Dynamics of the last ice sheet on the northern fringe of Poland: reconstruction inferred from landform analysis and 10Be surface exposure dating

Karol Tylmann , Vincent Rinterknecht, Piotr P. Woźniak, Damian P. Moskalewicz, Aleksandra Bielicka-Giełdoń, Aster Team

The paper presents new results of glacial landforms mapping and analysis based on high resolution Digital Elevation Model (DEM), and 10Be surface exposure dating of erratic boulders on the northern fringe of Poland. We aimed to reconstruct the main ice-marginal positions, local ice flow directions and timing of the ice margin oscillations during the last deglaciation. A total number of 715 glacial landforms has been mapped, including: 274 moraine ridges, 68 subglacial lineations, 74 overridden moraines, 52 eskers, 169 kames, 14 zones of hummocky moraines, 47 subglacial valleys, 5 subglacial meltwater corridors (SMCs), and 12 ice-marginal valleys. Nine erratic boulders have been dated giving 10Be age range between 2.2 ± 0.3 ka and 17.8 ± 1.8 ka with the most reliable ages between 12.5 ± 1.1 ka and 17.8 ± 1.8 ka. Our results suggest dynamic oscillations of the ice sheet with episodes of the ice margin retreat, stillstands and re-advances. The Gardno moraines, described in the literature as a distinct ice-marginal belt correlated with the last Pleistocene ice re-advance in the Polish Lowland, are in fact diversified ice-marginal landsystems representing discontinuous and asynchronous ice sheet dynamics of particular ice streams/ice lobes with the main ice margin positions dated between ~17.5 ka and ~15 ka. The significant occurrence of meltwater-related glacial landforms and deposits in the study area suggests the presence of large volumes of meltwater within the ice sheet leading to the development of intensive subglacial and/or ice-marginal drainage systems during deglaciation. This likely triggered asynchronous, and ice-stream bounded episodes of ice margin retreat, stillstands, and readvances, which largely hinder efforts to correlate ice-marginal belts along the ice sheet and to date them as distinct phases of glaciation/deglaciation, i.e. discrete time intervals.