COMPARISON OF RARE EARTH ELEMENT COMPOSITIONS IN DIFFERENT GRAIN-SIZE FRACTIONS OF SEDIMENTS FROM THE YANGTZE AND YELLOW RIVERS AND THE SEA

To seek effective proxies for discriminating the Yangtze River sediments from the Yellow River sediments in the Yellow and East China Seas, six sediment samples were taken from the Yangtze and Yellow River mouth areas as end members. ≤ 63 μm fractions of the bulk samples were separated at intervals of 1Φ,and then concentrations of rare earth elements (REE) in these sediments were measured by Inductively Coupled Plasma-Mass-Spectrometry (ICP-MS). The results show that:(1)The ranges of REEs in sediments from the Yangtze and the Yellow Rivers are 145.49~256.77 and 121.22~135.56 μg/g respectively,and the REE distributions with increasing grain sizes show bi-modal type for the Yangtze River sediments, and inverse "S" for the Yellow River sediments.(2) REE concentrations in the Yangtze River sediments are relatively higher.REE values are 1.5 times of those in the Yellow River sediments, and the lowest REE in the Yangtze River sediments is 20% higher than the highest value in the Yellow River sediments.(3) 2~4 and 8~16 μm are the sensitive grain-size fractions to differentiate the Yangtze and Yellow River sediments, and diagnostic parameters of REEs such as REE, LREE/HREE and (La/Yb)_n are clearly different in these two fractions of the Yangtze and Yellow River sediments. The result largely enhanced the difference of REE in sensitivity and reliability in the two rivers' sediments, which makes the usage of REE as an effective provenance proxy become possible.