The interrelation of glaciotectonic and glaciodepositional processes within the glacial environment

Abstract

In recent years it has been recognised that ice/sediment coupling occurred beneath the Quaternary ice sheets that advanced over the soft sediments of lowland areas. This paper looks in detail at the effects of this coupling on the sediments, which results in glaciotectonic deformation, and also discusses the interaction of deformation and deposition within the subglacial environment. Two types of glaciotectonic deformation are discussed that are produced by the active movement of ice: (1) proglacial tectonics at the margin, which include compressive fold styles such as listric thrusts and faults and open folding; (2) subglacial tectonics formed beneath the glacier, which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone. Styles of deformation associated with stagnant ice are also investigated. We argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets. It is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet, and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats. It is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare, whilst deformed till is very common.