Abstract Various forms of sediment deformation can be detected within glacial sediments at the microscopic scale. Analyses of these forms leads to a preliminary classification of microfabrics and microstructures of brittle, ductile and polyphase modes of deformation in glacial sediments. With the development of a taxonomy of different microfabrics and microstructures these processes, once differentiated, permit insights into glacial sediments to a scale and level of detail hitherto unknown. Examples are presented that illustrate some of these different forms of deformation often within a single glacial sediment sample. This research suggests many of the past ideas with regard to details of glacial depositional processes, especially in terms of diamicton deposition and subsequent classifications, need to be re-evaluated.