Yubetsu Gr
Period:
Paleogene
Age Interval:
Province:
Hokkaido
Type Locality and Naming
Hidaka Belts (Yubetsu-Nakanogawa Sub-belt)
Synonym: 湧别
Lithology and Thickness
The Yubetsu Group occurring near the Okhotsk coast of northeastern Hokkaido is characterized by turbidite sandstone and mudstone accompanied by conglomerate and red mudstone.
Taiika (1988) identified west-verging imbricate structures of thrust sheets, each of which comprises coarsing-upwards sedimentary sequences from basal red and green pelagic and hemipelagic mudstone to turbidite sandstone.
Sandstones of the Yubetsu Group are lithic, containing abundant rock fragments of mafic to intermediate volcanics (Kontani & Kiminami 1980). Whole-rock geochemistry of the sandstones suggests sedimentary provenances of an immature island arc (Kumon & Kiminami 1994).
Lithology Pattern:
Clayey sandstone
Relationships and Distribution
Lower contact
No data.
Upper contact
No data.
Regional extent
The Yubetsu Group occuring near the Okhotsk coast of northeastern Hokkaido.
GeoJSON
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Fossils
See “age” section.
Age
Red and green mudstones yield radiolarians fossils which were initially assigned a Late Cretaceous age (Iwata & Taiika1986; Iwata & Kato 1986). However, they contain species later known to be diagnostic of Paleocene times and were therefore re-examined and re-assigned as early Paleocene by Iwata & Taika (1992).A Late Paleocene K-Ar age of a tuff bed (Kiminami et al. 1990b) and Early Eocene dinofagellate cysts from a mudstone (Kurita & Tajika 1998) suggest that the turbidities are also early Paleogene in age.
Age Span:
Beginning stage:
Danian
Fraction up in beginning stage:
0
Beginning date (Ma):
66.04
Ending stage:
Bartonian
Fraction up in the ending stage:
0
Ending date (Ma):
41.03
Depositional setting
Depositional pattern:
Additional Information
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.