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This study investigates the dissolution characteristics of a stalactite from Küpeli Cave in southern Turkey, employing a holistic approach that includes macroscopic and microscopic analyses alongside advanced techniques such as X-ray diffraction, and scanning electron microscopy. The studied stalactite exhibits distinct morphological features: an upper main body with visible growth layers and dissolution channels, and a lower pendant made of solid sparite calcite crystals. The outer surface of the main body exhibits partial dissolution corrosion and protrusion-like structures resulting from channel infilling resisting corrosion. Notably, the pendant section of the stalactite remains largely unaffected by the dissolution, preserving its original structure. The longitudinal cross-section of the main body reveals dissolution channels along the growth layer's surface, partially filled with calcite cement. Secondary channels branch off the main channels, some connected to the outer surface at certain points, allowing cave water to enter. The dissolution processes also lead to microscale changes in the primary microfabrics, including the widening of intercrystalline pores, microperforated zones, microchannels, rhombohedral microcrystalline blocks, spiky calcite, pits, and abiotic micritization. The recurring dissolution features inside the stalactite indicate synchronous dissolution during stalactite formation, where the precipitation/dissolution conditions repeat cyclically. Dissolution typically occurs during the rainy season when cave water is unsaturated with calcite, otherwise, calcite precipitates, forming overgrowth layers and/or cement. [ABSTRACT FROM AUTHOR]

The effect of saline on the shear strength of compacted bentonite is important to investigate the safety assessment of engineering barriers of deep geological repositories. Different methods used for saturating compacted specimens yield inconsistent relationships between shear strength and salt solution concentration. In this study, we performed direct shear tests on compacted Na–bentonite saturated with distilled water and Na solutions using the constant-vertical stress (CP) method and the constant-volume (CV) method. Scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) measurements were conducted to investigate the microstructural characteristics of compacted bentonite. The results show that the measured shear strength increases with increasing vertical stress or solution concentration. Furthermore, the shear strength of specimens prepared through the CV method is larger when distilled water is used for saturation; at the same time, when salt solutions are used for saturation, CP samples show greater shear strength. On the microscale, both SEM images and NMR results show that specimens become increasingly aggregated with increasing pore-water salinity and that saline solution has a greater effect on the microstructure of the compacted bentonite when using the CP method for saturation because of the change in volume during saturation. The intergranular stress equation, which considers physicochemical effects, is introduced to theoretically characterize the mechanical behavior of compacted bentonite. It is found that the relationship between intergranular stress and shear strength is unique, independent of the saturation method. In other words, the salt solution concentration affects the microstructure, thereby affecting the interparticle stress of compacted bentonite. [ABSTRACT FROM AUTHOR]

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Plastic clays in subgrade may cause major engineering defects such as excessive heave or settlement during the wet season that contribute to the formation of uneven geometry at the pavement surface. Soil stabilization is often a requisite to ameliorate the engineering properties of soft soils or reactive clays. This study investigates the application of nano-silica and nano-alumina to improve the California bearing ratio (CBR) of a local clay. The clay was treated with cement (2%–8%), with nano-additive (0.1%–1.5%) and with cement and nano-additive (3% cement + 0.1%–1.5% nano-additive). The compacted sample was cured for 7 days and subjected to soaked and unsoaked CBR tests. The soaked CBR of the nontreated clay increased by 49% and 27% for 1% nano-silica and 1% nano-alumina treated clay, respectively. Although 3% cement addition improved the CBR of the soaked clay by 28%, the combination of 3% cement with 1% nano-silica and nano-alumina resulted in 196% and 164% increase in the soaked CBR of the nontreated clay, respectively. The combination of nano-additives and cement yielded the same soaked CBR as if 6%–7% cement would have been used. Clay treated with 1% nano-silica and 3% cement achieved the highest CBR value within the tested samples and the sample treated with 1% nano-alumina and 3% cement achieved the lowest free swell potential. The scanning electron microscopy (SEM) micrographs of the treated clay showed the formation of uniform fabric with fewer pore spaces and calcium silicate hydrate (CSH)/calcium aluminate hydrate (CAH) products within the fabric of nano-additive treated clay. [ABSTRACT FROM AUTHOR]

Microbialites are formed through two processes, the trapping and binding of sediment grains and mineral precipitation. Sediment trapping and binding result in coarse sandy textures, whereas fine micritic textures are produced by mineral precipitation. Although well‐studied modern microbialites (e.g. Bahamas and Shark Bay) are formed through the former process, purely trapped‐and‐bound examples are rare throughout the geologic record and limited to shallow‐marine environments. Through the use of conventional microscopy and 3D micro‐computed tomography (µ‐CT) scanning, this study found that South African coastal microbialites have a primarily mineral precipitated texture, although detrital material is included sporadically. Furthermore, these modern microbialites exhibit both micritic and fibrous layering with high porosity. The novel use of 3D microtomography rotational scans has revealed that microbialites are extensively burrowed by metazoan activity and was also able to distinguish the occurrence and distribution of heavy minerals and detrital shell material in the samples. Some of the detrital grains appeared to be accidental/random inclusions, while in other cases the metazoan burrows provided space for the accumulation of sediment once abandoned. In both cases, sediment was incorporated as a product of intermittent accumulation, rather than systematic trapping and binding. The microfabric texture of South African microbialites is therefore a function of both biological (e.g. microbially mediated precipitation) and environmental (e.g. sporadic sediment deposition and inorganic cementation) influence. Overall, the findings presented here highlight the importance of these systems regarding microbialite formation, ichnology and taphonomy. [ABSTRACT FROM AUTHOR]

The requirements of complex subsoil use are increasing in the Pripyat potash-bearing basin: potash ore of new technologic types, with lower contents of useful components, increased concentrations of harmful impurities. Using all complex of quality indicators assessment of natural types of potash ore is undoubtedly prioritized by characteristic of potash deposits. The study of structural and textural features and composition of potash deposits has been given attention since the time of discover of the Starobin deposit. Systematic study of salt rock petrology has been started after the discovery of the Starobin deposit. Until now in the petrology, there is no recognized rational genetic classification of the structures of salt rocks being potash (potassium-magnesium) ore. The name of certain structure is based on the secondary features that are brightly expressed, color or similarity with different objects. The aim of the present work is an element recognition of the primary sedimentary features of rocks, systematization of primary and secondary characteristics and their typification according to petrochemical parameters. In the article the main microfabric types of potash ore that are typical for the deposits of red-colored and mottled hypersaline association of the Pripyat basin.

