Dominant Clay Mineral Research Articles

Thermal Analysis: A Complementary Method to Study the Shurijeh Clay Minerals

Clay minerals are considered the most important components of clastic reservoir rock evaluation studies. The Shurijeh gas reservoir Formation, represented by shaly sandstones of the Late Jurassic-Early Cretaceous age, is the main reservoir rock in the Eastern Kopet-Dagh sedimentary Basin, NE Iran. In this study, X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopic (SEM) studies, and thermal analysis including differential thermal analysis (DTA), and thermogravimetric analysis (TGA) techniques were utilized in the characterization of the Shurijeh clay minerals in ten representative samples. The XRF studies showed that silica and aluminum oxides are present quantities. The XRD test was then used to determine the mineralogical composition of bulk components, as well as the clay fraction. The XRD patterns indicated the presence of dominant amount of quartz and plagioclase, with moderate to minor amounts of alkali feldspar, anhydrite, carbonates (calcite and dolomite), hematite and clay minerals. The most common clays in the Shurijeh Formation were illite, chlorite, and kaolinite. However, in very few samples, glauconite, smectite, and mixed layer clay minerals of both illite-smectite and chlorite-smectite types were also recognized. The XRD results were quantified, using the elemental information from the XRF test, showing that each Shurijeh exhibited low to moderate amounts of clay minerals, typically up to 21%. The amount of illite, the most dominant clay mineral, reached maximum of 13.5%, while the other clay types were significantly smaller. Based on the use of SEM and thermal data, the results of the identification of clay minerals, corresponded with the powder X-ray diffraction analysis, which can be taken into account as an evidence of the effectiveness of the thermal analysis technique in clay typing, as a complementary method besides the XRD.

Heavy metal and clay mineral analyses in the sediments of Upper Gulf of Thailand and their implications on sedimentary provenance and dispersion pattern

Forty-eight sediment samples collected in the Upper Gulf of Thailand (UGOT) and its nearby rivers including the Mae Klong, Tha Chin, Chao Phraya, and Bang Pakong were analyzed for grain size, heavy metals (Cu, Pb, Zn, Cr, and Cd), and clay minerals. The results reveal that fine-grained sediments with Mz<30μm concentrate in the northern coastal area and coarse-grained fractions increase in a seaward direction. The grain size of the sediments mainly controls heavy metal concentrations. The concentrations of Cu, Pb, Zn, and Cr are higher in the northern part of UGOT, with ranges above 20, 23, 45, and 50mgkg−1, than in other sampling areas. Meanwhile, Cd content is greater than 120μgkg−1 in sediments near the Bang Pakong River mouth and area between the Tha Chin and Mae Klong rivers mouth. The concentrations of heavy metals are higher than background data, and statistical analysis of geo-accumulation index indicates that the study area is either unpolluted to moderately polluted or moderately polluted by heavy metals. Our results also verify that illite is the dominant clay mineral, followed by kaolinite, chlorite, and smectite in terms of semi-quantitative content. Smectite/kaolinite can be used as an indicator to trace the riverine sediment in the study area, which present a counterclockwise dispersion pattern of sediment from the Chao Phraya River.

Research on loess-paleosol engineering geology features from the borehole cores of a typical section in Baoji area, Shaanxi province, China

