PLEISTOCENE PERMAFROST OF WEST SIBERIA AS A DEFORMABLE GLACIER BED

Subglacial permafrost is usually referred to as a factor impeding basa l glacial processes, and the deformation of soft substrata in particul ar. In West Siberian, widespread glacial disturbances present in perma frost of Pleistocene age suggest that frozen sediments, if clayey and/ or icy, can readily deform, thus translating basal. glacial stress int o sliding of the entire glacier/sediment complex along subglacial shea r zones. Ductile deformations such as folds and diapirs are also wides pread. The mode of deformation of frozen subglacial sediments is depen dent on their lithology, ice content and temperature conditions. Signa tures of former subglacial permafrost in currently thawed sediments ar e deduced from contrasting deformation behaviours of lithologically di fferent sedimentary formations.