Geochemistry of paleosols and calcretes from Quaternary sediments of Purna alluvial basin, central India: An emphasis on paleoclimate

Abstract

The paleosols and calcretes therein, represented by root calcretes, calcrete nodules and groundwater calcretes have been geochemically analyzed to interpret various geological processes and conditions responsible for their formation. Paleosols comprise of high SiO2 followed by Al2O3, CaO and Fe2O3 that suggest basaltic to andesitic nature as revealed by the plot of total alkali (Na2O + K2O) versus silica (SiO2). The minor elements are characterized by enriched LREE, low HREE and observable Ce and Eu anomalies, whereas, trace elements exhibit low content of HFSE i.e., Zr, Y, Nb compared to LILE i.e., Sr, Ba, Rb, Cu, Co and V. Depositional process led changes in the concentrations of mobile and immobile elements have also been discussed.Calcretes, despite of their different morphologies and processes of formation, exhibit almost similar geochemical composition as no significant change in their coefficients is noticed. Major oxides exhibit the trend of CaO > SiO2>Fe2O3>Al2O3, of which, high content of CaO suggests precipitation of CaCO3 in the sediments during high alkaline condition of water. The minor elements also exhibit almost similar trends of both LREEs and HREEs, however, characterized by the presence of negative Ce anomaly. HFSE is characterized by low contents of Zr, Y and Nb, whereas, LILE show high contents of Sr, Ba, V, Cu and Co. Effects of weathering and diagenesis, leading to mobility of ions, have also been discussed on the basis of various coefficients of trace element.