Palaeoecological response to Greenlandian (Early Holocene) climatic changes: Insight from an abandoned-channel sequence of the Meuse River at Autrecourt-et-Pourron (Ardennes, France)

Abstract

A Greenlandian (Early Holocene) palaeochannel of the Meuse River is described from Autrecourt-et-Pourron in the Ardennes region of northern France. During the Younger Dryas, fluvial deposits represent a high-energy, sinuous palaeochannel, but at the onset of the Holocene, progressive channel abandonment resulted in the establishment of a low-energy meandering river system. Well-dated studies using palynology, carpology, malacology and geomorphology reveal a Greenlandian succession of changes in fluvial dynamics and vegetation. Between 11,700 and 11,400 cal yr BP, warmer temperatures led to the development of a birch community (Betula sp.) within an open grassland, dominated by herbaceous cold-adapted plants (Linum alpinum, Plantago montana, Artemisia sp., Juniperus sp.). Between 11,400 and 11,100 cal yr BP, the river and the vegetation dynamics reflected two short-term climate events. Around 11,400 cal yr BP, the palaeochannel became separated from the active channels of the Meuse River but remained dominated by waterlogged wetlands. This cold and wet phase represents the “Preboreal Oscillation” also referred as the “11.4 ka event”. Around 11,300 cal yr BP, the records suggest that fire frequency increased close to the channel, and may indicate a dry episode that reflects a sharp, short-lived rise in temperature. Between 11,100 and 10,700 cal yr BP (Late Preboreal phase), the channel received flood deposits again. Salix and helophytes developed while Populus colonised the riverbank. From 10,700 cal yr BP, at the beginning of the Boreal phase, the palaeochannel was finally abandoned and dense temperate woodland with Corylus avellana and Quercus spp. became established. Based on its high chronological resolution, Autrecourt-et-Pourron represents a key locality in north-western Europe to investigate environmental change in connection with Early Holocene short climate variations. In addition, the results highlight the valuable contribution of carpological analyses in improving the spatial resolution of reconstructions of vegetation cover.