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International audience; During the Late Pleistocene, an ice cap temporarily rested on the highest summit of the Black Forest, Feldberg, and on the surrounding region. Moraines inside the last glaciation maximum ice extent document subsequent glacial standstills and/or re-advances, but the chronology of the deglaciation remains largely unknown. In Sankt Wilhelmer Tal, moraines were mapped, and suitable moraine boulders were sampled for 10 Be cosmic ray exposure (CRE) dating. Equilibrium line altitudes (ELAs) during moraine formation were reconstructed to evaluate whether these can be used for local stratigraphical correlations. Geomorphological mapping revealed numerous icemarginal positions in the main valley and in two tributary valleys. CRE ages and ELAs indicate two discrete phases of glacial standstills and/or re-advances by 17-16 ka at the latest and no later than 14 ka, respectively. Differing ELAs across the study area preclude the use of ELAs for local stratigraphical correlations. Recalculated 10 Be CRE ages from other localities in Central Europe indicate similar periods of moraine formation, thus raising the question of a common climatic forcing. Additional sets of CRE ages are needed to answer this question. In addition, future studies should concentrate on determining the age of the last glaciation maximum in the Black Forest.

Geomorphologists classically compute denudation rates from in situ cosmogenic 10Be concentrations. A major assumption is that denudation rates remain steady during the 10Be integration time scale. But early 14C-10Be data we presented last year at this conference suggested that this is hardly tested in environments slowly deformed by tectonics, with integration time covering thousands of years, and erosion rates from 10 to 100 mm/ky.Here, we extended our 14C-10Be dataset to test recent and substantial shifts in denudation. 14C is more sensitive than 10Be to recent and short-term changes in denudation, because of a shorter half-life (5,700 y versus 1.4 My). Studies (Hippe, 2017; Mudd, 2017; Skov et al., 2019; Hippe et al., 2021) have discussed this application of coupled 14C - 10Be measurements.We carried out in situ 14C measurements on river sand which has available 10Be date (Desormeaux et Al., 2021). The studied mountain range is called Massif Central and is west of the European Alp foreland, in southern France. Elevation is ~700 m on average, with an elevated low-relief surface and a steep escarpment along the Cevennes Fault bordering the Alp foreland. The area has a homogeneous lithology rich in quartz. Past glaciations were of limited extent. There is little space for sediment storage, thin soils, no dams, and presently limited anthropic activity. Massif Central is only impacted by slow tectonic deformation. Landslides are very rare but erosion processes are active.Our new 14C results combined with Desormeaux et al., 2021's 10Be data confirm the substantial 14C-10Be disequilibrium. 14C apparent denudation rates are several times higher than 10Be denudation rates. We explore four end-members which could explain such a disequilibrium. This exploration suggests that only major and recent events in denudation could produce such a disequilibrium, and that the landscape we presently see is rather transient than steady.

International audience; Current mass balance and meteorological surveys of Mera glacier located about 30 km south of Mount Everest in Nepal show the dominant role of Asian monsoon precipitation on interannual mass balance variability while temperature controls the altitude of snow-rain threshold. As these observations on mass balance variability only explore the recent decades, studies on paleo glacial extents are useful to investigate the long-term climate forcing on glacier evolution. To do so, we investigated the long-term evolution of the debris-free Mera glacier and a neighbouring small debris-free South Khare glacier. Fifty-one 10Be CRE ages were obtained from samples collected on moraine boulders and roches moutonnées. 10Be CRE ages of the boulders span from the end of the Lateglacial (19.0–11.7 ka) to the Little Ice Age (∼0.6–0.1 ka). The oldest dated moraine in this study was observed at the base of South Khare glacier with an age of 13.6 ± 0.5 ka. The two glaciers subsequently experienced their largest Holocene extent in the Early Holocene with moraines dated to 11.0 ± 0.3 ka at the base of Mera glacier and 10.8 ± 0.5 ka at the base of South Khare glacier. We did not observe any moraine from the Mid-Holocene. During the Late Holocene several glacier advances were recorded around 2.3 ± 0.2 ka, 1.5 ka and then during the last centuries at Mera glacier and around 2.8 ± 0.6 ka, and during the Little Ice Age at South Khare glacier. To explore the links between long-term Nepalese glacier changes and climate, we used oceanic and terrestrial Indian Summer monsoon reconstructions and temperature and precipitation output from two transient global climate models TraCE and LOVECLIM. These climate data outputs were corrected by a reconstruction of the Atlantic Meridional Overturning Circulation (AMOC) over the Holocene and its associated climatic impacts. We also used sensitivity experiments from the IPSL (Institut Pierre Simon Laplace) model to discuss the possible influence of horizontal resolution, land hydrology, vegetation and runoff on changes in Asian summer monsoon. Importantly, we show this long-term Nepalese glacier pattern does not perfectly conform neither to the Indian monsoon precipitation that is documented from terrestrial and marine records nor to temperature and precipitation changes simulated by the models. While the maximum glacier extent in the Early Holocene corresponds to enhanced precipitation documented by proxies and models, the Late Holocene glacier advance remains puzzling. We claim that new paleo glacier records and improved climate simulations are necessary to get a better understanding of past glacier changes and the associated climate dynamics, which might be crucial to gain confidence in both glacier and climate future evolutions.

The migration of Homo erectus in Southeast Asia during Early Pleistocene is cardinal to our comprehension of the evolution of the genus Homo. However, the limited consideration of the rapidly changing physical environment, together with controversial datings of hominin bearing sites, make it challenging to secure the robust timeline needed to unveil the behavior of early humans. Here, we reappraise the first appearance datum of Javanese H. erectus by adding the most reliable age constraints based on cosmogenic nuclides $$^{10}$$ 10 Be and $$^{26}$$ 26 Al produced in situ to a compilation of earlier estimates. We find that H. erectus reached Java and dwelled at Sangiran, Java, ca. 1.8 Ma. Using this age as a baseline, we develop a probabilistic approach to reconstruct their dispersal routes, coupling ecological movement simulations to landscape evolution models forced by reconstructed geodynamic and climatic histories. We demonstrate that the hospitable terra firma conditions of Sundaland facilitated the prior dispersal of hominins to the edge of Java, where they conversely could not settle until the Javanese archipelago emerged from the sea and connected to Sundaland. The dispersal of H. erectus across Sundaland occurred over at least tens to hundreds kyr, a time scale over which changes in their physical environment, whether climatic or physiographic, may have become primary forcings on their behavior. Our comprehensive reconstruction method to unravel the peopling timeline of SE Asia provides a novel framework to evaluate the evolution of early humans.

To understand the timing of deglaciation of the northernmost marine-terminating glaciers of the Cordilleran Ice Sheet (CIS), we obtained 2610Be surface-exposure ages from glacially scoured bedrock surfaces in Prince William Sound (PWS), Alaska. We sampled six elevation transects between sea level and 620 m and spanning a distance of 14 to 70 km along ice flow paths. Most transect age–elevation patterns could not be explained by a simple model of thinning ice; the patterns provide evidence for lingering ice cover and possible inheritance. A reliable set of 20 ages ranges between 17.4 ± 2.0 and 11.6 ± 2.8 ka and indicates ice receded from northwestern PWS around 14.3 ± 1.6 ka, thinned at a rate of ~120–160 m/ka, and retreated from sea-level sites at 12.9 ± 1.1 ka at a rate of 20 m/yr. The retreat rate likely slowed as glaciers retreated into northern PWS. These results are consistent with the growing body of reported deglacial constraints on collapse of ice sheets along the Alaska margin indicating collapse of the CIS soon after 17 ka. These data are consistent with paleotemperature data indicating that a warming North Pacific Ocean caused catastrophic collapse of this part of the CIS.