Despite the vast amount of research regarding loess-paleosol engineering geology features on the Loess Plateau in Northwest China, a completely systematic study from Holocene series (Q4) to Lower Pleistocene series (Q1) is absent. Investigation into this yet unexplored problem was done firstly by sampling undisturbed cores in a typical loess-paleosol section at Jiacun Terrace in Baoji area, Shaanxi province, China. Then physical–mechanical parameters and material formation of the cores were systematically tested in the office. The results show that there is an inversely proportional correlation between density and void ratio, and a directionally proportional correlation between liquid limit and plastic index. The results also show an inversely proportional correlation between compression modulus and compressible factor, and an inverse relationship between internal cohesion and internal friction angle. The depth of collapsible soils in the borehole is about 7.8 m, which is more accurate than published data. The analysis on grain sizes and carbonate content shows that there is a directionally proportional correlation between 0.075–0.010 mm grain content and carbonate content, both of which have inversely proportional correlations with internal cohesion and are directly proportional to internal friction angle. Testing on major clay minerals has proven that there are directly proportional relationships between <0.002 mm colloid grain content with major clay minerals and internal cohesion, as well as an inversely proportional relationship with internal friction angle. In addition, testing also shows that the dominant clay minerals in loess-paleosol series are the mixed-layer illite/montmorillonite (I/S), and are not single illite or montmorillonite or kaolinite. This testing and analyzing of undisturbed core samples from a typical loess-paleosol section is important to the exploration of landslide-triggering mechanisms and engineering construction safety.

Potentiality of clay raw materials from Gram area (Northern Tunisia) in the ceramic industry

The geological study of Miocene clays from Gram area, North West of Tunisia shows an important series of clay materials to use them in the faience ceramic. Selected samples were studied with the objective of analyzing their chemical and mineralogical composition, morphology, particle size, plasticity, thermal analysis and their ceramic aptitude to be used in the faience ceramic. Raw materials are mainly composed of illite and kaolinite are the dominant clay minerals with minor quartz and dolomite.The plasticity indexes are lower than 15.40%, suggesting that these clays are not plastic. Technical characterization was carried out on one representative mixture of Miocene clay samples. The firing characteristics (shrinkage and water absorption) were measured. The optimum firing temperature of clay mixture (M) has been established. These clays could be used in the manufacture of ceramic pieces.

Species Determination and Spectral Characteristics of Swelling Clay Minerals in the Pliocene Sandstones in Xinghai, Qinghai

X-ray diffraction (XRD) and Fourier infrared absorption spectroscopy (FTIR) were conducted to deepen our research on specific species and spectral characteristics of swelling clay minerals in the Pliocene sandstones in Xinghai, Qinghai province. XRD results show that swelling clay minerals are dominant clay minerals in the sandstones, which can be up to 97% in percentage. XRD patterns show 060 reflections of the samples occur both remarkably at 1.534 Å and 1.498 Å, indicating the samples contain physical mixtures of trioctahedral and dioctahedral swelling clay minerals, respectively. Further treatment of Li-300 degrees C heat and glycerol saturation shows the swelling clay minerals collapse to 9.3-9.9 Å with a partial expansion to -18 Å. This indicates the swelling clay minerals dominate montmorillonite and contain minor saponite. The montmorillonite shows no swelling after Li-300 degrees C heat and glycerol saturation because of Li+ inserting into the octahedral layers, which balances the layer charge caused by the substitution of Mg to Al. FTIR results show the samples are composed of a kind of phyllosilicate with absorbed and structural water, which is in agreement with the results of XRD. Absorbed peaks at 913, 842, 880 cm(-1), corresponding to OH associated with Al-Al, Al-Mg, and Al-Fe pairs, further indicates the minerals are dominant dioctahedron in structure. Meanwhile, absorbed peaks at 625 and 519 cm(-1), corresponding to coupled Si-O and Al-O-Si deformation, indicates parts of Si is replaced by Al in tetrahedron. The spectral characteristics of the samples are against the presence of beidellite and nontronite based on the results of XRD and FTIR, while demonstrating an,existence of montmorillonite. This study, to distinguish the specific species of swelling clay species in clay minerals, would be of great importance when using clay mineralogy to interpret provenance and climatic information.

Mineralogical and Geochemical Characteristics of Caprock Formations Used for Storage and Sequestration of Carbon Dioxide

The main objective of the present study is to characterize cap rock formation used for geological storage of carbon dioxide (CO2). The petrophysical properties of several rocks were studied before CO2 injection. This step is necessary for an understanding of CO2-brine-rock interactions. The mineralogical composition of several clay samples collected from real storage sites located in the south of Tunisia was determined by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) coupled to a probe EDS, infrared spectroscopy, thermal analysis and fluorescence spectra. The obtained experimental results reveal that illite, calcite and quartz are the dominant clay minerals. Dolomite and albite are also present. Besides, SEM analysis shows laminated structure for these samples which suggests low crystallinity. This sample contains a higher content of Fe, Cl, Ca and O. The clay cover may also be useful in storage process by immobilizing the migration of CO2 outer of the geological site and activating the process of mineral sequestration.

