# Late Pleistocene glaciation in the Cantal Mountains and on the Cézallier Plateau (western Massif Central, France): Insights from glacial geomorphology and surface exposure dating

Arthur Ancrenaz, Stéphane Pochat, Emmanuelle Defive, Alexandre Poiraud, Regis Braucher, Vincent Rinterknecht, Johannes Steiger

► To cite this version:

Arthur Ancrenaz, Stéphane Pochat, Emmanuelle Defive, Alexandre Poiraud, Regis Braucher, et al. Late Pleistocene glaciation in the Cantal Mountains and on the Cézallier Plateau (western Massif Central, France): Insights from glacial geomorphology and surface exposure dating. Geomorphology, 2023, 442, pp.108909. 10.1016/j geomorph.2023.108909. hal-04232834

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# Late Pleistocene glaciation in the Cantal Mountains and on the Cézallier Plateau (western Massif Central, France): insights from glacial geomorphology and surface exposure dating

5 Arthur Ancrenaz<fnref n="1" />, Stéphane Pochat<fnref n="2" />, Emmanuelle Defive<fnref n="1" />, Alexandre Poiraud<fnref n="1" />, Régis Braucher³, Vincent Rinterknecht³, Johannes Steiger<fnref n="1" />

10 ³ Aix Marseille Univ, CNRS, IRD, INRAE, CEREGE, BP 80, 13545 Aix-en-Provence Cedex 4, France

Correspondence to: Arthur Ancrenaz (arthur.ancrenaz@ext.uca.fr)

## Highlights

* Revisions of glacial landform-sediment assemblages define four distinct glacial events.

15 * Glacial fluctuations are dated to the MIS 2 with surface exposure ages using ¹⁰Be, ²⁶Al and ³⁶Cl (n=48).

* Two major glacier advances occurred during the Last Glacial Maximum, at 29-24 and 24-20 ka.

* The paleoglacier is limited to the Cantal cirques from ~16 ka.

* Paleoglacier from the western Massif Central are sensitive to north Atlantic paleoclimatic changes.

<footnote n="1">¹ Université Clermont Auvergne, CNRS, GEOLAB, F-63000 Clermont-Ferrand, France</footnote>

<footnote n="2">² Laboratoire de Planétologie et Géosciences, LPG, UMR 6112, Nantes Université, CNRS, France</footnote>
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**Abstract.** The aim of this work is to build a new chronology of the Late Pleistocene glacial fluctuations in the Cantal Mountains and on the Cézallier Plateau (western Massif Central, France) through a study of glacial landform-sediment assemblages and supported by the production of new exposure ages (n = 43) from (i) erratic boulders ($^{36}$Cl and $^{10}$Be) spread over twelve glacial landforms, (ii) two ages from polished bedrocks ($^{10}$Be) and (iii) three ages from depth profiles ($^{10}$Be and $^{26}$Al) in tills. The results indicate that the majority of glacial deposits are attributed to Marine Isotopic Stage 2 (29 to 11 ka). From this dataset, four glacial stadials are discriminated: the Early-Local Last Glacial Maximum at 29-24 ka, (ii) Late-Last Glacial Maximum at 24-20 ka, (iii) a glacial still stand at approximately 17 ka, during a general deglaciation phase between 20-16 ka and finally (iv) a cirque stadial localized only in the Cantal Mountains at <16 ka. This new chronology strengthens the chronostratigraphy of the western Massif Central and highlights the sensitivity of the area to atmospheric circulation changes.

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# 1 Introduction

Late Pleistocene glacial fluctuations in mid-latitude mountains are valuable paleoclimatic proxies. At the local scale, knowledge of these fluctuations may provide a key for the quantification of climatic conditions at high elevations, where other proxies for studying paleoclimates are rare or absent (Ohmura et al., 1992; Osmaston, 2005; Rea, 2009). At the regional scale, the regional dispersion of paleoglaciers provides milestones for past atmospheric circulation changes (Kuhlemann et al., 2008; Hughes and Woodward, 2017; Rea et al., 2020). The use of paleoglaciers as a proxy for the characteristics of the Late Pleistocene paleoclimate must be based on robust geomorphological reconstructions that clearly identify the successive extents and timings of glacier stadials. To this end, dating glacial landforms is a critical aspect and has been supported by the development of terrestrial cosmogenic nuclides (TCNs) as a direct dating tool. Indeed, TCN allows us to build robust glacial chronology for Pleistocene glaciers (Balco, 2011; Allard et al., 2021a). As a result, the multiplication of glacial

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chronologies highlighted the asynchronicity of paleoglacier maxima due to contrasting regional paleoclimatic forcings (Ehlers et al., 2011; Monegato et al., 2017; Batchelor et al., 2019; Allard et al., 2021b).

In Europe, two periods have been particularly studied: the global Last Glacial Maximum (LGM) between 26 and 19 ka (Clark et al., 2009) and the following Late Glacial-Interglacial Transition (LGIT; 19 to 11 ka). Interest in these periods relies on intensive paleoclimatic changes inducing paleoenvironmental changes in abiotic and biotic aspects. During the early part of Marine Isotopic Stage 2 (MIS 2; 29-24 ka) in western Europe, the southward migration of the Polar Front Jet Stream was deemed responsible for the reorganization of atmospheric circulations, inducing the displacement of westerlies. As a result, the glacier maxima in the Alps can be attributed to enhanced southerlies due to the southward displacement of westerlies (Florineth and Schlüchter, 2000; Luetscher et al., 2015; Monegato et al., 2017). More generally, paleoenvironmental studies pointed out the role of the Heinrich Stadials (HS) as primary controlling factors in the European paleoclimate, with forcings through southward extent of sea ice or the Atlantic Meridional Overturning Circulation (AMOC) reduction, leading to colder and drier paleoclimates (Toucanne et al., 2022 and references therein).

The French Massif Central is located at a key position, as it forms the first orographic barrier to westerlies, between 44° to 46°N, with current climatic influences from the Mediterranean Sea in its southern part (Jubertie, 2006). In this context, paleoglacier fluctuations are regarded as key paleoclimatic proxies to constrained timings and intensities of paleo-atmospheric circulation changes. However, reconstructions of paleoglacier fluctuations in this area are lacking. The only direct glacial chronology available was obtained from the Aubrac Mountains (44.60°N - 3.00°E) in the southwestern Massif Central (Ancrenaz et al., 2022) and highlights that the Local Last Glacial Maximum (LLGM) occurred from 27-24 ka and was followed by two glacier stadials: one from 23-20 ka and another from 19-16 ka. Finally, full deglaciation was estimated to have occurred from 18-16 ka. To strengthen glacial chronologies at the Massif Central scale, this work proposes to reconstruct paleoglacier fluctuations in the western part of the Massif Central: in the Cantal Mountains and the Cézallier Plateau. Two
reasons are highlighted to support this focus: (i) this region was the most glaciated area of the Massif Central and (ii) due to the relatively high elevation of the summits (culmination at 1855 m asl), this region is expected to record later glacier stadials.

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During the LLGM, paleoglaciers from the Cantal Mountains, the Cézallier Plateau and the Monts Dore (CCMD; 45.25°N – 2.75°E) coalesced, forming a glaciated area of $2.5 \times 10^3$ km². Major landform-sediment assemblages were found in the main valleys and allowed the identification of (i) ‘older’ moraines attributed to the penultimate glaciation (Veyret, 1978) and (ii) the Local Last Glacial Maximum (LLGM) followed by a glacier stadial (locally named the Recurrence Event, Fig. 1), both attributed to the MIS 2 (Veyret, 1978). Finally, a cirque stadial occurred in the Cantal cirques and was attributed to the Oldest Dryas or the Younger Dryas (Etlicher and Goër de Hervé, 1988 and references therein). The first attempt by the authors to produce a direct glacial chronology in the Cantal Mountains relied on six surface exposure ages ($^{36}$Cl) collected from end moraines in the Cère Valley located in southwestern Cantal. The results highlight that the studied glacial landform-sediment assemblages were disturbed by a period of postglacial aggradation favored by paraglacial environments. Indeed, the surface exposure ages obtained (13–12 ka) were interpreted as unsuitable for refining the chronology of paleoglacier retreats (Ancrenaz et al., 2023).

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The aim of this study is to constrain Late Pleistocene glacial fluctuations in the Cantal Mountains and on the Cézallier Plateau. To this end, investigations involving geomorphological mapping and TCN dating ($^{10}$Be, $^{26}$Al and $^{36}$Cl) are focused on key glacial landform-sediment assemblages to obtain the first direct glacial chronology. These results are integrated into the existing chronostratigraphy, forming a comprehensive chronostratigraphy for the western Massif Central during the MIS 2.

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# 2 Study area

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## 2.1 Geological settings

In this study, we focused on the Cantal Mountains and the Cézallier Plateau, two contiguous areas located in the western Massif Central; these areas are composed of comparable geological structures and have experienced a shared glaciation history since the paleoglaciers from the Cantal Mountains, the Cézallier Plateau and the Monts Dore (CCMD) were coalescent at least during the glaciation maximum (Figs. 1-2).

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The Cantal Mountains and the Cézallier Plateau are Miocene and Pliocene volcanic complexes of different origins developed after Oligocene rifting. They are underlain by a Paleozoic basement with basins filled during the Oligocene and Miocene by marls and limestones. The regional geological structures and volcanoes have produced two distinct morphologies. The Cantal Mountains are a radially dissected stratovolcano that culminated at 1855 m asl and extended over ~2000 km² (Figs. 1C and 1E) (Goër de Hervé, 1972; Varet, 1970; Veyret, 1978).

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The Cézallier Plateau is a volcanic highland with an area of ~300 km², ranging in elevation from ~1150 to 1547 m asl (Figs. 1D-E) and dotted with volcanic cones and maars. Three topographic domains are distinguished:

- The Cantal summits, ranging from 1400 to 1855 m asl, are trachytic domes or necks separated by deep amphitheaters or glacial cirques (250-700 m deep) dominated by high, sloping, sharp crests comparable to an alpine relief landform.

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- Radially overdeepened Cantal valleys, up to 400 m deep 3 km wide, are controlled by volcanic and structural contexts (Valadas, 1984).

- The Cantal basaltic plateaus and the Cézallier Plateau, which extended over 1500 km², are constituted mainly by basaltic lava flows with smooth surfaces and gentle slopes (from 10° to 5°).

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Finally, the Artense Plateau delimits the Cantal Mountains to the north and the Cézallier Plateau to the west. It is a granitic and metamorphic plateau with gentle slopes from east (~1200 m asl) to west (~500 m asl) along 25 km.
## 2.2 Current climate and paleoglaciers asymmetries

Present climatic conditions in the CCMD are marked by strong precipitation gradients due to Foehn effects, as the CCMD relief is the first orographic barrier encountered by North Atlantic westerlies. The relatively high precipitation rates on the west-facing slopes under oceanic climatic conditions change to lower precipitation rates on the east-facing slopes under a pronounced continental climate (Jubertie, 2006). Precipitation gradients can be highly variable at very local scales according to the slope orientation (Genevois et al., 2022).

This effect is thought to have also affected the development of paleoglaciers during the last glaciation, with a highly developed ice system occurring on the western flank and a short ice system developing on the eastern flank (Figs. 1D-1E). Three main glacial accumulation zones were centered on the highest-elevation zone of the Cantal Mountains, the Cézallier Plateau and the Monts Dore, forming near-continuous accumulation zones (Veyret, 1978). This climatic pattern associated with local topographic constraints has induced three general configurations:

- individual valley glaciers, longer toward the west than towards the east;

- individual plateau glaciers located on the Cantal southern plateaus;

- a glacier lobe from the coalescence of the northern Cantal glacier, the western Cézallier glacier and the southern Monts Dore glacier. This glacier system converged in the Artense Plateau to form an extensive lobe that reached the Orgues Plateau (40 km from the Cézallier summit and more than 50 km following the valley from the Cantal origin) (Figs. 1D and 2).

# 3 Methods

## 3.1 Geomorphological mapping and morphostratigraphic units

The study of glacial landforms and deposits was conducted following three steps: regional mapping with a digital elevation model (DEM; 5-m resolution) and orthophotographs (0.5-m resolution) obtained from the IGN (Institut
National de l'information Géographique et Forestière) followed by a field work validation. Local highlights are produced through detailed sedimentological characterization and geomorphological mapping of key sectors useful for providing glacier fluctuation information. This approach was enhanced by the establishment of a new typology that focuses on till sources and ice-marginal landforms that limits misinterpretations (Appendix A). Geomorphological maps were produced using ArcGIS (v.10.3).

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Glacial landform-sediment assemblages were used to define a comprehensive morphostratigraphic framework for representing glacial fluctuations. Using geometrical relationships between glacial landforms and sediments located in key areas of the Cantal Mountains and the Cézallier Plateau, such as end moraine positions, the landform-sediment assemblages were subdivided into morphostratigraphic units (Lukas, 2006; Hughes, 2013). This allowed us to compare deglaciation sequences from distant valleys or plateaus and target suitable landforms to be dated.

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## 3.2 Terrestrial Cosmogenic Nuclide dating using <sup>10</sup>Be, <sup>26</sup>Al and <sup>36</sup>Cl

### 3.2.1 Sample collection

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The glacial landforms and depositional features applied for TCN dating were selected for their potential ability to temporally constrain the glacial events identified from the morphostratigraphic units and according to their geomorphological contexts and their own sedimentological and morphological characteristics. Two limitations were defined: (i) a lack of dateable glacial features, as erratic boulders embedded in moraines are mostly removed for agricultural purposes, and (ii) in Cantal valleys, postglacial landform disturbances could be responsible for complex exposure histories (Ancrenaz et al., 2023). To overcome these limitations, two TCN dating approaches were combined: surface exposure ages from erratic boulders or polished bedrocks and surface exposure ages from depth profiles in tills.

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To investigate the geological diversity of the study area, three nuclides were used:
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- Clorine-36 ($^{36}$Cl) produced in volcanic whole rocks from various targets (primarily Ca and K) that constituted CCMD highlands and

- The beryllium-10 ($^{10}$Be) and aluminum-26 ($^{26}$Al) pair produced in quartz minerals that are abundant in the Paleozoic basement composing the CCMD lowlands.

## Erratic boulder and polished bedrock sampling

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Forty-three erratic boulders were sampled from twelve sites (Table 1): five end moraines and seven isolated moraines or groups of erratic boulders. Sampling focused only on the tallest boulders, ideally >1.5 m in height (Heyman et al., 2016), with broad bases embedded in the glacial landform (Fig. 3). Samples were collected at boulder surfaces, within the upper 1 to 7 cm, preferentially at the top of each boulder on a large and flat surface, using a hammer and a chisel. According to the availability of dateable erratic boulders at each site, between two and five boulders were sampled. Forty-one samples from volcanic boulders were prepared for $^{36}$Cl extraction, and two samples from gneissic boulders were prepared for $^{10}$Be extraction (Table 1).

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In addition, two polished bedrock surfaces with plucking fractures were sampled from granitic rocks for the $^{10}$Be and $^{26}$Al extractions. These samples were taken from the tops of these erosional surfaces located in valley thalwegs (Table 1).

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## Depth profile sampling in tills

Three depth profiles were obtained for the $^{10}$Be and $^{26}$Al measurements within unique sedimentological till units associated with unique depositional events. Altogether, three to four samples were taken from three distinct anthropogenic and vertical excavations (Table 1 and Appendix B). Samples were taken at depths between 0.175 and 3.350 m and were composed of an amalgamated till matrix with a maximum particle size of 2 cm. For descriptions of these sedimentological units and samples (Appendix B).

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### 3.2.2 Sample extraction and measurements

#### Beryllium-10 and Aluminum-26
Thirteen samples were prepared for the ¹⁰Be and ²⁶Al measurements, and two were prepared for the ¹⁰Be measurements (Table 1). The physical and chemical preparations followed the protocols described by Brown et al. (1991) and Merchel and Herpers (1999). The samples were crushed and sieved between 0.25 and 1 mm. After mineral separation using a Frantz barrier separator, the nonmagnetic grains (including quartz) received successive acid applications of H₂SiF₆ and HCl to eliminate nonquartz minerals and three partial dissolutions in HF to eliminate atmospheric ¹⁰Be. According to Merchel et al. (2008), ~0.15 g of a homemade (3025 ± 9 ppm) ⁹Be solution was added to the solution to fix the ¹⁰Be/⁹Be ratio before quartz was totally dissolved using a 40% HF solution. Natural concentrations of ²⁷Al were measured in liquid aliquots by inductively coupled plasma-optical emission spectrometry (ICP-OES, Thermo Icap6500). Afterward, beryllium and aluminum were extracted by successive anion and cation resins. Finally, the Be(OH)₂ and Al(OH₃) hydroxides were heated at 800 °C for one hour. The resulting powders were mixed with niobium (BeO) or silver (Al₂O₃) prior to the accelerator mass spectrometry (AMS) measurements. The measurements from samples CA12 and CA13 provided inconsistent ²⁶Al values due to high natural ²⁷Al contents of 7.36 ± 2.37×10⁵ and 6.04 ± 1.83×10⁵ at.g⁻¹, respectively (Table 2). Associated ²⁶Al/¹⁰Be ratio were not compatible with surface exposure, then the surface exposure ages were thus not calculated for these two samples.

¹⁰Be data were calibrated from an ASTER in-house preparation, “STD11”, with a ¹⁰Be/⁹Be ratio of (1.191 ± 0.013) × 10⁻¹¹ (Braucher et al., 2015) using a ¹⁰Be half-life of 1.387 ± 0.0012 Ma (Chmeleff et al., 2010; Korschinek et al., 2010). The reported analytical uncertainties were associated with counting statistics, machine stability and blank correction. Two measurement sessions were performed. For CA01 to CA13, the process blank (BLANK-Be-I) had a ¹⁰Be/⁹Be ratio of 2.59×10⁻¹⁵. For CTL-23 and CTL-25, the process blank (BLANK-Be-II) had a ¹⁰Be/⁹Be blank ratio of 8.35×10⁻¹⁶. The ²⁶Al data were calibrated using an ASTER in-house standard, “SM-AL-11”, with a ratio of 7.401 ± 0.064 ×10⁻¹² (Merchel et al., 2008) assuming a ²⁶Al half-life of 0.705 ± 0.017 Ma (Samworth et al., 1972). The reported analytical uncertainties included counting statistics, machine stability
(~0.5% for 10Be; Arnold et al., 2010), and blank correction uncertainties. The analytical data corresponding to the ¹⁰Be and ²⁶Al measurements are reported in Table 2 and Appendix B.

### Chlorine-36

The samples collected for the ³⁶Cl measurements (n = 41; Table 1) were crushed and sieved to 0.25-0.5 mm. Chlorine was extracted and purified from whole-rock samples to produce AgCl for AMS analysis, following the procedure described by Schimmelpfennig et al. (2011). Chemical analyses (trace and major elements) of the bulk rocks from ten samples and chemical analyses (trace and major elements) of the chemically treated fractions of all samples were performed at the SARM-Nancy laboratory and are summarized in Table 3 and Table 4, respectively.

For ³⁶Cl, the use of an isotopically enriched carrier allowed the simultaneous measurement of ³⁵Cl/³⁷Cl and the determination of the natural Cl contents of the dissolved samples. For the normalization of the ³⁶Cl/³⁵Cl ratio calibration, an ASTER in-house standard was used with a ³⁶Cl/³⁵Cl value of 1.42 ± 0.02 × 10⁻¹² (Merchel et al., 2011). Four measurement sessions were performed. Four process blanks (BKCTL-01, BKCTL-02, BKCTL-03, BKCA-01) with ³⁶Cl/³⁵Cl ratios of 2.32 × 10⁻¹⁵, 1.22 × 10⁻¹⁶, 1.23 × 10⁻¹⁶ and 3.52 × 10⁻¹⁵ were used to correct the ³⁶Cl concentrations by subtracting the number of ³⁶Cl and Cl atoms in the blanks from those in the samples. Typical uncertainties for raw AMS data are 1.7–3.0% for ³⁵Cl/³⁷Cl and 6.2–9.3% for ³⁶Cl/³⁵Cl.

