Trace element contents in microg/g measured on the <2 microns, 2-20 microns size fractions and bulk samples from LGM European loess sequences. Samples were crushed in an agate mortar and trace element concentrations were measured following Chauvel et al. (2011). Reproducibility for trace element analyses is better than 5% based on repeat measurements, and the accuracy is also better than 5%, based on the analyses of international rock standards (JSD-1, JSD-3 and LKSD-1.
Sr-Pb isotopic ratios for the <2 microns, 2-20 microns size fractions and bulk samples from LGM European loess sequences. Samples were crushed in an agate mortar and Sr and Pb isotopes were measured following Chauvel et al. (2011). Lead and strontium were analyzed after dissolution of the powder and without leaching procedure. Blanks run in parallel with the samples during the course of this work were less than 80 pg of Pb and 250 pg of Sr for the entire chemical separation procedure. These amounts are negligible relative to the amount of Pb and Sr present in the beakers after isolation of pure Pb and Sr (typically, 600 ng of Pb and 4 microg of Sr).
Grain size composition of loess samples from LGM European loess sequences. Loess samples of about 200 g were prepared to extract the grain size fractions studied. Grain size separations were performed on at least 10 g of dry sample. First, the entire sample was sieved with demineralized water on 63 microns and 20 microns sieves. The rejects were collected, dried and weighed. The clay fraction was obtained by decanting the fraction below 20 microns. The rest of the sample was mixed and left to settle for 1 hour. This procedure is repeated until a transparent supernatant is obtained. The two fractions thus obtained are dried and weighed. The size of the different fractions was then checked by laser granulometry.
In a previous analysis of bulk sediment from Last Glacial Maximum loess deposits over Europe, a local to regional origin of the deposited material has been demonstrated (Rousseau et al., 2014). In a refined study, the same European sequences have been analyzed studying the trace elements and the strontium and lead isotopic ratios from different grain-size fractions: <2 micron, 2-20 micron and bulk. The later was reanalyzed to compare with the previous study. First the new bulk values are similar to the previously published ones. Furthermore, the results show that the <2 micron fraction is different than the 2-20 micron or bulk ones when comparing the trace element. Second, the 87Sr/86Sr vs 208Pb/204Pb diagram shows that the sequences analyzed keep their regional to local signature, mainly along the 87Sr/86Sr axis for the 2-20 micron and bulk samples. On the contrary, the <2 micron samples are all grouped in a well identified cluster clearly indicating a different source and even a different transport. The comparison of the results of the geochemical analysis with climate modeling of dust transport at LGM supports this interpretation. The datasets correspond to i) the trace element contents for the <2 micron, 2-20 micron and bulk fractions, ii) the Sr-Pb isotopic ratios for the <2 micron, 2-20 micron and bulk fractions, and iII) the grain size composition of the studied LGM European loess samples.