Arthur Ancrenaz
email: arthur.ancrenaz@uca.fr

Régis Braucher

Emmanuelle Defive

Alexandre Poiraud

Johannes Steiger

Last glacial fluctuations in the southwestern Massif Central, Aubrac (France): first direct chronology from cosmogenic 10 Be and 26 Al exposure dating

Keywords: Late Pleistocene, glacial geochronology, cosmogenic exposure dating, moraine, plateau icefield, Massif Central, Aubrac

The chronology of the late Pleistocene glaciation in the Massif Central, France, is not well documented and there are divergent hypotheses regarding the timing of glacial events in this area. This study aims at reconstructing the chronology of late Pleistocene glacier fluctuations in the Aubrac massif. We present a new set of Be-10 and Al-26 exposure ages from twenty erratic boulders embedded in six glacial landforms. Glacial landforms were sampled to determine the timing of three glacial stades and the deglaciation of the Aubrac Mountains. These new data allowed us to constrain the timing of: (i) the Local Last Glacial Maximum, which is coeval to the early part of Marine Isotopic Stage 2 (MIS 2) (28-24 ka), and (ii) the Grandvals and Bouquincan stades, which are both coeval with the later part of MIS 2 (24-16 ka). Deglaciation occurred during Heinrich Stadial 1 (18-15.6 ka). This new direct glacial chronology is supported by regional paleoenvironmental proxies and it updates the chronostratigraphic framework available for the southwestern Massif Central. Western European atmospheric circulation changes (i.e., a southward shift in North Atlantic storm tracks and Mediterranean influences) during MIS 2 were identified as significant factors controlling glacier growth in the Aubrac Mountains as well as other glaciated mountains within the southwestern Massif Central, such as the Cantal, Margeride and Lozère mountains.

Introduction

Recent advances in glacial chronology highlight that glaciated areas in Europe did not experience their Local Last Glacial Maximums (LLGMs) synchronously during the late Pleistocene (129-11.7 ka) [START_REF] Gillespie | Asynchronous maximum advances of mountain and continental glaciers[END_REF][START_REF] Hughes | Timing of glaciation during the last glacial cycle: evaluating the concept of a global 'Last Glacial Maximum' (LGM)[END_REF]. In the western Alps [START_REF] Gribenski | Out-of-phase Late Pleistocene glacial maxima in the WesternAlps reflect past changes in North Atlantic atmospheric circulation[END_REF] and in the eastern Pyrenees [START_REF] Calvet | Recent Advances in Research on Quaternary Glaciations in the Pyrenees[END_REF] for example, the LLGM was probably not coeval with the global Last Glacial Maximum (LGM) between 27.5 and 23.3 ka, sensu [START_REF] Hughes | A stratigraphical basis for the Last Glacial Maximum (LGM)[END_REF].

LLGMs in Europe were controlled by both the North Atlantic and Mediterranean atmospheric circulation patterns, which evolve during the late Pleistocene [START_REF] Domínguez-Villar | Early maximum extent of paleoglaciers from Mediterranean mountains during the last glaciation[END_REF][START_REF] Delmas | The last maximum ice extent and subsequent deglaciation of the Pyrenees: an overview of recent research[END_REF][START_REF] Hughes | Quaternary glaciation in the Mediterranean mountains: a new synthesis[END_REF][START_REF] Monegato | The Alpine LGM in the boreal ice-sheets game[END_REF][START_REF] Gribenski | Out-of-phase Late Pleistocene glacial maxima in the WesternAlps reflect past changes in North Atlantic atmospheric circulation[END_REF][START_REF] Reixach | Climatic conditions between 19 and 12 ka in the eastern Pyrenees, and wider implications for atmospheric circulation patterns in Europe[END_REF]. This evolution is controlled by the southward displacement of the Polar Jet Front that induced reorganization of atmospheric circulations [START_REF] Florineth | Alpine Evidence for Atmospheric Circulation Patterns in Europe during the Last Glacial Maximum[END_REF][START_REF] Kuhlemann | Regional Synthesis of Mediterranean Atmospheric Circulation During the Last Glacial Maximum[END_REF][START_REF] Luetscher | North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems[END_REF]. In the Massif Central, France, the timing of LLGMs differed from one area to another, according to available relative and indirect chronologies, and thus it provides a key area to identify changes in atmospheric circulation patterns. [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF] first proposed a regional and comprehensive synthesis of late Pleistocene glacier fluctuations in the Massif Central based on geomorphological criteria, comprising delimitation of glacier extensions, the prominence of glacial features, the degree of the alteration of moraines and morphostratigraphy. The author thus identified three glaciated areas (Fig. 1), each controlled by topographic and climatic influences. The western glacier group is composed of the Cantal, Monts Dore and Cézallier coalescent glacier systems (Fig. 1). Its LLGM was in MIS 2 based on the limited weathering of glacial deposits [START_REF] Goër De Hervé | La Planèze de Saint-Flour : structure et géomorphologie glaciaire[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF]. A large glacier advance following the LLGM, locally named the Recurrence Event [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF], deposited end moraines within the main valleys of the Massif Central, followed by a phase of cirque glaciation that is only represented within the Cantal [START_REF] Valadas | Les hautes terres du Massif central français : contribution à l'étude des morphodynamiques récentes sur versants cristallins et volcaniques[END_REF]. The timing of full deglaciation is not well known, but it is associated with the Last Glacial-to-Interglacial Transition (LGIT) [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Valadas | Les hautes terres du Massif central français : contribution à l'étude des morphodynamiques récentes sur versants cristallins et volcaniques[END_REF][START_REF] Vergne | Les paysages végétaux d'Artense au Tardiglaciaire et à l'Holocène (Vegetal landscapes in the Artense region during Late-glacial and Holocene)[END_REF]. The southern glacier group was composed of the Margeride and Lozère Mount plateau icefields and by the Velay cirque glacier, that reached its LLGM extent during the MIS 2 [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF]. The Aubrac Mountains are located at the margins of the western and southern glacier groups (Fig. 1) [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF].

The eastern glacier group corresponds to the small icecap of the Forez. It reached its LLGM extent during the MIS 4 [START_REF] Etlicher | Les massifs du Forez, du Pilat et du Vivarais : régionalisation et dynamique des héritages glaciaires et périglaciaires en moyenne montagne cristalline[END_REF].

Inferences of climate change from deglacial sequences rely on direct dating tools applied to ice-marginal landforms that provide robust glacial chronology [START_REF] Kleman | A new value for the half-life of 10Be by Heavy-Ion Elastic Recoil Detection and liquid scintillation counting[END_REF][START_REF] Stokes | On the reconstruction of palaeo-ice sheets: Recent advances and future challenges[END_REF]. In particular, terrestrial cosmogenic nuclides (TCNs) have been widely applied to glacial landforms, such as end moraines, glacial deposits or subglacially eroded bedrock. Resultant exposure ages constrain the timing of the advance and decay of late Pleistocene glaciers [START_REF] Balco | Contributions and unrealized potential contributions of cosmogenic-nuclide exposure dating to glacier chronology, 1990-2010[END_REF][START_REF] Stokes | On the reconstruction of palaeo-ice sheets: Recent advances and future challenges[END_REF]Allard et al., 2021). Previous reconstruction of the late Pleistocene glaciation of the Massif Central was based on morphostratigraphic evidence and relative correlations with local and regional paleoenvironmental proxies [START_REF] Goër De Hervé | La Planèze de Saint-Flour : structure et géomorphologie glaciaire[END_REF][START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Valadas | Les hautes terres du Massif central français : contribution à l'étude des morphodynamiques récentes sur versants cristallins et volcaniques[END_REF][START_REF] Etlicher | Les massifs du Forez, du Pilat et du Vivarais : régionalisation et dynamique des héritages glaciaires et périglaciaires en moyenne montagne cristalline[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. Indirect paleoenvironmental proxies, such as pollen sequences [START_REF] Etlicher | Le Haut Forez (Massif Central, France) après le pléniglaciaire würmien : environnement et tephra du volcan de La Nugère[END_REF][START_REF] Reille | History of the Würm and Holocene vegetation in western Velay (Massif Central, France): a comparison of pollen analysis from three corings at Lac du Bouchet[END_REF][START_REF] Ponel | Lateglacial and Early Flandrian Coleoptera from La Taphanel, Massif Central, France: Climatic and Ecological Implications[END_REF][START_REF] Vergne | Les paysages végétaux d'Artense au Tardiglaciaire et à l'Holocène (Vegetal landscapes in the Artense region during Late-glacial and Holocene)[END_REF][START_REF] Gandouin | Environmental and climate reconstruction of the late-glacial-Holocene transition from a lake sediment sequence in Aubrac, French Massif Central: Chironomid and diatom evidence[END_REF][START_REF] Ponel | Novel insights from coleopteran and pollen evidence into the Lateglacial/Holocene transition in Aubrac, French Massif Central[END_REF] or sedimentological stratigraphies [START_REF] Valadas | Les hautes terres du Massif central français : contribution à l'étude des morphodynamiques récentes sur versants cristallins et volcaniques[END_REF][START_REF] Laville | Le dernier interglaciaire et le cycle climatique würmien dans le Sud-Ouest et le Massif Central Français[END_REF][START_REF] Vliet-Lanoë | La paléogéographie de l'Europe centre-occidentale au Weichsélien. Réflexions sur les paléosols et l'inertie climatique : la place du Massif Central[END_REF], are available and provide indirect chronological boundaries for glacier fluctuations. However, resulting chronologies differ for the various glaciated areas of the Massif Central (cf. [START_REF] Etlicher | La déglaciation würmienne dans le Massif Central français, le point des travaux récents / The Würmian déglaciation in the French Massif-Central, review of recent works[END_REF][START_REF] Defive | L'englacement quaternaire du Massif central, in: Histoire de la découverte géologique du Massif central français[END_REF]. Hence, without direct dating of glacial deposits, important uncertainties and inconsistencies remain, especially concerning the timing of both the LLGM and full deglaciation. During the last glacial cycle, two periods, locally named the Early and Late Pleniglacial (sensu [START_REF] Laville | Le dernier interglaciaire et le cycle climatique würmien dans le Sud-Ouest et le Massif Central Français[END_REF][START_REF] Vliet-Lanoë | La paléogéographie de l'Europe centre-occidentale au Weichsélien. Réflexions sur les paléosols et l'inertie climatique : la place du Massif Central[END_REF], that correlate with Marine Isotopic Stage 4 (MIS 4;71-57 ka;Lisiecki and Raymo, 2005) and MIS 2 (29-11.7 ka;[START_REF] Lisiecki | A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records[END_REF], respectively, were recognised as two major phases of glacier growth in the Massif Central [START_REF] Etlicher | La déglaciation würmienne dans le Massif Central français, le point des travaux récents / The Würmian déglaciation in the French Massif-Central, review of recent works[END_REF][START_REF] Defive | L'englacement quaternaire du Massif central, in: Histoire de la découverte géologique du Massif central français[END_REF]. In general, in the literature and according to the considered glaciated area, the LLGM is attributed to one of these two periods.

