Orientador: Fabiano Tomazini da Conceição / Resumo: O processo de denudação continental é controlado por fatores exógenos como intemperismo químico e erosão dos solos. Nesse processo, os sistemas fluviais desempenham um papel fundamental ao transportar os materiais sólidos e dissolvidos de seu local origem até atingir os oceanos. Visando investigar o balanço de denudação no Planalto Alcalino de Poços de Caldas – MG, adotou-se o método de balanço de massa geoquímico aplicado em escala de bacia hidrográfica, cuja análise quantitativa foi baseada nos fluxos de entrada e saída de elementos/compostos químicos em duas pequenas bacias hidrográficas situadas na borda noroeste do planalto. A média da descarga fluvial de sólidos dissolvidos foi estimada em 32,5 t km-2 ano-1 sendo que cerca de 40 % desse fluxo foi atribuído à deposição atmosférica (14,0 t km-2 ano-1) enquanto o restante foi associado ao intemperismo químico das rochas (18,5 t km2 ano-1), enquanto a descarga sólida, estimada em 5,4 t km-2 ano-1, demostra um sistema fluvial de baixo fluxo de sedimento. A taxa de intemperismo químico de fonólitos, tinguaítos e nefelina sienito de Poços de Caldas (2,1 m Ma) foi inferior à taxa de remoção dos solos do planalto (4,0 m Ma), revelando uma tendência de exumação das rochas do maciço a uma velocidade de 1,9 m Ma. A taxa de denudação do Planalto de Poços de Caldas foi reduzida com o passar do tempo geológico e sob o clima atual o relevo de Poços de Caldas tende a se manter na paisagem com pouca alteração em sua forma em um lento pro... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The continental denudation process is controlled by exogenous factors such as chemical weathering and soil erosion. In this process, river systems play a key role in transporting solid and dissolved materials from their source site to the oceans. In order to investigate the denudation balance in the Poços de Caldas Alkaline Plateau - MG, the geochemical mass balance method applied in a watershed scale was adopted, whose quantitative analysis was based on the input and output flows of chemical elements / compounds in two small watersheds situated on the northwest edge of the plateau. The average fluvial discharge of dissolved solids was estimated at 32.5 t km-2 year-1 and about 40% of this flow was attributed to atmospheric deposition (14.0 t km-2 year-1) while the remainder was associated with the chemical weathering of the rocks (18.5 t km-2 year-1), while the solid discharge estimated at 5.4 t km-2 year-1 demonstrates a low sediment flow river system. The chemical weathering rate of phonolites, tinguaites and nepheline syenite from Poços de Caldas (2.1 m Ma) was lower than the removal rate from the plateau soils (4.0 m Ma), revealing a tendency for rock mass exhumation at a speed of 1.9 m Ma. The denudation rate of the Poços de Caldas Plateau has been reduced over time and under current weather the relief of Poços de Caldas tends to remain in the landscape with little change in its form in a slow process of exhumation of the rocks. / Doutor

