Formation of ribbed bedforms below shear margins and lobes of palaeo-ice streams

Abstract

Abstract. Conceptual ice stream land systems derived from geomorphological and sedimentological observations provide constraints on ice–meltwater–till–bedrock interactions on palaeo-ice stream beds. Within these land systems, the spatial distribution and formation processes of ribbed bedforms remain unclear. We explore the conditions under which these bedforms may develop and their spatial organization with (i) an experimental model that reproduces the dynamics of ice streams and subglacial land systems and (ii) an analysis of the distribution of ribbed bedforms on selected examples of palaeo-ice stream beds of the Laurentide Ice Sheet. We find that a specific kind of ribbed bedform can develop subglacially through soft-bed deformation, where the ice flow undergoes lateral or longitudinal velocity gradients and the ice–bed interface is unlubricated; oblique ribbed bedforms develop beneath lateral shear margins, whereas transverse ribbed bedforms develop below frontal lobes. We infer that (i) ribbed bedforms strike orthogonally to the compressing axis of the horizontal strain ellipse of the ice surface and (ii) their development reveals distinctive types of subglacial drainage patterns: linked cavities below lateral shear margins and efficient meltwater channels below frontal lobes. These ribbed bedforms may act as convenient geomorphic markers to reconstruct lateral and frontal margins, constrain ice flow dynamics, and infer meltwater drainage characteristics of palaeo-ice streams.

The Kola Peninsula and Russian Lapland: A review of Late Weichselian glaciation

“…Fields of ribbed moraine (Fig. 2, 7c), identified by Hättestrand and Clark (2006a), support ice streaming interpretations, and may indicate the lateral margins of individual ice stream trunks within the Tuloma Ice Stream (Stokes et al, 2016b;Vérité et al, 2021). However, there are several instances of cross-cutting bedforms and apparent divergent lineations orientated west-east (Hättestrand and Clark, 2006a).…”

“…However, the development of robust identification criteria of ice streaming -including highly convergent flow patterns, highly attenuated bedforms, and abrupt lateral margins Clark, 1999, 2001;Stokes et al, 2016b) -had not been established when these initial interpretations were made. Furthermore, recent advances in palaeo-ice stream identification suggest (i) the likely occurrence of ribbed moraines along ice stream pathways, which are thought to develop concomitantly with glacial lineations (Stokes et al, 2016b;Vérité et al, 2021), and (ii) esker development is not necessarily contemporaneous with ice streaming Clark, 1999, 2001;Stokes et al, 2009;Hughes et al, 2014). These recent advances in understanding, and identifying, palaeo-ice streaming cast doubt on the early ice streaming interpretations of Punkari (1993Punkari ( , 1995Punkari ( , 1997 and Kleman et al (1997).…”

GIS dataset: geomorphological record of terrestrial-terminating ice streams, southern sector of the Baltic Ice Stream Complex, last Scandinavian Ice Sheet, Poland

“…Further raster processing steps were performed using the GDAL library (Warmerdam, 2008). Merging A second raster dataset was produced by de-trending the DEM data.…”

GIS dataset: geomorphological record of terrestrial-terminating ice streams, southern sector of Baltic Ice Stream Complex, last Scandinavian Ice Sheet, Poland

“…Further raster processing steps were performed using the GDAL library (Warmerdam, 2008). Merging , and a variable vertical exaggeration factor from 15 to 45 (estimated empirically for each subregion to emphasise small landforms).…”