bluuebunny/crossref_metadata_2025_split huggingface dataset:
Transmission and Analytical Electron Microscopy of the Smectite-To-Illite Transition
Authors: Ahn Juno Ho , Peacor Donald R. 
Published: September 2006

AbstractThe smectite to illite reaction was studied by transmission and analytical electron microscopy (TEM/AEM) in argillaceous sediments from depths of 1750, 2450, and 5500 m in a Gulf Coast well. Smectite was texturally characterized as having wavy 10- to 13-Å layers with a high density of edge-dislocations, and illite, as having relatively defect-free straight 10-Å layers. The structures of smectite and illite were not continuous parallel to (001) at smectite-illite interfaces. AEM data showed that the smectite and illite were chemically distinct although smectite had a more variable composition. Illite formation appeared to have initiated with the growth of small packets of illite layers within subparallel layers of smectite matrix. With increasing depth, ubiquitous thin packets of illite layers increased in size until they coalesced.A model for the transition requires that the structure of smectite was largely disrupted at the illite-smectite interface and reconstituted as illite, with concomitant changes in the chemistry of octahedral and tetrahedral sites. At least partial Na-K exchange of smectite preceded illite formation. Transport of reactants (K, Al) and products (Na, Si, Fe, Mg, H20) through the surrounding smectite matrix may have taken place along dislocations.The smectite-to-illite conversion process for the studied samples does not necessarily appear to have required mixed-layer illite/smectite as an intermediate phase, and TEM and AEM data from unexpanded samples were found to be incompatible with the existence of mixed-layer illite/smectite in specimens whose XRD patterns indicated its presence.
The Polymer Model of Thermochemical Clay Mineral Stability
Authors: Sposito Garrison 
Published: September 2006

AbstractThe Nriagu polymer model of 2:1 layer type clay minerals develops from the premise that clay minerals are condensation copolymers of solid hydroxides. In the Mattigod-Sposito formulation of the model, standard state chemical potentials (standard Gibbs energies of formation from the elements) of 2:1 clay minerals are predicted quantitatively with a linear correlation equation relating the standard Gibbs energy of the polymerization reaction (ΔGor) to the half-cell layer charge of the clay mineral and to the valence and ionic radius of the exchangeable cation. It is now shown that this correlation equation can be derived from two basic assumptions: (1) that the standard Gibbs energy change for the transfer of a cation in a pure hydroxide solid to a hydroxide component in the tetrahedral or octahedral sheet of a 2:1 clay mineral is independent of the nature of the cation and (2) that the difference between ΔGor for the polymerization reaction to form a 2:1 clay mineral and ΔGor for the same reaction to form the zero layer-charge analog of the clay mineral is proportional to the number of interlayer exchangeable cations per unit cell of the clay mineral and to the radius of its exchangeable cation. Both of these assumptions can be tested experimentally, independent of the polymer model.
Quantitative Determination of Aluminum-Substituted Goethite-Hematite Mixtures By Mössbauer Spectroscopy
Authors: Amarasiriwardena D. D. , DeGrave E. , Bowen L. H. , Weed S. B. 
Published: September 2006

AbstractMixtures of synthetic Al-substituted goethite (α-Fe0.814Al0.186OOH) and hematite (α-Fe1.658Al0.342O3) (75, 50, 25, 3% hematite by weight) were studied by Mössbauer spectroscopy to evaluate the use of that technique for quantitative analysis. Mössbauer spectra for these mixtures, obtained in the temperature range 12–130 K, were better fitted by a distribution of magnetic fields than by two magnetic sextets. Spectra at 80 K were equally as good as those from lower temperature to determine the hematitegoethite ratio. The recoil-free fractions of the individual components were about equal at any fixed temperature, but thickness effects caused as much as 30% error in the determination of the ratio of components in mixtures.
Textural Variation and Composition of Bentonite Derived from Basaltic Ash
Authors: Konta Jiri 
Published: September 2006

