Mineralogical and Geochemical Behavior of Sediments Solely Derived from Bundelkhand Granitic Complex, Central India: Implications to Provenance and Source Rock Weathering

Abstract

Small rivers commonly drain in a few lithologies making their sediments as a good candidate for investigating provenance and weathering environments. We investigated spatial variation in compositional changes in the sediments of a modern river (Khurar River) from its source to sink for 35 km in Khajuraho area, Madhya Pradesh, India. The Khurar River in its entire course is surrounded by the Bundelkhand granitic complex that provides uniform source to the sediments. The possible physical and chemical controls on the bed-load sediments i.e. grain-size, mineralogy, geochemistry and their climatic control are investigated in detail here. Bed- load sediments of the Khurar River are very coarse to coarse sand-size ranging from –0.63 to 0.80 phi and they are devoid of fine sediments such as clay. The mineralogy of the sediments suggests that they are arkosic in composition. The spatial variation in the chemical composition of the sediments is negligible in the river basin from source to sink in the very coarse to coarse sand size range. The sediments are rich in SiO2 (≤82.93) and Al2O3 (≤11.03 wt %) and they have lower values of TiO2 (≤0.27), Fe2O3 (≤1.49), CaO (≤1.12), MgO (≤0.77), K2O (≤5.25) and Na2O (≤3.48 wt %). The trace elements such as Cr (≤66), Co (≤8), Cu (≤19) and Ni (≤12 ppm) have lower values than UCC; but the Pb (≤21) and Rb (≤142 ppm) have higher values than UCC. Lower concentrations of transition elements, such as V, Ni and Cr imply enrichment of felsic minerals in these sediments, a feature also confirmed by the mineralogical study. The high Zn content at some stations suggests anthropogenic contamination in the sediments. A-CN-K ternary plot suggests total alteration of plagioclase resulting in more removal of CaO and Na2O due to continuous weathering in the catchment area. Also, in this plot, sediments lie near to the albite concentration above the anorthite-albite line with gradual depletion in anorthite indicating that they are the weathering products of albite-enriched parent material. The A-CNK-FM ternary plot shows that all the samples plot close to the feldspar apex indicating higher abundance of feldspars. Further, the CIA (54 to 57), PIA (58 to 64) and CIW (70 to 78) values of the sediment samples suggest low to intermediate weathering environment. Chondrite-normalized pattern of REE (Rare earth elements) exhibits depletion of HREE with weak positive Eu anomaly suggesting low fractionation of the plagioclase feldspar. Thus, the major, trace and rare earth elements geochemistry of the bed-load sediments from the Khurar River suggest that they are derived from the weathering of felsic rocks and the original signatures of the granitic provenance remain there even after weathering under sub-humid climatic conditions in the river basin.