Sedimentary Facies and Stratigraphic Significance of Cumbum and Bairenkonda Type Sections of Nallamalai Fold Belt, Cuddapah Basin, Andhra Pradesh

Sedimentary facies in the Cumbum and the Bairenkonda type sections include banded slate, graded rhythmite. quartzite and dolomite (Cumburn Formation), quartzite-slate, massive quartzite, parallel stratified quartzite and medium to thick bedded quartzite (Bairenkonda Formation). The quartzite-slate facies marks the gradational contact between the Cumburn and the Bairenkonda Formations. Stratigraphic disposition of sedimentary facies between these two type sections is identical and correlatable. These sediments are deformed into NNE-SSW trending tight to open folds and NW-SE to E-W trending cross folds. It is now indicated that the Cumbum Formation is stratigraphically older than the Bairenkonda Formation and the resultant succession is at variance to the hitherto held stratigraphic framework. The argillite-dominated Cumbum sedimentary facies indicates deep-water depositional setting, whereas the arenite - dominated Bairenkonda facies represents shallow water environment, thereby pointing to the shallowing up of the basin during Nallamalai sedimentation.