Glacial - periglacial transition in the Ratera Cirque (Central Pyrenees) from the Younger Dryas to the Holocene

The transition from glacial to deglacial environments in mid-latitude mountains leaves a wide range of landforms of glacial, periglacial and paraglacial origin, of which the chronology and evolution are still debated. This work provides geomorphological and geochronological evidence for the last phases of deglaciation in the Ratera Valley and cirque (upper Noguera Pallaresa Valley-Central Pyrenees) by applying cosmic-ray exposure (CRE) dating to a set of 19 samples from moraine boulders, rock glaciers and glacially polished surfaces. The results indicate the occurrence of several glacial and periglacial phases between the end of Heinrich 1 (HS-1) event and the Mid-Early Holocene. The deglaciation of the Ratera area occurred between ca. 15.3 and 13.4 ka, interrupted by small glacial advances and/or standstills evidenced by the formation of moraine ridges. The moraine complex closing the Ratera Cirque was formed during the Bølling/Allerød (B-A) – Younger Dryas (YD) transition at ca. 12.6-12.4 ka. Later, during the Early Holocene, this glacier developed into a debris-covered glacier, which stabilised at ca. 9.9 ± 0.9 ka. Subsequently, this debris-covered glacier was partly fossilised by a rock glacier consisting of two differentiated units which stabilised at ca. 8.8 ± 0.8 and 5.8 ± 0.6 ka, respectively. Finally, a small debris-free glacier built a moraine ridge at the foot of the cirque wall. Thus, this spatio-temporal pattern of deglaciation of the Ratera Cirque represents a unique case spanning 10 ka, providing evidence of the major environmental changes that followed the disappearance of glaciers in the Pyrenees and demonstrates the importance of past periglacial and paraglacial dynamics in shaping the present-day mountain landscape in this range. • We examine the deglaciation process of the Ratera Valley, Central Pyrenees • The cirque includes a wide range of glacial and periglacial landforms. • YD advance formed three close moraine systems within the glacial cirque. • In the Early Holocene, a debris-free glacier became debris-covered. • It later formed a two-unit rock glacier, which stabilized in the Mid Holocene.