ABSTRACT: Sediment load of shore ice and ice rafting potential, Upper St. Lawrence Estuary, Quebec, Canada.

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Abstract

Sediment-laden ice is a prerequisite for ice rafting and sediment delivery to offshore zones and for deep-water sedimentation in cold region sedimentary basins. In the upper St. Lawrence estuary, Quebec, Canada, the sediment load of the ice cover was studied from 1982 to 1992, with observations and measurements made on both shores in the area between Quebec City and Grondines, with emphasis on two sites in particular (Neuville and Grondines). Shore ice in this area contains a large volume of debris susceptible to be rafted at breakup, and ice rafting is a major process in the sedimentary budget of the study area. Up to one million metric tons of debris (approximately 25,000 tons per sq km) are involved annually, including 70 to 75% coarse material. Large clasts of shale and limestone and small Precambrian boulders are an important component of the terrigenous load imprisoned in the ice cover and rafted in ice floes. The best period for surveying sediment-laden ice is during breakup, at which time there are many exposures available in the ice cover and several ice floes are grounded in the intertidal zone at low tide. Also, at that time the snow cover at the surface of the ice has disappeared, allowing the observer to see the debris at the surface. Direct observations seem to be a more valuable method than coring, particularly for coarse debris content. Data from the St. Lawrence compare well with those from other ice-dominated shore and nearshore environments

Bibliography of Canadian Geomorphology