AbstractThe Rokle bentonite deposit is part of an accumulation of argillized volcanoclastic rocks in the Tertiary stratovolcanic complex of the Doupovské Mountains east of Karlovy Vary (Carlsbad), about 100 km westnorthwest of Prague, Czechoslovakia. The arenite basalt ash was originally composed of hyaloclasts and subordinate biotite. The following types of montmorillonite aggregates were produced during the alteration of the ash in a stagnant, lacustrine environment: (1) extremely fine-grained micro-crystalline aggregates that have honeycomb textures and that replace the original hyaloclasts, and (2) coarse crystalline aggregates that have more open honeycomb textures and that fill pores and cracks in altered hyaloclasts and in pumice vesicles. Both types of aggregates have the same chemical composition according to energy dispersive X-ray analysis.Montmorillonite, separated as the <1-¼m size fraction from olive gray bentonite, has the following crystallochemical formula: (K0.09Na0.02Ca0.29Mg0.10) (Al2.43Fe3+1.05Fe2+0.005Mn2+0.005Mg0.50) (Si7.62Al0.38) O20(OH)4. Biotite was apparently stable during the alteration of the hyaloclasts. Anatase and possible accessory heulandite-clinoptilolite were also formed in small amounts, but were not observed by scanning electron microscopy. Goethite is the youngest oxidation product in some parts of the bentonite. Minute fragments of sodium-rich plagioclase, potassium feldspar, quartz, and muscovite are ubiquitous accessories of the original hyaloclasts. Together with kaolinite, they formed from the underlying fresh or kaolinized orthogneiss.
57Fe Mössbauer Spectroscopy of Montmorillonites: A New Interpretation
Authors: Cardile C. M. , Johnston J. H. 
Published: September 2006

AbstractThe 57Fe Mössbauer spectra of several montmorillonites, measured at room temperature and 453 K, showed a considerably broadened Fe3+ resonance which can be computer-fitted with a similarly broadened Fe3+ doublet. In some spectra, particularly if all linewidths were constrained to be equal, this broadened Fe3+ resonance was further resolved into overlapping inner and outer Fe3+ doublets, also having broad linewidths. In accordance with recent electron diffraction evidence, the assignment by previous workers of the inner doublet to Fe3+ in the octahedral sites having the cis-arrangement of OH groups and the outer doublet to the octahedral site having the trans-arrangement of OH groups is incorrect. Instead, the Fe3+ was found to be located largely in the trans-octahedral sites. Because of the relatively low iron content of the montmorillonite examined, the next and more distant neighboring-cation environment varied considerably about the octahedral Fe3+ ions. This variation produced a broadened experimental resonance, and the resulting two-doublet computer fits probably represent the mean extremes of a continuum of slightly different Fe3+ resonances arising from the variable nature of the environment surrounding these such trans-sites, rather than distinct cis- and trans-sites. In addition, a small resonance indicating the substitution of Fe3+ into the tetrahedral sites was observed. The interlayer species probably influenced the Mössbauer resonance of Fe3+ in the tetrahedral and octahedral sites.
Hydroxy-Cu-Vermiculite Formed By the Weathering of Fe-Biotites at Salobo, Carajas, Brazil
Authors: Ildefonse Philippe , Manceau Alain , Prost Dominique , Groke Maria Christina Toledo 
Published: September 2006

AbstractWeathering of a copper stratiform deposit (schist) at Salobo, Brazil, has produced two distinct Cu-bearing minerals from a biotite parent: vermiculite and a manganese oxide containing as much as 13% and 25% CuO, respectively. Manganiferous products were formed as the result of an interhorizon transfer of solutions through a fissure system. Thus, the structural orientation of the schists was a major factor in controlling the supergene concentration of Cu. The Cu-vermiculite formed by the weathering of Fe-biotite, although the unweathered biotites in the parent rocks were found to contain no copper, suggesting that Cu was supplied by weathering solutions. X-ray powder diffraction (XRD) and cationexchange capacity data for the Cu-vermiculite differ from those of typical Mg-vermiculite and are similar to those of hydroxy- Al-vermiculite. A comparison of the XRD pattern of the Cu-vermiculite with that of a Cu-free vermiculite indicates that Cu atoms are located in interlayer sites. Cu probably occurs in a brucite-like layer. The position and structure of the Cu K-absorption spectrum suggest that the Cu is divalent and exists in 6-fold coordination.
Chemistry of Illite/Smectite and End-Member Illite
Authors: Środoń Jan , Morgan David J. , Eslinger Eric V. , Eberl Dennis D. , Karlinger Michael R. 
Published: September 2006