Analyzing climate changes by loess sediment deposits formed after the last glacial maximum gives us information about how the environment was dynamically before humans physically could record climate changes. Sampling and analyzing loess from different places in the world give us a more reliable view of when events and changes in climate took place. Loess is a last step eolian transported, fine grained sediment and can be a good record as a Quaternary climate archive (Muhs 2013; Stevens et al. 2020). Loess-paleosol sequences can be used as a relative record for climate change. The paleosols in the sequence corresponds to soil which can indicate warmer interglacial/interstadial periods when chemical weathering was active at site. Loess in these sequences reflects on cold and dry climate during glacial periods (Buggle et al. 2008; Muhs 2013). By analyzing geochemical composition of bulk-samples from chosen site one can get information about if paleosols or loess deposits are present at certain depths of profile. Also, if a glacial or interglacial period was present then (Buggle et al. 2011; Johansson 2017). In this study X-ray fluorescence Spectroscopy (XRF), will be used to analyze elemental composition of loess. This to see how soluble and mobile elements relate to immobile and non-soluble ones. This can indirectly tell how paleosols and loess are distributed over the site and if shifts attempt by depth. The samples of loess in this study were taken from north-western France at a site called Primel-Tregastel. Soil weathering indexes will be used in this study to calculate weathering intensities for deposit. Na/Al-based indices called CIA, CIW, CPA, PIA, Index B and Sr-based ratios Ba/Sr and Rb/Sr was used (Buggle et al. 2011). The purpose of the study is to see if weathering has been active at site. And if, to reconstruct at which depths and to make a paleoclimatic interpretation of the site. Na/Al-based indices CIA, CIW, CPA, PIA and Index B shows indications of active weathering at site. Sr-based ratios Ba/Sr and Rb/Sr do also show same indications but with more dramatically variations. The content of mobile and immobile elements does also follow the principle that when mobile elements decrease in percentage, immobile elements get enriched in bulk-sample. The trends shown are a long time of cold climate due to low weathering intensities followed by one warmer and more humid period. Increasing weathering intensities, indicating an interglacial/interstadial period happens as a first development. Continuously a decrease happens in weathering intensity which would indicate a start of a colder period. Topmost layer has been improved and re-worked by human activity and will be misleading to use in a geochemical analysis and paleoenvironmental interpretation. / Att analysera klimatförändringar genom lössjordar formade efter senaste glaciala maximumet ger oss information om hur miljön såg ut dynamiskt innan människan hade möjligheten att mäta klimatvariationer. Genom analys och provtagning av lössjordar från olika platser i världen ger oss en mer trovärdig bild över när händelser och förändringar i klimat skedde. Lössjord är ett slutligen vindtransporterad, finkornigt sediment som även fungerar bra som register för Kvartära klimatarkiv (Muhs 2013; Stevens et al. 2020). Loess-paleosol sekvenser kan användas som ett relativt register för klimatförändringar. Paleosolerna i sekvensen motsvarar jord som indikerar varmare interglaciala/interstadiala perioder när kemisk vittring kan ha varit aktiv. Lössavlagringar i sekvensen reflekterar kallare och torrare klimat under glaciala istider (Buggle et al. 2008; Muhs 2013). Genom att analysera geokemiskt innehåll av prover från lokal kan man få fram information om paleosoler eller lössavlagringar finns vid visst djup i profilen. Indirekt även om en glacial eller interglacial period pågick då (Buggle et al. 2011; Johansson 2017). I den här studien används X-ray fluorescens Spektroskopi (XRF) för att analysera geokemiskt innehåll av lössjord. Detta för att se hur lösliga och mobila element är relaterade till icke-mobila och icke-lösliga element. Det kan indirekt peka på hur paleosoler och löss är fördelat över en lokal och visa om skillnader finns vid olika djup. Proverna i denna studie är tagna från nord-västra Frankrike vid en lokal som heter Primel Trégastel. Jord vittrings index kommer att användas i studien för att beräkna vittringsintensiteter för avlagringen. Na/Al-baserade index som heter CIA, CIW, CPA, PIA och Index B och Sr-baserade förhållanden Ba/Sr och Rb/Sr kommer användas (Buggle et al. 2011). Syftet med studien är att se om vittring har skett vid lokalen. Och om vittring påvisas, kunna rekonstruera vid vilka djup och slutligen göra en paleoklimatisk tolkning över lokal. Na/Al-baserade index CIA, CIW, CPA, PIA och Index B visar indikationer av vittring som varit aktiv vid studerad lokal. Sr-baserade förhållanden Ba/Sr och Rb/Sr visar samma indikation men med mer dramatiska variationer. Innehållet av mobila och icke-mobila element följer även principen om att när mobila element minskar i procent så ökar dom icke-mobila elementen. Trenderna som visas är en lång tid av kallt klimat med låg vittringsintensitet som följs av en varmare och fuktigare period med högre vittringsintensitet. Utvecklingen av denna ökande vittringsintensitet indikerar en pågående interglacial/interstadial period. Fortsättningsvis sker en minskning i vittringsintensitet vilket påvisar en början av en kallare period. Det översta lagret i lokalen har bevisats blivit förändrat av mänsklig aktivitet och kan var missvisande i en geokemisk analys och paleoklimatologisk tolkning.

Content of Doctoral thesis is a methodology for juridical experts on the assessment of structures manufactured of weathering steel, with special attention to evaluation of the protective corrosion layer.

The thesis deals with the influence of the base material of the coating systems for wood durability when we exposed them to external conditions. The theoretical part is devoted to wood durability and weather resistance with a detailed description of the tests the durability of coating systems. A substantial part of the theory is devoted to description binder component of the coating material. In the practical part was performed the experiment, which examined the influence of the thickness of the coating system, the type of coating material (paint or lasure) as well as the type of binder (water dispersion with an alkyd or acrylic resin, respectively solution coating system with the alkyd resin). All coating systems were exposed to natural and artificial durability tests. The criterions for evaluation were chosen differences of colours.

