Platy Clay Minerals Research Articles

GNSS and Sentinel-1 InSAR Integrated Long-Term Subsidence Monitoring in Quetta and Mastung Districts, Balochistan, Pakistan

Land subsidence (LS) is a global phenomenon that has affected several urban centres around the world such as Jakarta (Indonesia), Mexico City (Mexico), Xi’an (China), and Iron County (US). It has mainly been attributed to anthropogenic activities such as groundwater exploitation, especially in unconsolidated aquifer systems rich in highly compressible clay and silt. The platy clay minerals rearrange into horizontal stacks after dewatering, leading to a volume change due to overburden. In this study, land subsidence is investigated in the Quetta and Mastung districts, Balochistan, Pakistan, by employing Small Baseline Subset (SBAS) Interferometric Synthetic Aperture Radar (InSAR), Global Navigation Satellite System (GNSS), and groundwater level (GWL) variations. This study represents the first attempt in Pakistan to measure the long-term land subsidence by fusing GNSS and InSAR data for improved validity. InSAR data from the Sentinel-1 satellite in the Ascending (195 scenes) and Descending (183 scenes) tracks were used to analyse LS from December 2015 to December 2022. High-accuracy Trimble NetRS GNSS receivers were used in five locations from October 2006 to December 2022. An average subsidence ranging from 3.2 cm/y to 16 cm/y was recorded in the valley mainly due to the GWL decline and clay-rich sediments, which are prone to compaction due to dewatering. An accumulative LS of 2 m was recorded by the permanent GNSS station in central Quetta from October 2008 to January 2023 (14.2 years). An acceleration in the subsidence from 12 cm/y to 16.6 cm/y after 2016 was recorded by the continuous GNSS. Additionally, the InSAR and GNSS values were compared for validation, resulting in a good correlation between both techniques. A GWL decline ranging from 1.7 m to 6 m was recorded by the piezometers in Quetta during the period 1987–2022. Large- and small-scale fissures were observed in the study area during the surveys. These fissures are responsible for damage to the city’s infrastructure and aquifer contamination. The subsidence profile also agrees with the subsurface lithology. Our assessment concludes that Quetta may be the fastest-sinking metropolitan city in Pakistan. The overexploitation of groundwater and the population explosion may be the main contributing factors for the land subsidence.

Swiss deep drilling campaign 2019–2022: Geological overview and rock properties with focus on porosity and pore-space architecture

A recently completed deep drilling campaign, comprising 9 deep boreholes penetrating the Mesozoic sedimentary sequence of northern Switzerland, yielded >6 km of drillcore. One of the main objectives was to characterise the low-permeability sequence with the lower Jurassic Opalinus Clay in its centre, motivated by the site selection for a deep geological repository for radioactive waste. In this context, the chemical and isotopic composition of the porewater, as well as the mineralogical and petrophysical properties of the rocks, were among the main study targets. In this paper, the main objective was the characterisation of the lithologically diverse Jurassic rock sequence with focus on mineralogy, porosity and pore-space architecture. Given the large amount of data, a well constrained relationship between clay content (relating to fine-grained sheet-silicate minerals) and porosity could be established. Porosity increases with clay content along a concave curve, but in detail minor formation-specific differences of the positions relative to the best-fit curve were identified. These are attributed to the highly variable deposition rates that resulted in different times available for early diagenesis to alter the rock fabric by mineral dissolution and cementation, thereby affecting the compaction behaviour. Pore-size distributions were obtained from N2 ad-/desorption isotherms. A distinct peak at a radius of 3 nm can be clearly correlated with clay minerals, whereas limestones are dominated by pore sizes in the range of 40–100 nm, and marls show intermediate distributions. A conceptual framework is proposed distinguishing a nanometric porosity that is proportional to the clay content and a contribution of larger pores that are related to the geometric incompatibility between platy clay minerals and isometric calcite or quartz. The contribution of these larger pore is thought to explain the curvature of the clay content-porosity relationship and the more limited compaction of the clay in pressure shadows adjacent to the larger grains. A number of outliers towards high porosity at a given clay content were identified in oolites (most strongly in Fe-rich oolites), sandstones and a unit containing coral-reef material. All these units have in common the presence of competent calcite or quartz grains at the time of deposition, leading to grain-supported fabrics and therefore to a more limited compaction in the interstitial pore space.