En Mendoza (Centro-Oeste argentino), ciudad colonial meridional, los alfareros indígenas locales manufacturaron cerámica desde el siglo dieciséis, aunque su origen étnico fue documentalmente invisibilizado. La presencia de platos tipo Viluco Colonial en los contextos urbanos evidencia que los artesanos integraron técnicas locales, ligadas a la anterior dominación inca, con técnicas y formas de origen europeo. Con el objetivo de conocer las tecnologías de producción de los platos, realizamos análisis macroscópicos, petrográficos y con microscopía electrónica de barrido. A partir de esto, caracterizamos sus pastas, microfábricas y huellas de superficie. Proponemos que dichas vasijas fueron producidas tempranamente en la colonia por alfareros huarpes —sin excluir la posibilidad de participación de artesanos de otros grupos— quienes incorporaron el torno, pero continuaron con la tradición alfarera prehispánica y los lenguajes visuales andinos ligados al imperio inca. Analizar la producción cerámica como parte de la agencia social permitió visibilizar a los alfareros como agentes de cambio en la conformación de las nuevas identidades y culturas coloniales mendocinas, ya que sus productos híbridos pudieron ser usados por los colonos europeos, generando transformaciones identitarias como parte del proceso de etnogénesis. [ABSTRACT FROM AUTHOR]

The effects of inorganic cations and organic polymers on the physicochemical properties and microfabrics which including the floc size distributions of kaolinite suspensions were systematically investigated by batch sedimentation tests. Kaolinite surface charges, salt concentrations and polymer polarity as well as polymer dosage were found to be the key factors that affect the particle associations, floc sizes, zeta potential, and turbidity of a kaolinite suspension. The relationship between flocs sizes, turbidity, and zeta potential of kaolinite sediments were established and the significance of understanding the polymer induced flocculation and aggregation of suspended kaolinite sediments was discussed. Assisted by the zeta potential measurements, an increase of ionic strength was found to compress the electrical double layer (EDL) of kaolinite and result in imbalance of the interparticle forces, thus the particle associations and floc sizes varied significantly. The addition of polymers was found to facilitate flocculation of kaolinite through long-range polymer bridging and short-range ion-dipole interaction, including the hydrogen bonding and Colombian interactions, which in turn affected the flocs size, zeta potential, and turbidity of the suspensions. Test results also showed that the clay-polymer suspensions possessed a unimodal lognormal particle size distribution (PSD) which leading to a more quantitative understanding of floc sizes of suspended sediments. • The microfabrics of polymer-kaolinite suspensions were investigated. • Factors affect floc size, turbidity, and zeta potential were evaluated. • Polymer-kaolinite suspensions exhibited a unimodal lognormal PSD. • Correlations among flocs size, turbidity, and zeta potential were established. [ABSTRACT FROM AUTHOR]

Quantifying the rock microfabric is one of the most important research interests and challenges in the field of rock drilling and excavation. In this study, the relationship between quantitative parameters of the rock microfabric and the rate of top-hammer drilling was studied. For this purpose, a drilling operation was performed on five soft rock samples and three hard rock samples and drilling rates were recorded. Thin sections from the rock samples were prepared and micrographs of the sections were reviewed using AutoCAD software and digital boundaries of the grains were clarified and drawn. After preparation and filtering of the digitized thin sections, four basic properties of each grain, including maximum diameter, minimum diameter, area and perimeter, were calculated with the help of the software. These parameters were then analyzed statistically and used to obtain six indexes including equivalent diameter, grain compactness, shape factor, aspect ratio, interlocking index and grain size homogeneity index. Finally, the microfabric and drilling rate data were subjected to regression analysis and the significance of the relationships between the grain parameter values and drilling rate were explored. Drilling rate was found to increase with increasing equivalent diameter and shape factor. In contrast, drilling rate decreased with increasing grain compactness, aspect ratio, grain size homogeneity and grain interlocking index. Grain compactness showed the most significant relationship (R2 = 0.8) with drilling rate among the studied parameters. [ABSTRACT FROM AUTHOR]

This study applied methods previously used on contemporary ooids to describe recent Arabian Gulf ooids with the aim to better understand their ultra-structure and attendant symbiotic relationship with microorganisms in their immediate environments. Petrographic, morphological, and microscopic techniques were applied to describe samples collected from three sites on an ooid shoal. Observations made on dominant grains (ooids) are size distribution, mineralogy, morphology, internal cortical architecture. Mean grain sizes of ooids for the three stations are 329, 429, and 412 µm and the samples fall into two textural categories, described as poorly to moderately sorted medium-grained sand, and poorly sorted sand. Microorganisms in symbiotic relationships with the ooids belong to cyanobacteria and foraminifera. They were found boring or attached to the surfaces of the ooids and were taxonomically described. These observations will serve as an update of previous accounts of ooid types in the Arabian Gulf. [ABSTRACT FROM AUTHOR]

The distinction between turbidites, contourites and hemipelagites in modern and ancient deep-water systems has long been a matter of controversy. This is partly because the processes themselves show a degree of overlap as part of a continuum, so that the deposit characteristics also overlap. In addition, the three facies types commonly occur within interbedded sequences of continental margin deposits. The nature of these end-member processes and their physical parameters are becoming much better known and are summarised here briefly. Good progress has also been made over the past decade in recognising differences between end-member facies in terms of their sedimentary structures, facies sequences, ichnofacies, sediment textures, composition and microfabric. These characteristics are summarised here in terms of standard facies models and the variations from these models that are typically encountered in natural systems. Nevertheless, it must be acknowledged that clear distinction is not always possible on the basis of sedimentary characteristics alone, and that uncertainties should be highlighted in any interpretation. A three-scale approach to distinction for all deep-water facies types should be attempted wherever possible, including large-scale (oceanographic and tectonic setting), regional-scale (architecture and association) and small-scale (sediment facies) observations.

In this study, a series of laboratory experiments for the response of wave induced clay-sand seabed were carried out to clarify the mechanism of liquefaction of clayey seabed. The experiments were conducted in an 80 m long wave flume. In the tests, the sand-clay beds were mixed with various clay contents (CC) from 0.5% to 15% and were tested for given wave conditions. The pore water pressure and the water elevation were measured in each test. Soil properties tests and scanning electron microscope (SEM) experiments on different seabed samples were carried out to further explore the mechanism of liquefaction. The experimental results indicated that the amplitude and accumulation of the excess pore water pressure (EPP) varied with different CC in the sand-clay bed. With the introduction of CC, micro-structure and properties (such as permeability and compressibility) of bed soils changed. Sand-clay bed presented more susceptibility to liquefy compared with pure sand bed. CC promoted seabed liquefaction, even if the added amount was very small (CC is 0.5%), however when CC exceeded a certain value (10% in this study), the mixed bed will not be liquefied. This phenomenon can be well explained by the micro-structure of sand-clay bed. CC within a sandy seabed, does not only affect the permeability, but also change the compressibility of seabed soils. For example, the microfabric of seabed vulnerable to liquefaction is loose. Clay aggregations generally gathered at the sand particle contact points. This microfabric is easily compressed under wave loads and allowed pore water to flow, resulting in the accumulation of pore water pressure. On the other hand, the microfabric of seabed that was resistant to liquefaction appeared to be more compact. Due to clay-filled gaps between the sand particles, the pore water is more difficult to flow when seabed was compressed. Furthermore, the tendency of seabed liquefaction is closely related to CC.

