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

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Abstract
Detailed mineralogy and chemistry of the clay fraction of 5 placio-lacustrine deposits and of 1 Cretaceous marine shale (Ashville) were studied. Fine clay separates (< 0.2 .mu.m) of the 5 parent materials were predominantly smectite with an average chemical composition: [(Si7.72Al0.28)(Al2.00Fe1.37Mg0.62)O20(OH)4]X+0.98, X-ray diffraction, dehydration, IR, and chemical analyses, and the Greene-Kelly test showed that the smectite was an Fe rich montmorillonite. Similarities in the crystal structure of the 5 soil parent material clays suggest that they were likely transported from the same source. Despite the differences in percentage of clay minerals, similarities between 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 Fe may have caused a distortion in the crystal lattice and a slightly favorable weathering condition of smectites. However, presence of high exchangeable and soluble Mg 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.