Complex hydrothermal alteration and illite K–Ar ages in Upper Visean molasse sediments and magmatic rocks of the Variscan Badenweiler-Lenzkirch suture zone, Black Forest, Germany

Post-collisional Upper Visean molasse sediments and magmatic rocks of the Badenweiler-Lenzkirch Zone reveal by microscopy of thin sections different degrees of hydrothermal illitization of feldspar and mica particles, and XRD, IR and XRF data of the <2 µm fractions show illitic material as the dominant clay mineral consisting of a mixture of 1M and 2M1 polytypes. Moreover, small amounts of illite/smectite mixed-layer minerals of R1-ordering are proved in the granites. In the separates, two illite mixing lines with different Fe + Mg contents are verified between authigenic illite from feldspar alteration and detrital illite in the molasse sediments, as well as between authigenic illite from feldspar alteration and altered mica flakes in the granites. Fe-rich detrital chlorite is present within the molasse sediments, while mixtures of high aluminous Fe-poor dioctahedral/di-trioctahedral chlorite with randomly interstratified chlorite/smectite mixed-layer minerals are formed from feldspar alteration in the granites. Illite K–Ar dating of the <2 and <0.63 µm fractions yields hydrothermal illitization of feldspar and partial resetting of the K–Ar system of detrital illite and mica flakes in the molasse sediments at ≥200 °C during Upper Permian to Middle Triassic times, while the granites in the eastern part of the study area were not altered contemporaneously. In contrast, hydrothermal activity at ≤200 °C during Upper Jurassic to Lower Cretaceous times occurred in the granites, whereas these temperatures were too low for resetting the older ‘Permo–Triassic’ illite K–Ar ages in the molasse rocks. Within both K–Ar age clusters, the data are seen to decrease with grain size and portion of illite 2M1 polytype. The alteration phenomena indicate multiple hydrothermal episodes in the study area, and they match those from the Central and Western European crust as fluid supply was controlled geodynamically by episodic break up of Pangea.

Hyperspectral analysis of clay minerals

Abstract. A study was carried out by collecting soil samples from parts of Gwalior and Shivpuri district, Madhya Pradesh in order to assess the dominant clay mineral of these soils using hyperspectral data, as 0.4 to 2.5 μm spectral range provides abundant and unique information about many important earth-surface minerals. Understanding the spectral response along with the soil chemical properties can provide important clues for retrieval of mineralogical soil properties. The soil samples were collected based on stratified random sampling approach and dominant clay minerals were identified through XRD analysis. The absorption feature parameters like depth, width, area and asymmetry of the absorption peaks were derived from spectral profile of soil samples through DISPEC tool. The derived absorption feature parameters were used as inputs for modelling the dominant soil clay mineral present in the unknown samples using Random forest approach which resulted in kappa accuracy of 0.795. Besides, an attempt was made to classify the Hyperion data using Spectral Angle Mapper (SAM) algorithm with an overall accuracy of 68.43 %. Results showed that kaolinite was the dominant mineral present in the soils followed by montmorillonite in the study area.

