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Nallamalai Gr
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Nallamalai Gr base reconstruction

Nallamalai Gr

Period: 
Calymmian

Age Interval: 
Early Calymmian (?)


Province: 
Proterozoic S.India – Cuddapah basin

Type Locality and Naming

Named after the Nallamali Fold Belt in mid-Cuddapah basin. The Nallamalai Group outcrops mainly as folded, faulted and cleaved low-grade sedimentary succession.


Lithology and Thickness

Sandstone and shale: Comprised of a lower Bairenkonda Quartzite Fm and upper Cumbum Fm. Very thick – total of 6000 m (6 km). In the east central part of the NFB, the Nallamalai Group consists of quartzite, quartz phyllite, slate, and minor dolomitic limestone, with cumulative thickness of 1200 m.

[Figure: Field photographs showing lithology and deformation features of the Nallamalai Group. (A) Bairenkonda Quartzite Fm (upper part): Thin bedded, intercalated sandstone-shale alternating with thicker sandstone. (B) Cumbum Fm: Plane laminated shale. (C) West vergent folds and faults truncating fold limbs, west margin of Nallamalai fold belt (NFB). (D) Tight folds and axial plane cleavage in intercalated phylliteequartzite, eastern margin of NFB. (from Saha et al., 2016)]


Lithology Pattern: 
Clayey sandstone


Relationships and Distribution

Lower contact

Unconformity (tectonic contact) onto Gandikota Quartzite Fm (upper Chitravati Gr; ca. 1850 Ma)

Upper contact

Unconformity (tectonic contact), overlain by Srisailam Quartzite Fm (ca. 1450 Ma)

Regional extent


GeoJSON

{"type":"Feature","geometry":{"type":"MultiPolygon","coordinates":[[[[80.38,16.74],[79.24,15.25],[79.73,13.45],[77.64,14.72],[77.99,16],[80.38,16.74]]]]}}

Fossils


Age 

Arbitrarily assigned as 1600 to 1550 Ma based on vague correlations in Saha et al. (2016). Intrusion of Chelima lamproite/Racherla syenite (c.1350 Ma) in upper part

Age Span: 

    Beginning stage: 
Calymmian

    Fraction up in beginning stage: 
0.0

    Beginning date (Ma): 
1,600.00

    Ending stage: 
Calymmian

    Fraction up in the ending stage: 
0.25

    Ending date (Ma):  
1,550.00

Depositional setting

Fan-delta at base to outer shelf, then peritidal at top


Depositional pattern:  


Additional Information


Compiler:  

From: Saha D. (Dilip), Patranabis-Deb, S., and Colllins, A.S. (2016) Proterozoic stratigraphy of southern Indian cratons and global context. In: Stratigraphy & Timescales, 1: 1-59.