The confluence area of Rhine, Meuse, and Belgian rivers: Late Pliocene and Early Pleistocene fluvial history of the northern Lower Rhine Embayment

The fluvial history of the northern Lower Rhine Embayment shows interplay of three main river systems: Rhine, Meuse and smaller rivers draining the central and northern part of Belgium. The Pliocene and Early Pleistocene (pre-)Rhine and Meuse river systems had their conjunction in the southern part of the Roer Valley Graben between Aachen and Julich. Despite slight differences in the heavy-mineral assemblages the lithological. composition of the Pliocene deposits of the three river systems shows close resemblance and therefore they cannot be mapped separately. However, due to a marked change of the petrographical composition the Upper Pliocene and Lower Pleistocene deposits of the Rhine are easily recognised and as a result Rhine and Meuse deposits can be mapped separately upstream of their confluence. The Lower Pleistocene deposits of Rhine, Meuse and the Belgian rivers show a clear interrelationship. They are bounded by two regional well-mapabte unconformities and are preserved in from west to east changing lithostratigraphical sequences. Revision of the lithostratigraphical schemes in Germany and the Netherlands and the better defined lithostratigraphical position of Meuse deposits in Germany now strongly constrain the correlation of the various fluvial deposits. As a result existing reconstructions of the fluvial deposition and tectonic history of the southern Roer Valley Graben can be evaluated and re-adjusted. It is concluded that the main course of the Meuse was aligned through the so-called East Meuse valley during the larger part of the Early Pleistocene. Available pollen data do not conflict with this conclusion. At the same time the Rhine ceased to enter the southern part of the Roer Valley Graben. Instead, the Meuse accumulated here a series of deposits derived from the East-Meuse valley. Simultaneously, the Belgian rivers filled available accommodation space in the Roer Valley Graben of the southern Netherlands. The conclusions are based primarily on the revised lithostratigraphical framework. In general they simplify the picture of fluvial and tectonic behaviour of the area.