The objectives of the present study were to assess the existing relative glacial chronologies [START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Goër De Hervé | Notice explicative, Carte géol[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF] and to provide the first direct dating chronology for fluctuations of the Aubrac plateau icefield. In that respect, key glacial landforms identified by the morphostratigraphy are targeted. In combination with an extensive literature review on glacier fluctuations within the Massif Central, a revised and comprehensive chronostratigraphic framework is proposed that focuses on the southwestern Massif Central. Furthermore, inferences of glacier fluctuations from regional paleoclimates, especially favourable glacier-growth phases, are proposed.

Study area

The Aubrac Mountains, in the south western Massif Central, extend over 1300 km 2 and culminate at the Signal de Mailhebiau at 1467 m above sea level (a.s.l.) (Fig. 1). Three geomorphological subareas divide the Aubrac Mountains (Fig. 2). The Aubrac Highlands are composed of a SSE to NNW alignment of rounded summits composed of Miocene volcanic rocks [START_REF] Goër De Hervé | Le volcanisme de l'Aubrac (Massif central) : un bref épisode basaltique (250 000 ans) au Miocène supérieur (7,5 Ma)[END_REF][START_REF] Leibrandt | Reconstitution de l'évolution morpho-structurale et de la dynamique éruptive du massif du Cantal: relation avec la distribution spatio-temporelle du volcanisme du Massif Central[END_REF]. This topographic ridge extends along 25 km with an elevation decrease from 1400 m in the SSE to 1200 m in the NNW. The Aubrac Highlands separate the two following subareas: the Aubrac Plateau to the northeast and Aubrac Valleys to the southwest (Fig. 2). The Aubrac Plateau, with elevations between 1000 and 1200 m, formed within granitic Carboniferous rocks [START_REF] Couturié | Le massif granitique de la Margeride (Massif Central Français)[END_REF]. The Bès valley oriented from SSW to NNE represents the major hydrographic basin that drains this subarea. In addition, the Aubrac Valleys, incised into the margins of the highlands, are deep and steep valleys that are 10 to 20 km long and cut in metamorphic rocks.

The Aubrac Mountains constitute the first orogenic obstacle that is encountered by atmospheric lowpressure systems pushed by the westerlies from the North Atlantic into the European continent. Current precipitation is characterised by a maximum during winter and a minimum during summer [START_REF] Jubertie | Les excès climatiques dans le Massif central français[END_REF]. Precipitation of more than 1500 mm.y -1 was recorded for the Aubrac Highlands at Nasbinals, 1284 m a.s.l. (ID station: 48104002; https://donneespubliques.meteofrance.fr). Snowfall and snow cover during winter highlights the role of the Aubrac Highlands as a preferential area for snow accumulation [START_REF] Valadas | Englacement quaternaire et enneigement actuel de l'Aubrac et du Cantal[END_REF].

The late Pleistocene Aubrac glaciation

Evidence for a plateau icefield glaciation

The topographic setting of the Aubrac Mountains exert a strong control on the spatial extension and dynamics of the former plateau icefield. The plateau icefield accumulation zone was centred on the Aubrac Highlands (Fig. 2), with an estimated thickness between 200 and 300 m [START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. The ice divide of the plateau icefield followed the SSE-NNW orientated Aubrac Highlands and separated two distinct zones of glacial dynamics. The Aubrac Plateau that was situated to the east of the ice divide and was predisposed to the establishment of a plateau glacier because of its relatively low-lying topography (Figs. 23). This plateau glacier is recorded by ice-scoured knock and lochan topography, with bedrock forming roches moutonnées and rock basins partly infilled by glacial or associated sediments [START_REF] Poizat | Sédimentation et phénomènes glaciaires et fluvio-glaciaires en Aubrac[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Goër De Hervé | Notice explicative, Carte géol[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. According to the orientation of roches moutonnées [START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF] and the dispersion of erratics [START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF], the Bès valley was the preferential drainage route for the Aubrac plateau glacier. In the Aubrac Valleys, isolated glacial deposits were associated to phases of glacier retreats and overdeepened morphologies were recognised and associated with subglacial erosion by outlet valley glaciers (Rousset, 1963(Rousset, , 1970;;[START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF].

Local plateau icefields are sensitive to climatic changes when the regional Equilibrium Line Altitude (ELA) is close to the plateau elevation. Indeed, climatic changes inducing variations in ELAs lead to substantial changes in the distribution of glacier ablation/accumulation zones, i.e. small increase or decrease of the ELA induce significant glacier advance or retreat in response to strong modification of the accumulation/ablation zones distribution [START_REF] Manley | On the Occurrence of Ice Domes and Permanently Snow-Covered Summits[END_REF][START_REF] Rea | Plateau icefields as contributing areas to valley glaciers and the potential impact on reconstructed ELAs: a case study from the Lyngen Alps, North Norway[END_REF][START_REF] Rea | Plateau Icefield Landsystems[END_REF][START_REF] Boston | A Younger Dryas plateau icefield in the Monadhliath, Scotland, and implications for regional palaeoclimate[END_REF]. This observation is in accordance with the landform assemblage identified in the Aubrac Plateau, indicating rapid and in situ glacier downwasting during deglaciation (Section 2.3) driven by small changes in the ELA. The accumulation zone of the Aubrac plateau icefield was located along the topographic ridge of the Aubrac Highlands [START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF].

The mass balance adjustment of this zone is argued to control the former glacier extent in the Aubrac Plateau and in Aubrac Valleys [START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. A glacier advance (or retreat) in the Aubrac Plateau was coeval with a glacier advance (or retreat) in the Aubrac Valleys in response to the thickening (or thinning) of the glacier accumulation zone in the Aubrac Highlands.

Deglaciation sequence in the Aubrac Plateau

The majority of glacial landforms in the Aubrac Mountains are located on the Aubrac Plateau (Figs. 23). Three distinct glacier advances were reconstructed in previous studies from investigations of landform assemblages (Table 1, Fig. 3). First, the extent of the LLGM was defined by the maximum extent of volcanic erratic boulders on the Aubrac Plateau (Figs. 2,3A) that matched the maximal extent of glacial sediments [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Goër De Hervé | Notice explicative, Carte géol[END_REF]. On this basis, the LLGM outer limit matched the occurrence of tors or saprolite associated with periglacial environments [START_REF] Goër De Hervé | Notice explicative, Carte géol[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. Moreover, the Allatieux end moraine (1199 m), which corresponds to a group of three discontinuous ridges that are one hundred metres long, demarcates the LLGM in the Aubrac Plateau (Table 1; Fig. 4A.) [START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. This landform matches (i) the maximal extent of erratic boulder dispersion and (ii) the occurrence of periglacial features such as bloc fields or tors.