### 3.2.3 Surface exposure age calculation

The ¹⁰Be concentrations measured from the erratic boulders and bedrock were computed into surface exposure ages using the CHRONUS-Earth online calculator v.3 (Balco et al., 2008; http://stoneage.ice-d.org/math/v3/v3_age_in.html). The ¹⁰Be and ²⁶Al production rates at sea level and high latitudes (SLHL) from spallation were used as the default calibration dataset (Borchers et al., 2016): 4.13 ± 0.22 at.g⁻¹.yr⁻¹ and 29.950 ± 2.955 at.g⁻¹.yr⁻¹, respectively. These production rates were scaled using the Lal-Stone time-dependent scaling
scheme (Lal, 1991; Stone, 2000), the ERA40 atmosphere model and the magnetic field reconstruction from Lifton et al. (2014).

The <sup>36</sup>Cl concentrations were computed into surface exposure ages using the Excel spreadsheet of Schimmelpfennig et al. (2009). The <sup>36</sup>Cl production rates at SLHL from spallation are 42.2 ± 4.8 atoms <sup>36</sup>Cl (g Ca)<sup>-1</sup> yr<sup>-1</sup> (Braucher et al., 2011; Schimmelpfennig et al., 2011), 148.1 ± 7.8 atoms <sup>36</sup>Cl (g K)<sup>-1</sup> yr<sup>-1</sup> (Schimmelpfennig et al., 2014), 13.0 ± 3.0 atoms <sup>36</sup>Cl (g Ti)<sup>-1</sup> yr<sup>-1</sup> (Fink et al., 2000), 1.9 ± 0.2 atoms 36Cl (g Fe)<sup>-1</sup> yr<sup>-1</sup> (Stone et al., 1996), and 696 ± 185 neutrons (g air)<sup>-1</sup> yr<sup>-1</sup> for the production rate of epithermal neutrons from fast neutrons in the atmosphere at the land/atmosphere interface (Marrero et al., 2016). These production rates were scaled with the Lal-Stone time-invariant scaling scheme (Lal, 1991; Stone, 2000).

The resulting surface exposure ages were corrected for topographic shielding using a GIS model (Li, 2018) and DEM (25-m resolution). Since no local measurements of erosion rates on boulders from the Cantal are available and considering the lithological diversity of the sampled boulders, surface exposure ages were not corrected for erosion ages. The null erosion hypothesis is considered the minimalist assumption. The method used to compute the surface exposure ages of the <sup>10</sup>Be and <sup>26</sup>Al depth profiles in tills is presented in Appendix B.

### 3.2.4 Landform age interpretation

For each landform sampled for TCN dating, the surface exposure ages were used to define the landform age using a probabilistic approach with the Probabilistic Cosmogenic Age Analysis Tool (P-CAAT; Dortch et al., 2022). P-CAAT produced composite probability density estimates from ages and their uncertainties (internal or external) related to isolated Gaussian components. This tool allows a user-choice bandwidth estimator to model Gaussian components. For small datasets (fewer than 6 samples), setting the arithmetic mean of the external age uncertainties as the numeric bandwidth gives more accurate solutions (Dortch et al., 2022). For this work, the exposure ages obtained for each landform are clustered, considering the age uncertainties. Then, the landform age
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given by the unique Gaussian component was interpreted as the best approximation of the landform age (Table 5). Exceptions are discussed in the main text (Section 4.2).

# 4 Results

## 4.1 Glacial geomorphology

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Key glacial landform-sediment assemblages were identified and mapped in eleven subareas of the Cantal Mountains and the Cézallier Plateau (Fig. 2 for locations): (i) the Alagnon Valley, the Epie Valley and the Lagnon Cirque in eastern Cantal (Fig. 4); (ii) the Brezons Valley, the Lacapelle Plateau and the Cère Valley in southern Cantal (Fig. 5); (iii) the Rhue, Mars and Petite Rhue valleys in northern Cantal (Fig. 6); and (iv) the northeastern Cantal and the Cézallier Plateau (Fig. 7). The detailed geomorphological mapping results obtained from field prospecting are presented in the following subsection.

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### 4.1.1 Eastern Cantal

#### Alagnon Valley

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The Alagnon Valley, from the Alagnon Cirque (~1200 m asl) to the Alagnon gorge (~750 m asl), is the major glaciated valley of the eastern Cantal and separates the St-Flour Plateau to the south and the Cézérat Plateau to the north (Figs. 2 and 4A). The slopes of the Alagnon Valley are affected by (i) deep-seated gravitational landslides constituted by multiple slide and tilted rock masses (mainly basaltic) that conserved their coherence and highlight failures in the upper DGSD parts (Appendix A) and (ii) vegetized and active screes associated with basaltic cornices that demarcate the St-Flour plateau and Cézérat Plateau (Fig. 4A). On the valley floor, between Murat city and the Alagnon Gorge, three distinct glacial landform sediment assemblages are identified: the Entraygues Plain, the Neussargues Plain and the Murat Valley filling (Figs. 4A-B).

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The Entraygues Plain is composed of distal glacial deposits in the Alagnon Valley (Fig. 4) constituted by tills that form a perched plain 2 km long +30 to +15 m above the current Alagnon and Allanche rivers. This landform is
interpreted as a till drift remodeled and buried by proglacial outwash associated with the end moraines located in
the Neussargues Plain.

The Neussargues Plain is a continuous till drift that fills the valley along ~8 km between the Entraygues Plain and Murat (Fig. 4), punctuated by several end moraines separated by proglacial meltwater channels, resulting from the Alagnon and Allanche outlet glacier stillstands. The first stillstand was associated with the Pouzat end moraine (~800 m asl) that demarcated the coalescent Alagnon and Allanche glacier outlets. This landform is breached in its center by the Entraygues Plain. Upstream, end moraines are associated with the Alagnon and Allanche glacier outlet disconnection and individual recessions, such as the Canals end moraine (823 m asl) in the Allanche Valley or the Prades (845 m asl), the Champs (894 m asl) and the Chapelle (881 m asl) end moraines in the Alagnon Valley. The Entraygues Plain and the Neussargues Plain are incised by the Alagnon River by ~30 to 20 m with two postglacial terrace levels: T1 at +10-8 m and T0 at +5-3 m (Fig. 4).

Upstream of the Prades end moraine, the morphology of the valley bottom—the flat floor along 2 km—is interpreted as a postglacial valley filling (Fig. 4). Here, no alluvial terraces are reported.

## St-Flour Plateau

The southern slopes of the Alagnon Valley are dominated by the St-Flour Plateau on which overflow tills are identified, attesting to the overflow of the Alagnon paleoglacier (Fig. 4A). These deposits form a series of subparallel and nearly continuous ridges up to 10 m high. Their general orientation is interpreted as typical end moraines from outlet glacier lobes. Multiple positions of the Alagnon overflow toward the St-Flour Plateau are demarcated between the Pierre Grosse end moraines (985 m asl) and the Cheylanes erratic boulders (1120 m asl).

The latter are associated with the Alagnon glacier thinning that caused the end of the overflow toward the St-Flour Plateau.

## Epie Valley
The Epie Valley, located within southeastern Cantal (Fig. 5A), is a narrow (< 1-km width), poorly incised (~100-m) valley that delimits the St-Flour Plateau to the east and the Cézens Plateau to the west. The Epie outlet glacier was alimented mainly by the Epie amphitheater and by a glacial diffluence from the Lagnon Cirque toward the Prat de Bouc Pass at 1392 m asl (Fig. 5B). In the Epie Valley, no distinct glacial landforms or sediment assemblages are reported. Only isolated moraine patches are identified and associated with glacier recessions. The Rials moraine, the distal glacial deposits from the Epie glacier found 15 km from the glacier source, is an isolated patch of overflow till located on the St-Flour Plateau (Fig. 5A). On the Cézens Plateau, the Caire watershed is partly covered by overflow moraines that match the occurrence of autochthonous basaltic blockfields (periglacial landforms) (Fig. 5A).

## Lagnon Cirque

The east-facing Lagnon Cirque alimented the Lagnon Valley, an Alagnon tributary. It is the most developed glacial cirque of the Cantal Mountains with steep head walls up to 1800 m and pseudofloors at ~1600 and ~1300 m asl. The Lagnon glacier alimented the Epie glacier through a glacial transfluence at the Prat de Bouc Pass at an elevation of 1392 m asl (Fig. 5B).

Moraines cover the cirque floors with near-continuous deposits along the Prat de Bouc Pass. The latter is associated with the end of the glacial transfluence toward the Epie Valley and demarcates the containment of the Lagnon cirque glacier (Fig. 5B). Above the Prat de Bouc Pass, a minor end moraine is identified: the Jambe end moraine. It is a 1-m-high ridge parallel to slopes with an associated glacier surface of approximately 0.25 km². Periglacial features are also common in the Lagnon Cirque and the neighboring Chamalières Cirque, especially a protalus rampart at ~1550 m asl (Fig. 5B).

## 4.1.2 Southern Cantal

### Brezons Valley
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The Brezons Valley, the main valley of the southern Cantal Mountains, is a deep (200 to 400 m) and large (1 to 2 km wide) valley nourished by three glacial cirques, the Mandre, the Encloux and the Livernade cirques, and multiple tributaries from the Lacapelle Plateau to the west and the Cézens Plateau to the east (Fig. 6A). The Brezons Valley flanks are covered by basaltic screes nourished by basaltic cornices associated with plateau rims and affected by deep-seated gravitational landslides (Fig. 6A). Four glacial features are associated with the Brezons glacier: the Boutragot end moraines, the Moulinges moraine, and the St-Martin and the Brezons terraces.

The Boutragot end moraines are distal glacial deposits of the Brezons outlet glacier, found on the Cézens Plateau at 1025 m asl. These end moraines consist of overflow till sourced from the Brezons Valley. The Boutragot end moraines demarcate the maximal extent of the Brezons paleoglacier overflowing toward the Cézens Plateau (Fig. 6A). According to the elevation of the Boutragot end moraines, the associated glacier thickness reached ~250 m ~13 km from its source. The Boutragot moraines are located downstream of the Montrozier boulder fields (1108 m asl) constituted by autochthonous basaltic boulders and associated with periglacial environments (Fig. 6A).

In the Brezons Valley, glacial remnants are reported along the ~8-km stretch before the Brezons River flows into gorges where the Moulinges moraine, composed of distal glacial deposits, is identified (Fig. 6A). This moraine is a thick till drift perched at +25 m above the present-day river, forming an irregular terrace 2 km long. Upstream, two series of relatively low and discontinuous terraces perched between +15 and +12 m are reported: the Brezons and St-Martin terraces (Fig. 6A). Sparse sections show a diamicton composed of rounded and heterogeneous volcanic clasts (with a maximum long axis of 50 cm) dominated by pebbles and embedded in an unconsolidated sandy and/or gravelly matrix. These deposits are associated with fluvio-glacial deposits, such as kame terraces, formed during two distinct steps of the Brezons glacier downwasting: the first one constructed the St-Martin terraces, and the second one constructed the Brezons terraces. The Brezons River cut off these terraces at the level of the alluvial terrace, T1, at +10-8 m (Fig. 6A).

## Lacapelle Plateau
The Lacapelle Plateau is a south-facing basaltic plateau between the Brezons Valley and the Cère Valley. It is crossed by the Siniq and Goul valleys (Fig. 6A). Around the Siniq Valley, three distinct glacial landforms and sediment assemblages are recognized: (i) the local plateau tills from the Lacapelle Plateau, (ii) the ice-marginal landforms of the Siniq lobe glacier and (iii) the postglacial valley filling of the Siniq Valley.

330

The Lacapelle Plateau is covered by thin (up to 1-m-thick) plateau tills, forming low mounds hundreds of meters long separated by closed depressions (Fig. 6A). Locally, the plateau tills can be thicker, up to 4 m, especially in present-day drainage networks or in association with residual basaltic relief. In the latter case, these landforms are interpreted as glacial lineations, from which specific characteristics can be derived (Appendix A).

335

Overflow moraines sourced from the Siniq Valley are identifiable by isolated patches of erratic boulders (trachytic and trachyandesitic rocks). Their distribution forms a lobate extent of 3 km associated with the glaciers that overflowed from the Siniq Valley toward the adjacent Lacapelle Plateau (Fig. 6A-B). Upstream in the valley, a series of end moraines demarcated multiple glacier stillstands, from the Laparra (1013 m asl) to the Laygo (1005 m asl) end moraines. The Laygo end moraine enclosed a valley filling, identified from the flat valley floor at 696 m asl along a length of 6.5 km (Fig. 6A-B).

340

## Cère Valley

The Cère Valley is the major Cantal valley, oriented toward the southwest. The Cère glacier was alimented by a glacial transfluence toward the Fond de Cère Pass (1290 m asl) from the Fond d'Alagnon Cirque and by secondary cirques or amphitheaters along the valley. The glacial and associated deposits in this area were mapped by Ancrenaz et al. (2023). Here, the study site was restrained to the Vézac pass at 664 m asl, 27 km from the Fond de Cère Pass, above the Carnéjac end moraine (Fig. 6C).

345

The Vézac Pass is filled by till associated with a glacial transfluence from the Cère Valley toward the Couffins Valley. This deposit corresponds to the distal glacial remnants found in the Couffins Valley. Its deposition is associated with a glacial recession phase responsible for the kame terrace edifications (700 m asl) along

350
interfluves that dominated the Vézac Pass to the east (Fig. 6C). This glacial retreat phase occurred before the
glacier stillstands produced the Carnéjac and Polminhac end moraines.

4.1.3 Northern Cantal

Mars Valley

The Mars Valley is a west-facing, deep (300 to 500 m) and wide (4 to 2-km) valley alimented by the Falgoux Cirque. The associated valley glacier is estimated to have had a length of up to 26 km (Fig. 7B). At 9 km from the glacier source, the valley intersects the Paleozoic basement at ~900 m asl (Fig. 7B). Here, granitic and metamorphic outcrops present typical *roches moutonnées* morphologies forming a valley step.

Orgues Plateau

The Orgues Plateau is a phonolitic dome that culminates at 859 m asl and is located above the Dordogne and the Rhue confluence ~35 km from the Cantal summits (Fig. 7A). Here, the distal glacial deposits toward the west are attributed to the Rhue paleoglacier, which was alimented by northern Cantal and western Cézallier valleys.

On the east-facing slopes of the Orgues Plateau, a group of erratic boulders is identified, named the Orgues erratics (Fig. 7A). Postglacial landforms masked or reworked part of these glacial deposits, especially phonolitic screes and heads (Fig. 7A). Heads are slope deposits constituted by angular to subangular clasts (centimetric to decametric size) embedded in a clayey, silty and/or sandy matrix. To the north of the Orgues Plateau at the Vioux settlement, deltaic deposits associated with the Bort proglacial lake are reported at 626 m asl. Interfluves of the western part of the Artense Plateau, inside the extent of the Bort proglacial lake, are covered by fluvio-glacial deposits. To the east of the Dordogne and the Rhue confluence, gneissic reliefs are scoured and covered by discontinuous morainic or fluvio-glacial deposits that fill the overdeepened morphologies and part of the hydrographic networks; perched terraces were identified at +20 m (Fig. 7A).

Petite Rue Valley
The Petite Rhue valley, a tributary of the Rhue valley, is a north-facing valley alimented by the Petite Rhue Cirque. At 11 km from its source, the valley intersects the Paleozoic basement, which is composed mainly of granites at ~900 m asl and presents typical *roches moutonnées* morphologies forming a valley step (Fig. 7B).

375

A second site was studied from the surrounding interfluves of the Petite Rhue Valley at 905 m asl (Fig. 2 for location); this site forms a flat plateau with *roches moutonnées* of one hundred meters long and dozens of meters high. Between these features, depressions originated by suggestive overdeposition are filled by tills (Fig. 7D).

### 4.1.4 Northeastern Cantal and Cézallier Plateau

380

#### Cézérat Plateau

The Cézérat Plateau refers to the Cantal northeastern basaltic plateau with elevations between 1300 and 1000 m asl (Fig. 2). Here, the landscape is composed of subglacially eroded morphologies with bared and scoured basaltic mounds separated by depressions occupied by lakes or peat bogs. At the Pinatelle site, a group of basaltic erratic boulders are reported at 1135 m asl (Fig. 8A). These boulders are locally accompanied by patches of plateau tills.

385

#### Cézallier Plateau

The glacial landforms identified at the two study sites on the Cézallier Plateau are dominated by groups of erratic boulders that cover slopes and interfluves, locally accompanied by bare rock surfaces and dismantled tor-like features. Two groups of erratic boulders were identified as being suitable for $^{36}$Cl dating (Fig. 2 for location) at the Combalut (Fig. 8C) and Pradiers (Fig. 8B) sites.

390

These two sites are located on the west-facing Cézallier slopes. The Combalut erratics are located on the western slopes of the Suc de Mourcairol (1224 m asl), a basaltic interfluve. The Pradiers erratics are located on the southern slopes of the Pradiers phonolitic dome (1360 m asl). These two groups of erratic boulders were deposited by the Cézallier paleoglacier recession.

395
## 4.2 Morphostratigraphy and surface exposure age

A comparison of the landform-sediment assemblages from the Alagnon and Siniq valleys and their surrounding regions, the St-Flour Plateau and Lacapelle Plateau, respectively, allowed us to integrate these distant glacial features into four morphostratigraphic units: (i) the Glacier Maximum (GM), (ii) the Internal Oscillations (IOs) in the Cantal valleys, (iii) the Cantal plateaus and Cézallier Plateau deglaciation and finally (iv) the Cantal cirque glaciation. Morphostratigraphic units and the associated surface exposure ages are presented with their external uncertainties in this section and compiled in Table 5. The surface exposure ages from samples CTL-10, CTL-26, CA12 and CA13 were unreliable due to large uncertainties in the Cl or Al measurements (Table 2) and are thus not discussed in the following text.

### 4.2.1 Glacier Maximum (GM) unit

Glacier maximum (GM) deposits are distal glacial depositional features. The majority of GM deposits are sparse patches of tills or groups of erratic boulders, and only one GM end moraine has been reported: the Pierre Grosse end moraine located on the St-Flour Plateau. In some localities, GM deposits are associated with the occurrence of periglacial features such as boulder fields, e.g., on the Cézens Plateau above the Epie Valley (Fig. 5A) or the Brezons Valley (Fig. 6A).

Four GM features were dated in this work: the Pierre Grosse end moraine, the Moulinges and the Louradou moraines and the Orgues group of erratic boulders (Table 5).

* At the Pierre Grosse end moraine, two erratic (trachytes) boulders were sampled: CA16 (125.19 ± 16.30 ka) from a boulder embedded in the morainic crest and CA17 (124.74 ± 16.24 ka) from a boulder located on the foot of the distal slope of the end moraine. The Gaussian age was 124.97 ± 16.27 ka (Table 5; Figs. 4A and 9).
* Two <sup>10</sup>Be and <sup>26</sup>Al depth profiles were performed in the Moulinges (Brezons Valley; 666 m asl) and the Louradou (Cère Valley; 725 m asl) tills (Appendix B for more details). The resulting ages were 24.24–25.57 and 27.69–28.35 ka (1-sigma uncertainty), respectively.

