Deglaciation history at the Alpine-Mediterranean transition (Argentera-Mercantour, SW Alps) from 10Be dating of moraines and glacially polished bedrock

Y. Rolland (1, 2) , Romain Darnault (3) , Regis Braucher (4) , D.L. Bourles (4) , Carole Petit (2) , Stéphane Bouissou (2)

1 EDYTEM - Environnements, Dynamiques et Territoires de Montagne
2 GEOAZUR 7329 - Géoazur
3 IFPEN - IFP Energies nouvelles
4 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement

Estimating the extent and age of the last glacial maxima as well as the chronology of glacial recessions in various environmental contexts is key to source-to-sink studies and paleoclimate reconstructions. The Argentera-Mercantour massif being located at the transition between the Alps and the Mediterranean Sea, its deglaciation chronology can be compared to the sediment budget of the Var River marine delta. In this paper, the deglaciation is constrained by 13 new and 22 reassessed Cosmic-Ray Exposure (CRE) 10Be datings of moraines and polished crystalline bedrocks. These data allow for the first time to fully reconstruct the deglaciation history at the scale of the entire massif, in agreement with a major glacier recession at ca. 15 ka, at the onset of Bølling transition. This contribution reveals a glacier–climate relationship more sensitive to warming phases in the southern Alps highlighted by a major decrease of glaciers after ca. 15 ka. This major deglaciation is correlated with a 2.5 fold decrease of sediment discharge of rivers into the Mediterranean Sea. Main deglaciation of the massif upper slopes (2,700-2,800 m a.s.l.) occurred after the LGM at 20.8-18.6 ka, followed by the lower slopes (2,300 m a.s.l.) at 15.3-14.2 ka. Finally, the flat polished surfaces above 2,600 m a.s.l. and the zones confined within narrow lateral valleys were likely affected by progressive ice melting of remaining debris covered glaciers and moraine erosion following the Younger Dryas re-advance stage between 12 and 8-9 ka. At lower elevations, a sediment core in the Vens Lake located at 2,300 m a.s.l., shows onset of lake sedimentation at ca. 14 ka and a transition towards a vegetated environment after 8 ka. Final stabilization of moraines occurred at 5 ka, which might reflect denudation acceleration during the Holocene humid phase.

Domaines: Interfaces continentales, environnement

Y. Rolland, Romain Darnault, Regis Braucher, D.L. Bourles, Carole Petit, et al.. Deglaciation history at the Alpine-Mediterranean transition (Argentera-Mercantour, SW Alps) from 10Be dating of moraines and glacially polished bedrock. Earth Surface Processes and Landforms, 2020, 45 (2), pp.393-410. ⟨10.1002/esp.4740⟩. ⟨hal-02319675⟩