First-principles study of illite-smectite and implications for clay mineral systems

Illite-smectite interstratified clay minerals are ubiquitous in sedimentary basins and they have been linked to the maturation, migration and trapping of hydrocarbons(1), rock cementation(2), evolution of porewater chemistry during diagenesis(3) and the development of pore pressure(4). But, despite the importance of these clays, their structures are controversial. Two competing models exist, each with profoundly different consequences for the understanding of diagenetic processes: model A views such interstratified clays as a stacking of layers identical to endmember illite and smectite layers, implying discrete and independently formed units (fundamental particles)(5), whereas model B views the clays as composed of crystallites with a unique structure that maintains coherency over much greater distances, in line with local charge balance about interlayers(6). Here we use first-principles density-functional theory to explore the energetics and structures of these two models for an illite-smectite interstratified clay mineral with a ratio of 1:1 and a Reichweite parameter of 1. We find that the total energy of model B is 2.3 kJ atom(-1) mol(-1) lower than that of model A, and that this energy difference can be traced to structural distortions in model A due to local charge imbalance. The greater stability of model B requires re-evaluation of the evolution of the smectite-to-illite sequence of clay minerals, including the nature of coexisting species, stability relations, growth mechanisms and the model of fundamental particles.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/62760/1/nature01155.pd

Dysphagia in Stroke: A New Solution

Dysphagia is extremely common following stroke, affecting 13%–94% of acute stroke sufferers. It is associated with respiratory complications, increased risk of aspiration pneumonia, nutritional compromise and dehydration, and detracts from quality of life. While many stroke survivors experience a rapid return to normal swallowing function, this does not always happen. Current dysphagia treatment in Australia focuses upon prevention of aspiration via diet and fluid modifications, compensatory manoeuvres and positional changes, and exercises to rehabilitate paretic muscles. This article discusses a newer adjunctive treatment modality, neuromuscular electrical stimulation (NMES), and reviews the available literature on its efficacy as a therapy for dysphagia with particular emphasis on its use as a treatment for dysphagia in stroke. There is a good theoretical basis to support the use of NMES as an adjunctive therapy in dysphagia and there would appear to be a great need for further well-designed studies to accurately determine the safety and efficacy of this technique

Sandstone Consolidation III Year End Report

Two areas of cap rock occurrence have been mapped, one in the upper Texas Coast and the other in South Texas. These may be related to ancient delta systems. Two high-resistivity zones have been identified in Brazoria County. The nature of the high-resistivity intervals remains enigmatic. Most of the carbonate they contain is microscopically and isotopically skeletal in origin. Few authigenic components have been identified. Isotopic data suggest minimal recycling of pore waters between shale and sandstone. Hydrolysis reactions and reactions between key pairs of minerals have been written. The goal is to plot formation waters on stability diagrams for these reaction pairs and to correlate log activity ratios with the presence or absence of cap rock and deep secondary porosity. Mineral compositions are based on microprobe data from earlier Sandstone Consolidation projects and new data collected in this project. Methods have been developed to estimate thermodynamic functions for most of these minerals at elevated temperatures. Methods differ depending on the mineral class and availability of published thermodynamic data.Bureau of Economic Geolog

Diagenetic smectite-to-illite transition in clay-rich sediments: A reappraisal of X-ray diffraction results using the multi-specimen method

International audienceSmectite illitization is a common mineralogical reaction occurring during the burial diagenesis of clay-rich sediments and shales, and has thus attracted sustained interest over the last fifty years. Prior studies have concluded that smectite illitization proceeds through a steady set of homogeneous reactions involving intermediate mixed layers of varying compositions. In these intermediate structures, illite and smectite, or, more generally, expandable layers (I and Exp layers, respectively) coexist among the same crystallites giving rise to non-periodic structures (I-Exp) characterized by specific diffraction effects. Consistent with this model, reaction progress was characterized by the simultaneous increase in the illite content in I-Exp and in their stacking order leading to the following mineralogical sequence: smectite → randomly interstratified I-Exp with high smectite contents (> 50% Exp layers) → ordered I-Exp with high illite contents (> 50% I layers) → illite. Although reaction mechanisms have been extensively debated, this structural characterization has not been challenged, possibly due to a methodological bias. In the present study, X-ray diffraction patterns typical of the diagenetic illitization of smectite are interpreted using modern approaches involving profile fitting (multi-specimen method). Novel insights into the structure of intermediate reaction products are thus obtained. In particular, original clay parageneses are described including the systematic presence of illite, kaolinite, chlorite and a mixed layer containing kaolinite and expandable layers (K-Exp). In contrast to previous descriptions, the early stages of smectite illitization are characterized by the coexistence of discrete smectite and of a randomly interstratified I-Exp with a high content of illite layers (>50% I layers). Both the smectite and the I-Exp are authigenic and form under shallow burial, that is at low temperature conditions. With increasing burial depth, the relative proportion of I-Exp increases, essentially at the expense of discrete smectite, and the composition of I-Exp becomes slightly more illitic. In the second stage of smectite illitization, two illite-containing mixed layers are observed. They result from two parallel reaction mechanisms affecting the randomly interstratified I-Exp present in the shallow section of the series. The first reaction implies the dissolution of this randomly interstratified I-Exp and leads to the crystallization of an ordered I-Exp without significant illitization, possibly because of the low K-availability. The second reaction affecting the randomly interstratified I-Exp implies the growth of trioctahedral (Mg, Al) hydroxide sheets in Exp interlayers, thus developing di-trioctahedral chlorite layers (Ch layers) in the initial I-Exp to form an I-Exp-Ch. A layer-by-layer mechanism is hypothesized for this reaction. In this scheme, Mg cations released by the dissolution-recrystallization reaction of I-Exp likely represent the source of Mg for the formation of brucite-like sheets in expandable interlayers, and thus of the I-Exp-Ch. The reported structural characterization of smectite illitization intermediate products contradicts the conventional wisdom of a homogeneous reaction through a series of pure mixed layers of variable composition. In contrast, the coexistence of different phases implies a heterogeneous reaction via a sequence of intermediate phases and requires reassessing the reaction mechanisms proposed in the literature. The compositional range (relative proportion of the different layer types) of these phases is limited and smectite illitization proceeds essentially as relative proportions of the different phases vary. In addition, reaction kinetics and stability of the different intermediate products also need to be reconsidered

