MINERALOGY OF CHAMPLAIN SEA SEDIMENTS AND A RIDEAU CLAY SOIL PROFILE

Abstract

Marine clays and silts of the Champlain Sea, or "Leda clays", from several locations in the Ottawa and St. Lawrence Valleys, and a Rideau Clay soil profile developed on this material have been examined. Although the textures of the marine sediments varied, there was a remarkable similarity in the nature of the mineral constituents of the sands, silts and clays; feldspars, quartz, amphiboles, micas, and chlorites occurred in all size fractions. In addition, the clay fractions contained small amounts of montmorillonite and interstratified illite-montmorillonite. All but two of the marine samples were slightly calcareous and, in general, the coarser textured materials contained the highest carbonate content. The main source of the deposits is believed to be the igneous and metamorphic rocks of the Canadian Shield, and there is very little evidence of weathering before, during and since deposition.The Rideau Clay is a moderately well-drained regosolic soil with very little difference in exchangeable cations or mineral composition with depth. The occurrence of illuviation could not be shown conclusively because of apparent depositional differences. The Rideau Clay differed from the marine materials in having no carbonates, in being slightly acid throughout, and in having a greater amount and a different type of interstratified clay minerals.