The Late Weichselian glacial record in northern Poland: A new look at debris transport routes by the Fennoscandian Ice Sheet

摘要

The area of the Kashubian Coastland and areas adjacent to the northern part of the Lower Vistula Valley (northern Poland) were involved in the major transgressive phases distinguished in Poland during the Late Weichselian. Due to the small scale of the regressions between the different phases of the Late Weichselian, the ice sheet usually deposited only one till, but with a complex vertical profile. Based on the studies of the directional properties, petrographic composition of the fine gravel fraction and the analysis of indicator erratics, the dichotomy of the till bed was demonstrated. The petrographic composition of the gravel fraction in tills together with the analysis of the indicator erratics and delimitation of the Theoretical Boulder Centres were used to determine the direction of the influx of ice masses. This allowed speculation on the reasons for the different dynamics of the Fennoscandian Ice Sheet (FIS) as well as the operation and time variability of the Baltic Ice Stream (BIS). It was emphasised that the delivery system of debris by the ice sheet might have been complex and multidirectional (more than one route). It has been suggested that changes in the petrographic composition of the gravel fraction of the glacial sediments did not have to be associated only with shifting the centre of glaciation, but may have resulted from a change in the thermal regime of the ice sheet's bed in the source area (especially with the spread of the cold regime zone), and depended on the dynamics of the ice sheet (stream or sheet flow) as well as the spatial and temporal conditions of its development in the deposition area. (C) 2015 Elsevier Ltd and INQUA. All rights reserved.