Magmatic sulfide liquids are effective at concentrating a range of metals. Within magmatic sulfide systems pentlandite, an exsolution product of monosulfide solid solution (MSS), is the primary host of Ni, Co and significant concentrations of Pd. Over the last decade, LA-ICP-MS mapping has revealed non-uniform metal distributions and complexity to the metal patterns such as zonation and the linear alignment of elements. Whereas the compatibility and partitioning behavior of chalcophile elements during sulfide fractionation are well constrained, there is little knowledge on the crystallographic control exerted on metal distributions. In this study, LA-ICP-MS mapping of globular sulfides from the Crystal Lake Intrusion, Ontario (Canada), is complimented by EBSD analysis, revealing a strong crystallographic control on both the concentration of metals and pentlandite exsolutions. Elements considered incompatible in the high temperature monosulfide solid solution (MSS) phase (e.g., Cr, V, As, Pb, Ag, Bi and Pd) are preserved as a microfabric, showing preferential concentration in association with the (0001) basal plane of pyrrhotite and adjacent pentlandite. Where the [0001] axis is viewed perpendicular to the cut surface, the microfabric is considered to be an intersection lineation between the basal (0001) plane and the surface of the cut section. Pentlandite textures described in magmatic sulfide deposits include granular, fan and laths/blades. Our observations indicate that marginal pentlandite exsolutions, are in optical continuity with granular exsolutions, providing insights into the growth of pentlandite at MSS grain boundaries. We conclude that all pentlandite forms are crystallographically controlled by the hexagonal mineral system of MSS/pyrrhotite, with the [0001] c -axis of pyrrhotite corresponding to the 〈111〉 axis of pentlandite. This axis also acts as a twinning rotation axis for the two identified pentlandite orientations. Fan and lath textured exsolutions are considered geometrically equivalent structures, being reconstructed as flat disc–shapes developed parallel to the basal (0001) plane of pyrrhotite, which acts as a preferred nucleation site. A network of low-angle grain boundaries are recognized as hexagonal or rectangular structures within pyrrhotite, with the morphology shown to be dependent on the orientation of the crystals. As these features are again geometric equivalents, they can be reconstructed as intragrain hexagonal prisms. We speculate due to their localized development, that they could represent a plastic response of the pyrrhotite to accommodate the increase in volume suggested to be associated with late pentlandite exsolutions and thus are the result of static lattice recovery. The microstructural and trace element observations presented here provide new context to some of the common textural features of magmatic sulfide deposits, while importantly highlighting the strong crystallographic control on both metal distributions and sulfide textures. This study also importantly recognizes the dominance of hexagonal pyrrhotite within the ores of the Crystal Lake Intrusion and likely other magmatic sulfide deposits. This has implications for mineral processing as its non-magnetic properties can result in dilution of Ni-Cu-PGE ores and thus requires special attention for the flotation strategy. • Structural impurities drive the preferential alignment of incompatible elements within magmatic sulfides • The growth, texture and orientation of pentlandite is controlled by the hexagonal crystal system • Element mapping and microstructural analyses, allow for a revised conceptual model of an evolving magmatic sulfide liquid [ABSTRACT FROM AUTHOR]

The Mesoproterozoic Tieling Formation, near Jixian, northern China, contains thick beds of vertically branched, laterally elongate, columnar stromatolites. Carbonate mud is the primary component of both the stromatolites and their intervening matrix. Mud abundance is attributed to water column 'whiting' precipitation stimulated by cyanobacterial photosynthesis. Neomorphic microspar gives the stromatolites a 'streaky' microfabric and small mud flakes are common in the matrix. The columns consist of low-relief, mainly non-enveloping, laminae that show erosive truncation and well-defined repetitive lamination. In plan view, the columns form disjunct elongate ridges <10 cm wide separated by narrow matrix-filled runnels. The stromatolite surfaces were initially cohesive, rather than rigid, and prone to scour, and are interpreted as current aligned microbial mats that trapped carbonate mud. The pervasive ridge-runnel system suggests scale-dependent biophysical feedback between: (i) carbonate mud supply; (ii) current duration, strength and direction; and (iii) growth and trapping by prolific mat growth. Together, these factors determined the size, morphology and arrangement of the stromatolite columns and their laminae, as well as their branching patterns, alignment and ridge-runnel spacing. Ridge-runnel surfaces resemble ripple mark patterns, but whether currents were parallel and/or normal to stromatolite alignment remains unclear. The formation and preservation of Tieling columns required plentiful supply of carbonate mud, mat-building microbes well-adapted to cope with this abundant sediment, and absence of both significant early lithification and bioturbation. These factors were time limited, and Tieling stromatolites closely resemble coeval examples in the Belt-Purcell Supergroup of Laurentia. The dynamic interactions between mat growth, currents and sediment supply that determined the shape of Tieling columns contributed to the morphotypical diversity that characterizes mid-late Proterozoic branched stromatolites. [ABSTRACT FROM AUTHOR]

Polyphase chocolate-tablet boudinage of competent anhydrite layers in incompetent Permian rock salt of the Morsleben repository (Germany) developed during Triassic/Jurassic graben formation and late Cretaceous graben inversion. The competence contrast between layers and matrix is related to the deformation mechanisms of anhydrite and halite, which have been constrained in the present study using deformation microfabrics and geochemical data. Boudinage implies a finite longitudinal strain of ca. 100% in NNW-SSE direction. There is a clear impact of the layer thickness on both the deformation mechanisms and the shape of anhydrite boudins. Pervasive solution-precipitation creep is the dominant deformation mechanism in thin anhydrite layers (thickness < 15 cm), which are dominated by drawn boudins with aspect ratios ranging from 1.5 to 5.4. Deformation of thick anhydrite layers (thickness > 15 cm) was accommodated by dislocation creep succeeded by localized solution-precipitation, kinking, twinning and fracturing resulting in torn boudins with aspect ratios between 0.5 and 2.0. Halite of the incompetent rock salt matrix deformed viscously under low differential stress (2.0–3.1 MPa). The deformation mechanisms were dislocation creep in form of subgrain formation and strain-induced grain boundary migration. Moreover, close to anhydrite boudins, solution-precipitation creep of halite is indicated by decreased bromide content in halite of necks between brittle torn boudins, which should have precipitated from a fluid phase. Halite in necks of drawn boudins, on the other hand, displays a continuous decrease of bromide content, pointing to predominantly crystal plastic inflow of halite. • Chocolate-tablet boudinaged anhydrite rock layers in halite matrix reveal a finite longitudinal elongation of ca. 100% • The aspect ratio of anhydrite rock boudins and deformation mechanisms in anhydrite depend on layer thickness • The bromide content in halite represents the sedimentary-diagenetic record with localized disturbances • Halite was deformed in the viscous, anhydrite in the brittle-viscous deformation regime [ABSTRACT FROM AUTHOR]

Anisotropy of magnetic susceptibility (AMS) is a frequently applied method in sedimentology, especially in the determination of the orientation of transport processes. We present an analysis of magnetic fabric (MF) studies on loess. New aspects of fabric development reveal: i) The deposition of the aeolian sediments was controlled by gravity, low-energy transport and local geomorphology, hence no clarified wind direction can be defined. ii) The influence of phyllosilicates is also significant among the magnetic components. iii) While the primary MF is relatively well-defined, the secondary MF is influenced by several processes. The analysis of stereoplots combined with the q–β diagram and photostatistics showed encouraging results during the characterization of various secondary MF such as redeposited MF and pedogenic fabric. iv) Changes in processes from aeolian to water-lain deposition and the increasing transportation energy were reflected by the connection between AMS and observed micro-scale sedimentary features. v) A relationship was obvious between the degree of pedogenesis and the transformation of sedimentary MF into a vertical MF typical for paleosols. vi) The significant role of very fine grained magnetite on the formation of inverse MF could not be excluded. [ABSTRACT FROM AUTHOR]

The examination of glacial sediments in thin sections has become a common procedure in recent years. Apparent sand grain orientation (microfabric) in thin sections is one of the key elements marking certain microstructures. In an attempt to make till micromorphology studies less subjective and investigate the orientation of sand-sized particles in tills, we have developed an image analysis procedure to measure and analyse the spatial distribution of the till microfabric. We studied 13 thin sections of the Weichselian subglacial till and basal shear zone outcropping in the Baltic Sea bluffs at the Ziemupe site in western Latvia. The results were visualized as a two-dimensional grid of rose diagrams covering the area of the thin section and were compared to macrofabric. We found that in larger areas microfabric, although much weaker than macrofabric, coincides with macrofabric orientation. In the sub-centimetre scale till microfabric in short distances appears to be highly variable both in strength and preferred orientation, and a domain-like pattern appears.

