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Virkot Formation
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Virkot Fm base reconstruction

Virkot Fm

Period: 
Statherian, Calymmian

Age Interval: 
latest Statherian-earliest Calymmian


Province: 
Nepal Lesser Himalaya

Type Locality and Naming

Tansen and lower Kali Gandaki region


Lithology and Thickness

"The Virkot Formation is represented by light pink to white quartzites and red-purple slates or phyllites. Owing to the intercalation of these white and red-purple rocks, this formation manifests a characteristic color banding (Sakai 1985, p. 348). The Virkot Formation is about 510 m thick and further subdivided into the following two members. Most of the Lower Member is a monotonous succession of red-purple shale or slate with well-developed crenulation cleavage. It contains the lowermost stromatolitic horizon encountered in the Kali Gandaki Supergroup (Sakai 1985, p. 348). … The Lower Member is about 300 m thick. Pink, white, and light green quartz arenites regularly alternate with red or green shales or slates in the lower portion of the Upper Member. … The uppermost part of the Upper Member is characterized by the abundance of very thick (tens of meters) pink quartzites. A 25-cm thick oolitic limestone bed is followed by a 15-cm thick stromatolitic limestone bed towards the top part of the Upper Member. These beds serve as a marker horizon, as they extend for a long distance."


Lithology Pattern: 
Clayey sandstone


Relationships and Distribution

Lower contact

The contact between the Virkot Fm and underlying Heklang Fm is placed at the first appearance of red-purple slate.

Upper contact

The Chappani Fm rests conformably over the Virkot Fm.

Regional extent


GeoJSON

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Fossils

Stromatolites


Age 

Martin (2017) schematically suggests ca. Statherian/Calymmian transition (ca. 1600 Ma)

Age Span: 

    Beginning stage: 
Statherian

    Fraction up in beginning stage: 
0.95

    Beginning date (Ma): 
1,610.00

    Ending stage: 
Calymmian

    Fraction up in the ending stage: 
0.05

    Ending date (Ma):  
1,590.00

Depositional setting

"The Virkot Formation was deposited in arid conditions. The thick quartzite beds were formed as sand dunes. The wavy and planar bedforms with cross-bedding, herringbone

cross-bedding, and ripple marks indicate a mixed origin of tidal and eolian environments near the shoreline. On the other hand, red-purple and green shales, predominating in the Lower Member, were deposited from suspension in a lagoonal environment, whereas the three stromatolitic horizons observed in the Upper Member indicate the deposition of these and associated rocks in an intertidal zone (Sakai 1985, p. 351)."


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.