Clay-rich Materials Research Articles

Geophysical mapping of gypsum for exploration of reserves in the Nong Bua area of Thailand

The increasing demand for gypsum as a raw material for construction projects motivates exploration for additional reserves. Electrical resistivity tomography (ERT) and seismic refraction geophysical methods, augmented with borehole and laboratory measurements on core samples, are used here to delineate the top, bottom and lateral boundaries of an important gypsum ore deposit in Thailand, an economically developing region. The gypsum-bearing formation is found throughout the study area to have an irregular upper boundary on account of karstic dissolution processes. The deeper transition from gypsum to anhydrite, however, is not constrained by the measurements. The P-wave velocity measured in the field is consistent with the core specimen measurements. The electrical resistivity of the core specimens, however, is substantially higher than the values measured in the field. The specimen measurements may depend on the presence of micro cracks, whereas electrical resistivity in the field may be affected by the enclosing clay-rich materials.

Potentiality of new dark clay-rich materials for porous ceramic applications in Ouled Sidi Ali Ben Youssef Area (Coastal Meseta, Morocco)

Potential use of raw clayey deposits from El Jadida, Morocco, in the manufacture of traditional ceramic products has been evaluated through a careful sampling and an in-depth characterization of the outcropping features around Ouled Sidi Ali Ben Youssef area (El Jadida city). We collected six representative clay-rich materials (C1–C6) for subsequent analyses by several spectroscopic and mineralogical techniques including physico-chemical, mineralogical, and thermal analyses. Our results revealed high amounts of oxides, mainly SiO2, Al2O3, Fe2O3, CaO and MgO. Those ferruginous clays were found suitable for dark ceramic bodies. Further mineralogical examination confirmed low to medium contents of clay minerals, but subordinated by quartz, calcite, dolomite and plagioclase as the main nonclay minerals. Ternary diagram plots indicated that the studied clays were suitable for structural clay products and clay roofing tiles. C5 sample exhibited the best physico-chemical and mineralogical properties due to its illitic nature (64%), low quartz content (28%), high plasticity index (32) and lower loss on ignition (10.84%). Therefore, C5 clayey sample was selected as a potential candidate to be mixed with expanded perlite (EP) for the production of insulating ceramics. Specimen were prepared from the new mixture (i.e., C5 and EP) by pressing and firing at 1100°C. The obtained ceramic bodies were ascertained by addressing their bulk density, water absorption, shrinkage, bending strength, thermal conductivity, structural and mineralogical properties.

Serpentinization and H2 production during an iron-clay interaction experiment at 90C under low CO2 pressure

Interactions between steel canisters and clay-rich material in deep geological repositories for high-level nuclear waste were studied by reacting metallic iron and a claystone from the Callovo-Oxfordian formation of the Paris Basin (COx). The experiment ran at 90 °C for 14 weeks in the presence of water and under 20 mbar of initial CO2 partial pressure (p(CO2)). At the end of the experiment, the pressure in the autoclave reached 50 bar due to H2 production. Water was almost entirely consumed and poorly crystallized 7 Å-greenalite-type clays were formed at the expense of illite and mixed-layered illite-smectite minerals (I/S). The dissolution of quartz and pyrite and the crystallization of pyrrhotite were also observed. Considering the results of Mössbauer and Fourier Transformed Infrared (FTIR) spectroscopies, iron carbonate and and/or ferrous hydroxycarbonate were suspected to precipitate but in very small amounts. A follow-up of the mineralogical evolution by XRD (X-ray diffraction), SEM (Scanning Electron Microscopy) and TEM (Transmission Electron Microscopy) shows that serpentinization of clays (formation of greenalite) is accompanied by a significant consumption of water and the production of H2 gas due to the oxidation and dissolution of metallic iron. Experimental results are in good agreement with geochemical modelling with the PHREEQC code. The kinetics of the iron corrosion was evaluated from H2 production and shows that diffusion processes are the rate limiting step.

