The Pacific-North America plate boundary in central and southern California has a complex tectonic history, and constraints are poor for inception of an extensional fault system linked to the southern San Andreas fault, a major tectonic element of this plate boundary. Furthermore, decades of research has shown relationships between climate, tectonics, and surface processes in most orogens across the globe (e.g. Alps, Himalaya, Andes, Alaska Ranges), however the role climate plays in modulating erosion and mass fluxes from extensional mountains blocks to sedimentary basins over 104-5 yr timescales is debated. In the eastern California-Walker Lane shear zone, exposures of sedimentary basin fill allow inversion of erosion- and sediment-flux rates from a linked catchment-fan system within an extensional block. In this dissertation, I present two field and geo-thermochronology based studies that explore research topics related by common tectonic setting and geography within the Pacific-North America plate boundary. First I present new low-temperature thermochronology (apatite U-Th-Sm/He) and thermal history modeling to document the kinematic evolution of the Santa Rosa mountains, where the cooling history constrains initiation timing of the west Salton Detachment fault, and the southern San Andreas fault system. I document an age of ca. 8 Ma for exhumation initiation of the Santa Rosa block, from paleodepths of ~4.5–3 km, at vertical rates of ~0.15–0.36 mm/yr, accelerating to ~1.3 km/Ma since ca. 1.2 Ma during initiation of the San Jacinto fault zone. Second, I present a new data set of cosmogenic radionuclide-derived burial ages and paleodenudation rates (26Al/10Be) from the Pleasant Canyon complex in the Panamint Range, and show that denudation rate and sediment flux have varied by a factor of ~2x since the middle Pleistocene. I conclude high frequency variability is driven by climate change, and not tectonic perturbations, as supported by published constraints for exhumation timing. The middle Pleistocene transition from 40–100 ka periodicity may drive the observed changes, a tentative conclusion that makes testable predictions for stratigraphic records of past climate in other locations. Empirical evidence for climate-modulated erosion and sediment flux provides valuable constraints for numerical models of landscape evolution and sedimentary basin architecture. / Ph. D.

The Daya Bay reactor neutrino experiment is a high sensitivity experiment designed to determine the last unknown neutrino mixing angle $theta_{13}$ by measuring disappearance of reactor antineutrinos emitted from six 2.9 $GW_{th}$ reactors at the Daya Bay Nuclear Power Station. There are eight identical Gd-loaded liquid scintillator detectors deployed in two near (flux-weighted baseline 512 $m$ and 561 $m$) and one far (1579 $m$) underground experimental halls to detect the inverse beta decay interaction. This dissertation describes the Daya Bay Experiment and individual contributions to this experiment. Chapter 1 reviews the history of the neutrino and the neutrino oscillation phenomena. The reactor based neutrino experiments in different times are described in this chapter in detail. It presents the motivation of the Daya Bay Experiment. In Chapter 2, the neutrino detection method and the $theta_{13}$ relative measurement method are introduced. This chapter focuses on the design of the Daya Bay Experiment, including antineutrino detector, calibration system, muon veto system and muon tagging system. Chapter 3 shows the design, development, construction, and assembly of Muon Pool PMT calibration system, and presents an algorithm of calculating the muon pool PMT timing offset values. Chapter 4 focuses on the manufacture, installation and commissioning of RPC HV system. Chapter 5 presents the analyses of the radioactive isotopes induced by comic muons. The Daya Bay detector energy response model is also described in detail. The relative rate analysis results exclude a zero value from $sin^22theta_{13}$ with a significance of 7.7 standard deviation using 139 days of data, 28909 (205308) antineutrino candidates which were recorded at the far hall (near halls) and shows $sin^22theta_{13} = 0.089pm0.011$ in a three-neutrino framework. A combined analysis of the $overline nu_e$ rates and energy spectra based on the detector energy response model improved measurement of the mixing angle $sin^22theta_{13} = 0.090^{+0.008}_{-0.009}$ by using 217 days of data, 41589 (203809 and 92912) antineutrino candidates were detected in the far hall (near halls). Also the first direct measurement of the $overline nu_e$ mass-squared difference $|Delta m^2_{ee}|= (2.59^{+0.19}_{-0.20})times10^{-3}$ $eV^2$. It is consistent with $|Delta m^2_{mumu}|$ measured by muon neutrino disappearance, supporting the three-flavor oscillation model. / Ph. D.

