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Sopyang Formation
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Sopyang Fm base reconstruction

Sopyang Fm

Period: 
Ordovician

Age Interval: 
late Ordovician


Province: 
Nepal Lesser Himalaya

Type Locality and Naming

Katmandu region (Tethyan sequence)


Lithology and Thickness

"The Sopyang Formation is represented by a mixed lithology of siliciclastic rocks as well as carbonates, and occupies a transitional zone between the Tistung Fm and overlying Chandragiri Limestone Fm. A wide facies variation is noticed within this formation. In its type area, soft-weathering, thin-bedded, argillaceous to marly phyllitic slates contain lenticular beds of argillaceous limestone. The rock exhibits typically dark gray to black colors. Some worm tracks are present on bedding planes of slates. In other places, black slates are intimately associated with a dark gray limestone, and there are also areas where a few isolated limestone beds are found. In the upper part, the limestone bands vary in thickness from a few meters to 20 m or more, and they are intercalated in green or gray sandy phyllites of Tistung affinity. The Sopyang Formation ranges in thickness from 100 to 300 m (Stöcklin and Bhattarai 1977, p. 31).


Lithology Pattern: 
Shallow-marine marl


Relationships and Distribution

Lower contact

Underlain by the Tistung Fm.

Upper contact

The Sopyang Fm invariably grades into the Chandragiri Limestone Fm through thin-bedded argillaceous limestones (Stöcklin and Bhattarai 1977, p. 31).

Regional extent


GeoJSON

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Fossils


Age 


Age Span: 

    Beginning stage: 
Katian

    Fraction up in beginning stage: 
0.25

    Beginning date (Ma): 
450.87

    Ending stage: 
Katian

    Fraction up in the ending stage: 
0.5

    Ending date (Ma):  
448.98

Depositional setting


Depositional pattern:  


Additional Information


Compiler:  

Descriptions from Megh Raj Dhital (2015, Geology of Nepal: Regional Perspective of the Classic Collided Orogen, Springer Publ., 499 pp.). Age spans estimated from correlation diagrams in Martin, A.J. (2017, "A review of Himalayan stratigraphy, magmatism, and structure", Gondwana Research, 49: 42-80; http://dx.doi.org/10.1016/j.gr.2017.04.031), but these are often controversial.