Industrial micro X-ray computed tomography (μCT) is applied to link the macroscopic shaking table tests with the microscopic sand particle–pore structure evolution. Based on 3D image reconstruction, the variation in the particle–pore fabric of coral sand during earthquakes was studied. Moreover, the special evolution of coral sand was revealed through a comparative experiment using Fujian sand. The results show that the variation in the coordination number of the coral sand is positively correlated with the excess pore pressure ratio. The uniformity of the pore diameter decreases after earthquakes, and the reduction degree of the coral sand is smaller than that of Fujian sand. This result is related to the irregular shape and larger surface friction coefficient of coral sand particles. This study provides a deeper understanding of the microscopic evolution of coral sand liquefaction. • A deeper understanding of the microscopic evolution of coral sand liquefaction is provided. • The macroscopic shaking table tests and the microscopic sand particle-pore structure evolution are linked. • The variation of particle-pore fabric of coral sand during earthquakes is clarified based on the 3D image reconstruction. • The special evolution of coral sand is revealed by the comparative experiment with Fujian sand. [ABSTRACT FROM AUTHOR]

Electro-osmosis is a process coupling electrolyte flow and associated hydraulic flow under an external electrical field, resulting in the permeation of both electrolyte and pore fluid in porous media. One-dimensional column experiments were conducted to comprehend the effects of electro-osmosis treatment on the physical and chemical properties of a Na-bentonite by varying the electrode materials, including copper and iron as reactive electrodes and graphite and stainless steel as inert ones. Soil plasticity, free swelling ratio, zeta potential, and cation exchange capacity decrease after electro-osmosis, especially for the reactive electrodes. Moreover, soil microfabric is converted from the flocculated microplatelets to smectite aggregates of 10–30 µm in size. The original Na+ cations absorbed into smectite interlayer and adsorbed onto smectite external surfaces are exchanged with the released Cu2+ and Fe3+ for copper and iron electrodes, and the pre-existing multivalent cations such as Ca2+ for graphite and stainless steel electrodes. The resulting change in soil microfabric and chemical compositions decreases the water adsorption and holding capacity and also affects the physical and chemical properties of the Na-bentonite. [ABSTRACT FROM AUTHOR]

This study sheds light on the tectonic and structural knowledge of the mélange facies located to the south of Chañaral city, Chile. The Chañaral mélange has been related to an accretionary prism at the western active continental margin of Gondwana. Based on the fossil content, the original turbidite sequence would have been deposited during Devonian to Carboniferous times. The Chañaral mélange is included in the Las Tórtolas Formation, which corresponds to the Paleozoic metasedimentary basement located in the Coastal Range in northern Chile. It consists of a monotonous sequence of more than 90% of interbedded sandstones and shales, with a few limestones, pelagic chert, conglomerates and basic volcanic rocks, metamorphosed to the greenschist facies. In the study area, the Las Tórtolas Formation is divided into two structural domains separated by a major reverse dextral structure, called here the Infieles fault. To the east, the Las Tórtolas Formation is characterized by a brittle–ductile deformation, defined by the original sedimentary contacts in the turbiditic sequence. Besides, thrust faults and associated thrust propagation folds promotes a penetrative axial plane foliation. Mélange facies are located to the west of the Infieles fault. Although lithologies comprising this domain are similar to the rest of the Las Tórtolas Formation, mélange facies (ductile domain) are characterized by the complete disruption of the original architecture of the turbidite succession. The most significant structures in the mélange are the ubiquitous boudinage and pinch and swell structures, asymmetric objects, S–C structures and tight to isoclinal folds. This deformation is partitioned in the Chañaral mélange between linear fabric domains (L), characterized by quartzite blocks with prolate shape in a phyllite matrix with pencil structures, and linear-planar fabric domains (L-S), where quartzite objects show oblate shape and phyllites present a penetrative foliation. The intensity of deformational process is reflected in the high aspect ratios yielded by the quartzite constrictive (L) and flattened (L-S) object axes. Meso-scale shape preferred orientation (SPO) has been compared with quartz microtextures in quartzite blocks, resulting aspect ratios considerably lower than those obtained from the mesoscopic fabric. Main deformation mechanism observed in quartz microtextures are bulging-subgrain rotation recrystallization and dissolution-precipitation creep for pure and impure quartzites respectively. The temperatures deduced from these microtextures are between 350 and 400 °C, which coincides with the greenschists facies metamorphism observed in the Las Tórtolas and the mélange facies. Extremely dissociation between micro- and meso-scale deformation could be generated by dissolution at high differential stress in the boundaries of the quartzite layers and precipitation at low differential stress parts, which would increase the aspect ratio of the lenses whereas internally, quartz would have remained virtually unstrained. We propose here a tectonic setting for the Chañaral mélange formation based on the geodynamic evolution of the western active margin of South America during Late Paleozoic to Early Jurassic. Thus, the study area is located in a LT-HP zone of an accretionary complex, where rocks from the subduction channel (mélange facies) and the basal domain of the prism (brittle–ductile domain of the Las Tórtolas Formation) are in contact through the Infieles fault. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new PGE enriched microfabric is documented within magmatic sulphide phases in association with globular textured sulphides. • A close spatial association is observed between globular sulphides, segregation vesicles, taxites and a trace element microfabric. • Trace element zonation patterns in pentlandite and chalcopyrite preserve former grain boundaries. • Contact pentlandite exsolved from monosulphide solid solution rather than by peritectic reaction. • As, Pd and Ag locally remobilised and concentrated along fractures within heavily altered sulphide assemblages. • Findings have implications for the behaviour and mobility of metals during sulphide fractionation and hydrothermal interaction in Ni-Cu-PGE systems. Within the magmatic pyrrhotite-pentlandite-chalcopyrite assemblage, which is ubiquitous of many Ni-Cu-PGE deposits, the spatial distribution of PGEs and semi-metals during both sulphide fractionation and low temperature alteration is not well documented. In-situ characterisation of sulphides provides a mechanism to trace the behaviour of elements during ore formation, with trace element distribution patterns providing valuable insights at the microscale into the genesis of magmatic sulphide deposits. Here we report trace element data determined by quantitative LA-ICP-MS mapping for a suite of variably altered samples from the taxitic rocks of the undeformed Crystal Lake Intrusion, within the 1.1 Ga Midcontinent Rift. Combining LA-ICP-MS data with detailed petrography and multivariate statistics helps identity the processes responsible for elevated metal concentrations and observed trace element distribution patterns within Ni-Cu-PGE systems. Such data can also improve our understanding of the effects fluid interaction and assimilation of volatile rich rocks has on the metal contents of sulphides. Element maps reveal complex distribution patterns throughout the disseminated sulphides of the Crystal Lake Intrusion, which are notably enriched in Pd relative to the massive sulphides developed locally along the basal contact. Replacement of the primary sulphides by low temperature phases is restricted to the northern limb of the intrusion and results in heterogeneous distributions and elevated concentrations of As, Pd, Ag and Bi along fractures. Zonation of As, Mo, Ru, Rh, Re and Bi is observed in both pentlandite and chalcopyrite. Within the globular ores, petrographic observations suggest the pyrrhotite-chalcopyrite contact with which 'contact' pentlandite resides along, may not be indicative of the initial boundary between monosulphide solid solution (MSS) and the residual sulphide liquid. This has implications for the interpretation of trace element zonation patterns, which in the case of this study are not considered to be indicative of formation by peritectic reaction. This is further supported by the spatial distribution of multivariate clusters which show features in the granular and contact pentlandite that are consistent with exsolution from MSS. Within the locally vapour saturated taxites of the southern limb, a new microfabric is documented within the globular ores, revealing a close spatial relationship between enhanced trace element concentrations and microstructures within undeformed magmatic sulphides. The microfabric, which is defined by V, Cr, As, Pb and Bi and less frequently by Mo, Rh, Pd and Re, is prevalent in unaltered coarse pyrrhotite and in contact, granular and fan textured pentlandite, and is developed in association with both silicate-capped and uncapped sulphide globules. Regardless of the exact mechanism by which the microfabric formed (e.g., fluid interaction, exsolution, gravitational compaction), this study highlights that regional deformation is not required to drive the preferential enrichment of select elements along discrete planes. Only as more high resolution element map data become available will it become apparent if the microfabric is a common feature of magmatic Ni-Cu-PGE deposits or a unique characteristic of the Crystal Lake Intrusion. [ABSTRACT FROM AUTHOR]