Reconstruction of former Central Asian glaciers extents can provide valuable information about past atmospheric circulation variations. These extents, often marked by terminal moraines, need to be chronologically constrained. Cosmogenic nuclide exposure (CNE) dating is widely used to directly date moraines. In addition, there is increasing interest on using optically stimulated luminescence (OSL) techniques for dating glacial landforms. This thesis focuses on the methodological aspects of directly dating glacial landforms to perform paleoglacial reconstructions in Central Asia, with an emphasis on OSL dating. For OSL dating of sediments from glacial settings, it is important to measure the luminescence signal at the single grain scale, because the sediments are likely affected by partial bleaching due to short light exposure during glacial or glaciofluvial transport. The use of an Electron Multiplying Charges Coupled Device (EMCCD)-based imaging system for single grain OSL measurements would offer larger flexibility in light stimulation and sediment type, compared to the current Single Grain Risø reader. An automated image processing procedure has been developed to compensate for sample carrier displacement over repeated measurements and for attributing pixels to each grain for signal integration when using this imaging system. However, significant cross talk contamination, demonstrated by laboratory and simulation experiments, prohibits accurate single grain luminescence measurements. Preliminary experiments using a basic image processing algorithm show good potential for software correction solutions. Paleoglacial reconstructions conducted in the Altai Mountains, Central Asia, using both CNE and OSL dating demonstrate that luminescence measurements of glaciofluvial sediments performed at the multi-grain scale result in large age overestimates, and that single grain measurements allow for more accurate dating of glacial landforms. However, uncertainties remain that are related to the model used for extracting equivalent doses for well-bleached grains and to fading corrections when using feldspar minerals. The timing of glaciation can be inferred from scattered CNE moraine boulder ages if most of the ages are concentrated within a few thousand years, with only few ages clearly older or younger. Overall, combining CNE and OSL techniques for dating a glacial landform is a powerful approach for producing robust glacial chronologies, despite uncertainties inherent to each technique. Paleoglacial reconstructions from the Altai Mountains indicate Marine Isotope Stage (MIS) 2 and MIS 4/late MIS 5 local Last Glacial Maximums. In Central Asia, in addition to a regional MIS 2 glaciation, previous studies indicate a period of major glacial advances during MIS 3 that is out of phase with global ice volume records. However, most MIS 3 glacial chronologies from Central Asia are based on too few or too heavily scattered CNE data sets, or on OSL or Electron Spin Resonance (ESR) ages for which partial bleaching has not been properly investigated. Hence, at this stage, chronological evidence is insufficient to demonstrate a regional MIS 3 glaciation in Central Asia. Surge-related glacial features identified in the Russian Altai also highlight the importance of conducting detailed geomorphology and sedimentology studies to understand former ice dynamics, which is essential for inferring appropriate paleoclimate information from paleoglacial reconstructions. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 4: Manuscript.</p>

Constraining past episodes of climate change and glacial response is critical for understanding future impacts of climate change, especially in the high latitudes where warming is expected to be rapid and most of Earth's glaciers exist. Many studies of past glacier size utilize rare isotopes called cosmogenic nuclides to perform surface exposure dating. Since most areas of Earth's surface that were previously glaciated were covered by erosive ice, which stripped away pre-existing cosmogenic nuclides, surface exposure dating yields the timing of the most recent deglaciation. However, in some high latitude areas where glacial ice is cold-based and non-erosive (so-called 'ghost glaciers'), the assumptions of surface exposure dating are violated. Alternate approaches are required to constrain the complex histories of such landscapes. My doctoral dissertation focuses on both developing and employing alternative approaches to studying glacial history in the high latitudes, where glacial ice is non-erosive and dating rock surfaces with a single cosmogenic nuclide does not yield exposure ages. Here, I utilize optimized laboratory methods, paired analyses of two cosmogenic isotopes (10Be and 26Al), numerical models to assess possible exposure/burial histories, and Monte Carlo simulations to constrain uncertainties. To study the exposure and burial