Revisiting the chronostratigraphy of Late Pleistocene loess-paleosol sequences in southwestern Ukraine: OSL dating of Kurortne section

摘要

Due to the general lack of other high-resolution paleoclimate records, loess-paleosol sequences are crucial archives for disentangling past climate variability in southeastern Europe. Here we present results of a multi proxy sedimentological and geochemical investigation of Kurortne loess-paleosol section from southwestern Ukraine, coupled with detailed optically stimulated luminescence (OSL) dating. OSL investigations were carried out on quartz grains of different grain sizes (4-11 mu m, 63-90 mu m and 90-125 mu m), using the single aliquot regenerative (SAR) protocol. The OSL dating results are in line with previous findings on dating loess-paleosol sequences along the Black Sea shore in Romania, as well as worldwide: (i) ages obtained on different grain sizes are in agreement for equivalent doses of less than 200 Gy, whereas for higher equivalent doses 4-11 mu m ages underestimate the coarser fraction ages; and (ii) an inverse correlation between dated grain size fractions and saturation characteristics is reported.Our combined dating and sedimentological approach would confirm that the investigated uppermost 4.5 m at Kurortne cover the Last Glacial Cycle, adding important data in better constraining local and regional chronostratigraphic correlations. The application of the SAR protocol on 63-90 mu m quartz grains on samples collected from the lower part of S1 soil (the Kaydaky unit) and from the Kaydaky/Pryluky units boundary produced ages of 123 +/- 10 ka and 85 +/- 6 ka, respectively. As the temporal range covered by these units in the Ukrainian Quaternary stratigraphic framework is still debatable, our results confirm the broad correlation of the Kaydaky-Pryluky paleosol units at Kurortne with the last interglacial (i.e., MIS 5). Dating the Uday and Bug loess units produced ages corresponding to MIS 4 and MIS 2, respectively, whereas the sample collected from the Vytachiv unit provided an age of 37.7 +/- 2.4 ka, assigning this paleosol to MIS 3. On the basis of trends in the magnetic enhancement, the onset of pedogenetic processes likely commenced already around 20 ka, but the formation of the topmost S0 soil has begun after 13.8 +/- 1.0 ka.