The Lokpanta Shale of Anambra Basin, a potential unconventional hydrocarbon resource, has limited studies on its microstructure, diagenetic history and fluid storage-transport capacity. This study presents geochemical, imaging and petrophysical analyses on shallow samples (<25 m) to characterize their rock properties. The unit contains thermally immature and non-porous type II kerogen with patchy-amorphous, sub-lenticular and structured morphologies. The laminated (texturally anisotropic) microfabric is defined by its sub-lenticular organic matter, weakly aligned clays and few subparallel microfractures. Calcite dissolution, moldic-dissolution and phyllosilicate framework are the dominant pores in an isolated pore network consisting of 0.2 − 60.2 μ m large near-spherical to ellipsoidal pores and 2 − 180 nm nanopores. Calcite minerals underwent diagenetic alterations, including dissolution, cementation and neomorphism. The clay minerals in the analyzed core of the Lokpanta Shale include two tracts of R3 I/S mixed clay layers (ordered interstratified illite-smectite), rectorite (partially ordered illite-smectite), illite and negligible smectite, which suggests limited smectite to illite diagenesis. The organic matter reached immature thermal maturation (T max of 429 − 434 °C), which is close to the oil window threshold (435 °C). The organic matter maturity status and clay profile at shallow depths (<25 m) suggest an earlier exposure to a higher but time-limited thermal stress regime (burial then uplift). Higher clay and organic matter content in the unit directly correlate with wider pore distribution, lower tortuosity, higher external specific surface area and higher dielectric constant (higher fluid storage, transport, and adsorption capacity). This study enhances source rock and/or reservoir characterization, which could be vital for exploration strategies in the Lokpanta Shale. • Geochemical, advanced imaging and petrophysical characterization of Lokpanta shale, Anambra Basin. • Cenomanian-Turonian Lokpanta shale contains thermally immature and non-porous type II kerogen. • The fine-grained texturally anisotropic microfabric is primarily due to aligned clays, organic matter and microfractures. • The dominant pores in the isolated pore network are the intraparticle calcareous dissolution and phyllosilicate framework. • Organic matter and clays dominantly control the microstructural and petrophysical properties. [ABSTRACT FROM AUTHOR]

Eutrophication-induced hypoxia has resulted in preservation of laminated sedimentary fabric in coastal areas of the northern Baltic Sea. These laminites offer a potential technique for dating recently deposited organic-rich muds, but their formation mechanisms have been inadequately understood. In this study, microfabric of the modern laminated sediments in the coastal Gulf of Finland and Archipelago Sea was investigated through X-radiography and scanning electron microscopy of samples embedded in epoxy resin. The sedimentary fabric comprises rhythmic biogenic and lithogenic lamina successions reflecting seasonal changes in the composition of accumulating material. The diatom-rich biogenic lamina succession is formed during the vernal phytoplankton bloom through rapid sedimentation of aggregates composed of intact diatom frustules and minor proportions of clay-rich lithic material that are enclosed in a sticky matrix of amorphous phytodetritus, analogous to the formation of the marine snow. Accumulation of the lithogenic lamina succession results from decline in primary production towards late summer, enhanced recycling of organic carbon due to grazing by zooplankton and intensified resuspension of lithic-rich terrigenous material concomitantly with increased cyclonic activity towards late autumn and winter. The inclusion of silt grains and isolated diatoms and faecal pellets in the lithogenic laminae attests to lateral transport and deposition from near-bottom flows, contradicting the generally accepted view that laminated sediments accumulate by suspension settling under quiescent conditions only. Accumulation rates inferred from 137 Cs dating are consistent with the biogenic–lithogenic lamina succession-couplet thickness, supporting the interpretation that the couplets reflect an annual cycle of deposition. The results indicate that these modern laminated sediments provide a high-resolution archive for assessing recent human-induced environmental changes as well as a robust tool for evaluating the lateral expansion of seafloor oxygen deficiency due to anthropogenic eutrophication in the area during the past decades. [ABSTRACT FROM AUTHOR]

The present contribution summarizes the results of a study focusing on the influence of quartz microstructures on the seismic wave velocities in the quartzites of the Garhwal Himalaya. Quartzites being monomineralic were chosen for the present study so as to nullify the effect of other mineral constituents on the seismic velocity. Samples were collected from different tectonic settings of the Higher and Lesser Himalayas which are separated from one another by the major tectonic zone 'Main Central Thrust' (MCT). These are mainly Pandukeshwar quartzite, Tapovan quartzite and Berinag quartzite. The samples of Berinag quartzite were collected from near the klippen and the thrust, termed as Alaknanda Thrust. The vast differences in microstructures and associated seismic wave velocities have been noted in different quartzites. It has also been observed that quartzites of the MCT zone and Alaknanda Thrust have higher seismic velocities. This is because of their coarse-grained nature of the rocks as evidenced by the strong positive relation between seismic velocities and grain area. The coarsening is either due to the operation of grain boundary migration and grain area reduction process or high aspect ratio/shape preferred orientation. The quartzites located around Nandprayag Klippen have undergone static recrystallization and exhibit the lowest seismic wave velocities. [ABSTRACT FROM AUTHOR]

Various rock types-including highly deformed to undeformed quartzites, granites, granitic gneisses, gneisses, metabasics (meta-amphibolites and meta-dolerite), and dolomites-collected from different formations of the Lesser and Higher Himalayas were tested to evaluate correlations between the uniaxial compressive strength (UCS) and the point load test (PLI), Schmidt hammer rebound (SHR) value, and compressional wave velocity ( Vp). Various equations between UCS and PLI, SHR, and Vp were obtained using regression analysis. It was found that there is high scatter in the data when all lithologies are considered together, whereas this scatter is reduced when the lithologies are considered individually. This was attributed to wide variations in the mineralogical and textural characteristics of different rocks. Furthermore, it was also noted that quartzites exhibit high scatter in their data points, even though they are monomineralic. Thin section studies revealed that different microfabrics have been produced in the quartzites, due to the actions of different deformational phases during tectonic activity in the area. Therefore, it is necessary to treat deformed and undeformed rocks separately when deriving such equations. [ABSTRACT FROM AUTHOR]

Researchers previously thought the only ways to investigate the microfabric of clayey soil were through a scanning electron microscope (SEM), a transmission electron microscope (TEM), an X-ray, and an optical microscope. However, in this research, ultrasonic equipment was used to disperse clayey soils (bentonite, illite, and kaolinite) for different lengths of time. After dispersion, an atomic force microscope (AFM) was employed to take three-dimensional (3D) photographs. While the samples were intact, AFM was able to take 3D photographs in different environments. The IA_P9_BUILD software was employed to analyze the data to obtain the angle of particle orientation and the particle size distribution. In this investigation, it was observed that with the use of an ultrasonic device with 30 KHz of power, bentonite, illite, and kaolinite reached a dispersion state after 12, 8, and 6 min, respectively. [ABSTRACT FROM AUTHOR]