AbstractChemical data from three different series of diagenetic illite/smectites (I/S), analyzed statistically by two regresion techniques, indicate that the content of fixed-K per illite layer is not constant, but ranges from ~0.55 per O10(OH)2 for illite layers in randomly interstratified I/S (R=0; >50% smectite layers) to ~ 1.0 per O10(OH)2 for illite layers formed in ordered I/S (R>0; <50% smectite layers). By extrapolation of the experimental data, the following chemical characteristics were obtained for end-member illite derived from the alteration of smectite in bentonite: average fixed-K per illite layer = 0.75 per O10(OH)2; total charge = about -0.8; cation-exchange capacity = 15 meq/100 g; surface area (EGME) = 150 m2/g.
Chemical and Physical Properties of Paleozoic Potassium Bentonites from Kinnekulle, Sweden
Authors: Brusewitz Ann Marie 
Published: September 2006

AbstractThe < 1-μm fraction of 17 bentonite samples from Kinnekulle, southwest Sweden, were studied by chemical analysis, X-ray powder diffraction, and cation-exchange capacity. The bentonites are interbedded with undeformed, flat-laying Ordovician and Silurian sediments and were formed by the transformation of volcanic ash (dated at about 450 Ma) into smectite, which later converted to mixed-layer illite/smectite (I/S). The reaction, possibly driven by heat from an overlaying diabase intrusion (about 300 Ma), stopped at different stages of conversion, as evidenced by the I/S which ranges in composition from 60 to 10% smectite layers. A 2-m-thick bed shows zonation, with decreasing smectite proportions towards the upper contact. The zonation is not symmetrical towards the lower contact. In thin beds the illite proportion is higher and the regularity of ordering is inversely proportional to the thickness of the bed. K:Sr and K:Rb ratios follow the illite pattern; the ratios are highest at the contact and in thin beds. The inhibiting effect of Ca and Mg on the smectite-to-illite conversion probably was the cause of less-reacted smectite in the center of the thick bed.
Infrared Spectroscopic Study of the Formamide-Na-Montmorillonite Complex. Conversion of s-Triazine to Formamide
Authors: Nguyen T. T. 
Published: September 2006

AbstractThe adsorption and degradation on montmorillonite of s-triazine, the parent compound of a major group of triazine-based herbicides, were studied by Fourier-transform infrared spectroscopy. The original s-triazine appeared to hydrolyze with residual bound water in montmorillonite at 20°C to produce formamide, which formed an intercalate with the clay. A mechanism for the conversion of s-triazine to formamide was proposed which does not support earlier reports that formic acid and ammonia are the reaction products. The infrared spectrum of the formamide-Na-montmorillonite intercalate suggests that formamide reacted with the exchangeable Na cation and that the NH2 group hydrogen bonded with the clay. Assuming the intercalated formamide molecule to be planar, the molecular plane was found to be inclined at ~33° with respect to the plane of the silicate sheet. C-N and C-O bonds were also found to be tilted at the same angle with respect to the clay surface. The proposed orientation is in good agreement with the measured value of d(001) for the formamide-Na-montmorillonite complex. The proposed model of the formamide-montmorillonite complex serves as a basis for comparison of other clay-amide complexes that are important in protein-clay interactions.
Reduction of the Cation-Exchange Capacity of Montmorillonite by Take-Up of Hydroxy-Al Polymers
Authors: Keren R. 
Published: September 2006

AbstractThe cation-exchange capacity (CEC) of Na-Al- and Ca-Al-montmorillonite after neutralization with NaOH or Ca(OH)2 was studied at three Al levels: 10, 25, and 50% of the CEC. Hydroxy-Al polymers were effective in reducing the CEC of Na-montmorillonite (by more than 46%), the exact effectiveness being dependent on the hydroxy-Al content. The hydroxy-Al polymers were less effective in reducing the CEC of Ca-montmorillonite (less than 26%). The CEC reduction was equal to or larger than the amount of the untitrated Al. The electrostatic charges of the clay which were blocked by the hydroxy-Al polymers were compensated for by both the positive charge of the hydroxy-Al polymers and the trapped cations on the clay surfaces. These cations remained on the clay even after extensive washing with 0.1 M KCl.
Transformation of Synthetic Birnessite to Cryptomelane: An Electron Microscopic Study
Authors: Chen Cy-Chain , Golden D. C. , Dixon J. B. 
Published: September 2006

