Ice sheet maximum limit of the Vistulian Glaciation in the mid-eastern Chełmno-Dobrzyń Lakeland, northern Poland

Abstract

The maximum extent of the Vistulian Glaciation in the mid-eastern Chełmno-Dobrzyń Lakeland fell on the Maximum Phase of the Main Substage (ca. 20-18 ka BP). Geomorphologic and sedimentologic record of this phase combines a separate horizon of a lodgement till and associated glaciotectonites, a broad higher level of the Dobrzyń sandur, hills and ridges of end moraines, a push moraine ridge, tunnel valleys, as well as melt-out tills and sands with boulders. The ice sheet maximum limit is marked by a sedimentary scarp to the south of Bryńsk, a morphologic scarp within a higher level of the Dobrzyń sandur to the south of Lidzbark Welski, and a morainic hill to the south-east of Koszelewy. Two glacial lobes became distinct within the ice sheet during the maximum phase: the Bryńsk lobe in the west (unfrozen to the bed, with its ice front in steady-state conditions), and the Lidzbark Welski lobe in the east (with complex thermal conditions). A well-developed subglacial drainage system was active within the Bryńsk ice lobe, with meltwaters runoff along the glacial tunnel valleys of the Lake Bryńsk and the Lake Lidzbark. At the maximum extent, the Lidzbark Welski lobe was in the steady-state conditions, similarly to the Bryńsk lobe, and the higher level of the Dobrzyń sandur was formed to the south of Lidzbark Welski. To the south of Koszelewy, short ice-marginal fans were formed. A minor oscillation of the ice front and development of a push moraine occurred in the western part of the Lidzbark Welski ice lobe.