Papers by Christian Crouzet
Http Www Theses Fr, Jun 19, 2012
Ca y est, ma thèse est terminée ; une page s'est tournée. Et elle s'est tournée d'autant plus agr... more Ca y est, ma thèse est terminée ; une page s'est tournée. Et elle s'est tournée d'autant plus agréablement que j'ai été très heureux que Michel Magny et Thierry Mulder aient accepté d'en être rapporteurs. Je tiens tout particulièrement à les remercier d'avoir pris le temps de le faire. Je tiens également à remercier Flavio Anselmetti, Julien Boé, Valérie Masson-Delmotte et Hervé Piégay pour l'intérêt qu'ils ont montré pour ce travail, en ayant accepté de l'examiner. Cette page tournée, c'est le moment de souffler un peu, de jeter un coup d'oeil dans le rétro et de faire un point sur ces années qui viennent de filer à toute vitesse. C'est à ce moment là qu'on se rend compte à quel point une thèse est une véritable aventure, notamment une sacrée aventure humaine ! Je me rends compte que ma thèse m'a conduit à rencontrer une foule de personnes ; depuis ceux avec qui j'ai juste échangé quelques mots (mais qui m'ont parfois suivi tout au long de la thèse !), jusqu'à ceux qui sont devenus de véritables amis au fil des rencontres. Si je repars depuis le début, je me souviens combien obtenir un financement de thèse était déjà une aventure en soi, et que l'aspect humain en était déjà très imprégné ! Françoise, Jean-Jacques, Fabien et Claude. Pas moins de 4 personnes pour écrire des projets, les ficeler, les proposer, se les voir refuser ou devoir les transformer pour les reproposer. Une agitation folle pour arriver en quelques petits mois à m'obtenir le graal de l'étudiant de master… Je commençais à peine ma thèse que je leur devais déjà une fière chandelle ! Un merci infini à vous 4 pour m'avoir soutenu sur ce projet alors que nous nous connaissions à peine. Françoise… une incroyable rencontre du hasard pour un stage de master. 5 ans plus tard, elle est devenue une amie proche. Elle n'aura pas loupé une miette de cette saga ! Françoise, je te remercie de ton éternel soutien, de ta gentillesse, de ta générosité à tous les égards et de ta franchise de tous les instants. Jean-Jacques m'a vu construire mon chemin, petit à petit, au fil des années. Parfois avec satisafaction, d'autres fois moins… La présence discrète et assidue, le mot juste et admirablement bien placé, tu a su être un directeur de thèse bien veillant et de bon conseil à chacun des moments clés. Merci Jean-Jacques ! Dans ma direction de thèse, il y aura aussi eu Fabien, qui à l'entendre semble s'être fier aux adages en acceptant de me prendre sous son aile, se disant sûrement que l'habit ne fait pas le moine ! Ou en se disant peut-être que d'avoir une blouse blanche tachetée de sédiments, ça ne me changerait pas tant que ça finalement. Ou encore, en se disant peut-être que je pourrai faire un bon bourricot ! Quelle que soit la raison qui l'a poussé à me soutenir au début, puis durant toutes ces années, je ne peux que lui en être extrêmement reconnaissant. Surtout qu'il ne s'est pas contenté de me soutenir ! Mais bon je ne vais lister ici tout ce que je lui ai fait supporter… En tout cas, Fabien, mille merci pour ces 4 années et quelques mois. Je Merci aux Byzantins de Chrono-environnement, aussi nombreux soient-ils ! Merci à Agnès Stock pour son accueil et sa gentillesse. Merci au bureau DDM (au fait qu'est-ce que vous avez fait du chocolat ?). Une fine équipe… heureusement que je n'ai pas atterri dans leur bureau. Une superbe amitié qui débouche déjà sur de belles collaborations, et pourtant c'était pas gagné ! Un très grand merci à Claire Delhon pour son dévouement et sa patience ; ton aide m'aura été précieuse. Là encore un échange aussi sérieux que déconnant (et oui Claire, je les ai vus tes clips…). Un grand merci également à Jean-Robert Disnar qui m'a permis de passer en un temps record une belle