Geological Significance of Magnetic Depth Estimates Over Western Part of Cuddapah Basin, South India

Results of interpretation of magnetic total intensity anomalies, observed over the western part of the Cuddapah Basin, have shown that the magnetic sources are, mainly distributed at two levels and they are widely separated in depth. The shalJow sources ranging in depth from 400 m to 1900 m below ground are inferred to be due to shallow basement or due to basic intrusives within the basin sediments. The deeper sources ranging in depth from 5.0 to 8.0 km below ground are attributed to basic intrusives at or within the underlying bas(ment. The wide range of variation in depth to the magnetic sources point to the presence of basement faults paralleling the western margin, particularly around Yadiki and between Parnapalli and Vempalli in the south western part of the basin.

Magnetic interpretation has brought out positive evidence for post-Tadpatri-pre Gandikota and post-Gandikota-pre-Kurnool igneous episodes in this part of the basin and helped to resolve the large discrepancy in the geological estimate of the thickness of Gandikota quartzites. The maximum thickness of Kurnool sedimems is of the order of 500 m and it is likely that the Kurnools have been deposited on an uneven and eroded top of Cuddapahs allowing for local thickening of Kurnool sediments. The results of magnetic interpretation tend to support the concept of sub-basins and the Bairenkonda quartzites appear to have been deposited directly over the Archaean granites and gneisses without the intervention of Papaghni and Chitravati groups of sediments, at least in the southeastern part of the Cuddapah Basin.