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Tobigamori Formation

Tobigamori Fm

Period:

Devonian

Age Interval:

Late Devonian (Famennian), (8a)

Province:
South Kitakami Belt-Okago region

Type Locality and Naming

Nagasaka-Soma district

Synonym:

Lithology and Thickness

consists mainly of mudstone and thin alternating beds of sandstone and mudstone with purple-coloured tuff and tuff breccia interbedded in the middle part.

[Figure 1: Stratigraphy of the Palaeozoic of the South Kitakatmi Belt, NE 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 Ainosawa Fm

Upper contact

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

Regional extent

Nagasaka-Soma district

GeoJSON

null

Fossils

Yabe & Noda (1933) reported the Late Devonian (Famennian) brachiopod Spirifer verneuili (Cyrtospirifer tobigamoriensis; Noda & Tachibana 1959) from the Tobigamori Formation, these being the first Devonian fossils discovered in Japan. The middle part of the formation yielded the land plant Leptophloeum rhombicum (Tachibana 1950), whereas in the uppermost part Ehiro & Takaizumi (1992) reported two Late Devonian (and an earliest Carboniferous) ammonoids.

Age

The main part of the formation is therefore assumed to be Late Devonian in age, ranging up to earliest Carboniferous.

Age Span:

Beginning stage:

Famennian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

371.10

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.