history of long-preserved landscapes in the Arctic, I investigate landscapes in two high-latitude locations: Thule, northwestern Greenland; and Cumberland Sound, southern Baffin Island, Canada. Bedrock surfaces, sampled on Baffin Island, exhibit evidence of long-lived subaerial weathering and have simple 10Be exposure ages up to 160,000 yr, despite being glaciated until ~10,000 yr. Simple exposure ages tend to increase with elevation, suggesting more effective erosion in the fjords and longer-term preservation of the uplands. Minimum limiting total histories calculated with 26Al/10Be range up to several million years, with periods of exposure representing ~20% of the total history, describing surfaces that have been alternately preserved beneath non-erosive glacial ice and weathered subaerially over many glacial/interglacial cycles. Boulders, sampled at both sites, have simple 10Be exposure ages up to 78,000 yr in Thule and 79,000 yr on Baffin Island, and yield multi-modal age distributions. Simple exposure ages of boulders tend to under-estimate bedrock ages in the cases of paired bedrock/boulder samples. Minimum limiting total histories calculated with 26Al/10Be range up to 700,000 yr in Thule and several million years on Baffin Island, with periods of exposure representing only a small portion of the total history. Forward numerical models suggest that boulders have been repeatedly reworked, likely experiencing partial or complete shielding during interglacial periods because of rotation and/or burial by till. The landscapes I assess here preserve histories of hundreds of thousands to millions of years, and represent a complex interplay of interglacial exposure, subglacial preservation beneath cold-based ice, periglacial processes, and subaerial weathering. Although such landscapes represent methodological challenges, they contain valuable information about long-term variations in glacial extent and climate.

The mountain-systems of Central Asia, act as barriers to atmospheric circulation patterns, which in turn impose striking climate gradients across the region. Glaciers are sensitive indicators of climate change and respond to changes in climate gradients over time by advancing during cold and wet periods and receding during warm and dry periods. The aim of this thesis is to investigate whether there are large-scale patterns in how past glaciers in the Tian Shan and the Altai Mountains of Central Asia responded to climate change. Multiple methods have been used, including: remote sensing, terrain analysis, field investigations, and cosmogenic nuclide (CN) dating. The glacial landform records indicate that the region experienced mainly alpine-style glaciations in the past. Large complexes of ice-marginal moraines in high elevation basins are evidence of outlet glaciers sourced from large valley glaciers, ice caps and ice-fields, and these moraine sequences, record the maximum extent of paleoglaciation. In the Ikh-Turgen Mountains, located in the continental, eastern Altai Mountains, deglaciation of these moraines occurred during marine oxygen isotope stage (MIS) 3 at ~45 ka. This is consistent with a colder and wetter climate during this time, inferred from ice core and lake level proxies. Another deglacial phase occurred during MIS 2 at ~23 ka, synchronous with the global Last Glacial Maximum. In the Russian Altai Mountains, lobate moraines in the Chuya Basin indicate deglaciation at ~19 ka, by a highly dynamic paleoglacier in the Chagan-Uzun catchment, which experienced surge-like behaviour. Furthermore, across the Tian Shan, an evaluation of new and existing CN glacial chronologies (25 dated moraines) indicates that only one regional glacial stage, between 15 and 28 ka (MIS 2), can be defined and spatially correlated across the region. These paleoglaciers were mainly restricted to valleys as a result of arid conditions during this time and variation in their extents is interpreted to reflect topographic modulation on regional climate. The ages of the oldest evidence for robust local glacial stages in the Tian Shan are not yet well constrained, however, moraines in the central Kyrgyz Tian Shan and the eastern Chinese Tian Shan have apparent minimum ages overlapping with MIS 5 and MIS 3 (with missing MIS 4 and 6 stages). However, different geological processes, such as inheritance and post-depositional shielding (e.g. deposition by surging glaciers or hummocky terrain deposition), have influenced the dating resolution, making several moraine ages inappropriate for regional comparison. Finally, to quantify regional patterns of paleoglaciation, the hypsometry (area-elevation distribution) of glacial landforms is used to estimate average paleo equilibrium line altitudes for the region. This analysis shows that while present-day ELAs mirror strong climate gradients, paleoglaciation patterns were characterised by more gentle ELA gradients. The paleo-ELA depressions across Central Asia were most prominent in the continental southern and eastern regions (500–700 m). Finally, the results from this thesis, show that Central Asia was repeatedly glaciated in the past, but underscore the importance of considering 1) catchment characteristics and styles of glaciation and 2) other non-climatic factors controlling glacier dynamics when interpreting CN chronologies to make paleoclimate inference. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 4: Accepted. Paper 5: Manuscript.</p> / Central Asia Paleoglaciology Project (CAPP)

