Influence of bedrock on the Quaternary deposits in the central Krajna Lakeland

Abstract

An elevated bedrock (Więcbork Elevation), caused by uplifting related mostly to salt tectonics, significantly affected types of the Quaternary sediments in the central Krajna Lakeland. It caused development of destructive processes which resulted that the older Pleistocene deposits, from sediments of the Odranian Glaciation (Drenthe, Older Saalian), have not been preserved. The bedrock topography also affected thickness variability of the Quaternary deposits, from 80 to 95 m in topographic depressions and from 30 to 60 m at elevations. Sediments of three stadials of the Wartanian Glaciation (Warthe, Younger Saalian), which constitute more than 50% of the entire thickness, are the most significant. They caused considerable planation which reduced effects of bedrock topography on deposition of sediments of the Vistulian Glaciation (Weichselian). Ice sheets of the Early and Middle Vistulian Glaciation, advancing to the Lower Vistula Region as well as the Warmia and the Mazury, have not reached the study area. Hence, occurring here the sediments of the Vistulian Glaciation were deposited during the Main Stadial (about 20-16 ka BP). The bedrock elevated at the watershed resulted in a very poor development of fluvial ice-dam lake, and lake-marshy deposits. The latter are the most important among the Holocene sediments. Six tills of five glacial episodes, forming about 70% of the entire deposit thickness, are the main Pleistocene sediments. Petrographic composition of tills of the Wartanian and the Vistulian Glaciations is closely related to the one of tills from central Wielkopolska (Great Poland), reflecting similar directions of advancing ice sheets. A till of the Mława Stadial of the Wartanian Glaciation, which occurs in the Krajna Lakeland, probably does not occur in central Wielkopolska. The Krajna Lakeland, as far as thickness and structure of the Quaternary deposits is concerned, belongs to the Kujawy-Pomeranian Region which is significantly different from the Lower Vistula Region, Warmia and Mazury.