Identifying a reference frame for calculating mass change during weathering: A review and case study utilizing the C# program assessing element immobility and critical ratio methodology

The first step in calculating mass changes that occur during the transformation of plutonic rock to saprock involves the determination of a reference frame, i.e., an immobile element whose mass was conserved during the alteration process. Procedures for identifying the statistical properties of immobile elements have been available since 1990, but have not generally been applied. We therefore developed the C# program, Assessing Element Immobility (AEI) that allows for rapid assessment of those elements possessing the statistical properties of immobility. AEI utilizes algorithms that test for equal distributions and unchanging means of ratios, subcompositional independence, and subcompositional invariance. Following discussion of the general mathematical and statistical procedures implemented in AEI, we utilize it in a case study involving three sites in an ~30m thick section of regolith. ZR I is located near the base of the regolith, while ZR II and ZR III are located at depths of ~20m and ~5m respectively. From each site previous workers chemically analyzed a number of samples from saprock and adjacent unweathered corestones. In addition, XRD work showed that from ZR I to ZR II to ZR III biotite was altered to vermiculite, vermiculite+kaolinite, and vermiculite+mixed-layer biotite/vermiculite+kaolinite respectively. At ZR III the most dominant clay mineral is kaolinite. AEI performs a series of tests to assess whether or not a given set of elements possess the statistical properties for immobility. It identified the following elements as a potential reference frame: Al, Na, Fe, Mg, Ti, and P at ZR I; Si, Al, Fe, Mn, Mg, Ti, and P at ZR II; and Mg and Mn at ZR III. However, critical ratio methodology indicated that the precision, as measured by the smallest 95% confidence interval, is greatest for Al2O3corestone/Al2O3saprock and Na2Ocorestone/Na2Osaprock at ZR I, for SiO2corestone/SiO2saprock at ZR II, and for MgOcorestone/MgOsaprock at ZR III. Mass balance results using Al2O3 and Na2O at ZR I were nearly identical, and as a result, only the results derived from Al2O3 are reported here. Using Al2O3, SiO2, and MgO as reference frame elements for ZR I, ZR II, and ZR III respectively revealed the following statistically significant losses of K mass; ~14% (+9%/−8%) at ZR I, ~28% (+11%/−9%) at ZR II, and ~33% (+8%/−7%) at ZR III. In addition, at ZR III, the statistically significant loss of ~36% (+13%/−11%) P mass is attributed to the dissolution of apatite, and the small nominal loss of ~6% (+5%/−5%) Ca mass may reflect incongruent leaching of plagioclase and/or apatite. In contrast, the small additions of ~5% (+5%/−4%) Al, 5% (+2%/−2%) Fe, and 4% (+2%/−2%) Ti mass at ZR III are likely the result of the translocation of kaolinite and kaolinitized biotite particles into the crack system by downward percolating fluids, and the exchange and adsorption of Al, Fe, and Ti ions onto the illuviated clay lining as it evolved over time. Overall, the interplay between eluviation and illuviation at ZR III translates into a statistically significant 5% (+3%/−3%) increase in bulk mass.

Fourth IGS-Ferroco Terzaghi Oration: 2014

Engineering behavior of fine-grained soils depends upon the clay mineralogical composition of the soils and the pore medium chemistry as well. A greater part of the soil–pore liquid interaction is both physical and physico-chemical in nature. This can be attributed to the charge deficiency on the surfaces and edges of the clay platelets and the associated electrical attractive and repulsive forces. Clay minerals that are present in the fine-grained soils can be broadly grouped into kaolinitic and montmorillonitic types. This paper discusses in detail the physical and engineering behavior of fine-grained soils as influenced by the dominant clay minerals composing them and by the pore medium chemistry. It has been brought that the liquid limit, sediment volume, undrained shear strength and compressibility behavior of kaolinitic and montmorillonitic clayey soils are quite opposite to changes in the pore medium chemistry. The drained strength and secondary compression coefficient of both kaolinitic and montmorillonitic fine-grained soils are primarily controlled by the modified effective stress (i.e., net contact stress at the particle level), which takes into consideration both attractive and repulsive forces in addition to the conventional effective stress. The hydraulic conductivity of fine-grained soils is significantly influenced by the nature of the fluid, especially so in montmorillonitic soils.

