Guidelines for Rock-Eval analysis of recent marine sediments

International audienceRock-Eval pyrolysis, a widely used petroleum screening technique developed primarily for ancient sedimentary rocks and kerogens, has now been increasingly applied to the characterization of recent lacustrine or marine sediments. However, as illustrated by previous results from various authors and by the analysis of recent sediments from various areas, the thermally labile character of recent organic matter (OM), the presence of poorly crystallized mineral (e.g. carbonate) and the eventual presence of salts (NaCl, sulfate) might perturb the detection of the pyrolysis effluent. The aim here was to outline the problems generated by such perturbation and to demonstrate that specific operating conditions needed for proper analysis o frecent marine sediments. A modified Rock-Eval pyrolysis program, starting at lower temperature (180 °C) with a heating rate of 30 °C/min, is proposed as a standard mode for the analysis of recent OM in order to avoid misleading interpretation of Rock-Eval data and make possible the inter-comparison of results whatever the Rock-Eval device used

Analyse de composés organiques purs par pyrolyse Rock-Eval et influence de la matrice minérale

International audienceL’utilisation croissante de la pyrolyse Rock-Eval pour caractériser les matières organiques des sols et des sédiments récents a conduit Carrie et al. (2012) à analyser des produits organiques purs en vue d’interpréter les signaux et paramètres classiques de cette technique : S1, S2, S3, Tmax, index d’hydrogène et d’oxygène, etc. Si leur démarche est intéressante, elle a toutefois été menée avec une méthode inappropriée puisqu’ils ont utilisé le mode ‘bulk rock basic’ adapté aux roches mères pétrolières. En effet, la température initiale de 300°C qui caractérise ce mode conduit à une thermovaporisation brutale et précoce des produits organiques purs d’où des pics S1 très forts et des Tmax parfois aberrants.Il nous a semblé important de reprendre l’approche de Carrie et al. (2012) en commençant la pyrolyse à 200 °C, tel que préconisé par Disnar et al. (2003) pour l’analyse des sols. Nous avons choisi d’analyser de l’albumine de sérum bovin, de la cystéine, du glucose, de la cellulose et du cholestérol comme composés modèles représentant des protéines, des carbohydrates et des lipides. Par ailleurs, nous avons examiné l’influence de différentes matrices minérales lors de la pyrolyse de ces produits purs à l’image de ce qu’avaient fait Espitalié et al. (1984) avec les kérogènes. Du sable de Fontainebleau, de la calcite, de la kaolinite, de la montmorillonite et des oxy-hydroxydes de fer (ferrihydrite et goethite) ont ainsi été ajoutés à sec à chacun de ces produits purs. Le bilan carbone fourni par la pyrolyse Rock-Eval a été comparé avec les résultats d’une analyse élémentaire sur les mêmes mélanges synthétiques.Les résultats montrent que dans la plupart des cas le bilan carbone du Rock-Eval est déficitaire et que celui-ci l’est d’autant plus que les produits sont associés à des oxy-hydroxydes de fer. Ces oxydes ont un effet catalytique qui favorise le craquage thermique du produit (fort pic S1) et la génération de composés oxygénés (CO et CO2) aux dépens du S2. Le sable n’apparait pas aussi inerte que prévu sur les produits purs. La kaolinite et la montmorillonite ont des effets contrastés selon la nature des produits. Il semblerait que la montmorillonite favorise la formation de coke pendant la phase de pyrolyse d’où une diminution de la part de carbone pyrolysable au profit du carbone résiduel.Carrie et al. (2012) – Org. Geochem., 46, 38-53.Disnar et al. (2003) – Org. Geochem., 34, 327-343.Espitalié et al. (1984) – Org. Geochem., 6, 365-382

Peut-on calculer la valeur de paramètres Rock-Eval pour la couche 0-50 cm à partir des valeurs mesurées sur les couches 0-30 et 30-50 cm ?

