Mohammed Boussafir

Electron microscopy and pyrolysis of kerogens from the Kimmeridge Clay Formation, UK: Source organisms, preservation processes, and origin of microcycles

Abstract Recent studies revealed short-term cyclic variations (microcycles) in total organic carbon (TOC) and the hydrogen index (HI) in the Kimmeridge Clay Formation, an organic-rich deposit considered to be a lateral equivalent of the main source rocks of the North Sea. In addition, three different types of organic matter that all appear to be amorphous when observed by light microscopy (AOM) were recognized. Together, these AOM types account for over 80% of total kerogen and their relative abundances show large variations along each microcycle. In the present work, transmission electron microscopy (TEM) observations were carried out on samples (whole kerogens, kerogen subfractions only comprising a single type of AOM, selected rock fragments) corresponding to typical points within a microcycle and obtained via high resolution sampling. The nature and the relative abundances of the products generated by Curie-point Py-GC-MS and off-line pyrolyses of isolated kerogens were also determined for two selected samples corresponding to the beginning and the top of the microcycle. Combination of such ultrastructural observations, including some semiquantitative studies, and the analysis of pyrolysis products allowed (1) determination of the ultrastructural features of the three AOM types thus providing what we believe to be the first example of correlations between light microscopy (palynofacies, in situ maceral analysis) and TEM observations on “amorphous” fossil materials; (2) identification of the source organisms and elucidation of the mode of formation of the different AOM types in the Kimmeridge Clay; (3) explanation of the variations in their relative abundances taking place along a microcycle and establishment of tight correlations with TOC and HI changes; and (4) explanation of the origin of the microcyclic variations in kerogen quantity (TOC) and quality (III) occurring in the Kimmeridge Clay Formation. Interrelationships between primary productivity, sulphate reduction intensity, and lipid “vulcanization” likely played a major role in the control of such variations.

Comparative study of organic matter preservation in immature sediments along the continental margins of Peru and Oman. Part I: Results of petrographical and bulk geochemical data

Abstract Detailed petrographical and bulk geochemical investigations of organic matter (OM) have been performed on sediments deposited below or close to upwelling areas offshore Peru (ODP-Leg 112; Sites 679, 681, 688) and Oman (ODP-Leg 117; Sites 720, 723, 724) in order to obtain a quantitative understanding of its accumulation and degradation. Microscopical as well as nanoscopical investigations reveal that the OM in sediments affected by upwelling mechanisms mainly (up to 98%) consists of unstructured (amorphous) organic aggregates without any apparent biological structures. In sediments which are not or to a lesser extent affected by upwelling (Site 720) terrestrial OM predominates. Organic carbon (TOC) contents are highly variable and range between 9.8% in sediments deposited below upwelling cells and 0.2% in sediments outside the upwelling zone. The TOC/sulphur ratios of the sediments scatter widely. The samples from the deep-water locations (Sites 688 and 720), show C S - ratios of “normal” marine sediments, whereas at the other locations no correlation or even a negative correlation between sulphur and TOC concentration exists. In most of the upwelling-influenced sediments OM contains a significant amount of sulphur. The incorporation of sulphur into the OM followed microbial sulphate reduction and occurred in the upper meters of the sedimentary column. Below, OM is still present in vast amounts and relatively hydrogen-rich, but is nevertheless non-metabolizable and becomes the limiting factor for bacterial sulphate reduction. According to mass balance calculations 90–99% of the OM produced in the photic zone was remineralized and 1–3% was consumed by microbial sulphate reduction. The aerobic and anaerobic processes have greatly affected degradation and conservation of OM.

