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Dhading Dolomite Formation
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Dhading Dolomite Fm base reconstruction

Dhading Dolomite Fm

Period: 
Calymmian

Age Interval: 
earliest Calymmian


Province: 
Nepal Lesser Himalaya

Type Locality and Naming

Katmandu region (Lesser Himalayan succession). The Dhading Dolomite forms prominent hills and ridges around Dhading.


Lithology and Thickness

It is essentially a microcrystalline and dense dolomite, exhibiting light gray color and splintery fractures (Stöcklin and Bhattarai 1977, p. 17). It is thick-bedded and massive in the main part, but is thinner-bedded to platy in its basal portion. There are thin lenticular and nodular chert bands at various levels. In some places, the upper, rather darker dolomite contains black siliceous and argillaceous slate bands of up to 20 m in thickness. Although the dolomite appears massive from afar, it is generally finely laminated. Frequently, such laminae are of algal nature and pass into stromatolites. The Dhading Dolomite varies in thickness from 500 to 1,000 m.


Lithology Pattern: 
Dolomite


Relationships and Distribution

Lower contact

With a decrease in the phyllite content, the Upper Member of the Noupui Fm transitionally passes into the overlying Dhading Dolomite Fm.

Upper contact

The contact of the Dhading Dolomite Fm (uppermost formation of Lower Nawakot Gr) with the overlying Benighat Slates Fm (lowermost formation of the Upper Narakot Gr) is quite abrupt in the Budhi Gandaki section of central Nepal, where the black Benighat slates override the dolomites without any transitional zone. At the base of the Benighat Slates, there is an approximately 50–100 cm thick weathered zone alluding to an erosional unconformity at the top of the Dhading Dolomite Fm (Stöcklin and Bhattarai 1977, pp. 17–18). However, in west Nepal and in other parts of the country, such a sharp disconformity is not observed. In places, the dolomites and slates are interbedded and this formation transitionally passes into the black slates of Benighat.

Regional extent

The Dhading Dolomite forms prominent hills and ridges around Dhading.


GeoJSON

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Fossils

Stromatolites are distributed in almost all levels of the Dhading Dolomite. Generally, they are of columnar and branching types, resembling conophyton and collenia reported from the Northwest Himalaya.


Age 


Age Span: 

    Beginning stage: 
Calymmian

    Fraction up in beginning stage: 
0.05

    Beginning date (Ma): 
1,590.00

    Ending stage: 
Calymmian

    Fraction up in the ending stage: 
0.1

    Ending date (Ma):  
1,580.00

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.