Till: A glacial process sedimentology / Тиллиты. Ледниковая седиментология

The process sedimentology of tills is crucial to the understanding of the glacier ice–bed interface as a complex depositional, erosional and shear boundary layer. Consequently, it also plays a central role in deciphering the genesis of enigmatic subglacial bedforms such as drumlins, flutings and ribbed terrain. Yet, unlike the study of other boundary layers such as those that operate at the bed of fluvial, aeolian and deep water systems, our knowledge of subglacial process–formrelationships is relatively impoverished, largely due to the inaccessibility of glacier and ice sheet beds. Notwithstanding the important contributions now being made to this research problem by remotely sensed and localised borehole observations as well as reductionist laboratory experiments, it is critical that glacial scientists continue to refine their interpretations of ancient archives of subglacial processes, specifically those that are represented by tills and associated deposits, as these archives formthemostwidespread and accessible record of processes at the ice–bed interface (Figure 1.1). Such an inductive approach to the reconstruction of former subglacial processes has some considerable shortcomings, largely because it relies on actualist principles that are in turn based on process–form relationships that we cannot as yet unequivocally validate.This often has been compounded by the glacial geomorphology literature, wherein the traditional, uncritical acceptance of thick sequences of diamicton as ‘lodgement tills’ has assumed a definitive knowledge of process–form relationships even though that knowledge base is far from definitive. This has been exposed more recently in the apparent incompatibility betweenmodern processmeasurements (indicating thin subglacial deformation/till construction) and ancient glacigenic sequences interpreted to contain often very thick subglacial tills. Moreover, the existence of ambiguous diagnostic criteria for identifying processes of subglacial sedimentation in ancient diamictons does not inspire confidence in the glacial research community when turning to till sedimentology for some guidance! <...>