Modalité d'infiltration dans le sol de carbone et de matière organique d'origine routière dans un bassin d'eau pluviale absorbant.

Le lessivage des routes par les eaux pluviales peut apporter à l'environnement des quantités importantes de matière organique produites par la circulation automobile (1, 2). Le long des grandes voies de circulation des bassins d'orage atténuent en général la charge polluante des eaux avant leur retour aux cours d'eau. En région calcaire les bassins sont cependant le plus souvent absorbants, les eaux pluviales rejoignant la nappe phréatique rapidement en s'infiltrant à travers le sol (3). Dans cette étude préliminaire nous avons cherché à évaluer le comportement de la charge organique dissoute des eaux pluviales de routes lors de l'infiltration dans une zone d'effondrement karstique. La charge organique a été quantifiée par dosage du carbone organique dissous (COD) et mesure de l'intensité de fluorescence dans les échantillons bruts et dans des fractions obtenues par ultrafiltration tangentielle ou par chromatographie sur résines polymériques hydrophobes (XAD8). La présence de nanoparticules de carbone dans ces échantillons a été recherchée par microscopie électronique à transmission (MET) (4)

Temperatures reached by the roof structure of Notre-Dame de Paris in the fire of April 15th 2019 determined by Raman paleothermometry

When the Notre-Dame de Paris Cathedral burnt, the oak frame was almost completely destroyed. The temperatures reached were determined by an original method of Raman paleothermometry applied to charcoals collected after the fire. The Raman spectra of the charcoals evolve monotonically and irreversibly with the carbonization temperature and can therefore be used as “fossil thermocouples”. A calibration curve was constructed from the carbonization between 500 and $1300~^{\circ }$C of unburnt oak pieces from the cathedral. Thus, the maximum charcoal formation temperature during the cathedral fire can be determined. The Raman analysis of charcoals sampled in situ serves to construct the first cartography of the carbonization temperatures. The temperatures reach values above $1200~^{\circ }$C in the crossing. These experimental data are the basis for a discussion of the consequences of the fire regarding possible lead dissemination and thermal alterations of limestone

Temperatures reached by the roof structure of Notre-Dame de Paris in the fire of April 15th 2019 determined by Raman paleothermometry

When the Notre-Dame de Paris Cathedral burnt, the oak frame was almost completely destroyed. The temperatures reached were determined by an original method of Raman paleothermometry applied to charcoals collected after the fire. The Raman spectra of the charcoals evolve monotonically and irreversibly with the carbonization temperature and can therefore be used as “fossil thermocouples”. A calibration curve was constructed from the carbonization between 500 and $1300~^{\circ }$C of unburnt oak pieces from the cathedral. Thus, the maximum charcoal formation temperature during the cathedral fire can be determined. The Raman analysis of charcoals sampled in situ serves to construct the first cartography of the carbonization temperatures. The temperatures reach values above $1200~^{\circ }$C in the crossing. These experimental data are the basis for a discussion of the consequences of the fire regarding possible lead dissemination and thermal alterations of limestone

Electron Paramagnetic Resonance Study of a Photosynthetic Microbial Mat and Comparison with Archean Cherts

International audienceOrganic radicals in artificially carbonized biomass dominated by oxygenic and non-oxygenic photosynthetic bacteria, Microcoleus chthonoplastes-like and Chloroflexus-like bacteria respectively, were studied by Electron Paramagnetic Resonance (EPR) spectroscopy. The two bacteria species were sampled in mats from a hypersaline lake. They underwent accelerated ageing by cumulative thermal treatments to induce progressive carbonization of the biological material, mimicking the natural maturation of carbonaceous material of Archean age. For thermal treatments at temperatures higher than 620 °C, a drastic increase in the EPR linewidth is observed in the carbonaceous matter from oxygenic photosynthetic bacteria and not anoxygenic photosynthetic bacteria. This selective EPR linewidth broadening reflects the presence of a catalytic element inducing formation of radical aggregates, without affecting the molecular structure or the microstructure of the organic matter, as shown by Raman spectroscopy and Transmission Electron Microscopy. For comparison, we carried out an EPR study of organic radicals in silicified carbonaceous rocks (cherts) from various localities, of different ages (0.42 to 3.5 Gyr) and having undergone various degrees of metamorphism, i.e. various degrees of natural carbonization. EPR linewidth dispersion for the most primitive samples was quite significant, pointing to a selective dipolar broadening similar to that observed for carbonized bacteria. This surprising result merits further evaluation in the light of its potential use as a marker of past bacterial metabolisms, in particular oxygenic photosynthesis, in Archean cherts

