Dominant Clay Mineral Research Articles

Mineralogical study of kaolinitic clays from Sidi El Bader in the far north of Tunisia

The study concerns kaolinitic clay deposits occurring at Sidi El Bader, near Tabarka, north of Tunisia. At this site, clay is mined for the manufacture of the renowned Nabeul pottery. Two clay samples, SB1 and SB19, were selected that represent the lower and upper part of the quarry section, respectively. The clay deposits at the base of the quarry are brown whereas the clay deposits at the top are white to beige. These clays are associated with the Numidian Flysch of the Kroumiries mountain chain. The data from several analytical techniques (XRD, chemical analysis, SEM, infrared absorption spectroscopy, thermal analysis (TG/DTA) and optical proprieties) reveal that kaolinite and illite are the dominant clay minerals. Quartz and trace amounts of titanium oxide are also present. The size of clay particles of sample SB1 is about 2 μm and their shape is sub-rounded, which suggests low crystallinity. In contrast, the size of clay particles of sample SB19 is up to 6 μm and particles are elongated pseudo-hexagonal flakes consistent with higher crystallinity. This sample contains a lower content of Fe2O3 and TiO2 compared with the SB1 clay sample. The higher amounts of impurities including illite, titanium oxide and iron affect the whiteness and may also reduce the size and the crystallinity of the clay platelets from the clay deposits of the lower part of the quarry.The lowermost poorly crystalline kaolinite could be used for the fabrication of various ceramics (pottery and binding materials, as bricks and tiles). This clay may also be useful in environmental protection by immobilizing pollutants. The uppermost more crystalline kaolinite may be suitable for processing to produce a kaolin that meets specifications for industry fillers and other uses that demand high whiteness and low impurity contents.

Clay mineralogy of archaeological soil: an approach to paleoclimatic and environmental reconstruction of the archaeological sites of the Paharpur area, Badalgacchi upazila, Naogaon district, Bangladesh

A geo-archaeological examination was carried out in and around the Paharpur area, Badalgacchi upazila of Naogaon District in the north-western part of Bangladesh. Clay mineralogy and global paleo-temperature curves were used to determine the paleoclimatic and depositional environmental conditions of the Holocene archaeological soils (Barind clay residuum) of the Paharpur archaeological spot. Clay mineralogical data show that the dominant clay mineral is illite with subordinate amounts of kaolinite and chlorite. The high illite and low kaolinite content implies a marine or estuarine deposit. The clay mineral ratio log diagram, constructed by plotting the 7–10°A integrated intensity ratios versus depth, supports this assumption. The presence of illite, together with quartz and feldspar, suggests high detrital input under generally cool to temperate and dry climates. Chlorite is another common by-product of weathering reactions with low hydrolysis, which is typical for cool to temperate and dry climates. The results suggest the existence of a marine–estuarine influence under a generally cool to temperate and dry climates around Paharpur and the surrounding region throughout the Pala dynasty around mid-century 700 a.d. to early 1100 a.d. Furthermore, this observation is consistent with the global paleo-temperature curves.

Late Quaternary climate and sea-level changes recorded in sediment composition off the Büyük Menderes River delta (eastern Aegean Sea, Turkey)

Influences of Holocene climatic and sea level changes on sedimentation on the continental shelf off the Büyük Menderes River delta, SW Turkey were investigated using grain size and X-ray clay mineralogical data on surficial and 14C-dated core sediments collected at 19–81m water depths. Modern, fine-grained, siliciclastic sediments cover most of the seafloor of inner to mid-shelf areas. A narrow, relict belt extends from northwest to south (at 66–81m water depths), where sediments are characterized by abundant sand and gravel (27–52%) and biogenic carbonate (16–44%) contents, and microscopic examination suggests an older origin. The radiocarbon ages of mid and lower sections in cores (3670–10,380yrBP) reflect sedimentation under depositional conditions from early to late Holocene in the study area. Additionally, downcore changes of grain size toward coarser-grained sediments most probably record global climatic effects with sea level changes, specifically the transition from lowstand in early Holocene to highstand at mid–late Holocene. The presence of this relict belt in offshore waters can be attributed largely to active uplift tectonics. The coarser-grained relict belt, compared with available seismic profiles, corresponds to an lowstand unconformity of bottomset beds of the prograding Büyük Menderes Delta.Reconstruction from nautical charts clearly showed the presence of an E–W-trending submarine canyon (“Paleo-Büyük Menderes River valley”) in the course of Büyük Menderes Graben. This is interpreted as product of combination of sea-level lowstands and subsidence tectonics throughout the late Quaternary.Smectite (35–62%), illite (28–51%) and kaolinite (12–19%) constitute the dominant clay minerals in the <2μm fraction of the surface sediments. The patterns of clay mineral distribution suggest sediment transport from the Büyük Menderes River and dispersal from the river to the outer continental shelf by the prevailing current regime. Downcore changes in the clay mineral assemblages (downward-decreasing smectite/illite ratios) reflect changes in weathering conditions of the terrigenous source, from a colder climate during early Holocene to relatively warmer periods toward the present. Widely occurring partly metamorphosed volcanic rocks characterize the major geological sources of clay minerals on the adjacent hinterland.