The fresh aspect with no boulder weathering rind and the well preserved glacial sediments support an interpretation of that the LLGM correlates with the global LGM [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF].

The end of the LLGM is characterised by a pronounced retreat of the Aubrac plateau icefield (Fig. 3C).

An early still-stand is recorded in the Bès valley at the Longevialle end moraine (1040 m a.s.l.), composed of a group of parallel and subdued ridges with pronounced crest attenuation (Table 1; Fig. 4B). It is located only 2 km behind the maximum erratic boulder dispersion that demarcates the LLGM limit and also behind fluvio-glacial sediments deposited during LLGM retreat. Subsequent glacier recession is recorded by numerous, well-preserved glacial, glacio-fluvial and glacio-lacustrine sediment landform assemblages that were identified within the Aubrac Plateau [START_REF] Poizat | Sédimentation et phénomènes glaciaires et fluvio-glaciaires en Aubrac[END_REF][START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Goër De Hervé | Notice explicative, Carte géol[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. These sediments were associated with the formation of ice-dammed lakes which infilled the major depressions of the plateau and comprise kame hills and proglacial outwash. These landforms suggest in situ glacier downwasting [START_REF] Livingstone | The Brampton kame belt and Pennine escarpment meltwater channel system (Cumbria, UK): Morphology, sedimentology and formation[END_REF][START_REF] Lovell | Complex kame belt morphology, stratigraphy and architecture[END_REF]. Indirect chronological control on this phase of deglaciation was obtained from 14 C dating of sediment sequences infilling depressions along deglaciated areas of the Aubrac Mountains. At the Roustières site, located in the Aubrac Plateau inside the LLGM limit (see Fig. 2 for the location), proglacial lake sediments are dated to the Oldest Dryas between 17.7 and 16.6 ka [START_REF] Gandouin | Environmental and climate reconstruction of the late-glacial-Holocene transition from a lake sediment sequence in Aubrac, French Massif Central: Chironomid and diatom evidence[END_REF][START_REF] Ponel | Novel insights from coleopteran and pollen evidence into the Lateglacial/Holocene transition in Aubrac, French Massif Central[END_REF]. However, the base of the sequence was not reached and thus these ages provide only a minimum age constraint.

A glacier re-advance interrupted this retreat sequence and truncating these sediments and landforms and depositing till. This glacial event is referred to as Grandvals Stade (Fig. 3C) [START_REF] Poizat | Sédimentation et phénomènes glaciaires et fluvio-glaciaires en Aubrac[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. It is demarcated in the Bès valley by the Grandvals end moraine (1059 m a.s.l.) (Table 1; Fig. 5A). This landform is divided into two features: one on each valley flank. Fluvioglacial deposits associated with the Grandvals end moraine formed proglacial outwash that aggraded overLLGM deposits. After the glacier retreats, the Bès River deeply incised the Grandvals end moraine and constructed fluvial terraces [START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. Other end moraines in the Aubrac Plateau encompassed truncated LLGM deposits and were correlated to the Grandvals stade [START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. These include the Rateylou end moraine. It is located in a flat depression between the Bès and the Rimeize catchments (Table 1; Fig. 5B). This landform is composed of two subdued ridges and is correlated with the Grandvals stade.

A final glacier advance in the Bès valley is recorded by the Bouquincan end moraine that is located upvalley from the Grandvals end moraine (Table 1; Fig. 3B) [START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. This end moraine contains fluvio-glacial sediments deformed by glacio-tectonic processes, interpreted as the result of a glacier advance in the Bès valley. All glacial deposits that were identified in the Aubrac Highlands were associated with the final plateau icefield decay. For example, the Bonnecombe till demarcated the very last deglaciation phase as it is located at the Bonnecombe pass (1340 m a.s.l.), one of the most elevated area of the Aubrac Mountains.

The Aubrac plateau icefield was a climatically-sensitive system located between the western and southern sectors of the Massif Central. Three distinct groups of end moraines record three glacier advances in the region, especially along the Bès valley (see section 3.2), but the absolute ages of these moraines (and thus the associated advances) is poorly constrained. This paper addresses this through TCN dating of end moraines and erratic boulders and in doing so establishes, for the first time, a direct chronological framework for the late Pleistocene glacial history of the Aubrac Mountains.

4 Be-10 and Al-26 exposure dating

Sampling strategy, collection and preparation

This study aims to determine the timing of three main glacier advances, as well as the timing of deglaciation in the Aubrac Mountains (section 3.2). Glacial landforms and deposits in the identified from the literature were checked in the field and candidates for TCN dating selected according to two requirements. First, glacial landforms should be clearly identified by morphostratigraphic evidence In that respect, end moraines were especially targeted [START_REF] Kleman | A new value for the half-life of 10Be by Heavy-Ion Elastic Recoil Detection and liquid scintillation counting[END_REF]. Secondly, the glacial landform or deposit should match prerequisites for sampling, especially the availability of moraine boulders and low post-depositional disturbance from natural processes or anthropogenic activities (Figs.

4, 5, and 6).

Sample collection was guided by recommendations established elsewhere [START_REF] Putkonen | Accuracy of cosmogenic ages for moraines[END_REF]Dunai, 2010;[START_REF] Heyman | Boulder heightexposure age relationships from a global glacial 10Be compilation[END_REF]. The availability of dateable moraine boulders limited the number of samples per landform. For subdued end moraines, three samples were collected when available [START_REF] Putkonen | Accuracy of cosmogenic ages for moraines[END_REF]. Tall boulders with their bases broadly embedded in the landform were targeted [START_REF] Heyman | Boulder heightexposure age relationships from a global glacial 10Be compilation[END_REF]. Rock samples with a thickness of between one and three centimetres were obtained from top and flat surfaces of moraine boulders, using a hammer and a chisel.

Samples were prepared for the extraction of Be-10 and Al-26 [START_REF] Brown | Examination of surface exposure ages of Antarctic moraines using in situ produced 10Be and 26Al[END_REF][START_REF] Merchel | An Update on Radiochemical Separation Techniques for the Determination of Long-Lived Radionuclides via Accelerator Mass Spectrometry[END_REF]. Rock samples were crushed and sieved. A grain size between 0.25 and 1 mm was chosen for further analysis. After magnetic separation using a Frantz Barrier separator, the nonmagnetic grains (including quartz) were subjected to leaching with H2SiF6 and HCl to eliminate non-quartz minerals.

Three partial dissolutions were performed with HF to eliminate atmospheric 10 Be. According to [START_REF] Merchel | Towards more precise 10Be and 36Cl data from measurements at the 10-14 level: Influence of sample preparation[END_REF], ~0.15 g of a homemade (3025±9 ppm) 9 Be solution was then added to the solution to fix the 10 Be/ 9 Be ratio. To determine if an 27 Al spike is needed, natural concentrations of 27 Al were measured in liquid aliquots by inductively coupled plasma-optical emission spectrometry (ICP-OES, Thermo Icap6500). Quartz was totally dissolved in 40% HF solution. Afterwards, beryllium and aluminium were extracted by successive anion and cation resins. Finally, the hydroxides Be(OH)2 and Al(OH)3 were heated at 800°C for one hour. The resulting powders were mixed with niobium (BeO) or silver (Al2O3).

All 10 Be and 26 Al measurements were performed at the French Acceleratory Mass Spectrometry (AMS) National Facility "ASTER" located at CEREGE in Aix-en-Provence, France [START_REF] Arnold | The French accelerator mass spectrometry facility ASTER: Improved performance and developments[END_REF]. Be-10 and Al-26 were determined for all samples except for AU31, AU32 and AU33 for which only Be-10 measurements are available. Be-10 data were adjusted to the ASTER in-house standard, "STD11", with a Be-10/Be-9 ratio of (1.191±0.013)x10 -11 [START_REF] Braucher | Preparation of AS-TER in-house 10Be/9Be standard solutions[END_REF] and the Be-10 half-life of (1.387±0.0012)x10 6 years [START_REF] Chmeleff | Determination of the 10Be half-life by multicollector ICP-MS and liquid scintillation counting[END_REF][START_REF] Kleman | A new value for the half-life of 10Be by Heavy-Ion Elastic Recoil Detection and liquid scintillation counting[END_REF]. Al-26/Al-27 ratios were calibrated with an ASTER in-house standard, "SM-AL-11", with a ratio of 7.401±0.064x10 -12 (Merchel and Bremser, 2004) assuming an Al-26 half-life of 7.05±0.17x10 5 years [START_REF] Samworth | Beta Decay of the 26 Al Ground State[END_REF].

