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

Abstract

The Lower Vindhyan (Semri) Group substantially consists of unmetamorphosed and undeformed sedimentary sequences of Palaeoproterozoic age. A detailed geochemical study has been carried out to infer the paleoenvironment and the source of REEs for the Palaeoproterozoic Kajrahat Limestone, Vindhyan Supergroup, Central India. This study investigates the geochemical composition of major, trace and rare earth elements (REEs). The studied limestones, have a high percentage of CaO (ranging from 30.87 to 48.59) implies that calcite was the primary mineral phase in these carbonates. SiO₂ is second most abundant major oxide. Sr is dominant trace element showing a negative correlation with CaO. All trace elements exhibit depletion with respect to Post-Archean Australian Shale (PAAS). The PAAS-normalized REE pattern of studied limestone has a relatively uniform pattern, with slightly enriched LREE compared to HREE with negative Ce anomaly. Collectively, low concentration of U and U/Th, Ce/Ce* ratios clearly indicates an oxic depositional condition for the samples. The ΣREE shows a positive correlation with SiO₂, TiO₂ and Al₂O₃ (r² = 0.87, 0.84and 0.91 respectively) and a week positive correlation with CaO (r² = 0.12) suggested that siliciclastic sediments also serve as a source for the REEs beside seawater. This, in turn, indicates that the deposition of this limestone occurred in a coastal/shallow marine environment with some contribution from continental part.