Reconstruction of ice sheet movement from the orientation of glacial morpholineaments (crevasse landforms) : an example from northeastern Poland

Analysis of the orientation of both positive and negative glacial morpholineaments (crevasse landforms) was performed on the areas coveredby 12 selectedmap sheets of the Detailed Geological Map of Poland, scale 1:50 000, situated in NE Poland. Axes of these landforms formanet composed of four conjugate sets. This isaclassicaljointnet developeddue to horizontal stress, and composed of an orthogonal (extensional) system consisting of longitudinal and transversal sets, and a rhomboidal (shear) system consisting of two diagonal sets. Based on the orientation of glacial morpholineaments, inherited after the originaljoint net in the ice body, ice sheet advance directions - averaged for the area - were determined. This method of reconstructing ice flow direction creates new possibilities of making synthetic regional analyses, in particular in terms of Pleistocene palaeogeographic investigations. The best potential for the method’suse lies in areas of young post-glacial relief. In the region of NE Poland analyzed, these investigations enabled determination of different directions of ice flow within the Mazurian, Warmian and Vistulian ice sheet lobes of the last glaciation. Local changes in ice sheet movement directions were identified, and these reflected basement elevations (e.g. the Wiżajny Elevation). In other cases, basement irregularities influenced the opening of separate crevasse sets (e.g. outside of the Góra Dylewska massif) giving rise to a dominance of individual directions (sets) in the morpholineament orientation. This method can also be used in geological mapping.