* Finally, at the Orgues Plateau, a group of erratic boulders was sampled. Three samples from phonolitic boulders gave <sup>36</sup>Cl surface exposure ages of 19.33 ± 2.81 ka (CTL-22), 26.07 ± 3.86 ka (CTL-24) and CTL-26 (n.a). Two samples were taken from gneissic boulders, and the corresponding <sup>10</sup>Be surface exposure ages were 19.56 ± 1.70 ka (CTL-23) and 20.99 ± 1.89 ka (CTL-25). Two composite Gaussians were modeled by P-CAAT; one gave an age of 20.01 ± 2.66 ka (n=3), and the second gave an age of 25.98 ± 2.60 ka (n=1). The first Gaussian result was interpreted as the most likely age for the Orgues erratics (Table 5; Figs. 6A and 9).

### 4.2.2 Internal Oscillation (IO) unit in Cantal valleys

In the Cère Valley (Ancrenaz et al., 2023) as well as in the Allagnon and Siniq valleys, a series of end moraines were found up-valley of the GM deposits (Figs. 4A and 6A). The number of end moraines and the longitudinal extents of these end moraines differed: three sets of end moraines were observed over a length of 7 km in the Alagnon Valley, and two sets of end moraines were observed over a length of 3 km in the Siniq Valley. Despite these differences, these glacial features were grouped into the same morphostratigraphic unit: the Internal Oscillations (IOs) unit, which demarcates multiple glacier stillstands in those two Cantal valleys. The glacial features reported from other Cantal valleys located behind the GM deposits were integrated into this unit.

#### Older IO

The most distal end moraines in the Alagnon and the Siniq valleys are the Pouzat and the Laparra end moraines, respectively, that demarcated the older glacier stillstands and were attributed to the ‘older’ IO subunit.
- At the Pouzat end moraine, five large trachybasaltic erratics were sampled (Table 5): n.a. (CTL-10), 24.85 ± 7.36 ka (CTL-11), 27.45 ± 13.84 ka (CTL-12), 29.20 ± 14.25 (CTL-13) and 18.79 ± 5.73 ka (CTL-14). The resultant Gaussian age was 24.36 ± 11.07 ka.

440

- At the Laparra end moraine, three erratic boulders were sampled: CA27 from a trachyandesitic boulder aged 22.80 ± 2.76 ka (CA27), 21.94 ± 2.48 ka (CA28) and 21.13 ± 3.15 ka (CA34). The associated Gaussian age was 22.01 ± 2.87 ka (Table 5).

## Intermediate IO

In addition to a series of end moraines reported from the Alagnon and Siniq valleys, other glacial features located in the Cantal valleys were attributed to the IO unit, as they were located behind the GM deposits. However, since no specific morphostratigraphic framework was identified, these features were integrated into an intermediate IO subunit. Five glacial features were dated using TCN.

445

- Samples from the Espinouze (CA12) and St-Hypolite (CA13) *roches moutonnées* gave $^{10}$Be surface exposure ages of 20.18 ± 2.13 ka and 21.22 ± 2.15 ka, respectively (Table 5, Fig. 9).

450

- The Caire moraine (1000 m asl; Epie Valley) was located less than 1 km upstream of the GM deposits. Three trachyandesitic boulders were sampled and gave $^{36}$Cl surface exposure ages of 19.65 ± 2.90 ka (CA25), 19.35 ± 2.70 ka (CA26) and 17.97 ± 2.65 ka (CA33). The associated Gaussian age was 19.01 ± 2.85 (Table 5).

- The Cheylanes group of erratics (1095 m) was associated with the end of the Alagnon glacier overflowing toward the St-Flour Plateau. Two samples were taken from trachyandesitic erratics, and the $^{36}$Cl exposure ages were 19.18 ± 2.57 ka (CA18) and 16.65 ± 2.58 ka (CA18). The associated Gaussian age was 18.02 ± 2.58 ka (Table 5).

455

- The Mougueyre $^{10}$Be and $^{26}$Al depth profiles from the Mougueyre till at 900 m asl appeared to be in a steady state (Appendix B). The modeled erosion rate was 38.61-39.80 mm.ka$^{-1}$ (1-sigma uncertainty),

460
yielding a ²⁶Al integration time of 20.44 ± 1.94 ka (Appendix B). This latter age was interpreted as the
minimum age of the Mougeyres till.

Younger IO

The end moraines farthest upstream ascribed to the IO unit in the Alagnon and Siniq valleys were the Chapelle and Laygo end moraines, respectively, which demarcate the last glacier stillstands reported in the studied Cantal valleys. These features also demarcated the occurrence of valley filling (Figs. 4, 6 and 8).

465

- Three erratic boulders (trachyandesitic) were sampled from the Laygo end moraine: 16.97 ± 2.06 ka (CA30), 15.65 ± 1.95 ka (CA31) and 18.85 ± 2.27 ka (CA32). The associated Gaussian age was 17.15 ± 2.52 ka (Table 5).

470

4.2.3 Deglaciation units from the Cantal Plateau and the Cézallier Plateau

Simultaneously with the identification of the IO unit in the Cantal valleys, glacial retreats on the Cantal plateaus and the Cézallier Plateau were identified from a variety of glacial features. However, a distinct morphostratigraphical framework could not be determined from the field evidence. In that respect, all glacial features attributable to local plateau glaciers were grouped within the deglaciation unit. As a result, the ages of glacial features were expected to follow trends primarily controlled by their topographic position and their location between the northeastern Cantal, western Cézallier and southern Cantal regions.

475

- The southern Cantal plateau deglaciation was dated at the Amagat group of erratics (1065 m asl). Three basaltic erratic boulders were sampled and gave ³⁶Cl surface exposure ages of 11.78 ± 1.36 ka (CA41), 12.19 ± 1.36 ka (CA42) and 21.34 ± 2.14 ka (CA43). The two youngest ages (those of CA41 and CA42) were interpreted as having been affected by postdepositional reworking since deglaciation of this plateau was dated at 15 ka (Miras and Guenet, 2013). Consequently, only the age of the CA43 sample was suitable for dating the Amagat group of erratics, with an age of 21.34 ± 2.14 ka.

480
- The northeastern Cantal Plateau deglaciation was dated at the Pinatelle group of erratic boulders (1135 m asl) with five erratic boulders dated using $^{36}$Cl to 18.28 ± 2.44 ka (CTL-05), 15.28 ± 2.28 ka (CTL-06), 16.62 ± 2.15 ka (CTL-07), 17.30 ± 2.17 ka (CTL-08) and 19.83 ± 2.53 ka (CTL-09). The associated Gaussian age was 17.50 ± 2.80 ka (Table 5; Fig. 9).

485

- The Cézallier Plateau deglaciation was dated from two groups of glacially transported volcanic boulders (mainly basalts and phonolites) at the Combalut (1200 m asl) and Pradiers (1325 m asl) groups of erratic boulders (Fig. 8B-C). At the Combalut site, five erratic boulders were sampled, and the calculated $^{36}$Cl surface exposure ages were 18.31 ± 1.99 ka (CTL-15), 19.25 ± 3.6 ka (CTL-16), 18.19 ± 3.24 ka (CTL-17), 21.24 ± 3.18 ka (CTL-18) and 16.19 ± 1.78 ka (CTL-19). The associated Gaussian age was 18.40 ± 3.26 ka. For the Pradiers site, five boulders were sampled, and the calculated $^{36}$Cl surface exposure ages were 17.71 ± 2.51 (CTL-27), 15.24 ± 2.13 (CTL-28), 17.45 ± 2.42 (CTL-29), 17.18 ± 2.47 (CTL-30) and 19.69 ± 2.33 ka (CTL-31). The associated Gaussian age was 17.54 ± 2.80 ka (Table 5; Fig. 9).

490

495

### 4.2.4 Cantal cirque unit

Finally, the last glacial morphostratigraphic unit was found to be associated with the Cantal cirque glaciation, using glacial remnants found in the Lagnon Cirque. Three subunits were discriminated: (i) the Lagnon cirque glacier confinement, demarcated by the Prat de Bouc moraine, (ii) the Lagnon cirque glacier retreats demarcated by abandoned moraines on cirques floors and (iii) the Lagnon cirque glacier fragmentation characterized by a discontinuous cirque glaciation that produced small, local glaciers, as reported from the Jambe end moraine (Fig. 5B).

500

Only the Prat de Bouc moraine was dated from two trachytic boulders with $^{36}$Cl surface exposure ages of 14.06 ± 1.99 ka (CA36) and 16.63 ± 2.38 ka (CA37) and a Gaussian age of 15.34 ± 2.18 (Table 5; Fig. 9).
# 5 Interpretations and discussion

505

## 5.1 New glacial chronology for the CCMD

The surface exposure ages obtained from TCN dating combining $^{10}$Be, $^{26}$Al and $^{36}$Cl from erratic boulders, polished bedrocks and depth profiles in tills provide, with very few exceptions, a coherent global chronological dataset. Indeed, the forty-four surface exposure ages produced in this study from seventeen glacial features (Table 5; Fig. 9) were consistent with the relative chronology provided by the morphostratigraphical framework established here, indicating increasingly young ages toward upstream areas. Indeed, all surface exposure ages framed MIS 2 (29 to 11 ka) except that of the Pierre Grosse end moraine (~125 ka; n = 2). These older results are not discussed here because this study focuses on Late Pleistocene paleoglacier fluctuations.

510

The chronology of the following glacier stadial was specified as follows: (i) the Early-LLGM, (ii) the Late-LLGM, (iii) a general glacier retreat punctuated by glacier stillstands that led to the Cézallier Plateau deglaciation and finally (iv) the Cantal cirque glaciation. Due to individual surface exposure age uncertainties and associated landform age uncertainties, the chronological boundaries of these major glacial stadials overlapped.

515

### 5.1.1 Early-Local Last Glacial Maximum (Early-LLGM) and Late Local Last Glacial Maximum (Late-LLGM)

The surface exposure ages obtained from the GM and the Older IOs were attributed to the global LGM (26 to 19 ka; Clark et al., 2009) but were chronologically well-demarcated between two events:

520

- the Early-LLGM dated between 28-24 ka according to the two $^{10}$Be and $^{26}$Al depth profiles from the Moulinges and the Louradou tills, that defines the paleoglacier maximal extent during the last glaciation,

- the Late-LLGM centred at 22 ka according to the Laparra end moraine providing clustered ages with a Gaussian age of 22.01 ± 2.85 ka (n = 3), that defines a paleoglacier extent that almost reach the Early-LLGM.

525
However, two landforms, the Orgues group of erratic boulders and the Pouzat end moraine, provided surface exposure ages that overlapped with these two peaks. For the Orgues group of erratic boulders, three surface exposure ages were centered at ~20 ka ($^{10}$Be and $^{36}$Cl), and one erratic boulder was 26.07 ± 3.86 ka (CTL-24; $^{36}$Cl). For the Pouzat end moraine, the surface exposure ages obtained were centered at 29–24 ka, but high individual uncertainties did not allow us to interpret the landform age.

One geomorphological scenario was deemed plausible for investigating the potential sources of these two chronological peaks at least at the Orgues group of erratic boulders: the polygenic landform. Two glacier advances that reached nearly the same frontal position during the Early-LLGM and again during the Late-LLGM could produce two surface exposure age peaks. Polygenic landforms have been reported in other European mountains, such as the Alps (Roattino et al., 2021), the Pyrenees (Delmas et al., 2011) and the Serra da Estrela (Vieira et al., 2021). For these cases, multiple glacial advances reworked older (previously exposed) and fresh (no prior exposure) sediments into the same landform. This interpretation implies that the Rhue paleoglacier and probably other paleoglacier outlets of the CCMD reached approximately the same extents during the Early-LLGM (29-24 ka) and the Late-LLGM (24-20 ka).

According to these results, the age of the Bort proglacial lake could be stated. This lake was produced by the Rhue paleoglacier that reached and dammed the ice-free Dordogne Valley at the Orgues Plateau (Figs. 2 and 7A). Our chronological results at the Orgues erratics show that this ice-dammed proglacial lake existed during the Early-LLGM (29 to 24 ka) and the Late-LLGM (24 to 20 ka).

### 5.1.2 Deglaciation trends

The rhythm and steps of the following deglaciation in the Cantal valleys can only be specified roughly by the surface exposure age results obtained from the Intermediate and Younger IO units and by the Cantal plateaus and the Cézallier Plateau deglaciation unit (Fig. 9). The surface exposure ages obtained for these units covered a long period between 21 and 15 ka, and the individualization of the glacial events is not clear.
In the Cantal valleys, surface exposure ages pointed toward ~19 ka (Fig. 9):

550 - 20.44 ± 1.94 ka in the Mougueyres till (Rhue Valley; 890 m asl),

- 19.01 ± 2.85 ka in the Caire moraine (Epie Valley; 1050 m asl), and

- 18.02 ± 2.58 ka in the Cheylanes erratics (Alagnon Valley; 1100 m asl).

This rapid deglaciation after the Late LLGM was supported by geomorphological evidence from other areas, such as the kame terraces in the Brezons Valley and the valley filling reported from the Alagnon and the Siniq valleys (Fig. 9) and the Cère Valley (Ancrenaz et al., 2023).

Glacial retreat in valleys was accompanied by deglaciation on the Cantal plateaus and Cézallier Plateau. A strong topographic influence was highlighted by the earlier deglaciation in the southern Cantal, with the Amagat erratics at 1065 m asl (21.34 ± 2.14 ka), whereas the northeastern Cantal and Cézallier Plateau deglaciation was centered at 19–17 ka:

560 - approximately 17.50 ± 2.80 ka in the Pinatelle erratics (eastern Cantal; 1140 m asl),

- approximately 18.40 ± 3.26 ka in the Combalut erratics (Cézallier Plateau; 1150 m asl), and

- approximately 17.54 ± 2.80 ka in the Pradiers erratics (Cézallier Plateau; 1300 m asl).

This retreating trend is interrupted by at least one stillstand or readvancement at 17.15 ± 2.52 ka at the Laygo end moraine (southern Cantal; 1005 m asl). However, due to the overlapping ages of the Cézallier Plateau deglaciation and the Laygo end moraine, this work could not precisely determine the chronological order of these two events.

These results were in good agreement with the ages of the kame terraces in the Santoire Valley at 15.7-17.1 ka cal BP (Veyret, 1978; 2 sigma radiocarbon age calibrated with CLAM v.2.3.2 software and the 'IntCal20' calibration curve; Blaauw, 2010; Reimer et al., 2020).
570

### 5.1.3 Cantal cirque glaciation

The Prat de Bouc moraine was dated to 15.34 ± 2.18 ka and was the youngest glacial landform dated in this study (Figs. 9 and 10), implying that continuous deglaciation occurred in the Alagnon Valley and its tributaries between the deposition of the Cheylanes erratics (18.02 ± 2.58 ka) and the Prat de Bouc moraine, located in the Lagnon Cirque. The latter landform demarcated the confinement of the glacier in the Lagnon Cirque and provided an upper chronological limit for the Cantal cirque glaciation. The Lagnon Cirque, and likely other glacial cirques from the Cantal Mountains, were glaciated during the Oldest Dryas end, while the Cézallier Plateau was probably already fully deglaciated at this time (~17 ka). Considering the elevations and orientations of Cantal cirques, a relatively long subsistence period of these cirque glaciers was expected, probably until at least the beginning of the Bølling/Allerød (14.8–12.8 ka), since this latter period was associated with warmer climate in the area (Duprat-Oualid et al., 2022; Gandouin et al., 2016; Ponel et al., 2016, 1991; Vergne, 1991).

575

580

### 5.1.4 Limitations

Two exceptions to this general deglaciation scheme were found in the ages obtained from the Espinouze and St-Hypolite polished bedrocks, inferred to belong to the Intermediate IO unit. These two ¹⁰Be ages, 20.18 ± 2.13 and 21.22 ± 2.15 ka, were older than expected considering the sampling positions (Fig. 9). Indeed, the Cantal valley deglaciation was expected to have occurred between 20-16 ka. This time lag was interpreted as the effect of inheritance from preglaciation exposure, a common result for polished bedrocks that have not experienced intensive subglacial erosion (Crest et al., 2017); i.e., subglacial erosion does not remove sufficient material (<4-5 m deep) to set the *in situ* nuclide concentration to zero.

585

## 5.2 Comparisons with the local paleoenvironment and paleoclimatic implications

The main outcome of the presented reconstruction of glacial fluctuations in the Cantal Mountains and on the Cézallier Plateau supports synchronicity with the glacial fluctuations reconstructed in the Aubrac Mountains, 50

590
km south of the study area (Ancrenaz et al., 2022). This corroborates that the western Massif Central, in which
the CCMD and the Aubrac Mountains are located, could be taken as a homogenous paleoclimatic domain. On
this basis, the glacier-favorable periods highlighted by the glacial chronology identified in this study strengthened
and extended the chronostratigraphy available for the western Massif Central (Ancrenaz et al., 2022).

* During the early part of MIS 2 in the western Massif Central, between 29–24 ka, the Early LLGM in the CCMD occurred between 28–23 ka (this work, Figs. 9 and 10) and the LLGM in the Aubrac Mountains occurred between 27–23 ka (Ancrenaz et al., 2022). These results match the global LGM *sensu* Hughes and Gibbard (2015) that occurred during Greenland Stadial (GS) 3 between 27.5–23.3 ka (Rasmussen et al., 2014). In France, the Last Permafrost Maximum (LPM), for which widespread thermal contraction cracking events were identified between 30–24 ka, demonstrated a cold and arid climate (Andrieux et al., 2018). In particular, high sedimentation rates of coversands in southwestern France have been reported and dated to the Heinrich Stadial 2 (HS2), which was recorded between 26.5–24.3 ka (Sanchez Goñi and Harrison, 2010; Sitzia et al., 2015; Bertran et al., 2020).

The LLGM of an alpine icefield was also attributed to this period (Wirsig et al., 2016; Monegato et al., 2017), with air mass advection from the Mediterranean basin as the dominant moisture source centered at 25.3 ka (Luetscher et al., 2015). These data provide a basis to propose that during this period, the southward displacement of westerlies in the North Atlantic favored cyclogenesis in the Mediterranean basin, which in turn favored enhanced landward moisture advection (Florineth and Schlüchter, 2000; Kuhlemann et al., 2008; Luetscher et al., 2015; Monegato et al., 2017).

Altogether, these proxies depicted reduced westerlies and stronger southerlies in western Europe. As a result, the Early LLGM in the western Massif Central was likely to be supported by enhanced southerlies. However, the glacier length asymmetry between the western and eastern valleys indicated that westerlies still greatly impacted the glacier mass balance.
615

620

625

630

635

* The second part of the MIS 2 in the western Massif Central, between 24–19 ka, was demarcated by the Late LLGM in the CCMD (23–19 ka) and a major glacier advance in the Aubrac Mountains at 23–20 ka (Ancrenaz et al., 2022). This period was coeval with the maximal extent of the Eurasian ice sheet (Hughes et al., 2015) and centered on the minimal sea level of -125 m (Mix, 2001). The sea surface temperatures reconstructed from the Iberian margins provided minor cooling during this period, between 1 to 2 °C compared to the current temperature, a much lower amplitude than those estimated during the HS2 and HS1 (Eynaud et al., 2009). Coversands from southwestern France experienced a sedimentation rate reduction associated with a more humid and/or warmer climate (Sitzia et al., 2015).

This period was synchronous with major glacier advances in the Alps (Wirsig et al., 2016; Monegato et al., 2017) and the Pyrenees (Delmas et al., 2022). According to the work of Luetscher et al. (2015), moisture advection from the Mediterranean basin was less important at this time than during the early part of the MIS 2 but still greater than it is today.

