Abstract

Till at two localities in the Edmonton area, Alberta was formed mainly by passive melt-out from glacier ice and not by lodgment by active ice or as a result of supraglacially derived flows. This interpretation is based on the implications of in situ stratified glacial sediment below and within till and of large unlithified clasts of sediment derived from subtill deposits. The interpretation is also supported by more general regional, stratigraphic, and structural observations. Such associated properties as subtill deformation, a sharply planar till – preglacial sediment contact, sole marks, and fabric support formation by melt-out or illustrate local exceptions to this process. Regionally consistent preferred orientation of clasts is interpreted to represent preferred englacial orientation. Collective analysis of the principal eigenvectors of individual englacial fabrics and flow or resedimented till fabrics from a modern glacial environment and similar analysis for till at Villeneuve near Edmonton show the Edmonton till to occupy the intermediate position in terms of orientation strength predicted by the melt-out hypothesis. In places, preferred orientation is considered to have been disturbed by flow and diapirism induced by the process of thaw–consolidation. Thus, preferred clast orientation in till may show considerable deviation from a regional trend. Stratigraphy and sedimentology are used to classify the till and to relate individual exposures to regional environments of deposition.

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