Rock avalanches are voluminous debris instabilities originated from a fallen portion of bedrock that suffers pervasive disintegration [1]. Tough rock avalanches are foreseen as low-frequency events, their volume (>106 m3) and runout distance (kilometric scale) make them extremely hazardous processes in populated mountain settings and key contributors to landscape denudation [2]. Deciphering the timing of recurrent rock avalanches is crucial to understand the triggering factors involved in their origin (e.g., role of seismicity) and for risk assessment.This study focuses on a rock avalanche cluster preserved in the southern flank of Sierra de la Sobia; a limestone massif located in the Cantabrian Mountains (North Spain). The rock avalanche cluster analyzed is spatially related to the Marabio Fault trace, which shows unequivocal evidence of Quaternary activity [3]. Rock avalanches in this area have been interpreted as coseismic based on the following evidence [4]: (i) boulder populations show fractal block-size distributions consistently with dynamic fragmentation; (ii) the kinematic analysis of local minor transverse and parallel faults points to a horizontal N-S compression consistent with the regional stress field; and (iii) slope stability analysis indicates that headscarps will turn unstable if ground acceleration peak rises to 0.10–0.15 g during an earthquake, which is within the values expected according to the 2013 European Seismic Hazard Map. A first attempt of numerical dating was performed through the U-Th technique on calcite cements found in the oldest rock avalanches. Results suggest multiple episodes of cementation during the last ~280 ka, but age dispersion hinders the age bracketing of instability events4. Here we present a collection of twenty cosmic ray exposure ages relying on the isotope Cl-36 obtained from limestone boulders sampled in the youngest accumulation bodies of the Entrago and Carrea rock avalanches. Results allow to constrain up to 5 instability events spanning the last ~22 ka and occurring at average recurrence intervals of ~3.6 ka. The youngest rock avalanche event took place 8.5 ka ago and left boulder accumulations close to the headscarp of both rock avalanches. Boulder age dispersion increases accordingly with the increase in runout distance from the headscarp, possibly due to the spatial overlapping of accumulation bodies resulting from different instability events of seismic origin. These preliminary results are promising, because if extended to other rock avalanche clusters of the Cantabrian Mountains, they could help to decipher the recurrence time of severe earthquakes in mountain settings where tectonic deformation occurs at low to moderate rates.[1] Hermanns, R. L. Encyclopedia of Natural Hazards. vol. 2 (2013).[2] Davies, T. Rock Avalanches. In Oxford Research Encyclopedia of Natural Hazard Science 58 (Oxford University Press, 2018). doi:10.1093/acrefore/9780199389407.013.326.[3] Fernández, F. J., Alonso, J. L. & Pando, L. Evidence for quaternary tectonic activity in the western cantabrian Zone (Passes of Marabio, Sobia nappe). Geogaceta 64, 1–3 (2018).[4] Fernández, F. J., Menéndez-Duarte, R., Pando, L., Rodríguez-Rodríguez, L. & Iglesias, M. Gravitational slope processes triggered by past earthquakes on the Western Cantabrian Mountains (Sierra de la Sobia, Northern Spain ). Geomorphology 390, 107867 (2021).

The Greenland Ice Sheet (GrIS) is a key component of the global climate system. However, our current understanding of the spatio-temporal oscillations and landscape transformation of the GrIS margins since the last glacial cycle is still incomplete. The objective of this work is to study the deglaciation of the Zackenberg Valley (74°N, 20°E), NE Greenland, and the origin of the derived landforms. Based on extensive fieldwork and high-detail geomorphological mapping we identified the different types of landforms, from which those of glacial and paraglacial origin were used to understand the processes driving regional environmental evolution. We applied cosmic-ray exposure (CRE) dating to 32 samples taken from erosive and depositional glacial landforms distributed across the valley. Geomorphological evidence shows that >800-m-thick Late Quaternary glacier filled the valleys and fjords and covered mountain summits. In subsequent phases, as ice thickness decreased, the glacier was limited to the interior of the valley, leaving several lateral moraines. The deglaciation of the Zackenberg Valley that started by ~13.7–12.5 ka also accelerated slope paraglacial processes. Many blocks from lateral moraines were remobilized and fell, reaching the valley floor where they covered the thinning glacier tongue; transforming it into a debris-covered glacier that subsequently melted gradually. By ca. 10.5 ka, the last remnants of glacial ice disappeared from the Zackenberg Valley floor, a chronology of deglaciation that is similar to that observed in other sites across NE Greenland. The results of this work must be considered in similar studies, reinforcing the need to support CRE ages of the different geomorphological phases with paleoclimatic data from other sedimentary records.

The Miocene is a key time in the evolution of African mammals and their ecosystems witnessing the origin of the African apes and the isolation of eastern coastal forests through an expanding biogeographic arid corridor. Until recently, however, Miocene sites from the southeastern regions of the continent were unknown. Here we report discovery of the first Miocene fossil teeth from the shoulders of the Urema Rift in Gorongosa National Park, Mozambique, at the southern East African Rift System. We provide the first 1) radiometric age determinations of the fossiliferous Mazamba Formation, 2) reconstructions of past vegetation in the region based on pedogenic carbonates and fossil wood, and 3) description of fossil teeth from the southern rift. Gorongosa is unique in the East African Rift System in combining marine invertebrates, marine vertebrates, terrestrial mammals, and fossil woods in coastal paleoenvironments. The Gorongosa fossil sites offer the first evidence of persistent woodlands and forests on the coastal margins of southeastern Africa during the Miocene, and an exceptional assemblage of fossil vertebrates including new species. Further work will allow the testing of hypotheses positing the formation of a northeast-southwest arid corridor isolating species on the eastern coastal forests from those elsewhere in Africa.BriefThe Miocene is a key time in the evolution of African mammals and their ecosystems encompassing hominine origins and the establishment of an arid corridor that isolated eastern Africa’s coastal forests. Until now, however, Miocene sites from southeastern Africa have been unknown. We report the discovery of the first Miocene fossil sites from Gorongosa National Park, Mozambique, and show that these sites formed in coastal settings. We provide radiometric ages for the fossiliferous sediments, reconstructions of past vegetation based on stable isotopes and fossil wood, and a description of the first fossil teeth from the region. Gorongosa is the only paleontological site in the East African Rift that combines fossil woods, marine invertebrates, marine vertebrates, and terrestrial mammals. Gorongosa offers the first evidence of persistent woodlands and forests on the coastal margins of southeastern Africa during the Miocene.

International audience; The aim of this work is to study the process of transformation of debris-free mountain glaciers into debris-covered glaciers and rock glaciers, and to examine the factors driving diverging evolution in similar glacial systems. The study area is the Hofsdalur valley, in the Trollaskagi peninsula (northern Iceland), where several cirques host a great diversity of glaciers and rock glaciers as well as various glacial landforms. Four adjacent cirques have been analysed through a multidisciplinary approach: geomorphological analysis, boulder surface displacement tracking, quantification of recent glacier changes, three dimensional palaeoglacier reconstruction, equilibrium-line altitude calculations and relative and direct dating methods applied to surface boulders. Dating methods included in situ Cl-36 cosmic-ray exposure dating, Schmidt hammer weathering measurements and lichenometric dating. The results confirm that glaciers in Hofsdalur followed an evolution pattern similar to that observed in other cirques in the Trollaskagi peninsula. During the Younger Dryas (12.9-11.7 ka) many of those cirques hosted debris-free glaciers, whose retreat started in the early Holocene. Distinct retreat dynamics and cirque floor elevation conditioned the subsequent glacial evolution. In some Trollaskagi cirques, the ice completely covered the headwalls, which consequently did not supply debris onto the glacier surface, which remained debris-free. In most of these cirques, however, glacier retreat enhanced paraglacial processes and the ice-free cirque walls generated a high debris supply onto the glacier surface. As a result, the glaciers evolved towards debris-covered glaciers or rock glaciers, depending on the local topographical setting. In the lower cirques they collapsed immediately after their formation. At higher altitudes, above the lower permafrost limit, these ice-cored landforms have survived until the present day, but they have been stagnant since the Holocene Thermal Maximum, while the heads of these cirques have hosted debris-free glaciers during the Late Holocene.

