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Chandragiri Limestone Formation
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Chandragiri Limestone Fm base reconstruction

Chandragiri Limestone Fm

Period: 
Ordovician

Age Interval: 
Katian


Province: 
Nepal Lesser Himalaya

Type Locality and Naming

Katmandu region (Tethyan sequence). The Chandragiri Limestone, one of the key formations of the Phulchauki Group, forms a number of imposing mountain ranges (Chandragiri, Nagarjun, Phulchauki), overlooking Kathmandu.


Lithology and Thickness

It is a pale yellow to brown (when weathered) limestone of massive appearance from a distance, but reveals well-developed bedding and platy partings at close inspection. Frequently the limestone is microcrystalline, partly siliceous, and even dolomitic. The fresh rock color varies from pale yellow and white to pale green and pink. There are also thin intercalations, partings, and films of sericite and chlorite. Generally, the lower portion of the limestone is relatively thinly bedded and more argillaceous than the rest of it. On the historic trail from Thankot to the Chandragiri Pass, an approximately 100–200 m thick band of thinly bedded, white quartzite is intercalated in the upper third of the formation. Above this band are thinner-bedded and more argillaceous, bright pink and green colored limestones, which contain conspicuous wave ripple marks on a number of phyllitic intercalations. The Chandragiri Limestone varies in thickness from 2,000 to 2,500 m."


Lithology Pattern: 
Limestone


Relationships and Distribution

Lower contact

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

Upper contact

Martin 2017 implies Hirnantian is absent=> Disconformity, then the overlying Chitland Fm slates. However, another interpretation (Dhital, 2015) is that the "last fossiliferous limestones gradually pass upwards into the slates, belonging to the Chitlang Formation."

Regional extent

The Chandragiri Limestone, one of the key formations of the Phulchauki Group, forms a number of imposing mountain ranges (Chandragiri, Nagarjun, Phulchauki), overlooking Kathmandu.


GeoJSON

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Fossils

These strongly rippled beds contain a profusion of well-preserved crinoid and other echinoderm fragments, yielding a Late Ordovician age.


Age 

" Because the Chandragiri Limestone is very thick, and the fossils are present in its upper part, its age may range from the Cambrian to Ordovician, as with many other Tethyan sequences developed in Dolpa, Thakkhola, and Manang (Stöcklin and Bhattarai 1977, p. 29)." However, Martin (2017) suggests a facies correlation to the upper-middle North Face Fm, which he implies is only upper Katian.

Age Span: 

    Beginning stage: 
Katian

    Fraction up in beginning stage: 
0.5

    Beginning date (Ma): 
448.98

    Ending stage: 
Katian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
445.21

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.