Due to their barrier effect claystones may serve as potential host rocks for final disposal of high-level radioactive waste. The Opalinus Clay, which occurs in northern Switzerland, eastern France and southern Germany, is subject of a recent study conducted under the leadership of the University of Fribourg (Switzerland).

In this paper published in the journal ‘Applied Clay Science’, PhD Géraldine Zimmerli and Prof. Anneleen Foubert present together with an international team of scientists a deposition model based on new findings on the formation of the Opalinus Clay Formation. This research, based on drill cores from Germany, Switzerland and France, suggests that thermohaline bottom currents played a key role in shaping the sedimentary succession, pointing to a shallow-water contourite origin. This perspective provides an alternative to earlier interpretations, which considered storm-related processes as the main transport mechanism.

A solid understanding of the depositional history of claystones is essential for their evaluation in the context of the site selection process for radioactive waste disposal. In Switzerland, the Opalinus Clay was selected as host rock for a planned deep repository due to its properties of impermeability, self-sealing and binding of radioactive substances.

Further reading:
Zimmerli, G.N., Wohlwend, S., Deplazes, G., Mann, T., Erbacher, J., Kneuker, T., Eberli, G.P., Foubert, A. (2025) The hidden message of fine-grained sediments: towards a new depositional model for the Opalinus Clay. Applied Clay Science 276 (2025) 107934, doi:10.1016/j.clay.2025.107934.