The lacustrine sediment sequence from Rodderberg near Bonn (Germany) challenges numerical dating of the Middle Pleistocene

While the marine realm provides quasi-continuous sediment records back into the Tertiary, terrestrial environmental and climatic archives are more complex, fragmentary and commonly short, i.e. they often provide evidence of just one interglacial. Sediment sequences comprising several glacial-interglacial cycles in superposition are exceptions and often encountered in crater basins. The sediment sequence from Rodderberg near Bonn, a paleolake record from a closed crater basin, provides such a record with several organic-rich (interglacial) intervals. A total of 86 luminescence ages was determined for numerical dating at two different laboratories. Furthermore, tephrochronology provides key markers, while cyclostratigraphy, applying the global marine stable isotope stack (LR05), expands this chronological approach. It is hypothesized that the archive spans the past 440 ka. However, the results obtained are of a surprising nature and will prompt further investigation.

The detection of sedimentological and elemental signatures from depositional records with high spatial resolution has become a standard since the advent of sediment scanning techniques. The example of Rodderberg is provided to demonstrate the potential of such high-resolution proxy data. However, correlating these natural archives in space and time requires reliable age/depth models, which are only available for the last two glacial-interglacial cycles. For older records of the entire Middle Pleistocene, the chronologies remain as running targets. In order to resolve the existing inconsistencies between sites and regions, further efforts are required to enhance numerical dating techniques. This can be achieved by extending the temporal range of luminescence dating and by refining radiometric dating methodologies.