ABSTRACT:The REE contents in the clay-sized fractions of nineteen Cretaceous and Pliocene continental sediments, Portugal, were found to be correlated with kaolinite. No correlation is apparent between clay mineralogy and La/Lu or Eu/Sm ratios. The Eu anomaly is generally smaller (or even absent) in the clay-sized fraction than in the corresponding whole sediment, probably due to a greater ability of the clay minerals to accommodate Eu (as Eu 2+) rather than the other REE released during weathering.It is well known that the rare earth element (REE) distribution in a sediment depends on the relative importance of several factors such as: (i) the REE contents in the parent rocks and their distribution in the mineral phases; (ii) the nature and the REE contents of the fluids passing through the parent rocks; (iii) the partitioning behaviour of the REE between the fluids and the mineral phases of those rocks; (iv) the ability of the secondary minerals formed during the reactions to accommodate the REE; (v) the changes which take place during the transport process; and (vi) the chemical reactions during and after deposition
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