Significance of the Tertiary sands of southern Ardennes: new data on the capture of the Meuse lorraine.

The study of the often polygenic Tertiary sands of southern Ardennes allows the local evolution of the drainage pattern during the Paleogene and the N eogene to be traced. The history of these sands starts with a strong Eocene weathering and the formation of a deep ferruginized quartzose saprolite. S ome fossilized outcrops remain unchanged: the outcrop of Regniowez is inter preted as a thick colluvium on which a ferruginous pedogenesis took place d uring the Eocene, resulting in an allothigenous cuirasse protecting the san ds from erosion. Others undergo a complex evolution: the outcrop of Doische represents the rehandling of the same kind of Eocene sands, first in a mar ine Oligocene environment, then by continental Miocene streams. In that cas e, nevertheless, the heavy minerals assemblage shows the link with the almo st in situ sands such as those of Regniowez, and therefore the local origin of the material. The lack of allogenic heavy minerals (characteristic of t he Meuse lorraine) in the fluvial sands of the Ardennes plateau prior to th e Trainee mosane (attributed to the Middle Miocene) confirms the Miocene ca pture of the Meuse lorraine, flowing westward so far, between the Paleozoic basement and the Sormonne valley, as assumed by Pissart in the early sixti es. On the other hand, as the topographic glacis between the Ardennes and t he Paris Basin was still active during the Stampian, the drainage pattern o f the Meuse lorraine before the capture is post-Oligocene. (C) 2000 Edition s scientifiques et medicales Elsevier SAS.