quantité d'échantillons avec un « service après-vente » efficace et toujours présent ! Merci à Jean-Pascal Dumoulin pour les échanges fructueux pour essayer de faire parler au mieux ces tous petits débris organiques. Merci à Sidonie Revillon pour les discussions délirantes et le passage d'échantillons aussi express que possible ! Je remercie les services RTM 04, 05 et 06 (Restaurations des Terrains de Montagne) de l'ONF pour les données sur les crues historiques qu'ils m'ont fournies et qui m'ont permis de valider les séries reconstituées. Les lacs Blanc Aiguilles Rouges, d'Eychauda et d'Allos faisant partie de la réserve naturelle des Aiguilles Rouges, du Parc des Ecrins et du Parc du Mercantour (respectivement), je ne pouvais oublier de remercier les gardes d'ASTER et des parcs nationaux pour leur aide précieuse sur le terrain. J'ai pu profiter de leur présence et de leur forme physique sur les manips de carottage. Merci également aux différentes administrations d'avoir autoriser les manips et les prélèvements, sans quoi ce travail de thèse n'aurait pas pu se faire ! La bonne ambiance au sein des doctorants a sans nul doute contribué à la réussite de mon travail de thèse. Je leur souhaite à tous bon courage pour la fin de leur thèse. Un merci tout particulier à mes logeuses préférées qui ont su transformer mes jours de transhumance en instants délectables ; Marie, Laine, Amandine (et Pascale !). Plus largement la bonne ambiance au sein du laboratoire a sans nul doute contribué à la réussite de mon travail de thèse. Les échanges du quotidien, autour d'un café, au détour d'une porte, autour d'un repas, etc. Merci à vous tous pour ces instants qui ne paient pas de mine mais qui offre un espace de vie des plus agréables. Un merci immense à ma famille. C'est toujours bête à dire mais c'est si vrai ; sans eux on ne serait pas là… Des choix parfois tortueux mais accepté avec tolérance, et une liberté accordée avec confiance. Un merci éternel à vous deux pour m'avoir laissé faire mon bout de chemin, et d'en avoir accepté les conséquences. Et enfin merci à celle qui aura supportée un quotidien de fin de thèse avec calme et patience. Ta présence m'aura été indispensable ; merci, Justine ! Que nos vies trouvent leur rythme !
Managing scientific data is probably one the most challenging issues in modern science. In plaeos... more Managing scientific data is probably one the most challenging issues in modern science. In plaeosciences the question is made even more sensitive with the need of preserving and managing high value fragile geological samples: cores. Large international scientific programs, such as IODP or ICDP led intense effort to solve this problem and proposed detailed high standard work- and dataflows thorough core handling and curating. However many paleoscience results derived from small-scale research programs in which data and sample management is too often managed only locally – when it is… In this paper we present a national effort leads in France to develop an integrated system to curate ice and sediment cores. Under the umbrella of the national excellence equipment program CLIMCOR, we launched a reflexion about core curating and the management of associated fieldwork data. Our aim was then to conserve all data from fieldwork in an integrated cyber-environment which will evolve toward lab...
CATENA, 2017
Highlights • Lake sediment archives are used to reconstruct past soil evolution. • Erosion is qua... more Highlights • Lake sediment archives are used to reconstruct past soil evolution. • Erosion is quantified and the sediment geochemistry is compared to current soils. • We observed phases of greater erosion rates than soil formation rates. • These negative soil balance phases are defined as regressive pedogenesis phases. • During the Middle Ages, the erosion of increasingly deep horizons rejuvenated pedogenesis.
