Bairenkonda Quartzite Fm

Lower formation of Nallamalai Gr

Synonym: Nagari Quartzite Fm -- In the western part of the Nallamalai Fold Belt (SanipaieBalrajupalle section), the Nagari Quartzite of coarse to pebbly sandstone and hummocky cross-stratified sandstone-siltstone is considered as equivalent of the Bairenkonda Quartzite.

Pebbly grit, quartzite, heterolithic shale-sandstone. Coarse to pebbly trough cross-stratified and rippled sandstone overlain by hummocky cross-stratified sandstone-siltstone. In the lower part straight crested ripples are common in the coarse sandstone with common desiccation features. In the upper part of the formation plane laminated shale with glauconitic medium-fine sand interbeds (Fig. – image A) give way to shaley rocks with thin dolomite and ferruginous quartzite, and thin oolitic ironstone, marking the transition to the overlying Cumbum Fm or equivalent Pullampet Fm.

[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)]

Fan-delta grading to peritidal to inner shelf, below storm wave base. The lower part of the Bairenkonda (Nagari) Quartzite shows features of a fan-delta grading upwards to a peritidal depositional setting. The oolitic ironstone together with mixed siliciclastic-carbonate in the transition zone to Cumbum Fm (Pullampet Fm) represents inner shelf deposition.