Processes of debris comminution in the glacial environment and implications for quarts sand-grain micromorphology

Abstract

Studies of till composition, rock crushing and abrasion experiments, and detailed consideration of the mechanics of the comminution processes which occur in the subglacial environment suggest that monomineral quartz sand grains are mostly produced by the brittle fracture of larger particles. Abrasive wear is an inefficient mechanism for producing and modifying quartz sand grains because of the relatively great hardness of quartz. Viewed under the scanning electron microscope, surface textures of subglacially derived quartz sand grains are typically those associated with brittle fracture of quartz. Since the release of quartz sand grains from bedrock by mechanical weathering may also involve brittle fracture, grains which have been passively transported through a glacier may exhibit similar textures to those actively produced in the glacial environment. Hence the examination of the surface textures of quartz sand grains under the scanning electron microscope is unlikely to be a satisfactory technique for the discrimination of active and passive transport paths through glaciers.