Integrated geophysical, sedimentological and geotechnical investigation of submarine landslides in the Gulf of Lions (Western Mediterranean)

Abstract The Gulf of Lions presents recurring mass-transport deposits (MTDs) within the Plio-Quaternary sediments, suggesting a long history of mass movements. The two large, surficial MTDs are located on the eastern and western levee of the Rhone canyon over an area exceeding 6000 km 2 and volumes exceeding 100 km 3 . Both MTDs were emplaced 21 ka ago (peak of the Last Glacial Maximum), suggesting a common trigger. Here, we present a multidisciplinary high-resolution geophysical, sedimentological and in-situ geotechnical study of the source and deposit areas of both MTDs to characterize distinct expressions of sediment deformation as well as their spatial and chronological distributions. We show the internal structure of mass movements and resulting MTDs with unprecedented details that were previously represented in the conventional seismic data as transparent and chaotic facies. The combination of multidisciplinary approaches shows new insights into the nature of basal surfaces of the slope failures. In particular, we show that the basal surfaces of the failures consist of clay-rich material contrasting with the overlying turbiditic deposits, suggesting that a strong lithological heterogeneity exists within the strata. We suggest that this change in lithology between clay-rich sediments and turbiditic sequences most likely controls the localization of weak layers and landslide basal surfaces.

The impact of the submarine volcano Kick ‘em Jenny on benthic foraminifera

Nothing is known about the impact on marine meiofauna of submarine volcanic eruptions in the Grenada Basin. The benthic foraminiferal fauna is here examined in piston cores taken within ∼8 – 38 km of the crater of Kick ‘em Jenny (KeJ), decadal eruptions of which disseminate ash to the NW via the Caribbean Current. Piston core Gs29, taken ∼8 km W of the crater, consists of clay-rich material from the Globorotalia menardii Zone U, ∼500 ka old, probably exposed by slumping. The remaining cores (from proximal to distal: GC59, GC90, GC99 and GC100), taken between 1000 – 3000 m water depth, comprise volcanic ash and are of presumed Holocene age. Recovery from GC59, GC90 and GC99, the last taken 27.3 km NW of the crater, was poor and apparently reflects volcanic ash impact. Recovery from GC100, 38 km NW of the crater and from the basin floor, was rich. Thus, KeJ disrupts seafloor colonization by foraminifera up to 32 – 38 km from the crater. Bolivina spp., indicative of low dissolved oxygen concentrations, dominated the assemblage in proximal core Gs29. Cassidulina spp. dominated the distal core GC100 assemblage, indicating somewhat higher dissolved oxygen concentrations. This might reflect a long-term change in productivity in the area, or a nutrient-rich surface eddy to the lee of Grenada. Allochthonous, shallow-water foraminifera, recovered throughout cores Gs29 and GC100, were more abundant in the latter. This might indicate that Grenada protects nearshore foraminifera from disruptive hurricanes.

Preliminary Gravity Study of Pre-Tertiary and Tertiary Rock in Northern Kebumen, Central Java, Indonesia

Luk Ulo Melange Complex is a Pre-Tertiary rock formation consisting of various lithological background and complicated geological structure. Located in Northern Kebumen Regency, this rock is originally interpreted as products of tectonic process caused by paleo-subduction between Indian Oceanic Plate beneath Eurasian Plate in Cretaceous age. According to previous study on geological surface investigation shows that the melange complex is tectonically overlain by Tertiary sedimentary formation. On the contrary, geophysical study of the subsurface condition of the area is still under discussion due to limited of measured data. In order to obtain detailed subsurface image, gravity profiling was measured and interpreted across both Tertiary and pre-Tertiary rock. Frequency domain filter and designed moving average filter were used to separate residual and regional anomaly. The results denote gravity value of residual anomaly varying from -5 to +5 mGal, while regional anomaly is ranging from 150-180 mGal respectively. The preliminary interpretation was developed by taking into account the geological information and also the data that was collected during field campaign. Overall, high gravity anomaly is interpreted as diabase intrusion in the middle of research area. Meanwhile, low gravity anomaly indicated clay rich rock material related to matrix content of Luk-Ulo Melange Complex in the northern area.