HAL (Le Centre pour la Communication Scientifique Directe), Nov 1, 2021
EGU General Assembly Conference Abstracts, Apr 1, 2015
Quaternary Research, May 1, 2017
Local glacial fluctuations and flood occurrences were investigated in the sediment sequence of pr... more Local glacial fluctuations and flood occurrences were investigated in the sediment sequence of proglacial Lake Muzelle. Based on geochemical analysis and organic matter content established using loss on ignition and reflectance spectroscopy, we identified six periods of increased glacial activity over the last 1700 yr. Each is in accordance with records from reference glaciers in the Alps. A total of 255 graded layers were identified and interpreted as flood deposits. Most of these occurred during glacial advances such as the Little Ice Age period and exhibit thicker deposits characterized by an increase in the fine grain-size fraction. Fine sediment produced by glacial activity is transported to the proglacial lake during heavy rainfall events. The excess of glacial flour during these periods seems to increase the watershed’s tendency to produce flood deposits in the lake sediment, suggesting a strong influence of the glacier on flood reconstruction records. Thus, both flood frequency and intensity, which is estimated based on layer thickness as a proxy, cannot be used in reconstruction of past extreme events because of their variability. There is a need to take into account changes in sediment supply in proglacial areas that could preclude satisfactory interpretation of floods in terms of past climate variability.
AGU Fall Meeting Abstracts, Dec 1, 2020
This study tests the application of combined detrital apatite fission track (AFT) and U-Pb dating... more This study tests the application of combined detrital apatite fission track (AFT) and U-Pb dating to infer both glacial erosion spatial patterns and long-term rock cooling histories in Alpine mountainous settings. We have dated 716 detrital apatite grains from glacial sediments collected in the Maurienne and Arve valleys (Western European Alps, France) from moraine deposits corresponding to different stages of glacial retreat since the Last Glacial Maximum (LGM, ca. 24-21 ka).The Maurienne valley crosses the internal and external Alps, which exhibit contrasting in-situ AFT and U-Pb ages. Here, we present the measured distribution of both detrital AFT and U-Pb ages at 6 locations along the valley, with catchment elevations ranging from 390 to 1740 m. We show that during glacial retreat, erosion is mainly concentrated in the downstream part of the glacier, near the sampled moraine deposits. This inference suggests that during glacial retreat, glacial erosion is more effective below the ELA (Equilibrium Line Altitude) and specifically close to the glacier front, in areas where ice flow velocity is high and subglacial water is abundant, as predicted by ice-dynamics reconstructions in the European Alps over the last 20 ka.In the Arve valley, previous studies showed that in situ AFT ages are systematically younger than 7 Ma for the Mont-Blanc massif. We compare the thermal history obtained from these literature bedrock-derived data to that derived from the new detrital AFT data collected in the Little Ice Age (LIA) moraine, just at the front of the Bossons glacier (~1300 m elevation). We also compare our results with 5 other samples down the valley at catchment elevations between 460 and 1050 m to evaluate potential changes in the detrital AFT signal as well as the consistency in the retrieved long-term cooling history.Based on these first results, we plan to extend our study to other areas (e.g., Patagonia) to investigate both (1) spatial patterns of glacial erosion for older glacial periods (pre-LGM), and (2) long-term rock cooling histories from moraine deposits where modern bedrock is inaccessible (e.g. under modern glaciers or ice fields).
Sedimentology, Dec 9, 2022
HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.
Quaternary Science Reviews, Dec 1, 2022
Science of The Total Environment, Nov 1, 2020
Sustainably maintaining the densely populated upland plains of Madagascar as operationally safe s... more Sustainably maintaining the densely populated upland plains of Madagascar as operationally safe spaces for the food security of the nation and the urban growth of its capital city, Antananarivo, hinges critically on avoiding crop and infrastructure destruction by their through-flowing rivers. The flood regime, however, is also a function of two 'slow' variables hitherto undocumented: tectonic subsidence regime, and floodplain sedimentation rate. From a radiocarbon-dated chronostratigraphy and environmental history of the sediment sequences in three of Madagascar's semi-enclosed upland basins (Antananarivo, Ambohibary, and Alaotra), we quantify and compare how the precarious equilibrium between the two variables entails differentials in accommodation space for sediment and floodwater. Results show that all these plains have been wetlands for at least 40,000 years, but that the Antananarivo Basin is the most vulnerable because the imbalance between sedimentation and subsidence is the largest. Although the tectonic regime and the endemic forms of gully erosion that occur in the catchments are beyond human control, we advocate that flood mitigation strategies should focus on the natural grassland savanna, which makes up most of the contributing areas to surface runoff in the watersheds. Pastoralists are persistently left out of rural development programmes, yet the rangelands could benefit from the introduction of multipurpose grasses and legumes known to withstand high stocking rates on poor soils while combining the benefits of nutritiousness, fire and drought resistance, with good runoff-arrest and topsoilretainment abilities. Future-proofing Madagascar's upland grainbaskets and population centres thus calls for joined-up action on the sediment cascade, focusing on soil and water sequestration through integrated watershed management rather than on hard-defence engineering against overflowing rivers on the plains, which has been the costly but ineffectual approach since the 17th century.
