Lower Yezo Gr
Period:
Cretaceous
Age Interval:
c. Barremian-Aptian
Province:
Hokkaido
Type Locality and Naming
Sorachi-Yezo Belt (Yezo Main Zone)
Synonym:
Lithology and Thickness
The lower Yezo Group consists of deep-sea turbidites devoid of calcareous fossils except for slide blocks of shallow-marine Orbitolina limestone.
Lithology Pattern:
Sandy limestone
Relationships and Distribution
Lower contact
Sorachi Gr (conformable)
Upper contact
Middle Yezo Gr (conformable)
Regional extent
Sorachi-Yezo Belt (Yezo Main Zone)
GeoJSON
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Fossils
Age
Age Span:
Beginning stage:
Barremian
Fraction up in beginning stage:
0
Beginning date (Ma):
126.50
Ending stage:
Albian
Fraction up in the ending stage:
0
Ending date (Ma):
113.20
Depositional setting
Depositional pattern:
Additional Information
From the upper parts of the lower Yezo Group to the basal parts of the middle Yezo Group (Aptian-Albian), there are several kinds of characteristic deposits suggestive of regional tectonic events. In the middle and northern areas of the basin, deep-sea deposits containing slide blocks of shallow-water, Orbitolina limestones occur (Sano 1995; Iba & Sano 2007; Iba et al. 2011). In the middle-north areas of the basin, detrital serpentinites occur as blocks in stumps (Nagata et al. 1987) or clasts in debris-flow conglomerate and sandstone associated with calcareous bioclasts and ooids (Yoshida et al. 2003, 2010), suggesting exhumation and uplift of mantle materials within the basin. In the southern areas, submarine or locally fluvial unconformity can be recognized at several localities, where the middle Yezo Group overlies metabasites and meta-sediments of the Kamuikotan Zone rocks.
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.