Abstract The thesis is focused on the reconstruction of long-term cosmic ray variability using proxy data. The 11-year solar cycle in production/deposition rates of cosmogenic nuclides ¹⁰Be and ¹⁴C has been modelled for the conditions of grand minima and maxima of solar activity (namely, Maunder Minimum and Grand Modern Maximum). The result shows that contrary to the observed strongly suppressed amplitude of the solar cycle in sunspots during Maunder Minimum relatively to Grand Modern Maximum, the cosmic ray proxies have the comparable amplitudes during the two periods. This phenomenon is caused by the nonlinear relation between solar activity and production of cosmogenic nuclides. In addition to well-established proxies of cosmic rays, nitrate in polar ice has been recently proposed as a new proxy for the long-term variability of galactic cosmic rays. The thesis contains two tests of its applicability for this purpose with TALDICE and EPICA-Dome C ice core data from Central Antarctica. The results support the proposal for the multimillennial time scales. Lunar samples acquired during the Apollo missions are important data for estimating the averaged energy spectra of galactic cosmic rays and solar energetic particles at the Earth’s orbit. The development in modelling of the interaction between energetic particles and matter makes it necessary to revise the earlier results. Because of that, new production rates of ¹⁰Be and ¹⁴C in lunar samples by galactic cosmic rays and solar energetic particles have been computed. New accurate cosmic ray reconstructions from natural archives containing cosmogenic nuclides use sophisticated climatic models requiring yield functions of the nuclides with high altitude resolution. These functions have been computed for ⁷Be, ¹⁰Be, ¹⁴C, ²²Na, and ³⁶Cl in the Earth’s atmosphere. Overall, the major purpose of the studies presented in the thesis is to increase the quality of reconstructions of the long-term cosmic ray variability for better understanding of the solar and heliospheric physics. / Original papers The original publications are not included in the electronic version of the dissertation. Poluianov, S. V., Usoskin, I. G., &amp; Kovaltsov, G. A. (2014). Cosmogenic Isotope Variability During the Maunder Minimum: Normal 11-year Cycles Are Expected. Solar Physics, 289(12), 4701–4709. https://doi.org/10.1007/s11207-014-0587-6 Poluianov, S., Traversi, R., &amp; Usoskin, I. (2014). Cosmogenic production and climate contributions to nitrate record in the TALDICE Antarctic ice core. Journal of Atmospheric and Solar-Terrestrial Physics, 121, 50–58. https://doi.org/10.1016/j.jastp.2014.09.011 Poluianov, S., Artamonov, A., Kovaltsov, G., &amp; Usoskin, I. (2015). Energetic particles in lunar rocks: Production of cosmogenic isotopes. Proceedings of Science, 30-July-2015, art. no. 051 . Traversi, R., Becagli, S., Poluianov, S., Severi, M., Solanki, S. K., Usoskin, I. G., &amp; Udisti, R. (2016). The Laschamp geomagnetic excursion featured in nitrate record from EPICA-Dome C ice core. Scientific Reports, 6(1). https://doi.org/10.1038/srep20235 Poluianov, S. V., Kovaltsov, G. A., Mishev, A. L., &amp; Usoskin, I. G. (2016). Production of cosmogenic isotopes 7Be, 10Be, 14C, 22Na, and 36Cl in the atmosphere: Altitudinal profiles of yield functions. Journal of Geophysical Research: Atmospheres, 121(13), 8125–8136. https://doi.org/10.1002/2016jd025034

La haute montagne est un terrain particulièrement sensible aux variations climatiques. La hausse de température depuis plusieurs décennies a un fort impact sur les parois du massif du Mont Blanc : la dégradation du permafrost s’y traduit par une activité gravitaire majeure. Une augmentation du nombre d'écroulements (>100 m3) liés à des périodes chaudes a en effet été mis en évidence à plusieurs échelles de temps, lors des étés particulièrement chauds de 2003 et 2015 comme au cours des trois dernières décennies. La fréquence des écroulements dans le massif devrait continuer à s’accroitre avec l’augmentation de la température au 21e siècle.En revanche, la fréquence des écroulements dans le massif antérieurement à la fin du Petit Âge Glaciaire (PAG) est très largement inconnue. Pendant l'Holocène voire le Tardiglaciaire, les écroulements dans le massif du Mont Blanc ont-ils également été favorisés par les hausses