EGU21-9526, updated on 09 Jan 2024
https://doi.org/10.5194/egusphere-egu21-9526
EGU General Assembly 2021
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Ribbed bedforms, markers of palaeo-ice stream margins, basal meltwater drainage and ice flow dynamic

Jean Vérité1, Édouard Ravier1, Olivier Bourgeois2, Stéphane Pochat2, Thomas Lelandais1, Christopher D. Clark3, Paul Bessin1, Régis Mourgues1, David Peigné1, and Nigel Atkinson4
Jean Vérité et al.
  • 1Le Mans Université, UMR 6112 CNRS, Laboratoire de Planétologie et Géodynamique, Le Mans, France
  • 2Laboratoire de Planétologie et Géodynamique, UMR 6112, CNRS, Université de Nantes, 2 rue de la Houssinière, BP 92208, 44322 Nantes CEDEX 3, France
  • 3Department of Geography, University of Sheffield, Sheffield, UK
  • 4Alberta Geological Survey, 4th Floor Twin Atria Building, 4999-98 Ave. Edmonton, AB, T6B 2X3, Canada

Over the three last decades, great efforts have been undertaken by the glaciological community to characterize the behaviour of ice streams and better constrain the dynamics of ice sheets. Studies of modern ice stream beds reveal crucial information on ice-meltwater-till-bedrock interactions, but are restricted to punctual observations limiting the understanding of ice stream dynamics as a whole. Consequently, theoretical ice stream landsystems derived from geomorphological and sedimentological observations were developed to provide wider constraints on those interactions on palaeo-ice stream beds. Within these landsystems, the spatial distribution and formation processes of subglacial periodic bedforms transverse to the ice flow direction – ribbed bedforms – remain unclear. The purpose of this study is (i) to explore the conditions under which these ribbed bedforms develop and (ii) to constrain their spatial organisation along ice stream beds.  

We performed physical experiments with silicon putty (to simulate the ice), water (to simulate the meltwater) and sand (to simulate a soft sedimentary bed) to model the dynamics of ice streams and produce analog subglacial landsystems. We compare the results of these experiments with the distribution of ribbed bedforms on selected examples of palaeo-ice stream beds of the Laurentide Ice Sheet. Based on this comparison, we can draw several conclusions regarding the significance of ribbed bedforms in ice stream contexts:

  • Ribbed bedforms tend to form where the ice flow undergoes high velocity gradients and the ice-bed interface is unlubricated. Where the ribs initiate, we hypothesize that high driving stresses generate high basal shear stresses, accommodated through bed deformation of the active uppermost part of the bed.
  • Ribbed bedforms can develop subglacially from a flat sediment surface beneath shear margins (i.e., lateral ribbed bedforms) and stagnant lobes (i.e., submarginal ribbed bedforms) of ice streams, while they do not develop beneath surging lobes.
  • The orientation of ribbed bedforms reflects the local stress state along the ice-bed interface, with transverse bedforms formed by compression beneath ice lobes and oblique bedforms formed by transgression below lateral shear margins.
  • The development of ribbed bedforms where the ice-bed interface is unlubricated reveals distinctive types of discontinuous basal drainage systems below shear and lobe margins: linked-cavities and efficient meltwater channels respectively.

Ribbed bedforms could thus constitute convenient geomorphic markers for the reconstruction of palaeo-ice stream margins, palaeo-ice flow dynamics and palaeo-meltwater drainage characteristics.

How to cite: Vérité, J., Ravier, É., Bourgeois, O., Pochat, S., Lelandais, T., Clark, C. D., Bessin, P., Mourgues, R., Peigné, D., and Atkinson, N.: Ribbed bedforms, markers of palaeo-ice stream margins, basal meltwater drainage and ice flow dynamic, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9526, https://doi.org/10.5194/egusphere-egu21-9526, 2021.

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