The parameters above imply an Al-26/Be-10 spallation production ratio of ~6.61±0.52. Reported analytical uncertainties include counting statistics, machine stability (~0.5% for 10 Be; [START_REF] Arnold | The French accelerator mass spectrometry facility ASTER: Improved performance and developments[END_REF], and blank correction. The Be-10/Be-9 and Al-26/Al-27 blank ratios were 2.45x10 -15 (± 29%) and 9.00x10 -16 (± 100%), for AU01 to AU17 samples respectively. The Be-10/Be-9 blank ratio was 2.60x10 - 15 (± 15%) for theAU31, AU32 and AU33 samples.

Minimum Exposure Age (MEA) calculation

Be-10 and Al-26 exposure ages were calculated using the CHRONUS-Earth online calculator v.3 (Balco et al., 2008) (http://stoneage.ice-d.org/math/v3/v3_age_in.html). Cosmogenic Be-10 and Al-26 production rates at Sea Level and High Latitudes (SLHL) from spallation were computed from default calibration datasets from [START_REF] Borchers | Geological calibration of spallation production rates in the CRONUS-Earth project[END_REF], with: 4.132±0.218 at.g -1 .y -1 for Be-10 and 29.950±2.955 at.g -1 .y -1 for Al-26. Production rates at SLHL are scaled using the Lal-Stone time corrected scaling scheme (Lal et al., 1991;Stone, 2000), the ERA40 atmosphere model and the magnetic field reconstruction from Lifton (2016). Corrections for topographic shielding were applied following Dunai (2010) and using the inclination of the visible horizon from each sample point extracted from a Digital Elevation Model (DEM) in GIS software (ArcGis 10.3v) and compiled in Table 2. The rock density was set to 2.65 g.cm -2 for all samples (Table 2). Contribution from muons were calibrated according to Balco (2017).

Calculated exposure ages for a given nuclide concentration is named the Minimum Exposure Age (MEA) because: (i) no correction for post-glacial denudation nor for snow cover were applied, and (ii) simple exposure histories, without pre-exposure to cosmic rays, were assumed (see section 5.2 for more details). Hereafter, MEAs were expressed with their external uncertainty that includes analytical uncertainty and production rate uncertainty. In order to compare Be-10 and Al-26 MEAs obtain from a glacial landform, for MEA groups with n ≤ 3, the reduced chi square statistic (𝑋 𝑅 2 ) was used. Only Be-10 MEAs were compared for the Bonnecombe site. For a MEA group with a 𝑋 𝑅 2 ≤ 1, an uncertaintyweighted mean was calculated with the standard deviation of the uncertainty-weighted mean. For MEA groups with a 𝑋 𝑅 2 > 1, the sample with the farthest MEA from the uncertainty-weighted mean was manually rejected and interpreted as an outlier. Outliers are repeatedly rejected until we obtained a 𝑋 𝑅 2 ≤ 1 or we obtained a MEA group with n < 3 for which no uncertainty-weighted mean was calculated.

Manually rejected MEAs were interpreted as the effect of geomorphologic processes and are discussed in section 5.2 below.

Results and interpretations

Minimum Exposure Ages

Twenty moraine boulders were sampled from six different glacial landforms. Resultant cosmogenic nuclide measurements and MEAs, with their external uncertainty, were compiled in Tables 2 and3 3).

Only the Al-26 MEA from the AU14 sample was interpreted as an outlier. Four moraine boulders embedded in two features composing the Rateylou end moraine (AU03, AU04, AU05 and AU06) gave scattered MEAs from 2.17±0.41 to 20.55±1.84 ka (Table 3; Figs. 5B and6). No uncertainty-weighted mean was calculated. In addition, two isolated erratic boulders at the Rateylou site (AU01 and AU02)

were sampled near the end moraine (Fig. 5B) and MEAs ranged from 6.55±0.65 to 21.48±1.86 ka. At the Bouquincan end moraine, three samples (AU07, AU08 and AU09) were taken from boulders with low heights: < 0.5 m above the ground (Fig. 3B). Results ranged from 6.84±1.41 to 18.27±1.66 ka. An uncertainty-weighted mean of 16.59±0.9 ka was calculated with rejection of the AU09 sample. Finally, samples AU31, AU32 and AU33 are collected from moraine boulders embedded in the Bonnecombe glacial deposit (Figs. 5C and6). Only 10 Be MEAs are available, and calculated MEAs are 18.66±1.60 (AU31), 16.60±1.43 (AU32) and 16.68±1.48 ka (AU33), with a calculated 10 Be uncertainty-weighted mean of 16.64±1.03 ka.

Glacial landform age

The distribution of exposure ages on end moraines often displays scattered results for the same landform [START_REF] Heyman | Too young or too old: Evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages[END_REF][START_REF] Applegate | Improved moraine age interpretations through explicit matching of geomorphic process models to cosmogenic nuclide measurements from single landforms[END_REF]. Two common explanations are identified (see [START_REF] Heyman | Too young or too old: Evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages[END_REF]: incomplete exposure and the pre-exposure. Boulders with incomplete exposure tend to underestimate ages for end moraine formation. This generally reflects post-depositional processes, such as erosion (e.g. moraine matrix erosion), leading to the landform lowering and smoothing and to boulder exhumation. Exhumed boulders by post-depositional processes, were exposed during a shorter period than the true landform age [START_REF] Zreda | Cosmogenic 36 Cl accumulation in unstable landforms: 2. Simulations and measurements on eroding moraines[END_REF][START_REF] Putkonen | Accuracy of cosmogenic ages for moraines[END_REF][START_REF] Putkonen | Degradation of unconsolidated Quaternary landforms in the western North America[END_REF][START_REF] Chevalier | Constraints on the late Quaternary glaciations in Tibet from cosmogenic exposure ages of moraine surfaces[END_REF][START_REF] Heyman | Too young or too old: Evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages[END_REF][START_REF] Palacios | The challenging application of cosmogenic dating methods in residual glacial landforms: the case of Sierra Nevada (Spain) Geomorphology[END_REF][START_REF] Allard | Late Pleistocene glaciers in Greece: A new 36Cl chronology[END_REF]. Then, boulder with incomplete exposure the end moraine depositionThis is the case for outliers with younger MEAs than the uncertainty-weighted mean: AU09 (Table 3; Fig. 7). AU01, AU03 and AU04, from the two Rateylou sites, provided Holocene MEAs (11.7 ka to present) that were younger than expected and interpreted as moraine boulders with incomplete exposure histories (Table 3; Fig. 7). The proximity with quarries (> 100 m; Fig. 5C) could lead to potential modifications of the glacial landform morphology, especially exhumation of buried boulders. For the AU14 moraine boulder, only the Al-26 MEA was interpreted as an outlier since the Be-10 measurement is coherent for the landform age (Table 3; Fig. 7).

Conversely, moraine boulders with pre-exposure provide overestimated ages for moraine deposition due to inherited cosmogenic nuclides from a previous episode(s) of exposure [START_REF] Heyman | Too young or too old: Evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages[END_REF]. Preexposed boulders were estimated to account to 3% of exposure ages from datasets analysed in [START_REF] Putkonen | Accuracy of cosmogenic ages for moraines[END_REF]. In our dataset, only one moraine boulder with a much older MEA than others was identified: AU11 (Table 3; Fig. 7). As this moraine boulder was associated with a glacial landform inside the LLGM extent, it was interpreted as an overestimated MEA due to cosmogenic nuclide inheritance.

Geomorphological context provides a strong control on processes affecting moraine boulder exposure history and MEA scattering [START_REF] Palacios | The challenging application of cosmogenic dating methods in residual glacial landforms: the case of Sierra Nevada (Spain) Geomorphology[END_REF]Tompkins et al., 2021). In the Aubrac Mountains, post-depositional erosion of end moraines is argued to be low because: (i) subdued ridges were poorly affected by post-depositional processes such as run-off or slope destabilization [START_REF] Putkonen | Accuracy of cosmogenic ages for moraines[END_REF] and (ii) the sedimentological composition of these glacial landforms, dominated by sand, gravel and boulders [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF], favoured end moraine stabilization (Tompkins et al., 2021). These local geomorphological settings were concordant with a rapid stabilization of glacial landforms after their deposition. As a consequence, a MEA cluster and its uncertainty-weighted mean is argued to best represent the age of the moraine stabilisation [START_REF] Allard | Late Pleistocene glaciers in Greece: A new 36Cl chronology[END_REF][START_REF] Tomkins | Moraine crest or slope: An analysis of the effects of boulder position on cosmogenic exposure age[END_REF].