Pyrobitumen occurrence and formation in a Cambro{Ordovician sandstone reservoir, Fahud Salt Basin, North Oman

The Cambro–Ordovician Barik Sandstone reservoirs in the Fahud Salt Basin in Oman contain bitumen which may fill up to 40% of the porosity. In well Jaleel-1, this bitumen was isolated (according to kerogen procedure) and typed by NMR, elemental analysis and density measurements. The isolated bitumen is characterized by: (1) a highly aromatic character (NMR 75% CAro, H/C atomic ratio: 0.65), (2) a very high sulphur content (4.2%) and (3) a relatively high density (1.3–1.4 g/cm3). The insolubility and the reflectivity of the bitumen (1.2% Vr) qualify it as a low mature pyrobitumen. The combination of Rock-Eval and density data was used to calculate the actual volume of the pyrobitumen in the rock, as a percentage of porosity. It was found that the pyrobitumen volume shows a negative correlation with total porosity, indicating that small pores are more invaded by bitumen than larger ones. Finally, closed system pyrolysis experiments, performed on oils with different NSO contents, indicate that an in situ oil with a very high content of NSO compounds is required to generate such large amounts of pyrobitumen in the pore system. These observations suggest that the precursor oil of the current pyrobitumen was a very heavy oil tentatively assumed to be the result of a severe biodegradation. Basin modeling shows that the reservoir was charged already in Devonian times. A major uplift brought the oil accumulation near the surface during the Carboniferous and a rather regular burial to the present day position (4500 m, 140°C) (Loosveld et al., 1996). This scenario, involving a residence time at shallow depth, strengthens the biodegradation hypothesis. The numerical modeling, which involves the IFP kinetic model for secondary oil cracking, suggests that pyrobitumen formation is a very recent event. Inclusion of pyrobitumen particles within quartz overgrowth, containing fluid inclusions, provides an upper temperature limit for the beginning of pyrobitumen formation which comforts the result of kinetic modelling.

Productivity-induced sulphur enrichment of hydrocarbon-rich sediments from the Kimmeridge Clay Formation.

This work aims to highlight the relationship between primary productivity, sulphate reduction and organic carbon preservation in cyclic marine sediments from the Kimmeridge Clay Formation. A concomitant increase of the total sulphur content with the preserved organic content (TOC), shows the progressive supply of both metabolisable organic matter and resistant organic matter is linked to primary productivity. However, variations in sulphate reduction efficiency, based on elemental abundance and isotopic composition of sulphur, reveal that the proportion of metabolisable vs. resistant organic matter has varied along the cycles. This is interpreted in terms of the variation in organic delivery. Organic sulphur content is found to be proportional to the organic matter content, whereas concentrations of pyritic sulphur are constant at very high (> 10% TOC) values. This result is explained by a limitation of available iron for pyritisation at times of very high organic flux. Under such conditions, HS- in excess could be responsible for the early formation of organo-sulphur compounds and thus for the preservation of highly aliphatic (i.e. lipid-rich) organic matter.

Adsorption Mechanisms of Emerging Micro-pollutants with a clay Mineral: Case of Tramadol and Doxepine Pharmaceutical Products

A sodium exchanged smectite clay mineral (Mt) was used as geo-sorbent for the adsorption of tramadol and doxepin: two pharmaceutical products (PPs) defined as emerging pollutants due to their presence at significant concentration in numerous water compartments. The adsorption isotherms for both the temperatures of 20 and 40°C and the derived data determined through the fitting procedure by using Langmuir, Freundlich and Dubinin-Radushkevich equation models explicitly pointed out that the sorption of both tramadol and doxepin is mainly driven by electrostatic interaction. The studied PPs are intercalated in a monolayer arrangement within the interlayer space through a cation exchange in stoichiometric proportion with the Na(+) cations leading to adsorbed PPs amounts that match the cation exchange capacity (CEC) of Mt. Due to their hydrophobic character, additional doxepin molecules could be adsorbed by weak molecular interaction driving to an increase of the adsorbed amount beyond the CEC at low temperature (20°C). The confinement of PPs within the interlayer space of Mt confirms the use of clay minerals as potential material for the wastewater treatment as well as it drives to an amorphous or glassy state, which can find echo in biopharmaceutical applications for a controlled release of PPs.

