The composition of the clay-mineral fraction is of importance for the evaluation of processes such as sorption or swelling. In the Mesozoic profile, it includes illite, illite-rich illite/smectite mixed layers, kaolinite, chlorite, and small proportions of chlorite/smectite mixed layers. Trace amounts of smectite may also occur. In the Opalinus Clay, the relative proportions of endmember clays13 show only slight variability (Fig. 5‑6). Only a slight upward increase in the illite/kaolinite endmember ratio is observed (Fig. 5‑6). This means that relevant properties such as swelling and sorption behaviour can be considered constant throughout the formation. Above and below the Opalinus Clay, the illite/kaolinite endmember ratio increases substantially.
Fig. 5‑6:Composition of the clay-mineral fraction in the TBO boreholes in profile view
Clay endmembers are shown. Data are projected to profile STA2. DAO: Dogger Group above Opalinus Clay.
For the endmember compositions, the illite, chlorite and smectite components of mixed-layer phases were added to the respective pure phases. The smectite endmember refers almost exclusively to mixed-layer phases. ↩