Major soil classes of the metropolitan region of Curitiba (PR), Brazil: I - mineralogical characterization of the sand, silt and clay fractions

The aim of this work was to evaluate the mineralogical and chemical characteristics of most representative soils of the Region of Curitiba, Paraná State. Samples were collected at different depths. The results showed: (a) the quartz was the only identified mineral at the silt and sand fractions. The dominant clay mineral was Kaolinite, with contents ranging from 676.7 to 820.8 g kg-1. The gibbsite was also an important constituent of the most weathered horizons and the hematite and goethite contents were low, mainly in the Histosol; (b) at the C horizon of the Inceptisol, high intensity of vermiculite/smectite reflections were detected (X-ray diffraction), justifying the high capacity of expansion and contraction, normally showed for this soil horizon; (c) was observed a good relation between pedogenetic degree and crystallographic mineral characteristics.

Fibrous-clay mineral formation and soil evolution in Aridisols of northeastern Patagonia, Argentina

Recent studies of soil–landscape relationships in northeastern Patagonia identified fibrous-clay minerals in calcic and petrocalcic horizons developed on old fluvio-glacial plains called “Rodados Patagónicos” (RP). The objectives of this study were: i) to evaluate the occurrence of fibrous-clay minerals in the arid soil environment, and ii) to establish the relationship between the soil properties and degree of the calcic horizon development, including the age of the soils containing fibrous-clay minerals in extra-Andean Patagonia. The soil studied were Calciargids, Natrigypsids, and Petrocalcids, located at elevations of 50, 70, and 130 m a.s.l., respectively. The soils are polygenetic, where the clay mineralogy is related to the age of the pedogenetic periods that affected the formation of geomorphic surfaces. In the surface horizons, illite proved to be the dominant clay mineral and was slightly altered to interstratified illite–smectite and smectite. An older pedogenic episode was identified in argillic and calcic horizons, in which smectite was prevalent. The following soil-formation period was recorded in calcic and calcic-gypsic horizons appearing in the upper limit of the RP. In these horizons, palygorskite is the dominant clay mineral. Pedogenetic carbonate was qualified as low-Mg calcite, indicating that during its precipitation, the Mg 2+ activity increased in the soil solution, favoring the smectite → palygorskite transformation. The soil environment, favorable for this transformation, was the textural transition between the fine materials of sub-surface horizons and the coarsest deposit of RP, where temporary waterlogging occurred. The petrocalcic horizons, and their re-transported fragments, represent the oldest pedogenetic period, where sepiolite was the dominant clay mineral. During the calcretization processes, the sepiolite was precipitated from the soil solution following the formation of palygorskite. Fluorite was identified in the petrocalcic horizon, and its association with calcite and sepiolite indicated a successive precipitation of these minerals under alkaline conditions during evaporation processes.

