Landform and sediment imprints of fast glacier flow in the southwest Laurentide Ice Sheet

• Published in: Journal of Quaternary Science
• Main Authors: Evans, David J. A., Clark, Chris D., Rea, Brice R.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2008
• Subjects: Ice Sheet
• Online Access: http://dx.doi.org/10.1002/jqs.1141; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1002%2Fjqs.1141; https://onlinelibrary.wiley.com/doi/pdf/10.1002/jqs.1141

Abstract Evidence for former fast glacier flow (ice streaming) in the southwest Laurentide Ice Sheet is identified on the basis of regional glacial geomorphology and sedimentology, highlighting the depositional processes associated with the margin of a terrestrial terminating ice stream. Preliminary mapping from a digital elevation model of Alberta identifies corridors of smoothed topography and corridor‐parallel streamlined landforms (megaflutes to mega‐lineations) that display high levels of spatial coherency. Ridges that lie transverse to the dominant streamlining patterns are interpreted as: (a) series of minor recessional push moraines; (b) thrust block moraines or composite ridges/hill–hole pairs constructed during readvances/surges; and (c) overridden moraines (cupola hills), apparently of thrust origin. Together these landforms demarcate the beds and margins of former fast ice flow trunks or ice streams that terminated as lobate forms. Localised cross‐cutting and/or misalignment of flow sets indicates temporal separation and the overprinting of ice streams/lobes. The fast‐flow tracks are separated by areas of interlobate or inter‐stream terrain in which moraines have been constructed at the margins of neighbouring (competing) ice streams/outlet glaciers; this inter‐stream terrain was covered by more sluggish, non‐streaming ice during full glacial conditions. Thin tills at the centres of the fast‐flow corridors, in many places unconformably overlying stratified sediments, suggest that widespread till deformation may have been subordinate to basal sliding in driving fast ice flow but the general thickening of tills towards the lobate terminal margins of ice streams/outlet glaciers is consistent with subglacial deformation theory. In this area of relatively low relief we speculate that fast glacier flow or streaming was highly dynamic and transitory, sometimes with fast‐flowing trunks topographically fixed in their onset zones and with the terminus migrating laterally. The occurrence of minor push moraines ...