Glacial stages in the Peña Negra valley, Iberian Range, northern Iberian Peninsula: Assessing the importance of the glacial record in small cirques in a marginal mountain area

Abstract

The objective of this study was to assess whether it is possible to obtain a comprehensive record of the last deglaciation from the small Peña Negra glacial cirque in a marginal mountain range in the Iberian Range (northern Iberian Peninsula). The cirque is located in Sierra Cebollera, at an elevation slightly over 2000 m a.s.l. in the divide, and has relatively low elevational difference between its uppermost and lowest parts. The Peña Negra glacial cirque was selected because of the presence of several lateral moraines indicating the occurrence of a glacial tongue of 1.8 km length and a small rock glacier, enabling identification of the main glacial stages that affected the paleo-evolution of the glacier. Using cosmogenic exposure dating techniques and geomorphological mapping it was possible to reconstruct the historical Peña Negra glacier and to distinguish: (i) the maximum ice extent (MIE) at approximately 18–20 ka, coinciding with the Global Last Glacial Maximum (GLGM), although the occurrence of a previous stage was not ruled out; (ii) a stage of glacial re-advance at 16–17 ka, coinciding with the Oldest Dryas, followed by rapid ice melting; (iii) the development of a rock glacier in a minor structural cirque near the headwall at 14–15 ka, when paraglacial processes were probably dominant; and (iv) evidence of ice melting in the uppermost cirque at 13.5 ka. Study of the Peña Negra glacier revealed the history of a minor valley glacier affected by distinct stages, including the formation of a small rock glacier in the final phases of deglaciation. No evidence of a Younger Dryas re-advance was found.