Eskers formed in the soft‐bed region – a comprehensive study of Late Saalian strata from Poland

ABSTRACT The study presents the first comprehensive sedimentological analysis of eskers formed on soft beds. It was conducted in selected esker exposures in the area of Saalian Glaciation in Poland. Three glacial sub‐environments were distinguished based on the lithofacies analysis of 30 sedimentological profiles. Division validity of lithofacies associations was confirmed using Markov chain analysis. The subglacial channel facies (1) are mainly composed of planar cross‐stratified gravels, horizontally stratified gravels and massive gravels. They often exhibit very poor sorting, widespread imbrication and the presence of intraclasts. The deposits of the subglacial channel were primarily accumulated during turbulent flow, but hyperconcentrated flows also played a significant role in their formation. The flow was predominantly under hydrostatic pressure. The facies of the ice crevasse channel (2) are built with trough cross‐stratified and horizontally stratified gravels and sands as well as massive gravels. These deposits are characterised by varying sorting, the presence of outsized clasts, and the occurrence of syn‐depositional and post‐depositional deformation of different types. Sediments of this sub‐environment were formed under atmospheric pressure during high‐energy turbulent flow. The facies of the open channel (3) are mainly composed of sandy lithofacies with horizontal stratification, massive structure and ripple‐lamination. In some cases, the deposits are interbedded with massive gravels. The sediments are characterised by the presence of extensional deformation associated with the disappearance of ice support. Water flow within the channel could occur across its entire width or had the form of braided channels.