Earth Surface Processes and Landforms, Apr 1, 2020
Cosmogenic nuclide dating of glacial landforms may lead to ambiguous results for ice retreat hist... more Cosmogenic nuclide dating of glacial landforms may lead to ambiguous results for ice retreat histories. The persistence of significant cosmogenic concentrations inherited from previous exposure may increase the apparent exposure ages for polished bedrocks affected by limited erosion under ice and for erratic boulders transported by glaciers and previously exposed in highaltitude rock walls. In contrast, transient burying by moraines, sediments and snow decreases the apparent exposure age. We propose a new sampling strategy, applied to four sites distributed in the Arc and Arve valleys in the Western Alps, to better constrain the factors that can bias exposure ages associated with glacial processes. We used the terrestrial cosmogenic nuclide 10 Be (TCN) to estimate the exposure time from paired sampling of depth profiles in polished bedrock and on overlying erratic boulders. For a given sampling site, the exposure ages for both the polished bedrock and boulder are expected to be the same. However, in six cases out of seven, boulders had significantly higher 10 Be surface concentrations than those of the associated polished surfaces. In present and past glacial processes, the 10 Be distribution with depth for boulders and bedrocks implies the presence of an inheritance concentration of 10 Be. Our study suggests that 10 Be concentrations in erratic boulders and in polished bedrocks provide maximum and minimum exposure ages of the glacial retreat, respectively.
Journal of Soils and Sediments, Feb 12, 2019
Purpose Knowledge of suspended sediment provenance in mesoscale catchments is important for apply... more Purpose Knowledge of suspended sediment provenance in mesoscale catchments is important for applying erosion control measures and best management practices as well as for understanding the processes controlling sediment transport in the critical zone. As suspended sediment fluxes are highly variable in time, particularly given the variability of soil and rainfall properties in mesoscale catchments, knowledge of sediment provenance at high temporal resolution is crucial. Materials and methods Suspended sediment fluxes were analyzed at the outlet of a 42-km 2 Mediterranean catchment belonging to the French critical zone observatory network (OZCAR). Spatial origins of the suspended sediments were analyzed at high temporal resolution using low-cost analytical approaches (color tracers, X-ray fluorescence, and magnetic susceptibility). As the measurements of magnetic susceptibility provide only one variable, they were used for cross-validation of the results obtained with the two alternative tracing methods. The comparison of the tracer sets and three mixing models (non-negative least squares, Bayesian mixing model SIMMR, and partial least squares regression) allowed us to estimate different sources of errors inherent in sediment fingerprinting studies and to assess the challenges and opportunities of using these fingerprinting methods. Results and discussion All tracer sets and mixing models could identify marly badlands as the main source of suspended sediments. However, the percentage of source contributions varied between the 11 flood events in the catchment. The mean contribution of the badlands varied between 74 and 84%; the topsoils on sedimentary geology ranged from 12 to 29% and the basaltic topsoils from 1 to 8%. While for some events the contribution remained constant, others showed a high within-event variability of the sediment provenance. Considerable differences in the predicted contributions were observed when different tracer sets (mean RMSE 19.9%) or mixing models (mean RMSE 10.1%) were used. Our result shows that the choice of the tracer set was more important than the choice of the mixing model. Conclusions These results highlighted the importance of using multi-tracer multi-model approaches for sediment fingerprinting in order to obtain reliable estimates of source contributions. As a given fingerprinting approach might be more sensitive to one type of error, i.e., source variability, particle size selectivity, multi-tracer ensemble predictions allow to detect and quantify these potential biases. High sampling resolution realized with low-cost methods is important to reveal within-and between-event dynamics of sediment fluxes and to obtain reliable information of main contributing sources.
