The Vindhyan basin (~1.7-1.0 Ga) is the largest Precambrian sedimentary succession, covering the central (Son Valley, Bundelkhand) and western (Rajasthan) parts of India. Stratigraphically, it is divided into Semri, Kaimur, Rewa and Bhander Groups, and is well exposed in both the Son Valley and the Rajasthan area. The present study aims to provide detailed geology and geochemistry of the Lower Kaimur Sequence (LKS), that is, Chittor Fort Sandstone (CFS; ~1.1 Ga) of Rajasthan, Western India, and to compare it with the so-called contemporaneous deposits preserved in the Son Valley, consisting of Sasaram Sandstone (SS), Ghurma Shale (GS) and Markundi Sandstone (MS), in order of superposition. The CFS of Rajasthan consists of three lithofacies, comprising alternating shale and sandstone. The SiO 2 /Al 2 O 3, K 2 O/Na 2 O, and CIA values from CFS, Rajasthan, indicate a moderate to high degree of chemical weathering in a warm, humid climate, leading to the derivation of compositionally mature sediments. The Th-Sc-Zr/10 and La/Sc-Ti/Zr diagrams imply that the sandstones of CFS belong to a passive margin setting, whereas the shales bear a signature of a continental island arc. The average trace element ratios, Th vs Sc and Gd/Yb N versus Eu/Eu*, indicate that the siliciclastics have post-Archean continental-to-intermediate compositions. The trace element ratio plots of La/Sc versus La/Co and La/Sc versus Th/Co revealed that the Hindoli Group (~1.8 Ga) of the Aravalli-Delhi Fold Belt (ADFB) is the source for the shales of the CFS of Rajasthan. The sandstones likely received detritus from the Berach granite (~2.5 Ga) of the Banded Gneissic Complex. At 1.6 Ga, due to this collisional activity, the compressional and extensional stresses caused the opening of the Vindhyan basin, which is separated from the Aravalli Fold Belts by the Great Boundary Fault (GBF). During the deposition of the LKS of Rajasthan/CFS the basin was active due to the reactivation of GBF. This caused a shift in provenance: the lower part of the Kaimur sequence received sediments from the Hindoli belt, while the upper part received sediment supply from the weathering of the Berach granite. Our study reveals that the LKS of Rajasthan has dissimilar lithology, geochemistry, provenance and tectonic setting from the contemporary sequence of the Son Valley. Our study thus suggests that a separate basin status should be given to the Rajasthan Vindhyans.
Sen et al. (Sun,) studied this question.