Rare earth elements (REE) and thorium in the youngest Pleistocene glacial tills in Poland

The study encompassed outcrops of glacial tills (topsoil, subsoil-1, subsoil-2) of the maximum stadial of the Vistulian Glaciation and of the Wartanian Stadial of the Odranian Glaciation, occurring along the maximum extent of the Vistulian ice sheet. The youngest Polish glacial tills show very similar concentrations of REE and Th. The concentrations of these elements vary across a wide range from 0.08 mg/kg (Tm and Lu) to 70.3 mg/kg (Ce), with slightly higher values for the older tills (Wartanian). Both these tills show clear fractionation of LREE and HREE, with a higher and more varied LREE concentration. The most prominent feature distinguishing one till from the other is the distribution of REE fractions along their vertical sections. In the younger (Vistulian) tills the maximum concentration of individual LREE is found at a depth of 1.0 m, and of HREE, Sc and Th, at 2.0 m; while in the older (Wartanian) tills the highest concentrations of all elements investigated are observed at a depth of 1.0 m. Also, the mineral compositions of the tills are very alike. The dominant minerals are quartz (average 56%) and feldspars (approximately 9%), with a trend of decreasing concentrations with depth. There are no carbonates in the topsoil (0.3 m level), and the clay minerals are dominated by illite (approximately 16%) and kaolinite (average 5%). Statistical analysis indicates over a dozen factors determining the concentration of REE and Th in both tills. Three of them have a crucial (96% of total variation) effect on the concentrations of these elements. These factors are probably of geogenic nature, intimately associated with similar source areas, and with similar processes of deposition, diagenesis and weathering of the tills.