RIVER RHINE AND CHANNEL RIVER RESPONSE TO LATE QUATERNARY ALLOGENIC FORCING: THE IMPORTANCE OF TECTONIC SETTING

We modelled the Late Quaternary development of the River Rhine longitudinal profile to gain insight into its response to climate change and sea-level change on a timescale of 103-105 years. The 1250-km River Rhine originates in the northwestern European Alps, crosses different tectonic domains and drains towards the European passive continental margin. Results indicate that areas with long-term uplift or long-term subsidence (separated by the hinge line) show very different fluvial response.

Long-term uplift prevails in the drainage basin upstream from the hingeline. Here, phases of aggradation and degradation in the fluvial system are controlled by glacial-interglacial climate change. The Alps and their foreland are uplifted rapidly. Degradation prevails in the Alpine Rhine, but during glacial/stadial periods accumulation is predicted in the foreland. The Upper Rhine Graben constantly subsides, and therefore sedimentary units are stacked during long-term aggradation. The Rhenish Massif and Lower Rhine Embayment are uplifting. Here, glacial/stadial valley aggradation and interglacial/interstadial valley incision have created a staircase of alluvial terraces. Terrace gradient lines have been reconstructed and deposits have been dated to verify the timing of events.

Downstream from the hingeline, the Rhine enters the long-term subsiding Rhine-Meuse delta and Channel region. The Weald anticline, however, is uplifting. Here, aggradation and incision phases along the longitudinal profile mainly result from glacio-eustatic sea-level changes. During the Eemian and early Weichselian sea-level highstands (OIS 5e, 5c, 5a) the Rhine entered and traversed a glacial trough basin (Saalian). The present Rhine takes a shortcut south of this basin towards the Holocene (OIS 1) estuary. Glacio-eustatic sea-level fall during OIS 6, 4 and 2 to max. -130 m extended the Rhine profile with ~900 km. The mouth of the axial Rhine/Channel-River system at those times was located midway between Cornwall and Normandy in the Channel region. The model reproduces the creation of interglacial coastal prisms as a result of increasing accumulation space during sea-level rise, and erosion during early-glacial sea-level fall. These phenomena coincide with a shift of the terrace intersection over hundreds of kilometres.