Effects of Different Parent Material on the Mineral Characteristics of Soils in the Arid Region of Turkey

Physical, chemical and mineralogical characteristics of seven soils developed on four different parent materials such as basalt, limestone, marine and alluvium were studied to determine the effect of parent material on the soil characteristics in the arid and semiarid regions in the Southeast Anatolia Region of Turkey. Parent material have affected the morphology and chemistry of the soils. Carbonate contents of the soils are changing between 14.1 and 42.6%. The high carbonate contents of the soils, developed on the basalt rocks, might be attributed to eolian additions from calcareous soils. The red colour of basaltic soils might be associated with the Fe2O3 content of the parent material. Available Fe2O3 content of the basaltic soils was relatively higher than other soils and measured between 0.56 and 2.05%. Available Fe2O3 content of the soils on the marine was very low and changed between 0.26 and 0.37%. Total Fe2O3 content of the basaltic soils was higher than other soils and changed between 4.36 and 6.70%. The total Al2O3 content of the basaltic soils was obtained relatively higher than other soils and changed between 4.92 and 8.72%. The high Al2O3 and Fe2O3 contents of the basaltic soils may be associated with the weathering of basalt rocks. Also analysis of the basaltic rock samples has showed similar mineralogical composition. X-Ray diffraction analysis data showed that smectite was the dominant clay mineral in all the soils. Palygorskite was the second most abundant mineral after smectite. Moreover, some mineralogical properties reflected the traces of climatic changed during the Holocene. The leaching factor were determined as >1 in the Profile PL2 and as < 1 in the Profiles PL1, PL3, PL4, PL5; PL6 and PL7. The low leaching factor (< 1) may be attributed to weathering of parent material. The soils were classified according to Soil Taxonomy as Aridisol, Entisol, Vertisol and Inceptisol.

Quantitative Mineralogy of Surface Sediments on the Iceland Shelf, and Application to Down-Core Studies of Holocene Ice-Rafted Sediments

Abstract Quantitative X-ray diffraction analyses on the < 2 mm sediment fraction from the Iceland shelves are reported for subglacial diamictons, seafloor surface sediments, and the last 2000 cal yr BP from two cores. The overall goal of the paper is to characterize the spatial variability of the mineralogy of the present-day surface sediments (18 non-clay minerals and 7 clay minerals), compare that with largely in situ erosional products typified by the composition of subglacial diamictons, and finally examine the late Holocene temporal variability in mineral composition using multi-mineral compositions. The subglacial diamictons are dominated in the non-clay-mineral fraction by the plagioclase feldspars and pyroxene with 36.7 ± 6.1 and 17.9 ± 3.5 wt % respectively, with smectites being the dominant clay minerals. The surface seafloor sediments have similar compositions although there are substantial amounts of calcite, plus there is a distinct band of sites from NW to N-central Iceland that contain 1–6 wt% of quartz. This latter distribution mimics the modern and historic pattern of drift ice in Iceland waters. Principal component analysis of the transformed wt% (log-ratio) non-clay minerals is used to compare the subglacial, surface, and down-core mineral compositions. Fifty-eight percent of the variance is explained by the first two axes, with dolomite, microcline, and quartz being important foreign species. These analyses indicate that today the NW–N-central Iceland shelf is affected by the import of exotic minerals, which are transported and released from drift ice. The down-core mineralogy indicates that this is a process that has varied over the last 2000 cal yr BP.

Effect of Clay Deposits on Physicochemical and Intermittent Evaporation Characteristics of Torripsamment

Clay minerals are the key component controlling water storage and movement in irrigated arid soils. This research aims to evaluate the effect of different rates of deposits varied in the clay minerals on physicochemical properties and intermittent evaporation of Torripsamment. Four clay deposits, bentonite, zeolite (clinoptilolite) and treated sewage sludge (TSS) samples were selected and mixed with sandy calcareous soils (five concentrations) followed by saturation with water for 5 wetting and drying cycles. Moisture losses in each cycle were monitored daily; after the 5th cycle penetration resistance and physicochemical properties were measured. Results indicated that increasing application rates alter most of the studied soil properties including cation exchange cpapacity (CEC), electrical conductivity (EC), clay%, silt%, and exchangeable Ca, Mg and Na. The extent of changes in sandy soil properties was variable depending on the deposits type and application rates. Increasing zeolite rates dramatically increase CEC and exchangeable Ca of the treated sandy soil while the corresponding increase of clay contents as a result of zeolite applications was relatively low. Increasing TSS application increased dramatically EC values (dS/m) and exchangeable K compared with all other deposits. TSS showed the lowest average pH, 7.92, whereas the highest pH value, 8.58, was found in Torripsamment-treated bentonite. Bentonite applications significantly increased exchangeable Na in treated sandy soils, followed by Sharqiah and Khulays deposits. Penetration resistance (PR) values of the untreated soil increased significantly with increasing application rate particularly in smectite-rich deposits. Data revealed that 10% application rate of smectite-rich deposits reflected on some physicochemical characteristics of Torripsamment. Application rates of 5% and 10% had the lowest and the highest evaporation (E), respectively. Smectite-rich deposits caused extensive cracking on the surface and consequently increased evaporation. The order of E during the first cycle was zeolite > TSS > Khulays > SharqiahDhurma > Rawdate > bentonite. The best fitting relation between E and t1/2 (E = Ct1/2) in the 1st wetting and drying cycle showed the lowest value of evaporation constant (C) at 5% and 1% application rates for bentonite and zeolite, respectively. The differences in C values between the studied deposits are related to CaCO3, clay contents and the dominant clay minerals.

