Glacial oscillations during the Bølling–Allerød Interstadial–Younger Dryas transition in the Ruda Valley, Central Pyrenees

Abstract

The Upper Garonne Basin included the largest glacial system in the Pyrenees during the last glacial cycle. Within the long-term glacial retreat during Termination-1 (T-1), glacier fluctuations left geomorphic evidence in the area. However, the chronology of T-1 glacial oscillations on the northern slopes of the Central Pyrenees is still poorly constrained. Here, we introduce new geomorphological observations and a 12-sample dataset of 10 Be cosmic-ray exposure ages from the Ruda Valley. This U-shaped valley, surrounded by peaks exceeding 2800 m a.s.l., includes a sequence of moraines and polished surfaces that enabled a reconstruction of the chronology of the last deglaciation. Following the maximum ice extent, warmer conditions prevailing at ~15-14 ka, during the Bølling-Allerød (B-A) Interstadial, favoured glacial retreat in the Ruda Valley. Within the B-A, glaciers experienced two phases of advance/stillstand with moraine formation at 13.5 and 13.0 ka. During the early Younger Dryas (YD), glacial retreat exposed the highest surfaces of the Saboredo Cirque (~2300-2350 m) at 12.7 ka. Small glaciers persisted only inside the highest cirques (~2470 m), such as in Sendrosa Cirque, with moraines stabilising at 12.6 ka. The results of this work present the most complete chronology for Pyrenean glacial oscillations from the B-A to the YD.

A continuous centennial Lateglacial-Early Holocene (15-10 cal kyr BP) palynological record from the Iberian Pyrenees and regional comparisons

“…A similar assemblage has not been found in our pollen sequence, which indicates that the LGEH vegetation was significantly different from the present. This is not surprising, as previous glaciological studies demonstrated that the site was near the snowline during the Lateglacial [9]. However, no modern pollen analogs exist on the uppermost sites close to the present snowline (∼2800 m), which indicates that Lateglacial vegetation was also different from the present, even at the highest vegetation belts.…”

“…Lateglacial-Early Holocene stratigraphy based on Greenland ice core NGRIP2[6] compared with the speleothem records from Ostolo cave (OST2), on the westernmost Pyrenean end[7] and Seso cave, on the central Pyrenees[8] (Fig.2). The glacier dynamics, as reconstructed in the Ruda valley (parallel to the Aiguamòg valley, where the record analyzed in this study lies), is indicated for reference[9]. GA, glacier advance; OD, Oldest Dryas.…”

Geomorphological record of the glacial to periglacial transition from the Bølling–Allerød to the Holocene in the Central Pyrenees: the Lòcampo cirque in the regional context

“…This study underpins the nonlinear long‐term deglaciation in the Upper Garonne Basin during the T‐1 that was proposed in earlier studies (Fernandes et al . 2017, 2021b, 2022; Oliva et al . 2021).…”

“…showed similar 10 Be exposure ages of 15.0±0.9 and 13.8±0.8 ka (Fernandes et al . 2021b). The horizontal glacial retreat was parallel to ice thinning: polished surfaces between 140 and 30 m (2380–2260 m a.s.l.)…”

“…During and following the LGM, the glacier retreated 95% of its length, reaching the cirque level by 15–14 ka, as shown by CRE dating in the Bacivèr cirque, next to Lòcampo cirque (Fernandes et al . 2021b; Oliva et al . 2021).…”