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Phulchauki Gr
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Phulchauki Gr base reconstruction

Phulchauki Gr

Period: 
Ordovician, Silurian

Age Interval: 
late Ordovician-early Silurian


Province: 
Nepal Lesser Himalaya

Type Locality and Naming

Katmandu region (Tethyan sequence). Upward succession of the Tistung Fm sandstone, Sopyang Fm claystone, Chandragiri Limestone Fm, Chitlang Fm claystone and Godavari Limestone Fm.


Lithology and Thickness

See individual formations for details. "The Phulchauki Group is about 5,000–6,000 m thick, and is constituted principally of limestones with a subordinate quantity of shales and sandstones. … The Phulchauki Group commences with the Tistung Fm, which is comprised mainly of slates, phyllites, and metasandstones. Also noticeable is a distinct decrease in metamorphic grade from bottom to top of this formation. … The Sopyang Fm is represented by a mixed lithology of siliciclastic rocks as well as carbonates, and occupies a transitional zone between the Tistung Formation and overlying Chandragiri Limestone Fm. A wide facies variation is noticed within this formation. … The Chandragiri Limestone Fm, one of the key formations of the Phulchauki Group, forms a number of imposing mountain ranges (Chandragiri, Nagarjun, Phulchauki), overlooking Kathmandu. 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. … The Chitlang Fm is found mainly in the core of the Mahabharat Synclinorium. It is made up mainly of dark gray and purple, soft-weathering slates." The Godavari Limestone Fm begins with a lower clayey limestone below the main body of massive, coarsely crystalline, white to brown dolomite.


Lithology Pattern: 
Clayey limestone


Relationships and Distribution

Lower contact

Probably a major disconformity (most of Cambrian and Ordovician absent) onto underlying Markhu Fm (topmost Bhimphedi Gr) of possible earliest Cambrian age) according to schematic correlation diagram of Martin (2017) to Tethyan Himalayan succession.

Upper contact

Quaternary?

Regional extent

"The Phulchauki Group (Fig. 17.2) is unique in respect to Paleozoic fossil occurrence in the Chandragiri and Phulchauki hills, bordering the Kathmandu Valley on the south. These rocks are interpreted as part of a Tethyan outlier, positioned to the south of the high Himalayan peaks"; and overthrust onto possible "Lesser Himalaya" lower Proterozoic sediments.


GeoJSON

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Fossils

See individual formations


Age 

Martin (2017) suggests a facies correlation to the North Face Fm and Dark Band Fm of the Tethyan Himalaya, which are late Ordovician to early Silurian.

Age Span: 

    Beginning stage: 
Katian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
452.75

    Ending stage: 
Telychian

    Fraction up in the ending stage: 
1.0

    Ending date (Ma):  
432.93

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.