La contribution, dans le cycle supergène, du carbone organique fossile (COF), issu de l’érosion des roches sédimentaires, est aujourd’hui une inconnue majeure du cycle du carbone. Le présent travail, initié dans le cadre du GIS Draix "étude de l'érosion en montagne », s'est intéressé au devenir de la matière organique contenue dans les "terres noires" (marnes jurassiques) des bassins versants de Draix (Alpes de haute Provence, France). Ceci a nécessité : - la mise en évidence de la contribution de COF au sein des compartiments supergènes (sols, particules fluviatiles, altérites) à travers une approche pluri-analytique (investigations géochimiques, optiques, isotopiques). - l’estimation de la part de COF disparue lors de son transfert d’un compartiment à un autre obtenue grâce au développement d’une nouvelle méthode analytique (palynofacies quantitatif) et en couplant approches terrain et expérimentale. - l’estimation et la modélisation des flux de COF libérés par les altérations mécaniques et chimiques des terres noires à l’échelle des bassins étudiés. Les résultats obtenus permettent : - 1) de confirmer la résistance du COF, dont les pertes n’excèdent pas 30 % et ne concernent que la part libérée par l’altération chimique; - 2) de rappeler la pluralité du COF, dont les familles réagissent différemment face aux différents types d’altérations ; - 3) de hiérarchiser les facteurs contrôlant les flux de COF (couvert végétal, pentes, précipitations) ; - 4) de mettre en évidence l’importance du COF libéré, exprimé en t/ha/an, par les « terres noires » aux échelles locales et régionales. / Initiated within the framework of GIS Draix « mountains erosion study), this work relates to the debate on the fossil organic carbon (FOC) input in modern environments and its possible implications for the carbon cycle. It focuses on the fate of FOC released by of jurassic marls weathering occuring in Draix watersheds (Alpes de haute Provence, France). Such work needed to : - confirm FOC occurrence both in weathered rocks, soils and riverine particles (multi-analytical approach); - quantify FOC losses during pools transitions by using a new analytical method (quantitative palynofacies) and combining field and experimental investigations; - estimate and model FOC fluxes released both by chemical and mechanical weathering in the studied watersheds. Obtained results permit us to : - point out FOC resistance to weathering processes. FOC losses only occur during chemical one and do not exceed 30 %. - highlight fossil organic matter plurality composed with labile and refractory components ; - hierarchize fluxes controlling factors such as vegetal cover, slope,and precipitations ; - emphasize FOC fluxes importance, expressed in t/ha/y, released by jurassic marls weathering at local and regional scales.

<p>Relict non-glacial surfaces occur in many formerly glaciated landscapes, where they represent areas that have escaped significant glacial modification. Frequently distinguished by blockfield mantles, relict non-glacial surfaces are important archives of long-term weathering and landscape evolution processes. The aim of this thesis is to examine the distribution, weathering, ages, and formation of relict non-glacial surfaces in the northern Swedish mountains.</p><p>Mapping of surfaces from aerial photographs and analysis in a GIS revealed five types of relict non-glacial surfaces that reflect differences in surface process types or rates according to elevation, gradient, and bedrock lithology. Clast characteristics and fine matrix granulometry, chemistry, and mineralogy reveal minimal chemical weathering of the blockfields.</p><p>Terrestrial cosmogenic nuclides were measured in quartz samples from two blockfield-mantled summits and a numerical ice sheet model was applied to account for periods of surface burial beneath ice sheets and nuclide production rate changes attributable to glacial isostasy. Total surface histories for each summit are almost certainly, but not unequivocally, confined to the Quaternary. Maximum modelled erosion rates are as low as 4.0 mm/kyr, which is likely to be near the low extreme for relict non-glacial surfaces in this landscape.</p><p>The blockfields of the northern Swedish mountains are Quaternary features formed through subsurface physical weathering processes. While there is no need to appeal to Neogene chemical weathering to explain blockfield origins, these surfaces have remained continuously regolith-mantled and non-glacial since their inception. Polygenetic surface histories are therefore indicated, where the large-scale surface morphologies are potentially older than their regolith mantles.</p>

