Methodology:

The clay fraction (less than 2 micrometers) was separated from the bulk sediment in settling tubes, and 40 mg clay suspension was mixed with 1 ml of an internal standard (0.04 % MoS2 suspension). The samples were then mounted as texturally oriented aggregates by rapidly filtering the suspension through a membrane filter (0.20 micrometer pore width), the filter cakes were dried at 50 °C, fixed on aluminium tiles and exposed to ethylene glycol vapour at a temperature of 60 °C for at least 18 h immediately before the X-ray analyses. The measurements were conducted on a diffractometer system Rigaku New Miniflex with CoK alpha radiation (30 kV, 15 mA). First, the samples were X-rayed in the range 3 - 40 °2 theta, with a step size of 0.02 °2 theta and a measuring time of two seconds per step. Then, the range 27.5 - 30.6 °2 theta was X-rayed with a step size of 0.01 °2 theta and a measuring time of four seconds per step in order to better resolve the (002) peak of kaolinite and the (004) peak of chlorite. The X-ray diffractograms were evaluated using the interactive MacDiff software (Petschick 2010, Petschick 1996). The main clay mineral groups were identified by their basal reflections at 16.5 Angstrom (smectite, after glycolisation), 10 and 5 Angstrom (illite), 14.2, 7, 4.72 and 3.54 Angstrom (chlorite), and 7 and 3.58 Angstrom (kaolinite) after the diffractograms had been adjusted to the MoS2 peak at 6.15 Angstrom. For semi-quantitative evaluations of the clay mineral assemblages, empirically estimated weighting factors on the integrated peak areas of the individual clay mineral reflections were used (Biscaye 1964, 1965). The crystallinity of illite was determined by calculating the integral breadth (IB, delta °2 theta) of the 10 Angstrom peak. High IB values indicate poor crystallinities, whereas low values indicate good crystallinities. Furthermore, we inferred the illite composition from the 5/10 Angstrom peak area ratio. Values more than 0.4 correspond to Al-rich illites (muscovite). The ratio decreases with Mg and Fe substituting the octahedral Al. Magnesium and iron-rich illites (biotite) have values less than 0.15 (Esquevin 1969).

Data collection:

A diffractometer system Rigaku New Miniflex with CoKα radiation (30 kV, 15 mA) was used for the X-raying.

The diffractograms were analysed with the interactive MacDiff (v. 4.2.5) software (Petschick 2010).

Data quality:

By preparing, analysing and evaluating samples six times, a standard deviation of c. 1% was obtained for the concentrations of smectite, chlorite and kaolinite, and of c. 1.5% for illite. The standard deviation for the 5/10 Angstrom peak area ratios is c. 0.05 and that for illite IB c. 0.02 delta °2theta.