A new microsedimentological conceptual framework of subglacial till formation

ABSTRACT Shear deformation is ubiquitous in most subglacial tills formed by traction conditions under basal ice. Microstructures identified in till confirm the existence of such basal conditions under continental and marine ice sheets, ice streams, and alpine glaciers. Thin sections of subglacial tills can be categorized within a new derivation, advection, emplacement (DAE) conceptual framework that assigns microstructures in a recurring spatio-temporal context. The formation and persistence of microstructures, and their degradation due to deformation and/or elimination, can be employed to place these evolving microstructures within complex deformation phases. Microstructures are discussed in the framework of the DAE schema and categorized in a newly formatted table of microstructures and microfabrics that extends our understanding of subglacial till sedimentology. This paper demonstrates where and how subglacial sedimentary microstructures form in active subglacial deformation. The formation of tills not only remains an important issue in understanding the Earth’s paleoenvironmental history but also is of considerable practical application, for example, in soil engineering, drift exploration, and glacial geology.