Palaeoenvironmental studies in NW Iberia (Cantabrian range): Vegetation history and synthetic approach of the last deglaciation phases in the western Mediterranean

At the north-western limit of the Mediterranean basin, in the Mediterranean–Oceanic transition zone, the multidisciplinary study of two palaeolakes: Villaseca and La Mata (Province of Leon), provides data on the last deglaciation. The juxtaglacial lakes were formed during a deglaciation phase of the last cold stage (Weichselian/Würm) estimated, from the regional and Pyrenean chronological data, between circa 48 ka and 32 ka (ka: 1000 years ago). Their drainage occurred circa 17 ka and 15 ka respectively, during the definitive glacial retreat phases. These results provide evidence for a glacial maximum extension preceding the global Last Glacial Maximum (LGM) and an early deglaciation. Comparisons with the Pyrenean data show that in the most important glacial basins of the Pyrenean–Cantabrian range, glaciers were still present at middle elevation circa 18–20 ka. The final deglaciation did not happen until around 16 ka.During the period 48–13.3 ka, along the Pyrenean–Cantabrian range, three stages can be distinguished in the deglacial processes. Between circa 48 and 32 ka, the deglacial retreats were contemporaneous with D–O events 12 to 6. Between circa 32 ka and 18 ka, major sedimentary modifications were rare. Two of them are synchronous with D–O 4 and 3. A glacial readvance also occurred during this period along the Pyrenean–Cantabrian range. Between 18 and 17 ka, major sedimentary changes and an increase in the δ18O records of the NGRIP ice-core record are synchronous. Between 15 and 13.3 ka, glacial retreats and sedimentary changes are synchronous with the climatic improvement observed from the end of the Oldest Dryas to the end of the Bölling–Alleröd period.These correspondencies suggest relationships between the deglacial processes in the western Mediterranean and the palaeoenvironmental events in the North Atlantic region during the last Glacial–Interglacial transition. During the Full Glacial period, the pollen data indicates dominant steppic environments. The Oldest Dryas was not a constant cooling phase and from around 15.5 ka, the pollen data indicates a slight warming. During the Holocene, until circa 2040 cal BP, mixed oak forests developed and pine was a prominent component of the Cantabrian landscape. Then the forests were destroyed due to mining, agriculture and fire, and this favoured the extension of heathland.