Poziom interglacjalny wśród osadów zlodowacenia środkowopolskiego w Dolinie Dolnej Wisły

Aurelia Makowska


W Dolinie Dolnej Wisły pod Kwidzynem stwierdzono obecn06ć osadów interglacjalnych występujących między dwiema glinami zwałowymi, poniżej rzecznych, jeziornych i morskich osadów eemskich i powyżej rzecznych osadów interglacjału wielkiego (mazowieckiego). Przyjmuje się, iż nowo poznane osady powstały w interglacjale, który miał miejsce między stadiałem maksymalnym a stadiałem Warty zlodowacenia środkowopolskiego.


A new horizon of lacustrinal deposits comprising lacustrinal chalk, clays and silts with humus as well as stagnant-water clays, silts and sands has been found by boreholes in the lower Vistula river valley near Kwidzyń (Fig. 1). It occurs at depths ranging from about a dozen to 415 m below floodplain surface and separates two till horizons: upper, underlying a series of Eemian deposits with good paleontological record, and lower, overlying alluvia from the Great (Masovian) Interglacial (Figs. 2-3). The composition of these lacustrinal deposits indicates certain facial differentiation (Fig. 6) and their development - deposition in a closed, evolving basin or basins. The most complete profile was obtained from three boreholes situated closely to one another at Grabówka (Fig. 3, boreboles 13, 14 and 15) and, therefore, the whole horizon was named as the G r a b ó w k a  s e r i e s. The total thickness of these deposits approaches 21.5 m. The deposits rest on uneven substratum built of tills (Fig, 5), which was formed, during deglaciation proceeding in separate melting holes. The holes along with the progress in melting of dead-ice blocks became infilled with sandy-clay-silty deposits and later with water. In this way a single great ice-dammed lake originated. This lake was extending north and east of the area studied. Further history of this water reservoir was reconstructed on the basis of the sedimentary sequence studied.

It appears difficult to date these deposits. Their geological setting indicates that they are older than the Eemian horizon which is relatively well known in this region thanks to the record of marine malacological and foraminifer assemblages and other data. The deposits appear to be younger than those of the Great (Masovian) Interglacial which were found to infill well-developed river walleye at Wełcz Wlelki (fig. 7). The pollen analysis carried out by Z. Janczyk-Kopikowa (1970) has shown four-period development of vegetation but failed to cast some light on the age of these deposits (Fig. 4A, B, C).

The most characteristic spectrum, obtained for the profile from Grabówka (Fig. 4D), is characterized by the share of Quercus approaching 22%. This would suggest that we are dealing here with an interglacial horizon. This is the first locality of such type in the northern Poland. In correlations with the central Poland it is assumed that the deposits from .Grabówka represent a new stratigraphic horizon corresponding to an interglacial which took place between the Radomka (maximum) stage of the Middle Polish Glaciation and the Warta stage. If this is the case, the Warta stage should be interpreted as a separate Glaciation. However, such dating may be regarded as disputable at least till a complete palynological diagrams is obtained for the Grabówka series.

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