The Pretty Hill Formation as a natural analogue for CO2 storage: An investigation of mineralogical and isotopic changes associated with sandstones exposed to low, intermediate and high CO2 concentrations over geological time

The Pretty Hill Formation of the Otway Basin (Australia) has been studied as a natural analogue for geological storage of anthropogenic CO2 in order to examine the effects that CO2 concentration and reservoir heterogeneity have on CO2-related reactions. New petrographic data are presented, which validate the use of Hylogger™ as a tool to investigate high-resolution vertical changes in reservoir mineralogy. The integrated data set confirms earlier interpretations, showing that chlorite has been altered to kaolinite and siderite/ankerite in reservoir facies exposed to moderate and high CO2 concentrations, while chlorite remains the dominant clay mineral in all parts of the formation where CO2 content is low.Differences have been observed in the degree of CO2-related reaction relative to CO2 concentration and reservoir heterogeneity. Where CO2 content is very high (c. 98mol%) and associated with high water saturations, both chlorite and detrital feldspars have undergone complete reaction in the reservoir facies, resulting in quartzose sandstones with a kaolinite matrix, and with siderite as the dominant carbonate precipitate. Conversely, where CO2 content is moderate (c. 29–57mol%) and within the gas leg of the reservoir, chlorite has undergone significant reaction, but much of the original feldspar is preserved, suggesting relatively minor reaction. Carbonate cements from the moderate CO2 gas-leg comprise calcite, siderite and ankerite, occurring as cemented zones associated with rock heterogeneities and the present-day gas–water contact. Heterogeneities within the gas-leg are likely to have associated pore fluid contacts, whereby relatively high water saturations will be present in the fine-grained baffles and seals. The most advanced feldspar reaction occurs locally at the contact between baffles and reservoir rock, while reactions have been significantly impeded in the finer grained units due to their low permeabilities.Stable isotope data presented for carbonate cements analysed from wells with low and moderate CO2 levels show no clear distinction. Relatively early formed calcite has δ13C values that require an organic carbon source, suggesting precipitation unrelated to the reservoir CO2 in the Otway Basin. In contrast, diagenetically late calcite and siderite samples display two distinct δ13C groups (dependent on carbonate type), where the calculated fluid carbon isotope compositions are similar to documented magmatic CO2 reservoired in the nearby Caroline Field. This suggests that magma-derived CO2 may have been more prevalent through the Pretty Hill Formation than previously thought. Although the CO2 has not been contained over the long term in the low CO2 sites, it may have caused the local dissolution of carbonate and laumontite cement, and also contributed a source of carbon for late-stage calcite cements.These studies illustrate the importance of understanding both the reservoir composition and vertical heterogeneity of potential storage systems. Fluid–mineral reactions are likely to be advanced within stacked reservoir facies and impeded within siltstone layers, while the distribution of carbonate cement may increase the reservoir heterogeneity by the formation of cemented siltstone/sandstone layers, thereby creating impermeable barriers or baffles to CO2.

Geological controls and estimation algorithms of lacustrine shale gas adsorption capacity: A case study of the Triassic strata in the southeastern Ordos Basin, China

High-pressure methane adsorption experiments on a series of Triassic lacustrine shale moisture-equilibrated samples from the southeastern Ordos Basin, China, were conducted at pressure up to 20MPa, two of which were measured at 30°C, 40°C, 50°C, 60°C, and 70°C, and seven were performed under reservoir temperature (from 48°C to 62°C) to investigate the effect of organic matter content, maturity, mineralogical compositions and reservoir conditions (temperature and pressure) on the methane sorption capacity. The total organic carbon contents (TOCs) range from 0.91wt.% to 6.11wt.%. The thermal maturities, as inferred from Rock-Eval Analysis, range from low mature to high mature. The minerals of the shale samples are dominated by clays (36–57wt.%) and quartz (19–44wt.%). For the entire shale samples the dominant clay minerals are mixed-layer illite/smectite with some illite and no smectite exists, corresponding to a stage of late diagenesis. The studied samples have N2 BET surface areas ranging between 1.47 and 9.21m2/g and pore volumes of 0.013–0.034cm3/g.The methane sorption capacities of moisture-equilibrated shale samples show a positive correlation with TOC contents and BET surface areas. No relationship was observed between the clay contents and methane sorption capacities, indicating that clay minerals do not significantly contribute to methane sorption capacity in these organic shales. The Langmuir pressure (PL) increases exponentially with temperature and the Langmuir volume (VL) decreases linearly with temperature. A computational scheme has been developed to calculate the methane sorption capacity of shales as a function of TOC content, temperature and pressure based on Langmuir sorption isotherm function. Using this algorithm methane sorption capacity of organic shales as function of depth can be obtained. Due to the predominating effect of pressure the methane sorption capacity increases with depth initially, through a maximum and then decreases due to the influence of increasing temperature at a greater depth. The maximum gas sorption capacity typically occurs at a depth range between 400 and 900m. With TOC content increasing, the maximum methane sorption capacities of organic shales and the corresponding depths increase.