Structural properties of shear zone materials of the Neogene soft-rock landslides in the northeastern margin of the Tibetan Plateau

Seven landslides among the 110 landslides on the northeastern margin of the Tibetan Plateau in China were selected to analyze the structural development processes within the shear zones. In addition, the platy clay mineral content and mineralogical composition of the shear zone were also investigated. The samples obtained from the vertical profiles were quantitatively studied from top to bottom with respect to their material composition, pore structure, and water properties to understand the changes in the cementation and frictional properties of the shear zone. The results indicate that the structure is progressively modified by fractures, cleavage, and plasticization. Even though there is no sliding surface liquefaction, clayey particles are observed to exhibit slipping and rearrangement. The illite–montmorillonite mixed-mineral layer accumulates near sliding surface in the core zone, and the platy clay minerals are arranged along shearing direction for long shear displacement.

Issues with integrating carbonate sand texture data generated by different analytical approaches: A comparison of standard sieve and laser-diffraction methods

Palaeoenvironmental reconstructive work relies on sediment-texture information as a proxy for particle-transport dynamics. As the integration of data from multiple sources is often sought for studies at the regional scale, a body of work exists that addresses compatibility levels of different analytical approaches. Past insights are derived predominantly from siliciclastic deposits. This study instead addresses standard sieve and laser-diffraction methods of texture analysis on a suite of carbonate beach sands from San Salvador Island, Bahamas. While the near-equant grain shapes of siliciclastic sands generate comparable results between methods, our findings show that laser diffraction tends to overestimate the coarser fractions in carbonate sands, given indiscriminate measurement of elongate particle axes. Peloidal grains that have width-to-length ratios on the order of 0.5 can pass through much smaller mesh sizes when sieved than diffraction would suggest. The resulting deviation in analytical outputs significantly influences measures of skewness, sorting, and other derivative metrics, which vary by up to several Wentworth classes between procedures. Meaningful integration of texture data obtained by different methods is ill-advised when dealing with carbonate beach sands. Similar problems are documented for muddy deposits, wherein platy clay minerals favor size-overestimation by laser diffraction and a size underestimation by settling tube technique. An improved understanding of methodological biases resulting from application of different particle-size methods is needed to help facilitate data-reconciliation efforts. This study provides a glimpse of issues facing the integration of carbonate sand-texture information, troublesome given prevalence of irregular grain shapes.

Results of downhole microseismic monitoring at a pilot hydraulic fracturing site in Poland — Part 2: S-wave splitting analysis

Observations of azimuthal seismic anisotropy provide useful information, notably on stress orientation and the presence of preexisting natural fracture systems, during hydraulic fracturing operations. Seismic anisotropy can be observed through the measurement of S-wave splitting (SWS) on waveforms generated by microseismic events and recorded on downhole geophone arrays. We have developed measurements of azimuthal anisotropy from a Lower Paleozoic shale play in northern Poland. The observed orthorhombic anisotropic symmetry system is dominated by a vertically transverse isotropy (VTI) fabric, produced by the alignment of anisotropic platy clay minerals and by thin horizontal layering and overprinted by a weak azimuthal anisotropy. Despite the dominating VTI fabric, we successfully identified a weaker horizontal-transverse isotropy fabric striking east–southeast. We do this by constraining the rock-physics model inversion with VTI background parameters incorporated from other geophysical methods: microseismic velocity model inversion, 3D reflection seismic, and borehole cross-dipole sonic logs. The obtained orientation is consistent with a preexisting natural fracture set that has been observed using X-ray micro-imaging (XRMI) image logs from a nearby vertical well. The present-day regional maximum horizontal stress direction differs from the observed fracture strike by approximately 45°. This implies that the SWS measurements recorded during hydraulic stimulation of a shale-gas reservoir are imaging the preexisting natural fracture set, which influences the treatment efficiency, instead of the present-day stress.

Silt content approximation of Neogene Surma group mudrocks, Sitakund anticline, Bengal basin

Petrography of the Neogene mudrocks in this study incorporates laser particle size analysis, thin sections and scanning electron microscopy (SEM). Ten representative mudrock samples were collected from outcrops of the Sitakund structure. From the studies, it is evident that mudrocks of Sitakund structure are characteristically silty. The silt content, as estimated by laser grain size analysis, of the mudrocks ranges from 39 to 77% with average of 58%. Significant amount of granular silt with the platy clay minerals is also evident from the SEM micrographs. The silts are mainly quartz, feldspar and micas. The high silt content in the Neogene mudrocks implies an enormous flux of silty sediments with a very high rate of sedimentation allowing little time for a more selective sorting. This supports the geologic history that the uplifting and erosion of Himalaya was at the peak during Miocene and the Ganges mega delta received highest rate of sedimentation and growth rendering shale consistently silty.Bangladesh J. Sci. Res. 30(1&2): 35-43, December-2017

