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CGG-02 Subglacial environments: Processes, sediments, landforms, modelling and experiments
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Quantitative ratio of illite polytypes in the contact zone of till and basin sediment
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Ilze Lūse, University of Latvia (Latvia)
Anatolij Mishnev, University of Latvia (Latvia)
Agnese Stunda, Riga Tehnical University (Latvia)
Valdis Seglins, University of Latvia (Latvia)
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Clay minerals have a tendency to adapt to different physicochemical and thermodynamic conditions fixing changes of various geological conditions in their crystal lattice structures. X-Ray analysis of clay minerals and studies on structural changes in the illite crystal lattice can give new information concerning the processes proceeding under various geological conditions and be helpful in solving problems associated with sedimentation and weathering peculiarities. The objectives of the study are to carry out quantitative X-ray phase analysis of the clayey sediments from till and basin sediment contact zones, quantify the clay mineral phases in the samples and analyze illite polytypes. An effort is undertaken to explain a connection between obtained results and the influence of glacier geological activity accumulating subglacial material on the illite structures or clayey fraction transport.
Identification of minerals is complicated due to a large number of phases present in samples. Diffraction maxima for some phases are overlapped in X-ray powder patterns obtained. Modifications of illite structures are studied for samples containing fractions of size < 1,5ìm. The illite structure modifications are determined in the range from 22.903° to 35.193° 2θ.
Besides reflections of illite, strong maxima of quartz, albite, hematite and other phase can be observed in this region. The latter overlap some illite reflexes. The overlapping reflections are not used in determination of illite structures.
Differences in the illite polytypes are semi-quantitatively obtained from X-ray powder diffraction data. 1Md polytype is dominating in the samples studied. Structural fragments of 2M1 and 2M2 polytypes can exist in the 1Md polytype structures. Several 2M1 reflections are detected in samples of basin and glacigenic sediments. With regard to previous studies an individual approach is necessary for quantitative comparison of illite polytypes in the samples bearing many phases and the data processing with intensity profile simulation by computer program has to be applied. The first results on determination of illite polytypes quantitative relation will be presented.
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