The spectacular cross-striated outcrops of James Bay, Quebec

Abstract

Bedrock on the east coast and on some James Bay islands shows spectacular examples of cross-striations that reveal a shift from initial northwestward ice flow, followed by westward, southwestward, and local southeastward and southwestward flows related to the opening of James Bay during deglaciation of the region. The high quality of striated outcrops is attributed to their freshness, which results from a combination of postglacial uplift, the protective effect of glacial deposits, and recent erosion of these deposits by wave action. Photographs and schematic illustrations are used to explain the processes at work in this particular marine environment.

Ice-Flow Chronology and Palimpsest, Long-Distance Dispersal of Indicator Clasts, North of the St. Lawrence River Valley, Quebec

“…While Low could not provide a detailed configuration of the ice mass, his interpretation of the shifting centres of dispersion, derived from striation measurements taken along the coast only, is most remarkable, because the proposed locations of his ice divides correspond to positions south of Lake Mistassini for the oldest northwestward ice flow, and north of the lake for the second oldest west-southwestward ice flow, as proposed in the present paper. This chronology of striated surfaces and associated glacial transport was throrougly validated along the James Bay eastern coast and inland as far east as Matagami and Chibougamau Veillette, 1995Veillette, , 1997Veillette and Roy, 1995;Parent et al, 1996). Low's insightful interpretation was overlooked by glacial geoscientists for nearly a century.…”

Le rôle d’un courant de glace tardif dans la déglaciation de la baie James

“…Les linéaments d'origine glaciaire du secteur Cochrane se recoupent dans une séquence difficile à reconstituer dans un ordre chronologique distinct. Cette contrainte a été au moins partiellement amoindrie par l'étude des surfaces striées sur le pourtour de la baie James (Veillette, 1995).…”

“…Des levés récents le long des côtes, dans les îles à l'inté-rieur de la baie James et à l'intérieur des terres (Veillette, 1995), révèlent la répartition d'une séquence d'écoulement glaciaire dont Low (1889Low ( , 1903 avait correctement reconnu l'ordre chronologique de formation un siècle auparavant, le long de la côte est des baies James et d'Hudson ( fig. 3).…”

“…Le courant aurait occupé la dépression topographique de la baie James peu de temps avant sa déglaciation finale. Les mesures d'écoulement glaciaire et la séquence de déglaciation de la région résultant de travaux antérieurs (Lee efa/.,1960 ;Hardy, 1976), ont été revues à la lumière de la chronologie relative de l'écoulement glaciaire récemment proposée pour tout le bassin de la baie James et de l'Abitibi (Veillette, 1995 ;Veillette et McClenaghan, 1996). Cet examen conduit à conclure que la déglaciation des parties mé-diane et nordique de la baie James a été rapide, peut-être même catastrophique, et que contrairement à la partie sud, il FIGURE 1.…”

A Quaternary geological perpective on geochemical exploration in glaciated terrain

“…Striations pre-dating the last glacial maximum occur on exposed outcrop surfaces as crosscutting sets, and on surfaces sheltered from later ice flow (e.g. Bouchard & Martineau 1985;Veillette 1986;Kleman 1990;Lundqvist 1990;Klassen & Thompson 1993;Stea 1994;Veillette & Roy 1995;Parent et al 1996;Veillette & McClenaghan 1996). Their preservation, despite subsequent glaciation, indicates: (1) limited, differential glacial erosion of bedrock; (2) the potential importance of topography and bed roughness to both the formation and preservation of dispersal trains; and (3) the significance of ice flow direction relative to the aspect of bedrock slopes.…”