This special issue contains the papers presented during the 2004 DEUQUA meeting. The papers provide an overview of recently carried out Quaternary geological studies on different aspects of the river Rhine system. The introductory paper follows the pathway of the Rhine downstream from its source in the Swiss Alps to the delta in the Netherlands. Along this route geological and geographical factors determine the regional subdivisions of the river: the Alps, the Upper Rhine Graben, the Rhenish Massif, and the Lower Rhine Embayment as part of the southern North Sea Basin. Each of these regions can be typified by a characteristic geological evolution.

New evidence from heavy-mineral analyses provides an improved lithostratigraphy and insight in the Quaternary evolution of the Rhine in the Upper Rhine Graben. The Plio-Pleistocene transition is determined by a palaeomagnetic study. The same paper emphasis on the impact of climate change on the composition of the magneto-mineralogy. Pollen analytical results show a complex interrelationship of a number of Middle Pleistocene interglacial periods in the northern part the Upper Rhine Graben. In the same area geomorphological analysis demonstrates a clear influence of tectonics on the preservation of fluvial terrace accumulations. A detailed pollen analytical study on the Late Glacial and Holocene development of the Rhine in the northern Upper Rhine Graben discusses the relation between vegetation cover and river behaviour. Finally, two papers from the Lower Rhine Embayment discuss a revised provenance based lithostratigraphy and its implications for understanding the fluvial history.

The River Rhine and its tributaries represent one of the largest drainage systems in Europe. Its prominence among other fluvial systems is due to the location of its headwaters within the central Swiss Alps, which were repeatedly glaciated during the Quaternary, and the concurrence of major parts of the River Rhine course with the European Cenozoic Rift System. Sediments of the Rhine have thus recorded both changes in climate and tectonic activity as well as sea level change in the lower part of the river course.

The River Rhine is composed of different subdivisions characterised by distinct geographical and geological settings. Vorder-and Hinterrhein in the headwaters are inner-alpine rivers frequently influenced in their course by tectonic lines and the blockage of valley floors by the deposits of mass movements. The Alpenrhein is located in a main Alpine valley that drains into a large foreland basin, the Bodensee (Lake Constance). The Hochrhein flows out of the lake following the Jura Mountains in a western direction. All these areas display a series of geological features such as moraine ridges and outwash plains, which directly reflect Quaternary glaciations of the Alps. The Oberrhein (Upper Rhine) Valley, as a graben structure, is part of the rifting system that started to develop during the middle Tertiary. The northern end of the graben is represented by the triple junction of the Mainz Basin, which is mainly characterised by the remains of marine transgressions that occurred during the initial rifting phase. The Rhine continues following the western branch of the tectonic system by passing through the Rhenish Massif. Uplift in this so-called Mittelrhein (Middle Rhine) area is well documented by a flight of late Tertiary to Quaternary river terraces. This region is also characterised by young volcanic activity as found, for example, in the Eifel volcanic field. The Niederheinische Bucht (Lower Rhine Embayment), especially the Roer Valley Rift System, represents the northern continuation of the rifting system. This area is characterised by differential uplift in the southern and subsidence in the northern part of the basin, which continues into the Netherlands. Here, the main stream of the River Rhine is separated into different branches developing an active delta at the coast of the North Sea. When the North Sea Basin was covered by ice during the Elsterian, Saalian and probably also the Weichselian glaciation and global sea level was low, the Rhine continued its course through the English Channel and flowed into the North Atlantic off Brittany.

The Pliocene and Quaternary unconsolidated sediments of the Upper Rhine Graben (URG) were petrographically analysed in numerous high quality drill cores. The heavy mineral composition of the Graben sediments was compared to those from the Graben margins. In addition, the sedimentary lithofacies were investigated. The chronological classification of the sedimentary successions was established by the interpretation of sporadic palaeontological and palaeomagnetic data.

