THE NATURE OF SMECTITES IN SOME FINE TEXTURED LACUSTRINE PARENT MATERIALS IN SOUTHERN SASKATCHEWAN

Abstract

Detailed mineralogy and chemistry of the clay fraction of five glacio-lacustrine deposits and of one Cretaceous marine shale (Ashville) were studied. Fine clay separates (< 0.2 μm) of the five parent materials were predominantly smectite with an average chemical composition:[Formula: see text]X-ray diffraction, dehydration, infrared, and chemical analyses, and the Greene-Kelly test showed that the smectite was an iron rich montmorillonite. Similarities in the crystal structure of the five soil parent material clays suggest that they were likely transported from the same source. Despite the differences in percentage of clay minerals, similarities between chemical composition of the coarse and the fine clays is interpreted as an indication of close diagenetic relationships between the predominant smectite and soil mica. High silicate bound iron may have caused a distortion in the crystal lattice and a slightly favorable weathering condition of smectites. However, presence of high exchangeable and soluble magnesium in the soil complex is likely retarding the smectite alteration. Thus, weathering by elemental substitution may have been restricted to the smectite end member only. Key words: Swelling clay soils, iron montmorillonite, chemical composition of smectites, dehydration of smectites