Small headwater stream evolution in response to Lateglacial and Early Holocene climatic changes and geomorphological features in the Saint-Gond marshes (Paris Basin, France)

Abstract

The study focuses on river dynamics and vegetation changes during the last Glacial-Interglacial transition from a headwater stream located in the eastern part of the Paris Basin. We adopt a spatial multiproxy approach combining image analyses, geophysical surveys, sedimentary and pollen record analyses to document the impact of Lateglacial climate changes and geomorphological features on vegetation and fluvial dynamics in the small Boitet catchment (ca. 20 km2). Our results show that the sedimentary record is organized into six successive alluvial sequences reflecting changes in discharge and channel morphology in response to short phases of climate oscillations during the Lateglacial and Early Holocene periods. The Boitet alluvial sequences present some similarities with other NW European rivers that are interpreted as large-scale fluvial system evolution to climate changes. However, some local differences have also been highlighted partly related to the upstream position of the catchment. Among them, two distinctive features of the Boitet catchment are 1) the preservation of the Oldest Dryas deposits, which have been rarely described in this area, and 2) the recognition of multichannel river dynamics during the Oldest Dryas and Younger Dryas. We demonstrate that the fluvial evolution is firstly triggered by climate changes and that land surface features may also influence specifically upstream areas revealing contrasting responses of the river system.