A combination of cosmogenic and Schmidt hammer exposure dating in the study of the deglaciation timing of Sierra de Guadarrama National Park (Spain)

Abstract

ABSTRACT The objective of the work is to calibrate the Schmidt hammer exposure dating (SHD) method in the Sierra de Guadarrama National Park in correlation with the dates previously obtained by Cosmogenic Radiation Exposure (CRE) dating methods. The dates were recalculated according to the new production models of 36Cl and 10Be cosmogenic isotopes. For this purpose, three glacial cirques were selected (Dos Hermanas, Laguna and Pepe Hernando), located on the eastern slope of Peñalara Peak, Spain (40°51'N, 3°57'O; 2428 m), the highest altitude of this mountain range. The application of the SHD method seems to be influenced neither by the different altitude of the samples nor by their height with respect to the current ground level. The degree of roughness of the rock surfaces (gneiss) has a slight influence, but does not change the actual volume of the results. The results of this work show a clear relationship between the CRE ages and the SHD R-values. The oldest landforms (31–19 ka) give mean values R < 50, both for moraine boulders and polished bedrock. The boulders of a rock glacier (16–15 ka) and the boulders of the innermost moraine yielded higher values: R-value >50. The youngest polished bedrock surface, located under the Peñalara Peak (12–11 ka), yielded R-value >60.