Hydration Properties and Interlayer Organization of Water and Ions in Synthetic Na-Smectite with Tetrahedral Layer Charge. Part 1. Results from X-ray Diffraction Profile Modeling

International audienceThe dehydration of two Na-saturated synthetic saponites with contrasting layer charge was studied by modeling the X-ray diffraction (XRD) patterns recorded along a water vapor desorption isotherm. The interlayer configurations used to reproduce the XRD data over a large angular range include Na+ cations located in the interlayer midplane and H2O molecules normally distributed about one or two main positions for mono- and bihydrated layers, respectively. Although strongly reduced in comparison to natural smectites, hydration heterogeneity was systematically observed for these synthetic saponites, especially along the transition between two hydration states. Using improved models for the description of the interlayer organization, the influence of layer charge on the structure of interlayer water can be precisely assessed. In addition, the comparison with water contents obtained from water vapor gravimetry experiments allows discriminating the relative contributions of H2O molecules from 1W and 2W interlayers (crystalline water) and from the pore space network

Illite-smectite mixed-layer minerals in hydrothermal alteration of volcanic rocks: I. One-dimensional XRD structure analysis and characterisation of component layers.

International audienceFor a series of mixed-layer illite-smectite (I-S) minerals from a drill hole near the Kakkonda geothermal field, one-dimensional structure analysis by X-ray diffraction (XRD) was performed using Ca-saturated specimens at both air-dried and ethylene glycol solvated states. The expandability characteristics of component layers were also examined by means of alkylammonium exchange and Li-saturation. The K content in illite layer was almost constant at 1.5-1.7/O20(OH)4 in the I-S series from 3% to 85% of I-layer content (% I). The layer charge of smectite layer varied slightly within the ranges of R1 I-S samples showed complicated expandability with alkylammonium exchange. The XRD patterns of dodecylammonium exchanged I-S samples can be interpreted by random interstratification of several types of sub-units such as layer-doublets, layer-triplets and layer-quarutets present in the crystallites. This interpretation is consistent with the variation in the occurrence probabilities of layer-multiplets calculated from the junction probabilities and the proportions of layers. Because the interpretation indicates that I-S is a stack of various types of the sub-units, the smectite illitization can be described by a systematic change in the type and proportion of the sub-units constituting crystallites

Diagnosis and Management of Oropharyngeal Dysphagia and Its Nutritional and Respiratory Complications in the Elderly

Oropharyngeal dysphagia is a major complaint among older people. Dysphagia may cause two types of complications in these patients: (a) a decrease in the efficacy of deglutition leading to malnutrition and dehydration, (b) a decrease in deglutition safety, leading to tracheobronchial aspiration which results in aspiration pneumonia and can lead to death. Clinical screening methods should be used to identify older people with oropharyngeal dysphagia and to identify those patients who are at risk of aspiration. Videofluoroscopy (VFS) is the gold standard to study the oral and pharyngeal mechanisms of dysphagia in older patients. Up to 30% of older patients with dysphagia present aspiration—half of them without cough, and 45%, oropharyngeal residue; and 55% older patients with dysphagia are at risk of malnutrition. Treatment with dietetic changes in bolus volume and viscosity, as well as rehabilitation procedures can improve deglutition and prevent nutritional and respiratory complications in older patients. Diagnosis and management of oropharyngeal dysphagia need a multidisciplinary approach

Comparison of thermal maturation indicators within hydrocarbon bearing sedimentary rock

