Isotopic Variations in Limestones from Kurnool Sediments in Cuddapah Basin, India

The Kurnool Sediments (Upper Proterozoic), have been isotopically examined for the identification of carbonate isotopic signatures that might indicate subaerial diagenesis. The sequence contains limestones at two stratigraphic levels. The Narji Limestones are in the first cycle and the Koilkuntla limestones in the second cycle of deposition. The δO¹⁸ values for Narji limestones show a progressive increase from the basal to top horizons. The gradation in the δO¹⁸ value might be due to interaction of various horizons with fresh water in the later geological periods and possible consequent exchange. The δC¹³ values of the Narji Limestones lie within the range of marine limestones. The δO¹⁸ values for Koilkuntla limestones, are lower compared to the values of Narji limestones. This might possibly be due to greater interaction with fresh water and exchange during diagenesis.