Petrophysical Characterization of Gondwana Shales of South Karanpura Coal Field, Jharkhand, India

Sedimentary rocks such as shales are the most abundant sedimentary rocks in the earth’s crust. Shales are characterized by preferred particle orientations of platy clay minerals, strong laminations and presence of fissility. In petroleum geology, organic shales behave as both source rocks as well as seal rocks that trap oil and gas. In seismic exploration, shales interface with other rocks to form good reflectors. As a result, seismic and petrophysical properties of shales and the relationships among these properties are important for both exploration and reservoir management. The Gondwana shale of South Karanpura coalfield, Eastern India of Barakar (lower Permian) and Barren-Measures (Middle Permian) formation, majorly characterized by non-marine sedimentary fill and narrow graben structures, are used for petrophysical characterization. Because of thermal maturity and high content of organic matter in shale rock, South Karanpura coalfield is considered as one of the potential shale gas field in Damodar Valley Basin and it is a part of the “Gondwana” basins of Eastern India. This paper discusses various experimental techniques that are applied to shales to obtain velocity, elastic properties structure, minerals composition, texture/fabric and pore types. These techniques include ultrasonic acoustic measurements, X-ray diffraction (XRD), and scanning electron microscopy (SEM). The frequency values used for acoustic measurements are 54 KHz (P-wave) and 250 KHz (S-wave). The resolution of these imaging techniques varies from micrometres to angstroms and the resulting images generally reflect the composition, topography, or combination of both. The estimated P-wave velocity for Barren-Measures and Barakar formation varies from 1463–1890m/s and 2110–3947m/s, respectively while the Shear-wave velocity varies from 898m/s–1232m/s to 1306m/s–2515m/s respectively which suggest that formation is hard and compact in the latter case. XRD and SEM analysis reveals the presence of clay minerals and other minerals, organic matter, texture/topography and pore types in the shale rock sample. The clay minerals identified consist of Kaolinite, Illite while Quartz, Siderite, Muscovite, Orthoclase and Rutile comprises of non-clay minerals in the sample.

Modeling the effects of microscale fabric complexity on the anisotropy of the Eagle Ford Shale

Microscale fabric influences the elastic properties of rock formations. The complexity of the microscale fabric of shale results from composition, platy clay minerals, kerogen, and their preferred orientation patterns. This microscale fabric is also the likely cause of the elastic anisotropy of the rock. In this paper, we have developed a comprehensive three-step rock-physics approach to model the anisotropic elastic properties of the Upper Eagle Ford Shale. We started with anisotropic differential effective medium modeling, followed by an orientation correction, and then a pressure adjustment. This method accounts for the microscale fabric of the rock in terms of the complex composition, shape, and alignment of clay minerals, pore space, and kerogen. In addition, we accounted for different pressure-dependent behaviors of P- and S-waves. Our modeling provides anisotropic stiffnesses and pseudologs of anisotropy parameters. The modeling results match the log measurements relatively well. The clay content, kerogen content, and porosity decreased the rock stiffness. The anisotropy increases with kerogen content, but the influence of clay content was more complex. Comparing the anisotropy parameter pseudologs with clay content shows that clay content increases anisotropy at small concentrations; however, the anisotropy stays constant, or even slightly decreases, as the clay content continues to increase. This result suggests that the preferred orientation of clay clusters is preserved at low clay concentration but vanishes at high clay concentration. This method could also be applied to other shales with carefully chosen parameters to model anisotropic elastic properties.

Multimethod 3D characterization of natural plate-like nanoparticles: shape effects on equivalent size measurements

The fundamental properties and processes that govern nanoparticle behavior in colloidal dispersions are critical to predict their performance in applications and also their environmental and health implications. Illite is a platy clay mineral that is present in large amounts in aquatic environments and can be used as a model natural particle for environmental risk assessment. However, the high-aspect ratio of illite makes conventional analysis, usually assuming a spherical size, insufficient for the assessment of shape-dependent properties. In the current paper, a multimethod characterization of a suspension of illite particles was done using atomic force microscopy, scanning electron microscopy, dynamic light scattering (DLS), nanoparticle tracking analysis, differential centrifugal sedimentation, and centrifugal-field flow fractionation coupled to multiangle light scattering and DLS. The relation between the different measurands was investigated, and the effect of the shape on the equivalent particle size was reported. While some of the used techniques are capable of assessing the aspect ratio of illite, the results confirm the need for multiple techniques and analysis of different types of measurands especially for high-aspect-ratio particles.