When a clay sample is reconstituted from a slurry state to a normally consolidated state, a higher initial water content generally derives a higher void ratio in e –log p relationship. However, in undisturbed Holocene clay samples collected from a soil layer under the seabed, void ratio is much higher than that for the reconstituted, even though the reconstituted sample was consolidated from a sample slurry state with a very high initial water content. Therefore, the higher void ratio for undisturbed Holocene clay cannot be explained by the initial water content. There must be another key factor to explain the higher void ratio for undisturbed Holocene clay. In this study, the difference between the microfabric of deposited clay from suspension state and reconstituted clay from a slurry state is investigated to clarify the key factors contributing to the higher void ratio. The clay in this study is Osaka Bay Holocene clay sampled from GL −15 to −19 m below the seabed. Sedimentation tests from the suspension state were carried out in various conditions of initial water content, salt concentration, and pH. A series of sedimentation tests was carried out with two types of hollow cylinders: an observation glass cylinder with an inner diameter of 60 mm and a height of 400 mm (specimen height of 350 mm), and a cylindrical acrylic container with an inner diameter of 100 mm and a height of 1800 mm (specimen height of 1500 mm). In the 100-mm diameter cylinder, the deposited sample was consolidated by a pressure of 19.6 kPa, then mounted in an oedometer ring with an inner diameter of 60 mm and a height of 20 mm. An incremental loading oedometer test was then carried out up to 39.2 kPa. The microfabric of the consolidated specimen was observed by scanning electron microscope (SEM) and quantitatively investigated by mercury intrusion porosimeter (MIP). It was shown that the high void ratio of natural clay deposit is not only due to the high initial water content but also to the sedimentation process with flocculation. This plays an important role in the formation of the microfabric of natural clay deposits characterized by a significantly higher void ratio than reconstituted samples. [ABSTRACT FROM AUTHOR]

A flanking structure developed along a secondary shear zone in calcite marbles, on Syros (Cyclades, Greece), provides a natural laboratory for directly studying the effects of strain rate variations on calcite deformation at identical pressure and temperature conditions. The presence and rotation of a fracture during progressive deformation caused extreme variations in finite strain and strain rate, forming a localized ductile shear zone that shows different microstructures and textures. Textures and the degree of intracrystalline deformation were measured by electron backscattered diffraction. Marbles from the host rocks and the shear zone, which deformed at various strain rates, display crystal-preferred orientation, suggesting that the calcite preferentially deformed by intracrystalline-plastic deformation. Increasing strain rate results in a switch from subgrain rotation to bulging recrystallization in the dislocation-creep regime. With increasing strain rate, we observe in fine-grained (3 μm) ultramylonitic zones a change in deformation regime from grain-size insensitive to grain-size sensitive. Paleowattmeter and the paleopiezometer suggest strain rates for the localized shear zone around 10 −10 s −1 and for the marble host rock around 10 −12 s −1 . We conclude that varying natural strain rates can have a first-order effect on the microstructures and textures that developed under the same metamorphic conditions. [ABSTRACT FROM AUTHOR]

Electro-osmotic stabilization has long been studied as a soft soil improvement technique, while the influence of an applied electrical field on the soil microfabric and minerals is always ignored. In this study, three laboratory experiments were conducted on sodium bentonite using copper, iron and graphite electrodes to investigate the microfabric and chemical composition change before and after electro-osmotic stabilization. The soil samples near the anode were identified using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The microfabric of the sodium bentonite changed from flocculated fabric to aggregated fabric after electro-osmotic stabilization. Regular calcium sulfate tubes were generated near the copper and iron anodes. EDX tests showed that the content of sodium near the anode decreased, while the copper, iron and calcium presented substantial increase, indicating that the sodium ions were substituted by copper, iron, and calcium ions in copper, iron and graphite experiments respectively. The change of microfabric and the ion exchange reactions between sodium, copper, iron and calcium ions are the main reasons for the significant decrease of the plasticity index and free swelling ratio. [ABSTRACT FROM AUTHOR]

Abstract: This work aims at studying rate of densification, resistance to hydration and slag attack of 0.0–2.0wt.% ilmenite-doped MgO-dolomite refractories fired at 1400–1700°C, in relation to their thermal equilibrium and microfabric. XRF, XRD, SEM, EDAX and mercury intrusion were used to characterize the fired samples. The modular system MgO-MF(MA)-C2S-M2S was applied in determining their thermal equilibrium data. The rate of hydration and attack by steel-slag were also measured using CLM. It is concluded that doping the dolomitic-magnesite with 0.5wt.% ilmenite leads to maximize rate of densification after firing for 4h at only 1500°C. Direct-bonded MgO-MgO network is shown enclosing merwinite and monticellite with minor magnesio-ferrite spinel solid solution ex-soluted within the periclase network. Due to the dense microfabric, the hydration resistance is enhanced 8 times compared with the un-doped samples. Also, there is deeper infiltration of the slag/refractory reaction products of the un-doped MgO-dolomite sample as compared with the doped one. [Copyright &y& Elsevier]

This paper studies the changes in thermal conductivity, temperature, and unconfined compressive strength of gold tailings and fly ash mixtures during the curing period of 5 days. The microfabric of the cured mixtures was investigated with mercury intrusion porosimetry (MIP). The mixture samples were prepared at their maximum dry unit weight and optimum moisture content. Effect of adding fly ash to gold tailings (i.e., 0, 20, and 40% of the dry weight of tailings) was examined, and a comparison was made on samples prepared at the same fly ash content by replacing gold tailings with humic acid (i.e., gold tailings and humic acid ratios of 100:0, 90:10, and 80:20 by weight) or by varying pore fluid chemistry (i.e., water and salt solutions of 1M NaCl and CaCl2). The results show that the initial thermal conductivity of the samples is sensitive to the mixture proportion and a declination in the thermal conductivity is observed due to hydration of fly ash and evaporation. Inclusion of fly ash and salts into gold tailings improves the unconfined compressive strength but the presence of humic acid in samples leads to the decrease of the strength. MIP results reveal the pore structure changes associated with the packing states of the samples that reflect the influential factors considered. [ABSTRACT FROM AUTHOR]

For the safe disposal of high-level radioactive waste, different host rocks are currently being considered. The favorable properties of clay are low permeability, some retention capacity concerning radionuclides, and the ability to self-seal cracks and fissures, e.g. by swelling or time-dependent compaction creep. In Switzerland, the Jurassic Opalinus Clay is envisaged as a potential host rock which-at Mont Terri-is subdivided into the sandy, shaly, and carbonate-rich facies, the latter being less abundant. For long-term safety assessments, the understanding of the relations of properties (e.g. mineralogical composition and microstructure) and performance (e.g. mechanical behavior) of clays and claystones is essential. In the case of the sandy Opalinus Clay, the mechanical strength increases with increasing carbonate content, because carbonates form the matrix. The mineralogical investigation of a set of sandy facies samples proved a significantly larger carbonate content (20-40 mass %) when compared to the shaly facies (10-20 mass %). The carbonates of the shaly Opalinus Clay, on the other hand, are mostly localized fossils aligned parallel to the bedding, acting as predetermined breaking points. Image analysis of SEM images of polished sections proved the determined microstructural differences. In addition, carbonate particles of the sandy facies are mostly isometric, whereas carbonate particles of the shaly facies cover a greater range of shapes. The mechanical tests were accompanied by investigations of the p- and s-wave velocities, which revealed that the anisotropy of the sandy facies is less pronounced than sedimentological analyses would suggest. The mechanical strength, which, for the first time, presents results of real triaxial tests of the sandy facies. The samples of the sandy facies exhibit a failure strength of σ, approximately twice as high as was found for the shaly facies considering the deformation axis parallel to the bedding. Similar values were obtained when measuring perpendicularly to the bedding. [ABSTRACT FROM AUTHOR]