Mudstone Petrology of the Mesoproterozoic Unkar Group, Grand Canyon, U.S.A.: Provenance, Weathering, and Sediment Transport on Intracratonic Rodinia

Abstract The synthesis of mudstone petrology and interbedded sandstone detrital zircon geochronology provides insights into the provenance, weathering regime, hydrodynamic effects, and diagenesis of the Mesoproterozoic Unkar Group. Unkar mudstones were derived largely from the Grenville Orogen (GO) of southwest Texas and the adjacent Yavapai–Mazatzal (YM) and Southern Granite Rhyolite (SGR) terranes. Detrital zircon data indicate distinct pulses of GO-derived sediment during Hakatai and Dox Formation deposition whereas Shinumo sediment contains a larger component of YM and SGR material. An increase in plagioclase and biotite abundances in the Dox further suggest an orogenic pulse. Bulk chemistry, including elevated Cr and Ni abundances and REE systematics, implicate a heterogeneous provenance for Unkar sediment best approximated by a mix of granite or granodiorite with some basalt. Weathering of Unkar sediment, as determined from mudstone and crystalline-source bulk-chemical trends, is characterized as moderate (CIA values between 55 and 70) indicative of a temperate climate in an orogenic setting. Small (less than 10 wt%) amounts of detrital kaolinite and chlorite are consistent with a moderate (temperate) weathering regime. Illite, the dominant clay mineral in the Unkar Group, is largely the 2M1 polytype and detrital in origin. However, it is estimated that ~ 7% of the K in the Escalante Creek Member results from K-metasomatism and may form up to ~ 15 wt% authigenic 1M or 1Md illite. The clay-size fraction and zircon are the chief contributors to the REE budget in Unkar mudstones. Lithostratigraphic variations in the HREE distributions can be attributed partially to variable zircon abundance in the silt-size fraction, a likely function of hydrodynamic sorting. Age constraints on the duration of Unkar Group sedimentation range from 30 to 100 My for the ~ 1100 m conformable Shinumo–Dox succession and result in compacted sedimentation rates of between 1.0 and 3.6 cm/103 yr. These rates are comparable to Mesozoic foreland-basin settings.

Mineralogical study of some arsenic contaminated soils of West Bengal, India

Five arsenic affected soil profiles, one each from Ghentugachhi and Gotera village of Chakdah block, Gayeshpur, Kalyani block, Nadia district; Ramnagar village of Baruipur block and Sonarpur mouza of Sonarpur block of South 24 Parganas district of West Bengal, India covering the soils of Typic Haplustepts, Typic Endoaquepts, Vertic Haplustepts and Aquic Haplustepts respectively have been studied for their detail mineralogical, chemical composition and also to know the level of arsenic contamination and their probable source. These soils are very deep, developed on Alluvium and are under rice, vegetable and guava cultivation. Sand mineralogy data of these soils are dominated by opaque and limonite, whereas silt is mainly constituted of micas followed by kaolinite and chlorite. The clay mineralogy of the soils indicates that smectite is in higher proportion in Ghentugachhi and Gotera soils followed by mica, kaolinite, chlorite and vermiculite and in the other soils, mica is the dominant clay mineral. In some of these soils, the interstratified mixed layer minerals are also present. The mineralogy class for the soils of Ghentugachhi, Gayeshpur, Baruipur is ‘mixed’ and for Gotera and Sonarpur it is ‘illitic’. Differential thermal analysis (DTA) of clay fraction of surface soil of the profiles displayed the presence of the minerals like magnetite, marcasite, arsenopyrite, illite, montmorillonite and quartz. The source of arsenic in these soils are probably due to the presence of arsenic bearing minerals, marcasite and arsenopyrite, and also it may occur as adsorbtion on iron hydroxide coated sand grains and clay minerals. Arsenic concentration is very high in the surface horizon of pedon 2 (20.2 mg kg − 1 ) and it shows a decreasing trend down the subsurface horizon. The higher concentration of arsenic in the surface horizon may be due to higher abundance of opaque minerals, limonite, and marcasite.

