Home – Home – Jornals – Russian Geology and Geophysics 2005 number 8

Data on the lithology of Lower Toarcian (Lower Jurassic) terrigenous sediments in the southeast of the West Siberian Plate are presented. Using cores from three parametric boreholes (mudstone (I), mudstone-siltstone (II), and sand (III) sections), the petrography and mineralogy of the sediment clays have been studied. The mineral composition was determined by optical and electron microscopy, X-ray diffraction, and IR spectroscopy. A comparative analysis of the associations, crystal chemistry, and structure of clay minerals from the three sections was carried out by simulation of X-ray diffraction spectra. The clay matter from all sections is dominated by minerals of the kaolin group (kaolinite, dickite) and mica group (illite, muscovite). Chlorite minerals (chlorite, chlorite-smectite) are subordinate and occur in sections I and II only. It is shown that the degree of structural ordering of the kaolin group minerals varies depending on the grain size of rocks: from disordered kaolinites in the mudstones to more regular dickite in the sandstone and gravelstone cement.