Sedimentary and structural record of the Scandinavian Ice Sheet margin dynamics at the SE part of the Głubczyce Plateau, a foreland of the East Sudetes Mountains (S Poland)

Abstract

A sedimentological and structural study is presented of a push-moraine formed in front of the Scandinavian Ice Sheet margin on the Głubczyce Plateau located at the forefield of East Sudetes Mountains. The glacial succession, which is composed of basal and flow tills, and sand/gravelly-sand deposited mainly from sheet flows at the surface of the glacier's marginal fan, developed in the culmination zone of an inter-valley hill, the base of which constitutes tectonic horst built of Carboniferous sandstones. In the central part of the hill, glacial deposits form a set of up-thrust slices, on the basis of which the succession is interpreted as thrust-block moraine. It was formed most likely during the maximum extent of the Saalian (Drenthe) glaciation. The substratum's topography and geology strongly determined the moraine development. Resistant Palaeozoic bedrock formed a rigid surface along which overlying unconsolidated sediments were pushed in front of the advancing ice sheet margin. The diamicton, lying above the bedrock and beneath the glaciofluvial sand, was of key importance for glaciotectonic shortening and development of the push moraine. It underwent ductile shearing, and a décollement surface developed within it, possibly because of thin permafrost, which caused high pore-water pressure within underlying unfrozen diamicton during the ice sheet advance. The ice-marginal deformation was induced by compression forces developed within the ice sheet margin moving against a reversed bedrock slope. A complete understanding of the process of this glaciomarginal form development and its paleoclimatic meaning requires a three-dimensional analysis of the ice sheet behaviour during the time over a much larger area also outside the Głubczyce Plateau. The varied topography of the ice sheet substratum induced time-transgressive changes of the ice distribution within the marginal part of the ice sheet. High friction in some elevated areas resulted in progressive concentration of ice flow in lower lying areas, such as valleys, where friction was much lower. This phenomenon essentially influenced the ice sheet margin dynamics and thus could determine the distribution and scale of glaciotectonic deformations.