Alluviation in the Meurthe and Moselle valleys (Eastern Paris Basin, France): Lithological contribution to the study of the Moselle capture and Pleistocene climatic fluctuations

Geomorphological and lithostratigraphic analysis allow the definition of a record of eleven alluvial stepped units in the Meurthe valley downstream from the Vosges Massif. The deposits are mainly composed of sands derived from Permo-Triassic strata. A similar system of stepped terraces is identified in the Moselle valley near Toul, where the deposits are coarser and contain more crystalline sediments than those of the Meurthe. A distinction is made in these units between the levels deposited before the capture of the Upper Moselle river by the Paleo-Meurthe, which follow the former course towards the Meuse valley, and the post-capture levels, which follow the modem valley. Downstream from the present Moselle-Meurthe confluence, the higher deposits (above 25 m relative height) are similar to the Meurthe sediments (Permo-Triassic origin), as opposed to the youngest deposits (0 to 25 m relative height) which contain crystalline sediments from the Upper Moselle basin. This contrast allows the Moselle capture to be positioned between formations F4 and F3 of the alluvial system downstream from the present confluence. The correlation between these sections of valley underlines the parallelism of the terraces and the weakness of the syn-capture altitudinal gradient between the Upper-Moselle and the Paleo-Meurthe rivers. In certain parts of the valleys, a contrast is shown between sandy lithofacies from the Permo-Triassic cover and coarse lithofacies with crystalline elements. The deposition of the sandy series is attributed to full-glacial episodes, while that of the coarse series is correlated with periods of retreat of the Vosgian glaciers, especially during lateglacial episodes. The consensus of absolute dates of the capture (250-300 000 years B.P.) allows the incision rate for the Meurthe and the Moselle valleys to be estimated at 0.11 mm/y-1 since the capture. This rate is comparable with the rate already obtained for the Moselle valley in Germany.

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