Extending NMR data for permeability estimation in fine-grained sediments

We combine nuclear magnetic resonance (NMR) transverse relaxation time data and gamma ray data to estimate lithology-dependent permeability in silt- and clay-rich sediments. This approach extends the utility of the Schlumberger-Doll Research (SDR) permeability equation from reservoirs to aquicludes and seals, and thus improves the value and robustness of NMR data. Data from Keathley Canyon, northern Gulf of Mexico show that NMR data can be used to define permeability from 10 −18 to 10 −14 m 2 (0.001–10 millidarcies) as calibrated and tested by direct measurements on core samples. We performed uniaxial, constant rate-of-strain consolidation experiments on sediments from Keathley Canyon to determine core-scale permeability. Permeabilities from these experiments were compared to permeabilities calculated from logging-while-drilling data. A better fit between log-derived permeability and laboratory-measured permeability was obtained using the SDR equation with a variable coefficient A, rather than a constant A as is typically used. We show how A is a function of lithology and can be modeled from gamma ray data. The relationship between A and gamma ray values suggests that variations in A are caused by platy clay minerals and the effect they have on the pore system. Our results provide improved means for permeability estimation for application in basin flow modeling, hydrocarbon migration modeling, and well completion design.

Authigenic palygorskite in Miocene sediments in Linxia basin, Gansu, northwestern China

AbstractThe mineralogical characteristics of authigenic palygorskite occurring with chlorite and illite in Miocene sediments in Linxia basin were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). The XRD results suggest that the mineral composition of the sediments includes mainly quartz, chlorite, illite, calcite, plagioclase, orthoclase, minor palygorskite and small amounts of gypsum and ankerite. Two kinds of palygorskite were observed in the sediments, relatively straight fibrous particles found in matted, felted masses associated with platy chlorite and silky aggregates found in the void spaces. The former probably replaces chlorite grains, growing from the edges or the fissures of chlorite particles. Chlorite grains exhibit bay-shaped or rounded edges, with ambiguous felted boundaries between chlorite particles, indicative of an intensive dissolution process and the growth of palygorskite at the expense of chlorite. Palygorskite is also observed as inclusions within calcite, sprouting from or coating calcite surfaces, suggesting that palygorskite crystallized from solution. The textural relations of palygorskite and the occurrence of ankerite and the characteristically Fe-bearing palygorskite in the sediments suggest the destruction and hydrolysis of chlorite. The ankerite seems to be preferentially present in the void spaces, closely associated with chlorite and illite; fibrous palygorskite crystallizes at the edges of these clay mineral particles and the platy clay mineral particles are gradually replaced by fibrous palygorskite crystals, suggesting that alteration of chlorite to palygorskite involves an interaction with water during the diagenetic process.

Rheological Properties of Aqueous Suspensions of Palygorskite

The rheology of aqueous suspensions of six palygorskites with different particle morphologies has been investigated as a function of clay concentration, adsorbed ion, pH, and electrolyte concentration, using a rotary viscometer. Rheological parameters (plastic viscosity, Bingham yield value, and apparent viscosity) increase with the length/width ratio of individual palygorskite fibers. The plastic viscosity increases linearly with clay concentration within the range investigated (up to 5% w/v). The rheological parameters are higher for clays saturated with divalent ions than those for clays saturated with monovalent ions. For ions of the same valency the rheological parameters tend to increase with decreasing radius of the hydrated ion. The flow of suspensions is pseudoplastic regardless of the nature of the adsorbed ion. Measurements of electrophoretic mobility in very dilute suspensions suggest that the point of zero charge of the palygorskite surface is at pH 4 to 4.5. Scanning electron microscopy indicates significant differences in fiber arrangement between low and high pH values. Face‐to‐face particle association occurs at low pH values, giving rise to close‐packed domains of fibers, while at high pH values the fibers adopt a random orientation. The flow of suspensions is pseudoplastic at pH ≤ 7 and changes to Newtonian at pH ≥ 9. At pH ≤ 7 the rheological parameters remain relatively constant even at high electrolyte concentrations, but at pH ≥ 9 they are influenced significantly by electrolyte addition. Electrolyte‐free palygorskite suspensions at pH 7 are antithixotropic. When the pH falls below 7 or when electrolyte is added, the suspensions coagulate and become thixotropic. Some rheological properties of palygorskite are similar to those of platy clay minerals such as kaolinite and montmorillonite, while other rheological properties deviate considerably. The models developed to explain the rheological behavior of platy clay minerals do not always account for the behavior of palygorskite, because of differences in particle morphology and surface structure.

