Seismic imaging of the Proterozoic Cuddapah basin, south India and regional geodynamics

• Enigmatic nature of Proterozoic Cuddapah basin studied by detailed seismic imaging.
• Only 4 km thick sediments delineated contrary to more than 10 km reported earlier.
• Two layers with distinct velocities of Proterozoic Cuddapah sediments are demarcated.
• The basin dips from west to east, with maximum thickness below the fold belt.
• A peripheral foreland origin for the Cuddapah basin development is inferred.

Cuddapah basin has been believed to be one of the largest intra-cratonic Proterozoic sedimentary basins of India situated in the eastern part of the Dharwar craton of the south Indian shield, which is magmatically infested and contain thick column of sediments. Its overall sedimentary thickness as well as the nature of crustal evolution has remained enigmatic. Based on deep seismic sounding and other geological studies in the past, it was perceived that this basin may contain as much as 10–12 km thick sediments. The results of our present analysis derived up to a depth of ∼12 km reveals five layered upper crust associated with velocities (i) 4.50 km/s, (ii) 5.20–5.30 km/s, (iii) 5.50–5.80 km/s, (iv) 5.85–6.00 km/s, and (v) 6.40 km/s, out of which second and third layers correspond to upper and lower Cuddapah sediments. The results suggest the presence of only 4.0 km thick sediments in the deepest part of the basin below the Nallamalai fold belt, which has its implications in the developmental history of the basin. A thermal driving force was invoked by earlier workers to account for estimated 10–12 km thick sediments. However, the present estimate of only 4 km basement depth in the Cuddapah basin shows that the role of the thermal driving force may be marginal, particularly in the deeper eastern Cuddapah, as isostatic subsidence due to sedimentary accumulation alone is enough to explain the basin depth. Further, a basement sag of about 10 km would have logically needed lateral extension of the order of several hundreds of kilometers. However, as our present estimate of the sediment thickness gets reduced from earlier 10 km to only 4 km, the size of the basin (44,500 km2) would be in conformity with isostatic subsidence due to sedimentary accumulation hypothesis. The structural features derived from present analysis like maximum depth observed near the thrust/suture on the basin margin from where it decreases away from it, its association of shallow marine sediments, the arcuate shape of the basin along with its areal dimension resembles foreland basin between continent–continent collisions.