Source rock composition of Kaimur Group siliciclastics from Vindhyan Supergroup, Central India: A response to thermal events associated with Bundelkhand Craton and Chhotanagpur Gneissic Complex at ~1.1 Ga

Abstract

The Kaimur Group of the Vindhyan Supergroup has been divided into six Formations in Son valley sector, in Central part of India, i.e., Sasaram Sandstone, Ghurma Shale, Markundi Sandstone, Bijaigarh Shale, Mangesar Formation, and Dhandraul Sandstone. The comprehensive geochemical datasets for all the individual Formations of the Kaimur Group were generated in order to evaluate the source rock composition, weathering history, and provenance. The field observations, petrography, and geochemistry depict the deposition of the Kaimur sedimentary rocks in two cycles—the fining‐upward sequence from Sasaram to Markundi Sandstone, that was followed by the coarsening‐upward sequence from Bijaigarh shale to Dhandraul Sandstone. The petrography, geochemical classification, and A‐CN‐K plot depicts K‐metasomatism in siliciclastics of Kaimur Group. A‐CN‐K systematics and the CIA values (62–85) reveal that the source rocks of the Kaimur Group siliciclastics have suffered high degrees of chemical weathering under warm and humid climate. Zr/Sc vs. Th/Sc and Rb/Sr values depict zircon addition and sediment recycling. Ternary plots based on modal analysis and tectonic discrimination diagrams based on incompatible elements exhibit the deposition of Kaimur siliciclastics in the craton interior /passive margin (Bundelkhand Craton; BC) to recycled orogen (Chhotanagpur Gneissic Complex;CGC). The incompatible elemental ratios and Qm‐F‐Lt plots shows a fluctuation in provenance of the Kaimur Formations in the lower and upper part. The percentage contribution from the two sources was calculated using a simple arithmetic formulae [ Percentage contibution from a single source= Number of comparable ratios/ Total ratios*100]: Sasaram Sandstone = 82% BC + 18% CGC, Ghurma Shale = 76% BC + 24% CGC, Markundi Sandstone = 65% BC + 35% CGC, Bijaigarh Shale = 62% BC + 38% CGC, Mangesar Formation = 61% BC + 39% CGC, and Dhandraul Sandstone = 42% BC + 58% CGC. Tectonics of the hinterland supplying detritus played an important role in deciphering the provenance of Kaimur siliciclastics. The episodic crustal growth and thermal events taking place in Bundelkhand Craton at 1.1 Ga were witnessed by the emplacement of dykes, which led to the increased detrital input from the source (BC). Later on the upliftment of CGC towards the south during Satpura Orogeny‐II led to increase in input to the Formations of Kaimur Group. Petrological, geochemical signatures, and the evidences of change in paleocurrent direction from SSE–SSW to NW–NNW during Kaimur sedimentation strongly support the gradual shift of provenance from BC to CGC.