Saroma Gr
Period:
Cretaceous
Age Interval:
Province:
Hokkaido
Type Locality and Naming
Tokoro Belt
Synonym:佐吕間,さるま
Lithology and Thickness
The Saroma Group comprises coherent sedimentary sequences of conglomerate, sandstone and mudstone, The basal conglomerates contain poorly sorted and rounded boulders and cobbles, and show a generally finings-upward succession grading into turbidites.
Sandstones and conglomerates within the sequence are highly volcanogenic. Sandstones are lithic wacke consisting dominantly of mafic to intermediate volcanic rock fragments and plagioclase (Kiminami & Kontani 1983D), with abundant clinopyroxene clasts with island-arc-type chemistry (Kanamatsu et al. 1992).
Conglomerates are dominated by pyroxene- or hornblende-andesite clasts, with lesser amounts of basalt, rhyolite, alkali plutonic rock and sedimentary rock clasts (Research Group of the Tokoro Belt 1984).
Lithology Pattern:
Aus Conglomerate
Relationships and Distribution
Lower contact
Nikoro Gr (synclines unconformably)
Upper contact
No data.
Regional extent
Tokoro Belt
GeoJSON
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Fossils
See “Age” section.
Age
Late Cretaceous ages have been assigned using bivalves (Sakakibara & Tanaka 1986; Obata et al. 1993) and radiolarians (Iwata et al. 1983b; Kanamatsu et al. 1992).
Age Span:
Beginning stage:
Coniacian
Fraction up in beginning stage:
0
Beginning date (Ma):
89.39
Ending stage:
Maastrichtian
Fraction up in the ending stage:
0
Ending date (Ma):
72.17
Depositional setting
The Saroma Group is therefore considered to represent deposits of a forearc basin developed over a Nikoro Group accretionary complex (Kiminami & Kontani 1983a; Kiminami et al.1985a, b).
Depositional pattern:
Additional Information
Clasts of alkali plutonic rocks such as monzonite and syenite suggest close genetic Finks with the Nemuro Gr.
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.