International audience; The Upper Garonne Basin included the longest glacier in the Pyrenees during the Late Pleistocene. During major glacial advances, the Garonne palaeoglacier flowed northwards along similar to 80 km from peaks of the axial Pyrenees exceeding 2800-3000 m until the foreland of this mountain range at the Loures-Barousse-Barbazan basin (LBBb), at 420-440 m. Here, the palaeoglacier formed a terminal moraine complex that is examined in this work. Based on geomorphological observations and a 12-sample data set of Be-10 Cosmic-Ray Exposure (CRE) ages, the timing of the maximum glacial extent was constrained as well as the onset of the deglaciation from the end of the Last Glacial Cycle (LGC). Chronological data shows evidence that the external moraines in this basin were abandoned by the ice at the end of the Penultimate Glacial Cycle (PGC) and the onset of the Eemian Interglacial, at similar to 129 ka. No evidence of subsequent glacial advances or standstills occurred during the LGC in this basin were found, as the few existing datable boulders provided in the internal moraine showed inconsistent ages, thus probably being affected by post-glacial processes. The terminal basin was already deglaciated during the global Last Glacial Maximum at 24-21 ka, as revealed by exposure ages of polished surfaces at the confluence of the Garonne-La Pique valleys, 13 km south of the entrance of the LBBb. This study introduces the first CRE ages in the Pyrenees for the glacial advance occurred during the PGC and provides also new evidence that glaciers had already significantly shrunk during the LGM.

Evaluating the impact and implications of eolian repositories that mark large-scale climatic transitions requires knowledge about the timing of their emplacement and the mechanisms responsible for their production, which remain highly uncertain. Here we apply numerical modeling of cosmogenic nuclide data, measured in the largest continuous terrestrial body of sand on Earth, to determine settings under which the sand was generated, by constraining the timing of sand introduction into the interior of southern Africa. Our findings reveal that major events of sand formation and accumulation in the Kalahari Basin occurred between ~2.2 and 1 Myr ago. The establishment of the Kalahari sand field corresponds to regional, continental, and global scale morphotectonic and climatic changes that contributed to the mass production and widespread dispersion of sand. These changes substantially altered existing habitats, thus constituting a crucial milestone for flora, fauna, and hominins in southern Africa during the Pleistocene.

International audience

International audience; Since the discovery of shatter cones (SCs) near the village of Agoudal (Morocco, Central High Atlas Mountains) in 2013, the absence of one or several associated circular structures led to speculation about the age of the impact event, the number, and the size of the impact crater or craters. Additional constraints on the crater size, age, and erosion rates are obtained here from geological, structural, and geophysical mapping and from cosmogenic nuclide data. Our geological maps of the Agoudal impact site at the scales of 1:30,000 (6 km(2)) and 1:15,000 (2.25 km(2)) include all known occurrences of SCs in target rocks, breccias, and vertical to overturned strata. Considering that strata surrounding the impact site are subhorizontal, we argue that disturbed strata are related to the impact event. Three types of breccias have been observed. Two of them (br1-2 and br2) could be produced by erosion-sedimentation-consolidation processes, with no evidence for impact breccias, while breccia (br1) might be impact related. The most probable center of the structure is estimated at 31 degrees 59 ' 13.73"N, 5 degrees 30 ' 55.14"W using the concentric deviation method applied to the orientation of strata over the disturbed area. Despite the absence of a morphological expression, the ground magnetic and electromagnetic surveys reveal anomalies spatially associated with disturbed strata and SC occurrences. The geophysical data, the structural observations, and the area of occurrence of SCs in target rocks are all consistent with an original size of 1.4-4.2 km in diameter. Cosmogenic nuclide data (Cl-36) constrain the local erosion rates between 220 +/- 22 m Ma(-1) and 430 +/- 43 m Ma(-1). These erosion rates may remove the topographic expression of such a crater and its ejecta in a time period of about 0.3-1.9 Ma. This age is older than the Agoudal iron meteorite age (105 +/- 40 kyr). This new age constraint excludes the possibility of a genetic relationship between the Agoudal iron meteorite fall and the formation of the Agoudal impact site. A chronolgy chart including the Atlas orogeny, the alternation of sedimentation and erosion periods, and the meteoritic impacts is presented based on all obtained and combined data.

The Kerguelen Archipelago (49°S, 69°E) is an excellent location for the study of multi-millennial glacier fluctuations, since it is the largest still glaciated emerged area (552 km2 in 2001) in the sub-Antarctic sector of the Indian Ocean, where many glacio-geomorphological formations such as moraines may be dated. To investigate the so-far little-known Late Glacial and the Holocene glacier fluctuations in Kerguelen, we apply cosmogenic nuclide dating of moraines in 3 glacial valleys: Val Travers valley, Ampere glacier valley and Arago glacier valley. We use in situ 36Cl dating of the basaltic moraine boulders at the first two sites, and 10Be dating of the quartz-bearing syenite boulders at the third site. The new 36Cl and 10Be exposure ages provide time constraints over the last 17,000 years. A glacial advance was highlighted during the Late Glacial at 14.4 ± 1.4 ka ago, probably linked to the Antarctic Cold Reversal event. These results are consistent with those previously obtained on the archipelago (Jomelli et al., 2017, 2018; Charton et al., 2020) and more generally those from other the sub-Antarctic regions (e.g. Sagredo et al., 2018). This suggests that all glaciers at this latitude were broadly sensitive to this specific climatic signal. No Early nor Mid Holocene advances were evidenced in Kerguelen glacier evolution during the Holocene due to missing moraines that may have formed in these specific periods. Radiocarbon-dated peat, published in the 1990s, provides evidence of less extensive glacier extents during the Early Holocene than during the Late Holocene (Frenot et al., 1997). Finally, glaciers seem to have re-advanced only during the Late Holocene, especially within the last millennium, at ⁓1 ka, ⁓620 years and ⁓390 years (Verfaillie et al., submitted). A comparison of this new dataset with the available 10Be ages from other sub-Antarctic regions allows for the identification of 3 different glacier evolution patterns during the Holocene. The glacial fluctuations experienced by Kerguelen glaciers seems particularly uncommon, and are likely due to its singular location in the Southern Indian Ocean. Finally, climatic factors that may explain the Kerguelen glacier evolution (temperature, precipitation) are discussed. To this end, we investigate the chronology of glacier advance/retreat periods with (i) the variation in atmospheric temperatures recorded in ice cores in Antarctica and (ii) the variation in precipitation (Southern Westerly Winds, Southern Annular Mode).Charton et al., 2020 : Ant. Sci. 1-13Frenot et al., 1997 : C.R. Acad. Sci. Paris Life Sciences 320, 567-573Jomelli et al., 2017 : Quat. Sci. Rev. 162, 128-144Jomelli et al., 2018 : Quat. Sci. Rev. 183, 110-123Sagredo et al., 2018 : Quat Sci. Rev. 188, 160-166Verfaillie et al., submitted

The Cook Ice Cap (CIC) on the sub-Antarctic Kerguelen Islands recently experienced extremely negative surface mass balance. Further deglaciation could have important impacts on endemic and invasive fauna and flora. To put this exceptional glacier evolution into a multi-centennial-scale context, we refined the evolution of the CIC over the last millennium, investigated the associated climate conditions and explored its potential evolution by 2100 ce. A glaciological model, constrained by cosmic ray exposure dating of moraines, historical documents and recent direct mass balance observations, was used to simulate the ice-cap extents during different phases of advance and retreat between the last millennium and 2100 ce. Cosmogenic dating suggests glacial advance around the early Little Ice Age (LIA), consistent with findings from other sub-Antarctic studies, and the rather cold and humid conditions brought about by the negative phase of the Southern Annular Mode (SAM). This study contributes to our currently limited understanding of palaeoclimate for the early LIA in the southern Indian Ocean. Glaciological modelling and observations confirm the recent decrease in CIC extent linked to the intensification of the SAM. Although affected by large uncertainties, future simulations suggest a complete disappearance of CIC by the end of the century.

