TIMING OF DEGLACIATION IN THE SERRA DO GERÊS MOUNTAINS (NW PORTUGAL NATIONAL PARK) BASED ON AMS DATING

Late Quaternary glacier fluctuations are good indicators of changes in climate and therefore can provide integrated proxy records of recent climatic and related environmental changes. AMS dates obtained from a 3.55 m deep peatbog present in the upper portion of the Couce glacial valley of the Serra do Gerês Mountains were used to reconstruct the timing of deglaciation in these mountains. The Couce valley was home to the second largest glacier (>5 km long) in this range and is also home to the largest array of glacial deposits present in these mountains. A Russian peat borer was used to core the peatbog and revealed the presence of two major distinctive sedimentary units. The bottom unit is 15 cm thick and is composed of a glaciolacustrine deposit. One sample collected from the bottom 1 cm disclosed an age of 19,320 cal yr BP. The second unit is 3.4 m thick and is composed of a peat deposit. One sample was also collected from the bottom 1 cm and revealed an age of 14,060 cal yr BP.

The AMS dating of the glaciolacustrine deposits revealed that by 19,320 cal yr BP, after the local Last Glacial Maximum (LGM), glacial recession was underway with the ice receding to the upper portions of the range’s glacial valleys and also creating a glacial lake in the upper Couce valley where a large glacier still existed. The 14,060 cal yr BP age obtained from the peat deposit represents a relevant change in the environmental conditions that probably indicates the deglaciation of these mountains, which correlates with an age of 13,800 cal yr BP presented by other researchers for the complete deglaciation of the Serra da Estrela Mountains in central Portugal.