Within the Pliocene sediments, two distinguishable heavy mineral assemblages indicate different source areas of the Graben fill. At first, a heavy mineral assemblage of stable minerals (turmaline, zircon and anatase) indicates a contribution of debris supplied from Buntsandstein areas at the Graben margins. Secondly, a mixed association of stable minerals in combination with unstable (garnet, hornblende, less epidote) and distinct rare minerals (e.g. monazite, xenotime) can be traced back to debris derived from the crystalline rocks of the southern Graben margins (Black Forest, Vosges). The distribution of sediments with this mixed heavy mineral assemblage proves the fluvial sediment transport from south to north and therefore the course of the Pliocene proto-Rhine along the Graben.

The correlation between the Quaternary sediment successions in the south and the north of the Graben is problematic due to their variable thicknesses as well as their changing lithofacies.

In the southern URG, the Quaternary strata could be subdivided into the older Breisgau Formation and the younger Neuenburg Formation based on characteristic lithofacies. Within this succession, the lower part of the Breisgau Formation (lower Breisgau beds) can be distinguished by noticeable lower contents of hornblende, which probably reflects the effects of weathering and solution of these unstable minerals due to repeated discontinuities during the sediment accumulation. The sediments of the upper part of the Breisgau Formation (upper Breisgau beds) and of the Neuenburg Formation contain a heavy mineral assemblage of garnet, epidote and hornblende, which is typical for Rhine deposits with Alpine contribution. This probably unaffected composition indicates a more unvaried and rapid accumulation of predominantly Alpine debris. In the northern URG, the Quaternary strata are subdivided into three aquifers and intercalated fine-grained horizons. Here, the Quaternary sediments can be petrographically classified into Rhine deposits (garnet, epidote and hornblende) and local accumulations contributed from the Graben margins (turmaline, zircon and anatase) without contemporaneous influence of the Rhine. The analytical results obtained from several drill cores in the northern URG provide evidence for the spatial and temporal variability of the course of the Rhine during the Quaternary.

Recent carried out core drillings in the Ludwigshafen/Speyer area permit an improved stratigrahical differentiation of the Plio-Pleistocene deposits in the northern Upper Rhine Graben. Lithofacies analysis, pollen analysis, heavy mineral analysis, and palaeomagnetical results, lead to a subdivision of ‘Kieslager’ (gravel-layers) and ‘Zwischenhorizonte’ (interlayers). In the scope of geological mapping near Mannheim and Speyer, the genesis and the stratigraphic position of Middle and Late Pleistocene fluvial terraces was re-assessed (‘Frankenthaler Terrasse’). The terrace has a complex composition, marking two phases of accretion followed by abandonment: a first phase took place in (Elsterian? to) Saalian times, the second phase during the Weichselian. Tectonism further complicates the sequence, in particular in the area between Ludwigshafen and Speyer, which is the SW rim of the ‘Heidelberger Loch’-structure. In this area ‘terraces’ occur they are the result of faulting rather than fluvial dissection alone.

This paper summarizes results of magnetostratigraphic and rock magnetic investigations performed on fluvial sediments from the Ludwigshafen-Parkinsel drilling project (Upper Rhine Graben (URG) Germany). The drilling penetrated into Pleistocene gravel, sand, silt and clay, and unconsolidated Pliocene deposits. Its primary objective was the exploration of groundwater resources in the area of Ludwigshafen. Our rock magnetic investigations together with results of heavy mineral analyses (see Hagedorn & Boenigk, 2008) show a clearly structured sediment profile. It was possible to identify the change from mainly locally controlled sedimentation from the Graben margins to a more distinct Alpine controlled sedimentation at a depth of 177 m by magnetic data. Based on lithostratigraphic correlation with other sedimentary records from the URG and also based on palynological evidence, this event happened at the end of Late Pliocene during a time of normal polarity of the Earth's magnetic field (Gauss Chron?). The well-documented characteristic change in magneto-mineralogy from goethite to greigite almost at the same stratigraphic level, we interpret solely as a climatic signal which can be correlated with the global climate change at ∼2.5 Ma that is well documented in a wide range of sedimentary environments (e.g. deep-sea sediments, loess).

