Abstract

The paper presents a case study of sediment, termed soft lodgement till (a product of subglacial deposition by active ice), described previously on the basis of macro-evidence from Poland and Canada but not yet studied in detail in one particular site. The till at Anielinek (about 7 m thick) was examined by macroscopic observation, thin section description, and qualitative and quantitative scanning electron microscopy (SEM) analyses. It shows a macroscopic massive structure and overlies a flat top of glaciolacustrine sediments. These sediments form upward intrusions within the till—owing to the existence of reversed density gradients among the deposits—and the upper parts of the intrusions are tilted in consistent directions within the successive parts of the till. Moreover, SEM images also record uniformly oriented microintrusions within this diamictic material. The occurrence of these macro- and microstructures within the successive parts of the till point to an almost continuous process of intrusion during ongoing deposition of the till and to water saturation of the subglacial environment. Such conditions reduced friction of the glacier bed against its substratum, and glacial debris must have been mainly melt-released from the moving glacier base. This process was responsible for deposition of sediment (soft lodgement till) that was immediately and continuously deformed by glacial stress during the ongoing accretion of debris from the glacier base.

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