Geochemical characterisation of stream sediments and soil samples from Karewa deposits of south Kashmir, NW Himalaya, India

摘要

Thirty-six sediment samples from twelve soil profiles have been collected from Karewa deposits of south Kashmir with an objective for evaluating weathering of the source area, palaeoclimate and environmental contamination. Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Chemical Index of Weathering (CIW) values of the sediments averaged at 53.99, 68.6 and 72.53 indicating low to moderate degree of weathering. Higher values are observed in the samples collected at top surface. The samples taken at 15cm depth and 60cm depth showed almost similar but lesser values than top soil samples. A-CN-K and A-CNK-FM diagrams showed an almost similar contents for Al2O3, CaO, Na2O, K2O and MgO as those of upper crust, reflecting very poor to moderate weathering history. The ratio plots of SiO2 vs Al2O3+K2O+Na2O and CIA (molar) vs Al2O3 indicate semi-arid climatic conditions with a mean annual precipitation of 846mm per year and mean annual paleo-temperature of 10.91 degrees C. Metal concentration in sediment samples ranged from 331.1 to 571ppm (Ba), 146 to 292ppm (Zr), 82 to 587ppm (Sr), 70 to 130ppm (Cr), 58.9 to 120ppm (Rb), 37.6 to 112ppm (V) and 43 to 112ppm (Zn). The enrichment ratio of 6 for As, 3 for Cr and 2 for Ni, Sb and Tb indicate the enrichment of these metals in the sediment samples. The QoC plot of As, Ni, Co and Cr illustrated an anthropogenic source and Ba, Rb, Sr, Nb, and Ta were mainly derived from geogenic sources with no evidence of anthropogenic contamination.