de température ? Pour répondre à cette question, cette thèse poursuit quatre objectifs :i. Dater un grand nombre d'écroulements dans la partie centrale du massif pour comprendre leur distribution pendant l'Holocène et le Tardiglaciaire. L'âge des niches d’arrachement est obtenu par datation cosmogénique.ii. Vérifier les possibles corrélations entre périodes à forte occurrence d’écroulements et périodes climatiques post-glaciaires.iii. Quantifier le volume des écroulements par reconstruction 3D de la forme des blocs écroulés, et étudier la relation entre volumes écroulés et périodes climatiques.iv. Etudier la relation entre âge d'exposition et couleur des niches d’arrachement quantifiée avec la spectroscopie de réflectance.Un total de 70 surfaces a été échantillonné dans les parois du massif au cours de trois campagnes de terrain en 2006, 2011, et 2015-2016. Les âges d'exposition de 63 surfaces ont été obtenus, compris entre 30 ± 20 ans et 100.50 ± 8.50 ka. Trois groupes d’âges peuvent être corrélés aux périodes climatiques chaudes que sont : les Périodes Chaudes de l'Holocène moyen (7.50 – 5.70 ka), l'Optimum de l'âge de Bronze (3.35 – 2.80 ka) et le Période Chaude Romaine (2.35 – 1.75 ka) ; un quatrième groupe d'âges est daté entre 4.91 et 4.32 ka. Le groupe d'âges le plus nombreux, entre 1.09 ka et l'Actuel, aux volumes généralement réduits, est interprété comme représentatif de l'activité gravitaire annuelle du massif avec le climat actuel.Les données spectrales des échantillons datés ont permis de développer un index de la couleur du granite (GRIGRI) par combinaison des valeurs de réflectivité de deux longueurs d'onde différentes. Cet index est corrélé avec l'âge d'exposition (R=0.861) ; il a permis de proposer la datation de 10 échantillons d'âge inconnu à partir de leurs caractéristiques spectrales. / High mountain is particularly sensitive to climate variations. The raising temperature that is currently taking place due to climate change has a strong impact on the Mont Blanc massif rock walls: a higher rockfall (>100 m3) occurrence has been noticed, caused by permafrost thawing. The raising in number of rockfalls has been successfully correlated to warm periods at different timescales, e.g., during extreme warm episodes like the 2003 and 2015 heat waves, and during the last 30 years. According to the expected raising temperatures, during the 21st century rockfall occurrence should continue to rise.Rockfall frequency in the Mont Blanc massif before the Little Ice Age is still largely unknown. During Lateglacial and Holocene, high occurrence has been related to warm periods as well? In order to answer this question, this PhD thesis has four aims:i. To date several rockfalls having taken place in the central part of the Mont Blanc massif, in order to understand their frequency during Lateglacial and Holocene. Exposure age of rockfall scars is obtained using Terrestrial Cosmogenic Nuclide dating.ii. To verify possible relationships between high rockfall occurrence periods and post-glacial climate periods.iii. To quantify rockfall volumes by means of 3D reconstruction of the rockfall shapes, to explore the possible relationship between cumulate volumes and climate periods.iv. To study the relationship between exposure ages and colours of rock surfaces. Colours are quantified by reflectance spectroscopy.A total of 70 rock surfaces have been sampled during three field campaigns that took place in 2006, 2011 and 2015-2016. 63 exposure ages were obtained, ranging 30 ± 20 a to 100.50 ± 8.50 ka. Three age clusters can be correlated to warm periods, corresponding to: two Holocene Warm Periods (7.50 – 5.70 ka), the Bronze Age Optimum (3.35 – 2.80 ka) and the Roman Warm Period (2.35 – 1.75 ka). A fourth age cluster has been detected with ages ranging 4.91 – 4.32 ka. The biggest cluster, ranging 1.09 ka – recent, shows rather small volumes. This is interpreted as the normal erosion activity corresponding to the current climate.The samples reflectance spectra allowed to develop a granite colour index (GRIGRI) by combining the values of two different wavelengths. This index is correlated to the samples exposure age (R = 0.861), and has been used to date the exposure age of 10 samples where Terrestrial Cosmogenic Nuclide dating failed

