10Be data on erosional surfaces in the Mayombe massif (SW Congo)

International audienceErosional surfaces, mainly in quartzites of Neoproterozoic age, have been sampled for 10 Be Cosmic Ray Exposure (CRE) dating in different places of the Mayombe Massif (SW Congo). Four types of occurrences have been studied: 1/ denuded and abraded horizontal surfaces sampled at different altitudes along the flanks of the Kouilou valley; 2/ vertical cliffs at different heights in the topographic profile; 3/ incised river banks; 4/ large boulder in a surficial breccia (Stone line). Three groups may be distinguished according to their 10 Be concentrations. A first group of ten samples displays 10 Be concentrations ranging from ~18 000 to 60 000 at/g. These samples were collected from erosional surfaces on the Kouilou valley and incised bank on a secondary river. A second group displays 10 Be concentrations ranging from ~ 80 000 to 330 000 at/g. These samples are from vertical cliffs located in the summit part of an abrupt mountain and massive rocks forming the bed and banks of the Loukoulariver. A third group with a 10 Be concentration of ~ 1 500 000 at/g includes the unique quartzite boulder sampled in the Stone line. After correction of the topographic shielding effect, the equation expressing the 10 Be concentration as a function of the CRE duration and of the denudation rate has been solved for each sample assuming no inherited 10 Be. For the first group, this calculation implies a recent (i.e. 30 m/Ma). For the second group, it is consistent with steady state conditions operating under moderate denudation rates (~ 5-10 m/Ma). For the quartzite boulder, the 10 Be concentration implies that this rock was exposed to cosmic rays for at least 1 Ma. The results on the first group are consistent with the occurrence of a very efficient and recent denudation event having affected the valley flanks and caused incision along thehydrographic system. It is suggested that this event should be the same that caused the formation of the Stone line by erosion and reworking of pre-existing alteration profilesless than 10 ka ago. The results obtained from the second group suggest that this event did not affect some parts of the landscape. The result obtained from the boulder shows that this rock fragment was probably displaced a long time ago, with no relation with the recent denudation event

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

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

Geomorphic Records along the General Carrera (Chile)–Buenos Aires (Argentina) Glacial Lake (46°-48°S), Climate Inferences, and Glacial Rebound for the Past 7–9ka

International audienceWe present geomorphic, stratigraphic, and chronological data acquired along the General Carrera-Buenos Aires (GCBA) glacial lake located along a majormorphological incision across the Andes. Complementing relevant available data, relative chronology of morpho-climatic records together with 18 10Be Cosmic Ray Exposure (CRE) ages allow constraining the timing of the Patagonian ice-sheet fluctuations since the LGM. It improves the knowledge of the Patagonia climate evolution in the 46-48°S area, and allows documenting the uplift rates (glacial rebound) for the past ~7-9 ka. The first major ice lobe retreat occurred after 17.3 ± 0.6 ka and has likely continued during the ACR from ~12.9 to 14.5 ka. Between ~12.9 ka and ~10.9 ± 1.3 ka, the General Carrera Lake evolved as an endorheic basin. Terraces T4 to T1 (top to bottom) have recorded abrupt lake regressions likely controlled by rainfalldeficit. They have accumulated in the time interval ~17.3-12.3 ka (maximum limits). Two glacial re-advances at ~10.9 ± 1.3 and ~7.9 ± 1.1 ka marked a major climate change that led the lake to be ice-dammed again. A major transgression occurred subsequently that have flooded the previously accumulated terraces. Since then, a pervasive regression has steered the GCBA Lake to the situation at Present. The highest shoreline of the transgression is used as a passive marker in order to quantify the magnitude and character of the regional deformation. At 72°30' W, the GCBA Lakearea uplifted (glacial rebound) at a rate between 15 to 33.5 mm.yr--1 during the past ~7.9 ± 1.1 ka. We infer that the high uplift rate mainly originates from the North Patagonian icefield ice loss

The Prados del Cervunal morainic complex: Evidence of a MIS 2 glaciation in the Iberian Central System synchronous to the global LGM

