Response of the Rhine-Meuse system (west-central Netherlands) to the last Quaternary glacio-eustatic cycles : A first assessment

An almost 50-m-deep core from the Weichselian Rhine-Meuse palaeovalley, near the present Dutch coast, reveals new insights into how this continental-scale fluvial system responded to relative sea-level fluctuations associated with the last Quaternary glaciations. A multidisciplinary study of this core included sedimentological and stratigraphic analysis augmented with data on shell, diatom and pollen content to infer depositional environments. Optically stimulated luminescence dating provides a first numerical chronostratigraphy for these strata. Net fluvial incision due to relative sea-level fall associated with the Weichselian glaciation (notably oxygen-isotope stage 4) is estimated at > 10 m, and we argue that this amount of incision decreases both updip and downdip, because our study area is located near the thickest part of the Eemian/Early Weichselian (oxygen-isotope stage 5) highstand coastal prisms that were particularly sensitive to erosion during ensuing relative sea-level falls. Coastal prism geometry, with a relatively steep upper shoreface, is extremely important in promoting erosion, as demonstrated by the Rhine-Meuse system that borders an exceptionally wide, low-gradient continental shelf. Our results show that fluvial deposits associated with relative sea-level fall (80-40 ka) can constitute a considerable part of preserved strata ('falling-stage systems tract'). Interglacial transgressive and highstand systems tracts tend to have a relatively low preservation potential; in our core these are represented by estuarine deposits scoured into underlying fluvial strata. Furthermore, we note that sequence boundaries in such settings may be relatively undistinct, whereas tidal ravinement surfaces can be more conspicuous and may represent considerably longer time gaps.