On this basis, it seems that the major glacier advance recorded in the western Massif Central occurred during a period of potential westerly enhancement with less but still important southerlies.

* The third part of the MIS 2 in the western Massif Central, between 20–16 ka, was demarcated by generalized glacier retreats, both in the CCMD and the Aubrac Mountains, with glacier stabilization or readvancement at ~17 ka in the southern Cantal Mountains and at ~18 ka in the Aubrac Mountains (Ancrenaz et al., 2022). This deglaciation event was coeval with the HS1 (18.0–15.6 ka; Sanchez Goñi and Harrison, 2010), which started with the progressive cooling of the North Atlantic between 19.0–17.4 ka (Pascual et al., 2020), inducing long-term effects on the southwestern European climate until 15.6 ka (Sanchez Goni and Harrison, 2010; Kageyama et al., 2005). The cold culmination in sea surface temperature (SST) in the Gascogne Gulf was reached between 17.4–16.2 ka (Pascual et al., 2020).
During this period, a peak in coversand sedimentation was recorded in southwestern France, highlighting the return of a cold and arid climate (Bertran et al., 2020).

The Eurasian ice sheet recession started at 20–19 ka in relation to the relatively high summertime insolation in the Northern Hemisphere (Hughes et al., 2015). The same trends were reported for the Alps icefield (Wirsig et al., 2016), but an enhanced trend was indicated by the progressive reduction in southerlies that nourished the Alps during this period (Luetscher et al., 2015). In the peri-Mediterranean mountains, generalized glacier recessions were attributed to the aridity induced by the HS1 (Allard et al., 2021).

In the western Massif Central, the same glacial trends were reported. In this context, both the westerlies and southerlies were reduced. The combination of higher summertime insolation with aridity was deemed responsible for the rapid deglaciation observed in the area.

* Finally, during the end of the MIS 2 (16–11 ka) in the western Massif Central, cirque glaciers subsisted only in relatively high Cantal cirques and likely in high Monts Dore cirques (> ~1400 m asl). This cirque stadial began at ~16 ka according to this work (Figs. 9-10). This timing was coeval with the transition between the HS1 and Bølling/Allerød that demarcated slight climatic warming in the Cantal (Duprat-Oualid et al., 2022) and Aubrac (Gandouin et al., 2016).

In the Alps or in the Pyrenees, paleoglaciers were restrained to higher-elevation areas after large glacier retreats occurred during the Bølling/Allerød (Ivy-Ochs et al., 2008) at 2400 m asl (Reixach et al., 2021).

In the western Massif central, no surface exposure ages constrained the full deglaciation of the Cantal nor Monts Dore cirques. However, the abundance of periglacial landforms in these areas suggested pronounced cold conditions after the deglaciation stage.
# 6 Conclusion

Our geomorphological reconstitutions of landform-sediment assemblages in combination with terrestrial cosmogenic nuclide (TCN) dating ($^{10}$Be, $^{26}$Al and $^{36}$Cl) from the valleys (Alagnon, Brezons, Siniq, Cère and Rhue) and plateaus of the Cantal Mountains and the Cézallier Plateau depicted a robust glacial chronology. These findings strengthened and extended northward the existing chronostratigraphy available for the western Massif Central. From the 48 surface exposure ages obtained, two are potentially attributed to pre-MIS 2 glacial event (~125 ka), the other allow to distinct four glacial events within the MIS 2:

- the Early-Local Last Glacial Maximum (LLGM) occurred between 29–24 ka, synchronous with paleoclimatic configuration characterized by reduced westerlies and enhanced southerlies;

- the Late LLGM occurred between 24–20 ka, synchronous with a paleoclimatic configuration characterized by the potential improvement of westerlies with a slight reduction of southerlies;

- the deglaciation that occurred between 20–16 ka, with a stillstand at ~17 ka, was synchronous with reduced westerlies and southerlies and increased summertime insolation;

- finally, the Cantal cirque glaciation that occurred after ~16 ka demonstrated the long persistence of cold conditions in Cantal cirques at least above ~1400 m asl.

These outcomes are partly based on TCN depth profiles coupling $^{10}$Be and $^{26}$Al, a valuable tool when alternatives (for example, erratic boulders) are unavailable. Two out of three $^{10}$Be and $^{26}$Al depth profiles obtained in this work provide chronological constraints for till deposition, with three to four samples obtained per site. One depth profile reached steady state and did not constrain the exposure age but indicated erosion rates of 3.66–3.98 cm.ka⁻¹, consistent with published data from unconsolidated Pleistocene tills (1.5–6.9 cm.ka⁻¹; Wüthrich et al., 2017). However, this work did not account for the effect of density evolution with thickness, which could have influenced the resulting surface exposure ages and denudation rates.
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It appears that glacier-favorable periods in the western Massif Central followed the main paleoclimatic trends recorded by the neighboring paleoenvironmental proxies in western Europe. By its location, at the intersection of paleoclimatic influences from the North Atlantic and the Mediterranean Sea, paleoglaciers of the Cantal Mountains and the Cézallier Plateau, throught coupled glacial/climate simulations, provide a high potential to constrain paleoclimatic conditions, especially regarding atmospheric circulation changes during the MIS 2. For this purpose, this work provides new and robust geomorphological and chronological constraints.

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# 7 Appendix A - Adapted geomorphological typology for glacial features identified and mapped in the Cantal Mountains and the Cézallier Plateau

The aim of mapping glacial depositional and erosional features from the Cantal Mountains and the Cézallier Plateau is to provide geomorphological arguments to reconstruct the extents and timing of late Pleistocene glaciations. To this end, mapping processes focus on glacial geomorphological features that are significant for such reconstructions, such as ice-marginal landforms (end moraines, proglacial outwashes, meltwater channels, etc.). This approach relies on the establishment of a comprehensive typology that considers the local contexts, such as the specific geological and topographical settings, from each study site that directly influence glacial dynamics and the associated glacial landform-sediment assemblages.

Other landform-sediment assemblages from periglacial, fluvial or gravitational landscapes are also studied, as some of these features are involved in glaciation reconstructions or in the postglacial evolution of glacial landforms and sediment assemblages.

## 7.1 Glacial deposits in the CCMD with a focus on tills

Glacial sediments in the CCMD were identified and mapped by geomorphologists and geologists between 1951 and 1986 (Boisse de Black, 1951; Goër de Hervé, 1972; Valadas, 1984; Van Dorsser, 1986, 1982; Varet, 1970; Veyret, 1978). Resultant typologies used sedimentological criteria to distinguish at least three glacial sediments: tills, fluvio-glacial deposits and glacio-lacustrine deposits.

Till identification relied on these main characteristics: unsorted diamicton with the presence of erratic and rounded clasts. Additional criteria have been used to discriminate till subunits, such as (i) the topographic position of the tills, e.g., valley tills, valley-slope tills or plateau tills (Goër de Hervé et al., 1988; Nehlig et al., 2001a); (ii) the surficial morphology of the deposits, e.g., moraine crests or ridges, hummocky terrains and terraces; and (iii) the freshness aspect, which is based on the thickness of the alteration cortex of clasts and the degree of rubefaction within younger and older tills (Brousse et al., 1972; Goër de Hervé et al., 1988).
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These broad identification criteria lead to disparate mapping coverages (Fig. 1). Moreover, without direct
observations of superficial deposits through sections, these criteria are often too broad and could potentially lead
to misinterpretations, mainly due to the CCMD geological settings. To produce comprehensive and restrictive
criteria for identifying tills in the field while limiting sources of misinterpretation, a new typology is provided
here. The main criteria used, the size, shape and sources of boulders and surficial morphology, are discussed in
light of their geological context and geomorphological considerations.

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The CCMD geological context (volcanized pre-Cambrian dissected plateaus, Fig. 1) largely influences the nature
of Quaternary sediments. Concerning the identification of glacial deposits, some geological particularities
complicated the use of classical criteria in till recognition. These classical criteria included the erratic sources, the
size or shape of boulders, the matrix textures and the surficial morphology. The major source of uncertainty is
related to volcanic breccia. Indeed, volcanic breccia encompasses various debris flows and avalanche debris with
kilometric boulders (trachyandesitic megaboulders) and represents almost 90% of the Cantal stratovolcano
volume (Arnaud et al., 2002). These rocks contain all main volcanic lithologies and pyroclastics (pumices, ash,
etc.). Fossilized alluvium and lacustrine clays are locally intercalated in volcanic breccias. These characteristics
interfere with classic field criteria applied for the recognition of glacial deposits. Bare volcanic breccias,
especially in the Cantal valleys, produce volcanic clasts of all sizes, shapes and lithologies. In these contexts, the
use of the classic criteria is not sufficiently selective.

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These structural conditions highlight the potential for misinterpretations when mapping glacial features but are
restricted to Cantal valleys. In these areas and in the absence of direct observations of superficial deposits, these
criteria must be carefully used to identify glacial features. The typology of the geomorphological features mapped
in this work is presented in the following section.

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## 7.2 Typology of glacial sediments and landforms

### 7.2.1 Glacial erosional features

#### Scoured bedrock

Scoured bedrocks are rock outcrops with distinct subglacial erosional features such as polished surfaces, striae and plucking fractures (Benn and Evans, 2010). Scoured bedrocks can take various morphologies from large roches moutonnées (with axes hundreds of meters long) to local bedrock steps (with axes tens of meters long). The lithological context strongly modulates the aspects of scoured bedrocks. In granitic and metamorphic terrains, these landforms are easily identifiable, for example, on the Artense Plateau (Veyret, 1972) or in the lower parts of the Cantal valleys. In contrast, in volcanic terrains, these morphologies are subtler. This distinction is interpreted as the effects of more intensive postglacial erosion leading to rim cicatrizations, striae and polish destruction due to the relatively weak volcanic rocks.

### 7.2.2 Tills and moraines

Three distinct till categories are defined according to a combination of their lithological contents and their topographic positions: valley tills, plateau tills and overflow tills (Fig. 2). These units allow us to roughly identify the clast sources with a focus on delimiting the extent of local glaciation on plateaus and extensive outlet valley glaciers. In addition, two morphological descriptors are associated with these till units to identify the following landforms: moraine ridges and moraine lineations.

#### Valley tills

Valley tills encompass the extent of unsorted and heterogeneous materials supported by a developed silty and/or sandy matrix and found in the Cantal valleys (Fig. 2D-E). These deposits are constituted by a mix of volcanic lithologies in the upper parts of the Cantal or Cézallier valleys and by mixes of volcanic and plutonic rocks in the lower valley areas. These deposits possess typical till characteristics (Dreimanis and Schlüchter, 1985; Menzies, 2003; Menzies et al., 2006). Their thicknesses can vary from less than one meter to ten meters.
## Plateau tills

Plateau tills are units composed of regrouped glacial deposits containing subautochthonous materials, i.e., basaltic materials with no erratics, located on the Cantal Mountains and Cézallier Plateaus. The absence of 'true' erratics provides evidence of local ice flow attributed to local plateau glaciers. Typical plateau tills consist of reworked basaltic saprolites with rounded to subangular clasts supported by a coarse sandy-gravelly matrix (Fig. 2A-C and F). The shape of the clasts depends mainly on altered basalt facies. Generally, plateau tills are thin, less than 1 m thick, except for glacial lineations (see glacial lineation landforms).

## Overflow tills

Overflow tills present the same sedimentological characteristics as valley tills but are located on the Cantal Plateau. In the field, overflow tills are easily identifiable by the erratic materials sourced from the Cantal valleys (mainly trachyandesitic or trachytic lithologies). These deposits highlight ice flows from valleys that overflowed on the adjacent plateaus. Overflow tills can extend along plateau tills but are clearly delimited.

## Moraine ridge

Moraine ridges are ice-marginal landforms consisting of linear or curvilinear ridges that delimit glacier frontal positions. In the Cantal valleys, moraine ridges are arcuate and discontinuous with heights of dozens of meters and delimited confined glacier snouts. On the Cantal Plateau, moraine ridges are found only in association with overflow tills. Their morphologies are also discontinuous but generally relatively low (up to 5 m) and delimit lobate glacier margins, i.e., unconfined glacier snouts.

## Glacial lineation

Glacial lineations are subglacial landforms associated with plateau tills. Glacial lineations are linear landforms that are hundreds of meters long and up to ten meters high, subparallel to the direction of ice flow. These landforms consist of thick plateau till accumulations (Fig. 2A). These landforms are favored by residual basaltic reliefs that nourish basal ice (Stroeven et al., 2013).
### 7.2.3 Fluvio-glacial and glacio-lacustrine features

#### Fluvio-glacial and glacio-lacustrine deposits

Fluvio-glacial and glacio-lacustrine deposits are defined using sedimentological criteria in association with specific geometry such as terraces or plain morphologies. This unit regroups coarse fluvio-glacial deposits and fluvial or lacustrine deposits connected with glacial features as end moraines.

#### Meltwater channels

Meltwater channels are erosion channels in tills or fluvio-glacial deposits and often do not contain contemporary drainage channels (Greenwood et al., 2007). These features are found mainly in the Cantal valleys in combination with moraine ridges. Meltwater channels can be perpendicular to moraine ridges and cut off these features or can be subparallel to the moraine ridges.

#### Valley fillings

Valley fillings are flat-bottomed valleys associated with aggradation dynamics controlled by valley deglaciation in a postglacial-dominated context (Murton and Ballantyne, 2017). These morphologies are common in the Cantal valleys and have been identified in previous works (Ancrenaz et al., 2023). These features are characterized by (i) being closed by end moraines, (ii) the absence of postglacial erosion leading to the establishment of alluvial terraces and (iii) being connected to large alluvial fans alimented by tributaries.

### 7.2.4 Periglacial features

#### Scree

Scree is a ubiquitous landform in the Cantal Mountains, especially on valley slopes and in cirques or amphitheaters. Generally, scree is associated with basaltic escarpments or basaltic plateau rims and consists of basaltic angular to subangular boulders. The majority of scree is vegetized.

#### Pronival ramparts
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Pronival ramparts are accumulations of heterometric debris (boulder- to sand-sized) forming ridges (up to one meter high but more often represented only by a high boulder density) located downslope of persistent snow patches. The processes involved in pronival rampart establishment are generally assumed to be rockfall coupled with rolling and sliding rocks across snow patches. Other processes, such as debris flows, avalanches and solifluction, could also be involved in their formation (Matthews et al., 2017).

### Blockfield

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Nonglaciated parts of the Cantal Plateau are covered by blockfields, which are groups of openwork rounded to angular blocks. The shapes and sizes of these boulders are dependent on the rock alteration type. These features are especially common on basaltic residual reliefs, usually at elevations above 1000 m a.s.l., and are associated with tor-like features. Blockfields are interpreted as remnants of periglacial conditions.

## 7.2.5 Fluvial features

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### Alluvial plains

Alluvial plains are modern inland plains that generally lie +2 m above the corresponding channel networks. These features are generally framed by alluvial terraces.

### Alluvial terraces

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Alluvial terraces are perched alluvium above alluvial plains, forming discontinuous landforms. These features are regrouped into generations by comparing their relative elevations above the corresponding alluvial plains. Generally, alluvial terraces are flat with an abrupt riser toward the active channel network.

### Alluvial fans

Alluvial fans are alluvium accumulated at the outlets of streams and are often steep and incised in the host rocks. These accumulations are shaped into triangles with variable thicknesses and sedimentological facies.
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### 7.2.6 Gravitational features

#### Deep-seated Gravitational Slope Deformation (DGSD)

Deep-seated gravitational slope deformations (DGSDs) are large-scale and slow-motion rock mass deformations (Coquin et al., 2015) that affect the slopes of deep and large Cantal valleys. The largest DGSD reported from the Cantal valleys is the Vixouze landslide in the Cère Valley, with an area of 11.5 km² (Ancrenaz et al., 2023). The general morphology of DGSDs is characterized by two components: (i) multiple slide and tilted rock masses (basalt and/or volcanic breccias) that conserved their coherence and highlight failures in the upper DGSD parts and (ii) landslide feet with disorganized morphologies formed by lobate accumulation that reworked the DGSD materials spread on the valley bottom. The filling of DGSD counterslopes by volcanic deposits (tills or volcanic deposits) demonstrated that these landforms preexisted to at least the last glaciation period. These major features can be particularly well observed in slopes constituted by volcanic breccias capped by basaltic lava flows, with well-identifiable head scarps that generally correspond to Cantal basaltic plateau rims.

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#### Superficial landslides

Superficial landslides, in opposition to DGSDs, are regrouped localized landslides that affect the soils of the study area through a variety of processes such as slides, flows or creeps.

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#### Colluvial thickening

A colluvial thickening is an accumulation of colluvia, unsorted fine debris that can contain rounded to angular clasts and is generally located downslope. These features can be locally enriched in sands due to volcanic breccia weathering and/or in organic matter and can accumulate up to 10 m.

## 8 Appendix B - In situ terrestrial cosmogenic nuclide (TCN) depth profiles in tills from the Cantal Mountains using coupled 10Be and 26Al.

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Three sections in tills from the Cantal Mountains are sampled for ¹⁰Be and ²⁶Al depth profiles: the Moulinges till (Brezons Valley), the Louradou till (Cère Valley) and the Mougueyres till (Rhue Valley). Each is integrated into
the local morphostratigraphy (Sections 4.1 & 4.2). The following sections describe the studied sections, the methodology of ¹⁰Be and ²⁶Al depth-profile modeling, and the results and interpretations. Descriptions of the physical and chemical extractions and measurements of ¹⁰Be and ²⁶Al are provided in the main text (Section 3.2.2).

# 8.1 Material and Methods

## 8.1.1 Moulinges depth profile

The Moulinges till (44.8982°N; 2.5184°E; 666 m asl) is the distal glacial feature reported in the Brezons Valley in the southern Cantal Mountains. It is associated with the Early Local Last Glacial Maximum (Early LLGM). In the Moulinges till, a section 200 to 800 cm deep and up to 50 m long was generated by a local landslide (this landslide occurred between summer 2019 and summer 2020 according to the author observations).

This section shows a uniform and compacted diamicton that contains rounded volcanic clasts (50 cm max.) with rare quartz pebbles (5 cm max.) supported by an unsorted sandy matrix rich in volcanic granules and gravels (Fig. 1B). Locally, lenses of gravels or coarse sands enriched in quartz grains are intercalated. In the upper part, between 75 and 120 cm deep, the till is reworked by typical head deposits with clasts that point downstream and a relatively silty matrix. The head is capped by a thick colluvial soil, from a 75-cm depth to the top. Three samples, CA01, CA02 and CA03, were taken from the Moulinges till at depths of 100, 200 and 335 cm, respectively (Table 1). Sample CA01 was taken from the base of the head deposits. Samples CA02 and CA03 were taken in the till unit (Fig. 1).

## 8.1.2 Louradou depth profile

The Louradou till (44.8957°N; 2.7984; 725 m asl) is located at the Vézac pass, above the Cère Valley in the southeastern Cantal Mountains (see the main text, Section 4). This till is associated with the retreat of the Cère outlet glacier after the Early LLGM. The studied section is 250 cm deep and 15 m long (Fig. 1). The Louradou
till is a uniform and compacted diamicton with rounded volcanic clasts (50 cm max) dominated by volcanic pebbles (20 cm max) and accompanied by quartz pebbles (max 10 cm). The matrix is dominated by coarse sands with intercalated gravel lenses. Four samples were taken directly in the till unit for the 10Be and 26Al measurements: CA04 at 45 cm, CA05 at 90 cm, CA06 at 135 cm and CA07 at 230 cm (Fig. 1).

