Fluvial architecture of Belgian river systems in contrasting environments: implications for reconstructing the sedimentation history

Abstract

Accurate dating is necessary to get insight in the temporal variations in sediment deposition in floodplains. The interpretation of such dates is however dependent on the fluvial architecture of the floodplain. In this study we discuss the fluvial architecture of three contrasting Belgian catchments (Dijle, Geul and Amblève catchment) and how this influences the dating possibilities of net floodplain sediment storage. Although vertical aggradation occurred in all three floodplains during the last part of the Holocene, they differ in the importance of lateral accretion and vertical aggradation during the entire Holocene. Holocene floodplain aggradation is the dominant process in the Dijle catchment. Lateral reworking of the floodplain sediments by river meandering was limited to a part of the floodplain, resulting in stacked point bar deposits. The fluvial architecture allows identifying vertical aggradation without erosional hiatuses. Results show that trends in vertical floodplain aggradation in the Dijle catchment are mainly related to land use changes. In the other two catchments, lateral reworking was the dominant process, and channel lag and point bar deposits occur over the entire floodplain width. Here, tracers were used to date the sediment dynamics: lead from metal mining in the Geul and iron slag from ironworks in the Amblève catchment. These methods allow the identification of two or three discrete periods, but their spatial extent and variations is identified in a continuous way. The fluvial architecture and the limitation in dating with tracers hampered the identification of dominant environmental changes for sediment dynamics in both catchments. Dating methods which provide only discrete point information, like radiocarbon or OSL dating, are best suited for fluvial systems which contain continuous aggradation profiles. Spatially more continuous dating methods, e.g. through the use of tracers, allow to reconstruct past surfaces and allow to reconstruct reworked parts of the floodplain. As such they allow a better reconstruction of past sedimentation rates in systems with important lateral reworking.

Holocene floodplain deposition and scale effects in a typical European upland catchment: A case study from the Amblève catchment, Ardennes (Belgium)

“…For each coring a detailed in-field description was made with a vertical resolution of c. 5 cm, describing sediment texture, color, quantity, nature and size of gravel, presence of plant material, peat or other inclusions, and soil horizons. For each cross-section the fluvial architecture was established (for detailed descriptions see Notebaert et al, 2011a).…”

“…This paper focuses on identifying the fine sediment introduced into the fluvial system during the Holocene, and does not take into account the gravel bedload sediments. These gravels are Pleistocene deposits which are reworked by the Holocene rivers as bedload, and can easily be distinguished (Notebaert et al, 2011a). Although part of the gravel may result from Holocene soil erosion processes, this fraction cannot be differentiated in the field from the reworked Pleistocene deposits, and as such is not considered in the sediment quantifications.…”

“…The different floodplain units are based on their fluvial architecture and are discussed in detail in Notebaert et al (2011a). A value of 1.42 was taken for DBD MS , consequent with previous studies .…”

“…Notebaert et al (2011a) have indicated the importance of understanding the fluvial architecture in such a setting, and have shown how dating using tracers can contribute in calculating net sedimentation rate for the floodplains. In addition, also specific-point dates such as those yielded with radiocarbon dating can be used when carefully considering the fluvial architecture.…”

Evolution morpho-sédimentaire et enregistrement pollinique atlantique dans le nord de la France : la séquence de Valenciennes "le vignoble" (vallée de l’Escaut, nord)

“…Un décalage important peut exister entre les différents bassins versants mais aussi à l'inté-rieur d'un même bassin, parfois de faible superficie. Le cas est clairement mis en évidence dans le bassin de la Beuvronne, affluent de la Marne (Orth et al, 2004) ou dans de petits bassins affluents de la partie aval de l'Escaut comme la Dijle (Notebaert et al, 2011) et surtout la Mark (Huybrechts, 1989, 1999, où le colmatage argileux intervient précocement dès la première partie de l'Atlantique dans la section amont (datation vers 7 600 BP, environ 8 500 ans cal. BP).…”