Changes in depositional environment for the past 35 years in the Thane Creek, central west coast of India: inferences from REEs, metals and magnetic properties

The role of diagenetic processes in influencing the behaviour of metals (Fe, Mn, Cu, Ni, Zn), rare earth elements (REEs) and environmental magnetic parameters in two sediment cores from a polluted creek environment (the Thane Creek, Mumbai) was investigated. The sediment age was determined using Pb-210 analysis. Silty clays were dominant sediments in both the cores. Mineralogy showed the presence of quartz, calcite and plagioclase feldspar in bulk sediments, while smectite was the abundant clay mineral in the finer fraction. The mean Sigma REE in both the cores was lower than in post-Archaean average Australian shale (PAAS). The PAAS-normalized REE patterns showed MREE and HREE enrichment with strong positive Eu and Y anomalies. The source rocks in the hinterland played an important role on the REE composition. Magnetic mineralogy showed dominance of magnetite. Both the cores showed low magnetic concentration of Al, Ti, Fe and Mn coinciding with high magnetic grain size at the middle portions. The early diagenetic changes at the middle portion of the cores were masked by significant abundance of clay content at the creek head and with OC and fine magnetite at the lower creek region. Metals (Cu, Ni, Zn; enrichment factor >1.5) and magnetic concentration in sediments were enriched in both the cores suggesting of an anthropogenic source.