Chronological and geomorphological investigation of fossil debris-covered glaciers in relation to deglaciation processes: A case study in the Sierra de La Demanda, northern Spain

Fernández-Fernández, José M. et. al.- 18 páginas.- Ilustraciones.- © 2017 Elsevier Ltd. All rights reserved.
In this study, fossil debris-covered glaciers are investigated and dated in the Sierra de la Demanda, northern Spain. They are located in glacial valleys of approximately 1 km in length, where several moraines represent distinct phases of the deglaciation period. Several boulders in the moraines and fossil debris-covered glaciers were selected for analysis of Be-10 surface exposure dating. A minimum age of 17.8 +/- 2.2 ka was obtained for the outermost moraine in the San Lorenzo cirque, and was attributed to the global Last Glacial Maximum (LGM) or earlier glacial stages, based on deglaciation dates determined in other mountain areas of northern Spain. The youngest moraines were dated to approximately 16.7 +/- 1.4 ka, and hence correspond to the GS-2a stadial (Oldest Dryas). Given that the debris-covered glaciers fossilize intermediate moraines, it was deduced that they developed between the LGM and the Oldest Dryas, coinciding with a period of extensive deglaciation. During this deglaciation phase, the cirque headwalls likely discharged large quantities of boulders and blocks that covered the residual ice masses. The resulting debris-covered glaciers evolved slowly because the debris mantle preserved the ice core from rapid ablation, and consequently they remained active until the end of the Late Glacial or the beginning of the Holocene (for the San Lorenzo cirque) and the Holocene Thermal Maximum (for the Mencilla cirque). The north-facing part of the Mencilla cirque ensured longer preservation of the ice core. (C) 2017 Elsevier Ltd. All rights reserved.
Support for this research was provided by the projects ESPAS (CGL2015-65569-R) (MINECO/FEDER), MOUNTAIN WARMING (CGL2015-65813-R) (Spanish Ministry of Economy and Competitiveness). The study was assisted by the High Mountain Physical Geography research group (Complutense University of Madrid) and the research group on Geomorphology and Global Change, which is supported by the Aragon Government and the European Social Fund. The 10Be measurements were performed at the ASTER AMS national facility (CEREGE, Aix en Provence, France), which is supported by the INSU, CNRS and the ANR through the "Projets thematiques d'excellence" program for the "Equipements d'excellence" ASTER-CEREGE action and IRD. Jose M. Fernandez-Fernandez received a grant from the FPU programme (FPU14/0650) (Spanish Ministry of Education, Culture and Sport).