The Cuddapah Basin is a crescent shaped, N-S trending Proterozoic basin in east-central part of the Dharwar craton.
- The crescent shaped basin is easterly concave covering an area of approximately 44,500 km2
- The eastern margin of the basin is demarcated by a thrust fault while all other boundaries are part of the ‘Eparchaean Unconformity’.
- The western half of the basin is undeformed and consists of 4 subbasins: the Papaghni, Kurnool, Srisailam and Palnad.
Papaghni Group :-
The Papaghni Group consists of two formations: the siliciclastic-dominant Gulcheru Quartzite; and the mixed siliciclastic–carbonate-bearing Vempalle Formation. The basal Gulcheru Quartzite consists of a matrix to clast-supported thick-bedded polymictic conglomerate with occasional interbeds of gritty trough cross-bedded feldspathic sandstone. •The Gulcheru Formation grades upwards to a mixed siliciclastic–carbonate unit with silicified stromatolitic limestone– dolomite beds, calcareous cross-bedded to rippled sandstone and laminated grey-green–brown shale, known as Vampalle formation.
Chitravati (Cheyyair) Group :-
The Chitravati Group consists of two formations: the Pulivendla Quartzite and the Tadpatri Formation. The transition from the Papaghni Group to the Chitravati Group is marked by the intermittent occurrence of mafic flows and associated shallow-crustal intrusives. There is deposition of a siliciclastic system – the Pulivendla Quartzite – that grades upwards into a mixed siliciclastic–carbonate system of the Tadpatri Formation. The Tadpatri Formation is overlain by another formation, the Gandikota Quartzite.(tidal flat).
Nallamalai Group :-
The Nallamalai Fold Belt (NFB) in the eastern part of the Cuddapah basin has folded and faulted metasedimentary rocks constituting the Nallamalai Group. The Nallamalai Group consists of the lower sandstone-dominated Bairenkonda Quartzite and the upper Cumbum Formation, consisting mainly of shales with sandstone and dolomite intercalations.
Srisailam Quartzite Formation :-
The Srisailam Quartzite (600+ m) unconformably overlies the granite gneiss basement along its western contact and is in thrust contact with the Nallamalai Group along its southern boundary.
AGE OF THE CUDDAPAH BASIN : –
- Radiometric dating by Ar/Ar method of mafic dykes/sills within the Tadpatri Formation or U–Pb ages of Baddeleyite from the same horizon, suggests that sedimentation was initiated before 1.9 Ga.
- The Chelima lamproites, which intrude into the Cumbum Formation, the upper formation of the Nallamalai Group, gives a 1.38 Ga age.
- The assemblages of algal stromatolites in different formations of the Supergroup indicate a middle to upper Riphean age.
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