Relict non-glacial surfaces occur in many formerly glaciated landscapes, where they represent areas that have escaped significant glacial modification. Frequently distinguished by blockfield mantles, relict non-glacial surfaces are important archives of long-term weathering and landscape evolution processes. The aim of this thesis is to examine the distribution, weathering, ages, and formation of relict non-glacial surfaces in the northern Swedish mountains. Mapping of surfaces from aerial photographs and analysis in a GIS revealed five types of relict non-glacial surfaces that reflect differences in surface process types or rates according to elevation, gradient, and bedrock lithology. Clast characteristics and fine matrix granulometry, chemistry, and mineralogy reveal minimal chemical weathering of the blockfields. Terrestrial cosmogenic nuclides were measured in quartz samples from two blockfield-mantled summits and a numerical ice sheet model was applied to account for periods of surface burial beneath ice sheets and nuclide production rate changes attributable to glacial isostasy. Total surface histories for each summit are almost certainly, but not unequivocally, confined to the Quaternary. Maximum modelled erosion rates are as low as 4.0 mm/kyr, which is likely to be near the low extreme for relict non-glacial surfaces in this landscape. The blockfields of the northern Swedish mountains are Quaternary features formed through subsurface physical weathering processes. While there is no need to appeal to Neogene chemical weathering to explain blockfield origins, these surfaces have remained continuously regolith-mantled and non-glacial since their inception. Polygenetic surface histories are therefore indicated, where the large-scale surface morphologies are potentially older than their regolith mantles.

The Savannah River Site (SRS) deposits in the Southeastern US between 30-45 m of depth are calcium carbonate-rich, marine-skeletal, Eocene-aged sediments with varying clastic content and extensive diagenetic alteration, including meter-sized caves that coexist with brittle and hard limestone. An experimental investigation including geotechnical (P- and S-wave velocities, tensile strength, porosity) and geochemical (EDS, XRD, SEM, N2-adsorption, stable isotopes, K-Ar age dating, ICP-assisted solubility, groundwater) studies highlighted the contrast between hard and brittle limestones, their relationship with cave formation, and allowed calculation of parameters for geochemical modeling. Results demonstrate that brittle and hard limestones bear distinct geochemical signatures whereby the latter exhibits higher crystallinity, lower clastic load, and freshwater-influenced composition. Results also reveal carbonate diagenesis pathways likely driven by geologic-time seawater/freshwater cycles, microorganism-driven micritization, and freshwater micrite lithification. The second section of this investigation dealt with SRS surface soils which are largely coarse-grained and rich in iron oxides with various degrees of maturity. These soils were simulated in the laboratory using Ottawa sands that were chemically coated with goethite and hematite. Surface (SEM, AFM, N2-adsorption) and geotechnical properties (fabric, small-strain stiffness, shear strength) were investigated on the resulting "soil analog". Results indicate that iron-oxide coated sands bear distinct inherent fabric and enhanced small-strain stiffness and critical state parameters when compared to uncoated sands. Contact mechanics analyses suggest that iron oxide coatings yield an increased number of grain-to-grain contacts, higher surface roughness, and interlocking, which are believed to be responsible for the observed properties.