Żelaźniewicz, A., Kromuszczyńska, O. and Biegała, N. 2013. Quartz c-axis fabrics in constrictionally strained orthogneisses: implications for the evolution of the Orlica-Śnieżnik Dome, the Sudetes, Poland. Acta Geologica Polonica, 63 (4), 697-722, Warszawa. The Orlica-Śnieżnik Dome (OSD), NE Bohemian Massif, contains in its core several gneiss variants with protoliths dated at ~500 Ma. In the western limb of the OSD, rodding augen gneisses (Spalona gneiss unit) are mainly L>S tectonites with a prominent stretching lineation. The few quartz LPO studies have produced somewhat discrepant results. Reexamination of these rocks revealed that texture formation was a protracted, multistage process that involved strain partitioning with changing strain rate and kinematics in a general shear regime at temperatures of the amphibolite facies (450-600°C). Quartz c-axis microfabrics show complex yet reproducible patterns that developed under the joint control of strain geometry and temperature; thus the LPOs are mixed features represented by pseudogirdle patterns. Domainal differences in quartz microfabrics (ribbons, tails, quartzo-feldspathic aggregate) are common in the Spalona orthogneisses but uncommon in the sheared migmatitic gneisses. In the latter rocks, the constrictional strain was imposed on the originally planar fabric defined by high-temperature migmatitic layering. The constrictional fabric of the Spalona gneisses may have developed in the hinge zones of kilometer-scale folds, where the elongation occurred parallel to the fold axes. Other occurrences of rodding gneisses throughout the Orlica-Śnieżnik Dome are thought to occupy similar structural positions, which would point to the significance of large-scale folds in the tectonic structure of the dome. [ABSTRACT FROM AUTHOR]

The present paper evaluates the role of microfabric in strain localization patterns observed in soil specimens during its shear deformation in compression and extension triaxial testing. A series of compression and extension lubricated end triaxial tests are performed on Kaolin clay with extreme as well as intermediate microfabrics, which are obtained using slurry consolidation technique by varying calagon content from 0 to 3 %. Intermediate microfabric is the geometric arrangement of particles within the soil mass, which lies in between the particle orientation during two extreme microfabrics; flocculated and dispersed. Flocculated has random orientation of particles with face-to-edge particle contacts and dispersed has parallel orientation of particles with face-to-face particle contacts. When the specimen is subjected to large stress levels in triaxial testing, the particle orientation and geometric arrangement get affected due to the force acting on the clay platelets. In this experimental research, the variation in clay's stress-strain and pore pressure response and initiation, propagation and formation of shear bands at different levels of compression and extension shearing is evaluated using digital image analysis setup associated with triaxial system. [ABSTRACT FROM AUTHOR]

The effect of microfabric on the mechanical behaviour of clays has been explored previously based on the response of dispersed and flocculated microfabrics only. However, the natural clays often have the geometric arrangement of particles between these two extreme cases which can be termed as intermediate microfabric. This paper explores the formation of intermediate microfabric of kaolin clay and its impact on soil's consolidation behaviour by performing self-weight consolidation, slurry consolidation and 1-D consolidation tests. The effect of calgon content (dispersing agent) on geometric arrangement of the particles has been evaluated through cluster size distribution by performing double hydrometer tests. Then these clay slurries have been used to perform the AFM (Atomic Force Microscopy) test to obtain the variation in average angle of particle orientation with respect to the calgon content present in the slurry. AFM technique provides 3D image of the clay sample and 2D image with Z-information with the potential of measuring intermediate microfabric of clayey soil quantitatively including dispersed and flocculated microfabrics. Other traditional techniques such as SEM, TEM & XRD are limited to only qualitative analysis of soil's microfabric, thus, having no capability to measure intermediate microfabric of clay. A methodology of preparing bulk specimens of clay with intermediate microfabric has been developed using slurry consolidation technique; and then these specimens have been consolidated under 1-D loading to evaluate the effect of intermediate microfabric on compressibility and permeability of clay. In this study, all the experiments reports that the dispersed type geometric arrangement increases with the increase in calgon content in soil up to 2 % and then the reverse behaviour is observed at 3 %; which may depend on the required amount of sodium cations to neutralize the negatively charged faces of the clay platelets present in the slurry. [ABSTRACT FROM AUTHOR]

Abstract: In the Hallstatt salt mine (Austria), polyhalite rocks occur in 0.5–1 m thick and several metre long tectonic lenses within the protocataclasite to protomylonite matrix of the Alpine Haselgebirge Fm.. Thin section analysis of Hallstatt polyhalites reveals various fabric types similar to metamorphic rocks of crust-forming minerals, e.g. quartz and feldspar. Polyhalite microfabrics from Hallstatt include: (1) polyhalite mylonites, (2) metamorphic reaction fabrics, (3) vein-filling, fibrous polyhalite and (4) cavity-filling polyhalite. The polyhalite mylonites contain a wide range of shear fabrics commonly known in mylonitic quartzo–feldspathic shear zones within the ductile crust and developed from a more coarse-grained precursor rock. The mylonites are partly overprinted by recrystallised, statically grown polyhalite grains. Metamorphic reaction fabrics of polyhalite fibres between blödite (or astrakhanite) [Na2Mg(SO4)2.4H2O] and anhydrite have also been found. According to previous reports, blödite may occur primarily as nodules or intergrown with löweite. Reaction fabrics may have formed by exsolution, (re-)crystallisation, parallel growth or replacement. This fabric type was only found in one sample in relation with the decomposition of blödite at ca. 61 °C in the presence of halite or slightly above, testifying, therefore, a late stage prograde fabric significantly younger than the main polyhalite formation. [Copyright &y& Elsevier]

Abstract: Transmission Electron Microscopy (TEM) observations confirm theoretical predictions of the location of organic matter (OM) sequestered in fine-grained sediment. Organo-clay micro- and nanoscale fabric images validate for the first time the protective adsorption model of OM preservation. Preservation of OM against enzymatic digestion is demonstrated predominately at locations consistent with our model of the potential energy field that is developed through interactions of clay minerals, the OM, and pore water chemistry. Pores observed in 2-D fabric TEM images of clay muds commonly appear to be totally encapsulated. However, the great majority of these pores are clearly demonstrated to be open in one or more directions when observed in rotated 3-D images. Despite the scarcity of completely closed pores, OM is preserved against enzymatic attack in those locations where the predicted 3-D potential energy of interaction between clay domains and OM is attractive. [Copyright &y& Elsevier]

Abstract: Syntectonic plutons may record short-lived geological events related to crustal melting and deformation of the continental crust. Therefore, interpretation of microstructure and orientation of fabrics is critical in order to constrain space/time/temperature/deformation relationships during pluton crystallization. Here we describe the transition from magmatic to solid-state deformation in the late-Variscan Diorite-Granite Suite (DGS) emplaced along the Santa Lucia Shear Zone. The systematic collection of meso-, microstructural and quartz < c > axis data allow us to examine the spatial distribution and the mode of superposition of different fabrics. We identify three magmatic microfabric types, thought to reflect the microstructural evolution at decreasing melt content during pluton crystallization. Our data suggest that diffusion creep, dislocation creep and grain-scale fracturing cooperated in accommodating the shearing of the partially molten quartzofeldspathic aggregate. We suggest that the switch from upward to horizontal magmatic flow occurred at melt fractions gt; ∼0.40, and that most of the hypersolidus fabrics formed during horizontal flow, reflecting the stress field imposed by the shear zone, and preserving no memory of the ascent stage. [Copyright &y& Elsevier]