Palaeogeographic controls on palygorskite occurrence in Maastrichtian-Palaeogene sediments of the Western High Atlas and Meseta Basins (Morocco)

AbstractThe Maastrichtian-Palaeogene series of the Western High Atlas and Meseta Basins in Morocco are particularly rich in palygorskite. The present work is aimed at clarifying the genesis of palygorskite from the interbedded facies and gaining an understanding of their relationships with the depositional environment. The mineralogical characteristics of palygorskite from these series were studied by X-ray diffraction (XRD) and electron microscopy (SEM/TEM). The palygorskite content and microstructure show large geographical and stratigraphical variations in the deposits studied. The palygorskite occurrence is directly related to palaeobathymetry, since it is the dominant clay mineral in shallow marine and restricted environments. According to the morphology of palygorskite crystallites, four types of textures were distinguished. These types of palygorskite are polygenetic, formed by chemical precipitation, by the recrystallization of smectite clays or reworked by wind or water from sub-aerial environments. The difference between the two studied sub-basins with respect to palygorskite occurrence is attributed to the palaeomorphology of the hinterlands, to the tectonic differentiation and to the physical-chemical conditions of seawater.

Effective Stress in Clays of Various Mineralogy

The effective stress in clays possessing a significant proportion of one of the clay minerals kaolinite, illite, or montmorillonite was determined based on the suction stress characteristic curves (SSCCs) of the clays. The SSCCs were determined based on the drying soil‐water characteristic curves of the clays for a suction range of 0.03 to about 219.0 MPa. One‐dimensional compressibility behavior of initially saturated clays was also studied by loading clay specimens up to a maximum vertical stress of 21.0 MPa. The effective stress–void ratio responses of the clays during the drying process were compared with their saturated counterparts. The shapes of SSCCs and the magnitudes of minimum and maximum suction stress were strongly dependent on the mineralogy and the properties of the clays. For the clays with kaolinite and illite as the dominant clay minerals, the suction stress decreased, remained nearly constant, and then increased with an increase in the applied suction, whereas it decreased monotonically with increasing suction for the montmorillonite clay. A decrease in the suction stress caused an increase in the effective stress, which in turn reduced the volume of the clays. For applied suctions smaller than the air‐entry value of any clay, equal magnitudes of suction stress and effective stress produced a similar volume change of the clay. The study clearly showed that suction changes beyond the air‐entry value are less effective in producing volume changes in unsaturated soils, primarily because of a decrease in the effective stress due to an increase in the suction stress.

Influence of Clay Mineralogy on Plasticity of Lateritic Soils

Lateritic soils samples taken from four different locations were subjected to plasticity tests and clay mineralogical analysis using method of X-ray diffraction. The results of the plasticity test of the soils indicate liquid limit values of the soils ranging between 35.00 to 52.30 %. The plasticity index and linear shrinkage of the soils ranges from 15.73 to 24.70 % and 8.21 to 16.64 % respectively. The clay mineralogy results show three of the soil samples, having lower plasticity values, consisting of mostly kaolinite as clay mineral, while the soil having relatively higher plasticity value (liquid limit of 52.30 %, plasticity index of 24.70 % and linear shrinkage of 16.64 %), shows presence of a mineral of the chlorite group as the dominant clay mineral. This shows that the relatively lower and higher water affinity of kaolinite and chlorite respectively, present in this soils were responsible for the recorded plasticity values.

