Ice-flow directions of the last Scandinavian Ice Sheet in central Poland

Abstract

The article presents the results of studies on the ice-flow directions of the last Scandinavian Ice Sheet (SIS) in central Poland, at the southern periphery of the SIS, and particularly within the Płock lobe. The ice-flow pattern was derived mainly from direct indices, such as: till fabric; vergence of glaciotectonic compression structures; orientation of small-scale subglacial deformations formed beneath the flowing ice; orientation of pavement stone longitudinal axes; stone lee ends; and clast surface striae. The study is supplemented with a reconstruction of ice-movement directions based on orientation analysis of both concave (tunnel valley) and convex (eskers) glacial morpholineaments (linear glacial landforms). Till age was also determined, using luminescence (OSL) datings from sand deposits. These were collected directly at numerous sites, from under and above the last SIS till unit. Combined with previously published data, the results of the present investigation of the last ice-sheet advance during the Late Weichselian (ca 23–18 ka) indicate that there were two different ice-flow phases and that the maximum extent was asynchronous. The western part of the said area experienced two advances during the Leszno (Brandenburg) and Poznań (Frankfurt) phases, while during the earlier one the ice masses came from the NW, presumably along the eastern limb of the Odranian (B2 after Punkari 1997) ice stream, and then from the N, along the Vistulian (B3) stream. The last SIS occupied the eastern sector of the area only once, during the younger Poznań phase, building the Płock lobe. The lobe-shaped ice margin with a fan-like flow pattern within the lobe may be indicative of a palaeo-ice stream terminal zone.