Provenance and paleo-weathering of Paleoproterozoic siliciclastic sedimentary rocks of Bijawar Group, Sonrai Basin, Uttar Pradesh, India: using a geochemical approach

Abstract

Shales and sandstones of the Paleoproterozoic Bijawar Group (India) have been studied to decipher their paleo-weathering conditions and provenance based on geochemistry. Shale samples are composed of k-feldspars, mica, quartz, and fine iron-oxides, whereas sandstones are composed of quartz and k-feldspars. The predominant positive correlation of K2O vs TiO2, Na2O vs Al2O3, and K2O vs Al2O3 indicates that the elements are associated with detrital phases. Trace elements Sc, Rb, Ba,Th, Y, and Zr show a strong positive correlation with Al2O3 and K2O which indicates that the absolute abundances of these elements are controlled mainly by illite. A negative correlation of trace elements Ni, Cu, Co with Al2O3, and K2O represents their presence in iron oxides like magnetite, ilmenite, and hematite. Multi-element Post-Archaean Australian Average Shale (PAAS) normalized spider diagrams show enrichment of V, Pb, Zr, Y, Hf, Th, Rb, and depletion of Ni, Sr, Ba, Nb, U. The depletion of Sr indicates the least enrichment of plagioclase and the same is also supported by negative Eu-anomaly of the samples, though weak. The chondrite normalized rare earth element (REE) plots show a slightly light-REE (LREE) enriched and flat heavy-REE (HREE) pattern with weak negative Eu anomaly. The overall, high values of LaN/SmN (avg. 10.49), CeN/YbN (avg.0.37), LaN/YbN (avg. 34.28) and low values of GdN/YbN (avg. 1.82) and TiO2 (0.27–1.82, average 0.92 < PAAS) in most of the samples, show a relationship with the felsic source rocks. The index of compositional variability (ICV) of the samples is < 0.84 which indicates no enrichment of primary minerals. The chemical index of alteration (CIA) of present samples varies from 48.60 to 81.69, indicating low to moderate intensity of chemical weathering of the source. The plot between SiO2 and Al2O3 + K2O + Na2O depicts that majority of the samples belong to the environment from humid to semi-humid and have attained a high chemical maturity. The high SiO2/Al2O3 values (1.36–20.79) in studied samples indicate relatively high sediment maturity due to the extreme sorting of sediments in a stable cratonic regime. A stable cratonic regime, with a low upliftment rate that has allowed strong chemical weathering of protoliths, is further indicated by low CaO, Na2O, and Sr contents of the studied samples. The overall geochemical characteristics of the present samples—high SiO2, Al2O3 and K2O and low TiO2, MgO, Na2O, and CaO contents—suggest a felsic provenance. The felsic nature of the source rocks is also supported by the trace element ratios like (La/Lu)N (7.72–76.89), La/Sc (1.50–7.40), La/Co (0.39–11.48), Th/Co (0.80–15.90), and Cr/Th (0.08–5.10). Since the Bijawar Group is sited over the Bundelkhand Granite Gneiss Complex (BGGC), it is, therefore, plausible that the main source components of Bijawar Group siliciclastic rocks are the BGGC felsic rocks.