Glaciotectonic structures as useful ice-movement indicators in glacial deposits: four Canadian case studies

Abstract

Glaciotectonic deformation structures are useful directional indicators of ice movement but are rarely reported by North American authors. Being three-dimensional, they are commonly conspicuous in cleaned sections. Measuring just a few of them can provide accurate ice-movement directions at a site, and they assist in deciphering the interaction of past glaciers and their substrata. This paper concentrates on structures (generally less than 10 m long) in unconsolidated sediments that were induced by overriding glacial ice. Examples and interpretations of various types of structures are presented in four new Canadian case studies from British Columbia and southern Ontario that illustrate different deformational circumstances in sediments of various ages.Les structures de dkformation glaciotectoniques constituent d'excellents indicateurs du mouvement de la glace mais sont trop peu souvent rapportkes par les auteurs nord amkricains. Etant tridimensionnelles, elles sont frkquemment trks apparentes dans les coupes nettoykes. La mesure de seulement quelques unes peut fournier des directions prkcises du mouvement de la glace en un endroit et elles aident a clarifier I'interaction des glaciers antkrieurs et leur substratum. Notre Ctude porte particulierement sur les structures (gCnCralement infkrieures a 10 m de longueur) dans les skdiments nonconsolidks, lesquelles rksultent du chevauchement de la glace des glaciers. Nous prksentons des exemples et des interprktations de divers types de structures de quatre nouvelles Ctudes de cas canadiennes de la Colombie-Britannique et du sud de I'Ontario qui illustrent des modalitCs differentes de deformation dans des skdiments de divers Lges.[Traduit par le journal]Can.

Superimposition of ribbed moraines on a palaeo‐ice‐stream bed: implications for ice stream dynamics and shutdown

“…as in the case of compressional glacial flow (e.g. Hicock and Dreimanis, 1985). The orientation of these structures is consistent with that of the landforms and the main stone a-axis fabric modes, which supports a glacigenic origin for them.…”

“…Tension fractures in subglacial sediments that dip downglacier and thrust (shear) fractures that dip up-glacier in till, and in other subglacial sediment and in bedrock, have been used together as indicators of ice-flow direction and till rheology in several previous studies (e.g. Hicock and Dreimanis, 1985;Dreimanis, 1993). They tend to occur in situations where there is substantial drag at the sole of the glacier, i.e.…”

“…These data were used together to infer the genesis of the diamicton (e.g. Krüger, 1984;Stanford and Mickelson, 1985;Hicock and Dreimanis, 1985;Dreimanis, 1993;Hart, 1994;Lian and Hicock, 2000;Lian et al, 2003).…”

Calcareous Till Facies North of Lake Superior, Ontario: Implications for Laurentide Ice Streaming

“…Sand-filled extension fractures within the unit at site 4 (formed penecontemporaneously with till deposition; Fig. 3b) dip downglacier (Broster era/., 1979;Hicock and Dreimanis, 1985), a sand-filled shear plane at site 5 rises downglacier (Hicock and Dreimanis, 1985), and striated bedrock slabs west of site 6 along Highway 11 are slightly displaced downglacier and intervening spaces filled with lodgment till (Fig. 3a).…”

Polyphase Glacigenic Deformation of Advance Glaciofluvial Sediments, Near Big Creek, British Colombia

“…Broster et al, 1979;Hicock and Dreimanis, 1985;Broster, 1991). At our site, a clear relationship exists between different deformation phases affecting glacial sediments during and after ice advance.…”