Lorsque l’extension de la croûte sous les parties hautes des chaînes de montagnes est colinéaire à la direction de convergence, il est traditionnellement admis que le moteur est l’effondrement gravitaire. Pourtant, des études récentes remettent en cause ce paradigme en montrant que l’érosion induit un soulèvement et de l’extension dans la partie centrale des chaînes de montagne à faible taux de convergence. L’objectif de notre étude est d’étudier l’impact de la dénudation de la topographie sur le régime sismo-tectonique des chaînes de montagnes.La première partie de ce travail présente une compilation de données dans les chaînes de montagnes afin de dégager des relations entre régime sismo-tectonique et érosion. Sur la base de ces observations, un modèle cinématique simple permettant de prévoir le régime de la chaîne est proposé. Ainsi, pour les chaînes à faible taux de convergence et d’élévation moyenne, ce modèle prédit de l’extension lorsque le taux de dénudation est 15% plus élevé que le taux de convergence.La deuxième partie est consacrée au développement d’un modèle thermo-mécanique 2D en éléments finis pour étudier l’impact des processus de surface sur la déformation des Pyrénées. Les résultats montrent que la réponse isostatique à l’érosion permet de réactiver des structures pré-existantes. La cinématique d’un plan de faille hérité peut être prédite grâce au gradient du profil des vitesses de surface horizontales. Ainsi, un plan situé dans la zone d’érosion est réactivé en faille normale alors qu’en bordure de cette zone une faille est réactivée en régime inverse. Ces résultats suggèrent que la déformation actuelle des Pyrénées pourrait être la conséquence d’un processus d’érosion.Compte tenu du faible nombre d’études quantifiant les taux d’érosion dans les Pyrénées, les modèles développés dans la deuxième partie souffrent d’une forte incertitude. Pour y remédier, nous avons cherché à les quantifier dans les Pyrénées Centrales grâce à une étude qui combine deux types de données : taux de dénudation des bassins versants à partir des isotopes cosmogéniques, et vitesses d’incision à partir des sédiments piégés dans les karsts). Ces résultats sont présentés dans la troisième partie. Les profils de dénudation obtenus sont compatibles avec un rejeu en faille normale d’un plan situé dans la Zone Nord Pyrénéenne des Pyrénées Centrales. Dans les Alpes, une bonne corrélation apparaît entre la valeur du taux d’érosion et la vitesse verticale géodésique, ce qui pose la question de l’impact de la déglaciation tardi-Wurmienne dans les Alpes sur la déformation actuelle. Un modèle numérique détaillant cette relation est présenté dans le quatrième chapitre. Les résultats montrent que la déglaciation des Alpes occidentales est contrôlée par l’hétérogénéité rhéologique de la croute. Certains de nos modèles prédisent des vitesses de surrection compatibles avec celles mises en évidence par la géodésie. / When mountain ranges upper parts express crustal extension direction collinear to the convergence direction, it is traditionally accepted that the extensive motor is gravitational collapse. However, recent studies challenge this paradigm by showing that erosion induces uplift and extension in the central part of the low convergent mountain ranges. Our goal is to investigate the impact of the denudation on the seismotectonic regime of mountain ranges.In order to identify a relationship between seismotectonic regime and erosion, the first part of this work presents a compilation of data in the mountain ranges. Based on these observations, a simple kinematic model is proposed to predict the seismotectonic regime of the chain. Thus, for low convergence rate chains with a moderate mean elevation, this model predicts an extension regime when the denudation rate is 15% higher than the convergence rate.The second part is devoted to the development of thermomechanical 2D finite element model to study the impact of surface processes on the deformation of the Pyrenees. The results show that the isostatic response to erosion reactivates pre-existing structures. The kinematics of an inherited fault plane can be predicted due to the gradient of the horizontal surface velocities profile. Thus, a plane located in the eroded zone is reactivated in normal fault when in a border area of this same plane is reactivated in reverse fault. These results suggest that the current deformation in the North Pyrenean Zone could be the result of surface processes.Given the small number of studies quantifying erosion rates in the Pyrenees, the models developed in the second part suffer from high uncertainty. To remedy this, we sought to quantify it in the central Pyrenees through a study that combines two types of data: watershed denudation rates from cosmogenic isotopes concentration, and incision rates from sediments buried in the karst. These results are presented in chapter 3. Denudation profiles obtained are consistent with a replay of a normal fault plane located in the North Zone of the Central Pyrenees.In the Alps, a good correlation appears between the value of the rate of erosion and geodetic vertical velocities, which raises the question of the impact of the late-würmian deglaciation in the Alps on the present deformation. A numerical model detailing this relationship is presented in the fourth chapter. The results show that deglaciation of the western Alps is controlled by the rheological heterogeneity of the crust. Some of our models predict uplift rates consistent with those highlighted by geodesy.