AbstractNa-saturated bimessite was synthesized by oxidizing an alkaline MnCl2 solution with gaseous O2. Transmission electron microscopy (TEM) showed no morphological change upon K-saturation of the bimessite, but selected-area diffraction (SAD) revealed structural disorder. Stepwise heating of the K-birnessite to 800°C yielded cryptomelane, as indicated by X-ray powder diffraction (XRD). Various degrees of transformation to the final cryptomelane product were observed by TEM and SAD, but not by XRD. Unaltered bimessite formed chiefly as thin, platy crystals of apparent hexagonal outline. The cryptomelane crystals that formed by heating the K-saturated bimessite were acicular. Bimessite crystals, partially transformed to cryptomelane and displaying non-integral diffraction spots, formed plates having linear striations and rods twinned at 60° to each other. These intermediate products commonly retained some of the original hexagonal appearance of the parent bimessite. Structural disorder was detected in the partially transformed crystals by SAD. TEM revealed 6.8- and 4.8-Å spacings of the (110) and (200) planes of cryptomelane, respectively. The basal planes of bimessite layers (001) appeared to correspond topotactically to the (110) plane of cryptomelane during these transformations.
Molecular Motions, Surface Interactions, and Stacking Disorder in Kaolinite Intercalates
Authors: Lipsicas M. , Raythatha R. , Giese R. F. , Costanzo P. M. 
Published: September 2006

AbstractIntercalates of Georgia well-crystallized kaolinite with formamide, N-methylformamide (NMF), and dimethylsulfoxide (DMSO) were prepared at room temperature by dispersing the clay in the organic liquid. Several physical and chemical properties of the intercalated organic molecules and the clay, while intercalated and after de-intercalation, were examined using nuclear magnetic resonance (NMR), infrared (IR), and electron paramagnetic resonance spectroscopy (EPR), and specific heat (Cp) measurements. The chemical bonding between the inner-surface hydroxyls and the organic molecules, as indicated by IR, was strongest for DMSO and weakest for formamide. The distortion of the kaolinite layer, as shown by EPR, also was greatest for DMSO and least for formamide. NMR T1 measurements indicated a relatively strong DMSO-kaolinite surface interaction that slowed down the methyl group reorientation comparable to that in bulk solid DMSO. T1 measurements indicated a weaker interaction for NMF. De-intercalation by mild heating did not return the kaolinite to its original structural state as shown by EPR and Cp. The greatest disorder was found for the DMSO de-intercalate and the least for the formamide de-intercalate. These experiments show that for sufficiently strong bonding between the clay inner surface and the intercalating molecule, the structure of the clay is capable of distortion, which is partly temporary and partly permanent. The permanent changes probably involve the introduction of stacking faults.
Macaque V2 Neurons, But Not V1 Neurons, Show Choice-Related Activity
Authors: Nienborg Hendrikje , Cumming Bruce G. 
Published: September 2006

In the macaque extrastriate cortex, robust correlations between perceptual choice and neuronal response have been demonstrated, frequently quantified as choice probabilities (CPs). Such correlations are modest in early visual cortex, suggesting that CPs may depend on the position of a neuron in the hierarchy of visual processing. However, previous studies have not compared neurons with similar precision in equivalent tasks.We investigated the role of cortical hierarchy on CP using a task for which significant CPs have been described previously for middle temporal area (MT). We measured CPs in disparity-selective neurons from both V1 and V2. The stimulus was a dynamic random dot stereogram, presented with a near or a far disparity, masked by varying numbers of binocularly uncorrelated dots. Two macaque monkeys reported whether they perceived a circular patch in front or behind a surrounding annulus in a forced choice task.For V2 (n= 69), CP was on average 0.56, the first demonstration of systematic CPs in a visual area as early as V2. In V1 (n= 74), average CP was at chance level (0.51). The pattern was similar in a subgroup of neurons selected such that the statistical precision in the task was on average identical to that reported for MT (mean CP, 0.51 for V1,n= 33; 0.58 for V2,n= 54). This difference between V1 and V2 could not be explained by eye movements, stimulus size relative to the receptive field, or differences in disparity tuning. Rather, it seems to reflect a functional difference (at least in disparity processing) between striate and extrastriate cortex.
Gravel-Pack-Placement Limits In Extended Horizontal Offshore Wells
Authors: de Magalhães J. V. M. , Calderon A. , Martins A. L. 
Published: September 2006

