The origins of glacially related soft-sediment deformation structures in Upper Ordovician glaciogenic rocks: implication for ice-sheet dynamics

At the ice front, large glaciotectonic deformation structures (comparable with push moraines) developed during sustained periods of (re)advance that created composite thrust and fold systems. Deformation was transmitted for up to 1 km from the ice front and reduced in intensity with distance. Other deformation structures include dome-like folds that consist of central anticlines (30 to 70 m in width) with tight rim synclines that formed by the load-induced, diapiric intrusion of muds. An ice-sheet surging mechanism is inferred for the development of composite thrust and fold systems and the coeval sediment diapirs. These surges potentially caused the widespread reorganisation of a glacial load resulting in the pro- to subglacial extrusion of soft sediments.