Capturing the structural and compositional variability of Opalinus Clay: constraints from multidisciplinary investigations of Mont Terri drill cores (Switzerland)

Abstract Opalinus Clay is considered a potential host rock for radioactive waste disposal. The Jurassic claystone formation composed of several facies and subfacies types, which are characterized by varying amounts quartz, carbonates (cements fossils) clay minerals. To provide samples ongoing experimental numerical studies, complete core section was drilled in the Mont Terri laboratory. lithological structural variability (including tectonic fault structures) from borehole BAD-2 investigated using multidisciplinary approach including high-resolution geoelectric situ measurements, mineralogical/geochemical (micro)structural analyses. lithological–compositional captured successfully applying modified approach, independently confirmed geochemical data ERT (Electrical Resistivity Tomography) measurements. on cm to dm scale perpendicular bedding can be determined based mean resistivity variation amplitude. In particular, transitions could precisely located. new results suggest that both shaly types form homogenous part section, whereas sandy especially carbonate-rich represent more heterogeneous lithofacies Clay. attributed differences mineral carbonate content. Regarding variability, brittle faults were observed with frequency throughout section. Most planes occur some them concentrate along heterogeneities scale. striking reproducibility measurements observations comparison boreholes parallel, indicating rather low compositional–structural parallel bedding. applied well suited depict vertical lateral formation, allowing an assessment degree homogeneity/heterogeneity concept.