Nemuro Gr

Cenozoic

Cretaceous

Jurassic

Triassic

Permian

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Nemuro Gr

Period:

Cretaceous, Paleogene

Age Interval:

Province:
Hokkaido

Type Locality and Naming

Nemuro Belt.

Synonym: 根室; ねむろ

Lithology and Thickness

The group consists of clastic sedimentary rocks with volcanic and intrusive rocks (Kiminami 1983; Okada et al. 1987, Kiminamietal. 19920).

The lowermost formation (Campanian Nokkamappu Formation) contains lava and tuff breccia as well as coarse clastic rocks. The volcanic rocks consist of basalt, andesite and dacite with both tholeiitic and calc-alkaline chemical affinities (Kiminami et al. 19920).

Other upper sequences consist of maddy, sandy and conglomeratic formations, represented by turbidite, bottom current and slump deposits (Kiminami 1975, 1983; Naruse 2003; Naruse & Otsubo 2011).

The Nemuro Group is also characterized by occasional intrusions of mafic sills and associated pillow lavas within Maastrichtian-Paleocene horizons. These consist of highly potassic alkali dolerite (shoshonite) and monzonite (Yagi 1969; Ishikawa et al. 1971; Kiminauni et al. 1992c; Simura & Ozawa 2006).

Lithology Pattern:

Lava

Relationships and Distribution

Lower contact

The basement of the Nemuro Group is not exposed on land.

Upper contact

Unknown

Regional extent

Nemuro Belt

GeoJSON

null

Fossils

Cretaceous sections occasionally yield megafossils such as ammonoids and inoceramids (e.g. Naruse et al. 2000).

Age

Age Span:

Beginning stage:

Campanian

Fraction up in beginning stage:

Beginning date (Ma):

83.65

Ending stage:

Lutetian

Fraction up in the ending stage:

Ending date (Ma):

48.07

Depositional setting

The Nemuro Group has been regarded as representing forearc basin deposits based on their sedimentary facies (Kiminami 1983)， or as a frontal arc sequence based on the occurrences of effusive and intrusive rocks (Kimura & Tamaki 1985) .

Depositional pattern:

Additional Information

A carbonaceous bed assigned to the Cretaceous-Tertiary (K/T) boundary layer has been found by Kaibo & Saito (1986) and Saito et at. (1986) in the western parts of the belt (Shiranuka Hills).

Compiler:

Hayato Ueda. 2g Hokkaido. in Moreno, T., WALLIS, S., Kojima, T. & Gibbons, W. (Eds) 2016. The Geology of Japan. Geological Society. London. 201-220.