Clay minerals are a major constituent of the earth’s surface and are mainly found in the sediments of lakes, rivers and oceans. The properties of clay and claystone crucially depend on how the tiny sediment particles are orientated. Using the European Synchrotron particle accelerator in Grenoble (France), a research team from the Martin Luther University Halle-Wittenberg (MLU) has succeeded for the first time in observing in detail how some of the processes work. The study was published in the journal Communications Earth & Environment and provides researchers with insights into the structure and properties of sediments.
The formation of clay-rich sediments is difficult to study. “Sedimentation occurs, for example, on the hard-to-reach seafloor over a very long period of time. In addition, clay particles are only a few micrometres or less in size. As a result, conventional microscopy methods are not suitable for the observation of clay particles during sedimentation,” explains Dr Rebecca Kühn, a geoscientist at MLU, lead researcher of the study. In order to overcome these difficulties, the research team used state-of-the-art technology: the Synchrotron particle accelerator in Grenoble. “This instrument allowed us to observe sedimentation in real-time,” says geologist Professor Michael Stipp at MLU. The researchers placed water-filled cylinders with sinking clay particles into the particle accelerator’s high-energy x-ray beam. The experiments were carried out under various conditions, for example in fresh and salt water. In each case, they measured the time-resolved alignment of the particles. Extremely large amounts of data can be generated from such measurements; however, as there was no quick evaluation method for this, co-author Dr Rüdiger Kilian from MLU developed one for the new study.
The experiments showed that there is already an alignment of the clay particles in the first few millimetres of sediment. “The particles adopt a certain orientation very early on, i.e. in the boundary layer between the water and the sediment. This alignment increases further within the first few millimetres of sediment,” explains Kühn. “This was surprising because a common hypothesis on the alignment of clay particles is primarily determined by the sediment that lies on top, which is many metres thick,” says Stipp. The data generated by the group from Halle contradict or, at least, expand this hypothesis.
Understanding the alignment of clay particles is important for many applications. “For example, it influences diffusion and thermal properties of clays and claystones. Such properties are relevant for geothermal energy as well as host rocks in nuclear waste repositories,” says Kühn.