Glacial chronology and climate implications since the Penultimate Glacial Cycle in the Upper Garonne Basin, Central Pyrenees

Abstract The Pyrenean Range was intensively shaped by glaciers during the Late Pleistocene glacial cycles. The chronology of past glacial oscillations has been increasingly unveiled during the last decade, although comprehensive reviews of glacial evolution during the Late Pleistocene are still missing. Here, we review the glacial and periglacial chronology existing in the Upper Garonne Basin, which is organized in three moraine complexes at (i) the Loures-Barousse-Barbazan Basin (LBBB), (ii) valleys, and (iii) glacial cirques. The most external moraine preserved at 420–480 m asl in the LBBB unveiled the Maximum Ice Extent from the Penultimate Glacial Cycle during the MIS-6, as indicated by Cosmic-Ray Exposure ages of ca. 130 ka. During the Last Glacial Cycle, the Garonne paleoglacier reached the LBBB once again before 40 and 32 cal ka BP, marking the local Last Glacial Maximum in the Pyrenees. However, by the time of the global Last Glacial Maximum, the slopes of the Marignac Basin were already deglaciated, as evidenced by two polished surfaces dated to 21–24 ka at elevations of 520–540 m asl. Thereafter, glaciers shrank upvalleys during the last deglaciation, as shown by polished surfaces at 1860–1900 m asl in the Ruda Valley dated to 14–15 ka. The glacial retreat within the valleys was interrupted by two glacial advances or standstills during the second half of the Bølling–Allerød Interstadial, around 13.5 and 13.0 ka. During the Younger Dryas, glaciers advanced to elevations of 2370–2470 m asl within the glacial hollows, where moraines stabilized at 12.9 and 12.6 ka. Following this advance, paraglacial processes intensified, transforming the final debris-free glaciers into debris-covered glaciers and rock glaciers. The warming at the onset of the Holocene prompted the final stabilization of boulders around 11.9 ka in the relic rock glacier of Lòcampo Cirque and 7.2 ka in the debris-covered glacier of Bacivèr Cirque. This synthesis highlights the potential of the Upper Garonne Basin to serve as a key reference area for understanding the spatiotemporal evolution of glacial and periglacial dynamics in the Pyrenees throughout the Late Pleistocene and the Holocene.