A Preliminary Investigation on the Role of Brittle Fracture in the Kinematics of the 2014 San Leo Landslide

The stability of high rock slopes is largely controlled by the location and orientation of geological features, such as faults, folds, joints, and bedding planes, which can induce structurally controlled slope instability. Under certain conditions, slope kinematics may vary with time, as propagation of existing fractures due to brittle failure may allow development of fully persistent release surfaces. In this paper, the progressive accumulation of brittle damage that occurred prior to and during the 2014 San Leo landslide (northern Italy) is investigated using a synthetic rock mass (SRM) approach. Mapping of brittle fractures, rock bridge failures, and major structures is undertaken using terrestrial laser scanning, photogrammetry, and high-resolution photography. Numerical analyses are conducted to investigate the role of intact rock fracturing on the evolution of kinematic freedom using the two-dimensional Finite-discrete element method (FDEM) code Elfen, and the three-dimensional lattice-spring scheme code Slope Model. Numerical analyses show that the gradual erosion of clay-rich material below the base of the plateau drives the brittle propagation of fractures within the rock mass, until a fully persistent, subvertical rupture surface form, causing toppling of fault-bounded rock columns. This study clearly highlights the potential role of intact rock fracturing on the slope kinematics, and the interaction between intact rock strength, structural geology, and slope morphology.

Permeability of Clays and Shales

The low permeability of clays, shales, and other argillaceous lithologies makes them key controls of transport and deformation processes in the crust but is known for being challenging to characterize. As muds are modified by compaction and diagenesis to low-porosity shales, permeability can decrease by six or more orders of magnitude, but at large scales it is often dramatically and unpredictably increased by fractures, faults, and other features. Testing and inverse modeling show that petrophysical properties and the geological environment are dominant controls of clay and shale matrix permeability and its scale dependence. Active sedimentation and tectonism on continental margins cause large-scale permeability to vary with time, but in stable continent interiors it is unclear how regional permeability of argillaceous formations changes over time or, in most cases, what controls it. Although rarely considered, it is also unknown whether Darcian permeability adequately describes flow in clay-rich materials. ▪ Critical for problems in energy, water supply, waste isolation, and geologic hazards, clay and shale permeability remains problematic. ▪ Test data and inverse model analyses are beginning to reveal where and how permeability of clay and shale changes with scale. ▪ In clays and shales, causes of permeability scale effects, their time dependence, and even flow behavior continue to raise questions.

Plus \xe7a change: pots, crucibles and the development of metallurgy in Chalcolithic Las Pilas (Moj\xe1car, Spain)

This paper considers the structure of production, distribution and consumption of ceramics within Chalcolithic communities of SE Iberia, an important region for modelling social and technological change in the recent prehistory of Eurasia. Our research provides new data through the comparative analysis of domestic and metallurgical ceramics, as well as building and other clay-rich materials from the archaeological site of Las Pilas (2875–2620 cal. BC 2σ to 2460–2205 cal. BC 2σ) (Mojácar, Almería). In total, 56 samples are characterised by optical petrography, with SEM analysis of 22 of those individuals, in order to assess firing conditions. Results point to the existence of a local tradition in which domestic and metallurgical wares exhibit important similarities in their production processes. In terms of technology, the assemblage shows a relative homogeneity, although firing conditions, surface treatment and decoration seem to have played an important role in the differentiation of highly symbolic wares from other ceramics. We conclude that raw material procurement and processing at Las Pilas differ from those at other Copper Age sites already studied in SE and SW Iberia. This is in agreement with earlier archaeometallurgical studies on Las Pilas, suggesting the development of local and community-based technological traditions. As such, the paper attempts to bridge the recent divide between re-emergent top-down models and our detailed understandings of technological practice.

