Abstract. In this study modern sediments of the lower Vistula River were investigated to determine the relationship between the structure and texture (grain size, rounding and frosting) of the deposits and the possibility of their zeroing. The samples of modern fluvial deposits were collected from the lower Vistula River at two sites in Toruń and Ciechocinek. Sand bars newly emerged from the river were selected for testing. The coarse quartz grains were separated for OSL measurements. The single-aliquot regenerative (SAR) technique was applied for measuring equivalent doses from multigrain aliquots. The obtained dose estimates were found to be very low, proving the reliability of the OSL zeroing assumption. The dose rates were estimated by gamma-ray spectrometry, demonstrating homogeneity of the radiation field. Analysis did not show significant relationships between the examined sediments' capacity to zeroing and their structural and textural characteristics, or the sampling site. The obtained OSL ages of the studied sediments date back hundreds of years and are probably overestimated. The results related to fossil sediments of bars of the age of thousands of years confirm their suitability for the OSL dating method.
<p>Subglacial landforms are key elements of reconstructing ice sheets dynamics and processes. Among less studied are transverse and elongated glaciogenic ridges (TEGRs) perpendicular to ice flow usually classified as Ribbed (Rogen) Moraines (Barchyn, 2016; Cline, 2015). Their shape is closely connected to low ice movement speed as distinct from drumlins and large scale lineations that were formed under condition of a higher ice movement velocity. Typically, they are straight, up to 30 m high, up 1000 m long and 150-300 m wide. Rajgr&#243;d ridges, although similar to classic case, have unique features, both individual and related to their mutual position.</p><p>For the purposes of research XYZ LIDAR data with resolution of 4 points per sq meter was used to calculate high accuracy DEM, on the base of which hillshade model and topographic position index map were prepared. Initially all TEGRs were indicated and subsequently send to and evaluated independently by three researchers to determine their ridgelines and borders. For further steps only ridges with similar parameters within all researchers were examined and used for parameter calculation: (1) area, (2) length measured by ridge line, (3) height as a differential between highest and lowest elevation, (4) mean width calculated as ratio area to perimeter and (5) vertical sinuosity defined as the ratio of topographic length to length. All TEGRs were divided into five fields (clusters), similar in ridges number.</p><p>TEGRs located near Rajgr&#243;d lie close to the former ice margin and have the highest vertical sinuosity and mean width. They are fragmented, with doughnut landforms visible on TEGRs surface, whereas TEGRs located in cluster proximal part are better preserved, have higher area and lower mean width then those in distal part. The cross-profile through all the fields shows a clear arrangement of morphological levels referring to the stages of ridges formation. First level is connected to initial stage when certain areas had undergone quicker ice movement. The second one is correlated to creation of ridges in ice crevasses. The third and last one is the sign of deglaciation and creation of doughnut features.</p><p>This study was carried out as part of the scientific project financed by the National Science Centre (NCN) in Poland, project no. 2018/31/B/ST10/00976.</p><p><strong>References</strong></p><p>Barchyn, T. E., Dowling, T. P. F., Stokes, C. R., & Hugenholtz, C. H. (2016). Subglacial bed form morphology controlled by ice speed and sediment thickness. Geophysical Research Letters, 43(14), 7572&#8211;7580. https://doi.org/10.1002/2016GL069558</p><p>Cline, M. D., Iverson, N. R., & Harding, C. (2015). Origin of washboard moraines of the Des Moines Lobe: Spatial analyses with LiDAR data. Geomorphology, 246, 570&#8211;578. https://doi.org/10.1016/j.geomorph.2015.07.021</p>
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