### 8.1.3 Mougueyres depth profile

The Mougueyres till (45.3118°N; 2.6424°E; 891 m asl) is located in the northern Cantal Mountains. This deposit filled a depression in a subglacially scoured bedrock context. This deposit is associated with the Cantal plateau deglaciation (see main text Section 4). A 135-cm-deep section was sampled for 10Be and 26Al measurements. The Mougueyres till is composed of a compacted diamicton that combines rounded volcanic clasts and subangular gneissic clasts (25-cm maximum) embedded in a coarse sandy matrix. This till unit is found between 135 and 80 cm deep, and a thick soil is developed on the till (Fig. 1). Four samples are taken: CA08 at 17.5 cm, CA09 at 32.5 cm, CA10 at 72.5 cm and CA11 at 122.5 cm. The three upper samples are taken from the pedogenized part of the section. Sample CA11 is taken from the till unit.

## 8.2 Theoretical background of ¹⁰Be and ²⁶Al depth-profile modeling in tills

Terrestrial cosmogenic nuclides (TCNs), such as berylium-10 (¹⁰Be) and aluminum-26 (²⁶Al), result from primary and secondary cosmic ray particle interactions with atomic nuclei in rocks or sediments at the Earth's surface, typically between 0 and 5 m deep (Gosse and Phillips, 2001). The accumulation of TCN in the eroding surface is expressed as follows (Lal, 1991):

$$N(x, t) = N_{\text{inherited}}(x)e^{-\lambda t} + \sum_{i} \frac{P(x)_i}{\lambda + p\varepsilon/\Lambda_i} e^{-p(x+\varepsilon t)/\Lambda_i} (1 - e^{-(\lambda+p\varepsilon/\Lambda_i)t}) \quad (\text{Eq. 1})$$

where $N(x,t)$ is the TCN concentration (at.g⁻¹) for a given depth (x, in cm.g⁻²) after a given time (t, in yr) produced by production pathway i with $\Lambda_i$ (in at.g.yr⁻¹) being the attenuation length (in g.cm⁻²). Other parameters
are the density ($p$ in g.cm$^{-3}$), erosion rate at the surface ($\varepsilon$ in cm.yr$^{-1}$) and decay constant of the given TCN ($\lambda$ in yr).

Production pathways describe nuclear reactions in exposed sediments or rocks according to the particles involved (neutrons and muons) in TCN production, with specific production rates depending on particle energy and on the chemical compositions of target minerals or rocks. The main $^{10}$Be and $^{26}$Al production pathways are described as follows:

- High-energy neutrons produce $^{10}$Be and $^{26}$Al at high rates in the subsurface (0 to 2-3 m) through spallation reactions in quartz or volcanic whole rock, respectively.

- Slow muon capture and fast muon interactions produce $^{10}$Be and $^{26}$Al at relatively slow rates but are dominant production pathways at depths below 3 m.

The combination of these production pathways produces TCN concentrations that exponentially decrease with depth.

## 8.3 Application in glacial deposits

Theoretically, TCN depth profiles are a valuable method applicable to unconsolidated sediments, as these profiles allow us to calculate three variables: the exposure age, the denudation rate and the amount of inherited TCN (Braucher et al., 2009; Hidy et al., 2010). However, the main limitation to this approach is the steady-state and ‘pseudoinheritance’ (Delmas et al., 2018; Wüthrich et al., 2017). For cases without strong chronological or erosion rate constraints from exterior data, modeled TCN depth profiles have to produce triplet solutions: the age, erosion rate and inheritance. In some cases, high uncertainties could affect such triplet solutions. Thus, combinations of two nuclides, for example, $^{10}$Be and $^{26}$Al, allow better-constrained exposure histories to be obtained (Fülöp et al., 2015; Granger and Muzikar, 2001)
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The steady state is reached when TCN accumulation is balanced by TCN destruction through radioactive decay and erosion at the surface. The integration time ($T_{eff}$, in yr) is the time needed for a given TCN to reach the steady state under specific erosion rates (Lal, 1991). It is calculated as follows:

$$T_{eff} = \frac{1}{\lambda + \left(\frac{p}{\lambda}\right) * \varepsilon} \qquad (\text{Eq. 2})$$

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As production pathways are depth-dependent (Eq. 1), the integration time varies with depth. As a result, the steady state is reached faster in the subsurface (0 to 1 m, due to the high spallogenic production rates) than in the deep region (1 to 5 m, due to the dominant low-muogenic production). Following Lal (1991), to determine if a depth profile has reached the steady state, erosion rates are calculated for infinite exposure (a forced steady state) using Eq. 1 at each sampled depth. If the erosion rates increase with the depth, the steady state has not been reached, and TCN has continued to accumulate. If the erosion rates are constant with depth, the steady state has been reached, and only the minimum surface exposure ages can be calculated with the integration time ($T_{eff}$). If the erosion rates decrease with depth, the depth profile has experienced a complex exposure history due to inheritance and/or burial or erosional events. For example, in unconsolidated sediments, the ¹⁰Be concentrations reached a steady state after exposure at ~200 ka with a denudation rate of ~5 mm.ka⁻¹ in Pleistocene alluvial terraces (Delmas et al., 2018; Ruszkiczay-Rüdiger et al., 2016) and after 10 to 15 ka with a denudation rate of ~50 mm.ka⁻¹ in alpine LGM tills (Wüthrich et al., 2017).

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Another limitation of depth-profile modeling is related to the discrimination of inheritance and ‘pseudoinheritance’ as defined in Wüthrich et al. (2017). Inheritance is the nuclide concentration acquired during previous exposure, i.e., before the deposition of sediments. ‘Pseudoinheritance’ is a high nuclide concentration at depth due to a major erosional event (e.g., surface lowering) combined with a long exposure history. With a single nuclide depth profile (and in the absence of sedimentological evidence), discrimination between
inheritance and ‘pseudoinheritance’ is not possible. In these cases, the combination of two nuclides provides additional constraints about these exposure histories because the combination allows the sediment burial timing to be dated.

## 8.4 Modeling $^{10}$Be and $^{26}$Al depth profiles

The modeling approach used in this work was performed in Pappu et al. (2011). The aim of this approach is to determine the amount of inherited nuclides related to previous exposure in the profile. To this end, the typical $^{26}$Al/$^{10}$Be ratio of 6.61 was used. Indeed, this ratio is dependent on the exposure history. During shielding events, the different half-lives of $^{26}$Al and $^{10}$Be induced ratio modification. The longer the shielding period is, the lower the $^{26}$Al/$^{10}$Be ratio is because the $^{26}$Al concentration decreases more rapidly (radioactive decay of 705 ka; Samworth et al., 1972) than the $^{10}$Be concentration (radioactive decay of 1387 ka; Chmeleff et al., 2010; Korschinek et al., 2010). This approach is applied using the following equation (Eq. 3):

$$N_{model} = [N]_{AFTER} + [N]_{BEFORE} * e^{(\lambda t)} \qquad (Eq. 3)$$

As suggested in Eq. 3, the amount of nuclides modeled ($N_{model}$) is the result of three distinct periods.

- First, the previous exposure corresponding to preglacial exposure at the surface produced $^{10}$Be and $^{26}$Al in quartz grains. This is the nuclide concentration ($[N]_{BEFORE}$).

- Second, during the glaciation period, sediments are shielded from cosmic rays by ice. This is analogous to a burial event. During this period, the $^{10}$Be and $^{26}$Al concentrations ($[N]_{BEFORE}$) decrease due to radioactive decay and $^{26}$Al/$^{10}$Be lowering.

- Finally, after the deglaciation period, the sediments are again exposed, and $^{10}$Be and $^{26}$Al nuclides start to accumulate again ($[N]_{AFTER}$). The $^{26}$Al/$^{10}$Be ratio is inherited from preexposure.

This calculation was performed for each sample, and the statistically most likely model solution was obtained by minimizing the chi-squared ($\chi^2$) statistic (Braucher et al., 2009; Siame et al., 2004). Samples with $\chi^2$ statistics
are rejected for the surface exposure age and erosion rate modeling (Fig. 2B). For an $\chi^2$ value of ~1, the modeled TCN concentration fit the measured TCN concentrations. The 68% (1-sigma) confidence interval for the best-fitting parameter was given by the minimal $\chi^2+1$ value (Bevington and Robinson, 2003).

Two key parameters in the present depth-profile modeling are the material density and the typical $^{26}$Al/$^{10}$Be ratio. These parameters greatly influenced TCN depth profile modeling (Braucher et al., 2009). No field measurements constrained the material density, and a value of 2.2 g.cm$^{-2}$ was taken as acceptable for tills, as suggested by Schlüchter, 1989. According to Akçar et al. (2018), the typical $^{26}$Al/$^{10}$Be ratio varies from 6.75 to 8.4 according to the depth due to the $^{26}$Al production from muogenic production pathways being ~ +4% higher than that of $^{10}$Be. The effects of these two parameters were not accounted for in our approach.

## 8.5 Results and interpretations

### 8.5.1 Moulinges $^{10}$Be and $^{26}$Al depth profiles

The coupled $^{10}$Be and $^{26}$Al concentrations from the Moulinges depth profile were 4.29 and 27.32 (×10$^4$)at.g$^{-1}$ at the 100-cm depth (CA01), 1.73 and 9.19 (×10$^4$)at.g$^{-1}$ at the 200-cm depth (CA02) and 1.10 and 3.52 (×10$^4$)at.g$^{-1}$ at the 335-cm depth (CA03), and the corresponding $^{26}$Al/$^{10}$Be ratios are 6.37, 5.32 and 3.19, respectively (Table 1). The latter indicated the potentially complex exposure histories of the sediment samples in the lower part of the depth profile. However, the $^{10}$Be and $^{26}$Al concentrations exponentially decrease with depth (Fig. 1).

The calculated steady-state erosion rates increased with depth, between 47 and 70 mm.ka-1 for $^{10}$Be concentrations and from 52.3 to 167.29 mm.ka-1 for $^{26}$Al concentrations (Table 2). These results indicated that the Moulinges depth profile did not reach the steady state and that an exposure age could be calculated by modeling the $^{10}$Be and $^{26}$Al depth profiles.

The results of the Moulinges depth-profile modeling provided $^{26}$Al/$^{10}$Be ratios that fit the measured ratios with individual $\chi^2$ values of 0.5, 2.9 and 36 for the CA01, CA02 and CA03 samples, respectively. Then, the CA03 sample was rejected for the surface exposure age and erosion rate calculations (Table 3B; Fig. 2B). The resultant
surface exposure age of the Moulinges till was 24.24–25.74 ka (1 sigma) with an erosion rate of 0 mm.ka⁻¹ and a
χ² value of 3.14 (Table 3B).

**8.5.2 Louradou <sup>10</sup>Be and <sup>26</sup>Al depth profiles**

The ¹⁰Be and ²⁶Al concentrations from the Louradou section were 10.39 and 75.41 (×10⁴)at.g⁻¹ at the 45-cm depth (CA04), 6.69 and 42.76 (×10⁴)at.g⁻¹ at the 90-cm depth (CA05), 3.83 and 24.8 (×10⁴)at.g⁻¹ at the 135-cm depth (CA06) and 2.95 and 11.53 (×10⁴)at.g⁻¹ at the 135-cm depth (CA07), and the corresponding ²⁶Al/¹⁰Be ratios were 7.26, 6.39, 6.5 and 3.91, respectively (Table 2B). The latter indicated the potential complex exposure histories of the sediment samples in the lower part of the depth profile. However, the ¹⁰Be and ²⁶Al concentrations exponentially decreased with depth (Fig. 1B).

The steady-state erosion rates calculated for the ¹⁰Be concentrations were constant, between 27.56 and 37.63 mm.ka⁻¹ (Table 2B). For the ²⁶Al concentrations, the calculated steady-state erosion rates increased with depth from 31.68 to 62.47 mm.ka⁻¹ (Table 2B). This was interpreted as a non-reached steady-state but a complex exposure history with inheritance and burial stages. Then, an exposure age was calculated by modeling the coupled ¹⁰Be and ²⁶Al depth profiles.

Sample CA07 was rejected for modeling due to its high individual χ² value (87). The results show that the three upper samples (CA04, CA05 and CA06) give good model fits, with an χ² value of 1.90. Accordingly, the Louradou till surface exposure age was 27.69-28.35 ka with an erosion rate of 0 mm.ka⁻¹ (Table 3B).

**8.5.3 Mougueyres ¹⁰Be and ²⁶Al depth profiles**

The ¹⁰Be and ²⁶Al concentrations from the Mougueyres depth profile were 9.30 and 10.23 (×10⁴)at.g⁻¹ at the 17.5-cm depth (CA08), 10.98 and 81.26 (×10⁴)at.g⁻¹ at the 32.5-cm depth (CA09), 9.24 and 62.71 (×10⁴)at.g⁻¹ at the 72.5-cm depth (CA10) and 4.87 and 37.39 (×10⁴) at.g⁻¹ at the 122.5-cm depth (CA011), and the corresponding
$^{26}$Al/$^{10}$Be ratios were 1.10, 7.4, 6.78 and 7.68, respectively (Table 2). Except for the CA08 sample (upper sample), the $^{10}$Be and $^{26}$Al concentrations decreased exponentially with depth (Fig. 1).

By excluding data from the CA08 sample, the steady-state erosion rates calculated for the $^{10}$Be concentrations are near constant, between 30.68 and 41.18 mm.ka$^{-1}$ (Table 2). For the $^{26}$Al concentrations, the calculated steady-state erosion rates are nearly constant, between 33.40 and 39.66 mm.ka$^{-1}$. This was interpreted as indicating a steady state of the Louradou depth profile. The associated $T_{eff}$ values were between 11.75 ka and 22.42 ka for $^{10}$Be and between 20.97 and 24.79 ka for $^{26}$Al.

Sample CA08 was excluded from modeling due to its high individual $\chi^2$ value. The modeling results provided surface exposure ages of 398.82-759.55 ka. This was interpreted as the effects of a steady state for which accurate exposure ages could not be estimated. As a result, the surface exposure age of the Mougueyres till was best estimated by the $^{26}$Al integration time, as calculated with modeled erosion rates of 38.61-39.8 mm.ka$^{-1}$ (Table 3B) at 20.44 ± 1.94 ka. This provided the minimum surface exposure age of this till.
1010 **9 Author contribution**

**Arthur Ancrenaz** – Conceptualization, Methodology, Formal analysis, Investigation, Data Curation, Writing - Original Draft, Writing - Review & Editing, Visualization

**Régis Braucher** - Methodology, Validation, Formal analysis, Data Curation, Writing - Review & Editing

*Emmanuelle Defive* - Conceptualization, Investigation, Writing - Review & Editing, Supervision

1015 **Stéphane Pochat** - Conceptualization, Investigation, Writing - Review & Editing, Supervision, Funding acquisition, Project administration

*Alexandre Poiraud* - Conceptualization, Investigation, Writing - Review & Editing, Supervision

Vincent Rinterknecht - Methodology, Investigation, Validation, Formal analysis, Data Curation, Writing - Review & Editing, Supervision