High exchangeable calcium concentrations in soils on Barro Colorado Island, Panama

The soils on four lithologies (basaltic conglomerates, Bohio; Andesite; volcanoclastic sediments with basaltic agglomerates, Caimito volcanic; foraminiferal limestone, Caimito marine) on Barro Colorado Island (BCI) have high exchangeable Ca concentrations and cation-exchange capacities (CEC) compared to other tropical soils on similar parent material. In the 0–10cm layer of 24 mineral soils, pH values ranged from 5.7 (Caimito volcanic and Andesite) to 6.5 (Caimito marine), concentrations of exchangeable Ca from 134mmolckg−1 (Caimito volcanic) to 585mmolckg−1 (Caimito marine), and cation exchange capacities from 317mmolckg−1 (Caimito volcanic) to 933mmolckg−1 (Caimito marine). X-ray diffractometry of the fraction <2μm revealed that smectites dominated the clay mineral assemblage in soil except on Caimito volcanic, where kaolinite was the dominant clay mineral. Exchangeable Ca concentrations decreased with increasing soil depth except on Caimito marine. The weathering indices Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Weathering Index of Parker (WIP) determined for five soils on all geological formations, suggested that in contrast to expectation the topsoil (0–10cm) appeared to be the least and the subsoil (50–70cm) and saprolite (isomorphically weathered rock in the soil matrix) the most weathered. Additionally, the weathering indices indicated depletion of base cations and enrichment of Al-(hydr)oxides throughout the soil profile. Tree species did not have an effect on soil properties. Impeded leaching and the related occurrence of overland flow seem to be important in determining clay mineralogy. Our results suggest that (i) edaphic conditions favor the formation of smectites on most lithologies resulting in high CEC and thus high retention capacity for Ca and (ii) that there is an external source such as dust or sea spray deposition supplying Ca to the soils.

Mineralogical Composition Of Soils From Urir Char ? A Tiny Offshore Island Of Bangladesh

Mineralogical composition of three surface soils from Urir Char ? an environmentally vulnerable small offshore island of Bangladesh ? was determined by X-ray diffraction analysis. In the bulk soils layer silicates and quartz were the dominant minerals while the quantity of feldspars was around ten percent. Quantity of weatherable minerals was very high in the soils. Illite was the dominant mineral in the clay fraction of the soils. The second dominant clay mineral was smectite which comprised around one-fourth of the clay fraction closely followed by chlorite with a small quantity of kaolinite mineral. Soil vermiculite and mixed layer minerals were absent in these soils. These soils had a mixed mineralogical composition with a high cation exchange capacity and percent base saturation. Texturally the soils were silty loam. Exchangeable Ca++/ Mg++ ratio was less than unity. Magnesium solonization was considered as the dominant pedogenic process along with gleization. There was problem of salinity as the elevation of land was around one meter above the mean sea level. Natural calamities like tropical cyclones and tidal surges were highly devastating as the island was completely washed with sea water. J. Asiat. Soc. Bangladesh, Sci. 39(1): 95-104, June 2013 DOI: http://dx.doi.org/10.3329/jasbs.v39i1.16038

Effective strength of incoming sediments and its implications for plate boundary propagation: Nankai and Costa Rica as type examples of accreting vs. erosive convergent margins

