Lithologically-related rare earth element variations the Mio-Pliocene Poznań Formation (Poland)

Concentrations of rare earth elements (REEs) were determined in 129 clay samples collected from the Mio-Pliocene Poznań Formation in Poland. The REEs occur in a relatively wide range from 58.2 to 1,709 mg/kg. Low North American Shale Composite (NASC)-normalized total REE contents with heavy rare earth element (HREE) depletion were noted in most of the samples analysed. Small variations were detected in the REE contents in the lithologies distinguished. Red clays are characterised by slightly lower REE concentrations relative to green and grey clays. All the Poznań Formation clays exhibit a negative Eu anomaly when normalized to the average of chondrites. Values increase according to the following sequence: grey clays < red clays < green clays. The NASC-normalized REE concentration curves show a positive Eu anomaly. The LaNASC/YbNASC ratio indicates HREE depletion. A small variation in this ratio was observed in the sequence green clays > grey clays > red clays. The variability of the REE contents of the Poznań Formation decreased from west to east.