QUANTITATIVE ESTIMATION OF ILLITE-SMECTITE MIXED PHASES FORMED DURING BURIAL DIAGENESIS

With reference to the previously published papers by Reynolds and Hower (1970) and Perry and Hower (1970) pelitic sediments from bore hole samples from the Tertiary sequence of the Vienna Basin have been studied to investigate the layer silicate assemblages and to carry out a quantitative estimation of the mixed-layering in the illitesmectite mixtures. Beside these problems one of the primary purposes of this paper is to indicate how interfering reflections from detrital layer silicates can be handled and resolved from diffraction patterns. The samples correspond to clayey silts. Within the less than 0.2 micron fractions they essentially contain mica, kaolinite and illite-smectite as expandable phase. Dependent on depth the composition of these mixtures is intermediate between an interstratified mixed layer phase consisting of about 75 percent smectite layers and 25 percent illite and an ordered mixture which contains about 20 percent smectite and 80 percent illite layers. Since the mineral components maintain essentially constant portions throughout the samples, mica and kaolinite do not enter the illitization reaction. The necessary potassium and aluminum ions were derived from the nonclay constituents. © 1979 Springer-Verlag.