Comparer de manière approfondie la réponse des différents outils isotopiques choisis (Li, B et U) durant l’altération chimique dans un profil déjà connu (e.g. le profil du Sommet sur le Bassin versant du Strengbach ; Ackerer, 2017) afin de dégager les mécanismes moteurs des fractionnements isotopiques de chacun de ces éléments pour faire le lien entre la réponse de ces outils lors de l’altération chimique et remonter ainsi au régime d’altération des roches. Développer les observations réalisées sur le profil du Sommet et les appliquer sur cinq autres profils d’altération répartis sur l’ensemble du bassin versant en se concentrant sur la fraction <2µm. Cela permettra de voir si les observations faites dans le premier profil se retrouvent dans les autres profils et si nous sommes capables de remonter au régime d’altération. Étudier de manière préliminaire comment évolue le signal isotopique de l’altération chimique acquis dans les profils d’altération au cours du transport sédimentaire et s’il est possible de déterminer le régime d’altération d’un bassin versant à partir des sédiments de ce même bassin. / In-depth comparison of the response of various selected isotopic tools (Li, B and U) during chemical weathering in an already known profile (eg the Summit profile in the Strengbach watershed, Ackerer, 2017) to identify the driving mechanisms of isotopic fractionations of these elements to link the response of these tools compared to the chemical alteration to go back to the alteration regime. Develop the observations made on the Summit profile and apply them to five other weathering profiles distributed over the entire watershed focusing on the <2μm fraction. This will make it possible to see if the observations made in the first profile are found in the other profiles and if we are able to go back to the alteration regime. Preliminarily investigate how the isotopic signal of chemical alteration acquired in alteration profiles evolves during the sediment transportation and if it is possible to determine the alteration regime of a watershed from it sediments.

Diamonds are commonly present in an ore called kimberlite. Kimberlites vary extensively in mineralogy and therefore can complicate the processing and the extraction of diamonds. Weathering of kimberlite was investigated in this study and refers to the rapid physical breakdown of the kimberlite material. Kimberlite weathering by organic molecule adsorption was investigated utilising organic solutions; ethanol, formamide, n-hexane, oxalic acid, urea, pentanoic acid and acetic acid, was investigated. The extent of weathering was measured by XRD, TGA and FTIR analysis as well as by evaluating changes in the particle size distribution. The idea to predict the susceptibility of weathering of kimberlite based on TGA analysis was discredited as it was found that there was no correlation between the smectite content and the % weight loss from TGA analysis. In XRD analysis studies to relate the d-spacing to the extent of weathering, it was found that the technique was not sensitive enough to enable direct prediction of weathering behaviour. Organic solutions at 0.5 M generally did not significantly alter the d-spacing. In the case of utilising pure organic solutions, it was observed that switching from diluted to pure organic solutions did not increase the d-spacings but rather lowers the space. Cation pretreatment prior to organic weathering resulted in d-spacings up to 2 water layers (12.6 Å being equal to 1 water layer, 15.6 Å equal to 2 layers and 18.6 Å equal to 3 layer). The general trend was that the divalent cations Mg2+ and Ca2+ increased the d-spacings whereas monovalent cations Na+ and K+ decreased the spacing. In the case of pre-organic treatment prior to organic weathering, it was observed that the resulting d-spacing increased to 2 and 3 water layers. TGA analysis confirmed that the kimberlite structure did absorb organic reagents during weathering. It was observed that the amount of organic reagents adsorbed decrease in the following order: oxalic acid > urea > pentanoic acid > formamide > ethanol > n-hexane > acetic acid, with oxalic acid having been adsorbed the greatest. In addition, it was also shown that the extent of inorganic cation adsorption was more than that of organic solutions. The analysis also showed that organic pretreatments yielded promising results and the order followed was dimethyldioctadecylammonium chloride > cetylpyridium chloride > dodecylamine > pyridine in encouraging subsequent organic adsorption. FTIR analysis results indicated the mechanism by which organic molucules attached onto the mineral surface. It was observed that there was a disturbance of the bond between water in the interlayer and the silicate structure by a stronger H-bond gained through organic molecule attachment. Oxalic acid was observed to cause a structural change due to proton attack of the silicate structure. It was found that kimberlite weathering, in essence, occurred in the first 24 hours of contact with the solution. Oxalic acid was found to be the most effective weathering agent compared to the rest of the tested organic solutions. The effect of the tested solutions, at 0.5 M concentration, on kimberlite weathering followed the series Cu2+ > oxalic acid > ethanol > acetic acid > formamide > n-hexane > distilled water. This study therefore showed that the accelerated weathering of kimberlite utilising organic solutions was not as efficient as the Cu2+ solution. Comparing Cu2+ and oxalic acid treatments, results showed that 67 % of the particles passed 12 mm screen size due to Cu2+ weathering as opposed to 48 % in oxalic acid. In investigating the effects of variables, it was found that time of exposure had a small effect in the weathering of kimberlite. Increasing the organic concentration from 0.025 M to 0.5 M saw an increase in the amount of particles passing the 12 mm screen size by~20 %. There was however no improved weathering when the solution temperature was increased from approximately 25 °C to 40 °C. In the study of kinetics involved during organic weathering utilising oxalic acid and comparing with Cu2+ medium, a high mineral dissolution was observed in the first 24 hours of contact with the weathering solution. However, different weathering mechanisms were observed between Cu2+ and oxalic acid. Inorganic solutions foster weathering by interlayer cation exchange which results in the reduction of the surface energy and this encourages further crack propagation. Oxalic acid weathering mechanism was by proton attack of the structural cations which was then limited thereafter by oxalate salts precipitation. Al3+ and Mg2+ were the dominant cations in solution during weathering (reaching 40 mmol/L) at higher oxalic acid concentration. This indicated that the dissolution of the clay‟s octahedral structure occurred, making oxalic acid a more effective agent than the rest of the tested organic solutions. An alternative method to transform non-swelling clay minerals to swelling in kimberlites was highlighted. It was observed that cation exchange treatment in conjunction with acid and oxidation treatments on kimberlites containing non-swelling minerals: mica or forsterite that are at least 30 % in quantity may result in the presence of swelling clays after these treatments. Kimberlite that contained serpentine minerals was more resistant to alteration under these conditions. / Dissertation (MEng)--University of Pretoria, 2013. / gm2014 / Materials Science and Metallurgical Engineering / UPonly

