Luminescence dating of the Volochysk section : a key Podolian loess site (Ukraine)

The Volochysk site belongs to important and unique loess sites in the Podolia Upland (W Ukraine) because it contains relatively well-developed loess deposits representing the last and penultimate glacial cycles. This loess-palaeosol sequence consists of pedocomplex S1 (MIS 5) developed on loess L2, and loess L1 (MIS 4-2) with the palaeosols of lower, interstadial rank. In this sequence, different periglacial structures were found, including the largest ones of ice-wedge cast type. Different quartz and polymineral fractions separated from the samples collected in the Volochysk site were dated using luminescence methods (SAR OSL, post-IR IRSL and TL) in three Polish luminescence laboratories in Gdańsk, Gliwice and Lublin. In total, 69 luminescence dating results were obtained for 18 samples. The methodological and research aims were to carry out mutual verification of the obtained dating results as well as to analyse and interpret the differences between them, and to determine the age of distinguished deposit layers and the period of cryogenic activities. The luminescence dates of the sediments, which were deposited during MIS 2, 3 and 4, corresponded fairly well to the ages attributed to these stages. They also indicate the age of periglacial phenomena. However, the TL dates were generally older than the OSL ones, especially those obtained for the sediments deposited during MIS 5 and 6. The results of the research of the Volochysk sequence were compared with those obtained in past years for the loess deposits of the Volhynian Upland (north of Podolia) during similar inter-laboratory analyses conducted to determine their age. The results of OSL datings of the older deposits (MIS 5 and MIS 6) are underestimated irrespective of the used method, and the type (quartz, polymineral) and size of grains. Numerous attempts were made to explain this phenomenon, which, however, give no answer. It was only found that this underestimation corresponded to the equivalent dose value of ~150 Gy