Denudation rates are routinely derived from concentrations of terrestrial in situ produced cosmogenic nuclides (TCN), particularly from 10Be concentrations in river sand. Denudation rates are calculated assuming that they remain steady throughout the integration time scale of the TCN. However, such an assumption is possibly unverified in settings with negligible tectonics, where rates typically range from 10 to 100 mm/ky. In those settings, the TCN conveys a signal that integrates denudation over a time span longer than a few thousand years. The signal may include periods when anthropogenic and climatic forcing on denudation was distinct from modern times. For instance, agricultural practices were limited before 6,000 years B.P. and climatic conditions were colder and drier before 10,000 years B.P. A variable forcing may produce variable and transient denudation rates. In that case, the assumption of steady denudation rates is invalid, and their derivation may introduce a bias.To detect transient landscapes and resolve such a bias, we can take advantage of the different sensitivity of the 14C and 10Be TCNs to recent and short-term changes in surface denudation. In situ 14C is more sensitive than 10Be to such changes, because of a shorter half-life (5,700 y compared to 1.4 My). This potential application of coupled 14C - 10Be measurements has recently been discussed in several theoretical studies (Hippe, 2017; Mudd, 2017; Skov et al., 2019). Despite the improvement of 14C extraction lines and measurement facilities (Hippe et al., 2009; Lupker et al., 2019), sensitivity tests remain limited on natural cases (Hippe et al., 2012).Here, we propose assessing this new application by in situ 14C - 10Be measurements on river sand from the Cevennes and the Monts Margeride within the Variscan Massif Central in France. With an average elevation of ~700 m, this mountain range presents an asymmetrical topography, composed of a low-relief surface reaching 1,700 m, and bordered by a gently sloping flank to the west and a steep escarpment to the southeast, along the Cevennes fault. This escarpment receives frequent and seasonal extreme precipitation events (300-700 mm in 48h) on its southeast flank.The range is subject to very limited seismic activity and appears relevant for an application of the 14C-10Be couple. Basins are rich in quartz and have homogeneous lithology. The recent paleoclimatic context is well constrained, with substantial climatic variations but with limited Pleistocene glaciations (e.g. Fauquette et al., 1999; Magny et al., 2003; Mayewski et al., 2004). The Massif Central is subject to active erosion processes, without major contribution from stochastic events such as landslides. Denudation rates are in the range of the theoretical study of Skov et al. 2019 (Schaller et al. 2001; Molliex et al. 2016; Olivetti et al. 2016; Desormeaux et al., 2021) and several studies have suggested transient denudation patterns (Schaller et al. 2001; Olivetti et al. 2016). With our new measurements, we will verify whether the 14C-10Be couple has sufficient resolution to detect such transience in natural cases.

Debris-covered glaciers constitute a substantial part of the worldwide cryosphere (Scherler et al. 2018). However, their long-term response to multi-millennial climate variability has rarely been studied, in particular in the Southern Hemisphere. The presence of both debris-covered and debris-free glaciers on Kerguelen Archipelago (49°S, 69°E) offers therefore an excellent opportunity to investigate and compare long-term evolution of these two types of glaciers. To do so, we used the cosmogenic 36Cl surface dating method on moraine boulders that allows to establish temporal constraints of glacier oscillation. We provide here the first Late Glacial and Holocene glacier chronology of a still active debris-covered glacier from the archipelago: the Gentil Glacier. Results show that the Gentil Glacier advanced once at ~14.3 ka, i.e. during the Late Glacial (19.0 – 11.6 ka), and re-advanced during the Late Holocene at ~2.6 ka (Charton et al., 2020). Both debris-covered and debris-free glaciers experienced a broadly synchronous advance during the Late Glacial, that may be assigned to the Antarctic Cold Reversal event (14.5 – 12.9 ka) (Jomelli et al., 2017; 2018). This suggests that both types (debris-covered and debris-free) of glaciers at Kerguelen were sensitive to large amplitude temperature fluctuations recorded in Antarctic ice cores (WAIS divide Project Members, 2013), associated with increased precipitations (Van der Putten, 2015). However, during the Late Holocene, the advance at about ~2.6 ka was not observed on other glaciers and seems to be a specific response of the debris-covered Gentil Glacier, either related to distinct ice dynamics or an individual response to precipitation changes. Charton et al., 2020 : Ant. Sci. 1-13Jomelli et al., 2017 : Quat. Sci. Rev. 162, 128-144Jomelli et al., 2018 : Quat. Sci. Rev. 183, 110-123Scherler et al., 2018 : GRL. 45, 11,798-11,805Van der Putten et al., 2015 : Quat. Sci. Rev. 122, 142-157WAIS Divide Project Members, 2013: Nature. 500, 440-444

International audience; 10 Be-derived catchment-wide denudation rates are positively correlated with topographic indices in the southern Longmen Shan.  Erosion rates are consistent over short-and long-term timescales across the Longmen Shan, suggesting an exhumational steady state.  Rock uplift pattern and topographic evolution across the Longmen Shan have been largely controlled by upper crustal shortening and fault geometry.

Denudation is one of the main processes that shapes landscapes. Because temperature, precipitation and glacial extents are key factors involved in denudation, climatic fluctuations are thought to exert a strong control on this parameter over geological timescales. However, the direct impacts of climatic variations on denudation remain controversial, particularly those involving the Quaternary glacial cycles in mountain environments. Here we measure in situ cosmogenic 10Be concentration in quartz in marine turbidites of two high-resolution cores collected in the Mediterranean Sea, providing a near-continuous (temporal resolution of ~1–2 kyr) reconstruction of denudation in the Southern Alps since 75 kyr ago (ka). This high-resolution palaeo-denudation record can be compared with well-constrained climatic variations over the last glacial cycle. Our results indicate that total denudation rates were approximately two times higher than present during the Last Glacial Maximum (26.5–19 ka), the glacial component of the denudation rates being $$1.5_{ - 1.0}^{ + 0.9}$$ mm yr−1. However, during moderately glaciated times (74–29 ka), denudation rates were similar to those today (0.24 ± 0.04 mm yr−1). This suggests a nonlinear forcing of climate on denudation, mainly controlled by the interplay between glacier velocity and basin topography. Hence, the onset of Quaternary glaciations, 2.6 million years ago, did not necessarily induce a synchronous global denudation pulse. Constraints on the denudation of the Southern Alps over the last glacial cycle indicate a nonlinear influence of climate on landscape evolution in glaciated areas, according to a beryllium isotope record measured from quartz in a sequence of Mediterranean turbidites.

ASTER Team: Georges Aumaître, Didier L. Bourlès and Karim Keddadouche; International audience; Debris-covered glaciers constitute a large part of the world's cryosphere. However, little is known about their long-term response to multi-millennial climate variability, in particular in the Southern Hemisphere. Here, we provide first insights into the response of a debris-covered glacier to multi-millennial climate variability in the sub-Antarctic Kerguelen Archipelago, which can be compared to that of recently investigated debris-free glaciers. We focus on the Gentil Glacier and present thirteen new 36 Cl cosmic-ray exposure ages from moraine boulders. The Gentil Glacier experienced at least two glacial advancesthe first one during the Late Glacial (19.0-11.6 ka) at ~14.3 ka and the second one during the Late Holocene at ~2.6 ka. Both debris-covered and debris-free glaciers advanced broadly synchronously during the Late Glacial, most probably during the Antarctic Cold Reversal event (14.5-12.9 ka). This suggests that both glacier types at Kerguelen were sensitive to abrupt temperature changes recorded in Antarctic ice cores, associated with increased moisture. However, during the late Holocene, the advance at about ~2.6 ka was not observed in other glaciers and seems to be an original feature of the debris-covered Gentil Glacier, either related to distinct dynamics or distinct sensitivity to precipitation changes.

