Geochemistry of Palaeoproterozoic Kajrahat Limestone, Vindhyan Supergroup, central India: insights into depositional conditions and sources of rare earth elements

Abstract

This study investigates the geochemical composition of major, trace and rare earth elements (REEs) in the Palaeo-Proterozoic Kajrahat Limestone, Vindhyan Supergroup, Central India to infer the depositional environment and source for the REEs. The studied limestones, have a high percentage of CaO (ranging from42.27-66.53, n = 17), followed by SiO 2 as the major oxides. Sr is dominant trace element showing a negative correlation with CaO. This indicates that either Sr precipitated its own minerals or it was contributed by the siliciclastic material. All trace elements exhibit depletion with respect to Post-Archean Australian Shale (PAAS) values. The PAAS-normalized REE pattern of studied limestone has a relatively uniform pattern, with slightly enriched LREE compared to HREE, negative Ce anomaly (ranging from 0.66-0.89), negative Eu anomaly (largely ranging from 0.84-1.43), and low U/TH ratio (ranging from 0.12-1.25).The studied limestones exhibit a negative correlation between ΣREE and Fe 2 O 3 , MnO, MgO, Sr but a positive correlation with other elements. These positive correlations suggest that, in addition to seawater, siliciclastic sediments also serve as a source for the REEs. The (La/Yb) N , La/Sc, La/Th, and Th/Sc ratios imply that the terrigenous admixture in studied limestone likely originated from felsic source rocks. The geochemical investigation of studied limestone indicates a low U content (0.3-1.3, n = 17) and U/Th (0.12-1.25, n = 17) ratios suggest an oxygen-rich environment. This, in turn, indicates that the deposition of this limestone occurred in a coastal/ shallow marine environment with some contribution from continental part.