Electrochemical Properties of Na–Attapulgite

Analytical surface charge (σa), electrophoretic, and physicochemical properties of an homoionic form of Na–attapulgite show some similarity with those exhibited by homoionic sodium forms of the platy clay minerals kaolinite and illite. Both electrophoretic mobility (ue) and analytic or titratable surface charge show dependency on pH and electrolyte concentration (c). Transmission electron microscopic examination indicated that particles were 1000 nm long, lath-like, and of aspect ratios (length:width:thickness) 100:3:1. Estimates of (hydrodynamic) equivalent spherical particle diameter (dse), made with photon correlation spectroscopy (PCS), were found to be ∼400 nm and reflect extreme nonisometric particle shape. Failure of PCS at pH < 6.4 suggests the onset of colloidal instability in this region. The correlation betweenueand σawas found to be approximately linear in the range 3 < pH < 6.5 with more complex behavior at pH > 6.5. Apportionment of titratable charge to particle edges suggests a charge site density that is reasonable for the structure of this clay mineral.

The geotechnical characteristics of an ice-thrust mudstone, Wabamun Lake area, Alberta

This first detailed report of the geotechnical characteristics of ice-thrust soft rock examines Upper Cretaceous, once heavily overconsolidated mudstones in the Highvale coal mine, Alberta. The fissured and brecciated sample from an ice-thrust shear zone in the mine behaves as a lightly overconsolidated sediment in laboratory tests and shows a non-brittle mode of shear deformation with a maximum shear strength close to residual. This behaviour is due to weathering and glaciotectonic deformation, which have jointed, sheared, and remoulded the mudstone, thus eliminating the fabric formed by overconsolidation.In the ice-thrust mudstone, platy clay minerals dominate and have been grouped into aggregations or shear-remoulded matrices. The strength of the brecciated portion of the mudstone ranges from peak to residual. The strength along principal displacement shears is at or close to residual, as back analysis of a slope failure shows. Key words: ice-thrust shear zone, glaciotectonic deformation, consolidation, nonbrittle deformation, principal displacement shears, shear strength.

Loess in the Cypress Hills, Alberta, Canada

Loess deposits in the Cypress Hills were derived from a single, local source located adjacent to the southwestern margin of the plateau. The distributions of sand, clay, and heavy minerals, the changes in thickness of the deposits, and the orientation of the clasts all indicate that the direction of transport was from southwest to northeast. The changes in the textural composition of the loess are reflected in variations in the sorting, with the best sorted material being located in intermediate positions. The loess is depleted in feldspar relative to the source sediments. This depletion is due to the combined effects of weathering of the feldspar to hydrous mica clays and aeolian sorting. The platy clay mineral grains would be less likely to be incorporated into the aeolian load than the spherical and bladed angular quartz grains, and the partially weathered feldspar grains would be similarly preferentially winnowed. The variations noted indicate that loess deposits formed from a single local source will not have uniform textural characteristics, but will vary in texture, sorting, and mineralogy. Similar variations would be expected in continent-wide loess sheets, although the effects of each local source would be masked by the long-distance transport component of the sediment.

Similar Folds and Anisotropy: A Discussion

Previous articleNext article No AccessDiscussion and ReplySimilar Folds and Anisotropy: A DiscussionSusan H. TreagusSusan H. Treagus Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by The Journal of Geology Volume 80, Number 1Jan., 1972 Article DOIhttps://doi.org/10.1086/627718 Views: 1Total views on this site Copyright 1972 The University of ChicagoPDF download Crossref reports no articles citing this article.

The optical determination of spatial (three-dimensional) orientation of platy clay minerals in soil thin-sections

A technique is described to determine the three-dimensional orientation of platy clay minerals and mineral aggregates in soil thin-sections by means of a polarizing microscope equipped with a universal stage and a Berek compensator. The method utilizes the established geometrical relationships between the basal cleavage and the maximum or minimum apparent birefringence in an arbitrary cross-section of a platy clay mineral. Applying this method, it is unnecessary to know or determine the thickness of the thin-section, the refractive indices or the actual birefringence of the clay minerals involved.

Electron micrography of till matrix [Ohio

Wisconsin tills from northeastern Ohio were studied under the electron microscope as fragments from less than 1 to several microns and on surfaces as large as 1/4 inch, using carbon replica techniques. Subhedral grains are composed of illite and chlorite; anhedral grains are kaolinite. Kaolinite is absent from late Cary (just pre-Defiance) till. Nonclay minerals, quartz, feldspar, and calcite, are either absent or exceedingly rare in less than 2 micron sizes, but increase in amount in larger sizes and are common in larger than 4 micron grain sizes. The platy clay minerals are oriented more or less parallel to the horizontal plane of the till in place.