The age of the end moraine deposition is best represented by the oldest exposure age obtained on the glacial landform [START_REF] Zreda | Cosmogenic 36 Cl accumulation in unstable landforms: 2. Simulations and measurements on eroding moraines[END_REF][START_REF] Putkonen | Accuracy of cosmogenic ages for moraines[END_REF][START_REF] Briner | Cosmogenic exposure dating of late Pleistocene moraine stabilization in Alaska[END_REF][START_REF] Chevalier | Constraints on the late Quaternary glaciations in Tibet from cosmogenic exposure ages of moraine surfaces[END_REF][START_REF] Heyman | Too young or too old: Evaluating cosmogenic exposure dating based on an analysis of compiled boulder exposure ages[END_REF][START_REF] Chevalier | Deciphering old moraine age distributions in SE Tibet showing bimodal climatic signal for glaciations: Marine Isotope Stages 2 and 6[END_REF]. Considering this interpretation, glacial landform stabilization (best approximated by the corresponding uncertainty-weighted mean) occurred rapidly after the landform deposition (best approximated by the corresponding oldest MEA) in the Aubrac Mountains (Table 3; Fig. 7).

Three distinct glacial stades in the Aubrac Mountains

The LLGM is dated at the Allatieux end moraine to 25.41 ± 2.14 ka (Table 3). The Aubrac plateau icefield covered approximately 500 km 2 , with outlet valley glaciers in the Aubrac Valleys of 6 to 10 km in length (Figs. 2 and8) and an ELA estimated at 1331 ± 10 m a.s.l. [START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. Eastward, glacier margins terminate against topographic constraints (i.e., reverse slopes), which restricted plateau icefield extension (Figs. 2, 3A and 8). After the LLGM, the Aubrac plateau icefield retreated first back onto the plateau. A first glacial stillstand is documented by the Longevialle end moraine dated to 24.31±2.7 ka (Table 3). According to stratigraphic observations, the extension of glacier-free areas related to this glacier retreat can be estimated [START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF], and the deglaciated area after the LLGM is at least half that of the LLGM area (Figs. 89). The Grandvals stade is dated at three sites: the Grandvals end moraine (21.55±2.05 ka), the Rateylou end moraine (20.55±1.84) and the Rateylou isolated erratics (21.48±1.86 ka) (Tables 1 and3, Figs. 789).

These ages overlap, suggesting that these landforms are probably related to the same glacier advance [START_REF] Kirkbride | Correlation of Late Quaternary moraines: impact of climate variability, glacier response, and chronological resolution[END_REF][START_REF] Heyman | Boulder heightexposure age relationships from a global glacial 10Be compilation[END_REF], as suggested by the morphostratigraphic framework established for the Aubrac Mountains (Section 2.3). The last glacial stade is documented by the Bouquincan end moraine and dated to 18.27±1.66 ka. During this stade, the plateau icefield was restricted to the Aubrac Highlands with outlet glaciers confined to the main head valleys (Fig. 8). Steps of the following glacier retreat are not recognised in the field. Subsequent stillstands during glacier retreat were not recognized but tills were identified over the Aubrac Highlands (Goër de [START_REF] Goër De Hervé | Notice explicative, Carte géol[END_REF]. The Bonnecombe till is one of these deposits associated with the Aubrac plateau icefield decay (Table 1; Fig. 8). The ages of both the Bouquincan stade and the Bonnecombe till (18.66±1.60 ka)

suggest a rapid deglaciation. This trend is supported by paleoenvironmental reconstruction from the Roustières site (see Figs. 2 and8) [START_REF] Gandouin | Environmental and climate reconstruction of the late-glacial-Holocene transition from a lake sediment sequence in Aubrac, French Massif Central: Chironomid and diatom evidence[END_REF][START_REF] Ponel | Novel insights from coleopteran and pollen evidence into the Lateglacial/Holocene transition in Aubrac, French Massif Central[END_REF], where periglacial conditions in the Aubrac Plateau were active between 17.7 and 16.6 ka, with persistent winter snow cover in the Aubrac Highlands.

Chronological update of the southwestern Massif Central chronostratigraphy: correlations and climatic inferences

The direct glacial chronology presented in this work is in good agreement with the existing morphostratigraphic framework established in the Aubrac Mountains (Section 2.3) and provides robust chronological control of past fluctuations of the Aubrac plateau icefield. Considering that the Aubrac plateau icefield is a valuable climatic proxy (Section 2.2), this new chronology highlights the main climatic conditions for the southwestern Massif Central and allows us to update and revise the regional chronostratigraphy.

The GS-3: establishment of full glacial conditions

In the western Massif Central, a successive and gradual climatic deterioration with increasingly colder temperatures started with the onset of MIS 2 [START_REF] Laville | Le dernier interglaciaire et le cycle climatique würmien dans le Sud-Ouest et le Massif Central Français[END_REF] at ~29 ka [START_REF] Lisiecki | A Pliocene-Pleistocene stack of 57 globally distributed benthic δ18O records[END_REF].

A cold culminationis recorded and primarily associated to the beginning of the MIS 2 [START_REF] Laville | Le dernier interglaciaire et le cycle climatique würmien dans le Sud-Ouest et le Massif Central Français[END_REF], and then correlated to approximately 25 ka [START_REF] Vliet-Lanoë | La paléogéographie de l'Europe centre-occidentale au Weichsélien. Réflexions sur les paléosols et l'inertie climatique : la place du Massif Central[END_REF]. Dating of the infilling of thermal contraction cracks in discontinuous permafrost in the Aquitaine basin resulted in ages between 27 and 25.5 ka BP and suggests a climatic downturn at the beginning of MIS 2 [START_REF] Bertran | Distribution and chronology of Pleistocene permafrost features in France: Database and first results: Pleistocene permafrost features in France[END_REF]. This event is synchronous with the LLGM in the Aubrac Mountains, dated to 25.41±2.14 ka. This is also coeval with the global LGM between 27.5 and 23.3 ka, sensu [START_REF] Hughes | A stratigraphical basis for the Last Glacial Maximum (LGM)[END_REF], Greenland Glacial Stadial 3 (GS-3) between 27.5 and 23.3 ka (Rasmussen et al., 2014), Heinrich Stadial 2 (HS2) between 26.5 and 24.3 ka (Sanchez Goñi and Harrison, 2010) and finally the δ 18 O minimum of the 7H record from the Sieben Hengste cave (northern Alps) centred on 25.3 ka [START_REF] Luetscher | North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems[END_REF].

Moisture advection from the Mediterranean Sea, enhanced by cyclogenesis, led to favourable conditions for glacier growth in the circum-Mediterranean mountains [START_REF] Florineth | Alpine Evidence for Atmospheric Circulation Patterns in Europe during the Last Glacial Maximum[END_REF][START_REF] Kuhlemann | Regional Synthesis of Mediterranean Atmospheric Circulation During the Last Glacial Maximum[END_REF][START_REF] Luetscher | North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems[END_REF][START_REF] Monegato | The Alpine LGM in the boreal ice-sheets game[END_REF], such as the Pyrenees [START_REF] Delmas | Palaeogeography and 10Be exposure-age chronology of Middle and Late Pleistocene glacier systems in the northern Pyrenees: Implications for reconstructing regional palaeoclimates[END_REF][START_REF] Reixach | Climatic conditions between 19 and 12 ka in the eastern Pyrenees, and wider implications for atmospheric circulation patterns in Europe[END_REF], the Alps [START_REF] Monegato | The Alpine LGM in the boreal ice-sheets game[END_REF][START_REF] Wirsig | Dating the onset of LGM ice surface lowering in the High Alps[END_REF] and the Iberian Peninsula [START_REF] Domínguez-Villar | Early maximum extent of paleoglaciers from Mediterranean mountains during the last glaciation[END_REF].These cold and wet climatic conditions related to enhanced Mediterranean influences probably triggered the LLGM in the Aubrac Mountains, as well a simultaneous LLGM in other glaciated mountains of the southwestern Massif Central (Cantal, Margeride and Lozère Mountain). In this area, gelifluction and gelifraction deposits on non-glaciated slopes should be correlated to this period (Fig. 9) because effective gelifluxion or gelifraction processes are supported by cold and wet climatic conditions [START_REF] Valadas | Les hautes terres du Massif central français : contribution à l'étude des morphodynamiques récentes sur versants cristallins et volcaniques[END_REF] that reached their optimum during this period The question of an asynchronous LLGM between the southwestern (Aubrac, Cantal, Margeride and Lozère Mountain) and the eastern Massif Central remains.

