Late Pleistocene and Holocene glaciation in the Pyrenees: a critical review and new evidence from Be-10 exposure ages, south-central Pyrenees

摘要

A compilation and a critical assessment of the C-14 data set available show that the chronology of glacial events in the Pyrenees is not well constrained. After reviewing the literature on glacial reconstruction, we suggest a simplified subdivision of the Pyrenean last glacial cycle record into Last Pleniglacial, Deglaciation, and Neoglacial. To improve the numerical glacial chronology, we provide Be-10 surface exposure ages for 5 glacial erosion surfaces, 9 moraines and 2 erratics in the Upper Noguera Ribagor ana Valley (south-central Pyrenees). Published corrected C-14 data and new Be-10 exposure ages indicate that the major phase of moraine building recorded in this valley during the Last Pleniglacial probably occurred after 25 ka BP. This age calls in question the generally accepted hypothesis of a very early deglaciation of the Pyrenees ca 70-40 ka BP, and strongly suggests that the Pyrenees could have been in pleniglacial conditions during the Last Glacial Maximum (LGM). However, we do not exclude the possibility that the maximum glacier extent during the last glacial cycle had taken place much earlier than the LGM, as indicated by some published U-Th, AMS C-14 and OSL data. We suggest that pleniglacial conditions could have taken place during a longer ( 30-20ka) period than generally assumed, and that the Last Pleniglacial could include several glacier fluctuations recorded irregularly in different valleys, with a last major glacier readvance taking place around the LGM. In addition, the Deglaciation is represented by a series of moraines deposited between ca 13.7 +/- 0.9 and 10.1 +/- 0.6 ka. This moraine series indicates a highly variable climatic pattern that is partly correlated with Greenland Stadial 1 (the Younger Dryas), and suggests that the Deglaciation could have continued into the early Holocene. (c) 2006 Elsevier Ltd. All rights reserved.