Characterization of Hungarian Red Soils

Some pedological and micromorphological investigations were carried out on representative red clay samples selected from a large number of profiles. On the basis of conclusions drawn from the analytical results, the red clays can be divided into the following groups: - The red clays of the foothills of the Tokaj Mountains were formed on rhyolite or rhyolite tuff, and are covered by loess in some areas. They are relic soils, older than loess, formed under the warm climate of the Tertiary Period. In addition to quartz they contain feldspars, illite, montmorillonite and a small amount of kaolinite. - The red clays of Aggtelek Karst are Tertiary relic soils formed on Mesozoic limestone. The dominant clay mineral is kaolinite, but they contain a siginificant amount of smectite as well. - The red clays of the Northern periphery of the Hungarian Plain are situated on clay, silt and sand layers of different origin or between loess depositions. They were formed in the Pliocene and at the turn of the Pliocene and Pleistocene. These soils have a medium clay content, with a large quantity of montmorillonite and a small amount of kaolinite. - Red clays formed on Permian sandstones . These rocks were formed in the Permian period, and were issued from a mixture of sediments under tropical climate, tropical weathering. They are the signs of the oldest soil formation in Hungary. They can be characterized by their kaolinite, illite, montmorillonite and hematite contents. - The red clays of the Transdanubian hilly region wereformed by the weathering of thePannonian surface between the end of the Miocene Period and the lower Pleistocene. Medium clay content is characteristic of these red clays. They contain kaolinite, montmorillonite, chlorite and a small amount of hematite. Concerning micromorphological features, speckled and granostriated b-fabrics of the groundmass, mainly due to swelling and shrinking, were observed in some samples. Clay coatings are mainly interpreted as micromorphological features of illuviation. The investigated red clays are similar to tropical and sub-tropical ferrallitic soils in respect of their formation and mineral characteristics.

Microtextures on detrital quartz grains of upper Maastrichtian-Danian rocks of the Cauvery Basin, Southeastern India: implications for provenance and depositional environments

Quartz grains from the Kallamedu (late Maastrichtian) and lower Niniyur (Danian) Formations, Cauvery Basin, Southeast India were examined under a scanning electron microscope, and twenty three distinct microtextures were observed. These microtextures have been grouped into three modes of origin, viz. mechanical (thirteen features), mechanical and/or chemical (five features) and chemical (five features) origins. Quartz grains from the Kallamedu and lower Niniyur Formations show conchoidal fractures, straight steps and arcuate steps which are the characteristic microtextures of quartz grains derived from crystalline source rocks. Quartz grains from the upper Kallamedu and lower Niniyur Formations show angular to subangular outline, whereas those from the lower Kallamedu Formation show subangular to rounded outline. The dominance of angular to subangular grains and the presence of straight and arcuate steps suggest that these clastic sediments were undergone short transportation and rapid deposition. The presence of rounded grains in the lower part of the Kallamedu Formation suggests that significant amounts of quartz grains are of recycled origin. Vs, straight scratches and curved scratches, the characteristic features of marine environment, are common on the quartz grains from the lower Niniyur Formation, which is consistent with the previous interpretation. However, quartz grains from the lower Kallamedu Formation exhibit very low frequency of these features, whereas they are moderately present in the upper Kallamedu Formation, suggestive of a change in depositional conditions with time. The lower Kallamedu Formation exhibits planar and trough cross-beddings, which suggests the fluvial depositional environment. The unfossiliferous upper Kallamedu Formation contains appreciable amount of illite and mixed-layer (illite/smectite) clay minerals, which suggests that the saline conditions prevailed during its deposition. Microtextures on the quartz grains coupled with dominant clay mineral types suggest the deltaic depositional environments for the upper Kallamedu Formation.