6.1.2 The GS-2.1: aridity, a limiting factor for glacier growth

After the global LGM, full glacial conditions characterised by a cold and arid climate [START_REF] Laville | Le dernier interglaciaire et le cycle climatique würmien dans le Sud-Ouest et le Massif Central Français[END_REF][START_REF] Reille | History of the Würm and Holocene vegetation in western Velay (Massif Central, France): a comparison of pollen analysis from three corings at Lac du Bouchet[END_REF][START_REF] Vliet-Lanoë | La paléogéographie de l'Europe centre-occidentale au Weichsélien. Réflexions sur les paléosols et l'inertie climatique : la place du Massif Central[END_REF] prevailed across the whole Massif Central during GS-2. 1 (22.9 to 14.7 ka;Rasmussen et al., 2014). For example, at the Haute-Laugerie site (44°57′11″ N; 1°00′12″E), reconstructed anomalies for mean annual precipitation are -800 mmy -1 and -7.4 to -4.7 °C for mean air temperatures at ~21 ka [START_REF] Lécuyer | Temperature and precipitation regime in LGM human refugia of southwestern Europe inferred from δ13C and δ18O of large mammal remains[END_REF]. These data are comparable to those reconstructed from the Lake Bouchet sequence (see Fig. 1 for location), with -6 °C for the annual temperature anomaly and -772 mm for the annual precipitation anomaly (Peyron et al. 1998). Between ~24 to 17 ka, the Aubrac plateau icefield was in recession reflectingcold and dry climatic conditions in the Massif Central. It is suggested here that the aridity recorded in the Aquitaine Basin and in the Massif Central was the limiting factor for glacier growth during this period. In the Alps, the progressive starvation of Mediterranean moisture triggered glacier recession (Luestcher et al., 2015;Wirsig et al., 2016 and references therein). On non-glaciated slopes of the southwestern Massif Central, reduced gelifluction and gelifraction processes were associated with this period and highlight the climatic aridity [START_REF] Valadas | Les hautes terres du Massif central français : contribution à l'étude des morphodynamiques récentes sur versants cristallins et volcaniques[END_REF][START_REF] Vliet-Lanoë | La paléogéographie de l'Europe centre-occidentale au Weichsélien. Réflexions sur les paléosols et l'inertie climatique : la place du Massif Central[END_REF][START_REF] Degeai | Impacts environnementaux sur l'érosion des sols au Pléistocène supérieur et à L'holocène dans le cratère de maar du lac du Bouchet (Massif central, France)[END_REF]) (Fig. 9). However, two glacier advances at this time, the Grandvals stade (21.55±2.05 ka) and the Bouquincan stade (18.27±1.84 ka), indicated two phases of glacier favourable climatic conditions. Important glacier advances in the Alpine foreland at 21-20 ka were reported (Wirsig et al., 2016 and references therein). For example, the Tagliamento lobe (Italy) advanced at 23-21 ka [START_REF] Monegato | Evidence of a two-fold glacial advance during the last glacial maximum in the Tagliamento end moraine system (eastern Alps)[END_REF] and the Durance glacier (France)

advanced at approximately 20 ka [START_REF] Jorda | Données nouvelles sur l'âge du dernier maximum glaciaire dans les Alpes méridionales françaises[END_REF]. The Eurasian ice sheet reached its maximal extent at ~21 ka (Hughes et al., 2015).

This period is also characterised by climatic instabilities recorded in the western Massif Central as indicated by archaeological stratigraphic investigations [START_REF] Laville | Le dernier interglaciaire et le cycle climatique würmien dans le Sud-Ouest et le Massif Central Français[END_REF]. In the eastern Massif Central (Velay Mountains), slope instability (dated to ~20 ka) is interpreted as possible permafrost disappearance [START_REF] Poiraud | Les glissements de terrain dans le bassin tertiaire volcanisé du Puy-en-Velay (Massif central, France): caractérisation, facteurs de contrôle et cartographie de l'aléa[END_REF]. This period is also coeval with the deposition of aeolian coversands in the Aquitaine Basin, dated to 24 -14 ka, in association with cold and dry climatic conditions [START_REF] Sitzia | The Quaternary coversands of southwest France[END_REF]. During this phase, periods of reduced coversand accumulation, linked to reduced aeolian activity, permafrost degradation and/or milder climatic conditions, were reported between 20.8 and 17.0 ka [START_REF] Sitzia | The Quaternary coversands of southwest France[END_REF]. The HS1 started with the progressive cooling of the North Atlantic between 19 and 17.4 ka [START_REF] Pascual | Palaeoceanographic and palaeoclimatic changes during the last 37,000 years detected in the SE Bay of Biscay based on benthic foraminifera[END_REF]. Effects of this cooling in the southwestern European climate were reported between 18 to 15.6 ka (Sanchez Goñi and Harrison, 2010) and were characterized by cold and arid conditions [START_REF] Kageyama | The Last Glacial Maximum and Heinrich Event 1 in terms of climate and vegetation around the Alboran Sea: a preliminary model-data comparison[END_REF][START_REF] Ludwig | The Last Glacial Maximum and Heinrich event I on the Iberian Peninsula: A regional climate modelling study for understanding human settlement patterns[END_REF]. These conditions were associated with discontinuous permafrost in the Aquitaine basin [START_REF] Lenoble | Le site du Lac Bleu et la question de l'extension du pergélisol en France au Pléistocène supérieur 18[END_REF] and cold and dry climates in the Massif Central despite longer and warmer summers [START_REF] Reille | History of the Würm and Holocene vegetation in western Velay (Massif Central, France): a comparison of pollen analysis from three corings at Lac du Bouchet[END_REF]. The Grandvals and Bouquincan stades were potentially triggered by short-lived or slight climatic changes during the GS-2.1, especially a wetter period in overall dry climatic conditions. At the scale of the entire Massif Central, the Recurrence Event, i.e., glacier advance following the LLGM in the western Massif Central (Sections 1 and 2.3), was correlated to the Grandvals stade in the Aubrac Mountains, despite uncertainties in moraine correlations [START_REF] Kirkbride | Correlation of Late Quaternary moraines: impact of climate variability, glacier response, and chronological resolution[END_REF].

Finally, the decay of the Aubrac plateau icefield (18.66±1.60 ka) was coeval with the onset of the HS-1 (18 to 15.6 ka; Sanchez [START_REF] Sanchez Goñi | Millennial-scale climate variability and vegetation changes during the Last Glacial: Concepts and terminology[END_REF]. This event was recognised as a receding glacier phase in the circum-Mediterranean mountains related to enhanced aridity [START_REF] Allard | Heinrich Stadial aridity forced Mediterranean-wide glacier retreat in the last cold stage[END_REF]. In the southwestern Massif Central, HS-1 was a period of glacier recession. In the Roustières section (Fig. 2), cold but arid conditions were reconstructed between 17.7 and 15 ka [START_REF] Gandouin | Environmental and climate reconstruction of the late-glacial-Holocene transition from a lake sediment sequence in Aubrac, French Massif Central: Chironomid and diatom evidence[END_REF], while the Aubrac Mountains were probably deglaciated. Similar climatic conditions prevailed in the Cantal, the Cézallier and the Monts Dore deglaciated slopes (Ponel et al., 1991;[START_REF] Vergne | Les paysages végétaux d'Artense au Tardiglaciaire et à l'Holocène (Vegetal landscapes in the Artense region during Late-glacial and Holocene)[END_REF]Miras et al., 2006). This is consistent with a radiocarbon age obtained in the northern Cantal on a kame terrace deposit (17.1-15.7 ka cal BP; calibrated with CLAM software v.2.3.2 and the "IntCal20" calibration curve; Blaauw, 2010;Reimer et al., 2020). This glacial deposit was deposited during the Cantal glacier recession [START_REF] Veyret-Mekdjian | Première datation d'un épisode glaciaire récent dans le Massif central français[END_REF] and supported glacier retreats in the Cantal during the HS1, as the Aubrac plateau icefield. At the beginning of Greenland Interstadial 1 (GI-1; at 14.7 ka; Rasmussen et al., 2014), a slight summer warming (+4°C, compared to Oldest Dryas temperature) was recorded at the Roustières site [START_REF] Gandouin | Environmental and climate reconstruction of the late-glacial-Holocene transition from a lake sediment sequence in Aubrac, French Massif Central: Chironomid and diatom evidence[END_REF]. This climatic amelioration was coeval with a general trend of slope stabilisation caused by the development of vegetation cover across the whole of the Massif Central (Fig. 9) [START_REF] Reille | History of the Würm and Holocene vegetation in western Velay (Massif Central, France): a comparison of pollen analysis from three corings at Lac du Bouchet[END_REF][START_REF] Vergne | Les paysages végétaux d'Artense au Tardiglaciaire et à l'Holocène (Vegetal landscapes in the Artense region during Late-glacial and Holocene)[END_REF][START_REF] Degeai | Impacts environnementaux sur l'érosion des sols au Pléistocène supérieur et à L'holocène dans le cratère de maar du lac du Bouchet (Massif central, France)[END_REF][START_REF] Gandouin | Environmental and climate reconstruction of the late-glacial-Holocene transition from a lake sediment sequence in Aubrac, French Massif Central: Chironomid and diatom evidence[END_REF][START_REF] Ponel | Novel insights from coleopteran and pollen evidence into the Lateglacial/Holocene transition in Aubrac, French Massif Central[END_REF]. These milder climatic conditions potentially led to glacier recession into higher elevation cirques of the Cantal and Monts Dore massifs [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Valadas | Les hautes terres du Massif central français : contribution à l'étude des morphodynamiques récentes sur versants cristallins et volcaniques[END_REF][START_REF] Vergne | Les paysages végétaux d'Artense au Tardiglaciaire et à l'Holocène (Vegetal landscapes in the Artense region during Late-glacial and Holocene)[END_REF].

