Contenu du sommaire : Colloque C.N.R.S. Rythmes d'évolution morphologique depuis l'holocène en milieux tempérés et froids (C.N.R.S.-Meudon, 14-15 novembre 1991)

Abstract. - This report gives the content of 15 papers sent to the A.G.F.'s meeting in Meudon, devoted to the alluvial fills and linear erosion during holocenic and historical times along the mediterranean rivers. These papers has been published in Physio-Géo, the bulletin of the Laboratory of physical geography in Meudon (U.R.A. 141 of the C.N.R.S. It is divided in three parts. The first one summarizes stratigraphical and chronological datas since 10000 years, with alternatively accumulation and downcutting. The second part studies the meaning of the holocenic alluvial fills according to their natural environment. The last one is devoted to the lowest terraces, built during historical times, at varied periods, from the greek antiquity to the middle-age. It discusses the part played by land use and climatic changes in the morphogenesis of the valley floors.

Abstract. - A synthesis of recent studies dealing with the sedimentary fills of french valleys stresses the occurrence of three main phases. During the Tardiglacial period, the processes of river load generation and transport in braided rivers were intense and widespread. The first part of the Holocene was caracterized by the stabilisation of slopes, by the reworking of sediments inherited from the previous period and by the importance of organic sedimentation in floodplains. From the Subboreal and the Subatlantic onward, the valley bottoms experience a succession of crisis, precisely during the Early Iron Age and the Little Ice Age ; they may be described by dowmstream progradation of gravel outwash in the forelands, by river bed aggradation and by braided patterns.