Abstract

Geomorphic, stratigraphic, and sedimentologic evidence obtained from Quaternary sediments near Jasper, Alberta, is used to reconstruct depositional environments in the vicinity of two former confluent valley glaciers. Sedimentation occurred mainly in the valley centre in a pre-existing river channel. Lateral ice-marginal sedimentation along the inset valley walls was important during both the advance and the retreat stages. Prior to and during glacial advance, horizontally stratified gravels, sands, and silts were deposited in a braided stream. Near the valley bottom, diamictons containing trough-shaped sand lenses were deposited by subsequent proglacial debris flows and intermittent fluvial activity. At higher stratigraphic positions, outwash deposits confined to the valley wide are unconformably overlain by massive diamicton, interpreted as subglacial till, deposited as ice began to override the area. The diamicton grades towards the valley side into ice-contact debris deposited at the margins of the expanding glacier by water and sediment flows from the ice surface. Glaciers eventually overrode the entire area. During deglaciation, thick sequences of normally faulted, steeply dipping sand, gravel, and clast-rich diamicton were deposited in a kame terrace west of Jasper townsite. The orientation of bedding and faults and the nature of the sediments indicate they were derived from, and deposited in contact with, a linear belt of stagnating, debris-covered ice that extended along the valley centre east of Jasper. It is postulated that the stagnating ice originated from a well-developed medial moraine and debris septum that formed at the confluence of the large Athabasca and Miette valley glaciers. The knob-and-kettle topography, which eventually developed in the valley centre, was obscured by glaciofluvial and fluvial activity. A linear chain of kettle lakes remains as evidence of the possible existence of the moraine. Kettle chains and hummocky topography, formed in the positions of both medial and lateral moraines, may be relatively common geomorphic features in glaciated mountain valleys.

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