Geological and geophysical investigations for delineating karstic structures insouthwestern portion of Cuddapah Basin, Andhra Pradesh, India

A large number of karstic structures and cavernous zones occurring in calcareous formations of lower Cuddapahs and Kurnools of Proterozic period are reported from the southwestern portion of Cuddapah basin, Andhra Pradesh, India. These structures are abundantly found around Tadpatri (Anantapur district) and Betemcherla (Kurnool district) towns and are aligned in NNE-SSW direction. This region is infested by a large number of ENE-WSW, NNE-SSW and NW-SE lineaments as well as intersected by NE-SW and NW-SE trending major faults. Geological, structural and geomorphological set-up suggest the presence of many more such cavernous zones in this region. Geological (structural, geomorphological) and geophysical (geoelectric resistivity sounding, profiling, total magnetic intensity and shallow seismic refraction) studies were carried out around Chillavaripalle, Kona (Anantapur district), and Kuntalapadu (Κυ,ηηοοί district) to identify and delineate a few more new karstic structures in this region. Geological studies revealed the presence of a few shear and fault zones in this area. Geomorphological observations have been useful to identify a few horizontal cavernous zones occurring at different levels above the present river beds indicating the paleodrainage system. Some new karstic zones lying, at shallow depths, viz. around 25 _m, have been identified on the basis of the detailed geophysical investigations. The most important finding of these studies is the close correlation of the levels of cavernous zones with planation surfaces. Similar observations were made in Japan, UK, USA, Canada and Africa. Such correlation appears to be a global phenomenon. It appears that the eustatic movements which occurred during the Quaternary period might have played a significant role in causing karstification of carbonate rocks of this area.