Idades de soterramento de grãos de quartzo pelos isótopos cosmogênicos \'ANTPOT.26 Al\' e \'ANTPOT.10 Be\' foram obtidas em depósitos sedimentares que assorearam os sistemas de cavernas associados aos vales cegos dos riachos das Almas e Água de Rega, região de Iraquara (BA). Os resultados também incluem a caracterização faciológica e uma abordagem preliminar sobre a arquitetura dos depósitos, além do mapeamento em campo do contexto geomórfico dos sistemas de condutos e seu preenchimento sedimentar. Coberturas terciárias assentadas sobre todas as unidades pré-cambrianas testemunham que a superfície cárstica e os sistemas de condutosfazem parte de uma longa história de evolução, envolvendo episódios de exposição, soterramento e exumação. Durante os dois últimos milhões de anos, a drenagem superficial e os sistemas de cavernas estavam plenamente articulados na condução de água e sedimentos, com rotas de fluxo subterrâneas que incluíam ainda trechos labirínticos pré-existentes, que serviam de repositório de sedimentos durante os eventos de inundação, proporcionando também, rotas alternativas ao canal,na medida em que o sistema agradava. A sucessiva migração do canal por estas redes labirínticas originou o padrão distributário observado na Lapa Doce e na Gruta da Torrinha. Os depósitos sedimentares estudados nas cavernas dividem-se em dois grupos: fluviais e de água estagnada. Osdepósitos fluviais ocorrem na base e são constituídos por fácies de canal e fácies de inundação. As idades de soterramento de grãos de quartzo destes sedimentos apontam para um período de assoreamento fluvial compreendido entre 1,91±0,12 e 0,36±0,08 milhões de anos para o sistema Lapa Doce-Torrinha (riacho Água de Rega) e 1,37±0,15 e 0,87±0,17 milhões de anos para o sistema Cão-Talhão (riacho das Almas). No sistema Lapa Doce-Torrinha as idades de soterramento concentram-se no intervalo compreendido por dois períodos úmidos (350-450 Ka e 900-1000 Ka), registrados em estudos anteriores através do crescimento de tufas calcárias no semiárido baiano.Tal fato sugere que a agradação fluvial verificada, tanto nos rios quanto nas cavernas, esteja associada a fatores climáticos, particularmente o aumento da carga dos rios derivado da diminuição na estabilidade dos grãos nas vertentes exercida por uma vegetação arbustiva esparsa ou ausente. No topo, os depósitos de água estagnada, preferencialmente compostos por lamas, não possuem estruturas trativas ou de corrente e são associados a uma sedimentação em ambiente freático,para o qual é necessário considerar a subida do nível de base. Gretas de contração, além de relações estratigráficas e erosivas destes depósitos com crostas calcíticas evidenciam que eles não foram depositados em um evento único. Idades U/Th obtidas nas crostas calcíticas apontam para uma deposição durante o Pleistoceno Tardio. Interpreta-se que as lamas foram depositadas durante períodos de elevação do nível de base devido aos eventos úmidos abruptos de escala milenar que ocorreram no nordeste brasileiro ao longo dos últimos 210 ka. / \'ANTPOT.26 Al\' and \'ANTPOT.10 Be\' burial ages have been obtained from quartz grains sampled in extensive sedimentary deposits that fill cave systems associated with Das Almas and Agua de Rega creeks blind valleys, Iraquara region, Bahia (Brazil). The geomorphic context of the caves and their sedimentary record is presented, as well a facies analyses and a preliminary architecture approach for subterranean deposits. Tertiary covers deposited over all Precambrian geological units give evidence that karstic surface and conduit systems are features of a long term evolving landscape, sculpted during episodes of exposure, burial and exhumation. In the last two million years, surface drainage and cave systems were full connected in terms of water and sediment transport.Conduit systems still connected with preexisting passage networks, working as sediment repositories