Determination of depositional environment and luminescence dating of Pleistocene deposits in the Biely Váh valley, southern foothills of the Tatra Mountains, Slovakia

Abstract: The Tatra Mountains have had several glaciations during the Quaternary. The deposits located in the southern foothills were classified as glacifluvial, based on geomorphology, but its sediments have not been studied in detail. Therefore, this project focused on establishing the depositional history, processes, and age of the deposits in a gravel pit, located in the Biely Váh valley in these foothills. The combination of luminescence dating with sedimentological analysis, including clast shape and maximum particle size, were the methods of choice. For the luminescence dating eleven samples were collected from the units composed mainly of sand. Initially optically stimulated luminescence (OSL) dating was used, but after applying the standard Single Aliquot Regeneration (SAR) protocol quality tests, it was evident that the quartz was poorly behaved with low signal intensity. The dose estimation gave bad results, even after attempting pulsed OSL and differential OSL. Therefore, it was decided to move on to feldspar grains. Given that there is a risk of fading and the fact that feldspar grains take longer to bleach, the corrective measurements were done by calculating the g-value and use of IR50 and pIRIR225 signals for the bleaching. The sedimentological description yielded 13 units from the lower and upper outcrops in the study area. The results of the sedimentological analysis indicated that the process of deposition had a high energy component, representative of subaerial flows. Given the features of the sediments it was identified as a hyperconcentrated flow. Moreover, for the age determination the most likely water content of the sediments was chosen, the g-values and the equivalent dose were determined, using both IR50 and pIRIR225 signals. Subsequently, four ages were obtained per sample, one for each signal, and with and without correction for fading. From these, the uncorrected pIRIR225 ages were selected, since this signal has a lower fading rate which is supported by the obtained g-values, which were smaller than 1-1.5%. The results were compared to the known glacial history of the Tatra Mountains. The obtained luminescence ages, which range from ca 200 to 260 ka, would correspond to the Riss glaciation. Both ages and sediment characteristics match those of the other deposits from the northern and southern Tatra foothills that also have been correlated to the Riss glaciation. Taken together, these results suggest a glacial advance to the present-day foothills of the High Tatras during the Riss glaciation and extensive deposition of glacifluvial sediments outside the ice margin.