1020 Johannes Steiger – Conceptualization, Writing - Review & Editing, Supervision, Project administration

**10 Financial support**

¹⁰Be, ²⁶Al and ³⁶Cl 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). This project was co-funded by INSU-SYSTER and by the Ice-Collapse project (The dynamics of ice sheet collapse in deglaciation periods) supported by the French Agence Nationale de la Recherche through grant ANR-18-CE01-0009.
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<table><caption>Table 1. Locations and characteristics of samples from the Cantal Mountains and the Cézallier Plateau for TCN dating.</caption><thead><tr><th>Sample ID</th><th>Latitude</th><th>Longitude</th><th>Elevation</th><th>Glacial features</th><th>Lithology</th><th>Density</th><th>Topographic shielding</th><th>Snow shielding</th><th>Thickness</th><th>Nuclide measured</th></tr><tr><th></th><th>°N</th><th>°E</th><th>m (a.s.l.)</th><th></th><th></th><th>g.cm<sup>-3</sup></th><th></th><th></th><th>cm</th><th></th></tr></thead><tbody><tr><td>CA01</td><td>44.8982</td><td>2.5184</td><td>666</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>10.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA02</td><td>44.8982</td><td>2.5184</td><td>666</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>10.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA03</td><td>44.8982</td><td>2.5184</td><td>666</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>20.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA04</td><td>44.8957</td><td>2.7984</td><td>725</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>10.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA05</td><td>44.8957</td><td>2.7984</td><td>725</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>10.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA06</td><td>44.8957</td><td>2.7984</td><td>725</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>10.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA07</td><td>44.8957</td><td>2.7984</td><td>725</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>10.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA08</td><td>45.3118</td><td>2.6424</td><td>891</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>5.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA09</td><td>45.3118</td><td>2.6424</td><td>891</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>5.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA10</td><td>45.3118</td><td>2.6424</td><td>891</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>5.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA11</td><td>45.3118</td><td>2.6424</td><td>891</td><td>Till</td><td>-</td><td>2.20</td><td>1.00</td><td>1.00</td><td>5.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA12</td><td>45.1823</td><td>2.5797</td><td>796</td><td>Polished bedrock</td><td>Granite</td><td>2.65</td><td>0.99</td><td>1.00</td><td>2.50</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA13</td><td>45.2266</td><td>2.7110</td><td>916</td><td>Polished bedrock</td><td>Granite</td><td>2.65</td><td>1.00</td><td>1.00</td><td>2.00</td><td><sup>10</sup>Be & <sup>26</sup>Al</td></tr><tr><td>CA16</td><td>45.1161</td><td>2.9871</td><td>987</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>2.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CA17</td><td>45.1163</td><td>2.9779</td><td>985</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.75</td><td><sup>36</sup>Cl</td></tr><tr><td>CA18</td><td>45.0887</td><td>2.8828</td><td>1098</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.25</td><td><sup>36</sup>Cl</td></tr><tr><td>CA20</td><td>45.0890</td><td>2.8837</td><td>1095</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.25</td><td><sup>36</sup>Cl</td></tr><tr><td>CA25</td><td>44.9848</td><td>2.8994</td><td>1042</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>3.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CA26</td><td>44.9847</td><td>2.9000</td><td>1034</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.25</td><td><sup>36</sup>Cl</td></tr><tr><td>CA27</td><td>44.9186</td><td>2.7279</td><td>991</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CA28</td><td>44.9180</td><td>2.7367</td><td>1001</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>5.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CA30</td><td>44.9382</td><td>2.7335</td><td>1003</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>7.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CA31</td><td>44.9395</td><td>2.7353</td><td>1011</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>4.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CA32</td><td>44.9393</td><td>2.7365</td><td>1005</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.25</td><td><sup>36</sup>Cl</td></tr><tr><td>CA33</td><td>44.9845</td><td>2.9010</td><td>1022</td><td>Erratic boulder</td><td>Trachyandesite</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CA34</td><td>44.9174</td><td>2.7274</td><td>990</td><td>Erratic boulder</td><td>Trachyte</td><td>2.50</td><td>1.00</td><td>1.00</td><td>2.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CA36</td><td>45.0513</td><td>2.7946</td><td>1393</td><td>Erratic boulder</td><td>Trachyte</td><td>2.50</td><td>1.00</td><td>0.95</td><td>1.75</td><td><sup>36</sup>Cl</td></tr><tr><td>CA37</td><td>45.0527</td><td>2.7948</td><td>1394</td><td>Erratic boulder</td><td>Trachyte</td><td>2.50</td><td>1.00</td><td>0.95</td><td>1.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CA41</td><td>44.9397</td><td>2.7157</td><td>1067</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>2.25</td><td><sup>36</sup>Cl</td></tr><tr><td>CA42</td><td>44.9398</td><td>2.7157</td><td>1067</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>1.75</td><td><sup>36</sup>Cl</td></tr><tr><td>CA43</td><td>44.9392</td><td>2.7160</td><td>1066</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>2.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-05</td><td>45.1875</td><td>2.8935</td><td>1140</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>0.99</td><td>4.10</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-06</td><td>45.1875</td><td>2.8936</td><td>1140</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>0.99</td><td>2.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-07</td><td>45.1875</td><td>2.8939</td><td>1140</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>0.99</td><td>1.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-08</td><td>45.1876</td><td>2.8943</td><td>1140</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>0.99</td><td>3.30</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-09</td><td>45.1875</td><td>2.8945</td><td>1140</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>0.99</td><td>2.20</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-10</td><td>45.1299</td><td>2.9978</td><td>786</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>5.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-11</td><td>45.1270</td><td>3.0003</td><td>792</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>4.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-12</td><td>45.1272</td><td>2.9997</td><td>796</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>2.10</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-13</td><td>45.1267</td><td>2.9987</td><td>800</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>3.40</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-14</td><td>45.1256</td><td>2.9978</td><td>809</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>1.00</td><td>4.60</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-15</td><td>45.2138</td><td>2.9711</td><td>1208</td><td>Erratic boulder</td><td>Basalt</td><td>2.50</td><td>1.00</td><td>1.00</td><td>3.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-16</td><td>45.2138</td><td>2.9707</td><td>1207</td><td>Erratic boulder</td><td>Basalt</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.80</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-17</td><td>45.2161</td><td>2.9660</td><td>1195</td><td>Erratic boulder</td><td>Basalt</td><td>2.50</td><td>1.00</td><td>1.00</td><td>1.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-18</td><td>45.2174</td><td>2.9664</td><td>1208</td><td>Erratic boulder</td><td>Basalt</td><td>2.50</td><td>1.00</td><td>1.00</td><td>2.80</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-19</td><td>45.2205</td><td>2.9648</td><td>1195</td><td>Erratic boulder</td><td>Basalt</td><td>2.50</td><td>1.00</td><td>1.00</td><td>2.50</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-22</td><td>45.4021</td><td>2.4835</td><td>712</td><td>Erratic boulder</td><td>Phonolite</td><td>3.00</td><td>1.00</td><td>1.00</td><td>2.20</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-23</td><td>45.4030</td><td>2.4830</td><td>716</td><td>Erratic boulder</td><td>Gneiss</td><td>2.65</td><td>1.00</td><td>1.00</td><td>4.20</td><td><sup>10</sup>Be</td></tr><tr><td>CTL-24</td><td>45.4014</td><td>2.4816</td><td>745</td><td>Erratic boulder</td><td>Phonolite</td><td>3.00</td><td>1.00</td><td>1.00</td><td>3.20</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-25</td><td>45.4044</td><td>2.4843</td><td>716</td><td>Erratic boulder</td><td>Gneiss</td><td>2.65</td><td>1.00</td><td>1.00</td><td>1.90</td><td><sup>10</sup>Be</td></tr><tr><td>CTL-26</td><td>45.4044</td><td>2.4839</td><td>718</td><td>Erratic boulder</td><td>Phonolite</td><td>3.00</td><td>1.00</td><td>1.00</td><td>4.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-27</td><td>45.2950</td><td>2.9375</td><td>1324</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>0.99</td><td>4.80</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-28</td><td>45.2954</td><td>2.9373</td><td>1329</td><td>Erratic boulder</td><td>Phonolite</td><td>3.00</td><td>1.00</td><td>0.99</td><td>4.00</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-29</td><td>45.2952</td><td>2.9368</td><td>1328</td><td>Erratic boulder</td><td>Phonolite</td><td>3.00</td><td>1.00</td><td>0.99</td><td>1.60</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-30</td><td>45.2954</td><td>2.9377</td><td>1329</td><td>Erratic boulder</td><td>Phonolite</td><td>3.00</td><td>1.00</td><td>0.99</td><td>1.40</td><td><sup>36</sup>Cl</td></tr><tr><td>CTL-31</td><td>45.2949</td><td>2.9380</td><td>1323</td><td>Erratic boulder</td><td>Basalt</td><td>3.00</td><td>1.00</td><td>0.99</td><td>1.30</td><td><sup>36</sup>Cl</td></tr></tbody></table>
<table><caption>Table 2. Analytical data for the ¹⁰Be, ²⁶Al and ³⁶Cl measurements.</caption><thead><tr><th rowspan="2">Sample ID</th><th>¹⁰Be/²¹Be</th><th>¹⁰Be</th><th>²⁶Al/²⁷Al</th><th>²⁶Al*</th><th>³⁵Cl/³⁷Cl</th><th>³⁶Cl/³⁵Cl</th><th rowspan="2">[Cl] in sample<br>ppm</th><th>³⁶Cl</th></tr><tr><th>¹⁰¹³ at.g⁻¹</th><th>¹⁰⁴ at.g⁻¹</th><th>¹⁰¹⁵ at.g⁻¹</th><th>¹⁰⁴ at.g⁻¹</th><th>¹⁰¹⁴ at.g⁻¹</th><th>¹⁰¹⁴ at.g⁻¹</th><th>¹⁰⁴ at.g⁻¹</th></tr></thead><tbody><tr><td>CA12</td><td>0.75 ± 0.05</td><td>15.57 ± 1.08</td><td>4.55 ± 1.46</td><td>0 ± 1.46</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>CA13</td><td>1.14 ± 0.07</td><td>18.32 ± 1.14</td><td>6.32 ± 1.91</td><td>3.86 ± 5.47</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>CA16</td><td>-</td><td>-</td><td>-</td><td>-</td><td>6.05 ± 0.1</td><td>84.4 ± 4.04</td><td>106.23 ± 4.41</td><td>225.26 ± 11.76</td></tr><tr><td>CA17</td><td>-</td><td>-</td><td>-</td><td>-</td><td>6.97 ± 0.11</td><td>84.83 ± 3.89</td><td>85.07 ± 3.14</td><td>209.74 ± 10.23</td></tr><tr><td>CA18</td><td>-</td><td>-</td><td>-</td><td>-</td><td>12.02 ± 0.2</td><td>17.25 ± 1.02</td><td>39.4 ± 1.15</td><td>34.31 ± 2.08</td></tr><tr><td>CA20</td><td>-</td><td>-</td><td>-</td><td>-</td><td>28.82 ± 0.48</td><td>15.32 ± 1.21</td><td>12.72 ± 0.35</td><td>25.17 ± 0.24</td></tr><tr><td>CA25</td><td>-</td><td>-</td><td>-</td><td>-</td><td>19.51 ± 0.32</td><td>18.02 ± 1.15</td><td>19.93 ± 0.54</td><td>30.28 ± 2</td></tr><tr><td>CA26</td><td>-</td><td>-</td><td>-</td><td>-</td><td>22.05 ± 0.36</td><td>15.82 ± 0.81</td><td>18.82 ± 0.51</td><td>28.61 ± 1.52</td></tr><tr><td>CA27</td><td>-</td><td>-</td><td>-</td><td>-</td><td>7.8 ± 0.16</td><td>14.42 ± 0.83</td><td>90.76 ± 3.74</td><td>42.2 ± 2.56</td></tr><tr><td>CA28</td><td>-</td><td>-</td><td>-</td><td>-</td><td>4.52 ± 0.07</td><td>12.37 ± 0.72</td><td>407.41 ± 26.13</td><td>93.46 ± 6.63</td></tr><tr><td>CA30</td><td>-</td><td>-</td><td>-</td><td>-</td><td>7.48 ± 0.12</td><td>13.13 ± 0.8</td><td>80.14 ± 2.84</td><td>32.44 ± 2.06</td></tr><tr><td>CA31</td><td>-</td><td>-</td><td>-</td><td>-</td><td>11.76 ± 0.19</td><td>12.95 ± 0.72</td><td>38.34 ± 1.13</td><td>24.37 ± 1.42</td></tr><tr><td>CA32</td><td>-</td><td>-</td><td>-</td><td>-</td><td>6.68 ± 0.11</td><td>13.59 ± 0.79</td><td>96.46 ± 3.67</td><td>36.07 ± 2.22</td></tr><tr><td>CA33</td><td>-</td><td>-</td><td>-</td><td>-</td><td>20.22 ± 0.33</td><td>15.6 ± 1.18</td><td>19.21 ± 0.52</td><td>26.21 ± 2.03</td></tr><tr><td>CA34</td><td>-</td><td>-</td><td>-</td><td>-</td><td>27.05 ± 0.45</td><td>14.5 ± 0.89</td><td>19.13 ± 0.52</td><td>33.33 ± 0.21</td></tr><tr><td>CA36</td><td>-</td><td>-</td><td>-</td><td>-</td><td>10.35 ± 0.17</td><td>16.46 ± 0.94</td><td>47.41 ± 1.45</td><td>33.7 ± 2</td></tr><tr><td>CA37</td><td>-</td><td>-</td><td>-</td><td>-</td><td>9.32 ± 0.16</td><td>18.93 ± 1.21</td><td>55.98 ± 1.85</td><td>41.15 ± 2.71</td></tr><tr><td>CA41</td><td>-</td><td>-</td><td>-</td><td>-</td><td>20.18 ± 0.33</td><td>8.02 ± 0.53</td><td>24.48 ± 0.67</td><td>16.84 ± 1.18</td></tr><tr><td>CA42</td><td>-</td><td>-</td><td>-</td><td>-</td><td>7.7 ± 0.13</td><td>9.81 ± 0.67</td><td>72.86 ± 2.52</td><td>22.55 ± 1.63</td></tr><tr><td>CA43</td><td>-</td><td>-</td><td>-</td><td>-</td><td>6.05 ± 0.1</td><td>15.76 ± 0.84</td><td>114.33 ± 4.75</td><td>44.89 ± 2.6</td></tr><tr><td>CTL-05</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.92 ± 0.07</td><td>16.51 ± 0.96</td><td>222.61 ± 22.07</td><td>59.19 ± 5.82</td></tr><tr><td>CTL-06</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.81 ± 0.07</td><td>13.81 ± 0.93</td><td>241.35 ± 26.83</td><td>52.16 ± 5.94</td></tr><tr><td>CTL-07</td><td>-</td><td>-</td><td>-</td><td>-</td><td>4 ± 0.07</td><td>15.43 ± 0.89</td><td>200.11 ± 19.28</td><td>50.77 ± 4.82</td></tr><tr><td>CTL-08</td><td>-</td><td>-</td><td>-</td><td>-</td><td>4.09 ± 0.07</td><td>16.23 ± 0.93</td><td>183.85 ± 16.57</td><td>50.12 ± 4.5</td></tr><tr><td>CTL-09</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.99 ± 0.07</td><td>18.02 ± 1.04</td><td>205.65 ± 19.27</td><td>60.74 ± 5.69</td></tr><tr><td>CTL-10</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.12 ± 0.11</td><td>13.4 ± 0.67</td><td>n.a.</td><td>n.a.</td></tr><tr><td>CTL-11</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.53 ± 0.11</td><td>13.18 ± 0.64</td><td>386.65 ± 106.03</td><td>74.32 ± 18.35</td></tr><tr><td>CTL-12*</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.37 ± 0.11</td><td>13.59 ± 0.66</td><td>756.61 ± 344.67</td><td>143.15 ± 60.7</td></tr><tr><td>CTL-13*</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.36 ± 0.1</td><td>15 ± 0.7</td><td>768.48 ± 340.97</td><td>159.99 ± 66.26</td></tr><tr><td>CTL-14</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.52 ± 0.11</td><td>11.32 ± 0.56</td><td>449.83 ± 124.01</td><td>74.23 ± 18.44</td></tr><tr><td>CTL-15</td><td>-</td><td>-</td><td>-</td><td>-</td><td>4.78 ± 0.14</td><td>17.98 ± 0.83</td><td>103.89 ± 8.92</td><td>37.12 ± 2.68</td></tr><tr><td>CTL-16</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.91 ± 0.14</td><td>15.67 ± 0.73</td><td>248.86 ± 45.7</td><td>63.12 ± 9.68</td></tr><tr><td>CTL-17</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.82 ± 0.11</td><td>15.66 ± 0.74</td><td>247.1 ± 41.13</td><td>61.19 ± 8.78</td></tr><tr><td>CTL-18</td><td>-</td><td>-</td><td>-</td><td>-</td><td>4.53 ± 0.23</td><td>19.77 ± 0.9</td><td>123.23 ± 19.84</td><td>45.9 ± 5.46</td></tr><tr><td>CTL-19</td><td>-</td><td>-</td><td>-</td><td>-</td><td>5.41 ± 0.18</td><td>15.46 ± 0.88</td><td>84.38 ± 6.69</td><td>29.45 ± 2.14</td></tr><tr><td>CTL-22</td><td>-</td><td>-</td><td>-</td><td>-</td><td>12.45 ± 0.36</td><td>30.36 ± 1.34</td><td>18.43 ± 0.83</td><td>30.09 ± 1.37</td></tr><tr><td>CTL-23</td><td>1.49 ± 0.05</td><td>14.13 ± 0.49</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>CTL-24</td><td>-</td><td>-</td><td>-</td><td>-</td><td>4.47 ± 0.13</td><td>28.25 ± 1.23</td><td>125.81 ± 12.39</td><td>66.05 ± 5.34</td></tr><tr><td>CTL-25</td><td>1.54 ± 0.06</td><td>15.42 ± 0.64</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>CTL-26*</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.21 ± 0.11</td><td>19.78 ± 0.86</td><td>2179.89 ± 2857.25</td><td>571.37 ± 727.69</td></tr><tr><td>CTL-27</td><td>-</td><td>-</td><td>-</td><td>-</td><td>10.03 ± 0.31</td><td>31.4 ± 1.38</td><td>24.94 ± 1.25</td><td>33.53 ± 1.56</td></tr><tr><td>CTL-28</td><td>-</td><td>-</td><td>-</td><td>-</td><td>12.31 ± 0.46</td><td>27.22 ± 1.19</td><td>19.5 ± 1.08</td><td>28.23 ± 1.3</td></tr><tr><td>CTL-29</td><td>-</td><td>-</td><td>-</td><td>-</td><td>8.41 ± 0.32</td><td>30.05 ± 1.31</td><td>34.12 ± 2.21</td><td>36.51 ± 1.81</td></tr><tr><td>CTL-30</td><td>-</td><td>-</td><td>-</td><td>-</td><td>9.76 ± 0.35</td><td>31.38 ± 1.39</td><td>27.26 ± 1.54</td><td>35.59 ± 1.69</td></tr><tr><td>CTL-31</td><td>-</td><td>-</td><td>-</td><td>-</td><td>40.5 ± 1.57</td><td>7.65 ± 0.46</td><td>4.71 ± 0.26</td><td>7.35 ± 0.44</td></tr></tbody></table>

1195

<table><caption>Table 3. Major elements and trace bulk compositions of the samples obtained for the ³⁶Cl measurements, before the chemical treatment, as analyzed at SARM-CRPG (Nancy, France) by ICP-OES.</caption><thead><tr><th rowspan="2">Sample ID</th><th rowspan="2">Lithology</th><th colspan="10">Major elements</th><th colspan="6">Trace elements</th></tr><tr><th>SiO₂<br>wt. %</th><th>Al₂O₃<br>wt. %</th><th>Fe₂O₃<br>wt. %</th><th>MnO<br>wt. %</th><th>MgO<br>wt. %</th><th>CaO<br>wt. %</th><th>Na₂O<br>wt. %</th><th>K₂O<br>wt. %</th><th>TiO₂<br>wt. %</th><th>P₂O₅<br>wt. %</th><th>LOI<br>wt. %</th><th>Cl<br>ppm</th><th>Li<br>ppm</th><th>B<br>ppm</th><th>Sm<br>ppm</th><th>Gd<br>ppm</th><th>Th<br>ppm</th><th>U<br>ppm</th></tr></thead><tbody><tr><td>CTL-05</td><td>Basalt</td><td>41.37</td><td>13.21</td><td>13.91</td><td>0.21</td><td>9.75</td><td>11.06</td><td>3.55</td><td>1.83</td><td>2.93</td><td>0.82</td><td>0.13</td><td>1040</td><td>6.15</td><td>4.3</td><td>10.02</td><td>7.95</td><td>9.36</td><td>2.55</td></tr><tr><td>CTL-08</td><td>Basalt</td><td>41.39</td><td>13.24</td><td>14.56</td><td>0.21</td><td>9.81</td><td>10.82</td><td>3.49</td><td>1.89</td><td>2.96</td><td>0.80</td><td>0.05</td><td>840</td><td>6.82</td><td>4.8</td><td>10.20</td><td>8.02</td><td>9.78</td><td>2.64</td></tr><tr><td>CTL-11</td><td>Basalt</td><td>40.70</td><td>12.45</td><td>13.00</td><td>0.21</td><td>11.65</td><td>10.77</td><td>2.78</td><td>1.88</td><td>2.80</td><td>0.91</td><td>2.51</td><td>1040</td><td>7.91</td><td>3.20</td><td>9.19</td><td>7.36</td><td>7.20</td><td>1.82</td></tr><tr><td>CTL-16</td><td>Basalt</td><td>43.15</td><td>13.27</td><td>12.21</td><td>0.18</td><td>10.95</td><td>10.52</td><td>3.47</td><td>1.47</td><td>2.88</td><td>0.71</td><td>1.06</td><td>760</td><td>6.40</td><td>2.30</td><td>8.12</td><td>6.73</td><td>6.85</td><td>1.72</td></tr><tr><td>CTL-24</td><td>Phonolite</td><td>53.74</td><td>18.73</td><td>5.35</td><td>0.19</td><td>1.10</td><td>5.30</td><td>5.29</td><td>4.82</td><td>1.37</td><td>0.33</td><td>2.76</td><td>470</td><td>16.80</td><td>4.60</td><td>7.35</td><td>5.82</td><td>19.64</td><td>7.00</td></tr><tr><td>CTL-26</td><td>Phonolite</td><td>57.23</td><td>20.15</td><td>3.03</td><td>0.21</td><td>0.39</td><td>2.65</td><td>8.33</td><td>5.61</td><td>0.53</td><td>0.10</td><td>1.68</td><td>2870</td><td>20.40</td><td>8.90</td><td>3.82</td><td>3.14</td><td>26.47</td><td>7.47</td></tr><tr><td>CTL-28</td><td>Phonolite</td><td>60.43</td><td>15.59</td><td>5.88</td><td>0.15</td><td>2.16</td><td>3.80</td><td>4.60</td><td>3.79</td><td>1.25</td><td>0.34</td><td>1.74</td><td>82</td><td>25.60</td><td>7.20</td><td>6.48</td><td>5.46</td><td>20.28</td><td>5.81</td></tr><tr><td>CTL-29</td><td>Phonolite</td><td>60.45</td><td>15.31</td><td>5.52</td><td>0.08</td><td>2.10</td><td>3.76</td><td>4.58</td><td>3.81</td><td>1.17</td><td>0.36</td><td>2.21</td><td>100</td><td>28.00</td><td>10.40</td><td>6.52</td><td>5.33</td><td>20.66</td><td>5.70</td></tr><tr><td>CTL-30</td><td>Phonolite</td><td>61.43</td><td>15.29</td><td>5.39</td><td>0.10</td><td>2.32</td><td>3.75</td><td>4.64</td><td>3.90</td><td>1.12</td><td>0.32</td><td>1.52</td><td>83</td><td>26.50</td><td>8.30</td><td>5.70</td><td>4.57</td><td>19.80</td><td>5.71</td></tr><tr><td>CTL-31</td><td>Basalt</td><td>43.05</td><td>11.69</td><td>12.02</td><td>0.18</td><td>14.14</td><td>9.40</td><td>3.06</td><td>1.39</td><td>2.46</td><td>0.55</td><td>1.08</td><td>390</td><td>6.38</td><td>3.00</td><td>7.42</td><td>6.11</td><td>5.49</td><td>1.42</td></tr><tr><td>CTL-01*</td><td>Tr-a.</td><td>53.79</td><td>18.33</td><td>8.30</td><td>0.16</td><td>1.06</td><td>5.44</td><td>4.56</td><td>3.43</td><td>1.70</td><td>0.72</td><td>2.33</td><td>125</td><td>19.40</td><td>5.10</td><td>10.59</td><td>7.95</td><td>10.79</td><td>2.97</td></tr><tr><td>CTL-02*</td><td>Breccia</td><td>51.36</td><td>15.90</td><td>9.41</td><td>0.14</td><td>2.57</td><td>6.65</td><td>2.87</td><td>2.16</td><td>2.25</td><td>0.65</td><td>6.29</td><td>285</td><td>18.50</td><td>5.00</td><td>10.43</td><td>8.43</td><td>9.10</td><td>2.61</td></tr><tr><td>CTL-03*</td><td>Breccia</td><td>51.12</td><td>17.84</td><td>9.14</td><td>0.16</td><td>2.12</td><td>7.23</td><td>3.78</td><td>2.77</td><td>2.10</td><td>0.60</td><td>2.53</td><td>98</td><td>13.90</td><td>5.20</td><td>9.20</td><td>7.23</td><td>8.51</td><td>2.25</td></tr><tr><td>CTL-20*</td><td>Breccia</td><td>53.86</td><td>15.60</td><td>7.17</td><td>0.16</td><td>4.84</td><td>5.64</td><td>4.75</td><td>3.60</td><td>1.53</td><td>0.42</td><td>1.93</td><td>225</td><td>18.80</td><td>6.51</td><td>6.64</td><td>5.40</td><td>17.08</td><td>4.99</td></tr><tr><td>CTL-21*</td><td>Breccia</td><td>51.06</td><td>16.86</td><td>8</td><td>0.134</td><td>2</td><td>2.456</td><td>7.703</td><td>3.333</td><td>2.375</td><td>2.354</td><td>0.67</td><td>3.78</td><td>245</td><td>10.70</td><td>3.60</td><td>9.38</td><td>7.61</td><td>1.80</td></tr></tbody></table>