Mineralogy and geochemistry of clay samples from active hydrothermal vents off the north coast of Iceland

Active hydrothermal vent sites were sampled during 1997 in a series of submersible dives at the active Grimsey (GHF) and Kolbeinsey (KHF) hydrothermal fields off the north coast of Iceland. This study focuses on secondary clay minerals which were formed in two different settings. The GHF is characterized by the presence of clay minerals precipitated within active chimneys. By contrast, the KHF is characterized by the presence of secondary clay minerals, which are the products of hydrothermal alteration of lava fragments. Based on XRD, electron microprobe and ICP-MS analyses, the dominant clay mineral in both hydrothermal fields is saponite (Mg-rich smectite). Chlorite and chlorite–smectite mixed-layer minerals also occur at the KHF. The Mg-rich nature of saponite from the GHF chimneys suggests intense Mg metasomatism in the mixing zone where hydrothermal fluids interact with seawater at temperatures of 250 °C. Saponite formation resulted in the additional uptake of Cu, Zn, and Pb. Enrichment in Ba is evident in the almost pure saponite from the KHF. Based on oxygen isotope data, the saponite formation at the KHF occurred at 148 °C, which is close to the maximum measured fluid temperature of 131 °C in this field.

Climatic control on clay mineral formation: Evidence from weathering profiles developed on either side of the Western Ghats

Many physico-chemical variables like rock-type, climate, topography and exposure age affect weathering environments. In the present study, an attempt is made to understand how the nature of clay minerals formed due to weathering differs in tropical regions receiving high and low rainfall. Clay mineralogy of weathering profiles in west coast of India, which receives about 3 m rainfall through two monsoons and those from the inland rain-shadow zones (<200 cm rainfall) are studied using X-ray diffraction technique. In the west coast, 1:1 clays (kaolinite) and Fe—Al oxides (gibbsite/goethite) are dominant clay minerals in the weathering profiles while 2:1 clay minerals are absent or found only in trace amounts. Weathering profiles in the rain shadow region have more complex clay mineralogy and are dominated by 2:1 clays and kaolinite. Fe—Al oxides are either less or absent in clay fraction. The kaolinite—smectite interstratified mineral in Banasandra profiles are formed due to transformation of smectites to kaolinite, which is indicative of a humid paleoclimate. In tropical regions receiving high rainfall the clay mineral assemblage remains the same irrespective of the parent rock type. Rainfall and availability of water apart from temperature, are the most important factors that determine kinetics of chemical weathering. Mineral alteration reactions proceed through different pathways in water rich and water poor environments.

Dissolution of kaolinite induced by citric, oxalic, and malic acids

Kaolinite is a dominant clay mineral in the soils in tropical and subtropical regions, and its dissolution has an influence on a variety of soil properties. In this work, kaolinite dissolution induced by three kinds of low-molecular-weight organic acid, i.e., citric, oxalic, and malic acids, was evaluated under far-from-equilibrium conditions. The rates of kaolinite dissolution depended on the kind and concentration of organic acids, with the sequence R oxalate > R citrate > R malate . Chemical calculation showed the change in concentration of organic ligand relative to change in concentration of organic acid in suspensions of kaolinite and organic acid. The effect of organic acid on kaolinite dissolution was modeled by species of organic anionic ligand. For oxalic acid, L 2− oxalic and HL − oxalic jointly enhanced the dissolution of kaolinite, but for malic and citric acids, HL − malic and H 2L − citric made a higher contribution to the total dissolution rate of kaolinite than L 2− malic and L 3− citric, respectively. For oxalic acid, the proposed model was R Si = 1.89 × 10 −12 × [ ( 25 x ) / ( 1 + 25 x ) ] + 1.93 × 10 −12 × [ ( 1990 x 1 ) / ( 1 + 1990 x 1 ) ] ( R 2 = 0.9763 ), where x and x 1 denote the concentrations of HL oxalic and L oxalic, respectively, and x 1 = 10 −3.81 × x / [ H + ] . For malic acid, the model was R Si = 4.79 × 10 −12 × [ ( 328 x ) / ( 1 + 328 x ) ] + 1.67 × 10 −13 × [ ( 1149 x 1 ) / ( 1 + 1149 x 1 ) ] ( R 2 = 0.9452 ), where x and x 1 denote the concentrations of HL malic and L malic, respectively, and x 1 = 10 −5.11 × x / [ H + ] , and for citric acid, the model was R Si = 4.73 × 10 −12 × [ ( 845 x ) / ( 1 + 845 x ) ] + 4.68 × 10 −12 × [ ( 2855 x 1 ) / ( 1 + 2855 x 1 ) ] ( R 2 = 0.9682 ), where x and x 1 denote the concentrations of H 2L citric and L citric, respectively, and x 1 = 10 −11.16 × x / [ H + ] 2 .

