Morpho-sedimentary characteristics of Holocene paleochannels in the Upper Rhine alluvial plain, France

Abstract

Abstract. The French Upper Rhine alluvial plain is characterized by a complex system of paleochannels inherited from Late Glacial to Holocene fluvial dynamics of the Rhine and Ill river systems, among other smaller rivers. These paleochannels represent valuable archives for understanding and reconstructing the fluvial and landscape evolution of the area. However, the Holocene temporal trajectories of the paleochannels, in response to a range of environmental changes, remain poorly understood. This study presents a detailed and systematic mapping and characterization of an extensive network of paleochannels spanning the entire width (19 km) of a reach of the central French Rhine plain. Based on qualitative and quantitative lidar analysis, field investigations, and provenance investigations of paleochannel infill sequences, five distinct paleochannel groups (PG 1 to PG 5) were identified in the study area. These paleochannel groups differ considerably regarding their channel patterns, morphological characteristics, and sedimentary sources of the infilling sediments. The interpretation of the different datasets indicates that the development of these different paleomorphologies is attributed to significant changes in hydro-geomorphodynamic processes in the area during the Holocene, especially lateral migrations of the Rhine and Ill rivers. The findings reported here are promising and will have significant implications for reconstructing the long-term (Late Glacial to Holocene) evolution of the Upper Rhine fluvial hydrosystem in response to various controlling factors.

Late glacial to Holocene fluvial dynamics in the Upper Rhine alluvial plain, France

“…The contemporary floodplain has a distinct microtopography characterized by a dense and intricate network of paleochannels (Fig. 4) filled with a mix of clastic and organic deposits several meters thick (Schmitt et al, 2007(Schmitt et al, , 2011(Schmitt et al, , 2016Chapkanski et al, 2020;Abdulkarim et al, 2022). Some of these paleochannels, however, have a current connection to groundwater or the Rhine (during floods) or the Ill River and contain phreatic and semiphreatic rivers that are home to a diverse range of aquatic macrophytes (Carbiener, 1983a(Carbiener, , 1983bTrémolières et al, 1993;Schmitt, 2001;Schmitt et al, 2016).…”

“…Preliminary studies indicate the presence of at least five major paleochannel systems in the region, with considerable differences in their surface topographic features, geometry and architecture, and provenance of infill sediments (Abdulkarim et al, 2022). These differences in geomorphic features and sediment provenance are linked to significant shifts in hydro-geomorphological processes in the area, as well as lateral movements of the Rhine and Ill Rivers (the latter is a major tributary of the Rhine in the region; Fig.…”

“…Most studies conducted in this part of the Upper Rhine plain have focused on the historical fluvial dynamics or have been restricted to specific aspects such as neotectonics, historical flooding patterns, or human impacts on river dynamics (e.g., Lang et al, 2003;Ollive et al, 2006;Boës et al, 2007;Lämmermann Barthel et al, 2009;Mäckel et al, 2009;Eschbach et al, 2018). Few paleoenvironmental studies have been conducted in recent years to gain a deeper understanding of the Holocene evolution of the Upper Rhine fluvial hydrosystem, with a particular focus on the Ried Central d'Alsace region (located between Colmar and Strasbourg) within the French Upper Rhine plain (e.g., Boës et al, 2007;Schmitt et al, 2016;Chapkanski et al, 2020;Abdulkarim et al, 2022). This area is an extensive and exceptionally biodiverse alluvial landscape (Carbiener, 1983a(Carbiener, , 1983b) that features a remarkably well-preserved and complex network of paleochannels, providing an ideal and regionally significant fluvial archive for deciphering the long-term fluvial dynamics and evolution of the southern and central parts of Upper Rhine plain.…”

“…These differences in geomorphic features and sediment provenance are linked to significant shifts in hydro-geomorphological processes in the area, as well as lateral movements of the Rhine and Ill Rivers (the latter is a major tributary of the Rhine in the region; Fig. 1), which are believed to have persisted since at least the Early Holocene (e.g., Schmitt et al, 2016;Abdulkarim et al, 2022). However, these previous studies primarily relied on remote sensing data, hand-augured core sediment profiles, and very few radiocarbon ages.…”

Preface: Quaternary research from and inspired by the first virtual DEUQUA conference

“…They were able to reconstruct the shift from a running river to silting-up meanders that took place about 11 000 to 10 500 years ago. Abdulkarim et al (2022) analyze the patterns and provenance of paleochannels in the French Upper Rhine alluvial plain. They find at least five paleochannel groups which can be distinguished.…”