Evidence and effects of fluid circulation on organic matter in intramontane coalfields (Massif Central, France)

Abstract Recent evidence for a Late Carboniferous hydrothermal event responsible for Au–As mineralization within the Variscan belt of the French Massif Central adds a supplementary episode to the already rather complex thermal history of this area. To better understand this history, 45 coal samples from various sites in the Massif Central were studied petrographically (reflectance analysis) and geochemically (Rock-Eval pyrolysis). The results of this study suggest that the studied coal was buried to 1500 m and that the coalification took place within 25 Ma, probably ending at the boundary between the Early and Late Permian (marked by the Saalic orogeny). Two thermal end-members basins were identified: (i) the Carboniferous of Bosmoreau-les-Mines (Limousin) and West Graissessac (Montagne Noire) showing geothermal paleoflow values between 150 and 180 mW m −2 , and (ii) the Stephanian of Argentat and Detroit de Rodez (SW Massif Central) with values estimated at between 100 and 120 mW m −2 . By plotting the T max and R o values on a diagram, the samples were grouped into two populations, the first showing a positive correlation between R o and T max and the second with higher T max values than expected after R o values. Selected samples of the second group are also characterized by a high Oxygen Index (OI) that increases with T max . These divergence between R o and T max associated with a high OI may be the result of the circulation of slightly oxidizing hot fluids subsequent to coalification. The other kind of R o – T max divergence seems to be linked to local, particularly high thermal activity, especially in Graissessac and Bosmoreau basins. It is interpreted as being due to a difference in response of these two maturity indicators, respectively to the intensity and duration of the thermal events (e.g., short-lived hydrothermal circulation and thermal domes of regional extent).

Accumulation of organic matter in the Kimmeridge Clay formation (KCF): an update fossilisation model for marine petroleum source-rocks

Abstract A model for marine source-rocks based on previous microtextural and molecular characterisation of the immature organic matter from the KCF (UK) is developed, illustrating the relationship between the type of primary producers, the nature of organic matter (metabolisable or bioresistant) delivered to the sedimentary environment and the mechanisms of organic matter fossilisation. The fossilisation occurs because one of the following factors prevails: (a) The inherited bioresistant character of the initial organic matter in the case of (i) a selective preservation sensustricto when both the biological structure and the molecular composition are well preserved, and (ii) a re-organisation of resistant bio-macromolecules selectively preserved when only the molecular composition is conserved. (b) The acquisition of bioresistance, as in the case of (iii) natural vulcanisation, which produces a homogeneous and nanoscopically amorphous organic matter. The latter is hydrogen-rich and its genesis depends on the rate of delivery of metabolisable organic matter to the oxic-anoxic boundary. This is determined by primary productivity-controlled sinking rates and, as a consequence, by the occurrence in bottom waters of conditions promoting a prolific growth of sulphate-reducers along with a somewhat limited supply of iron so that H 2 S is not entirely trapped as pyrite. (c) The accumulation of hydrogen-rich organic matter in such source-rocks is not only due to the phytoplanktonic and micro-algal origin of natural bio-macromolecules, but also to sulphate-reduction which protects a part of the oil potential of deposited organic matter.

Enhancement of accumulation and anoxic degradation of organic matter controlled by cyclic productivity: a model

