Contribution a la connaissance des vallons élémentaires du nord de la France : l'exemple de la Creuse des Fosses ( Authieule, plateau picard) [Contribution to the knowledge of the elementary valleys of the north of France : the example of the Creuse des Fosses (Authieule, plateau picard )

Abstract

The survey deals with the morphodynamic evolution of a creuse. It is a ravine-like landform of kilometnc length that often cut the bottom of the small elementary valleys incised into the chalky plateaus of the Artois and Picardy. The morphosedimentary analysis takes into account the data (stratigraphy, micromorphological analysis) of 3 cross-sections distributed along a 500 m section and replaced in their geomorphological context (cartography based on a DTM, longitudinal profile). The recognition of characteristic deposits (bedded loess, palaeosol) and of medieval artefacts allows to set a chronology of the events since 30 000 BP Stratigraphie and landform analyses demonstrate the fluvial character of the creuse. Two main phases of incision, locally associated to a sinuous channel pattern, are described. Phases of infilling, probably of medieval age for the last one, correspond to episodic and violent floods of torrential type. Valley sides play an important role, delivering in abundance loess that infilled the creuse in present time.