<footnote>*High Cl uncertainty</footnote>

<footnote>*Bulk composition from Ancrenaz et al. (2023) used to produce mean by lithology</footnote>
<table><caption>**Table 4.** Major element compositions of the targets from the samples obtained for ³⁶Cl measurement, after the chemical treatment, as analyzed at SARM-CRPG (Nancy, France) by ICP-OES.</caption><thead><tr><th rowspan="2">Sample ID</th><th colspan="10">Major elements</th><th rowspan="2">Total Cl</th></tr><tr><th>SiO<sub>2</sub></th><th>Al<sub>2</sub>O<sub>3</sub></th><th>Fe<sub>2</sub>O<sub>3</sub></th><th>MnO</th><th>MgO</th><th>CaO</th><th>Na<sub>2</sub>O</th><th>K<sub>2</sub>O</th><th>TiO<sub>2</sub></th><th>P<sub>2</sub>O<sub>5</sub></th><th>LOI</th></tr><tr><td></td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>wt. %</td><td>ppm</td></tr></thead><tbody><tr><td>CA16</td><td>58.09</td><td>14.00</td><td>10.33</td><td>0.14</td><td>3.13</td><td>5.04</td><td>3.11</td><td>3.33</td><td>2.37</td><td>0.00</td><td>0.94</td><td>106.23</td></tr><tr><td>CA17</td><td>56.21</td><td>13.71</td><td>10.91</td><td>0.16</td><td>3.76</td><td>5.47</td><td>3.06</td><td>3.22</td><td>2.45</td><td>0.00</td><td>0.72</td><td>85.07</td></tr><tr><td>CA18</td><td>58.04</td><td>16.78</td><td>7.54</td><td>0.10</td><td>1.93</td><td>5.18</td><td>4.40</td><td>3.32</td><td>1.94</td><td>0.00</td><td>0.37</td><td>39.40</td></tr><tr><td>CA20</td><td>59.26</td><td>16.42</td><td>8.14</td><td>0.09</td><td>1.36</td><td>4.29</td><td>4.18</td><td>3.31</td><td>2.02</td><td>0.00</td><td>0.90</td><td>12.72</td></tr><tr><td>CA25</td><td>60.79</td><td>16.38</td><td>6.95</td><td>0.09</td><td>1.33</td><td>4.10</td><td>4.27</td><td>3.57</td><td>1.78</td><td>0.00</td><td>1.03</td><td>19.93</td></tr><tr><td>CA26</td><td>59.40</td><td>15.74</td><td>7.59</td><td>0.11</td><td>1.64</td><td>4.33</td><td>4.03</td><td>3.31</td><td>1.86</td><td>0.00</td><td>0.95</td><td>18.82</td></tr><tr><td>CA27</td><td>58.74</td><td>17.08</td><td>6.60</td><td>0.10</td><td>1.88</td><td>4.97</td><td>4.59</td><td>2.86</td><td>1.85</td><td>0.00</td><td>1.13</td><td>90.76</td></tr><tr><td>CA28</td><td>48.70</td><td>10.48</td><td>10.86</td><td>0.14</td><td>8.07</td><td>11.30</td><td>1.96</td><td>0.89</td><td>3.10</td><td>0.41</td><td>2.67</td><td>407.41</td></tr><tr><td>CA30</td><td>60.18</td><td>17.14</td><td>6.32</td><td>0.11</td><td>1.94</td><td>4.97</td><td>4.61</td><td>2.91</td><td>1.62</td><td>0.00</td><td>0.57</td><td>80.14</td></tr><tr><td>CA31</td><td>57.01</td><td>16.24</td><td>9.60</td><td>0.16</td><td>2.21</td><td>5.32</td><td>4.43</td><td>2.76</td><td>2.37</td><td>0.00</td><td>0.46</td><td>38.34</td></tr><tr><td>CA32</td><td>60.25</td><td>16.65</td><td>6.16</td><td>0.13</td><td>1.98</td><td>4.99</td><td>4.51</td><td>2.77</td><td>1.63</td><td>0.00</td><td>0.65</td><td>96.46</td></tr><tr><td>CA33</td><td>58.95</td><td>15.79</td><td>8.53</td><td>0.11</td><td>1.81</td><td>4.85</td><td>3.98</td><td>3.10</td><td>2.09</td><td>0.00</td><td>1.13</td><td>19.21</td></tr><tr><td>CA34</td><td>60.88</td><td>18.12</td><td>4.38</td><td>0.15</td><td>1.10</td><td>4.36</td><td>5.37</td><td>3.75</td><td>1.00</td><td>0.00</td><td>0.81</td><td>19.13</td></tr><tr><td>CA36</td><td>65.80</td><td>15.91</td><td>5.00</td><td>0.06</td><td>0.62</td><td>3.06</td><td>4.32</td><td>3.60</td><td>1.20</td><td>0.00</td><td>0.97</td><td>47.41</td></tr><tr><td>CA37</td><td>63.98</td><td>16.00</td><td>5.91</td><td>0.07</td><td>0.76</td><td>3.08</td><td>4.32</td><td>3.60</td><td>1.28</td><td>0.00</td><td>0.84</td><td>55.98</td></tr><tr><td>CA38</td><td>46.04</td><td>8.77</td><td>14.83</td><td>0.19</td><td>9.39</td><td>11.56</td><td>1.76</td><td>0.80</td><td>4.67</td><td>0.15</td><td>0.79</td><td>40.79</td></tr><tr><td>CA39</td><td>50.76</td><td>7.06</td><td>13.73</td><td>0.17</td><td>10.46</td><td>8.94</td><td>1.38</td><td>0.90</td><td>3.86</td><td>0.00</td><td>1.56</td><td>23.81</td></tr><tr><td>CA40</td><td>51.61</td><td>7.46</td><td>14.56</td><td>0.18</td><td>8.20</td><td>9.74</td><td>1.53</td><td>0.86</td><td>4.46</td><td>0.00</td><td>1.56</td><td>15.76</td></tr><tr><td>CA41</td><td>52.17</td><td>10.49</td><td>11.64</td><td>0.15</td><td>8.24</td><td>9.18</td><td>2.27</td><td>1.40</td><td>3.38</td><td>0.00</td><td>1.62</td><td>24.48</td></tr><tr><td>CA42</td><td>47.60</td><td>10.15</td><td>13.33</td><td>0.18</td><td>10.29</td><td>10.60</td><td>2.12</td><td>1.09</td><td>3.89</td><td>0.11</td><td>0.39</td><td>72.86</td></tr><tr><td>CA43</td><td>50.12</td><td>11.40</td><td>11.79</td><td>0.16</td><td>7.75</td><td>10.10</td><td>2.50</td><td>1.38</td><td>3.30</td><td>0.20</td><td>0.90</td><td>114.33</td></tr><tr><td>CTL-05</td><td>44.03</td><td>10.42</td><td>12.93</td><td>0.18</td><td>10.72</td><td>12.62</td><td>2.21</td><td>1.03</td><td>3.38</td><td>0.46</td><td>1.02</td><td>222.61</td></tr><tr><td>CTL-06</td><td>44.11</td><td>10.42</td><td>12.95</td><td>0.19</td><td>10.52</td><td>12.43</td><td>2.37</td><td>1.08</td><td>3.34</td><td>0.50</td><td>1.21</td><td>241.35</td></tr><tr><td>CTL-07</td><td>44.09</td><td>10.36</td><td>13.38</td><td>0.19</td><td>10.19</td><td>12.94</td><td>2.09</td><td>1.01</td><td>3.57</td><td>0.41</td><td>0.82</td><td>200.11</td></tr><tr><td>CTL-08</td><td>44.17</td><td>10.37</td><td>12.83</td><td>0.18</td><td>10.57</td><td>12.72</td><td>2.24</td><td>0.94</td><td>3.36</td><td>0.41</td><td>1.06</td><td>183.85</td></tr><tr><td>CTL-09</td><td>44.07</td><td>10.12</td><td>13.17</td><td>0.19</td><td>10.68</td><td>12.93</td><td>2.06</td><td>0.97</td><td>3.50</td><td>0.43</td><td>1.08</td><td>205.65</td></tr><tr><td>CTL-10</td><td>42.05</td><td>7.18</td><td>13.50</td><td>0.20</td><td>21.23</td><td>8.02</td><td>1.46</td><td>0.87</td><td>2.05</td><td>0.56</td><td>3.01</td><td>n.a.</td></tr><tr><td>CTL-11</td><td>42.31</td><td>4.75</td><td>14.74</td><td>0.22</td><td>26.62</td><td>6.34</td><td>0.81</td><td>0.48</td><td>1.60</td><td>0.42</td><td>1.38</td><td>386.65</td></tr><tr><td>CTL-12</td><td>44.79</td><td>7.30</td><td>12.91</td><td>0.19</td><td>16.84</td><td>9.53</td><td>1.32</td><td>0.77</td><td>2.40</td><td>0.65</td><td>3.03</td><td>756.61</td></tr><tr><td>CTL-13</td><td>41.37</td><td>8.29</td><td>12.83</td><td>0.19</td><td>18.10</td><td>8.76</td><td>1.68</td><td>1.05</td><td>2.22</td><td>0.63</td><td>4.15</td><td>768.48</td></tr><tr><td>CTL-14</td><td>43.72</td><td>7.62</td><td>12.58</td><td>0.18</td><td>15.86</td><td>10.27</td><td>1.31</td><td>0.78</td><td>2.60</td><td>0.68</td><td>3.64</td><td>449.83</td></tr><tr><td>CTL-15</td><td>43.91</td><td>7.68</td><td>13.67</td><td>0.21</td><td>18.05</td><td>10.44</td><td>1.55</td><td>0.52</td><td>2.27</td><td>0.24</td><td>0.40</td><td>103.89</td></tr><tr><td>CTL-16</td><td>44.22</td><td>8.54</td><td>13.03</td><td>0.19</td><td>15.03</td><td>11.35</td><td>1.92</td><td>0.62</td><td>2.72</td><td>0.44</td><td>1.17</td><td>248.86</td></tr><tr><td>CTL-17</td><td>44.88</td><td>10.28</td><td>11.92</td><td>0.18</td><td>11.60</td><td>11.81</td><td>2.43</td><td>0.95</td><td>2.94</td><td>0.58</td><td>1.91</td><td>247.10</td></tr><tr><td>CTL-18</td><td>43.69</td><td>7.02</td><td>13.77</td><td>0.21</td><td>18.96</td><td>10.71</td><td>1.45</td><td>0.47</td><td>2.23</td><td>0.28</td><td>0.50</td><td>123.23</td></tr><tr><td>CTL-19</td><td>44.03</td><td>6.65</td><td>14.28</td><td>0.22</td><td>20.36</td><td>10.27</td><td>1.35</td><td>0.44</td><td>2.17</td><td>0.26</td><td>0.25</td><td>84.38</td></tr><tr><td>CTL-22</td><td>58.50</td><td>16.74</td><td>5.15</td><td>0.18</td><td>1.20</td><td>4.74</td><td>4.58</td><td>4.83</td><td>1.42</td><td>0.16</td><td>2.81</td><td>18.43</td></tr><tr><td>CTL-24</td><td>58.16</td><td>16.90</td><td>5.11</td><td>0.19</td><td>1.13</td><td>4.86</td><td>4.90</td><td>4.97</td><td>1.41</td><td>0.18</td><td>2.14</td><td>125.81</td></tr><tr><td>CTL-26</td><td>61.01</td><td>17.55</td><td>3.12</td><td>0.20</td><td>0.55</td><td>2.70</td><td>6.26</td><td>5.62</td><td>0.61</td><td>0.10</td><td>2.16</td><td>2179.89</td></tr><tr><td>CTL-27</td><td>64.86</td><td>16.07</td><td>3.52</td><td>0.06</td><td>2.50</td><td>3.54</td><td>4.96</td><td>3.71</td><td>0.92</td><td>0.00</td><td>0.39</td><td>24.94</td></tr><tr><td>CTL-28</td><td>63.39</td><td>16.05</td><td>3.70</td><td>0.06</td><td>3.93</td><td>3.68</td><td>4.93</td><td>3.38</td><td>0.87</td><td>0.00</td><td>0.25</td><td>19.50</td></tr><tr><td>CTL-29</td><td>62.28</td><td>15.05</td><td>4.28</td><td>0.07</td><td>4.53</td><td>3.64</td><td>4.61</td><td>3.54</td><td>0.95</td><td>0.00</td><td>0.51</td><td>34.12</td></tr><tr><td>CTL-30</td><td>64.46</td><td>15.62</td><td>3.56</td><td>0.07</td><td>2.56</td><td>3.36</td><td>4.87</td><td>3.78</td><td>0.91</td><td>0.00</td><td>0.51</td><td>27.26</td></tr><tr><td>CTL-31</td><td>40.55</td><td>1.47</td><td>14.99</td><td>0.22</td><td>40.21</td><td>2.50</td><td>0.29</td><td>0.08</td><td>0.48</td><td>0.00</td><td>-0.84</td><td>4.71</td></tr></tbody></table>
<table><caption>**Table 5.** Surface exposure ages obtained from erratic boulders, polished bedrocks and depth profiles in moraines in the Cantal Mountains and on the Cézallier Plateau.</caption><thead><tr><th colspan="2">Morphostratigraphy</th><th rowspan="2">Glacial chronology</th><th rowspan="2">Sample ID</th><th rowspan="2">Surface exposure age ka</th><th rowspan="2">Gaussian age ka</th></tr><tr><th>Unit</th><th>Sub-unit</th></tr></thead><tbody><tr><td rowspan="12">Glacier Maximum (GM)</td><td rowspan="12">Older</td><td rowspan="3">potentially pre-LLGM</td><td>Pierre Grosse end moraine</td><td></td><td>124.97 ± 16.27</td></tr><tr><td>CA16</td><td>125.19 ± 6.54 (16.3)</td></tr><tr><td>CA17</td><td>124.74 ± 6.09 (16.24)</td></tr><tr><td rowspan="4">Early-LLGM</td><td>Moulinges moraine***</td><td>24.24 ± 3.77</td></tr><tr><td>Louradou moraine***</td><td>27.69 ± 2.14</td></tr><tr><td>Orgues erratics</td><td></td><td>20.01 ± 2.66</td></tr><tr><td>CTL-22</td><td>19.33 ± 0.88 (2.81)</td></tr><tr><td>CTL-23*</td><td>19.56 ± 0.68 (1.7)</td></tr><tr><td>CTL-24</td><td>26.07 ± 2.11 (3.86)</td></tr><tr><td>CTL-25*</td><td>20.99 ± 0.88 (1.89)</td></tr><tr><td rowspan="6">Early- & Late-LLGM</td><td>Pouzat end moraine</td><td></td><td>24.36 ± 11.07</td></tr><tr><td>CTL-10</td><td></td><td></td></tr><tr><td>CTL-11</td><td>24.85 ± 6.13 (7.36)</td></tr><tr><td>CTL-12</td><td>27.45 ± 11.64 (13.84)</td></tr><tr><td>CTL-13</td><td>29.2 ± 12.1 (14.25)</td></tr><tr><td>CTL-14</td><td>18.79 ± 4.67 (5.73)</td></tr><tr><td rowspan="4">Late-LLGM</td><td>Laparra end moraine</td><td></td><td>22.01 ± 2.87</td></tr><tr><td>CA27</td><td>22.8 ± 1.38 (2.76)</td></tr><tr><td>CA28</td><td>21.94 ± 1.56 (2.48)</td></tr><tr><td>CA34</td><td>21.13 ± 1.34 (3.15)</td></tr><tr><td rowspan="12">Internal Oscillations (IOs)</td><td rowspan="12">Intermediate</td><td rowspan="4">Cantal valleys deglaciation</td><td>Mougueyres moraine***</td><td>20.44 ± 1.94</td><td></td></tr><tr><td>Caire erratics</td><td></td><td>19.01 ± 2.85</td></tr><tr><td>CA25</td><td>19.65 ± 1.3 (2.9)</td></tr><tr><td>CA26</td><td>19.35 ± 1.03 (2.7)</td></tr><tr><td>CA33</td><td>17.97 ± 1.39 (2.65)</td></tr><tr><td>Espinouze roche moutonnée</td><td></td><td></td></tr><tr><td>CA12*</td><td>20.18 ± 1.41 (2.13)</td></tr><tr><td>St-Hyppolite roche moutonnée</td><td></td><td></td></tr><tr><td>CA13*</td><td>21.22 ± 1.33 (2.15)</td></tr><tr><td rowspan="4">Younger</td><td>Cheylanes erratics</td><td></td><td>18.02 ± 2.58</td></tr><tr><td>CA18</td><td>19.18 ± 1.16 (2.57)</td></tr><tr><td>CA20</td><td>16.65 ± 1.35 (2.58)</td></tr><tr><td>Laygo end moraine</td><td></td><td>17.15 ± 2.52</td></tr><tr><td rowspan="4">Southern Cantal</td><td rowspan="4">Cantal plateaus deglaciation</td><td>CA30</td><td>16.97 ± 1.08 (2.06)</td><td></td></tr><tr><td>CA31</td><td>15.65 ± 0.91 (1.95)</td></tr><tr><td>CA32</td><td>18.85 ± 1.16 (2.27)</td></tr><tr><td>Amagat erratics</td><td></td><td>n.a.</td></tr><tr><td rowspan="12">Deglaciation of Cantal plateaus and Cézallier Plateau</td><td rowspan="12">Cézallier Plateau</td><td>CA41</td><td>11.78 ± 0.82 (1.36)</td><td></td></tr><tr><td>CA42</td><td>12.19 ± 0.88 (1.36)</td></tr><tr><td>CA43</td><td>21.34 ± 1.24 (2.14)</td></tr><tr><td>Pinatelle erratics</td><td></td><td>17.50 ± 2.80</td></tr><tr><td>CTL-05</td><td>18.28 ± 1.8 (2.44)</td></tr><tr><td>CTL-06</td><td>15.28 ± 1.74 (2.28)</td></tr><tr><td>CTL-07</td><td>16.62 ± 1.58 (2.15)</td></tr><tr><td>CTL-08</td><td>17.3 ± 1.55 (2.17)</td></tr><tr><td>CTL-09</td><td>19.83 ± 1.86 (2.53)</td></tr><tr><td>Combalut erratics</td><td></td><td>18.40 ± 3.26</td></tr><tr><td rowspan="4">Cantal plateaus deglaciation</td><td>CTL-15</td><td>18.31 ± 1.32 (1.99)</td></tr><tr><td>CTL-16</td><td>19.25 ± 2.95 (3.6)</td></tr><tr><td>CTL-17</td><td>18.19 ± 2.61 (3.24)</td></tr><tr><td>CTL-18</td><td>21.24 ± 2.53 (3.18)</td></tr><tr><td rowspan="6">Cézallier Plateau</td><td>CTL-19</td><td>16.19 ± 1.18 (1.78)</td></tr><tr><td>Pradier erratics</td><td></td><td>17.54 ± 2.80</td></tr><tr><td>CTL-27</td><td>17.71 ± 0.82 (2.51)</td></tr><tr><td>CTL-28</td><td>15.24 ± 0.7 (2.13)</td></tr><tr><td>CTL-29</td><td>17.45 ± 0.87 (2.42)</td></tr><tr><td>CTL-30</td><td>17.18 ± 0.82 (2.47)</td></tr><tr><td rowspan="3">Cantal cirque stadial</td><td rowspan="3">Cirque glacier confinement</td><td>CTL-31</td><td>19.69 ± 1.18 (2.33)</td><td></td></tr><tr><td>Prat de Bouc erratics</td><td></td><td>15.34 ± 2.18</td></tr><tr><td>CA36</td><td>14.06 ± 0.84 (1.99)</td></tr><tr><td></td><td></td><td>CA37</td><td>16.63 ± 1.1 (2.38)</td><td></td></tr></tbody></table>