Abstract The aim of the study is to determine the relative influences of the genetic sources, the export efficiency, and the anaerobic degradation of organic carbon as factors controlling short-term cyclic organic-rich sedimentation in areas of high marine productivity. A cyclic organic sequence of the Kimmeridge Clay Formation of Yorkshire (U.K) was studied as an example of ancient sedimentation. This formation outcropping in the Cleveland basin near Marton is known as a lateral equivalent of the major oil source rock unit of the North Sea. On the basis of petrographic and geochemical results, a new model is proposed to explain the short-term cyclic sedimentation of organic carbon under continuously anoxic bottom conditions. The model assumes that the cyclicity is primarily controlled by variations of mineral-free phytoplanktonic productivity. Such variations are thought to induce changes in carbon recycling in the photic zone so that the export efficiency of the metabolizable organic matter is modified. A high sulphate reduction intensity relative to the organic matter flux is observed for the highest productivity periods, which also reflects an enhancement of export efficiency. As the redox conditions did not change significantly, such variations in sulphate reduction intensity must be attributed not only to quantitative variations in the export productivity, but also to its qualitative variations, with more metabolizable organic matter reaching the anoxic domain during high productivity periods. Biosedimentary processes depending on productivity, such as aggregation, are thought to play an important role in reducing the transit time of metabolizable organic matter to the sediment. Finally, the model implies that the amplitude of export productivity variations probably were larger than that of TOC variations recorded in sediment which are mainly due to biologically refractory organic matter from plankton.

Adsorption of diclofenac onto organoclays: Effects of surfactant and environmental (pH and temperature) conditions.

Among pharmaceutical products (PPs) recalcitrant to water treatments, diclofenac shows a high toxicity and remains at high concentration in natural aquatic environments. The aim of this study concerns the understanding of the adsorption mechanism of this anionic PP onto two organoclays prepared with two long-alkyl chains cationic surfactants showing different chemical nature for various experimental pH and temperature conditions. The experimental data obtained by a set of complementary techniques (X-ray diffraction, elemental analyses, gas chromatography coupled with mass spectrometry, and Fourier transform infrared spectroscopy) and the use of Langmuir, Freundlich and Dubinin-Radushkevish equation models, reveal that organoclays show a good affinity to diclofenac which is enhanced as the temperature is under 35°C and for pH above 4.5 (i.e. >pKa of diclofenac) while the chemical nature of surfactant appears to play a minor role. The thermodynamic parameters derived from the fitting procedure point out the strong electrostatic interaction with organic cations adsorbed within the interlayer space in the organoclays for the adsorption of diclofenac. This study stress out the application of organoclays for the adsorption of a recalcitrant PPs in numerous aquatic compartments that can be used as a complement with activated carbon for waste water treatment.

Clayey–sand filter for the removal of pharmaceuticals from wastewater effluent: percolation experiments

The objective of the study was to evaluate the sorption of a pool of pharmaceutically active compounds (PhACs) onto a clay–sand filter in a dynamic sorption experiment. The chosen adsorbent should have suitable chemical properties for the removal of the targeted PhACs and also a consistent hydrodynamic behavior regarding field application. In this aim, the impact of interfoliar cations (Ca2+ or Na+) intercalated into natural montmorillonite (Swy2) was tested by using different clay–sand ratios (from 0% to 100% of clay minerals). Only Ca-Swy2 showed a consistent hydraulic conductivity for field application with a value of 4.78 × 10−8 m s−1 for a 5%/95% clay–sand ratio. The sorption of PhACs onto this filter was investigated using œdometer cells by varying two parameters: the solution matrix (ultra-pure water or natural effluent) and the injection pressure (0.1 MPa and 0.2 MPa). The PhACs were effectively adsorbed onto the filter for each experiment at different levels. The drop in injection pressure was a favorable factor for sorption whatever the matrix was, with median global removal of ∼45% at 0.2 MPa and ∼75% at 0.1 MPa. The effect of the matrix exhibited two different trends as a function of the molecular charge of each PhAC. While cationic compounds were more effectively sorbed in the ultra-pure water matrix than in the effluent matrix, the sorption of anionic PhACs was more effective in the effluent matrix than in ultra-pure water. This indicates that the charge of the pollutant is a key parameter in controlling the efficiency of the adsorbent. Despite these removal variations, the filter exhibited a significant sorption capacity especially at 0.1 MPa. It can therefore be an efficient solution for the removal of PhACs by tertiary filtration.