The location of the seaward tip of a subduction thrust controls material transfer at convergent plate margins, and hence global mass balances. At approximately half of those margins, the material of the subducting plate is completely underthrust so that no accretion or even subduction erosion takes place. Along the remaining margins, material is scraped off the subducting plate and added to the upper plate by frontal accretion. We here examine the physical properties of subducting sediments off Costa Rica and Nankai, type examples for an erosional and an accretionary margin, to investigate which parameters control the level where the frontal thrust cuts into the incoming sediment pile. A series of rotary-shear experiments to measure the frictional strength of the various lithologies entering the two subduction zones were carried out. Results include the following findings: (1) At Costa Rica, clay-rich strata at the top of the incoming succession have the lowest strength (μres = 0.19) while underlying calcareous ooze, chalk and diatomite are strong (up to μres = 0.43; μpeak = 0.56). Hence the entire sediment package is underthrust. (2) Off Japan, clay-rich deposits within the lower Shikoku Basin inventory are weakest (μres = 0.13–0.19) and favour the frontal proto-thrust to migrate into one particular horizon between sandy, competent turbidites below and ash-bearing mud above. (3) Taking in situ data and earlier geotechnical testing into account, it is suggested that mineralogical composition rather than pore-pressure defines the position of the frontal thrust, which locates in the weakest, clay mineral-rich (up to 85 wt.%) materials. (4) Smectite, the dominant clay mineral phase at either margin, shows rate strengthening and stable sliding in the frontal 50 km of the subduction thrust (0.0001–0.1 mm/s, 0.5–25 MPa effective normal stress). (5) Progressive illitization of smectite cannot explain seismogenesis, because illite-rich samples also show velocity strengthening at the conditions tested.

Stress–strain characteristics of two natural soils subjected to long-term acidic contamination

This paper seeks to investigate the effect of acidic contamination on the stress–strain characteristics of two natural soils with different mineral compositions: Kawasaki mud that contains montmorillonite and Yurakucho silt that has kaolinite as the dominant clay mineral. To reproduce the process of soil contamination in the laboratory, a special container was designed in which soil samples were leached with solutions of sulfuric acid for a period of almost 300 days. The laboratory investigation included a series of undrained triaxial compression tests on the leached samples. The obtained results indicate that the acidic contamination had a strong influence on the strength characteristics of the soils, and that the mineralogy of the clay fraction as well as the concentration of acid in the pore fluid significantly influenced the stress–strain behavior of the studied soils. It was found that for the Kawasaki mud, a decrease in pH from 7.3 to 6.0 led to an increase in soil strength. For the Yurakucho silt, a small decrease in pH (pH=6.0) also brought about a slight increase in soil strength. However, a further decrease in pH (pH=4.0) caused a significant reduction in the soil strength. An attempt was made to provide a rational explanation for the observed behavior of the soils based on the fundamentals of colloid chemistry and the available literature.

Important Properties of Clay Content of Lateritic Soils for Engineering Project

Clay-sized particles have been shown to control the engineering performance of lateritic soils, while the mode of formation and mineralogical composition of parent rocks in evaluating properties peculiar to clay-sized particles are yet to be a subject of serious research. Fresh Gneiss (GN), Quartz-schist (QS) and Granite (GR) were sampled in parts of Southwestern Nigeria. Thirty samples each of disturbed and undisturbed soils were also obtained at depths of 1.0, 1.5, 2.0, 2.5 and 3.0 m from profiles over GN, QS and GR. X-ray fluorescence and X-ray diffraction were employed to determine the major oxide geochemistry and clay mineralogy respectively, while grain-size distribution, plasticity characteristics, undrained cohesion (Cu) and volume compressibility (Mv) were determined following the British Standards (BS-1337). Parent rocks petrography reveals quartz and muscovite in QS, and quartz, alkali feldspars and biotite in GN and GR. SiO2/Fe2O3+Al2O3 indicates that soils form GN and GR fall into a class different from QS. Kaolinite (52.3-75.5%) formed the dominant clay mineral in the soils with subordinate amount of illite (2.3-17.6%), while 1.9 and 0.9% of smectite occurred at 3.0 m depth in soils over GN and GR respectively. The relationship between Ip and Fe2O3 taking cognizance of parent rock factors reveals the form of iron oxide that reduces the plasticity of lateritic soils. The mode of formation and mineralogical composition of parent rocks caused variation in cohesion and compressibility characteristics of lateritic soils.