O papel da litologia e da organização tectônica Proterozóica para entendimento da gênese do relevo, em termos de erosão diferencial, tem sido relativamente negligenciado nos últimos decênios em favor de linhas de explicação baseadas nas mudanças paleoclimáticas, tectônica moderna, e geoquímica de superfície. Fato que tem permitido a formação de modelos explicativos fechados sobre a gênese e dinâmica do relevo. Entretanto, em áreas de embasamento cristalino a organização tectônica e a diversidade composicional químico-mineralógica das rochas auxilia fortemente o entendimento do papel da erosão diferencial, na explicação da diversidade de compartimentos geomórficos. A organização tectônica das rochas, através de sistemas de falhas e dobras de fundo (estudados na década de 1950 por Francis Ruellan), tem papel fundamental no entendimento dos processos de erosão diferencial responsável pela diversidade de compartimentos geomórficos. Neste sentido, este trabalho procura provar, através do método da Associação e Indeterminação Geomorfológica de Leopold e Langbein (1970), que a Região Serrana do Espírito Santo, e, em especial, a da bacia hidrográfica do Rio Benevente é resultante da erosão diferencial sobre rochas de rica diversidade químico-mineralógica, organizada por meio de dobras de fundo e sistemas de falhas transcorrentes conjugadas. Para realização desta investigação foi elaborado uma proposta de cartografia hidrogeomorfológica para pesquisa de bacias hidrográficas, estudando-se a evolução dos perfis fluviais longitudinais, perfis morfogeológicos, estruturas tectônicas e composição químico-mineralógica das unidades litológicas associado a compartimentação morfológica do relevo. Tudo fundamentado no método escolhido. O que certamente parece ser uma coisa óbvia, no entanto, evidencia a atuação de um verdadeiro sistema de dissecação fluvial, associado ao rebaixamento de níveis de base (knickzonas) que evoluem conforme o mergulho da foliação metamórfica dos flancos das dobras e da zona de dano associado às falhas. A conclusão que se chega é a de que o relevo da bacia do Rio Benevente, e por sua vez da Região Serrana do Estado, configura-se como compartimentos geomórficos residuais resultantes da evolução de knickzonas fluviais associadas à organização tectônica das dobras de fundo responsáveis pela gênese de níveis diferenciais de resistência litológica e de distribuição espacial das falhas e fraturas. A composição das unidades litológicas também influencia, fortemente, a compartimentação do relevo, estando o nível de convexização dos relevos e a dissecação na forte dependência do grau de participação dos minerais do grupo dos plagioclásios, anfibólios e piroxênios na constituição litológica das litoestruturas / The role of lithology and Proterozoic tectonic organization for understanding the genesis of relief in terms of differential erosion, has been relatively neglected in recent decades in boon of lines of explanation based on paleoclimatic changes, modern tectonics, and geochemistry. This fact has allowed the formation of \"closed\" on the genesis and dynamics of relief explanatory models. However, in sites of crystalline basement tectonics organization and compositional diversity chemical-mineralogical Rocks strongly supports the understanding of the role of differential erosion, in explaining the diversity of geomorphic compartments. The tectonic organization of the rocks through system failure and bottom folds (studied in the 1950s by Francis Ruellan) plays a fundamental role in understanding the processes of differential erosion responsible for the diversity of geomorphic compartments. In this sense, this work seeks to prove, by the method of the Association and Indeterminacy Geomorphological Leopold and Langbein (1970), the mountainous region of the Espírito Santo, and in special the river basin Benevente is the result of differential erosion of rocks rich chemical-mineralogical diversity, organized by folds background and strike-slip fault systems combined. To carry out this research hydrogeomorphological a proposed mapping is designed to survey watershed studying the evolution of longitudinal river profiles, profiles morphogeologicals, tectonic structures and chemical-mineralogical composition of rock units associated with morphological partitioning of relief. All based on the method chosen. This certainly seems like an obvious thing, however, highlights the work of a true system of river dissection, associated with the lowering of baseline levels (knickzones) that evolve according to the metamorphic foliation dipping flanks of the folds and the damage zone associated with the fault. The conclusion reached is that the relief Benevente River basin, and in turn the mountainous region of the state, appears as residual geomorphic compartments resulting from the evolution of river knickzonas associated with the organization of tectonic folds background responsible for the genesis of differential levels of lithologic resistance and spatial distribution of faults and fractures. The composition of the lithological units also influences strongly the partitioning of relief, being the level of reliefs and round dissecting the strong dependence of the degree of participation of the group of the minerals plagioclase amphibole and pyroxene in the lithological constitution of lithostructurals

