Environmental changes during the Late-Glacial and Early Holocene at the Gourd des Aill`eres mire in the Monts du Forez Mountains (Massif Central, France)

In the granitic part of the eastern Massif Central (France), the Gourd des Aille`res (GDA) mire provides one of the only Late-Glacial and Early Holocene sequences with a continuous sedimentation since the Oldest Dryas around 16000 years calibrated Before Present (16 ka cal. BP). Bioclimatic and hydrological changes were reconstructed based on sedimentological parameters, as well as by means of plant and animal macrofossils, pollen, and diatoms analyses through time. The environmental history of this site started with a small lake formed behind a morainedam. The multi-proxy study of the sedimentary sequence demonstrated that the coldest conditions took place around 14.3 ka cal. BP, at the very end of the Oldest Dryas. The B phi lling period (14.2-13.9 ka cal. BP) was obviously warmer than the Aller phi d period (13.9-12.8 ka cal. BP) in the Monts du Forez Mountains. However, both chronozones presented a short cooling phase: the Intra B phi lling Cold Period (IBCP) and the Intra Aller phi d Cold Period (IACP), respectively. The Older Dryas (14-13.9 ka cal. BP) was identified for the first time in this region based on pollen and diatom indicators. Thereafter, the Younger Dryas (12.9-11.7 ka cal. BP) was characterised by major temperature fluctuations. Windy conditions prevailed as indirectly demonstrated by the high frequency of Aulacoseira diatoms in the sequence. The onset of the Holocene was dated to 11.7 ka cal. BP. Peat-forming processes started thereafter due to the quick postglacial warming and the former GDA lake finally evolved into a limnogenous mire at the end of the Preboreal (10.4 ka cal. BP).