Conclusion

Five end moraines and one till in the Aubrac Mountains were selected, in accordance with field investigations, for surface exposure dating using 10 Be and 26 Al (n = 20). 9 Tables Table 1. Summary of key glacial landforms identified in the field fulfil criteria for cosmogenic exposure dating, with their significance in the existing morphostratigraphic framework for the Aubrac plateau icefield.

Local [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Goër De Hervé | Notice explicative, Carte géol[END_REF]Poizat and Rousset, 1974 Ancrenaz et al., [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF]De Goër et al., 1994 Ancrenaz et al., [START_REF] Etlicher | La déglaciation würmienne dans le Massif Central français, le point des travaux récents / The Würmian déglaciation in the French Massif-Central, review of recent works[END_REF] and the three groups of glaciated areas according to [START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF]. Localities cited in the main text are as follows: 1, the Aquitaine Basin; 2, the Sieben Hengste Cave 7H speleothem record [START_REF] Luetscher | North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems[END_REF]; and 3, the Lake Bouchet pollen sequence [START_REF] Reille | History of the Würm and Holocene vegetation in western Velay (Massif Central, France): a comparison of pollen analysis from three corings at Lac du Bouchet[END_REF]. [START_REF] Poizat | Sédimentation et phénomènes glaciaires et fluvio-glaciaires en Aubrac[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. The upper (black) and lower (red) ages refer to 10 Be and 26 Al minimum exposure ages, respectively. C) Glacial fluctuations reconstructed from the stratigraphic assemblages from the Rieutort section, located in the 486 Rieutort depression (modified from [START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. 487 [START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF][START_REF] Ancrenaz | Fluctuations glaciaires au Pléistocène supérieur dans les Monts d'Aubrac (Massif central, France) : nouvelles données[END_REF]. The black star represents the location of the Roustière site (Gandouin et al., 2016;[START_REF] Ponel | Novel insights from coleopteran and pollen evidence into the Lateglacial/Holocene transition in Aubrac, French Massif Central[END_REF]; note that it is located inside the LLGM outer limit (see Section 2.3 for further details). (Rasmussen et al., 2014). c) Summer Sea Surface Temperature (SST) reconstructed from the MD95-2040 oceanic sediment core from the western Iberian Margin [START_REF] Salgueiro | Temperature and productivity changes off the western Iberian margin during the last 150 ky[END_REF]. d) Sieben Hengste δ 18 O record [START_REF] Luetscher | North Atlantic storm track changes during the Last Glacial Maximum recorded by Alpine speleothems[END_REF]. e) Erosion rate in the Lake Bouchet watershed [START_REF] Degeai | Impacts environnementaux sur l'érosion des sols au Pléistocène supérieur et à L'holocène dans le cratère de maar du lac du Bouchet (Massif central, France)[END_REF]. f) Timing of episodes of permafrost in southwestern France [START_REF] Lenoble | Le site du Lac Bleu et la question de l'extension du pergélisol en France au Pléistocène supérieur 18[END_REF][START_REF] Bertran | Distribution and chronology of Pleistocene permafrost features in France: Database and first results: Pleistocene permafrost features in France[END_REF]. g) Timing of aeolian sand cover accumulation in the Aquitaine Bassin (southwestern France). The dashed part corresponds to period of reduced aeolian activity related to permafrost degradation [START_REF] Sitzia | The Quaternary coversands of southwest France[END_REF]. h) Resumed stratigraphic chronology for the Massif Central nonglaciated slopes [START_REF] Vliet-Lanoë | La paléogéographie de l'Europe centre-occidentale au Weichsélien. Réflexions sur les paléosols et l'inertie climatique : la place du Massif Central[END_REF]. i) Ages of glacial landforms in the Aubrac Mountains according to exposure ages for erratic boulders (this study). j) Reconstructed extension of the eastern part of the Aubrac plateau icefield. For the boundaries of the LGM, the Oldest Dryas (OD), the Younger Dryas (YD) and of the Heinrich Stadials 1 and 2 (HS-1 and -2), see [START_REF] Hughes | A stratigraphical basis for the Last Glacial Maximum (LGM)[END_REF], Shakun andCarlson (2010), Carlson (2013) and Sanchez [START_REF] Sanchez Goñi | Millennial-scale climate variability and vegetation changes during the Last Glacial: Concepts and terminology[END_REF], respectively.

  . Two boulders (AU16 and AU17) were taken from the Allatieux end moraine crests (Figs.4A and 6). A clustered group of MEAs is obtained, between 25.41±2.14 to 21.34±3.11 ka, with an uncertaintyweighted mean of 24.29±1.28 ka. Three samples (AU10, AU11 and AU13) were collected from boulders embedded in the Longevialle end moraine flattened crests (Figs.4 and 5B). MEAs range from 18.12±2.72 to 53.86±4.72 ka and provided the most scattered results in our dataset. No uncertaintyweighted mean was calculated. Three samples were taken from the crest of the Grandvals end moraine (AU13, AU14 and AU15) at the western end of the landform (Figs.5A and 6). MEAs were clustered, between 21.55±2.05 to 12.19±1.57 ka, with an uncertainty-weighted mean of 20.43±0.93 ka (Table

Figure 1 .

 1 Figure 1. Extent and chronology of late Pleistocene glaciation in the Massif Central (Etlicher and De

Figure 2 .

 2 Figure 2. Aubrac Mountains lithostructural context and glacial geomorphology, with the location of sample sites for cosmogenic exposure age dating.

Figure 3 .

 3 Figure 3. Locations of the main glacial landforms and sediments in the Aubrac Mountains from which

Figure 4 .

 4 Figure 4. Geomorphological settings of (A) the Allatieux and (B) Longevialle end moraines, with the locations of sampled moraine boulders. Upper (black) and lower (red) ages refer to 10 Be and 26 Al

Figure 5 .

 5 Figure 5. Geomorphological settings of (A) the Grandvals end moraine, (B) the Rateylou end moraine and associated isolated boulders and (C) the Bonnecombetill, with sample locations of morainic boulders. Upper (black) and lower (red) ages refer to 10 Be and 26 Al MEAs, respectively, with their uncertainty (analytical and production rate). White arrows indicate the direction of glacier flow.. For the location of the captions, see Fig. 2. Same legend as that for Fig. 4.

Figure 6 .

 6 Figure 6. Photographs of sampled granitic erratic boulders embedded in glacial landforms in the Aubrac Mountains. Only sample AU02 is collected from an isolated erratic boulder. The upper (black) and lower (red) ages refer to 10 Be and 26 Al minimum exposure ages, respectively. Glacier flow is indicated by the white arrows.

Figure 7 .

 7 Figure 7. Probability density function of MEAs by location versus stadials from the INTIMATE stratigraphy (Rasmussen et al., 2014). The landform age is inferred from the oldest MEA that is not rejected by the 𝑋 𝑅 2 test (Section 6.1). Only the internal uncertainty is shown.

Figure 8 .

 8 Figure 8. Diachronic reconstructions of the Aubrac plateau icefield extent during MIS 2. Red dots are glacial landforms whose exposure ages indicate the minimum age of deglaciation. Glacial limits are uncertain and based on geomorphological (subglacially moulded morphologies and topographic constraints) and sedimentological observations (extension of till)[START_REF] Poizat | Les calottes de glace quaternaires des Monts d'Aubrac (Massif central, France) : caractéristiques, contexte paléoclimatique[END_REF][START_REF] Veyret | Les modelés et formations d'origine glaciaire dans le Massif central français : problèmes de distribution et de limites dans un milieu de moyenne montagne[END_REF]

Figure 9 .

