Sequence stratigraphy of the Opalinuston-Formation in Southern Germany

The Opalinuston-Formation in Southern Germany comprises a thick (>100 m) sequence of Middle Jurassic claystones. In parts of Bavaria and Baden-Württemberg, the formation has been designated as a sub-area by the Federal company for radioactive waste disposal (BGE), indicating that favorable geological conditions for the final disposal of high-level radioactive waste can be expected there. However, coherent geological data for the complete formation is often lacking. Here we present new data on the geological variability of the Opalinuston-Formation based on four drill cores, each of which penetrated through the entire formation, and parts of the over- and underlying rock strata outside the sub-area. After completion of the drilling work, the cores were examined in high resolution for their petrophysical properties and element distribution using non-destructive analytical tools such as XRF core scanner and multi-sensor core logger. Furthermore, one sample per core meter was taken for a precise stratigraphic classification of the rocks and a geochemical-mineralogical and sedimentological characterization. Results exhibit notable geological variability at the investigated localities, particularly with respect to the Si/Al ratio. This is interpreted as changes in grain size due to relative sea-level fluctuations during deposition, and is thus useful to reconstruct stacking patterns of parasequences. In summary, this contribution highlights the geological variability of the Opalinuston-Formation in Southern Germany and discusses the possibilities of a sequence stratigraphic approach to identify the most suitable parts of sub-areas in claystone formations for the final disposal of high-level radioactive waste.