Niranohama Fm
Period:
Jurassic
Age Interval:
lowest Middle Jurassic (Hettangian), (8e)
Province:
South Kitakami Belt-Western Sub-belt
Type Locality and Naming
Shizugawa (Shizukawa)-Hashiura Sub-belt; Shizugawa area
Synonym:
Lithology and Thickness
It consists of sandstone and sandy mudstone
Lithology Pattern:
Sandy_claystone
Relationships and Distribution
Lower contact
The Niranohama Fm rests unconformably on the Saragai Gr
Upper contact
Regionally, the schematic strat column indicates the next younger unit as Hosoura Fm
Regional extent
Shizugawa (Shizukawa)-Hashiura Sub-belt; Shizugawa area
GeoJSON
null
Fossils
It has yielded abundant bivalves and middle-upper Hettangian ammonoids (Matsumoto 1956; Hayami 1961b); Sato 1962; Takahashi 1969; Sato & Westermann 1991). A diverse belemnite fauna has been reported from this formation (lba et al., 2012).
Age
Shown as lowest Middle Jurassic (middle-upper Hettangian), hence placed 50% up in Hettangian
Age Span:
Beginning stage:
Hettangian
Fraction up in beginning stage:
0.5
Beginning date (Ma):
200.41
Ending stage:
Hettangian
Fraction up in the ending stage:
1.0
Ending date (Ma):
199.46
Depositional setting
Brackish-littoral environment (Hayami 1961a)
Depositional pattern:
Additional Information
Compiler:
Moreno, T., Wallis, S., Kojima, T. & Gibbons, W. (Eds) 2016. The Geology of Japan. Geological Society. London. 1-24.