Complex genesis of N-channel eskers illustrated with the example of an esker near Tosie (east-central Poland)

Abstract

The study presents the problem of complex genesis of eskers formed in N-channels on the example of an esker located near Tosie in east-central Poland. The lithofacies analysis revealed a high diversity of structural and textural characteristics of sediments in this form. The esker consists of three sedimentation units. Coarse sediments of the esker core were deposited in the subenvironment of a subglacial tunnel, as an effect of bedforms migration under hydrostatic pressure. Opening of the tunnel resulted in the forming of an open crevasse, in which the cover of the esker core sediments was accumulated. These deposits recorded a significant variability of flow energy and sedimentation mechanisms, which indicates a strong influence of the ice-sheet ablation dynamics. During the final deglaciation stage, a part of the esker was covered with diamicton. Numerous soft-sediment deformation structures were identified within the esker. The sediments were dislocated vertically to the elevation of more than 8 metres. They constitute the record of buried dead-ice masses melting in the esker core sediments. Melting of the masses resulted in vertical displacement of sediments and formation of "the dead-ice structure". The complexity of esker genesis is characteristic of postglacial areas in Poland, where most eskers were formed in subglacial N-channels. Numerous research results confirm a considerably more frequent occurrence of the facies sequence of subglacial tunnel and open crevasse in eskers formed in N-channels than R-channels. This is indicated by a much greater dissimilarity of processes during different stages of esker formation on soft bed and solid substratum.

Classification of esker morphology on soft beds in the area of the Saalian and Elsterian Glaciations in Poland

“…Type 4a eskers, if their fragmentation results from post-depositional erosion, may also fit that scenario. According to sedimentological research, many eskers in Poland have a complex genesis and were initially formed in subglacial tunnels and then, after roof collapse, in an open channel (Michalska 1969;1971;Wysota 1990;Buraczyński, Superson 1992;Jaksa, Rdzany 2002;Fard, Gruszka 2007;Roman 2016;Frydrych 2016Frydrych , 2020Frydrych , 2021. Single ridge or highly continuous forms were also documented as a result of accumulation in subglacial tunnels (Brennand 1994;2000;Storrar et al 2014).…”

“…Eskers in the study area are usually associated with different types of meltwater channels (Fig. 3A-C) (Michalska 1969(Michalska , 1971Fard, Gruszka 2007;Roman 2016;Frydrych 2021Frydrych , 2022Salamon, Mendecki 2021;Szuman et al 2021). Eskers formed in N-channels occupy the entire width of these channels (Fig.…”

“…3C) but in the area to the south of the LGM their relations are much less clearly visible than in the area of the Vistulian Glaciation. Many eskers in Poland have a complex genesis and were initially formed in a subglacial tunnel and then, after roof collapse, in an open (ice-walled) channel (Michalska 1969;1971;Wysota 1990;Buraczyński, Superson 1992;Jaksa, Rdzany 2002;Fard, Gruszka 2007;Frydrych 2016Frydrych , 2020Frydrych , 2021Roman 2016).…”

“…Hence, in most esker studies, models of their formation and esker classifications focus on eskers on hard beds and formed in R-channels (Brennand 2000;Boulton et al 2007Boulton et al , 2009Livingstone et al 2015;Perkins et al 2016;Hewitt, Creyts 2019;Lewington et al 2020;Dewald et al 2021). However, numerous studies show that eskers may also form in areas of permeable sediments (Rotnicki 1960;Michalska 1969;Wright 1973;Brennand 2000;Storrar et al 2014;Frydrych 2020Frydrych , 2021Frydrych , 2022Szuman et al 2021). In Poland, eskers were formed on a soft bed in N-channels, R-channels and combination N-and-R channels (N-R channels) (Michalska 1969(Michalska , 1971Buraczyński, Superson 1992;Fard, Gruszka 2007;Frydrych 2016Frydrych , 2021Frydrych , 2022Roman 2016;Salamon, Mendecki 2021).…”

“…However, numerous studies show that eskers may also form in areas of permeable sediments (Rotnicki 1960;Michalska 1969;Wright 1973;Brennand 2000;Storrar et al 2014;Frydrych 2020Frydrych , 2021Frydrych , 2022Szuman et al 2021). In Poland, eskers were formed on a soft bed in N-channels, R-channels and combination N-and-R channels (N-R channels) (Michalska 1969(Michalska , 1971Buraczyński, Superson 1992;Fard, Gruszka 2007;Frydrych 2016Frydrych , 2021Frydrych , 2022Roman 2016;Salamon, Mendecki 2021). There is still limited knowledge about eskers formed on a soft bed and eskers formed in previous glaciations.…”