CEC input to evaluate the butyl diammonium dichloride as a swelling reducer in clay rich material

Previous research suggest that repeated swelling of the clay minerals involve differential strain during wetting and drying cycles which may induce decay under a fatigue of the clay rich material. Scaling due to this process has been observed on some stone binding clay but also on earthen material used in architecture. Since recent years, research on the conservation of clay-rich sandstones lead to the development of bifunctional cationic surfactants as swelling reducers for sandstones with high hygric and hydric dilatation. In this paper, the butyl diammonium dichloride surfactant was experimented on earthen material to reduce important hygric dilatation which leads to fast and important decay of earthen material. It has been directly added into the clay mixture of molded adobe brick that was to be physically and mechanically tested. The aim is to further investigate the interaction of the surfactant with clay minerals. Series of experiments showed great impact on various physical-mechanical properties of the molded earthen mixtures. Some could have been expected according to the function of the surfactant, which is to block the micropores within the clay mineral structures, responsible for the swelling. Thus, the decrease of the specific surface area as well as the hygric dilatation is understandable. However, according to the concentration of surfactant used within the adobe mixture, other properties are also affected such as the ultrasonic velocity, the water uptake coefficient, the hydric shrinkage and the compressive strength. Therefore this paper underlines important influences in changes of properties of molded adobe according to the concentration of surfactant used, and the cation exchange capacity of the material. The paper will show a new approach consisting in adapting the concentration of surfactant as a function of cation exchange capacity (CEC) of the material.

Vegetation growth and sediment dynamics in a created freshwater wetland

Understanding how the hydrological regime in relation to sediment type interferes with ecosystem development is important when wetlands are created with soft muddy material. Especially when plants are used as ecological engineers to promote crest stability and soil formation. We carried out a two-year mesocosm experiment with sediments derived from the Dutch lake Markermeer to identify the effects of the hydrological regime and sediment type on ecosystem functioning in terms of nutrient availability. We measured plant productivity, plant nutrient stoichiometry, and concentrations of N, P, and K in shoots and roots of Phragmites australis and Rumex maritimus and monitored how the clay-rich sediment from lake Markermeer changed into a wetland soil. Plants grown on Markermeer sediments tend to be N limited when periodically inundated and P limited when not inundated at all. The P availability was determined by the hydrological regime, while the N availability was determined by both the hydrological regime and the sediment type. Ecosystem development on created wetlands can be manipulated by adequate management of the hydrological regime, as plant species respond differently to changes in nutrient availability. This should be considered in eco-engineering projects where plants are used as ecological engineers to fasten ecosystem development on wetlands that are to be created from clay-rich material.

Influencia de las materias primas y de la técnica de moldeo en la fabricación de productos cerámicos tipo gres

Se empleó material arcilloso y caliza proveniente de minas cercanas a la zona metropolitana de Cúcuta, así como el material de rotura después del proceso de cocción de productos cerámicos (chamota) para la conformación de probetas de baldosas cerámicas mediante las técnicas de extrusión y prensado. Una vez realizado el proceso cerámico (con temperaturas de cocción entre 1050°C y 1250°C), se evaluó el efecto de las diferentes mezclas preparadas sobre las propiedades tecnológicas de resistencia mecánica a la flexión, abrasión profunda y porcenta­je de absorción de agua de acuerdo a la norma técnica colombiana. Los productos cocidos fueron caracterizados mediante difracción de rayos X, fluorescencia de rayos X y microscopía electrónica de barrido a fin de evidenciar efectos causados por las materias primas y el tipo de moldeo empleado. Los resultados obtenidos dejan ver la existencia de un efecto de la composición mineralógica de las muestras y de la técnica de conformado sobre la propiedades tecnológicas analizadas al momento de elaborar cerámicos gresificados. Se evidenció que para las mezclas de materias primas utilizadas, la técnica de extrusión permite una más rápida formación de fase vítrea y contribuye a una recristalización más rápida en altas temperaturas. Los mejores valores para las propiedades tecnológicas analizadas fueron encontrados en la temperatura de 1150°C.