Porosity and available water of temporarily waterlogged soils in a Quercus robur (L.) declining stand

Pedunculate oak (Quercus robur L.) is particularly sensitive to decline in clayey soils presenting a high-perched temporary water table. These soils induce two successive constraints in one-year cycle: water excess (and hypoxy) in winter and early spring, and water shortage in summer (water stress being more restrictive to oak). We determined the porosity and water properties of temporarily waterlogged clayey soils supporting forest stands of declining Quercus robur trees in a 101 yr-old oak stand in Belgium (50 degrees 06'N 4 degrees 16'E). Roots unevenly colonized the soil down to 1.6 in: fine roots (diameter < 5 mm) were mostly distributed on the surface horizons (0-0.3 in) and around 1.3 in deep, despite dense clayey horizons appearing at 0.35 in depth. Clay content below this depth reached 46-51%. Illite and vermiculite were the dominant clay minerals. The clayey horizons exhibited marked shrink-swell properties: bulk density at 30 kPa increased from 1.41 to 1.88 g cm(-3) from the surface to 2 m depth. There was also evidence of hypoxic conditions caused by water saturation of pore space in the rooting zone from October to mid-April. Extractable water (EW), calculated between moisture tensions of 5 and 1600 kPa was 152.8 mm. The level of perched temporary water table strongly depended on the seasonal rhythm of water uptake by trees and on the shrink-swell behaviour of soil.

Mineralogy, geochemistry and genesis of bentonites of the Ordu area, NE Turkey

AbstractA number of bentonitic clay deposits from the Ordu area (NE Turkey) have been investigated by optical and electron microscopy, X-ray diffraction and chemical analysis. The clays are the alteration products of Late Cretaceous trachytic and trachyandesitic pyroclastic rocks. They contain volcanogenic sanidine, plagioclase, biotite and pumice, along with the diagenetic minerals opal-CT, cristobalite and rare calcite and zeolite (clinoptilolite). Ca-smectite (montmorillonite) is the dominant clay mineral. The rare earth element patterns of all the bentonitic clays are generally similar, although there are variations in the Eu anomaly indicating formation from different types of pyroclastic rocks. Oxygen and hydrogen stable isotope values suggest that the smectite was formed at 20–40°C in pore water of mixed meteoric and marine origin during argillization. These features, together with mass-balance calculations, indicate the enhanced MgO and Sr content of the smectite resulted from formation at shallow burial depths within a dominantly marine environment.

Palaeoclimate reconstructions of the Middle Jurassic of Kachchh (western India): an integrated approach based on palaeoecological, oxygen isotopic, and clay mineralogical data