High-mountain environments in an active tectonic setting are prone to landsliding. The triggering mechanisms are still a challenge as these areas are influenced by several pre-conditioning factors coupled with active seismicity and climatic forcings. Understanding the intrinsic and external mechanisms in which these events are influenced would help to establish better constraints onto their timing and periodicity and, eventually, hazard assessment and prediction. Glacially eroded valleys are especially prone as they deeply incise mountain ranges leaving unstable slopes once they retreat. Establishing the timing of such events enables to link the causality and comprehend in a deeper level the triggering and pre-conditioning factors of landslides. To this aim, ¹⁰Be and ²⁶Al cosmogenic age determinations were performed in three landslide deposits in a poorly studied area of San Juan province, all of which are novel to the area. Coupled with remote sensing techniques, field observations and detailed stratigraphic and sedimentological studies, these new large landslides represent a first approach to understand this dynamic environment. The three landslides were categorized as rock avalanches found in the middle and lower reaches of the Blanco River, sourced from the Choiyoi Group with evidence of hydrothermal alteration and including/deforming moraine deposits during their fall. Ages range from 20.9±1.4, 10.8±0.7 and 12.8±0.9 ka from the lowermost deposit to the highest, respectively. Even though one sample per deposit is not enough to have statistically significant exposure ages, these values, along with the established chronostratigraphy, allow first order assumptions on the link between deglaciation processes and readjustment of the slopes via large landslide events.

International audience; The respective impacts of Northern and Southern Hemispheric climatic changes on the Tropics during the last deglaciation remain poorly understood. In the High Tropical Andes, the Antarctic Cold Reversal (ACR, 14.3-12.9 ka BP) is better represented among morainic records than the Younger Dryas (12.9-11.7 ka BP). However, in the Altiplano basin (Bolivia), two cold periods of the Northern Hemisphere (Heinrich Stadial 1a, 16.5-14.5 ka BP, and the Younger Dryas) are synchronous with (i) major advances or standstills of paleoglaciers and (ii) the highstands of giant paleolakes Tauca and Coipasa. Here, we present new cosmic ray exposure (CRE) ages from glacial landforms of the Bolivian Andes that formed during the last deglaciation (Termination 1). We reconstruct the equilibrium line altitudes (ELA) associated with each moraine and use them in an inverse algorithm combining paleoglaciers and paleolake budgets to derive temperature and precipitation during the last deglaciation. Our temperature reconstruction (ΔT relative to present day) yields a consistent regional trend of progressive warming from ΔT = −5 to −2.5°C during 17-14.5 ka BP, followed by a return to colder conditions around −4°C during the ACR (14.5-12.9 ka BP). The Coipasa highstand (12.9-11.8 ka BP) is coeval with another warming trend followed by ΔT stabilization at the onset of the Holocene (ca. 10 ka BP), around −3°C. Our results suggest that, during the last deglaciation (20-10 ka BP) atmospheric temperatures in the Tropical Andes mimicked Antarctic variability, whereas precipitation over the Altiplano was driven by changes in the Northern Hemisphere.

International audience; Coarse debris accumulations cover large areas in high latitude and mountain environments, but their age and origin remain mostly unknown. Here we reassess the morphology of a prominent coarse debris accumulation in the Sudetes Mountain range in central Europe and constrain its timing with 10Be surface exposure data. Our observations indicate that the landform in the south-eastern slope of the Suť ridge appears consistent with the morphology of a block slope. The oldest minimum age of 150.1 ± 4.8 ka obtained for the tor at the upper limit of the block slope indicates the disintegration of the ridge and surface lowering under periglacial conditions prior to the last glacial-interglacial cycle. Four exposure ages retrieved for block samples range from 84.3 ± 3.8 to 26.8 ± 2.6 ka, providing evidence for block emplacement during the last cold period. The exposure ages extend existing chronological dataset for peri/glacial landforms in the Sudetes and constrain the timing of cold environments in the area prior the Last Glacial Maximum. The ages are also consistent with surface exposure data reported for block fields and block slopes in Western Europe and confirm the formation of similar landforms over the last glacial period in the Sudetes.

Sediment accumulation rates and thermal trackers suggest a substantial and global increase in erosion rates over the past few million years. That increase is commonly associated with the impact of the Northern Hemisphere glaciation, but methodological biases have led researchers to debate this hypothesis. Here, we test whether Himalayan erosion rates increased by measuring beryllium-10 (10Be) in the sediment of the Bengal Bay seabed. Sediment originated from rocks that produced 10Be under the impact of cosmic rays during erosion near surface. Thus, the 10Be concentrations indicate erosion rates. The 10Be concentration of the Bengal Bay sediment depends on the contributions of the Ganga and Brahmaputra rivers. Their sediments have distinct 10Be concentrations because of distinct elevations and erosion in their drainage basins. Variable contributions could thus complicate erosion-rate calculation. We traced these contributions by a provenance study using the strontium (Sr) and neodymium (Nd) isotopic sediment compositions. Within uncertainties of ±30%, our reconstructed past erosion rates show no long-term increase for the past six million years. This stability suggests that climatic changes during the late Cenozoic have an undetectable impact on the erosion patterns in the Himalayas, at least on the ten thousand to million year timescales accounted for by our dataset. Long-term Himalayan erosion rates remained stable through the global climatic changes of the past six million years, according to the cosmogenic nuclide composition of terrestrial sediments recovered from the Bay of Bengal.

International audience; The dynamics of carbonate-dominated landscapes is still debated, and first-order questions pertaining to the respective importance of chemical and mechanical weathering processes or the influence of climatic variability on denudation rates are largely open. To address these issues, we investigate the denudation pattern across a climatic gradient in Provence, SE France. We focused on a series of major carbonate mountain ranges with elevation spanning 200 to 2000 m and associated with >2-fold variations in mean annual temperature and precipitation. We collected 25 samples from 10 different mountain ranges and quantified denudation rates through the measurement of their Cl-36 concentrations in order to explore tectonic and climatic controls on these carbonate landscapes evolution. We observe that most of our samples experience denudation rates in the 30-60 mm/ka range (averaged over 5 to 40 ka), with no evident dependence on variations of mean annual temperature or precipitation. One range (Lure mountain) stands out as a significant outlier, with much higher denudation rates (>100 mm/ka) than adjacent sites (Ventoux mountain) at the same elevation and experiencing similar present-day environmental conditions. We explore in details the climatic, tectonic and geomorphological contexts of these two ranges in order to understand the reasons for this apparent 3-fold difference in denudation rates. A regionally-documented major Holocene hillslope destabilization event appears to be a likely candidate to explain the observed lower Cl-36 concentrations at the top of the Lure mountain. At longer wavelengths, our regional dataset shows no clear control of modem precipitation gradients on denudation rates, consistent with previous observations in landscapes underlain by other lithologies.

International audience; The knowledge of the eruptive history of volcanic centers allows for improving the evaluation of the related risks and hazards in populated areas, but substantially depends on the ability of dating the lava flows. However, traditional methods such as U-Th/He, 40 Ar-39 Ar, 40 K-40 Ar and radiocarbon dating are not always suitable. Therefore, an alternative approach based on the combination of in situ-produced 36 Cl based cosmic ray exposure dating, lichenometry and dendrochronology was tested on two lava flows (called Lava flow "A" and "B") from Pico de Orizaba (Mexico), previously attributed to 16th and 17th century eruptions, respectively. The presented results show that both lava flows are significantly older than their assumed 16th and 17th century ages. Regarding lava flow "A", the measured in situ-produced 36 Cl concentrations lead to a mean age of 3.03 ± 0.70 ka, while dendrochronology and lichenometry yield minimum ages of 834 and 1130 years, respectively. Regarding lava flow "B", the measured in situ-produced 36 Cl concentrations lead to a mean age of 1.45 ± 0.35 ka, whereas lichenometry gives a minimum age of ∼1000 years. Overall, this demonstrates that the combination of in situ-produced 36 Cl based cosmic ray exposure dating, lichenometry and dendrochronology has a considerable potential for dating purposes on young deposits and landforms, in particular on lava flows at high elevation sites.

