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Reconstruction of the Vistula ice stream during the Last Glacial Maximum in Poland

Morawski W.

Geological Quarterly

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2009

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Vol. 53, No 3

305-316

EN

The variability ofice movement directions within the Vistula lobe of the Main Stadial ice sheet of the last glaciation is analysed. Reconstruction of the ice movement directions is made based on analysis of the orientation of glacial morpholineaments. Linear glacial land forms are analysed on the basis of data from 26 map sheets of the Detailed Geo logical Map of Poland (DGMP), scale 1:50 000, compiled earlier by various au thors. The morpholineaments were investigated in a belt of morainic plateau that adjoins the Vistula valley on both sides. The analysis revealed that the last glaciation ice sheet advanced directly from the north within the broadly un der stood Vistula ice lobe zone, and that the ice flow direction was constant. However, within a narrow belt of the pre-Vistula River valley that was formed in the Eemian Interglacial, the 30–50 km wide ice stream was characterized by locally variable ice flow directions consistent with the pre-existing valley trend. Changes in ice flow direction are recorded in the locally variable orientation of lin ear glacial landforms, indicating that the ice stream was active until the deglaciation period when the pres ent-day shapes of the glacial landforms developed.

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Warmińska prowincja paleogeograficzna plejstocenu (północno-wschodnia Polska)

Morawski W.

Przegląd Geologiczny

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2005

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Vol. 53, nr 6

477--488

EN

The historic area of Warmia (western part of NE Poland) can be considered as a separate geological unit. In particular it applies to its Pleistocene sedimentary complex with a very limited occurrence of morainic deposits, commonly forming discontinuous horizons. Intermorainic deposits predominate, including mainly ice-dam lake deposits which occur at different levels. The sub-Pleistocene relief variations reach up to 400 m, with glaciotectonic upthrustings of Neogene deposits extending to the topographic surface. The province area coincides with the Warmia ice-sheet lobe of the last glaciation (Main Stadial of the Vistulian Glaciation). The eastern boundary of the area is represented by an interlobe zone coincident with the western slope of the Mazury–Suwałki Anteclise. The boundary is a tectonic discontinuity zone extending down to the crystalline basement. The eastern, anteclise area was stable during the Pleistocene, while the area of Warmia (Peri-Baltic Syneclise) was unstable mainly due to cyclic ice-sheet loads which resulted in subsidence in the Warmia region. It, in turn, caused a bending of the ice sheet body, movement acceleration and a change in ice flow direction in Warmia. During interglacials, relaxation uplifting movements triggered stronger erosional processes. These movements were dependent on surface relief, stimulating the formation of deeply rooted glaciotectonic structures.

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

Morawski W.

Geological Quarterly

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2005

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Vol. 49, No. 4

403--416

EN

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.