Recent core drillings, carried out during water-economic exploration in the area of Mannheim/Ludwigshafen/Schifferstadt (Rhine-Neckar region, Germany), have produced a more differentiated stratigraphic division of the Pleistocene sediments of the northern Upper Rhine Graben. Pollen analytical investigations as well as malacological, heavy mineral, palaeomagnetic and lithological research have led to a stratigraphic reinterpretation of the gravel layers and intermediate horizons. Based on the results of the pollen analyses, the Mannheim interglacial period in the upper intermediate horizon (Oberer Zwischenhorizont, OZH) cannot be assigned to the Eemian as stated earlier. The occurrence of Fagus, Celtis and Azolla, along with the results of malacological analyses, indicate a Cromerian age for the Mannheim Interglacial. In addition, a pollen sequence from a different interglacial in the core sediments from Schifferstadt could also be assigned to the Cromerian. The Schifferstadt Interglacial is divided into a lower optimum phase with high values of Ulmus, Quercus and Corylus while Carpinus is completely absent, and an upper optimum phase with low values of Carpinus. Fagus is absent in the whole sequence. The OZH comprises not only the two interglacial pollen sequences described above but also parts of at least four Middle Pleistocene Interglacials. In the lower part of the drillings in Schifferstadt and Ludwigshafen, which are assigned to the Early Pleistocene, pollen assemblages with Fagus are likely to correlate with parts of the Tiglian A substage. There is a clear change to a Tertiary type of pollen flora at 91 m at Schifferstadt and at 186 m in Ludwigshafen.

The vegetation of the northern Upper Rhine Graben (southwestern Germany) is reconstructed for the end of the Lateglacial and the Holocene by means of palynological analyses in combination with AMS 14c dating. Analogous to adjacent lowland areas, the Younger Dryas climatic deterioration did not result in a complete deforestation of the area and open pine woodlands with locally birch stands and shrubs persisted. A subdivision of the Younger Dryas period, into a humid first phase, followed by a dry second phase was also reflected in our records. For the Holocene, the pollen diagrams show two regionally different vegetation developments, related to substrate and variations in annual precipitation: in the south the ‘classical’ succession of pine then hazel is followed by other deciduous trees, whereas in the northern part, pine kept its dominance far into the Subboreal.

The Plio-Pleistocene succession in the Lower Rhine Embayment was subjected to a thorough revision of existing stratigraphic concepts. The deposits were studied at key sites in the type area near Venlo and in the large open-cast mine Hambach in the southern part of the Lower Rhine Embayment by means of sedimentological, petrographical, as well as palaeo- and rockmagnetic methods.

The work has yielded improved insights of the drainage pattern and the Late Pliocene and Early Pleistocene depositional history of the region. As a result, a new comprehensive lithostratigraphical framework has been established.

Study of the succession at Hambach showed the occurrence of deposits of the Rhine, Meuse and a local river in the Lower Pleistocene part of the succession. Paleo- and rockmagnetic studies of the deposits marking the transition from Pliocene to Pleistocene indicate that the Gauss-Matuyama magnetic reversal occurs several meters above the top of the Reuver Clay at Hambach.

The study of the Lower Pleistocene succession in the type area has confirmed the recently new established lithostratigraphic framework of the Netherlands. As a consequence, the previous Dutch lithostratigraphic system which forms the basis of the chronostratigraphic subdivision of the Pliocene and Early Pleistocene of NW Europe has been proven to be inappropriate and should be abandoned. This chronostratigraphic framework is based on the interpretation of palynological data and was first established in the Netherlands during the 1960s. The new lithostratigraphic concept has revealed numerous contradictions with the chronostratigraphic framework. Based on these results it is proposed to abandon the chronostratigraphic subdivision of the Early Pleistocene in northwestern Europe.

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 Jülich. 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-mapable 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.