The lithomargic clay constitutes an important group of residual soils existing under lateritic soils. This soil is found on the western and eastern coasts of India over large areas. This soil is a problematic one and is very sensitive to water and loses a greater part of its strength when becomes saturated. These high silt deposits have invited many problems such as slope failures, foundation failures, embankment failures, uneven settlements etc. In this investigation an attempt is made to study the effect of cement and quarry dust on shear strength and hydraulic characteristics of the lithomargic clay after the stabilization. Microfabric and mineralogical studies were carried out to find out the reason for the strength development of the stabilized soil using SEM and XRD analysis. The results indicated that there is an improvement in the properties of the lithomargic clay with the addition of cement and quarry dust. The XRD results indicated the formation of CSH and CAH, which are responsible for strength development in the stabilized soil. [ABSTRACT FROM AUTHOR]

Abstract: Field, thin section, and magnetic fabric analyses of monoclinal, contractional kink bands in the Darrington Phyllite of northwestern Washington, USA, provide evidence of kinematic evolution and microstructural processes during kinking. Relationships among internal, external, and rotation angles of kink bands suggest that rotation was a primary mechanism of kinking, and a significant number of kink bands deviate from the “ideal” kink band geometry (equal internal and external kink angles). Dilation spaces (voids) filled with unrecrystallized quartz and/or calcite inside kink bands and along the boundaries are commonly observed in kink bands with unequal kink angles. Evidence for localized interlayer slip inside kink bands includes mica grains protruding into the hinge voids and stair-step geometry of the voids. Interlayer slip allowed for rotation of the internal foliation during kinking. Pressure solution is not ubiquitous inside kink bands from the study area; however, significant pressure solution is associated with “locked” kink bands (equal kink angles). A new approach using the anisotropy of magnetic susceptibility (AMS) shows that the magnetic fabric and susceptibility inside the kink bands differ more from the outside fabric than can be explained by simple rotation of the outside fabric into the kink attitudes. Combined, our observations suggest that fixed-hinge kinking operated at this location, and that veining, interlayer slip, and pressure solution were the dominant deformation mechanisms. [Copyright &y& Elsevier]

Damages to natural building stones induced by the action of frost are considered to be of great importance. Commonly, the frost resistance of building stones is checked by standardised freeze-thaw tests before using. Corresponding tests normally involve 30-50 freeze-thaw action cycles. In order to verify the significance of such measurements, we performed long-term tests on four selected rocks over 1,400 freeze-thaw action cycles. Additionally, numerous petrophysical parameters were analysed to compare the behaviour of rocks in the weathering tests according to the current explanatory models of stress formation by growing ice crystals in the pore space. The long-term tests yield more information about the real frost sensibility of the rocks. A clear deterioration cannot be determined in most cases until 50 weathering cycles have been completed. In the freeze-thaw tests, the samples are also stressed by changing temperature and moisture, indicating that different decay mechanisms can interfere with each other. Thus, thermohygric and moisture expansion are important damage processes. [ABSTRACT FROM AUTHOR]

Abstract: Microfabrics are discussed as features that minimise Helmholtz energy in a system undergoing deformation and metamorphism. The energy minimisation process leads to inhomogeneous deformations and hence the formation of microfabrics at a number of scales. This process together with the requirement for compatibility both with the imposed deformation and local gradients in deformation means the microfabric must refine on smaller and smaller scales in a self-similar manner leading to fractal geometries. Nine independent levels of refinement are necessary to match the nine independent components of a general imposed deformation gradient. The process of rotation recrystallisation is proposed as one example of self similar refinement so that crystallographic preferred orientations (CPO) associated with rotation recrystallisation are presented as fractals whose fractal dimensions reflect the conditions of deformation. Compatibility also has implications for the formation of other microstructures such as non-rational deformation lamellae. The evolution and orientations of microfabrics that minimise energy are related to the history of the imposed deformation gradient (as was originally proposed by Sander) and not the strain tensor as is commonly assumed. As examples, possible models for CPO development in deformed quartz aggregates by rotation recrystallisation and the development of deformation lamellae in deformed quartz grains are presented. [Copyright &y& Elsevier]

Abstract: One of the most commonly used marbles in Spain is “White Macael” marble, quarried in the Macael area of Almeria. Throughout Spanish history, White Macael has been in great demand as an ornamental stone and was used to build pieces of great importance and artistic beauty, such as the Fountain of Lions in the Alhambra (Granada). Over the centuries, such pieces have suffered from decay due to exposure to the elements, as has happened in many other marbles all over the world. The main purpose of this paper was to determine the durability of White Macael marble when subjected to changes in thermal conditions. It was observed that these changes in the presence of humidity were an important factor in marble decay. They produce a progressive loss of cohesion along grain boundaries and an increase in porosity, which are starting points for marble degradation and facilitate the development of other pathologies. [Copyright &y& Elsevier]

Abstract: Oedometric mechanical compaction tests were performed on brine-saturated synthetic samples consisting of silt-clay mixtures to study changes in microfabric and rock properties as a function of effective stress. The silt consisted of crushed quartz (∼100%) with grain size range between 4 and 40μm, whereas the clay consisted of 81% kaolinite, 14% mica/illite and 5% microcline of grain size between 0.4 and 30μm. Five sample pairs ranging in composition from pure silt to pure clay were compacted to 5 and 50MPa effective stress respectively. SEM studies were carried out to investigate microfabric changes in the mechanically compacted silt-clay mixtures. The degree of alignment of the different minerals present (quartz, mica/illite and kaolinite) were computed by using an image analysis software. Experimental compaction have measured the changes in the rock properties such as porosity and velocity as a function of effective stress for different mixtures of clay and silt. Clay-rich samples showed a higher degree of mineral orientation and lower porosity compared to silt-dominated samples as a function of effective stress. Pure clay sample had 11% porosity at 50MPa effective stress whereas the pure silt sample retained about 29% porosity at the same effective stress. The experiments showed that low porosity down to 11% is possible by mechanical compaction only. A systematic increase in strain was observed in the silt-clay mixtures with increasing clay content but the porosity values found for the 50:50 silt-clay mixture were lower than that of 25:75 silt-clay mixture. No preferential mineral orientation is expected before compaction owing to the high initial porosity suggesting that the final fabric is a direct result of the effective stress. Both P- and S-wave velocities increased in all silt-clay mixtures with increasing effective stress. The maximum P- and S-wave velocities were observed in the 25:75 silt-clay mixture whereas the minimum Vp and Vs were recorded in the pure silt mixture. At 50MPa effective stress P- wave velocities as high as 3km/s resulted from experimental mechanical compaction alone. The results show that fine-grained sediment porosity and velocity are dependent on microfabric, which in turn is a function of grain size distribution, particle shape, sediment composition and stress. At 5MPa effective stress, quartz orientation increased as a function of the amount of clay indicating that clay facilitate rotation of angular quartz grains. Adding clay from 25% to 75% in the silt-clay mixtures at 50MPa effective stress decreased the quartz alignment. The clay mineral orientation increased by increasing both the amount of clay and the effective stress, the mica/illite fabric alignment being systematically higher than that of kaolinite. Even small amount of silt (25%) added to pure clay reduced the degree of clay alignment significantly. This study demonstrates that experimental compaction of well characterized synthetic mudstones can be a useful tool to understand microfabric and rock properties of shallow natural mudstones where mechanical compaction is the dominant process. [Copyright &y& Elsevier]