Morphologic evolution of eastern Paris Basin: " ancient surfaces " and Quaternary incisions

International audienceThe investigations on the site of the Meuse/Haute-Marne underground laboratory to evaluate its geological have lagely contributed to revise the geomorphologic evolution of the Paris Basin by the study of the "ancient paleoweathering surfaces and the processes controllingerosion during the Quaternary. Field work (mapping, sampling) associated to dating methods (paleomagnetism on alterites, ESR on alluvial terraces and U/Th TIMS on speleotherms) and combinated with numerical modelisation, have been essential in all studies. They permit to unravel some debates such as the characterization of several paleosurfaces that were attributed to the Tertiary for all of them, to identify several sets of fluvial erosion forms in areas where they were supposed to be none of them , to understand the role of the karsts in the surficial erosion. The main results can be summarized as follow : 1) the "top surface" is in fact composed of several, well identified, paleoweathering surfaces that were shaped at various periods : early Cretaceous and lower Tertiary; 2) the evolution of the Quaternary landscap is driven by the river incisions and the cuesta retreat, karsts play a significant role but not determining; 3) modelling shows that a rectonic uplift has to be taken into account to simulate the incision. These results are important for the Geoprospective analysis : ancient surfaces bring valuable information about long term regional geodynamic evolution, continental weathering and its impact on teh geological formation characteristics, while the river incision give quantitative elements on the landscape recent evolution that permit to estimate the plausible evolutions of the site during the next one milion years