Master of ScienceGeologyMatthew W. TottenThe thermal maturity of hydrocarbon-rich source rocks can be estimated by several different methods. These methods focus on a specific geochemical or mineralogical aspect contained within the rock. Because each method has limitations, it is advisable to use several methods to better determine thermal maturation. This report summarizes two common methods used to determine thermal maturity, vitrinite reflectance and illitization. Vitrinite reflectance and illitization have both been shown to be effected by similar temperatures that are within the hydrocarbon generation window. In some previous studies these two methods give different levels of maturation when looked at in tandem. Formations such as the Woodford Shale of Oklahoma are made up almost completely of illite in the clay fraction, even at low levels of vitrinite reflectance. These are also without a clear source of potassium, which is often the limiting factor in the process of illitization. Totten et al. (2013) suggest that in place of potassium feldspars, which are a common source of K⁺ for illite (but lacking in the Woodford) that the needed K⁺ was provided by the organic material that was being altered under the same temperatures of the clay minerals. The Woodford contains large amounts of organic matter, This would be consistent with promoting illitization at lower thermal maturities than organic-poor shales

Active mud volcanoes on the continental slope of the Canadian Beaufort Sea

The major geochemical characteristics of Red Sea brine are summarized for 11 brine-filled deeps located along the central graben axis between 19°N and 27°N. The major element composition of the different brine pools is mainly controlled by variable mixing situations of halite-saturated solution (evaporite dissolution) with Red Sea deep water. The brine chemistry is also influenced by hydrothermal water/rock interaction, whereas magmatic and sedimentary rock reactions can be distinguished by boron, lithium, and magnesium/calcium chemistry. Moreover, hydrocarbon chemistry (concentrations and δ 13 C data) of brine indicates variable injection of light hydrocarbons from organic source rocks and strong secondary (bacterial or thermogenic) degradation processes. A simple statistical cluster analysis approach was selected to look for similarities in brine chemistry and to classify the various brine pools, as the measured chemical brine compositions show remarkably strong concentration variations for some elements. The cluster analysis indicates two main classes of brine. Type I brine chemistry (Oceanographer and Kebrit Deeps) is controlled by evaporite dissolution and contributions from sediment alteration. The Type II brine (Suakin, Port Sudan, Erba, Albatross, Discovery, Atlantis II, Nereus, Shaban, and Conrad Deeps) is influenced by variable contributions from volcanic/ magmatic rock alteration. The chemical brine classification can be correlated with the sedimentary and tectonic setting of the related depressions. Type I brine-filled deeps are located slightly off-axis from the central Red Sea graben. A typical " collapse structure formation " which has been defined for the Kebrit Deep by evaluating seismic and geomorphological data probably corresponds to our Type I brine. Type II brine located in depressions in the northern Red Sea (i.e., Conrad and Shaban Deeps) could be correlated to " volcanic intrusion-/extrusion-related " deep formation. The chemical indications for hydrothermal influence on Conrad and Shaban Deep brine can be related to brines from the multi-deeps region in the central Red Sea, where volcanic/magmatic fluid/rock interaction is most obvious. The strongest hydrothermal influence is observed in Atlantis II brine (central multi-deeps region), which is also the hottest Red Sea brine body in 2011 (*68.2 °C)

Petrology and burial diagenesis of Plio-Pleistocene sediments, northern Gulf of Mexico

Plio-Pleistocene sediments and rocks beneath the Louisiana and adjacent Texas shelves are the youngest of several thick packages of terrigenous sediment which prograded into the Gulf of Mexico during the Cenozoic. Comparison of diagenesis in these young sediments (more than 300 samples from 45 wells on the Louisiana-Texas shelf) to diagenesis of older Cenozoic rocks at similar burial depths elsewhere along the Gulf margin confirms that diagenesis is not strictly analogous among the various Cenozoic units. There has been an evolution of diagenesis during filling of the Gulf of Mexico. Differences in diagenesis cannot be attributed to differences in bulk mineralogy of the sands because PIio-Pleistocene sands are lithic arkoses and feldspathic litharenites with essentially the same QFR proportions as observed in subsurface Eocene and Oligocene sandstones along the Texas coast. Unaltered plagioclase is slightly more calcic (average An 24) than unaltered plagioclase in the older rocks. Burial diagenesis in Plio-Pleistocene sediments has involved essentially the same processes as observed in the older rocks, but overall, diagenesis has advanced to a lesser degree at any given depth. Cementation by quartz and carbonate, dissolution of potassium-feldspar and heavy minerals, albitization of plagioclase, and the transformation of smectite to illite have occurred in Plio-Pleistocene sediments, but cements and altered grains are not volumetrically significant shallower than 4 to 4.5 km. The temperature at which reaction of detrital constituents begins (approximately 90° C) is similar to that observed elsewhere in the Gulf, but the zone of reaction is spread over a greater depth range. The similar temperatures observed for the advent of detrital reactions across the Gulf basin suggest that these processes are more highly dependent upon temperature than upon time and that differences observed among the various units may be attributed, at least in part, to variations in the geothermal gradient. The degree of detrital grain alteration observed in these young sediments shows that significant loss of provenance information occurs quite early in the burial history. Alteration in the deep subsurface is very effective in modifying the primary detrital assemblage.Geological Science