 9 Figure 9. Synthetic chronological framework for the southwestern Massif Central against main 517

  The new glacial chronology produced for the Aubrac plateau icefield southwestern Massif Central is in good agreement with (i) the existing morphostratigraphy previously established in the Aubrac Plateau and (ii) other paleoenvironmental records from the Massif Central and more widely in western Europe. The new data indicate that the LLGM occurred during the early part of MIS 2 (28-23 ka). It was followed by two glacier advances, referred to as Grandvals and Bouquincan stades, during GS-2.1 at 24-19 ka and 20-16 ka, respectively. The Aubrac plateau icefield decay is dated to GS-2.1a at 18-14 ka, in accordance with local paleoenvironmental data. The glacial chronology presented here is the first comprehensive chronological framework for the late Pleistocene glaciation in the French Massif Central. First, the LLGM in the Aubrac Mountains is synchronous with favourable conditions for glacier expansion in Central Europe (Alps) related to reduced North Atlantic circulation and enhanced moisture advection from the Mediterranean Sea that reached at least the southern Massif Central. Second, GS-2.1 in the Massif Central is characterised by a cold and arid climate with possible wetter climate phases that potentially led to two glacier advances: the Grandvals stade in the Aubrac Mountains (named the Recurrence Event in the Cantal, Cézallier and Monts Dore) and the Bouquincan stade in the Aubrac Mountains. These phases are associated with the potential northward shift of the westerlies. This may have trigged glacier advances in the Aubrac Mountains. Aridity during this period was the main limiting factor for glacier growth, especially during HS1, which is coeval with Aubrac plateau icefield decay and glacier retreat recorded in the north Cantal.

  2020

	Local glacier stade	Landform & sample ID	Longitude	Latitude	Altitude (m a.s.l.)	Topographic schielding	Rock density (g.cm -2 )	Sample thickness (cm)	[ 10 Be] (×10 -3 at.g -1 )	[ 26 Al] (×10 -3 at.g -1 )
		Allatieux moraine
		AU16	3°13'52.9" 44°72'37.6"	1196	0.99	2.65	3.0	270.29 ± 7.6	1686.28 ± 192.2
		AU17	3°13'88.4" 44°72'12.9"	1192	0.99	2.65	2.0	266.75 ± 8.8	1559.80 ± 155.3
	LLGM	Longevialle moraine
		AU10	3°03'05.9" 44°76'50.7"	1039	0.99	2.65	2.0	230.70 ± 17.7	1343.50 ± 114.6
		AU11	3°02'93.8" 44°76'51.8"	1041	0.99	2.65	4.0	500.17 ± 17.5	2538.08 ± 125.0
		AU12	3°03'31.3" 44°76'50.8"	1036	0.99	2.65	4.0	176.16 ± 9.9	1156.15 ± 123.2
		Grandvals moraine
		AU13	3°02'85.7" 44°74'24.9"	1055	0.99	2.65	3.0	202.19 ± 7.7	1257.79 ± 84.1
		AU14	3°02'88.4" 44°74'25.5"	1057	0.99	2.65	2.0	207.31 ± 10.8	804.75 ± 60.5
		AU15	3°02'86.9" 44°74'25.8"	1055	0.99	2.65	2.5	192.84 ± 8.7	1250.80 ± 95.9
		Rateylou isolated erratic boulder
	Grandvals	AU01	3°10'14.0" 44°69'77.4"	1195	0.99	2.65	3.5	107.28 ± 4.6	450.02 ± 47.5
	stade	AU02	3°11'01.8'' 44°69'74.7"	1192	0.99	2.65	3.0	228.22 ± 7.8	968.18 ± 75.0
		Rateylou moraine
		AU03	3°10'93.0" 44°69'75.1"	1190	0.99	2.65	2.5	34.23 ± 2.7	159.10 ± 24.8
		AU04	3°10'93.1" 44°69'74.7"	1190	0.99	2.65	2.5	70.06 ± 4.2	393.36 ± 39.2
		AU05	3°11'17.3" 44°69'66.5"	1187	0.99	2.65	2.5	218.47 ± 9.1	1344.09 ± 72.1
		AU06 Bouquincan moraine 3°11'34.8" 44°69'61.6"	1183	0.99	2.65	3.0	Bonnecombe (glacial deposit) 207.74 ± 9.7 1087.26 ± 70.5 Aubrac Highlands Doulounet valley 1345 m
	Bouquin-	AU07	3°09'32.3" 44°66'15.5"	1158	0.99	2.65	4.0	172.94 ± 11.6	1051.46 ± 67.5
	can stade	AU08	3°09'25.3" 44°66'22.0"	1156	0.99	2.65	2.5	189.55 ± 8.4	1123.39 ± 76.2
		AU09	3°09'17.0" 44°66'25.4"	1153	0.99	2.65	3.5	75.28 ± 4.3	483.40 ± 85.2
		Bonnecombe till
	Deglacia-	AU31	3°12'28.1" 44°55'97.6"	1341	0.99	2.65	3.5	221.31 ± 7.2	n.a.
	tion	AU32	3°12'65.9" 44°56'16.2"	1342	0.99	2.65	2.5	198.66 ± 6.7	n.a.
		AU33	3°12'66.5" 44°55'98.8"	1339	0.99	2.65	2.0	199.92 ± 7.9	n.a.

Table 3 .

 3  Minimum Exposure Age (MEA) results of samples from the Aubrac Mountains

	Local glacier stade	Landform & sample ID	26 Al/ 10 Be	10 Be MEA (ka)	26 Al MEA (ka)	Landform stabilization (uncert.-weighted mean in ka)	Landform age (oldest MEA in ka)
		Allatieux end moraine
		AU16 AU17	6.2 ± 0.7 5.8 ± 0.6	25.41 ± 2.14 24.95 ± 2.15	23.21 ± 3.62 21.34 ± 3.11	24.29±1.28	25.41 ± 2.14
	LLGM	Longevialle end moraine
		AU10	5.8 ± 0.7	24.31 ± 2.7	20.7 ± 2.81
		AU11*	5.1 ± 0.3	53.86 ± 4.72	40.05 ± 4.7	n.a.	24.31 ± 2.7
		AU12	6.6 ± 0.8	18.88 ± 1.84	18.12 ± 2.72
		Grandvals end moraine
		AU13	6.2 ± 0.5	21.22 ± 1.87	19.31 ± 2.41
		AU14**	3.9 ± 0.4	21.55 ± 2.05	12.19 ± 1.57	20.43±0.93	21.55 ± 2.05
		AU15	6.5 ± 0.6	20.14 ± 1.84	19.11 ± 2.49
		Rateylou isolated erratic boulders
	Grandvals stade	AU01*** AU02	4.2 ± 0.5 4.2 ± 0.4	10.09 ± 0.91 21.48 ± 1.86	6.17 ± 0.92 13.29 ± 1.73	n.a.	21.48 ± 1.86
		Rateylou end moraine
		AU03***	4.6 ± 0.8	3.2 ± 0.36	2.17 ± 0.41
		AU04*** AU05	5.6 ± 0.7 6.2 ± 0.4	6.55 ± 0.65 20.55 ± 1.84	5.36 ± 0.77 18.49 ± 2.18	19.68±1.11	20.55 ± 1.84
		AU06	5.2 ± 0.4	19.67 ± 1.81	15.03 ± 1.86
		Bouquincan end moraine
	Bouquincan	AU07	6.1 ± 0.6	16.83 ± 1.75	14.95 ± 1.84
	stade	AU08	5.9 ± 0.5	18.27 ± 1.66	15.82 ± 1.98	16.59±0.9	18.27 ± 1.66
		AU09***	6.4 ± 1.2	7.31 ± 0.72	6.84 ± 1.41
		Bonnecombe till
	Bonnecombe	AU31	n.a.	18.66 ± 1.6	n.a.
	deposit	AU32	n.a.	16.6 ± 1.43	n.a.	17.23±0.87	18.66 ± 1.6
		AU33	n.a.	16.68 ± 1.48	n.a.
	* MEA rejected for the uncertainty weighted-mean calculation and interpreted as prior-exposure; ** Al-26 MEA rejected for the uncertainty-weighted mean

calculation; *** MEA rejected for the uncertainty-weighted mean calculation and interpreted as incomplete exposure age

Acknowledgements

The first author received a PhD contract from the French Ministry of Higher Education, Research and Innovation. We thank the Laboratory Magma et Volcan, UMR 6524 CNRS/UCA for access to their laboratory facilities during cosmogenic exposure sample preparation. 10 Be and 26 Al analyses were performed at the ASTER AMS national facility (CEREGE, Aix-en-Provence), supported by the INSU/CNRS, by the ANR through the "Projets thématiques d'excellence" program for the "Equipements d'excellence" ASTER-CEREGE action, and by the Institut de Recherche pour le Développement (IRD). We also thank the ASTER Team (G. Aumaître, D. Bourlès, and K. Keddadouche) for their AMS expertise. B. Chandler and an anonymous reviewer are warmly thanked for their constructive comments and their help to improve this paper.