Summary
Long horizontal-section wells are economical requirements for heavy-oil fields in deepwater environments. This article discusses the operational limits for gravel-pack placement in such wells in consideration of the maximization of the horizontal-section extension in low fracture-gradient scenarios. A parametric study on the variables governing the gravel-pack operations indicates that careful hydraulic design and detailed operational procedures can guarantee a successful job. Alternative strategies are proposed to extended hydraulic limits in critical conditions.
3D Porosity Modeling of a Carbonate Reservoir Using Continuous Multiple-Point Statistics Simulation
Authors: Zhang T. , Bombarde S. , Strebelle S. , Oatney E. 
Published: September 2006

Summary
Training images are numerical representations of geological conceptual models that provide prior information on reservoir architecture. A new emerging geostatistical approach named multiple-point statistics (MPS) simulation allows extracting multiple-point structures from such training images and anchoring these structures to the data actually observed in the reservoir. By reproducing multiple-point statistics inferred from training images, MPS enables the modeling of complex curvilinear structures (e.g., sinuous channels) in a much more geologically realistic way than traditional two-point statistics (variogram-based) techniques. However, in the original MPS implementation, all MPS moments computed from the training image are exported to the reservoir model without processing, which allows simulating only categorical or discretized variables. This implementation is appropriate with clastic reservoirs for which, typically, depositional facies are simulated first using MPS, then porosity and permeability are distributed within each simulated facies using traditional variogram-based techniques. But for reservoirs, in particular in carbonate environments, where porosity and permeability trends/cycles are not closely tied to any facies distribution, simulating porosity/permeability directly using corresponding continuous training images appears to be a more suitable approach.
In this paper, a new filter-based implementation of MPS, named filtersim, is proposed to reproduce features from continuous variable training images. First, a set of general filters is applied to the training image to transform (summarize) each training pattern into a set of scores accounting for different aspects of the pattern, such as north-south and east-west gradients and curvatures. The training patterns are classified in the score space and grouped into a small number of similarity classes. The simulation consists then of visiting each grid node along a random path, identifying the similarity class that best fits to the local conditioning data, and patching a pattern drawn from that selected similarity class. In our study, this new approach was applied to model the 3D porosity distribution of a carbonate reservoir in Kazakhstan. First, the original "categorical" MPS program snesim was used to model the two main reservoir regions, platform and slope, where the spatial porosity distribution is characterized by significantly different features. Interpreted well markers and seismic data were used to condition the modeling of these two regions. Then porosity was distributed in the platform region using the "continuous" filter-based MPS program filtersim, as described previously. The 3D training images used in that second step displayed porosity trends/cycles controlled by the type of geological sedimentation process believed to have occurred in the reservoir.
High-Precision Relative Depth and Subsidence Mapping From Seafloor Water-Pressure Measurements
Authors: Stenvold T. , Eiken O. , Zumberge M. A. , Sasagawa G. S. , Nooner S. L. 
Published: September 2006

SummaryA method to accurately measure seafloor subsidence away from platform locations is presented. The method is based on seafloor water pressure, which is measured on top of predeployed benchmarks visited one after another using a remotely operated vehicle (ROV) and is at the same time measured continuously throughout the survey at one or more reference locations. Because no significant subsidence is expected during a few days of data acquisition, high-precision relative depths representative for the average time of the survey can be obtained. Accurate subsidence estimates between seafloor surveys are found assuming negligible subsidence at benchmarks located outside the field.Results from six seafloor surveys performed at two gas fields in the North Sea are presented. For an area of 1 km2 at 80 m water depth, single-measurement relative depth precision (standard deviation) of 0.4 cm was obtained. Correspondingly, for an area of 700 km2 at 295 to 345 m water depth, 0.6 cm was obtained. Single-station subsidence accuracy down to 1 cm is achieved from the two most recent pressure surveys at the large field. A subsidence signal is seen for this difference, and it is compared with modeled subsidence. Error budgets for depth precision and subsidence, incorporating instrumental and environmental errors, are discussed.