Kinematic indicators of subglacial shearing

Abstract

Criteria to distinguish between sediments that have been subglacially deformed and those that are undeformed, or deformed by other mechanisms, are sparse. In this paper we develop structural criteria to reconstruct the deformation history of glacial sediments that can be readily applied in the field as well as to analyses of thin sections of tills and related materials.Progressive simple shear is the simplest model to describe the deformation history of subglacially deformed sediments. It includes most of their characteristic structural aspects and provides tools for the kinematic analysis of subglacially deformed sediments. Progressive simple shear generates asymmetric structures, in which the principal direction of finite extension is subparallel to the direction of shearing. This is the simple shear fabric's most distinctive characteristic, and that which most reliably defines the palaeo-ice flow direction.

Sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications: an example from Anglesey, north Wales, UK

“…Confident identification of subglacial meltwater sediments is therefore fraught with difficulty, especially when based simply upon hydrological parameters inferred from sedimentary evidence. Of critical importance is the recognition of other sediments and structures produced by subglacial processes and / or the geometric and sedimentary relationship to deposits of other deposits of subglacial origin (van der Wateren et al, 2000). Indicators employed within this and other published studies (Mathers & Zalasiewicz, 1986;Piotrowski & Tulaczyk, 1999;Fisher et al, 2003;Lesemann et al, 2010b; for the identification of subglacial meltwater scours, channels and sediments within the geological record are shown schematically in Figure 10.…”

Microstructures in subglacial and proglacial sediments: understanding faults, folds and fabrics, and the influence of water on the style of deformation

“…(see Bell and Rubenach, 1983;Vernon, 1989;Passchier and Trouw, 1996 and references therein). In contrast, the application of micromorphology to the interpretation of microstructures developed during subglacial and proglacial deformation is a relatively recent innovation (van der Meer and Laban, 1990;van der Meer et al, 1992van der Meer et al, , 1994van der Meer, 1993;van der Meer and Warren, 1997;Menzies, 2000;Phillips and Auton, 2000;van der Wateren et al, 2000;Khatwa and Tulaczyk, 2001;Hart and Rose, 2001;Hiemstra and Rijsdijk, 2003;van der Meer et al, 2003;Menzies et al, 2006). The detailed analysis of thin sections is being used with increasing success to aid our understanding of both progressive and polyphase deformation of glacigenic sequences (e.g.…”

Basal till and subglacial conditions at the base of the Upper Odra ice lobe (southern Poland) during the Odranian (Saalian) Glaciation

“…Benn and Ev ans, 1996; Van der Wateren et al, 2000). The subhorizontal and low-an gle shear sur faces in di cate brit tle de for ma tion.…”

“…Nu mer ous at ten u ated lenses and string ers of sand were cre ated as a re sult of fold ing and stretch ing of subglacial sed i ments in the shear zone (cf. Benn and Ev ans, 1996; Van der Wateren et al, 2000). To ward the top of the unit, the in ten sity of de for ma tion in creases, as ex pressed by smaller thick nesses of sorted sed i ment struc tures.…”