No description available.

L’objectif de cette thèse est de déterminer une reconstruction de l’altération continentale dans le bassin du Nil depuis 100.000 ans, afin de mieux comprendre l’impact des variations climatiques sur les sols, les apports à la Méditerranée et le cycle du carbone. Ce travail repose sur une étude géochimique fine des argiles extraites d’archives sédimentaires du delta du Nil sur une échelle de temps de 100.000 ans. Il repose sur une approche inédite du couplage d’un traceur de source (isotopes du néodyme) et de traceurs d’altérations (isotopes du lithium). Les résultats de cette étude mettent en évidence une réponse rapide de l’altération continentale aux variations hydro-climatique en Afrique du Nord. De plus, les changements climatiques en Atlantique Nord et du ralentissement de l’AMOC ont eu une influence importante sur la diminution de l’intensité d’altération continentale dans le bassin du Nil. A l’actuel, les taux d’altération, et la consommation de CO2 associée, des trapps d’Ethiopie sont relativement faibles par rapport aux autres régions basaltiques. Nos résultats montrent cependant que durant l’African Humid Period, la consommation de CO2 dans cette région était 2 à 3 fois plus importante qu’aujourd’hui. Cela indique que les trapps d’Ethiopie ont pu jouer un rôle non négligeable dans le cycle du CO2, et en particulier lors des périodes de fort runoff. Enfin, des développements analytiques ont été réalisés afin de pouvoir exploiter les compositions isotopiques en lithium des carbonates biogéniques marins, comme nouveaux traceurs des apports en eau douce du Nil. Les résultats obtenus suggèrent une influence des effets dits « vitaux » et des processus de diagénèse. / This thesis presents a reconstruction of the chemical weathering in the Nile basin since 100.000 years. His objective is to better understand the impact of climatic variations on chemical weathering, to better. This work is based on the geochemistry study on marine core recorded in the Nile delta, on a time scale of 100.000 years. It use a novel approach with the coupling of à source tracer (εNd) and chemical weathering tracers (δ7Li and elementary ratios) on the fine fraction (< 2µm). In addition, it was analyzed samples of each actual Nil sources and a core sample from Tana Lack (Ethiopie). The results of this studies have enabled to reconstruct the chemical weathering variations in the Nile basin since 100.000 years. It show a rapid respond of chemical weathering to climate variations. This was also observed by important impact of North Atlantic climate variations on the decrease of chemical weathering in the Nile basin. At present, the chemical weathering flux and the CO2 consumption of the Ethiopian traps are low comparted to the other basaltic regions, as the Deccan. However, our results show that during the most humid periods (African Humid Period) the CO2 consumption was 2 to 3 time higher than today. This indicates that the Ethiopian traps could be have played a non-negligible role in the global CO2 cycle during the Cenozoic, and principally during the most humid periods in North Africa. Finally, analytical developments have been realized to be able to exploit the lithium isotopes on biogenic carbonates as a new tracer of Nile water flood. The results suggest an influence of “vital” effect and diagenetic process.

