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Malekhu Limestone Formation
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Malekhu Limestone Fm base reconstruction

Malekhu Limestone Fm

Period: 
Calymmian

Age Interval: 
early Calymmian


Province: 
Nepal Lesser Himalaya

Type Locality and Naming

Katmandu region (Lesser Himalayan succession)


Lithology and Thickness

The Malekhu Limestone is one of the conspicuous units of the Upper Nawakot Group. It is constituted of thin-bedded, platy dolomitic and siliceous limestones of pale-yellow color. It is microcrystalline to dense, and hard with green sericite–chlorite partings and thin intercalations. Especially, its lower and upper parts comprise platy limestone, whereas the middle portion is rather thick-bedded dark gray dolomite or dolomitic limestone with bands of black chert and intercalations of black siliceous and carbonaceous slates. Frequently, there is an approximately 50 m thick basal limestone zone and it is separated by about 150 m thick black slates from the main limestone body. The Malekhu Limestone assumes a thickness of about 800 m at its type locality (Stöcklin and Bhattarai 1977, p. 20) and is presumably older than 1.3 Ga (Martin et al. 2011).


Lithology Pattern: 
Dolomitic limestone


Relationships and Distribution

Lower contact

The Malekhu Limestone exhibits perfectly gradational contacts with the underlying slate bands of the Benighat Slates Fm. The transition is generally marked by an approximately 20–30 m thick alternation of calcareous and argillaceous rocks.

Upper contact

The Malekhu Limestone exhibits perfectly gradational contacts with the overlying slate bands of the Robang Fm. The transition is generally marked by an approximately 20–30 m thick alternation of calcareous and argillaceous rocks.

Regional extent


GeoJSON

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Fossils

At Malekhu, sporadic domed stromatolites are observed in its middle part.


Age 


Age Span: 

    Beginning stage: 
Calymmian

    Fraction up in beginning stage: 
0.3

    Beginning date (Ma): 
1,540.00

    Ending stage: 
Calymmian

    Fraction up in the ending stage: 
0.25

    Ending date (Ma):  
1,550.00

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.