THEORY OF GLACIAL EROSION, TRANSPORT AND DEPOSITION AS A CONSEQUENCE OF SUBGLACIAL SEDIMENT DEFORMATION

A theory of erosion, transport and deposition of unlithified sediments by glaciers is presented. It predicts the large-scale areal distribut ion of zones and rates of erosion and deposition in time and space thr ough a complete glacial cycle, together with the resultant intensity o f large-scale lineations (drumlins) which will be incised in the lands cape. The theory also predicts tile dispersal patterns of subglacial l ithologies, together with the form of dispersal trains derived from di stinctive sources and the vertical and horizontal distribution of lith ologies within a till. It predicts major erosional discontinuities wit hin tills and the formation of boulder pavements. It suggests that the dominant proportion of the lowland tills produced by Pleistocene mid- latitude ice sheets was generated by subglacial deformation and explai ns why they are predominantly fine-grained. The theory is based on an analysis of glacier-dynamic processes and therefore can be used to inf er the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition.