Magali Delmas

Chapter 11 - Recent Advances in Research on Quaternary Glaciations in the Pyrenees

In the Pyrenees, new optically stimulated luminescence, 14C and 10Be ages, allows a more detailed image of the Pleistocene glaciations. MIS 6 moraines are dated on Ariege and Gallego. For the last glacial cycle, maximum ice extent occurred early, during MIS 4. A powerful advance during the global last glacial maximum is known on the Mediterranean side only. Deglaciation was very rapid after 20 ka.

Small, isolated glacial catchments as priority targets for cosmogenic surface exposure dating of Pleistocene climate fluctuations, southeastern Pyrenees

A new 10 Be data set from a small glacial catchment in the Pyrenees confirms almost full glacier extent during Marine Isotope Stage (MIS) 2, extends the oldest cosmogenic exposure ages of moraines in this mountain range to MIS 5, and constrains paleoclimate reconstructions in the Mediterranean region. It also illustrates the advantageous conditions for the long-term preservation of terminal moraines provided by small, low-gradient glacier catchments that did not merge with compound ice masses even during glacial maxima. These small, gently sloping, and isolated glacier catchments are proposed as priority targets for terrestrial cosmogenic nuclide dating of peak Pleistocene glacier advances, providing scope for greater accuracy in interregional paleoclimatic correlations.

Large-scale rock slope failures in the eastern Pyrenees: identifying a sparse but significant population in paraglacial and parafluvial contexts

Abstract This first overview of large‐scale rock slope failure (RSF) in the yrenees addresses the eastern third of the range. Around 30 principal RSFs greater than 0.25 km2 and 20 lesser or uncertain cases have been identified from remote imagery and groundtruthing. Compared with other European mountain ranges, RSF incidence is relatively sparse, displays no obvious regional trend or spatial clustering, and occurs across diverse landscape types, if mainly on metamorphic rocks. A transition is observed from paraglacial RSFs in formerly glaciated valleys to what are here termed ‘parafluvial’ RSFs, within wholly or mainly fluvial valleys but where slope failure is not directly provoked by or linked to river erosion. RSFs are particularly found in three topographic settings: at cirque and trough‐head thresholds (transition zones of elevated instability between cirque and main glaciated trough walls); near the upper or outer periphery of the ice field, where glacial adaptation of fluvial valleys is incomplete; and in fluvial valleys beyond glacial limits where incision is locally intense. RSF is absent from the range divide, from within cirques, and from most main valleys. In the montane areas, RSF is strongly associated with vestiges of preglacial summit surfaces, confirming that plateau ridges are less stable than sharpened crests and horns. RSF is contributing significantly to the progressive destruction of this paleic relief. The overall sparsity of RSF indicates insufficient rock mass stresses, including rebound after concentrated bedrock erosion. This may reflect a relatively weak imprint of glacial erosion, including breaching, in a context of relatively low mean rates of neotectonic uplift, possibly signalling overall that eastern yrenees landscapes are close to dynamic equilibrium.

Did Pyrenean glaciers dance to the beat of global climatic events? Evidence from the Würmian sequence stratigraphy of an ice-dammed palaeolake depocentre in Andorra

Abstract The ice-marginal depositional sequence of La Massana provides a chronostratigraphic benchmark for reconstructing the Würmian glacial evolution of the Valira catchment in Andorra, SE Pyrenees. The sedimentary record of Andorra confirms the asynchronous chronology of glacier fluctuations in different parts of the Pyrenean mountain range. A major ice recession occurred at the end of Marine Isotope Stage (MIS) 4. High magnitude valley-glacier fluctuations during MIS 3 constitute another important finding. Major readvances occurred toward the end of MIS 3, whereas MIS 2 (in particular, the global Last Glacial Maximum, or LGM) featured sharp contrasts in ice recession rates between Pyrenean valleys. Substantial distances separated MIS 4 glacier fronts (the Würmian maximum ice extent, or MIE) from those reached during the global LGM, in contrast to situations in the eastern Pyrenees, where Würmian MIE and global LGM ice fronts nearly coincided. Overall, the Valira glaciers reveal patterns that are more similar to those recorded elsewhere in the western and central Pyrenees than in the eastern Pyrenees. The rapid fluctuations recorded by Andorran glaciers during the second half of the Würm also suggest a response to global forcing events such as Heinrich events in the North Atlantic.

The Têt River Valley: A Condensed Record of Long-Term Landscape Evolution in the Pyrenees

While coinciding with a unique biogeographical hotspot where the Mediterranean and Atlantic biomes meet in the Eastern Pyrenees, the Tet river catchment displays a spectacular suite of tectonic, glacial, periglacial, fluvial and hillslope processes. Prominent fragments of smooth, pre-Quaternary Paleic relief survive where glacial erosion has not serrated the interfluves, and well-preserved exposures of both continental and marine basin fill sequences provide a compelling record of post-orogenic landscape evolution and base-level changes since the Early Neogene. The heritage value of the physical landscape is enriched by a palimpsest of agrarian, pastoral, industrial and cultural vestiges from the Neolithic to recent history.