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Chappani Formation
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Chappani Fm base reconstruction

Chappani Fm

Period: 
Calymmian

Age Interval: 
early Calymmian


Province: 
Nepal Lesser Himalaya

Type Locality and Naming

Tansen and lower Kali Gandaki region


Lithology and Thickness

"Mainly clayey sediments, containing small stromatolites at various levels. This formation is 400 m thick at its type locality and divided up into the following three members (Sakai 1985, p. 353). The Lower Member commences with a several meter-thick, silicified, columnar stromatolitic bed. The bed is overlain by a thick succession of gray slates, containing light green, thin, and parallel clay laminae at different stratigraphic rungs. … The Middle Member is a sequence of rhythmically alternating red-purple and green calcareous clay-slate. Its thickness ranges from 50 to 70 m, and it sporadically contains 5 to 10 cm thick, cream colored micritic limestone beds (Sakai 1985, p. 354). The Upper Member comprises white, light pink, and light green quartzose sandstones, intercalated in the same colored shales or slates. … One of the remarkable aspects of the Upper Member is the appearance of eolian sand beds and disseminated sand grains in dolomite beds (Sakai 1985, p. 355)."


Lithology Pattern: 
Continental marl


Relationships and Distribution

Lower contact

The Chappani Fm rests conformably over the Virkot Fm.

Upper contact

The overlying Khoraidi Fm begins with a large stromatolite-bearing dolomite bed, resting over the quartzites of the Chappani Fm.

Regional extent


GeoJSON

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Fossils

Stromatolites


Age 

Martin (2017) schematically suggests early Calymmian (ca. 1590 Ma)

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

"The clay-slates comprising the Lower Member of the Chappani Formation were deposited from suspension in the tranquil water of a lagoon, whereas the graded laminae presumably resulted from the turbidity currents related to sporadic flooding in an arid environment. The basal silicified stromatolites could have been formed in an intertidal zone. On the other hand, the small stromatolites, appearing in the Lower Member, were formed in supratidal ponds, marshes, or lagoons. Similarly, most of the Upper Member was deposited in lagoonal beaches and eolian dune complexes (Sakai 1985, p. 356)."


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.