Basin Introduction :.
The Cuddapah basin is located between latitudes 13˚30’N to 17˚N and longitudes 78˚E
to 80˚E. The crescent shaped, easterly concave and N-S trending Cuddapah basin (Fig.)
covers an area of 44000 sq. km in the east central part of Dharwar craton. The basin
extends for a length of about 450 km along the arcuate eastern margin with a mean
width of 150 km, and is the second largest Purana basin of Penninsular India, after
the great Vindhayan basin. The arcuate north, south and western boundary of the
Cuddapah basin marks the profound uncomformity (called Eparchaean Unconformity in
early literature) on basement granites enclosing the Eastern greenstone belts in
Kadiri, Veligallu and Tsundupalle in the south, and Raichur, Gadwal and Peddavuru
in the north. The arcuate eastern margin is marked by a prominent boundary thrust,
which is parallel to the Nellore schist belt, Eastern Ghats mobile belt and the
East Coast. A giant basic dyke swarm underlies the basin in the west from Chittoor
in the south to Mahbubnagar in the north.
Cuddapah basin is characterized by quartzite-carbonate-shale cycles having an aggregate
thickness that is estimated to vary between 6 and 12 km. The early sediments of
the basin are interspersed with basic volcanics and sills. Felsic volcanics and
tuffs are intercalated with sediments at many horizons. The basin is well known
for its mineral potential in the form of limestones and dolomites, bedded and vein
barites, chrysotile asbestos and steatite, besides occurrences of base metals, diamond,
phosphorite, uranium and abundant building and ornamental stones.
The western half of the basin is undeformed and consists of four sub-basins, the
Papaghni, Kurnool, Srisailam and Palnad. The Papaghni and Kurnool sub-basins are
geographically interlinked, but were sites of deposition at different times, the
Papaghni sub-basin containing lower Cuddapah sediments, and the Kurnool sub-basin
containing the younger Kurnool sediments that overlie the Cuddapah sequence with
a major unconformity. Srisailam sub-basin contains upper Cuddapah sediments and
Palnad sub-basin exposes only the younger Kurnool sequence. The eastern half of
the Cuddapah basin is occupied by the Nalamallai fold belt consisting of upper Cuddapah
sediments. Nallamalai fold belt is demarcated from the undeformed western sub-basins
by the prominent fault lineament called the Rudravaram Line along which cleavage
begins to develop in the Cuddapah sediments, which become intensely deformed towards
the boundary thrust in the east.