The subsurface igneous biome contains a vast portion of Earth's total biomass, yet we still know so little about it. Igneous environments such as iron-rich ocean crust and lava tubes may also host analogs to chemolithotrophically-driven life on other planets, so studying life in this biome is essential to understanding how life may survive on other planets. In this study, three igneous surface and subsurface environments were investigated for microbial preference for olivine, microbial physiologies and phylotypes present on olivine, and microbial growth on olivine in the laboratory via iron oxidation. These environments include a subseafloor borehole drilled into the ocean crust basalt basement, a lava tube with perennial ice, and a trio of Columbia River basalt-hosted freshwater terrestrial habitats. The subseafloor borehole (IODP Hole 1301A) is situated on the eastern flank of Juan de Fuca Ridge (JFR) and was used in the first long-term deployment of microbial enrichment flow cells using osmotically-driven pumps. The flow cells contained igneous minerals and glasses, for which cell density and microbial abundances were evaluated. Total cell density and viable oligotrophs were highest for Fe(II)-rich olivines. Organotrophic bacterial isolates were capapble of iron oxidation and nitrate reduction, and grew on olivine in the laboratory. Putative neutrophilic iron oxidizers were also isolated from igneous riparian and cave environments in northwest and central Oregon. Isolated bacteria from all three environments were capable of chemolithotrophic growth with olivine and oxygen or nitrate in the laboratory. Bacteria isolated from river basalt were putatively capable of producing alteration textures on olivine surfaces in culture. Microbial life in the igneous subsurface preferentially attach to Fe²⁺-rich minerals, which suggests that life in the subsurface is heterogeneously distributed. The isolation of oligotrophic iron oxidizers that grow on olivine suggests that olivine supports a chemolithotrophic subsurface community based on primary productivity via iron oxidation. This generation of biomass on olivine surfaces creates organic carbon-rich coated mineral surfaces that may support a more complex community. The identification of Mars analogs living in Oregon lava tubes and the discovery that iron oxidizers may produce biosignatures on olivine surfaces are key findings that may provide the foundation for a new chapter in the search for life on Mars.

Indiana University-Purdue University Indianapolis (IUPUI) / Subglacial chemical processes in Antarctica are potentially significant contributors to global geochemical cycles, but current understanding of their scale and nature is limited. A sequential chemical extraction procedure was developed and tested to investigate the utility of meteoric 10Be as a tracer for chemical weathering processes beneath the East Antarctic Ice Sheet. Subglacial meltwater is widely available under the Antarctic Ice Sheet and chemical constituents within it have the potential to drive geochemical weathering processes in the subglacial environment. Meteoric 10Be is a cosmogenic nuclide with a half-life of 1.39×106 years that is incorporated into glacier ice, therefore its abundance in the subglacial environment in Antarctica is meltwater dependent. It is known to adsorb to fine-grained particles in aqueous solution, precipitate with amorphous oxides, and/or be incorporated into authigenic clay structures during chemical weathering. The presence of 10Be in weathering products derived from beneath the ice therefore indicates chemical weathering processes in the subglacial environment. Freshly emerging subglacial sediments from the Mt. Achernar blue ice moraine were subject to chemical extractions where these weathering phases were isolated and 10Be concentrations therein quantified. Optimization of the phase isolation was developed by examining the effects of each extraction on the sample mineralogy and chemical composition. Experiments on 10Be desorption revealed that pH 3.2-3.5 was optimal for the extraction of adsorbed 10Be. Vigorous disaggregation of the samples before grain size separations and acid extractions is crucial due to the preferential fractionation of the nuclide with clay-sized particles. 10Be concentrations of 2-22×107 atoms g-1 measured in oxides and clay minerals in freshly emerging sediments strongly indicate subglacial chemical weathering in the catchment of the Mt. Achernar moraine. Sediment-meltwater contact in the system was calculated to be on the order of thousands of years, based on total 10Be sample concentrations, local basal melt rates, and 10Be ice concentrations. Strong correlation (R = 0.96) between 10Be and smectite abundance in the sediments indicate authigenic clay formation in the subglacial environment. This study shows that meteoric 10Be is a useful tool to characterize subglacial geochemical weathering processes under the Antarctic Ice Sheet.