Controls on the distribution and fractionation of yttrium and rare earth elements in core sediments from the Mandovi estuary, western India

Prajith, A. ; Rao, Purnachandra V. ; Kessarkar, Pratima M. (2015) Controls on the distribution and fractionation of yttrium and rare earth elements in core sediments from the Mandovi estuary, western India Continental Shelf Research, 92 . pp. 59-71. ISSN 0278-4343

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Mineralogy, major elements (Fe, Mn and Al), rare earths and yttrium (REY) of bulk sediments were analyzed in four gravity cores recovered along the main channel of the Mandovi estuary, western India, to determine the sources and controls on REY distribution. The accelerator mass spectrometer (AMS) ages of total organic carbon indicated modern age for the sediments of the upper estuary and, maximum mean ages of 1588 years AD and 539 years AD for the bottom sediments of the cores in the lower estuary and bay, respectively. The sediments of the upper/middle estuary showed abundant hematite, magnetite and goethite and high Fe, Mn, total-REE (ΣREE) and Y, while those in the lower estuary/bay showed abundant silicate minerals and relatively low Fe, Mn, ΣREE and Y. ΣREE showed significant correlation with clay and silt fractions and Y, Al and organic carbon (OC) content of the sediments. The light to heavy REE ratios (LREE/HREE) of sediments were lower than in Post-Archean Australian Shale (PAAS). The PAAS-normalized rare earths and yttrium (REY; Y inserted between Dy and Ho) patterns of sediments showed middle REE (MREE)- and HREE-enrichment with positive Eu anomaly (Eu/Eu⁎) and variable Ce anomaly (Ce/Ce⁎). The REY of sediments is primarily controlled by its texture and REE of source sediment, which is ore material-dominated in the upper/middle estuary and silicate material-dominated in the lower estuary/bay. Low LREE/HREE ratios suggest that very fine-grained sediments were carried away from the estuary because of high-energy conditions. Fractionations of REY (Y/Ho, Sm/Nd, Ce/Ce⁎ and Eu/Eu⁎) are controlled by different mechanisms. High Y/Ho ratios in clayey silts are due to redistribution of Y and Ho by adsorption onto organic-rich, clays. Variations in Sm/Nd ratios are similar to that of Eu/Eu⁎ in cores from the lower estuary/bay and are controlled by mineral constituents of the sediments. Positive Ce and Eu anomalies are inherited from ore material, and ore material and source rocks, respectively. Negative Ce anomaly is related to source rock material and influenced by lanthanum enrichment at certain sediment intervals.

Item Type:Article
Source:Copyright of this article belongs to Elsevier Science.
Keywords:Fractionation of REE; Sediment Cores; Mandovi Estuary; Western India
ID Code:99388
Deposited On:22 Apr 2016 12:14
Last Modified:22 Apr 2016 12:14

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