Recumbent folds and boudinage structures formed by subglacial shear: an example of gravity tectonics

Abstract

A contorted drift sequence involving displaced pre-Quaternary and Quaternary sediments is described from the coastal cliffs of southern and eastern Møn, SE Denmark. The principles of proglacial and subglacial deformations in a permafrozen sedimentary environment are outlined, and an analysis of the structures is presented. Large-scale thrusting and stacking of permafrozen thrust slices are referred to proglacial deformations. Superimposed simple-shear deformation, recorded by large recumbent folds with boudinage structures in their stoss-side flanks and with shortened to ultimately stretched leeward flanks, is ascribed to a subglacial origin. It is stressed that the driving force for these natural small-scale models of orogenic tectonics was nothing but the force of gravity.