REE geochemistry of Early Cambrian phosphorites of Masrana and Kimoi blocks, Uttarakhand, India

Abstract

Early Cambrian phosphorites of the Masrana block, Uttarakhand, India, show moderate rare earth element (REE) concentrations which are slightly higher than those of the Kimoi block of the same region. Light rare earth element (LREE) concentrations of the phosphorites of both the blocks of the study area are higher than those of heavy rare earth element (HREE) and show normal seawater pattern with decreasing HREE and negative Ce and positive Eu anomalies. Negative Ce anomaly reflects oxidising conditions by getting Ce3+ oxidized to Ce4+ in contrast to positive Eu anomaly which reflects the reducing conditions by getting Eu3+ reduced to Eu2+. These anomalies provide evidence of upwelling and mixing of organic-rich anoxic bottom water and oxic upper seawater before the formation of phosphorite deposits in the basinal site.