PORE-WATER CONTROLLED GRAIN FRACTURING AS AN INDICATOR FOR SUBGLACIALSHEARING IN TILLS

Genetic classification of glacial deposits still proves to be highly c ontroversial. In many cases, it remains unclear whether a particular s ediment has been sub-glacially deformed. In the present paper it is su ggested that micromorphological research is helpful where current tech niques fail to lead to unambiguous interpretations. It is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism. Deformational mechanisms associated with the fracturing process are outlined and explained. using a series of t hin sections from Wijnjewoude, The Netherlands.