HAL (Le Centre pour la Communication Scientifique Directe), May 1, 2017
International audienc
HAL (Le Centre pour la Communication Scientifique Directe), Nov 1, 2021
-Le glissement d'Avignonet (Isère) est constitué de sédiments paraglaciaires quaternaires parmi l... more -Le glissement d'Avignonet (Isère) est constitué de sédiments paraglaciaires quaternaires parmi lesquels des couches de till, glacio-lacustres et fluviatiles imbriquées. De nombreux forages ont été réalisés au milieu des années 1980 et 2010 pour préciser le cadre géologique et géotechnique de la partie habitée, au sud, de ce glissement de terrain lent. Les paramètres mesurés sont très hétérogènes et rendent l'interprétation difficile. Dans ce travail, il a notamment été cherché à combiner ces différents paramètres pour produire un modèle géologique. Les résultats révèlent une grande complexité géologique avec l'intrication de diverses unités sédimentaires. Deux anciens glissements de terrain de plusieurs dizaines de mètres de large ont été identifiés. Ce travail montre l'intérêt d'une approche multi-proxy dans les études impliquant des unités sédimentaires du Quaternaire.
Glacial/interglacial transitions in mountainous areas are marked by significant glacier retreat f... more Glacial/interglacial transitions in mountainous areas are marked by significant glacier retreat from forelands to inner massifs, resulting in large-scale and ephemeral lake formation that are subsequently filled (or not) by sediment transfer during lateglacial to postglacial times. When valley paleo-infills are preserved, they form precious archives to investigate (1) Alpine erosion dynamics and paleo-environmental conditions during key transition periods from full glacial stages to interglacials, and (2) glacial erosion patterns during susbequent glaciation.In this contribution, we investigate such sedimentary deposits (locally called as "banquettes") in the French western Alps, and more precisely along the Isère valley and Val du Bourget. Previous research have attributed these deposits to the Riss – Würm transition due to their position under a basal compact till and to the MIS 6/5 transition up to early MIS 4 from palynological constraints, although no absolute ages has been available so far. Based on existing mapping of their spatial distribution and stratigraphic reconstructions, we sampled coarse-sand and sandy-gravel layers within these deposits for constraining both sediment deposition time (OSL dating) and provenance (glacial/postglacial origin, using terrestrial cosmogenic nuclide TCN 10Be in quartz). In addition, their spatial distribution provides estimates of maximum glacial erosion during the last glacial cycle, which can be subsequently used as spatial constraints for ice model predictions.Our results confirm deposition times of these sedimentary units at the MIS 6/5 transition, with dating constraints from the late MIS 6 (ca. 145 ka) to the early MIS 5 (Eemien, 115-130 ka) for sandy layers. Upper sandy-gravel layers have younger deposition ages of ca. 80 ka, illustrating sediment fluxes at the transition from late MIS 5 to early MIS 4. We compare this temporal sequence to more recent sediment infills of the Isère valley (14C and OSL dating) during the Lateglacial to Holocene (MIS 2/1) transition. TCN data from sand samples also illustrate the sharp transition from full glacial to interglacial conditions, with a significant increase in 10Be concentrations from Lateglacial to post-glacial sediments. We propose that the observed signal can reflect changes in erosion rates, but also in glacier expansion or in paleo-environmental conditions, with export of stored subglacial sediments as well as the re-establishment of sediment/soil production and transfer along the catchment routing system following glacier retreat.
EGU General Assembly Conference Abstracts, Apr 1, 2019
HAL (Le Centre pour la Communication Scientifique Directe), 2015
PosterInternational audienc
Uploads
Papers by Christian Crouzet