Interglacjał eemski w Skierniewicach i jego znaczenie dla znajomości paleogeografii młodszego plejstocenu

Abstract

THE EEMIAN INTERGLACIAL AT SKIERNIEWICE (CENTRAL POLAND) AND ITS SIGNIFICANCE FOR THE KNOWLEDGE OF THE YOUNGER PLEISTOCENE PALAEOGEOGRAPHYSummaryThe Interglacial deposits at Skierniewice were found in 1964. Palynological analyses were made by Z. Borówko-Dłużakowa (1972). Below there is presented geological aspect of the problem, particularly its significance for the knowledge of the Younger Pleistocene palaeogeography in the south-western part of the Warsaw Basin.The Interglacial deposits (Fig. 1) occur in the bottom of a shallow, dead valley which branches out of the Skierniewka valley (Fig. 2). Most probably these are old river-bed deposits laid down within the Interglacial valley of the Skierniewka stream, which at present flows through a new valley directed north-westwards, and deviated from the old one by about 90°. The overlying deposits do not disclose any organic remains. According to K. Balińska-Wuttke (1960, 1965) this is an alluvial cone, according to the above author, of Interglacial age. Such cones are frequently found in the area of the so-called Warsaw Basin (Fig. 2). E. Wunderlich (1917), J. Samsonowicz (1927), and W. Mizerja (1947) were inclined to an opinion that these had been deposits of the rivers f]owing to the so-called “Warsaw ice-dammed lake”.The occurrence of the Eemian Interglacial deposits under the deposits of alluvial cones has also been encountered at some localities of the Warsaw Basin. This forces to move the accumulation time of these alluvial cones in this area to the last glaciation. This is also proved by a lot of other circumstances, among others by climatic factors. This opinion is also expressed by S. Z. Różycki (1967).An abrupt change in direction of the Skierniewka stream valley north-westwards and identical changes in directions of the neighbouring rivers are thought to be a regional phenomenon. In the Eemian Interglacial most rivers flowed to the east or north-east. At the beginning of the last glaciation the accumulation cones were characterized by predominant north-eastern direction, which gradually changed for a northern, and the north-western one. Simultaneously, the changes in the course of the river valleys led to the present-day system of drainage pattern. It results from this that the lower portion of the rivers developed during one of the later phases of the last glaciation (Leszno phase). To this phase, existing about 20–25 thousand years ago (S. Z. Różycki, 1967), is related the utmost range of the Baltic Glaciation.The change in the river valley directions and the accumulation of cones can best be explained by the yielding of the Earth's crust under the load of the invading glacier, the front of which was during its maximum extent approximately 60 km from Sierniewice. In that part of Poland the continental ice streached more than 100 km farther to the south, than in the eastern area of the country, where a more rigid East-European platform area resisted the pressure of the glacier (Fig. 3). At that time the change in the inclination of the Earth's crust towards the invading glacier in that area forced the rivers, flowing onto the levelled area, to groove new beds, in conformity with the inclination of the terrain. These changes developed due to the infilling of valleys under conditions of periglacial climate and considerable development of the accumulation cones.