Geochemical and stable isotope (δ13C & δ18O) signatures of Calcrete in and around Pandalgudi, Southern Tamilnadu, India and its implications on Palaeoclimate

Calcrete is an authigenic impure regolith carbonate deposit. It occurs as widespread deposits, which rest over the Proterozoic metamorphic basement rocks of the Pandalgudi region, Viruthunagar district of Tamilnadu, India. They occur as gravel, nodular, lumpy, chalky, and laminated or layered forms. Petro-mineralogical observation reveals micritic and microsparitic calcite precipitation around the detrital quartz and feldspar minerals, displacive and replacive structure in hornblende, hypersthene, and biotic minerals, veining, void lining, and lensoidal precipitation in the clay matrix. The X-ray diffraction analysis reveals the presence of clay minerals of montmorillonite, palygorskite, sepiolite, illite, chlorite, smectite, and kaolin. A major element geochemical analysis of calcrete samples indicates the predominant composition of CaO, MgO, SiO 2 , Al 2 O 3 , and Fe 2 O 3 against MnO, Na 2 O, K 2 O, TiO 2 , and P 2 O 5 . Geostatistical evaluation of major element geochemistry of calcrete through the methods of multiple correlations, principal component analysis (PCA), and cluster analysis illustrates the interrelationship and affinity among the major oxides. Depth-wise distribution trend analysis of stable isotopes of carbon δ 13 C and oxygen δ 18 O of calcrete profiles represents the meteoric diagenetic environment of freshwater carbonate sources. Proxies of major element geochemistry, clay mineralogy, and stable isotope signature of calcrete deposits illustrate arid and semiarid climates.