International audience; In this study, we present a new glacial chronology based on 20 in situ-produced 36Cl-based cosmic ray exposure datings from moraine boulders and bedrock from the Throne of Zeus (TZ) and Megala Kazania (MK) cirques on Mount Olympus. The 36Cl derived ages of glacial landforms range from 15.6 ± 2.0 to 0.64 ± 0.08 ka, spanning the Late-glacial and the Holocene. The Late-glacial, recorded in both cirques, is partitioned in three distinct phases (LG1-3): an initial phase of moraine stabilization at 15.5 ± 2.0 ka with subsequent deglaciation starting at ∼14 ka (LG1), followed by a shift to marginal conditions for glaciation at 13.5 ± 2.0 ka (LG2), sustained by large amounts of wind-blown snow, despite regional warming. Glacial conditions returned at 12.5 ± 1.5 ka (LG3) and were characterized by low air temperatures and glacier shrinking. The Holocene glacial phases (HOL1-3) are recorded only in the MK cirque, likely due to its topographic attributes. An early Holocene glacier stillstand (HOL1) at 9.6 ± 1.1 ka follows the regional temperatures recovery. No glacier activity is observed during the mid-Holocene. The Late Holocene glacier expansions, include a moraine stabilization phase (HOL2) at 2.5 ± 0.3 ka, during wet conditions and solar insolation minima, while (HOL3) corresponds to the early part of the Little Ice Age (0.64 ± 0.08ka). Our glacial chronology is coherent with glacial chronologies from several cirques along the northeast Mediterranean mountains and in pace with numerous proxies from terrestrial and marine systems from the north Aegean Sea.

Co-auteur étranger; International audience; Constraining the age of young lavas, which generally fall outside the effective range of traditional geochronologymethods, remains a key challenge in volcanology, limiting the development of high-resolution eruption chronologies.We present an in situ cosmogenic3He and36Cl surface-exposure chronology, alongside new minimum-limiting14Cages,documenting young eruptions at five sites in the Western Cordillera, southern Peru. Four3He-dated lavas on the NevadoCoropuna volcanic complex (hitherto thought to be dormant) indicate that the central dome cluster is young and potentiallyactive; two Holocene lavas on the easternmost dome are the youngest directly dated lavas in Peru to date. East ofCoropuna, lava domes and block-lava flows represent the most extensive output to date of Nevado Sabancaya, one ofPeru’s most active volcanoes. Two3He measurements confirm the Holocene age of these deposits and expand thechronology for one of the youngest major lava fields in Peru.36Cl surface-exposure ages from the Purupurini dome clusterand Nevado Casiri document middle-late-Holocene episodes of effusive activity, while basal14C ages from a lava-dammed wetland constrain an effusive eruption at Mina Arcata, north of Coropuna, to the late-glacial period. Thesenew data advance the recent Western Cordillera volcanic record whilst demonstrating both the considerable potentialand fundamental limitations of cosmogenic surface-exposure methods for such applications.

We present new age constraints for the late Miocene Volkovce Formation of Slovakia, alluvial facies that accumulated adjacent to Lake Pannon. Facies analysis and authigenic 10Be/9Be dating was undertaken at the Bernolakovo and Triblavina localities while the latter outcrop also yielded additional small mammal and mollusk assemblages as well as remains of flora. The results of seven radiometric dating ages yielded a weighted mean age of 9.65 ± 0.61 Ma for the Triblavina outcrop and 8.85 ± 0.32 Ma for the Bernolakovo outcrop. The small mammal assemblage at the Triblavina outcrop is indicative of the lowermost MN11 zone, which in the Western European standard definition suggests an age of

International audience; After 6 years of 36 Cl routine operation, more than 6000 unknown samples have been measured at the 5MV French accelerator mass spectrometry (AMS) national facility ASTER (CEREGE, Aix en Provence). This paper presents the long term behavior of ASTER through the analysis of the measurements of the most used chlorine standards and reference materials, KNSTD1600, SM-Cl-12 and SM-CL-13 over a 46 months' time period. Comparison of measured chlorine concentrations (both 35 Cl and 36 Cl) from ice samples on two AMS facilities operating at 5MV (ASTER) and 6MV (DREAMS, Helmholtz-Zentrum Dresden-Rossendorf) and normalizing to two different reference materials agree within uncertainties making both reference materials (SM-Cl-12 and KNSTD1600) suitable for 36 Cl measurement at ASTER.

International audience; The Central Pyrenees hosted a large ice cap during the Late Pleistocene. The cirques under relatively low-altitude peaks (2200–2800 m) include the greatest variety of glacial landforms (moraines, fossil debris-covered glaciers and rock glaciers), but their age and formation process are poorly known. Here, we focus on the headwaters of the Garonne River, namely on the low-altitude Bacivèr Cirque (highest peaks at ~2600 m), with widespread erosive and depositional glacial and periglacial landforms. We reconstruct the pattern of deglaciation from geomorphological observations and a 17-sample dataset of 10Be Cosmic-Ray Exposure (CRE) ages. Ice thickness in the Bacivèr Cirque must have reached ~200 m during the maximum ice extent of the last glacial cycle, when it flowed down towards the Garonne paleoglacier. However, by ~15 ka, during the Bølling-Allerød (B-A) Interstadial, the mouth of the cirque was deglaciated as the tributary glacier shrank and disconnected from the Garonne paleoglacier. Glacial retreat was rapid, and the whole cirque was likely to have been deglaciated in only a few centuries, while paraglacial processes accelerated, leading to the transformation of debris-free glaciers into debris-covered and rock glaciers in their final stages. Climate conditions prevailing at the transition between the B-A and the Younger Dryas (YD) favored glacial growth and the likely development of small moraines within the slopes of the cirque walls by ~12.9 ka, but the dating uncertainties make it impossible to state whether these moraines formed during the B-A or the YD. The melting of these glaciers favored paraglacial dynamics, which promoted the development of rock glaciers as well as debris-covered glaciers. These remained active throughout the Early Holocene until at least ~7 ka. Since then, the landscape of the Bacivèr Cirque has seen a period of relative stability. A similar chronological sequence of deglaciation has been also detected in other cirques of the Pyrenees below 3000 m. As in other mid-latitude mountain regions, the B-A triggered the complete deglaciation of the Garonne paleoglacier and promoted the development of the wide variety of glacial and periglacial landforms existing in the Bacivèr cirque.

Cave sediments pose dating challenges due to complex depositional and post-depositional processes that operate during their transport and accumulation. Here, we confront these challenges and investigate the stratified sedimentary sequence from Wonderwerk Cave, which is a key site for the Earlier Stone Age (ESA) in Southern Africa. The precise ages of the Wonderwerk sediments are crucial for our understanding of the timing of critical events in hominin biological and cultural evolution in the region, and its correlation with the global paleontological and archaeological records. We report new constraints for the Wonderwerk ESA chronology based on magnetostratigraphy, with 178 samples passing our rigorous selection criteria, and fourteen cosmogenic burial ages. We identify a previously unrecognized reversal within the Acheulean sequence attributed to the base of the Jaramillo (1.07 Ma) or Cobb Mtn. subchrons (1.22 Ma). This reversal sets an early age constraint for the onset of the Acheulean, and supports the assignment of the basal stratum to the Olduvai subchron (1.77–1.93 Ma). This temporal framework offers strong evidence for the early establishment of the Oldowan and associated hominins in Southern Africa. Notably, we found that cosmogenic burial ages of sediments older than 1 Ma are underestimated due to changes in the inherited 26Al/10Be ratio of the quartz particles entering the cave. Back calculation of the inherited 26Al/10Be ratios using magnetostratigraphic constraints reveals a decrease in the 26Al/10Be ratio of the Kalahari sands with time. These results imply rapid aeolian transport in the Kalahari during the early Pleistocene which slowed during the Middle Pleistocene and enabled prolonged and deeper burial of sand while transported across the Kalahari Basin.

