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>
<p>Rapid climate changes during the Late Weichselian glaciation caused a sudden increase in meltwater activity and significantly transformed land relief. This transformation was accompanied by the supply of considerable quantities of meltwaters in glacial lakes in the southern periphery of the Scandinavian ice sheet. Their sudden release was responsible for the development of the Megaflood Landform System in north-eastern Poland which includes floodwater flow pathways represented by the Western and Eastern Spillways (Weckwerth et al., 2019). In the proximal part of the Western Spillway, the Bachanowo and Szeszupka Outburst Fans developed, while scabland-like topography was formed at the front of the Prudziszki Gate in proximal part of the Eastern Spillway. Bachanowo and Szeszupka Outburst Fans have surface characterized by the existence of subsequent bedforms, which include (1) streamlined bars developed as downstream elongated ridges and separated by channels of the braiding pattern, (2) scours with channel lag sediments deposited from traction carpet and gravel bedload sheets, (3) scour infills originated due to hydraulic jumps, and (4) expansion bars or chute bars evolved during the waning flood stage. These bars consist of sheet-like beds dipping downstream, and were formed due to low-angle forests progradation under condition of pulsed deposition from the traction carpet and fast sheetflows, the energy of which gradually decreased. As a common, an openwork texture was observed in sedimentary successions of all recognized features.</p><p>The bottom of proximal part of the Eastern Spillway at the front of Prudziszki Gate is characterised by butte-and-basin topography with landforms representing different types of bedforms typical for high-energy supercritical outflow. These include longitudinal furrows, transverse furrows, potholes, furrows of different shape, kettle holes and associate obstacle marks including lateral and frontal scours (Weckwerth et al., 2022). Transverse furrows are oriented perpendicular to the floodwater outflow and compose longitudinal clusters separated by ridges. Sedimentary successions of these ridges reflect a clear deposition cyclicity related to reactivated upstream progradation of scour infills and sedimentation on downflow-side of hydraulic jump.</p><p>The outburst fans and their characteristic bedforms were formed at the mouth of deep subglacial tunnel valleys, while the scabland-like topography developed at the mouth of flat-bottomed subglacial valleys which were transformed into open ice-walled canyons. The bedforms typical for outburst fans and the scabland-like topography consist of similar facies deposited due to flood outbursts emanating from two different englacial systems, but these facies form different associations related with changeable riverbed morphology transformed under condition of the upper flow regime.</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>Weckwerth, P., Wysota W., Piotrowski J.A., Adamczyk A., Krawiec A., D&#261;browski M., 2019. Late Weichselian glacier outburst floods in North-Eastern Poland: landform evidence and palaeohydraulic significance. Earth-Sciences Review, 194, 216-233.</p><p>Weckwerth, P., Kali&#324;ska E., Wysota W., Krawiec A., Adamczyk A., Chabowski M., 2022. What does transverse furrow train in scabland-like topography originate from? The unique records of upper-flow-regime bedforms of a glacial lake-outburst flood in NE Poland. Quaternary International, 617, 40-58.</p>
<p>Extreme geological processes include cataclysmic glacial floods often contribute to glacial landscape evolution. Based on the geomorphological research the unique glacial megaflood landforms were discovered on the proximal part of the August&#243;w Sandur, NE Poland (Weckwerth et al., 2019). First-order and second-order megaflood-related landforms were distinguished. The latter includes straight-crested (two-dimensional) megadunes located south of Suwa&#322;ki. The megadunes have mean heights on stoss slopes between 2.3 and 3.9 m and mean heights on lee slopes between 2.5 and to 4.5 m, while the maximum recorded megadune height is 8.5 m, and the maximum length is 420 m. Characteristic features of the 2D megadunes south of Suwa&#322;ki are elongated depressions occurring along megadune crests. Megadunes located in the vicinity of Wigry Lake originated from depositional processes related to the reduction in flow energy and competence in the area of the broad outwash plain. The width of this plain rapidly increases and thus creates an accommodation space (unconfined outwash plain) for the aggradation of mega-scale, superimposed bedforms (Weckwerth et al. 2020b). Their three-stage evolution was recognised as a result of sedimentological and geophysical investigations. The first stage represents foreset deposition on the lee side of the megadunes, while the second was deposition from 2D and 3D superimposed bedforms and longitudinal gravelly bars climbing downstream on a megadune stoss slope, which were locally separated by gravelly pavement and scour infills. During the third stage, the crestal depressions evolved as a result of the development of both north- and south-dipping normal faults oriented parallel to the megadune crest, representing syn- and meta-sedimentary deformations (Weckwerth et al., 2020a, b).</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 and Danish Council for Independent Research (FNU) grant DFF-7014-00156.</p><p><strong>References</strong></p><p>Weckwerth P., Piotrowski J.A., Wysota W., Krawiec A., Adamczyk A., Kali&#324;ska E., Chabowski M., 2020a. Mature and immature megadunes : insights from morphology and sedimentary successions of mega-scale bedforms south of Wigry Lake (NE Poland). [In:] Weckwerth P., Wysota W., Kali&#324;ska E. (eds), Glacial megaflood landforms and sediments in North-Eastern Poland. Wydawnictwo Naukowe Uniwersytetu Miko&#322;aja Kopernika, Toru&#324;: 99-107.</p><p>Weckwerth P., Wysota W., Chabowski M., Krawiec A., Kali&#324;ska E., Adamczyk A., 2020b. Morphology, geological structure and development of two-dimensional megadunes formed on an outwash plain in NE Poland. [In:] Weckwerth P., Wysota W., Kali&#324;ska E. (eds), Glacial megaflood landforms and sediments in North-Eastern Poland. Wydawnictwo Naukowe Uniwersytetu Miko&#322;aja Kopernika, Toru&#324;: 89-97.</p><p>Weckwerth, P., Wysota, W., Piotrowski, J. A., Adamczyk, A., Krawiec, A., D&#261;browski, M., 2019. Late Weichselian glacier outburst floods in North-Eastern Poland: Landform evidence and palaeohydraulic significance. Earth-Science Reviews, 194: 216&#8211;233.</p>
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