Differentiation of subglacial conditions on soft and hard bed settings and implications for ice sheet dynamics: a case s
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ORIGINAL PAPER
Differentiation of subglacial conditions on soft and hard bed settings and implications for ice sheet dynamics: a case study from north‑central Poland Robert J. Sokołowski1 · Wojciech Wysota2 Received: 6 June 2019 / Accepted: 10 August 2020 © The Author(s) 2020
Abstract We reconstruct patterns of subglacial processes on a hard bedrock and a soft bed under the southern sector of Scandinavian Ice Sheet (SIS) occurring in the basal till of the Late Saalian Glaciation at the Wapienno, Barcin and Młodocin sites (northcentral Poland). Based on detailed sedimentological studies, two phases of SIS transgression were recognised. In the initial phase of the transgression, the SIS advanced onto a frozen substrate (continuous permafrost). The low permeability of the substratum led to a high subglacial water pressure (SWP) and increased basal sliding. The local increase of SWP led to the development of different types of structures and sediments. On a hard bedrock, with low SWP, abrasion predominated and linear structures were developing, while in the case of high SWP, the ice was decoupled from the hard substrate, pressurised liquefied sediment flowed, and structures of the p-form and s-form type developed. On a soft bed, the ice-bed contact was of a mosaic type and the ice movement had an ice-stream character. The ice-stream developed towards the east in the marginal zone of the SIS and used a W-E oriented valley filled by the Wapienno Formation fluvial complex. During a later phase, the ice movement was slower and did not have a stream character. Its direction changed to SE. The deposition of the main part of the diamicton occurred mainly as a result of the lodgement process. Keywords Abrasional forms · Boulder pavement · Basal till · Palaeo-ice stream · Late saalian glaciation
Introduction The dynamics of ice movement depends both on the amount and pressure of water in the subglacial zone and on the lithology and rheological properties of the substrate (Fischer et al. 1999; Piotrowski 2006; Harper et al. 2007; Benn and Evans 2010; Ravier and Buoncristiani 2018; Hart et al. 2019). The presence of permafrost in the forefield of an advancing ice sheet, or in its submarginal zone, can have an impact on the speed of ice flow and its stream character due * Robert J. Sokołowski [email protected] Wojciech Wysota [email protected] 1
Department of Geophysics, Institute of Oceanography, University of Gdańsk, Al. Piłsudskiego 46, 81‑378 Gdynia, Poland
Department of Geology and Hydrogeology, Faculty of Earth Sciences and Geospatial Management, Nicolaus Copernicus University, Lwowska 1, 87‑100 Toruń, Poland
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to a decreased effective drainage of water into the substrate (Waller et al. 2012; Narloch et al. 2013). The dynamics and directions of ice movement can be identified based on various types of erosion and deformation structures and landforms (van der Wateren et al. 2000; Stokes and Clark 2001; Glasser and Bennett 2004; Przybylski 2008; Lesemann et al. 2010). A faster ice flow, is inferred from g
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