ABSTRACT: The formation of eskers based on their morphology, stratigraphy, and litholologic composition, Labrador, Canada

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Abstract

The distribution and drainage patterns of eskers in Labrador, as well as the morphology, stratigraphy and lithologic composition of five systems located in central ('Gabbro' and 'Ossokmanuan' eskers), western ('Shabogamo' and 'Ashuanipi' eskers) and northern Labrador ('Lac Brisson' esker) were investigated to propose a model of esker formation and debris entrainment. Eskers are not uniformly distributed, and are more abundant on plateau areas while they are scarce to absent in mountainous terrain, near all coasts, and in a region centred over the presumed ice divide of the Labradorean sector of the Laurentide Ice Sheet. Eskers show a Horton drainage organization with up to third order segments (7 of 25 systems have 3 order segments). Organized esker systems are up to 400 km long, and service a subglacial drainage basin of up to 17,000 km2. Eskers are coarse-grained tunnel deposits, steep-sided, sharp-crested, straight (SI 1.07) single ridges, which pass into less than 5 km long double or multiple segments. Associated with esker ridges are finer-grained proglacial and supraglacial fluvioglacial deposits such as aprons lapping on to the ridge; flat pads, separated from the ridge by a shallow ditch; splays, highly kettled deposits otherwise resembling pads; and blankets of gravel which may or not mask older deposits. Adjacent associated deposits were formed after the sedimentation of the ridge. Lithologies found in an esker ridge are derived from up-esker till (in a corridor up to 3.5 km on either side of the ridge) which is itself derived from bedrock. Esker are deposited by the laying of shingle-like tabular sedimentation units in a subglacial tunnel (25-30 km long) near the margins of the ice sheet.

Bibliography of Canadian Geomorphology