Ice-crevasse sedimentation in the eastern part of the Głubczyce Plateau (S Poland) during the final stage of the Drenthian Glaciation

Abstract

Glacial sediments in the eastern part of the Głubczyce Plateau, at the Krowiarki site, were studied. Two units were distinguished within the sedimentary succession. The lower unit is composed of mainly sandy sediments with diamicton interbeds, the upper unit of very fine silt and clay sediments that exhibit rhythmic lamination in parts. Based on the textural and structural features of deposits, local deformations and palaeoflow directions, it was found that the sediments had been deposited within an ice crevasse, which was initially open and functioned as an ablation flow artery. The sediments were deposited in the form of a small fan dominated by sheetflows. Glacial tills were also redeposited on its surface. In a later phase, the crevasse was blocked. As a result, it was filled with water, leading to the development of a crevasse lake in which low-energy deposition dominated. The crevasse style of deposition indicates that, in the final stage of glaciation, the marginal part of the ice sheet was in a stagnant phase. This conclusion applies to the part located on the southern side of the watershed of the eastern Głubczyce Plateau. The probable reason for the stagnation of the ice sheet was the distinct loss of ice supply above the local topography barrier due to the decreasing thickness of the ice sheet in the studied area.