Application of the Rietveld Method in the Reynolds Cup Contest

AbstractThe Reynolds Cup (RC) is a unique round-robin competition that was established by The Clay Minerals Society in 2000 to assess the level of precision and accuracy that is attainable for the mineralogical analysis of a wide range of complex clay-rich materials. Although the Reynolds Cup roundrobin allows any possible analysis methods, X-ray diffraction (XRD) is by far the most frequently used technique. It is not only used to identify components, but also for quantitative phase analysis (QPA). QPA means determination of the relative concentrations of the coexisting phases in a mixture, commonly as a weight percent (wt.%) or mass fraction. Several approaches allow a quantitative determination of mineral contents, such as the Rietveld method (Rietveld, 1967). The successful application of the Rietveld method for QPA requires that all components are correctly identified and that the component diffraction patterns are appropriately described, which is preferably based on structure. In addition, the quality of a Rietveld quantification also depends on suitable sample preparation and measurement conditions, as well as a correct description of instrument configurations. Results from all previous Reynolds Cup contests show that a successful quantification depends strongly on the skill of users. Although the refinement procedure itself is automatic and, therefore, user independent, the results are strongly influenced by the structural models and refinable parameters that are selected and on the limitations of those parameters. Selected examples for the successful application of Rietveld refinement as well as the limitations of the method will be discussed in this article. The goal of the present work was to demonstrate that the Rietveld method is in principle capable of quantifying all Reynolds Cup samples with a high degree of accuracy, but sample specific difficulties and analysts’ inexperience may impede successful application. Incorrect results are often not indicated simply by low residuals or good fits. All refinement results should be validated and corrected using supplementary techniques, even if the results appear acceptable.

Gas transport properties through intact and fractured Callovo-Oxfordian mudstones

Abstract A series of controlled water and gas experiments was undertaken on samples of Callovo-Oxfordian (COx) mudstone using a synthetic fluid and helium gas. Data from this study demonstrate that the advective movement of gas through COx is accompanied by dilation of the original fabric (i.e. the formation of pressure-induced microfissures) at gas pressures significantly below that of the minimum principal stress. Flow occurs through a local network of unstable pathways, the properties of which vary temporally and spatially within the mudstone. The coupling of variables results in the development of significant time-dependent effects affecting many aspects of COx behaviour, from the gas breakthrough time to the control of deformation processes. Variations in gas entry, breakthrough and steady-state pressures may result from the arbitrary nature of the flow pathways and/or microstructural heterogeneity. Under these conditions, the data suggest that gas flow is along pressure-induced preferential pathways, where permeability is a dependent variable related to the number, width and aperture distributions of these features. This has important implications for modelling gas migration through low permeability, clay-rich materials.

Characteristics of clay-rich raw materials for ceramic applications in Denizli region (Western Anatolia)

This study focuses on the evaluation of the potential use of the clay-rich raw materials in Denizli region to manufacture traditional ceramic products with industrial processing and determination of the provenance of archaeological ceramics. For this context, physical, chemical (X-ray fluorescence, XRF), mineralogical (X-ray diffraction, XRD), and thermal analysis (Differential Thermal Analyser-Thermogravimetry, DTA-TG) were performed and plasticity indexes (PI) were determined on the five representative clay-rich materials from three different locations (Yenicekent, Başkarcı and Pamukkale) in Denizli region. Samples have been prepared by pressing and firing in the range of 700–1200°C, then bulk density (BD), water absorption (WA), and unconfined compression strength (UCS) values of the samples were determined. Highly plastic clays were mainly composed of illite, smectite, kaolinite and mixed-layered clay minerals. Quartz, calcite, dolomite and hematite were also detected as non-clay minerals. Chemical composition of the clay samples without carbonate minerals indicated that the main oxide compositions were SiO2, Fe2O3 and Al2O3 whereas other oxides were present only in small quantities. Fired clays exhibited no major differences in BD and WA (except TR1). UCS values of all samples increased with rising firing temperatures. All technological properties showed significant densification at temperatures above 1000°C. One of the studied clay-rich materials (TR3) has comparable characteristics for the production of structural ceramics as references sample (KRC). Furthermore, this sample could be a potential raw material source for the archeological ceramics in the region. In order to use TR2 sample it is necessary to add more plastic clays to enhance its workability, but other clays are not appropriate for such products.