International audience; The possibility of quantifying surface processes in mafic or volcanic environment using the potentialities offered by the in situ-produced cosmogenic nuclides, and more specifically by the in situ-produced Be-10, is often hampered by the rarity of quartz minerals in the available lithologies. As an alternative to overcome this difficulty, we explore in this work the possibility of relying on feldspar minerals rather that on quartz to perform in situ-produced Be-10 measurements in such environments. Our strategy was to cross-calibrate the total production rate of Be-10 in feldspar (P-10fsp) against the total production rate of He-3 in pyroxene (P-3px) by measuring He-3 and Be-10 in cogenetic pyroxene (He-3(px)) and feldspar (Be-10(fsp)). The samples were collected from eight ignimbritic boulders, exposed from ca 120 to 600 ka at elevations ranging from 800 to 2500 m, along the preserved rock-avalanche deposits of the giant Caquilluco landslide (18 degrees S, 70 degrees W), Southern Peru. Along with data recently published by Blard et al. (2013a) at a close latitude (22 degrees S) but higher elevation (ca. 4000 m), the samples yield a remarkably tight cluster of He-3(px) - Be-10(fsp) total production ratios whose weighted-mean is 35.6 +/- 0.5 (1 sigma). The obtained weighted mean He-3(px) - Be-10(fsp) total production ratio combined with the local He-3(py) total production rate in the high tropical Andes published by Martin et al. (2017) allows to establish a total SLHL Be-10 in situ-production rate in feldspar mineral (P-10fsp) of 3.57 +/- 0.21 at.g(-1).yr(-1) (scaled for the LSD scaling scheme, the ERA40 atm model and the VDM of Lifton, 2016). Despite the large elevation range covered by the whole dataset (800-4300 m), no significant variation of the He-3(px) - Be-10(fsp) total production ratios in pyroxene and feldspar was evidenced. As an attempt to investigate the effect of the chemical composition of feldspar on the total Be-10 production rate, major and trace element concentrations of the studied feldspar samples were analyzed. Unfortunately, giving the low compositional variability of our dataset, this issue is still pending. (C) 2017 Elsevier B.V. All rights reserved.

International audience; The 400-km-long Talas-Fergana Fault is one of a series of major right-lateral strike-slip faults that cross the Tien Shan Range. This fault has been recognized as active in the late Holocene and accommodates part of the deformation induced by the ongoing Indo-Asian collision. The kinematics and the role of this strike-slip fault are poorly understood with no large earthquakes reported in the instrumental or historical catalogs, and no well-constrained geological slip-rate estimates. Here we used high-resolution satellite imagery to present a first detailed analysis of the fault segmentation. We identified nine geometric segments based on strike variations for the Talas-Fergana Fault. Along the Kyldau segment, through morphological analyses of an offset alluvial fan and the application of multiple dating methods (Be-10, Al-26, Cl-36, luminescence, and radiocarbon), we calculated a late Quaternary slip rate ranging from 2.2 to 6.3 mm/year. This rate is higher than the geodetic measurements, but the discrepancy can be partly explained if the Talas-Fergana Fault accommodates shortening by counterclockwise rotation around a vertical axis. Paleoearthquakes identified by trenching indicate that at least two primary surface ruptures (and possibly a third) occurred in the past 3,800 years, and that no large earthquake has ruptured the Kyldau segment since at least 420 years B.P. (possibly within the last 2,700 years), making this fault segment a potential candidate to generate an earthquake with M > 7 in the near future.

International audience; The growing number of studies based on data provided by the accelerator mass spectrometry (AMS) technique from increasingly diverse matrices implies that developing very effective and reproducible sample processing techniques is crucial to meet the demand generated. After being dissolved, the isolation of the cosmogenic nuclide to be measured and its chemical purification imply complex processes throughout successive stages The presented automatic system was designed to perform the final steps of the Be-10 and Al-26 chemical extraction protocol from natural matrices (sediments, pure mineral phases, ...), previously purified, decontaminated and dissolved in the case of in situ-produced cosmogenic nuclides, or leached or dissolved in the case of meteoric cosmogenic nuclides. Driven by Labview software, the developed automatic system, in addition to freeing the operator from tedious tasks, allows reproducibly processing simultaneously up to eight samples of different volumes in roughly 40 min. This article presents the design of the automated extraction bench and its performance based on the recovery efficiency of the stable element and the reproducibility of the measurements of the cosmogenic nuclide concentrations by AMS.

International audience; High Be-10 contents in tektites reported in literature are taken as evidence of a source material, melted at the impact site, enriched in atmospheric Be-10; i.e., a soil or sediment. In 0.8 Ma Australasian tektites, Be-10 content increases with distance from the putative impact location in Indochina, with geographic averages from 69 x 10(6) atoms/g (Indochina) to 136 x 10(6) atoms/g (Australia). Here we report, for the first time, Be-10 contents in microtektites collected from Antarctica and the South China Sea. We show that microtektites are similar to 30 x 10(6) atoms/g richer in Be-10 than tektites from the same geographic areas. Antarctic microtektites, with an average Be-10 content of 184 x 10(6) atoms/g after correction for in situ production, are the richest impact glass ever measured. The simplest explanation for such systematic size and geographic trends is that the source depth of the melt within the target surface decreases with ejection velocity. Indeed, higher initial kinetic energy implies higher launch distances and higher fragmentation of the ejecta. Antarctic microtektite source depth may tentatively be restricted to the upper tens of centimeters at the impact site. Alternative models invoking a marine or loessic sediment source, or a secondary enrichment in the microtektite (either by atmospheric scavenging, selective fractionation by volatilization, or post-depositional contamination) fail to reproduce the observed relationships.

International audience; We present new magnetic (direction and relative paleointensity) and beryllium isotope (10 Be, 9 Be and 10 Be/ 9 Be ratio) results covering the last geomagnetic reversal, i.e., the Matuyama-Brunhes transition (MBT), from the Chiba composite section (CbCS), east-central Japan. The very high sedimentation rates (>90 cm/ka) of the studied site, a candidate site for the global boundary stratotype section and point (GSSP) of the Lower-Middle Pleistocene boundary, allow the acquisition of a dataset of exceptional resolution. Coupled cosmogenic 10 Be and magnetic results measured on the same samples demonstrate that the magnetization acquisition conserved the timing of rapid geomagnetic features, allowing accurate paleomagnetic interpretations. A polarity switch (PS) capturing most of the angular deviation occurring between 771.9 and 773.9 ka was followed by a directional instability rebound (IC1) until 768.5 ka. This sequence with 5.4 ka duration was characterized by a weak dipole field as low as 2.3 ± 0.3 × 10 22 Am 2. Four rapid episodes of directional instabilities preceding and following the PS-IC1 phase completed the reversal sequence. The asymmetry observed between the long-term dipole decay and sharp recovery, and rapid oscillations (

International audience

Located at the northeastern corner of the Adria microplate, the Alps-Dinarides junction represents a key region for understanding how the Adria microplate interacts with stable Europe. However, little is known on how the present-day deformation imposed by the rotation of the Adria microplate is absorbed across the Dinarides. Using morphotectonic analysis based on satellite and aerial images, accurate topographical maps, and digital elevation models combined with field investigations, we mapped in detail the three main active faults of the Northern Dinarides. Geomorphic and geological cumulative displacements ranging from a few meters to several kilometers have been identified on those faults and dated for the most recent ones using 36 Cl exposure dating. Those results yielded a total right-lateral motion of 3.8 ± 0.7 mm/yr oriented N317. Comparing our results with the motion expected from Adria rotation models suggests that the Northern Dinarides absorbs most of the predicted Adria-Eurasia motion, thus representing the eastern boundary of the microplate. However, a significant E-W component is lacking, suggesting that part of the stress imposed by the microplate rotation is transferred farther to the east. Finally, bounds placed on the Plio-Pleistocene kinematics confirm that faulting onset occurred during the Early Pliocene and evidence a significant kinematic change at the Early/Middle Pleistocene boundary.

