Quantification of Lithological Heterogeneity Within Opalinus Clay: Toward a Uniform Subfacies Classification Scheme Using a Novel Automated Core Image Recognition Tool

The Opalinus Clay is notable in Switzerland as being the selected host rock for deep geological disposal of radioactive waste. Since early 1990’s, this argillaceous mudstone formation Jurassic age has been intensively studied within framework national and international projects to characterize its geological, hydrological, mechanical, thermal, chemical, biological properties. While there no formal stratigraphic subdivision, lithology classically divided into several, dam- m-scale sub-units (or facies), depending on location. Recent multi-proxy studies (combining petrographic, petrophysical, geochemical, mineralogical analyses) have however demonstrated that high, intra-facies, lithological heterogeneity occurs at dm- cm-scale. To constrain small-scale distinct units (subfacies), present study aims defining presenting a convenient subfacies classification scheme covering overall across northern Switzerland. Petrographic (macro- microfacies), (X-ray diffraction) textural (image analysis, machine learning 3D X-ray computed tomography) analyses are performed diverse drill cores from Mont Terri laboratory (northwestern Switzerland), results extended further east (Riniken, Weiach, Benken). Most investigated can be described by use five distinctive types (SF1 SF5), which visually quantitatively distinguishable texture (grain size, bedding, fabric, color) composition (nature mineralogy components). refined additional attributes sedimentary characteristics (biogenic, diagenetic, structural). Eventually, widespread consistent standardized provides means harmonize petrographic descriptions multidisciplinary research projects, enhance reproducibility situ experiments, evidence tight relations between various