Coking properties of perhydrous low-rank vitrains. Influence of pyrolysis conditions.

Compositional transformations occurring during natural coalification generally lead to increased coking potential of coals characterised in the resulting cokes by large sizes of molecular orientation domains (MOD) determined through transmission electron microscopy with 002 dark field mode. In this study, two sets of perhydrous low-rank vitrains (WJV and UCV) have been pyrolysed using an open-system with two heating rates in an attempt to increase their coking potential. Results show that, despite the high potentialities of such vitrains for producing hydrocarbons, i.e. a suspensive medium efficient for their cokefaction, each of the pyrolysis methods does not lead to solid residues chemically equivalent to natural coking coals, since the cokes from these residues are always made of smaller MOD than those obtained for coking coals. For comparison, a similar characterisation, carried out on a conventional vitrain (Fouthiaux) pyrolysed in a confined-system which prevents the release of hydrocarbons, leads also to non-coking coals. The formation of such MOD is likely due to the peculiar chemical composition of the precursors and/or the pyrolysis conditions. FTIR data show that perhydrous vitrains are characterised by a low degree of condensation of aromatic units with a very small concentration of aromatic rings of large size. Thermal treatment originates depolymerisation reactions in the vitrinite network with the formation of low molecular weight products which are not efficient to form large anisotropic domains. The oxygen, present in relatively high amount in some vitrains (UCV and Fouthiaux) might also act as a crosslinking agent preventing the formation of large MOD. Furthermore, while open-medium pyrolysis leads to an important effluent release, as shown by the rapid decrease of H/C ratio, hydrocarbon effluents are conversely retained within the coal matrix in the case of confined-medium pyrolysis. However, the latter pyrolysis induces secondary cracking reactions leading to the formation of lighter products. Therefore, the enhancement of coking properties has not been totally reached by our experiments insofar as they did not lead to oxygen-poor artificially matured coals, similar to natural coking coals

Diamond formation from C60 crystals heated under high pressure

X-ray Diffraction (XRD) and Raman Microspectroscopy showed that diamond is detected when solid C60 crystals are heated above 1600°C, in the 9-15 GP range. These samples are here studied by High Resolution Transmission Electron Microscopy (HRTEM) in order to allow the structural characteristics of more or less organised co-existing carbon phases

Formation and thermal evolution of insoluble reservoir bitumen in Angolan carbonate reservoirs.

Pyrobitumen resulting from the thermal cracking of crude oil is a frequent occurrence in petroleum reservoirs. Despite the detrimental implications of pyrobitumen for the poroperm qualities of the reservoir; little is known about the evolution of pyrobitumen properties as a function of increasing thermal stress. A suite of pyrobitumen-bearing reservoir cores from the carbonate Jurassic Pinda formation in offshore Angola has been studied using geochemical and petrographic techniques (including elemental analysis, Rock Eval pyrolysis, GC, FTIR, XRD, SEM, TEM) in order to characterise the physical, chemical, and optical properties of the pyrobitumen as fully as possible. The 11 core samples contain pyrobitumen at reflectance values ranging from 0.55-2.24%Ro and display varying degrees of solubility in dichloromethane from 98% insoluble bitumen to 45% insoluble, indicating a substantial spread of maturity. However, these indicators of maturity, and further classical maturity indicators such as the H/C and Tmax show surprisingly poor mutual agreement