during floods and offering alternative routes to the channels as the systems aggraded. Sucessive channel migration led to the distributary pattern observed in the caves Lapa Doce and Gruta da Torrinha. The cave sedimentary record can be divided into two major categories: alluvial and slackwater deposits. At the bottom of the sediments, channel and flood facies were recognized in alluvial deposits. Quartz simple burial ages point to fluvial aggradation between 1,91±0,12 and 0,36±0,08 My in Lapa Doce-Torrinha cave system (Água de Rega creek) and between 1,37±0,15 and 0,87±0,17 million years in Cão-Talhão cave system (Das Almas creek). Burial ages from Lapa Doce-Torrinha samples group in between two past humid periods (350-450 Ky and 900-1000 Ky) recorded in previous studies from travertines growth in arid regions of Bahia State. This fact suggests that valley and cave aggradation is associated with climate factors, particularly an increase in river load derived from decreased stabilization of hillslopes due to a sparse or absent forest vegetation. At the top of sedimentary pile slackwater deposits are ordinarily muddy without tractive or current sedimentary structures. They are assigned to be deposited in a phreatic environment which, in turn, necessarily requires the base level to rise longer than seasonal floods. Mud cracks, erosive surfaces and stratigraphic relations to calcite crusts and flowstones prove that they were not deposited in a single event. U/Th ages from interstratal calcite crusts point to mud deposition during the Late Pleistocene. Slackwater deposits are interpreted to be a result of sedimentation during successive abrupt wet events defined on millennial time scale for the Brazilian northeast during the last 210ky.

The rapid rate of global warming currently underway highlights the need for a deeper understanding of abrupt climate change. The Younger Dryas is a Late-Glacial climate event of widespread and unusually rapid change whose study can help us address this need for increased understanding. Reconstructions from the glacial record offer important contributions to our understanding of the Younger Dryas due to (among other things) the direct physical response of glaciers to even minor perturbations in climate. Because the glacier equilibrium line altitude (ELA) provides a more explicit comparison of climate than properties such as glacier length or area, ELA methods lend themselves well to paleoclimate applications and allow for more direct comparisons in space and time. Here we present a physically based ELA model for alpine paleoglacier climate reconstructions that accounts for differences in glacier width, glacier shape, bed topography and ice thickness, and includes error estimates using Monte Carlo simulations. We validate the ELA model with published mass balance measurements from 4 modern glaciers in the Swiss Alps. We then use the ELA model, combined with a temperature index model, to estimate the changes in temperature and precipitation between the Younger Dryas (constrained by 10Be surface exposure ages) and the present day for three glacier systems in the Graubünden Alps. Our results indicate an ELA depression in this area of 320 m ±51 m during the Younger Dryas relative to today. This ELA depression represents annual mean temperatures 2.29 °C ±1.32 °C cooler relative to today in the region, which corresponds to a decrease in mean summer temperatures of 1.47 °C ±0.73 °C. Our results indicate relatively small changes in summer temperature dominate over other climate changes for the Younger Dryas paleoglaciers in the Alps. This ELA-based paleoclimate reconstruction offers a simple, fast, and cost-effective alternative to many other paleoclimate reconstruction methods. Continued application of the ELA model to more regions will lead to an improved understanding of the Younger Dryas in the Alps, and by extension, of rapid climate events generally.