Sediment dynamics, neotectonic activity and palaeoenvironments recorded in the Quaternary infill of the central Upper Rhine Graben

Abstract

The Upper Rhine Graben is a large-scale tectonic basin in central Europe that has accumulated a kilometre-thick sedimentary succession including, in some places, several hundred metres of mostly continuous Quaternary strata. Especially in the central graben part, these strata have hardly been scientifically explored. We introduce a new, 45-m-long drill core record from the vicinity of Offenburg. At its base, it comprises glaciofluvial gravels derived from the Alpine headwaters, which are superseded by aeolian deposits intercalated with locally derived gravels distinct by a different gravel spectrum. Post-infrared infrared-stimulated luminescence dating shows that the entire sequence reaches back beyond 300 ka, and that the glaciofluvial-aeolian transition occurred during the penultimate glaciation at ∼160 ka. By comparison with neighbouring boreholes, we infer repeated normal faulting south of the drill site since roughly the same time, with the resulting topography filled in by locally sourced gravel interbeds. Finally, two layers of fines indicating stagnant palustrine conditions contain interstadial pollen assemblages of the penultimate and last glaciation, and shells of gastropods typical of Pleistocene loess deposits and a glacial palaeoclimate are encountered in the aeolian succession. Thus, this study offers insights into Middle to Late Pleistocene sediment dynamics, neotectonic activity and palaeoenvironments, and highlights the wealth of stratigraphic information that the Upper Rhine Graben preserves.