<footnote>*¹⁰Be surface exposure ages</footnote>

<footnote>** Samples with high CI uncertainty (not discussed in main text)</footnote>

<footnote>***¹⁰Be and ²⁵Al depth-profiles. For more detailed see Appendix B</footnote>
<table><caption>**Table 1B.** $^{10}$Be and $^{26}$Al measurements from the samples obtained for TCN depth-profile dating in the Cantal Mountains.</caption><thead><tr><th>Depth-profile</th><th>Sample<br>ID</th><th>Depth<br>cm</th><th>10Be/9Be*<br>10<sup>14</sup>at.g<sup>-1</sup></th><th>[10Be]*<br>10<sup>4</sup>at.g<sup>-1</sup></th><th>26Al/27Al<br>10<sup>15</sup>at.g<sup>-1</sup></th><th>[26Al]*<br>10<sup>4</sup>at.g<sup>-1</sup></th></tr></thead><tbody><tr><td rowspan="3">Moulinges</td><td>CA01</td><td>95 - 105</td><td>2.09 ± 0.24</td><td>4.29 ± 0.49</td><td>49.43 ± 5.14</td><td>27.23 ± 3.83</td></tr><tr><td>CA02</td><td>195 - 205</td><td>0.89 ± 0.22</td><td>1.73 ± 0.42</td><td>16.28 ± 2.98</td><td>9.19 ± 1.90</td></tr><tr><td>CA03</td><td>325 - 345</td><td>0.39 ± 0.2</td><td>1.1 ± 0.56</td><td>5.94 ± 2</td><td>3.52 ± 1.22</td></tr><tr><td rowspan="4">Louradou</td><td>CA04</td><td>40 - 50</td><td>4.39 ± 0.24</td><td>10.39 ± 0.57</td><td>265.15 ± 14.54</td><td>75.41 ± 5.22</td></tr><tr><td>CA05</td><td>85 - 95</td><td>1.93 ± 0.21</td><td>6.69 ± 0.74</td><td>117.32 ± 11.05</td><td>42.76 ± 4.36</td></tr><tr><td>CA06</td><td>130 - 140</td><td>2.42 ± 0.22</td><td>3.83 ± 0.35</td><td>80.72 ± 7.22</td><td>24.88 ± 2.83</td></tr><tr><td>CA07</td><td>225 - 235</td><td>1.84 ± 0.24</td><td>2.95 ± 0.39</td><td>39.85 ± 5.4</td><td>11.53 ± 1.79</td></tr><tr><td rowspan="4">Mougueyres</td><td>CA08</td><td>15 - 20</td><td>4.47 ± 0.45</td><td>9.3 ± 0.95</td><td>27.74 ± 3.66</td><td>10.23 ± 1.52</td></tr><tr><td>CA09</td><td>30 - 35</td><td>4.98 ± 0.26</td><td>10.98 ± 0.57</td><td>236.76 ± 13.7</td><td>81.26 ± 7.15</td></tr><tr><td>CA10</td><td>70 - 75</td><td>4.33 ± 0.28</td><td>9.24 ± 0.59</td><td>105.65 ± 9.09</td><td>62.71 ± 10.01</td></tr><tr><td>CA11</td><td>120 - 125</td><td>2.1 ± 0.22</td><td>4.87 ± 0.52</td><td>95.95 ± 8.33</td><td>37.39 ± 4.11</td></tr></tbody></table>

<table><caption>**Table 2B.** Steady-state erosion rates calculated for each sample according to its depth and associated integration time. Calculations were made with the assumed density of 2.2 g.cm$^{-3}$.</caption><thead><tr><th rowspan="2">Depth-profile</th><th rowspan="2">Sample<br>ID</th><th rowspan="2">Depth<br>cm</th><th rowspan="2"><sup>26</sup>Al/<sup>10</sup>Be</th><th colspan="2">Be</th><th colspan="2">Al</th></tr><tr><th>Steady-state<br>erosion rate<br>mm.ka<sup>-1</sup></th><th>Integration<br>time<br>ka</th><th>Steady-state<br>erosion rate<br>mm.ka<sup>-1</sup></th><th>Integration<br>time<br>ka</th></tr></thead><tbody><tr><td rowspan="3">Moulinges</td><td>CA01</td><td>95 - 105</td><td>6.37 ± 0.99</td><td>46.75 ± 7.83</td><td>15.44</td><td>55.79 ± 7.83</td><td>16.09</td></tr><tr><td>CA02</td><td>195 - 205</td><td>5.32 ± 1.23</td><td>62.55 ± 19.7</td><td>11.56</td><td>95.42 ± 19.7</td><td>9.49</td></tr><tr><td>CA03</td><td>325 - 345</td><td>3.19 ± 1.18</td><td>69.19 ± 61.07</td><td>10.46</td><td>175.91 ± 61.07</td><td>5.26</td></tr><tr><td rowspan="4">Louradou</td><td>CA04</td><td>40 - 50</td><td>7.26 ± 0.56</td><td>33.55 ± 2.29</td><td>21.44</td><td>33.17 ± 2.29</td><td>26.57</td></tr><tr><td>CA05</td><td>85 - 95</td><td>6.39 ± 0.73</td><td>32.9 ± 3.96</td><td>21.86</td><td>38.77 ± 3.96</td><td>22.84</td></tr><tr><td>CA06</td><td>130 - 140</td><td>6.5 ± 0.8</td><td>40.95 ± 5.6</td><td>17.60</td><td>49.27 ± 5.6</td><td>18.08</td></tr><tr><td>CA07</td><td>225 - 235</td><td>3.91 ± 0.68</td><td>29.76 ± 10.43</td><td>24.14</td><td>67.12 ± 10.43</td><td>13.36</td></tr><tr><td rowspan="4">Mougueyres</td><td>CA08</td><td>15 - 20</td><td>1.1 ± 0.19</td><td>60.8 ± 60.13</td><td>11.89</td><td>405.32 ± 60.13</td><td>2.20</td></tr><tr><td>CA09</td><td>30 - 35</td><td>7.4 ± 0.7</td><td>42.69 ± 3.61</td><td>16.89</td><td>41.05 ± 3.61</td><td>21.18</td></tr><tr><td>CA10</td><td>70 - 75</td><td>6.78 ± 1.12</td><td>32.67 ± 5.66</td><td>22.01</td><td>35.48 ± 5.66</td><td>24.41</td></tr><tr><td>CA11</td><td>120 - 125</td><td>7.68 ± 0.94</td><td>39.2 ± 4.28</td><td>18.38</td><td>38.93 ± 4.28</td><td>22.31</td></tr></tbody></table>

<table><caption>**Table 3B.** Results of the $^{10}$Be and $^{26}$Al depth-profile simulations.</caption><thead><tr><th rowspan="2">Depth-profile</th><th rowspan="2">Sample<br>ID</th><th rowspan="2">Depth<br>cm</th><th colspan="2">Nuclides modelled before<br>burial</th><th colspan="2">Nuclides modelled after<br>exposition</th><th colspan="2">$^{26}$Al/$^{10}$Be</th><th rowspan="2">Modeled</th><th rowspan="2">Measured</th><th rowspan="2">$\chi^2$<br>value</th></tr><tr><th>$^{10}$Be<br>10<sup>4</sup>at.g<sup>-1</sup></th><th>$^{26}$Al<br>10<sup>4</sup>at.g<sup>-1</sup></th><th>$^{10}$Be<br>10<sup>4</sup>at.g<sup>-1</sup></th><th>$^{26}$Al<br>10<sup>4</sup>at.g<sup>-1</sup></th><th>Erosion rate<br>mm.ka<sup>-1</sup></th><th>Age<br>ka</th></tr></thead><tbody><tr><td rowspan="3">Moulinges</td><td>CA01</td><td>95 - 105</td><td>0.00</td><td>0.00</td><td>4.27 ± 0.66</td><td>29.76 ± 4.63</td><td rowspan="3">0</td><td rowspan="3">24.24 - 25.57</td><td>6.96 ± 1.08</td><td>6.37 ± 0.99</td><td rowspan="3">3.14</td></tr><tr><td>CA02</td><td>195 - 205</td><td>0.42</td><td>2.99</td><td>1.59 ± 0.37</td><td>12.04 ± 2.78</td><td>7.57 ± 1.75</td><td>5.32 ± 1.23</td></tr><tr><td>CA03</td><td>325 - 345</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.19 ± 1.18</td></tr><tr><td rowspan="4">Louradou</td><td>CA04</td><td>40 - 50</td><td>0.00</td><td>0.00</td><td>10.73 ± 0.83</td><td>72.61 ± 5.61</td><td rowspan="4">0</td><td rowspan="4">27.69 - 28.35</td><td>6.77 ± 0.52</td><td>7.26 ± 0.56</td><td rowspan="4">1.90</td></tr><tr><td>CA05</td><td>85 - 95</td><td>0.89</td><td>6.35</td><td>6.73 ± 0.77</td><td>46.6 ± 5.3</td><td>6.92 ± 0.79</td><td>6.39 ± 0.73</td></tr><tr><td>CA06</td><td>130 - 140</td><td>0.59</td><td>4.21</td><td>3.81 ± 0.47</td><td>27.1 ± 3.32</td><td>7.12 ± 0.87</td><td>6.5 ± 0.8</td></tr><tr><td>CA07</td><td>225 - 235</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>3.91 ± 0.68</td></tr><tr><td rowspan="4">Mougueyres</td><td>CA08</td><td>15 - 20</td><td>-</td><td>-</td><td>-</td><td>-</td><td rowspan="4">38.61 - 39.80</td><td rowspan="4">398.82 - 759.55</td><td>-</td><td>1.1 ± 0.19</td><td rowspan="4">0.06</td></tr><tr><td>CA09</td><td>30 - 35</td><td>0.00</td><td>0.00</td><td>11.29 ± 1.07</td><td>81.9 ± 7.76</td><td>7.26 ± 0.69</td><td>7.4 ± 0.7</td></tr><tr><td>CA10</td><td>70 - 75</td><td>3.14</td><td>22.20</td><td>9.39 ± 1.56</td><td>65.15 ± 10.8</td><td>6.94 ± 1.15</td><td>6.78 ± 1.12</td></tr><tr><td>CA11</td><td>120 - 125</td><td>0.74</td><td>5.28</td><td>4.98 ± 0.61</td><td>38.14 ± 4.68</td><td>7.66 ± 0.94</td><td>7.68 ± 0.94</td></tr></tbody></table>
<figure><img src="image_2.png" /><figcaption>**Figure 1.** Map of the Late Pleistocene glaciation extent in the French Massif Central. A. Location of the French Massif Central outlined by the black line. Late Pleistocene glacial maxima are delimited by blue hashing (Ehlers et al., 2011). The dashed black line delimits the paleocoastline (-130 m) during the Last Glacial Maximum. B. Late Pleistocene glaciation maxima in the Massif Central are delimited by white lines (Ehlers and al., 2011), and the sample location of surface exposure ages from the Aubrac Mountains (Ancrenaz et al., 2022) and the Cère Valley in the Cantal Mountains are shown (Ancrenaz et al., 2023). C. Focus on glacial fluctuations from the Cantal-Cézallier Monts Dore (CCMD). D. Transversal simplified geologic profile of the Cézallier Plateau with hypothetical LGM paleoglacier surface. E. Simplified geologic profile of the Cantal Mountains with the hypothetical LGM paleoglacier surface. Note asymmetry between the western and eastern flanks.</figcaption></figure>
<figure><img src="image_3.png" /></figure>

**Figure 2.** Map of the main glacial landforms in the Cantal Mountains and on the Cézallier Plateau with the locations of the study sites and glacial features sampled for terrestrial cosmogenic nuclide dating. White arrows highlight the iceflow directions (Veyret, 1978). Letters are located at the end of the longitudinal profile of Figure 10. 1). Lac Noir, 2) Godivelle (Gewelt and Juvigné, 1988), 3) Lastioulles (De Beaulieu et al., 1985), 4) Madic (Vergne, 1989), 5) Gioux, 6) Taphanel (Ponel et al., 1991), 7) Borie (Miras and Guenet, 2013), 8) Jolan, 9) Lapsou (Duprat-Oualid et al., 2022), and 10) Peyre (Miras et al., 2006).

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<figure><img src="image_4.png" /><figcaption>**Figure 3.** Annotated photographs of erratic boulders and scoured bedrock sampled for TCN dating from the Cantal Mountains and the Cézallier Plateau.</figcaption></figure>
<figure><img src="image_5.png" /><figcaption>**Figure 4.** Landform-sediment assemblages from the Alagnon Valley and the adjacent St-Flour plateau. A. Geomorphological mapping from the Alagnon Valley and the adjacent St-Flour Plateau. B. Longitudinal profile of the Neussargues and the Entraygues plains located in the Alagnon Valley. The surface exposure ages are shown in ka, and the calculated Gaussian ages are shown between brackets.</figcaption></figure>
<figure><img src="image_6.png" /><figcaption>**Figure 5.** Glacial geomorphological maps of the Epie Valley (A) and the Lagnon Cirque (B). For the locations and legend, referred to Fig. 2 and Fig. 4A, respectively.</figcaption></figure>
<figure><img src="image_7.png" /><figcaption>**Figure 6.** Glacial geomorphological map of the Brezons Valley with the adjacent Lacapelle Plateau (A), the longitudinal profile along the Siniq Valley (B) and a geomorphological map of the Vézac pass in the lower Cère Valley (C). For the locations and legend, referred to Fig. 2 and Fig. 4A, respectively.</figcaption></figure>

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<figure><img src="image_8.png" /></figure>

**Figure 7.** Glacial geomorphological map of the northern Cantal study sites, with the Dordogne and Rhue paleo-glacier confluence (A), the Espinouze valley step in the Mars Valley (B), the St-Hippolyte valley step in the Petite Rhue Valley (C) and the Mougueyre site (D). For the locations and legend, referred to Fig. 2 and Fig. 4A, respectively.
<figure><img src="image_9.png" /><figcaption>**Figure 8.** Annotated aerial photography of groups of erratics from the northeastern Cantal at the Pinatelle site (A), the Cézallier Plateau at the Combalut site (B) and the Pradiers site (C). For the locations and legend, see Fig. 2 and Fig. 4A, respectively.</figcaption></figure>
<figure><img src="image_10.png" /><figcaption>**Figure 9.** Glacial chronologies obtained from the comparisons of surface exposure ages obtained from erratic boulders, polished bedrocks and depth profiles from the Cantal Mountains and Cézallier Plateau morphostratigraphic units. A) Surface exposure ages from erratic boulders. B) Relative probability of the Gaussian component computed using P-CAAT (Dortch et al., 2022). C) Gaussian age and external uncertainty. D) Surface exposure ages obtained from *roches moutonnées*. E) Exposure ages from Be-10 and Al-26 depth-profile modeling (Appendix B). F) Early Local Last Glacier Maximum. G) Late Local Last Glacier Maximum. H) Deglaciation. I) Cantal cirque glaciation. No Gaussian age was available for the Pouzat end moraine.</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>**Figure 10.** Longitudinal profile of the Cantal Mountains glaciated valleys with key glacial morphostratigraphic units and associated exposure ages. For the locations of the profiles, see Fig. 2. A. Pierre Grosse end moraine, B. Entraygues moraine, C. Pouzat end moraine, D. Prades end moraine, E. Champs end moraine, F. Chapelle end moraine, G. Cheylanes erratics, H. Prat de Bouc moraine, I. Rials moraine, J. Caire moraine, K. Moulinges moraine, L. Boutragot end moraines, M. isolated LLGM deposits, N. Laparra end moraine, O. Laygo end moraine, P. Sapinières plateau moraine, Q. Amagat erratics, R. Tronquières deposits, S. Louradou moraine, T. Carnéjac end moraine, U. Polminhac end moraine, V. Espinouze verrou, W. Mougueyres moraine, and X. St-Hipolyte verrou.</figcaption></figure>
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<figure><img src="image_12.png" /></figure>

**Figure 1A.** Simplified geological map of the Cantal-Cézallier-Monts Dore (CCMD) with a focus on glacial deposits and the locations of glacial cirques in the Cantal Mountains. The extents of the LGM CCMD glaciers are outlined in white (Ehlers et al., 2011). The extent of the geological map survey (1:50000) is delimited by the dotted black line. Note that the coverage of the glacial deposit map varies in each geological sheet.

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<figure><img src="image_13.png" /><figcaption>**Figure 2A.** Annotated photographs of valley tills and plateau tills from the Cantal Mountains and the Cézallier Plateau.</figcaption></figure>
<figure><img src="image_14.png" /><figcaption>Figure 1B. Annotated photographs of the three <sup>10</sup>Be and <sup>26</sup>Al depth profiles sampled in the Cantal moraines.</figcaption></figure>
<figure><img src="image_15.png" /><figcaption>**Figure 2B.** $^{10}$Be and $^{26}$Al depth profile measurements and modeling results.</figcaption></figure>