The Heidelberg Basin, Upper Rhine Graben (Germany): A unique archive of Quaternary sediments in Central Europe

Abstract

The Heidelberg Basin, in the German part of the northern Upper Rhine Graben, hosts one of the thickest successions of Plio-/Pleistocene sediments in Central Europe. From reflection seismic surveys and new research boreholes, it is known that Pleistocene sediments amount to more than 500 m thickness. The basin sediments originated both from local source areas, i.e. the highlands along the graben shoulders, and from regional source areas, i.e. the Alps. Although temporal hiatuses probably exist, the deposits are expected to be more or less complete because this part of the Upper Rhine Graben has undergone continuous subsidence in the past.Currently, the Heidelberg Basin is under investigation by a scientific drilling project. New cored boreholes have been realized at three different locations, spaced 15 km from each other. This concept provides complementing information and enables a detailed characterization of the predominantly fluvial deposits. The project aims to develop a stratigraphic reference profile of the Quaternary for this region north of the Alps, to understand how the sedimentation was controlled by tectonics and past climate change, and to derive proxy data of environmental changes.The new core material demonstrates that the Heidelberg Basin would be a possible key location for Quaternary stratigraphy in Central Europe. Information about Pleistocene periods of cold and warm climate is found within this one sediment succession in superposition; the temporal resolution of the sediment succession is high. Due to its mid-continental location it links northern and southern Europe, as well as western and eastern Europe. Based on a detailed analysis of the new drill cores a new lithostratigraphy for the northern part of the Upper Rhine Graben is developed in a first step. With the Mannheim Formation, the Ludwigshafen Formation, the Viernheim Formation, and the Iffezheim Formation, four new lithostratigraphic units of the northern Upper Rhine Graben are officially introduced. Furthermore, a new debate about identification of Basal Quaternary arises from the new research boreholes. Whereas during the last decades petrological markers were used to define Basal Quaternary, i.e. the first deposition of Alpine sediments or carbonate content, this definition fails in the depocentre of the basin. Several rock physical properties, e.g. the natural gamma radiation and the magnetic susceptibilities, reveal significant changes at the Basal Quaternary. The driving forces of these changes have to be studied in more detail in the future.