The Middle Jurassic sedimentary succession of the Kachchh Basin shows significant changes in lithology, faunal content and diversity across the Bathonian–Callovian boundary. The change in lithology from predominantly carbonates in the Middle and Late Bathonian to siliciclastics in the Callovian is accompanied by a drop in species diversity from high to moderate. Characteristic faunal elements of the Bathonian (corals, sponges, the bivalves Eligmus and members of the Opinae) are absent or rare in the Callovian. In contrast, Callovian sediments contain comparatively high proportions of nuculid bivalves. The clay mineral assemblage reveals prominent variations in the smectite vs. kaolinite abundance, especially during the Bathonian to Callovian transition. From the Bajocian to the Middle Bathonian, smectite becomes the dominant clay mineral and is nearly exclusively present in the Late Bathonian. Towards the Middle Callovian, its content gradually decreases and kaolinite becomes the dominant clay mineral. Illite generally is only a minor component throughout the Middle Jurassic. Based on these results, the Bajocian to Middle Bathonian time interval is interpreted to represent subtropical climatic conditions with seasonal droughts and a moderate supply of terrigenous clastics to the basin. The Late Bathonian was a period with a semi-arid climate, hot seasonal droughts and a minor input of terrigenous clastics. The increase in kaolinite contents in the Callovian suggests a subtropical humid climate with less prominent seasonal droughts and a higher input of siliclastics into the basin accompanied by a higher nutrient influx. Oxygen isotope ratios measured on Bathonian to early Callovian brachiopod shells give palaeotemperatures of 19–24 °C. Callovian to Oxfordian paleotemperatures calculated from oxygen isotopes measured on belemnite rostra range from 11 to 21 °C. The lower palaeotemperatures estimated from the oxygen isotopic composition of belemnite calcite are explained by assuming that the belemnites spent most of their life span in colder regions of the Malagassy Gulf and migrated into the warmer subtropical waters of the Kachchh Basin. Combining these various lines of evidence, the changes in lithology and faunal composition taking place in the Kachchh Basin during the Middle Jurassic appear to reflect largely a change towards increasing humidity rather than a distinct decrease in water temperature.

Clay mineral records of East Asian monsoon evolution during late Quaternary in the southern South China Sea

High-resolution clay mineral records combined with oxygen isotopic stratigraphy over the past 190 ka during late Quaternary from core MD01-2393 off the Mekong River in the southern South China Sea are reported to reconstruct a history of East Asian monsoon evolution. The dominating clay mineral components indicate a strong glacial-interglacial cyclicity, with high glacial illite, chlorite, and kaolinite contents and high interglacial smectites content. The provenance analysis indicates the direct input of clay minerals via the Mekong River drainage basin. Illite and chlorite derived mainly from the upper reach of the Mekong River, where physical erosion of meta-sedimentary rocks is dominant. Kaolinite derived mainly from active erosion of inhered clays from reworked sediments in the middle reaches. Smectites originated mainly through bisiallitic soils in the middle to lower reaches of the Mekong River. The smectites/(illite+chlorite) and smectites/kaolinite ratios are determined as mineralogical indicators of East Asian monsoon variations. Relatively high ratios occur during interglacials and indicate strengthened summer-monsoon rainfall and weakened winter-monsoon winds; relatively lower ratios happened in glacials, indicating intensified winter monsoon and weakened summer monsoon. The evolution of the summer and winter monsoons provides an almost linear response to the summer insolation of the Northern Hemisphere, implying an astronomical forcing of the East Asian monsoon evolution.

Micromorphological Characteristics of Vertisols of Iran, Including Nonsmectitic Soils

ABSTRACT Vertisols of Iran occupy about 70,000 ha of arable land. They are located in four provinces mainly: Fars (16,000 ha), as soils on calcareous sediments of lowlands, with a ustic-hyperthermic soil climate; Kermanshah (34,000 ha) and Lorestan (6,000 ha), as soils on calcareous sediments in alluvial plains and on plateaux, with a xeric-thermic soil climate; and Ardebil (11,000 ha), as soils on volcanic parent materials in alluvial plains, with a dry xeric-mesic soil climate. They are classified as aridic gypsiusterts, halic haplusterts, chromic haploxererts, typic calcixererts, chromic calcixererts and vertic calcixerepts. They mostly have a mixed mineralogical composition. Smectite is almost absent in some of the vertisols on calcareous sediments, which have palygorskite and chlorite as dominant clay minerals, especially in the fine fraction. The dominant microstructure in subsurface horizons is a strongly developed angular blocky structure with wedge-shaped peds. The b-fabric is mostly calcitic crystallitic. Decalcified zones show a stipple-speckled b-fabric. The less calcareous soils of Ardebil province have a calcitic crystallitic b-fabric in some parts and a stipple-speckled b-fabric with common granostriation in other parts. Some subsurface horizons contain secondary carbonate accumulations in the form of nodules, coatings, or hypocoatings. Decalcified zones along pores are common in one profile of Kermanshah Province, with associated cytomorphic sparitic carbonate infillings. Fe/Mn hydroxide impregnations are omnipresent, which is an indication of seasonal hydromorphic conditions. Illuvial clay is observed only as thin discontinuous coatings, which are partly juxtaposed on CaCO3 hypocoatings.