River system evolution and environmental changes during the Lateglacial in the Paris Basin (France)

Abstract

Lateglacial sequences from the Paris Basin floodplains provide a general overview of the valley's evolution related to climatic changes from the Weichselian Upper Pleniglacial to the beginning of the Holocene. Comparison between morphostratigraphical and palaeobiological data allows discussion of fluvial dynamics and related palaeoenvironmental conditions. The Upper Pleniglacial/Oldest Dryas transition remains poorly documented. It is represented by sands and silts deposited by a braided channel network. The Bølling begins with a significant incision related to a meandering system which is followed by local organic and minerogenic deposition, contemporaneous with vegetation development. The Older Dryas is evident in several sequences. The Allerød appears more stable and the forest extension is accompanied by a thin soil formation on the banks. The Younger Dryas is characterised by a strong infilling of the valleys by calcareous silts. This last sharp event precedes a second major downcutting phase which takes place in the early Postglacial and is followed by a decline in river flow and sediment supply. This evolution reflects a broad regional pattern of fluvial response which illustrates its sensitivity to climatic change. The study of various morphosedimentary contexts shows their influence on the fluvio-dynamic record and bio-proxies which complicates the detection of minor phases.