© 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND licenseThe area of Prados del Cervunal (PC) is an intra-morainic topographic depression located at 1800 m asl in the divide or interfluve between Garganta de Gredos and Garganta del Pinar valleys (Central Gredos; Iberian Central System, ICS). Both valleys, along with the adjacent Hoya Nevada, were occupied by glaciers during the Upper Pleistocene, leading to the development of the Prados del Cervunal moraine complexes studied in this work. Using cartographic methods and morphostratigraphic analysis, the three main glacial formations established in the Regional Chrono-Evolutionary Pattern for the ICS, Peripheral Deposits (PD), Principal Moraine (PM) and Internal Deposits (ID), have been identified and mapped in this area. The chronology of these formations has been implemented by Cosmic Ray Exposure (CRE) techniques using 10Be (new data) and 26Cl (previous data, recalculated in this work) in samples from morainic boulders. With these data, the following chrono-evolutionary sequence has been established: (stage 1) local-Maximum Ice Extent (MIE), dated in 25.0 ± 1.4 ka and corresponding to the maximum age obtained in these paleoglaciers; (stage 2) period of oscillations around the MIE, corresponding to the development of the PD Formation between ∼25 ka and ∼21 ka; (stage 3) period of readvance and stabilisation, dated after ∼21 ka (average age obtained for the PD moraines attached to PM moraines) and previous to ∼18 (minimum age obtained for a main crest of the PM formation); and (stage 4) onset of deglaciation dated around to ∼18 ka (average of ages obtained for the first main crest of the ID formation). During the stages of maximum ice expansion, these three glaciers formed an Ice field whose tongues were interconnected on the PC flat by an ice transfluence system (stages 1 and 2, Plateau Glacier Period). In later stages, the ice masses were partitioned, giving rise to valley glaciers and large moraines forming morainic complexes like those of PC (stages 2, 3 and 4, Valley Glaciers Period). The local MIE and onset of deglaciation stages in this area show a good fit with the ages stablished to global level for the global Last Glacial Maximum (LGM) and the onset of the Last Glacial Termination (Termination I). They also show good correlation at local (with other areas of the ICS), peninsular (with other Iberian mountains) and continental (some areas of the Alps and mountains of Central Europe) level. Finally, this evolutionary sequence and its correlations allowed us to adjust and validate some units of the Regional Chrono-Evolutionary Pattern model and propose the Gredos-Pinar-Cabeza Nevada glacial system as benchmark for the glaciation of Marine Isotope Stage (MIS) 2 in the Iberian Peninsula.This work was supported by the Spanish Ministry of Science and Innovation (project PID2020-117685 GB-I00), Castilla-La Mancha University (UCLM, project 2023-GRIN-34112), ANID FONDECYT postdoctoral #3220537, ANID BASAL CHIC #FB210018 and ANID FONDECYT Regular #1220550. The ASTER AMS national facility (CEREGE, Aix-en-Provence) is supported by the INSU/CNRS, and IRD. The authors acknowledge the help and assistance received from the Sierra de Gredos Regional Park (Environmental Department of the Junta de Castilla y León, JCyL) and to the “Guarderia” (Staff of surveillance and control) of the Gredos Regional Reserve for their remarkable help in the fieldworks.Peer reviewe

UTILISATION DU 10BE COSMOGENIQUE PRODUIT IN-SITU POUR L'ETUDE DE LA DYNAMIQUE DES LATERITES EN ZONE INTERTROPICALE

The in-situ produced cosmonucleides result from the interaction of the energy particles resulting from the cosmic radiation with minerals exposed to the surface of the ground. The cosmogenic nuclide 10Be (T½=1,5Ma) was used in this work in order to study the modes of development of the laterites and to quantify the processes affecting them.Les cosmonucléides produits in-situ résultent de l'interaction des particules énergétiques issues du rayonnement cosmique avec les minéraux exposés à la surface de la terre. Le nucléide cosmogénique 10Be (T½=1,5Ma) a été utilisé dans ce travail afin d'étudier les modes de développement des latérites et de quantifier les processus les affectant. Au cours de cette étude, différents systèmes latéritiques ont ainsi été échantillonnés aussi bien en Afrique qu'au Brésil. La distribution des concentrations en 10Be mesurées par spectrométrie de masse par accélérateur dans des quartz issus de filons et prélevés dans des profils de sols permet 1/ de déterminer l'origine autochtone ou allochtone des matériaux lors de la mise en place des séquences étudiées, 2/ de quantifier les taux d'érosion ou d'enfouissement affectant ces surfaces, et 3/ de mettre en évidence et d'estimer l'extension de l'activité biologique. L'examen de l'évolution de la concentration en 10Be le long de "stone-lines" permet de préciser sans ambiguïté leur origine allochtone ou autochtone et, dans ce dernier cas, deux types de modèles développés au cours de ce travail permettent alors d'estimer la vitesse des déplacements latéraux superficiels des sols.Mots clés : Béryllium 10 cosmogénique, latérites, spectrométrie de masse par accélérateur, "stone-line", érosion, enfouissement, sol

\AMS\ 13 – Preface

The Thirteenth Accelerator Mass Spectrometry ConferenceInternational audienceno abstrac

The Late Quaternary slip-rate of the Kichera Fault (North Baikal Rift) from morphotectonic, paleoseismological and cosmogenic 10Be analyses

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Reply to comment by K. Pedoja et al. on "Tectonic record of strain buildup and abrupt coseismic stress release across the northwestern Peru coastal plain, shelf, and continental slope during the past 200 kyr"

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