Controls on the distribution and fractionation of rare earth elements in recent sediments from the rivers along the west coast of India

Abstract

The sediments of 90 rivers from 5 states along western India were analysed for their chemistry. The major element ratios of sediments suggest lateritic soils in Kerala, lateritic soils admixed with particulates weathered from Fe-Mn ores in Karnataka and Goa and, non-lateritic soils in Maharashtra and Gujarat. The sediments from Archean-Proterozoic (A-P) terrain are strongly weathered, while those from Deccan Traps (DT) terrain are intermediate to strongly weathered. The ∑REE of sediments from Kerala is much higher than in other states. It shows strong correlation with oxides of Fe, Mn and P from A-P terrain and Al, Fe and Ti from DT terrain and, strong correlation with heavy metals from both terrains. The low Sm/Nd and Y/Ho ratios corresponding to high CIA and, high ratios corresponding to high and low CIA are typical. The PAAS-normalized REE shows LREE- and MREE-enriched patterns in the sediments of Kerala and MREE- and HREE-enriched pattern in other sediments. Distinct positive Ce anomaly occurs in the sediments of Karnataka, Goa and south Maharashtra. The Eu anomaly is negative in the silts of south Kerala and positive in other sediments. The primary sources for REEs are adsorbed REEs onto secondary mineral phases and clay minerals and, heavy minerals. The change in REE patterns is primarily related to the source rock composition. Fractionation of REEs is related to the intensity of chemical weathering, supply of REE and transport processes. The average REE composition of river sediments from peninsular India is more mafic than in UCC and World Rivers Average clay.