Podłoże i stratygrafia osadów czwartorzędowych w SW części Pojezierza Mazurskiego

Abstract

 W zbadanym obszarze w podłożu osadów czwartorzędowych występują liczne depresje i elewacje, których powstanie jest prawdopodobnie związane z ruchami tektonicznymi, w mniejszym stopniu z deformacjami glacitektonicznymi. Osady czwartorzędowe zawierają osiem poziomów glin zwałowych: po dwa – zlodowacenia podlaskiego i krakowskiego, trzy – zlodowacenia środkowopolskiego i jeden – zlodowacenia bałtyckiego. Lądolód zlodowacenia bałtyckiego w czasie maksymalnego zasięgu zajął jedynie północną oraz zachodnią część terenu. SUBSTRATUM AND STRATIGRAPHY OF QUATERNARY DEPOSITS IN SOUTH-WESTERN MAZURY LAKELAND The studies have been carried through in the south-western part of the Mazury Lakeland situated in the upper Wkra and Drwęca river drainage basins (Fig. 1).A small number of deep boreholes enabled an approximative only interpretation of topography of the bedrock composed of Maestrichtian marls and Lower Palaeocene sandstones (Fig. 2). The bedrock is distinctly inclined eastwards, with considerable elevations close to Żuromin and Ostróda and with a depression in Iława.Map of Quaternary substratum could be prepared with a greater accuracy (Fig. 3). One can easily find a set of deep depressions running from north-west to south-east. At both sides of these depressions substratum topography is quite different. To the south-west there are also deep depressions and aside them, just under the Quaternary deposits, there are Pliocene variegated clays.To the north-east, depressions are generally small and shallow but the whole area is formed mainly of brown coal formation. It makes an impression of “flooding” the previous topography of earlierTertiary deposits by variegated clays. The present relief of Quaternary substratum is after all an effect of denudation as it is suggested by isolated patches of variegated clays in the northern area.Oligocene deposits occur in the Quaternary substratum mainly in depression bottoms.No examined interglacial sediments in the studied area made stratigraphy to be grounded on references to the surroundings, first of all to the Mława area.In the described region the Quaternary deposits are usually 70–l00 m thick and in the substratum depressions – even over 250 m. Generally, eight till horizons can be distinguished: two each of Cracovian (Mindel) and Podlasie (Gunz) glaciations, three of Middle-Polish (Riss) Glaciation and one – of Baltic (Wurm) Glaciation (Figs. 4 – 6). Three lowermost till horizons occur in substratum depressions only, the rest form already more or less continuous beds in a larger area.Some deposits of small rivers were also found; lack of larger rivers is caused by localization of the area in a watershed zone for most of Pleistocene. A more distinct, two-cyclic alluvial series in the western part of the area, was connected with Great (Holstein) Interglacial (Tab. 1); one-cyclic one close to Rybno – with an interglacistadial of Cracovian (Mindel) Glaciation (Fig. 6).The third, uppermost till horizon of Middle-Polish (Riss) Glaciation was referred to Mława Glacistadial.It forms vast morainic plateau in southern and south-eastern parts of the area (Fig. 7). On the plateau, there are fragments of fluvioglacial levels (fig. 8) and denuded end moraines, kames and eskers.Till horizon of Baltic (Wurm) Glaciation can be found only in the northern and western part of the area. Locally but especially in the south-western part on the area, this till series was removed by fluvioglacial erosion.