Towards a quantitative lithostratigraphy of Pleistocene glaciofluvial deposits in the southern Upper Rhine Graben

Abstract

The sediment fills of large terrestrial basins offer an opportunity to study and reconstruct regional-scale landscape history over time. An example of such a basin is the Upper Rhine Graben in central Europe, whose proximal, southern part has so far only sporadically been investigated sedimentologically. Three new drillings in close proximity have recovered the upper ∼ 40–60 m of the Quaternary sedimentary infill near the eastern graben margin north of Freiburg, Germany. Grain sizes, the rounding and shape of clasts, and the petrographic composition of the deposits have been determined and statistically analysed. The cored intervals consist of glaciofluvial gravels derived from and deposited by the Rhine system. While no consistent trends of the morphometric properties could be found, we succeeded in distinguishing two subunits within the topmost stratigraphic unit (Neuenburg Formation, Fm) based on compositional (i.e. gravel petrographic) data. An upper subunit (Hartheim Subformation, Sfm) enriched in lithologies representative of the Alpine orogen could be separated from a lower subunit (Nambsheim Sfm) that is enriched in lithologies of an outer-Alpine origin. We correlate these findings with a shift in the pattern of meltwater discharge from the Rhine glacier lobe that may have delivered more Alpine material into the study region during the last than during the penultimate glaciation and highlight the value of quantitative approaches and appropriate statistical evaluation for gravel petrographic studies.