Study of Provenance and Mineralogical Alteration of the Nagaur Sandstones at Shri Balaji Area, Northwestern India: Insights from Integrated Petrography, XRD and XRF analyses
Abstract
Understanding the provenance, weathering history, and depositional evolution of ancient siliciclastic successions requires an integrated evaluation of their petrographic, mineralogical, and geochemical characteristics. The present study investigates the Nagaur Sandstones exposed at the Shri Balaji area of Nagaur District, Rajasthan, northwestern India, with the aim of constraining their detrital provenance and evaluating mineralogical and geochemical signatures related to source-area alteration within the regional framework of the Marwar Supergroup. An integrated analytical approach involving optical petrography, modal framework-grain analysis, X-ray diffraction (XRD), and whole-rock X-ray fluorescence (XRF) geochemistry was applied to representative sandstone samples. Petrographic observations reveal quartz-dominated framework assemblages with subordinate feldspar and negligible lithic-fragment contributions, accompanied by variations in grain size, sorting, packing, and the abundance of argillaceous and ferruginous material. Modal framework compositions plotted on the Q–F–L diagram demonstrate a strong quartz and feldspar dominance, indicating derivation from quartz- and feldspar-bearing continental source rocks. XRD analysis confirms the predominance of quartz and identifies variable proportions of microcline, kaolinite, illite, and minor iron-bearing phases, reflecting differences in feldspar preservation and clay-mineral development among the samples. Whole-rock XRF data show high SiO₂ concentrations ranging from 76.79 to 93.65 wt.%, accompanied by variable Al₂O₃, Fe₂O₃, K₂O, MgO, CaO, P₂O₅, and TiO₂ contents, consistent with variations in feldspathic and clay-mineral components. The integrated petrographic, mineralogical, and geochemical evidence indicates derivation predominantly from quartz and feldspar-rich felsic igneous to metamorphic source rocks within the heterogeneous Precambrian continental framework surrounding the Marwar Basin.