Morphological and geological observations reveal that most Apenninic faults are highly segmented and that the majority of the fault segments are less than 10 km long. Although these faults have undergone numerous paleoseismological investigations, quantitative data remain crucially lacking for a large number of fault segments. Because such data are essential to understanding how these faults have ruptured and interacted in the past and how they might behave in the future, we investigated the Holocene seismic history of the Pizzalto normal fault, a 13 km long fault segment belonging to the Pizzalto-Rotella-Aremogna fault system in the Apennines. We collected 44 samples from the Pizzalto fault plane exhumed during the Holocene and analyzed the 36Cl and rare earth element (REE) contents. Together, the 36Cl and REE concentrations show that at least six events have exhumed 4.4 m of the fault scarp between 3 and 1 ka, with slip per event values ranging from 0.3 to 1.2 m. No major events have been detected over the last 1 kyr. The Rotella-Aremogna-Pizzalto fault system has a clustered earthquake behavior with a mean recurrence time of 1.2 kyr and a low to moderate probability (ranging from 4% to 26%) of earthquake occurrence over the next 50 years.

Fluvial terraces are valuable records to study and characterize landscape evolution and river response to base level lowering, and to decipher coupled responses between fluvial incision and regional tectonics. The opening of closed basins has a strong impact on fluvial dynamics, as it involves an abrupt base level lowering that accelerates landscape fluvial dissection. This study focuses on the time response of the Duero Basin, the largest and best preserved among the Cenozoic basins of the Iberian Peninsula, to exorheism. Fluvial incision due to basin opening has developed up to 13 un-paired strath terraces along the south margin of the Duero river, distributed at relative heights up to +136–128 m compared to the modern floodplain. Paired 10Be–26Al cosmogenic isotope depth profiles from six fluvial terraces, located ca. 30–80 km upstream from the opening zone, suggest Pleistocene ages for almost the entire fluvial terrace staircase (from T3 at +112 –107 m, to T12 at +13–11 m). The terrace density and the total lowering of the terrace surface, key parameters in limiting terrace exposure ages, were estimated based on field and geomorphological data. Apparent burial durations and basin denudation rates deduced from inherited 10Be–26Al concentrations provide valuable information on basin evolution. Apparent basin denudation rates remained relatively low (, This is a MITE project contribution, funded by the Spanish Ministry of Science and Innovation ( Plan Estatal de Investigación Científica y Técnica y de Innovación ; Ref. CGL2014-59516 and PR2011-0044 ). At the time of paper writing, L. Rodríguez-Rodríguez was recipient of an outgoing post-doctoral grant of the Clarín-Cofund program (Ref. ACA-17-19), financed jointly by the regional government of Principality of Asturias and the 7th WP of the European Union–Marie Curie Actions . The ASTER AMS national facility (CEREGE, Aix en Provence) is supported by the INSU/CNRS , the ANR through the “Projets thématiques d'excellence” program for the “Equipements d'excellence” ASTER-CEREGE action and IRD. Candela Pastor-Martín is thanked for providing GIS technical support (funded by the Spanish Ministry of Economy and Competitiveness under grant PEJ-2014-A-93258 ).

Although agriculturally accelerated soil erosion is implicated in the unsustainable environmental degradation of mountain environments, such as in the Himalaya, the effects of land use can be challenging to quantify in many mountain settings because of the high and variable natural background rates of erosion. In this study, we present new long-term denudation rates, derived from cosmogenic 10Be analysis of quartz in river sediment from the Likhu Khola, a small agricultural river basin in the Middle Hills of central Nepal. Calculated long-term denudation rates, which reflect background natural erosion processes over 1000+ years prior to agricultural intensification, are similar to present-day sediment yields and to soil loss rates from terraces that are well maintained. Similarity in short- and long-term catchment-wide erosion rates for the Likhu is consistent with data from elsewhere in the Nepal Middle Hills but contrasts with the very large increases in short-term erosion rates seen in agricultural catchments in other steep mountain settings. Our results suggest that the large sediment fluxes exported from the Likhu and other Middle Hills rivers in the Himalaya are derived in large part from natural processes, rather than from soil erosion as a result of agricultural activity. Catchment-scale erosional fluxes may be similar over short and long timescales if both are dominated by mass wasting sources such as gullies, landslides, and debris flows (e.g., as is evident in the landslide-dominated Khudi Khola of the Nepal High Himalaya, based on compiled data). As a consequence, simple comparison of catchment-scale fluxes will not necessarily pinpoint land use effects on soils where these are only a small part of the total erosion budget, unless rates of mass wasting are also considered. Estimates of the mass wasting contribution to erosion in the Likhu imply catchment-averaged soil production rates on the order of ~ 0.25–0.35 mm yr−1, though rates of mass wasting are poorly constrained. The deficit between our best estimates for soil production rates and measurements of soil loss rates supports conclusions from previous studies that terraced agriculture in the Likhu may not be associated with a large systematic soil deficit, at least when terraces are well maintained, but that poorly managed terraces, forest, and scrubland may lead to rapid depletion of soil resources.

Deglaciation chronology of the Polish High Tatra Mountains has been reconstructed based on 10Be exposure age dating. Fifty-seven rock samples were collected from boulders located on the terminal and lateral moraines that limit the horizontal extent of the LGM and the Lateglacial glaciers in the Biala Woda and Sucha Woda catchments. The uncertainty-weighted mean age of 21.5 ± 2.5 ka obtained for the maximum terminal moraine in the Sucha Woda Valley indicates that the oldest preserved moraines were formed during the global LGM. The age population ranges between 15.1 ± 1.0 and 28.3 ± 2.0 ka, and suggests that glaciers reached their maximum position (LGM I) as early as 28–25 ka and the final stabilization of the form occurred much later possibly after melting of buried dead ice. The younger glacial oscillation (LGM II) occurred no later than 20.5 ka and is represented by well-preserved termino-lateral moraine systems in the Panszczyca Valley. The first Lateglacial stage (LG1) in the study area is documented in the Rybi Potok Valley at the RP1 moraine (1300 m a.s.l.), which was stable at around 16.6 ± 0.3 ka. The younger LG2 stage has no defined absolute age, however, it is constrained between 16.5 and 15.5 ka by the timing of the LG3 stage. This cold event is represented by well-formed moraines in the Roztoka/Piec Stawow Polskich, Rybi Potok and Panszczyca valleys of which exposure age indicates their deposition between 15.0 ± 0.5 and 15.6 ± 0.1 ka. The LG1, LG2 and LG3 stages likely occurred during the Oldest Dryas cold stage (Greenland Stadial 2.1a) related to the North Atlantic cooling Heinrich Event 1. The youngest glacial oscillation is evidenced by moraines in the Pusta and Panszczyca valleys. These moraines are composed of very large granitic blocks of which exposure ages often exhibit isotope inheritance. This is reflected by the youngest P3 moraine in the Panszczyca Valley with a mean age of deposition close to the LGM. The R4 moraine system in the Pusta Valley, however, indicates two oscillations phases that occurred at around 13 ka and correlates well with the timing of RP5 moraine formation in the Za Mnichem Valley. The LG4 stage is related to the climate cooling during the Younger Dryas (Greenland Stadial 1). LGM ELAs reconstructed for the Biala Woda and Sucha Woda/Panszczyca glaciers were located at 1460–1480 m a.s.l. During the Oldest Dryas stages, the ELA in the High Tatras rose from 1600 to 1650 m a.s.l. in the Rybi Potok Valley and from 1700 to 1800 m a.s.l. in the Roztoka/Piec Stawow Polskich Valley. The Younger Dryas ELA, depending on glacier's exposition, was located between 1950 and 2000 m a.s.l. Climate modelling results show that the LGM glaciers (maximum advance) could have advanced in the High Tatras when the mean annual temperature was lower than today by 11–12 °C and precipitation was reduced by 40–60%. During the Lateglacial stages the temperature decrease in the study area changed from 10 °C during the Oldest Dryas to 6 °C during the Younger Dryas and precipitation lowering decreased from −50% to −30% or even −10%, respectively compare to modern conditions.