LITHOFACIES DESCRIPTION AND DEPOSITIONAL MODELLING OF A TUNNEL- MOUTH ENVIRONMENT BASED ON THE OUTCROP STUDIES IN NORTH CENTRAL POLAND

We have carried out a detailed analysis on the spatial distribution of ten distinguished lithofacies on the exposed outcrops of the Uniski elongated gravel pit in North Central Poland. The goal was to reconstruct the depositional environment and flow mechanism in a subglacial tunnel system in an area where the morphology reflects the impact of various glacial drainage systems at the time of the last deglaciation.

The 4 km long, 200 m wide esker is a ridge-formed, sinuous shape structure formed perpendicular to ice margin. The coarsest deposits occur in the core of the esker while to the east, the lithofacies laterally change into more fine-grained ones within a few meters. The flanks are deformed, and show a change in the nature of deformation from east to west; the eastern part is deformed by flexures with some exposed faults, whereas the esker-core deposits in the west are unconformably covered by a 4-5 m thick deformed package of various lithofacies types. The esker ridge is covered by a ca. 5 m thick diamicton.

The developed depositional model for the study area allows us to have a better understanding of the subglacial tunnel environment as well as the regional ice-sheet morphology during the last deglaciation event in Central Europe.