Wetland eco-engineering: measuring and modeling feedbacks of oxidation processes between plants and clay-rich material

Abstract. Interest is growing in using soft sediment as a foundation in eco-engineering projects. Wetland construction in the Dutch lake Markermeer is an example: here, dredging some of the clay-rich lake-bed sediment and using it to construct wetland will soon begin. Natural processes will be utilized during and after construction to accelerate ecosystem development. Knowing that plants can eco-engineer their environment via positive or negative biogeochemical plant–soil feedbacks, we conducted a 6-month greenhouse experiment to identify the key biogeochemical processes in the mud when Phragmites australis is used as an eco-engineering species. We applied inverse biogeochemical modeling to link observed changes in pore water composition to biogeochemical processes. Two months after transplantation we observed reduced plant growth and shriveling and yellowing of foliage. The N : P ratios of the plant tissue were low, and these were affected not by hampered uptake of N but by enhanced uptake of P. Subsequent analyses revealed high Fe concentrations in the leaves and roots. Sulfate concentrations rose drastically in our experiment due to pyrite oxidation; as reduction of sulfate will decouple Fe-P in reducing conditions, we argue that plant-induced iron toxicity hampered plant growth, forming a negative feedback loop, while simultaneously there was a positive feedback loop, as iron toxicity promotes P mobilization as a result of reduced conditions through root death, thereby stimulating plant growth and regeneration. Given these two feedback mechanisms, we propose the use of Fe-tolerant species rather than species that thrive in N-limited conditions. The results presented in this study demonstrate the importance of studying the biogeochemical properties of the situated sediment and the feedback mechanisms between plant and soil prior to finalizing the design of the eco-engineering project.

Fibrous clay mineral authigenesis induced by fluid-rock interaction in the Galera fault zone (Betic Cordillera, SE Spain) and its influence on fault gouge frictional properties

This study presents a mineralogical and mechanical analysis of the clay-rich materials and structures identified in the Galera Fault Zone, southern Spain that formed as a consequence of active deformation processes affecting this seismically active region. Significant differences in clay mineral assemblages and chemical composition were identified in rocks from the Galera Fault Zone, through a series of analytical techniques including XRD, SEM, TEM and XRF. Three distinct mineral assemblages were identified: 1) wall-rock assemblages including white marls and dark lutite layers, with the latter also found in injection features. Their assemblage includes dolomite, gypsum, quartz, calcite and phyllosilicates 2) smectite- and palygorskite-rich fault gouges formed on materials from the upper part of the stratigraphic sequence at the NE area of the fault (Galera Village), and 3) sepiolite-rich gouges in areas of the lower part of the stratigraphic sequence at the central SW segment of the fault (Rambla de los Pilares). Fibrous clay-rich gouges were formed by hydrothermal alteration during periods of fluid-rock interaction that was concentrated in fault planes and fractures. Their mineralogy is dominated by authigenic Mg-rich fibrous clay minerals; sepiolite, precipitated directly from an Mg-rich fluid; and palygorskite as the product of the interaction of the fluid with the Al-rich host rock. Experimental data from frictional sliding experiments on these clay-rich fault gouges reveal strong differences in their mechanical properties. Towards the north-eastern areas of the fault, the smectite- and palygorskite-rich gouge has a low friction coefficient (0.17 wet and 0.59 under vacuum) and its values of the friction stability parameter (a–b) are always positive indicating a stable regime that could be related with creeping and stable-sliding processes. In the central-south-western segment, however, the gouge is rich in authigenic sepiolite and presents complete absence of smectite. The higher friction coefficient (0.47 wet and 0.68 under vacuum) and negative values of a–b for this gouge suggest a more neutral to unstable regime that could favour earthquake nucleation.

