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Ochi Formation

Ochi Fm

Period:

Devonian

Age Interval:

Late Devonian (Frasnian), (15a)

Province:
Kurosegawa Belt- Shikoku

Type Locality and Naming

Kurosegawa Belt-central Shikoku

Synonym:

Lithology and Thickness

Mainly comprises alternating beds of sandstone and mudstone, with intercalated conglomerate, sandstone, mudstone and acidic tuff.

[Figure 1: Stratigraphy of the Paleozoic of the Kurosegawa Belt in the central part of Shikoku, Southwest Japan (after M. Ehiro et al., 2016)]

Lithology Pattern:

Clayey sandstone

Relationships and Distribution

Lower contact

Regionally, the schematic strat column indicates the next older unit as Nakahata Fm. It is in fault contact with the other formations (Yoshikura 1985), although Yasui (1984) has stated that there is a possibility that this formation unconformably rests on the underlying acidic tuff-dominated Devonian.

Upper contact

Regionally, the schematic strat column indicates the next younger unit as Yokokurayama Gr

Regional extent

Kurosegawa Belt-central Shikoku

GeoJSON

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Fossils

The Late Devonian plant Leptophloeum rhombicum has been reported (Hirata l966).

Age

Shown as Late Devonian, hence placed Base of Frasnian

Age Span:

Beginning stage:

Frasnian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

378.90

Ending stage:

Tournaisian

Fraction up in the ending stage:

1.0

Ending date (Ma):

346.73

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.