Chemical weathering of silicate rock consumes atmospheric CO2 and supplies the oceans with cations, thereby controlling both seawater chemistry and climate. The rate of CO2 consumption is closely linked to the rate of CO2 outgassing from the planetary interior, providing a negative feedback loop essential to maintaining an equable climate on Earth. Reconstruction of past global temperatures indicates that a pronounced episode of global cooling began ~50 million years ago, coincident with the collision of India and Asia, and the subsequent exhumation of the Himalayas and Tibet. This has drawn attention to the possible links between exhumation, erosion, changes in silicate weathering rates, and climate. However, many of the present-day weathering processes operating on the continents remain debated and poorly constrained, hampering our interpretations of marine geochemical archives and past climatic shifts. To constrain the controls on silicate weathering, this thesis investigates the lithium (Li) isotopic composition of river waters, suspended sediments and bed load sediments in the Alaknanda river basin, forming the headwaters of the Ganges. Due to the large fractionation of Li isotopes in the Earth’s surface environment, Li is sensitive to small changes in silicate weathering processes. As a consequence of the pronounced gradients in climate (rainfall and temperature) and erosion across the basin, the river waters show large variations in their Li isotopic composition (δ7Li), ranging from +7.4 to +35.4‰, covering much of the observed global variation. This allows a detailed investigation of the controls on Li isotope fractionation, and by extension silicate weathering. The Li isotopic composition is modelled using a one-dimensional reactive transport model. The model incorporates the continuous input of Li from rock dissolution, removal due to secondary mineral formation, and hydrology along subsurface flow paths. Modelling shows that the Li isotopic variations can be described by two dimensionless variables; (1) the Damköhler number, ND, which relates the silicate dissolution rate to the fluid transit time, and (2) the net partition coefficient of Li during weathering, kp, describing the partitioning of Li between secondary clay minerals and water, which is primarily controlled by the stoichiometry of the weathering reactions. The derived values of the controlling parameters ND and kp, are investigated over a range of climatic conditions and on a seasonal basis, shedding light onto variations in the silicate weathering cycle. In a kinetically limited weathering regime such as the Himalayan Mountains, both climate and erosion exert critical controls the weathering intensity (the fraction of eroded rock which is dissolved) and the weathering progression (which minerals that are being weathered), and consequently the fractionation of Li isotopes and silicate weathering in general. Modelling of the Li isotopic composition provides an independent estimate of the parameters which control silicate weathering. These estimates are then used to constrain variables such as subsurface fluid flux, silicate dissolution rates, fluid transit times and the fraction of rock which is weathered to form secondary clay minerals. The simple one-dimensional reactive transport model therefore provides a powerful tool to investigate the minimum controls on silicate weathering on the continents.

<div><div><div><p>The radionuclide 10Be is produced in the atmosphere and is delivered to Earth’s surface in meteoric rain and aerosols. The stable nuclide 9Be is present in trace concentrations within rocks in Earth’s crust and is released via chemical weathering. Together, these two isotopes have been employed to study a wide range of Earth processes. Here I explore new terrestrial archives of Be isotopes: cave speleothems and terrestrial Mn-oxides. Until this point, these archives have barely been studied. Only one published dataset of Be isotopes in cave speleothems exists (Lundblad, 2006), and to my knowledge, terrestrial manganese oxides are yet to be explored. However, since speleothems and Mn-oxides precipitate from groundwater, they have the potential to encode temporal variations in the 10Be/9Be ratio of water and colloids in the vadose zone.</p><p>I develop a framework for using the 10Be/9Be ratio in the dissolved phase and/or secondary weathering products as a metric of chemical weathering rate. I am motivated by several over-arching questions:</p><ol><li><p>1) Which factor, or factors, is/are dominant in controlling Be isotopes in speleothems and terrestrial Mn-oxides?</p></li><li><p>2) Can Be isotopes in speleothems be used as a metric of weathering rate over time, particularly across glacial/interglacial cycles?</p></li><li><p>3) Can Be isotopes be used to date the formation of terrestrial Mn-oxides?</p></li></ol><p>I measure Be-isotope concentrations in speleothems from Soreq Cave, Israel. By applying an equation that I derive in this thesis, I use the temporal variation in the speleothem10Be/9Be ratio to calculate chemical weathering rates over the last 168 ka. Chemical weathering varies with independent proxies for temperature. The weathering-temperature relationship can be fit to an Arrhenius relationship, and the calculated activation energy (Ea) matches other field-based estimates for feldspar, an abundant mineral in the soil above the cave. In the Appendices I present additional results of Be-isotope measurements in a flowstone from Buffalo Cave in South Africa, as well as Mn-oxides from the Appalachians.</p></div></div></div>

