Changhsingian), and a stratigraphic interval from the lower Induan (uppermost Changhsingian?) to lower Olenekian is missing (Ehiro 2002). Regionally, the schematic strat column indicates this is the oldest unit

Upper contact

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

Regional extent

GeoJSON

null

Fossils

Bando (1970) described a nearly Induan (Griesbachian) ammonoid Glyptophiceras cf. gracile from the Hiraiso Formation, but it was probably derived from the Osawa Fm and the specific assignment needs to be pre-examined (Ehiro 2002)

Age

Shown as Lower-Middle Triassic, hence placed Base of Induan

Age Span:

Beginning stage:

Induan

Fraction up in beginning stage:

0.0

Beginning date (Ma):

251.90

Ending stage:

Induan

Fraction up in the ending stage:

1.0

Ending date (Ma):

249.88

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.