Distribution of rare earth elements in the inner shelf sediments, off the southwest coast of India

Abstract

Shallow part of the seafloor adjoining the coast of Kerala is mostly covered by silty clay and clayey silt, from north of Quilon to Kasaragod. Sand dominate the shallow seafloor south of Quilon as well as the deeper part of inner shelf from Vizhinjam to Ponnani. Concentrations of Rare Earth Elements were determined in the surface sediments within the inner shelf off the coast of Kerala. ΣREE content in surface sediments varies between 9.15 mg. kg^-1 and 319.66 mg. kg^-1. Distribution pattern suggests higher concentration of REE in the inner shelf sediments off southern Kerala, between Ponnani and Vizhinjam. Sediments off northern Kerala have lower REE. ΣLREE ranges between 5.61 mg. kg^-1 and 306.31 mg. kg^-1 and is more in the southern sector. ΣHREE in inner shelf sediments is very low ranging between 2.91 mg. kg^-1 and 36.8 mg. kg^-1. REE in coastal sediments off Kerala is closely related to heavy mineral content. LREE is mostly contributed by detrital monazite, apatite and sphene in the fine fractions and HREE by detrital zircon, garnet, amphibole and pyroxene. Sediments from southern and central sectors show enrichment in ΣLREE compared to PAAS. There is a depletion in La, Ce and Pr in the shelf sediments from the northern sector and remaining LREE in this sector show enrichment. HREE is enriched in the central and northern sectors and depleted in the southern sector compared to PAAS.