Dans cette étude, nous cherchons à dresser le bilan de l’altération à l’échelle de l’île de Mayotte (en surface et en souterrain), à contraindre l’impact des facteurs de contrôle dominant l’altération, puis à caractériser les processus impliqués dans les fractionnements des isotopes du silicium à l’échelle du profil d’altération.Deux campagnes d’échantillonnage incluant des eaux de rivières et des eaux souterraines ont été réalisées en saison humide et sèche, complétées par le prélèvement mensuel de 5 rivières. La prise en compte des crues (3 % de l’année) dans le calcul des taux d’altération moyens annuels en rivière a entraîné une augmentation de ≈32 % du bilan annuel. Le taux d’altération chimique global de l’île de Mayotte s’élève à 94 t/km²/an (81 t/km²/an en surface & 131 t/km²/an en souterrain). Nos résultats mettent en avant le rôle prépondérant des écoulements souterrains dans le transport de matériel dissous directement à l’océan. La contribution du domaine souterrain au bilan de l’altération diminue avec l’âge des formations, soulignant l’implication de l’âge des roches du bassin versant comme paramètre clé dans le contrôle des taux d’altération.Les isotopes du Si ont été analysés sur des roches totales le long de profils d’altération associés à différentes conditions d'altération du régolite : météorique (basse température) ou hydrothermale (haute température). À l’échelle du profil, les deux types de régimes ont montré un appauvrissement en 30Si en fonction du degré d’altération. À l’échelle du minéral, le fractionnement des isotopes du Si s’est révélé plus négatif pendant la précipitation de kaolinite secondaire à haute température qu’à basse température. / In this study, we seek to establish the weathering budget at the scale of the island of Mayotte (rivers and groundwater), to constrain the impact of dominant control factors to the weathering both locally and at a global scale, and then to characterize the processes involved in the fractionation of silicon isotopes across the weathering profile.Two field campaigns, in order to sample river water and groundwater, were carried out during wet and dry season, supplemented by the monthly monitoring of 5 rivers. By taking account of river floods (3% of the year) in the calculation of average annual weathering rates in the river has increased the annual weathering budget by ≈32%. The overall rate of Mayotte Island chemical weathering is 94 t/km²/yr (81 t/km²/yr from surface & 131 t/km²/yr from underground). Our results highlight the important role of groundwater flow to the dissolved material export directly to the ocean. The contribution of groundwater to the weathering budget decreases with the age of the geological formations, highlighting the involvement of the age of the rocks of the watershed as a key parameter in the weathering rates control.Si isotopes were analyzed for whole rock along two weathering profiles associated with different alteration conditions of the regolith: meteoric (low temperature) or hydrothermal (high temperature). At the weathering profile scale, the two types of alteration regimes showed 30Si depletion as a function of the degree of weathering. At the mineral scale, Si isotope fractionation was more negative during the secondary kaolinite precipitation at high temperatures than at low temperatures.

No description available.

Nickel silicate laterite deposits developed on ultra-mafic rocks are similar in many general respects but they vary considerably in detail. The mineralogy of these surficial deposits is very complex and difficult to determine because of the fine grained nature and solid solution characteristics of the hydrous secondary minerals and because many of the phases are actually mineraloids that are poorly ordered or amorphous. To try some new approaches toward clarification of these phases, 24 samples from New Caledonia and Puerto Rico ranging from the ophiolite-ultramafic olivine-pyroxene-chromite-serpentine substrate rocks upward through intermediate phases of weathering to the final oxide -hydroxide iron cap phase were analyzed with the infrared spectrophotometer (IR -10) and with the automated X –ray diffractometer. Four limonite samples were also mineralogically analyzed. Goethite, secondary quartz, cryptomelane, hematite, chromite, talc, thuringite, and garnierite have been identified in various samples as weathering profile products.