Isotopic signatures of the Kallankurichchi Formation (Lower Maestrichtian) Ariyalur group, Tiruchy district, South India - Insightes from O and C data

Izotopski znaci Kalankuriči formacije (donji Mastriht) Arijalur grupe u oblasti Tiruči na jugu Indije - saznanja na osnovu podataka O i C

Abstract

The use of stable isotopes in the studies of carbonates is in ever increasing trend inview of their sensitivity with reference to the depositional and diagenetic agents acted. Keeping this in raind, an attempt had been made to understand the isotopic signals expressed by the rocks and rock components of the Kallankurichchi Formation. The analysed samples give negative values for O and C isotopes except the very low positive values for C isotope. The δ18O values vary from -7.23 ‰ to -2 .0 ‰. The δ13C values vary from -15.2 ‰ to 0.43 ‰. Presence of positive values of carbon isotope in shells even after considerable fresh water alteration indirectly imply the prevalence of high organic content of their original phases. The higher δ13C values indicate increased productivity caused either by increased precipitation and runoff to the depositional basin from land or upwelling. Generally these values indicate reequilibration of rock components with isotopically light waters (fresh water) although there are some marine signals (unaltered or less altered). The variable trend of the carbonates indicate the variable diagenetic zones and their respective intensity of alteration. Plotting of these results in a diagram and interpreting them led to interpret the prevalence of three types of diagenetic waters. Further, the salinity and temperature values of diagenetic waters have also been interpreted and presented in this paper.