Geomorphological record of the glacial to periglacial transition from the Bolling-Allerod to the Holocene in the Central Pyrenees: the Lo(sic)campo cirque in the regional context

In the highest tributaries of the Upper Garonne Basin, Central Pyrenees, cirques up to 2600 m a.s.l. were already deglaciated by 15-14 ka. The long-term deglaciation duringTermination-1 (T-1) was interrupted byglacial advances within the cirques during theBolling-Allerod(B-A) interstadial andtheYoungerDryas stadial. Thecirques preservea variety of glacial and periglacial landforms whose chronologies are poorly known. This study is focused on the Lo(sic)campo cirque (42 degrees 38' 06N and 0 degrees 59'10 E), Upper Garonne Basin, where a detailed geomorphological map and (10)Beterrestrialcosmicray exposure(CRE) dating allowedus to constrain the chrono-sequencebetweenthe glacialand periglacial domains. In the smallL Lo(sic)campo cirque, a glacier formed a cirque moraine between 2200 and 2300 m a.s.l., which surrounds a relict rock glacier encompassing several transversal ridges. Additionally, longitudinal ridges typicallyobserved in debris-coveredglaciers are preservedbetween the moraineandthe rock glacier. Theeight-sample data set ofCREages indicates the formation of the cirque moraine during the second half of the B-A, by 13.2 +/- 1.1 ka. Exposure ages fromthe rock glacier boulders showa rangebetween 13.6 +/- 0.9 and 11.9 +/- 0.7 ka, which did not allowits formation to be chronologically constrained. Therefore, the environmental evolution following the moraine stabilization could follow the formation of a debris-covered glacier at the bottom of the Lo(sic)campo cirque, with the subsequent formation of the rock glacier. After the rock glacier formation, its front rapidly ceased at 13.6 +/- 0.9 ka, while the upper ridges gradually stabilizeduntil itbecamedefinitively relict at 11.9 +/- 0.7 kaor afterwards. These results showevidence of the complex glacial to periglacial transition that needs more robust chronological data sets to better understand the role of climate forcing and local topography during the deglaciation in mid-latitude mountain environments.

Automated summary

In the Central Pyrenees, there are glacial and periglacial landforms in the Upper Garonne Basin, but their chronologies are poorly understood. This study focuses on the Lo(sic)campo cirque in this area and uses geomorphological mapping and CRE dating to determine the chronology of glacial and periglacial processes. The results suggest that the cirque moraine and rock glacier formed between 13.2 and 11.9 ka, indicating a complex glacial to periglacial transition. More robust chronological data sets are needed to further understand the role of climate and topography during deglaciation in mid-latitude mountain environments.