Induced polarization response of porous media with metallic particles — Part 4: Detection of metallic and nonmetallic targets in time-domain induced polarization tomography

Time-domain induced polarization (TDIP) is a nonintrusive imaging technique of the subsurface that can be used to localize polarizable bodies including metallic objects and clay-rich materials. We first reviewed recent advances in the interpretation of induced polarization data. Then, we performed laboratory and sandbox experiments to determine the frequency-domain and TDIP signature of (1) a metal bar in sand, (2) dispersed semiconductors (e.g., pyrite) in sand, and (3) bentonite. In the case of the sandbox experiments, the three types of bodies were localized in the center of the sandbox, which was filled with water-saturated sand. We determined that chargeability was the best parameter to characterize metallic bodies (the metallic bar and the dispersed pyrite), whereas normalized chargeability was the best parameter to characterize the cation exchange capacity and therefore the clay content of the subsurface at a given clay mineralogy. For interpretation purposes, it was therefore important to display the right parameters in TDIP depending on the type of target we wanted to image for engineering applications.

The visualization of flow paths in experimental studies of clay-rich materials

AbstractOne of the most challenging aspects of understanding the flow of gas and water during testing in clay-rich low-permeability materials is the difficulty in visualizing localized flow. Whilst understanding has been increased using X-ray Computed-tomography (CT) scanning, synchrotron X-ray imaging and Nuclear Magnetic Resonance (NMR) imaging, real-time testing is problematic under realistic in situ conditions confining pressures, which require steel pressure vessels. These methods tend not to have the nano-metre scale resolution necessary for clay mineral visualization, and are generally not compatible with the long duration necessary to investigate flow in such materials. Therefore other methods are necessary to visualize flow paths during post-mortem analysis of test samples. Several methodologies have been established at the British Geological Survey (BGS), in order to visualize flow paths both directly and indirectly. These include: (1) the injection of fluorescein-stained water or deuterium oxide; (2) the introduction of nanoparticles that are transported by carrier gas; (3) the use of radiologically tagged gas; and (4) the development of apparatus for the direct visualization of clay. These methodologies have greatly increased our understanding of the transport of water and gas through intact and fractured clay-rich materials. The body of evidence for gas transport through the formation of dilatant pathways is now considerable. This study presents observations using a new apparatus to directly visualize the flow of gas in a kaolinite paste. The results presented provide an insight into the flow of gas in clay-rich rocks. The flow of gas through dilatant pathways has been shown in a number of argillaceous materials (Angeli et al., 2009; Autio et al., 2006; Cuss et al., 2014; Harrington et al., 2012). These pathways are pressure induced and an increase in gas pressure leads to the dilation of pathways. Once the gas breakthrough occurs, pressure decreases and pathways begin to close. This new approach is providing a unique insight into the complex processes involved during the onset, development and closure of these dilatant gas pathways.

Role of the texture of fibrous clay minerals in the plasticity behavior of host materials (Plateau du Kik, Western High Atlas, Morocco)

Seven samples (MB2 to MB8) collected from the clays and silty clays formations belonging to the Paleogene sedimentary series of the Plateau du Kik (Western High Atlas, Morocco) were characterized for granulometric analysis, mineral composition, clay composition and textures and for Atterberg limits. All the studied samples are classified as MH–OH type soils according to the ASTM international standard. Palygorskite usually constitutes the more abundant mineral phase in all the samples (35 to 64). The liquid limit for the most samples is well above 50 indicating the highly plastic nature of the studied sediment. This work clearly evidences that fibrous clay rich clayey materials having similar grain distribution and identical mineral composition and contents can have very different plasticity behaviors. This suggests that the fibrous clay textures play a role of prime importance in the plasticity behavior of the studied materials.