Glacial landforms and their paleoclimatic significance in Sierra de Guadarrama, Central Iberian Peninsula

This paper investigates the glacial evolution on the east face of Pico de Peñalara (40°51′N, 3°57′W; 2428 m), the highest elevation of Sierra de Guadarrama in the center of the Iberian Peninsula. The geomorphologic stability of glacial landforms and permanence of snow cover were examined, and 18 samples were selected for dating with cosmogenic isotope 36Cl from moraine formations in four well-differentiated phases, as well as from a pre-glacial periglacial blockfield and a glacial threshold near the headwall. The results show the synchrony between the Last Glacial Maximum (LGM) advance and most results obtained recently by cosmogenic dating in southern Europe, within the MIS (Marine Isotope Stage) 2 stadial but earlier than the global LGM, i.e. between 25 and 19 ka BP. There was slow glacial retreat with minor re-advances between 19 and 16 ka and rapid deglaciation from 16 ka. This paper presents initial results, still pending confirmation, for the minimum age of the periglacial summit block formation around 80 ka for the existence of moraine formations older than the last advance and for the existence of glaciers during the Younger Dryas stadial. To explain the synchrony between two moraine formations at different altitudes, this paper formulates the hypothesis of the ‘secondary moraine’ evidenced in currently existing glaciers similar to those which existed on Peñalara.