ENVIRONMENTAL CHANGES FROM THE LATE GLACIAL TO THE MID-HOLOCENE IN THE EASTERN VELAY: THE SEDIMENTARY SEQUENCE OF LA NARCE DU BEAGE IN ARDECHE (MASSIF CENTRAL, FRANCE)

The renewed interest in the volcanic uplands of the Eastern Velay region (Massif Central, France) has led to the discovery of a new sedimentary sequence from the La Narce du Beage peatland, in Ardeche. Several cores were carried out to produce a high resolution interdisciplinary study. This paper deals with the sedimentological data (lithology, organic matter content, grain size, magnetic susceptibility) obtained on core D (357 cm long), extracted near the outlet of the peatland. A set of ten AMS radiocarbon dates supports these results. This study is a first step in order to reconstruct the evolution of the local environmental changes since the Upper Pleniglacial/Late Glacial transition. The sedimentary record shows a gradual silting of a Late Glacial lake (starting after 18,000 yr. cal. BP) and a gradual increase of organic matter content after 14,600 yr. cal BP. The peat initiation took place during the Early Holocene, after 10,800 yr. cal. BP. The study highlights major Late Glacial and Early Holocene bioclimatic changes at local and regional scales. These changes are characterized by high variations of the accumulation rate of anorganic sediments (TANO): during the Oldest Dryas, after the Bolling/Allerod transition and during the Younger Dryas. During the Preboreal and the Boreal, four main episodes of minerogenic accumulation are dated to (1) 11,200-10,800 cal. yr. BP, (2) 10,400-10,300 cal. yr. BP, (3) 9,900-9,150 cal. yr. BP and (4) 9,000-8,200 cal. yr. BP. The major TANO peak of the last episode (4), younger than 8,650-8,400 cal. yr. BP, could match with the 8,200 cal. yr BP climatic event. Since the mid-Holocene, at the end of the Early Atlantic period (i.e. during the Neolithic Period), a slower peat and sediment accumulation occurred. Therefore, only local changes in the environment are evidenced in connection with changes in the vegetation cover, eventually from climatic and/or anthropogenic origin. Finally, increasing anthropogenic pressure during the last centuries (XIXth and XXth centuries) disrupted the sedimentation processes, therefore not allowing a clear understanding of environmental changes during the Late Holocene.