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KrolA Formation
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KrolA Fm base reconstruction

KrolA Fm

Period: 
Neoproterozoic

Age Interval: 
Ediacaran


Province: 
N.India Lesser Himalaya

Type Locality and Naming

Simla (Shali Basin), Himachal Pradesh-Uttarakhand, the name Krol Series was first given by Medlicott (1864) to a series of limestone, red and green shales and sandstones seen in the Krol mountain near Solan in Simla area. [Original Publication: Auden, J.B.,1934. The geology of the Krol Belt. Rec. Geol. Surv. Indi. 67, 357-454.]


Lithology and Thickness

Clayey limestone. It comprises chiefly a rapid alternation of greenish grey calcareous shale and argillaceous limestone with variable gradation. Limestone beds are five to 30 cm in thickness. Particularly towards the top of the Fm one to five meters thick beds of oolitic limestone weathering to a buff colour make their appearance. Chert and phosphorite are also reported from the KrolA. The KrolA has variable thickness of about 100 to 120 m.

[Figure: Krol Gr lithology table (provided by O.N. Bhargava & Birendra Singh)]


Lithology Pattern: 
Clayey limestone


Relationships and Distribution

Lower contact

Gradational with InfraKrol Fm.

Upper contact

Gradational with KrolB Fm.

Regional extent

Himachal Pradesh to Uttarakhand


GeoJSON

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Fossils

cyanobacteria (C); Salome hubeiensis and acanthomorph acritarchs (AA); Ericiasphaera, Echinosphaeridium, Asterocapsoides from Tiwari and Knoll (1994).


Age 

Ediacaran, Relative age span estimates taken from the correlation chart from (H. Xu, J.G. Meert and M.K. Pandit, Geoscience Frontiers 13 (2022).

Age Span: 

    Beginning stage: 
Ediacaran

    Fraction up in beginning stage: 
0.35

    Beginning date (Ma): 
601.33

    Ending stage: 
Ediacaran

    Fraction up in the ending stage: 
0.40

    Ending date (Ma):  
596.52

Depositional setting

It represents deposition in an open shallow sea with moderate energy, the sedimentation taking place mainly in deeper subtidal zones in the basal part and shallow subtidal environment near fair weather wave base in the upper part. Detailed sequence stratigraphic studies identified several disconformable surfaces (Jiang et al. 2002) indicating interruptions in largely tidal to intertidal (Singh 1980) sedimentation in a shallow NW-sloping marine Krol Basin, with minor phases of deep-water environment (Jiang et al. 2003). The rocks of the KrolA show a great profusion of current formed structure. Parallel lamination, small-scale cross laminations and scour and fill structures are abundant. Thickness of cross-laminated units and the depth of scours are between two and 10 cm. Symmetrical ripple marks with wave length ranging between two and 15 cm are also frequently seen. It also displays graded bedding from fine to very fine in the form of light and dark bands particularly in the shale and argillite.


Depositional pattern:  


Additional Information

See Srikantia and Bhargava, 2021; Jain et al, 2020 and Jiang et al., 2002


Compiler:  

O.N. Bhargava & Birendra Singh.