Glacial landsystems of the southwest Laurentide Ice Sheet: modern Icelandic analogues

Abstract

Landform assemblages and associated stratigraphy, sedimentology and structure are used in the reconstruction of palaeo-ice-sheet dynamics in Alberta, western Canada. Interpretations are based upon the modern analogues from four outlet glaciers at the margins of Vatnajokull and Myrdalsjokull, Iceland. In the area between Lloydminster and Lac la Biche, central Alberta, an extensive landform assemblage of megaflutings, crevasse-squeeze ridges and thrust-block-moraine arcs document the former surging of part of the margin of the Laurentide Ice Sheet during later stages of recession. This landform assemblage, including numerous exposures of glacitectonised bedrock and Quaternary sediments, is comparable to the landsystem of the surging glaciers Eyjabakkajokull and Bruarjokull in Iceland. Near High River southern Alberta, the former existence of an ice lobe characterised by active recession is recorded by closely spaced, low-amplitude recessional push moraines that drape tunnel valleys. These are comparable in form and pattern to annual push moraines and fluted till surfaces produced by Breidamerkurjokull and Sandfellsjokull, Iceland, and also include rimmed depressions produced by the escape of artesian water during ice-marginal pushing. This study provides interpretations of the regional glacial geomorphology of Alberta based upon comparisons of form and stratigraphy with modern glacial analogues, and provides an alternative to recent models which invoke large floods of subglacial meltwater to explain many of these same features. Implications for ice dynamics and regional till stratigraphies are discussed. Copyright © 1999 John Wiley & Sons, Ltd.