Les sols sont généralement échantillonnés à différentes profondeurs fixes, sous forme de couches, mais ces profondeurs peuvent varier d’une étude à l’autre. Pour calculer des stocks de carbone organique du sol à des profondeurs données, les quantités de COS présentes dans les différents horizons peuvent être additionnées. Nous nous sommes demandés si, de la même manière, il est possible de combiner les valeurs d’indicateurs Rock-Eval mesurées sur différentes profondeurs pour obtenir des valeurs d’indicateurs représentatives des échantillons combinés.Pour tester la linéarité des indicateurs Rock-Eval, nous avons mélangé des échantillons de sol prélevés en surface (0–30 cm) et en profondeur (30–50 cm) dans les différentes proportions suivantes : 100:0 ; 90:10 ; 75:25 ; 50:50 ; 25:75 ; 10:90 ; 0:100. Ces mélanges ont été réalisés pour 8 sols de forêt française à pédologies contrastées. Nous avons ensuite analysé les échantillons purs (100:0 et 0:100) et les mélanges en Rock-Eval (n = 56 échantillons). Pour différents paramètres Rock-Eval, nous avons comparé les valeurs mesurées pour les différents mélanges aux moyennes pondérées (suivant la composition du mélange) des valeurs mesurées pour les échantillons de surface et de profondeur composant ces mélanges.Nos résultats montrent que la majorité des paramètres Rock-Eval sont linéaires et qu’il est donc possible de déterminer la valeur du paramètre choisi pour l’horizon 0–50 cm à partir des valeurs mesurées sur les horizons 0–30 cm et 30–50 cm. C’est en particulier le cas pour les paramètres suivants : TOC-RE6, HI, T50CO2pyr et T50CO2ox. Cependant pour deux des paramètres testés (OI et T50CHpyr) la relation entre valeurs mesurées et calculées est peu satisfaisante. Cette mauvaise adéquation est particulièrement observée dans certains types de sol avec des processus pédogénétiques marqués et qui conduisent à des horizons très contrastés. D’autre part, ces deux paramètres sont aussi ceux présentant la plus grande variabilité, ce qui explique au moins en partieles différences entre valeurs mesurées et calculées

Role of Tocochromanols in Tolerance of Cereals to Biotic Stresses: Specific Focus on Pathogenic and Toxigenic Fungal Species

International audienceFungal pathogens capable of producing mycotoxins are one of the main threats to the cultivation of cereals and the safety of the harvested kernels. Improving the resistance of crops to fungal disease and accumulation of mycotoxins is therefore a crucial issue. Achieving this goal requires a deep understanding of plant defense mechanisms, most of them involving specialized metabolites. However, while numerous studies have addressed the contribution of phenylpropanoids and carotenoids to plant chemical defense, very few have dealt with tocochromanols. Tocochromanols, which encompass tocopherols and tocotrienols and constitute the vitamin E family, are widely distributed in cereal kernels; their biosynthetic pathway has been extensively studied with the aim to enrich plant oils and combat vitamin E deficiency in humans. Here we provide strong assumptions arguing in favor of an involvement of tocochromanols in plant–fungal pathogen interactions. These assumptions are based on both direct effects resulting from their capacity to scavenge reactive oxygen species, including lipid peroxyl radicals, on their potential to inhibit fungal growth and mycotoxin yield, and on more indirect effects mainly based on their role in plant protection against abiotic stresses

Can we calculate the value of Rock-Eval parameters for the 0-50 layer from the measured values on the layers 0-30 and 30-50 cm?

International audienceCurrent studies investigating soils use different sampling methods. Generally, soils are sampled in different soil horizons and the sampling depths may vary across studies or according to the soil profile composition. For some soil properties such as soil organic carbon stock, it is possible to calculate the organic carbon content of a soil profile by adding the values measured in each horizon. Soil organic carbon stock is therefore independent from the sampling strategy. In the recent years, Rock-Eval has been proposed as a reliable method to investigate soil organic carbon stock and its stability. The objective of this study is to determine, whether Rock-Eval parameters of soil organic matter in a given soil horizon, can also be calculated from Rock-Eval parameters measured in subhorizons; an idea which would greatly facilitate the comparison of results of studies using different sampling methods. In this study, samples from 10 French forest sites encompassing a variety of pedoclimates were used. At each site, samples were collected from two depth ranges, 0-30 and 30-50 cm. To test the linearity of the mixing of RE indicators, binary mixtures of surface and deep soil were composed for each site using five different mixing ratios (10:90, 25:75, 50:50, 75:25, 90:10). All 70 samples were then analysed using Rock-Eval, resulting in five classical RE parameters for each sample. The values of the RE parameters measured on composite samples were generally in good agreement with theoretical values, which were calculated using values measured on 0-30 cm and 30-50 cm according to the mixing equation. This is particularly the case for the following parameters: TOCRE6, PC,RC and OI. However, for HI the relationship between measured and calculated values is unsatisfactory. For sites with a clay-rich deep soil horizon layer and a surface layer with a coarser texture the variation was the highest. Retention of hydrocarbons by clay minerals is a common mineral matrix effect in pyrolysis methods and could explain this observation. Future research should include quantification of the mineral matrix effect for different soil types and calculation of a correction factor for the addition of parameters in a soil profile. Therefore, we conclude that in most temperate soils, most classical RE parameters of a soil profile can be indeed calculated as a sum of the different horizons

