Glacitectonic rafts and their role in the generation of Quaternary subglacial bedforms and deposits

Evans, David J.A.; Phillips, Emrys R.; Atkinson, Nigel

doi:10.1017/qua.2021.11

Glacitectonic rafts and their role in the generation of Quaternary subglacial bedforms and deposits

Evans, David J.A.; Phillips, Emrys R.; Atkinson, Nigel

Authors

Professor David Evans d.j.a.evans@durham.ac.uk
Professor

Emrys R. Phillips

Nigel Atkinson

Abstract

Landforms and sediments on the palaeo–ice stream beds of central Alberta record glacitectonic raft production and subsequent progressive disaggregation and moulding, associated substrate ploughing, and grooving. We identify a subglacial temporal or developmental hierarchy that begins with incipient rafts, including en échelon hill-hole complexes, hill-hole pairs, and strike-slip raft complexes, all of which display patterns typical of transcurrent fault activation and pull apart. Many display jigsaw puzzle–style fragmentation, indicative of substrate displacement along shallow décollement zones and potentially related to patchy ice stream freeze-on. Their gradual fragmentation and smoothing produces ice flow-transverse ridges (ribbed moraine), hill-groove pairs, and paraxial ridge and groove associations. Initiator scarp and megafluting associations are indicative of raft dislodgement and groove ploughing, leading to the formation of murdlins, crag-and-tails, stoss-and-lee type flutings and drumlins, and Type 1 hogsback flutings. Downflow modification of rafts creates linear block trains (rubble stripes), stoss-and-lee type megaflutings, horned crag-and-tails, rubble drumlinoids, and murdlins, diagnostic of an immature palaeo–ice stream footprint. Lateral ice stream margin migration ingests disaggregated thrust masses to form ridged spindles, ladder-type morphologies, and narrow zones of ribbed terrain and Type 2 hogsback flutings, an assemblage diagnostic of ice stream shear margin moraine formation.

Citation

Evans, D. J., Phillips, E. R., & Atkinson, N. (2021). Glacitectonic rafts and their role in the generation of Quaternary subglacial bedforms and deposits. Quaternary Research, 104, 101-135. https://doi.org/10.1017/qua.2021.11

Journal Article Type	Article
Acceptance Date	Feb 9, 2021
Online Publication Date	May 6, 2021
Publication Date	2021-11
Deposit Date	May 16, 2021
Publicly Available Date	May 17, 2021
Journal	Quaternary Research
Print ISSN	0033-5894
Electronic ISSN	1096-0287
Publisher	Academic Press
Peer Reviewed	Peer Reviewed
Volume	104
Pages	101-135
DOI	https://doi.org/10.1017/qua.2021.11

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Copyright Statement
Advance online version © University of Washington. Published by Cambridge University Press, 2021. This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence
(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.