Timing and controls of Quaternary terrace formation in the lower Meuse Valley

The lower Meuse Valley contains one of the most complete Quaternary fluvial terrace staircases in northwestern Europe. Located between the uplifting Rhenish–Ardennes Massif and the Roer Valley Rift System, the lower Meuse terraces have long been the subject of geomorphological, sedimentological and stratigraphic studies. These studies established the spatial organization, sedimentological aspects, relative chronology, and morphological grouping of the terraces, broadening the understanding of the complexities encompassing terraces response to environmental changes. Building on these foundational studies, a key uncertainty remained: their absolute ages. With a robust chronological constraint, open questions regarding past environmental changes can be addressed, e.g., the causes of major geomorphic transitions, and the role of orbital-scale climate forcing during the Early Pleistocene. This thesis integrates mapping and quantitative subsurface data with new cosmogenic 26Al–10Be burial ages, allowing a refined chronology and evaluation of how climate and tectonics controlled terrace formation in the lower Meuse valley. Integration of geomorphological mapping and subsurface data reveals that the lower Meuse terrace deposits record progressive long-term evolution in composition and geometry in response to Quaternary cooling. Early Pleistocene terraces are dominated by sand and gravelly sand, whereas Middle and Late Pleistocene terraces become increasingly gravel-rich, reflecting enhanced physical weathering in the Ardennes source area. Terrace thicknesses and longitudinal gradients further indicate that tectonics influenced terrace formation and preservation. These results show that terrace composition and geometry integrate gradual climatic and tectonic trends. However, significant episodes such as the Mid-Pleistocene Transition (MPT), are not clearly expressed in the terrace records. This establishes a framework within which terrace formation can be interpreted. New cosmogenic 26Al–10Be burial ages refine the chronology of terrace formation and incision. These data reveal that multiple terrace levels formed and were preserved within short intervals during the Middle Pleistocene, when incision rates increased by an order of magnitude. This transient phase of accelerated incision coincides with a major morphological transition from a broad valley system to a narrower, more deeply incised valley. The magnitude and timing of this incision cannot be explained by climatic forcing alone and instead point to a short-lived phase of increased tectonic uplift in the Rhenish–Ardennes region, superimposed on longer-term uplift. Climatic variability modulated individual episodes of aggradation and incision, but tectonic forcing set the boundary conditions that enabled rapid incision and exceptional terrace preservation. Extending absolute age control into the Early Pleistocene reveals that terrace formation did not occur continuously or regularly with every glacial–interglacial cycle. Instead, Early Pleistocene terraces appear to cluster into specific formation episodes separated by long gaps. Correlation of terrace ages with orbital forcing suggests a preferential association with phases of enhanced 400-kyr eccentricity forcing, during which precession-driven climate variability is amplified. These intervals likely altered sediment supply and water discharge, raising the likelihood that the system crossed the thresholds required for terrace formation. This modulation may explain the mismatch between the number of preserved terraces and the number of glacial–interglacial cycles prior to the MPT. Overall, the lower Meuse terrace staircase shows that terrace formation reflects the interaction between climatic variability, long-term orbital modulation and tectonic boundary conditions. This thesis provides a refined chronological and process-based framework for interpreting discontinuous fluvial archives in the lower Meuse and comparable river systems.