Assessing SOC labile fractions through respiration test, density-size fractionation and thermal analysis – A comparison of methods

Assessing SOC labile fractions through respiration test, density-size fractionation and thermal analysis – A comparison of methods. EGU 2017, European Geophysical Union General Assembly 201

The contribution of deep soil horizons to persistent organic carbon sequestration in French forest soils

International audienc

Improvement of Adhesion Properties and Corrosion Resistance of Sol-Gel Coating on Zinc

Corrosion is a major problem for durability of many metals and alloys. Among the efficient classical surface treatments, chromate-based treatments must be banished from industrial use due to their toxicity. At the same time, sol-gel routes have demonstrated high potential to develop an efficient barrier effect against aggressive environments. By this process, the anti-corrosion property can be also associated to others in the case of the development of multi-functional hybrid coatings. In this paper, the main goal is precisely to improve both the corrosion resistance and the adhesion properties of phosphated zinc substrates by the deposition of a hybrid (organic-inorganic) sol-gel layer. To reach this double objective, a choice between two formulations 3-glycidoxypropyltrimethoxysilane (GPTMS)/aluminum-tri-sec-butoxide (ASB) and 3-(trimethoxysilyl)propylmethacrylate (MAP)/tetraethylorthosilicate (TEOS) was firstly made based on the results obtained by microstructural characterizations using SEM, optical analysis, and mechanical characterization such as shock and/or scratch tests (coupled to climatic chamber and salt spray exposure). Several investigations were performed in this study, and the best formulation and performances of the system were obtained by adding a new precursor (1-[3-(trimethoxysilyl)propyl]ureido-UPS) under controlled conditions, as detailed in this paper

Predicting Rock-Eval (R) thermal analysis parameters of a soil layer based on samples from its sublayers; an experimental study on forest soils

International audienceSoil sampling depths strongly vary across soil studies. Stocks of elements (such as C, N) or organic matter in a soil layer can be simply calculated from stocks measured in its sublayers. This calculation is less obvious for other soil characteristics, such as soil organic carbon (SOC) persistence, complicating the comparison of results from different studies. Here, we tested whether Rock-Eval (R) parameters of a soil layer, characterizing soil organic matter and its biogeochemical stability, can be determined using Rock-Eval (R) data measured on its sublayers. Soil samples collected in 10 plots located in eight French forest sites, taken up at two different depths (0-30 cm, 30-50 cm), and their mixtures were analysed with Rock-Eval (R). Expected values for the Rock-Eval (R) parameters of the soil mixtures were calculated either: (1) as the weighted mean of Rock-Eval (R) parameters measured on the two sublayers, or (2) based on a signal reconstructed as the weighted mean of Rock-Eval (R) thermograms recorded on the two sublayers. Our results showed a good agreement between measured and expected Rock-Eval (R) parameter values. However, when the clay content strongly differed between the two soil sublayers, the amount of pyrolyzed hydrocarbons measured on the soil mixtures was slightly lower than expected. We conclude that it is reasonable to calculate Rock-Eval (R) parameters of a soil layer, from the Rock-Eval (R) signature of its sublayers. Our findings facilitate the harmonization of Rock-Eval (R) data from large scale soil studies using different sampling depths

Rock-Eval analysis of French forest soils: the influence of depth, soil and vegetation types on SOC thermal stability and bulk chemistry

Rock-Eval analysis of French forest soils: the influence of depth, soil and vegetation types on SOC thermal stability and bulk chemistry. EGU 2017, European Geophysical Union General Assembly 201