Скачать или смотреть Glacier tectonics 1: chalk rafts, thrusting and folding at Overstrand

The erosive forces of glaciers and ice sheets can be unimaginably large. This is demonstrated abundantly on the N Norfolk coast where a ridge of detritus around 500 m high, 5 km wide and tens of kilometres long was bulldozed from the underlying and proximal sediments as the ice sheet advanced following an interglacial period about 400 thousand years ago. Here are Overstrand we are looking at a cross section of the ridge and can see rafts of chalk tens of metres long which have been stacked on top of each other with highly distorted soft sediments in between. The process of crustal shortening along tightly focussed lines of deformation to form repeated sequences stacked on top of each other is called thrusting, and these thrusted chalk rafts and the related deformation are very similar to much larger-scale features we can see in many mountain belts around the world. In Scotland analagous features are seen associated with the Moine Thrust Belt which formed at the start of the Caledonian mountain building event around 500 million years ago.