Neoformation Of Palygorskite Research Articles

Neoformation of palygorskite in Calcids of Central Iran

Palygorskite has been reported in alluvial sediments and in soil clays in Central Iran, but it is not known if it is inherited or formed in situ. Here, we sampled Calcids developed from Triassic and Cambrian dolomitic formations in the southwestern part of Yazd and performed soil and clay characterization by X-ray diffraction and fluorescence, optical and scanning electron microscopy and energy dispersive X-ray spectrometer analyses. Our results suggested palygorskite neoformation in the calcic soil horizons in Calcids. The soils with aridic soil moisture regime and high Mg concentration, during the formation of a calcic horizon by precipitation of secondary calcite, conditions were suitable for authigenic palygorskite crystals of long size (>10–20 μm) and their stability. In addition, the occurrence of short-size (about 2 μm) palygorskite fibers in the lower gypsic horizon probably resulted from its translocation from the upper horizons. Therefore, such results suggested palygorskite neoformation in the calcic soil horizons in these Calcids of Iran.

Evolution and significance of clay minerals in the Esna Shale Formation at Dababiya area, Luxor, Egypt

The Esna Shale Formation is broadly distributed in Egypt and one of the most of its important clay deposits. These deposits in the Dababiya area, Luxor region were subjected to intensive laboratory investigations (XRD, IR, and SEM analyses). The bulk and clay mineralogy of this formation varies from one layer to the next and comprises the phyllosilicates, calcite as principal minerals with remarkable amounts of quartz, feldspars dolomites, and anhydrite. Fluorapatite, pyrite, schaurteite, despujolsite, goethite, and halite are present in some beds but minor quantities. The clay mineralogy consists of smectite (41%), sepiolite-palygorskite (28%), illite (13%), smectite/illite mixed layers (13%), and kaolinite (6%). Smectite was differentiated into three species: nontronite (21%), Na-and Ca-montmorillonites (13%), and beidellite (8%). Smectites are dioctahedral with a typical fully turbostratic stacking mode and crystallite sizes varying from 2 to 3 nm. The detrital input is the dominant aspect responsible for distributing clay minerals in these marine sediments. The presence of shallow Paleogene constrained basins between arose land areas in Egypt, favorable to the neoformation of palygorskite and sepiolite, It indicates that most of the fibrous clay minerals present in this part of the Tethys could have formed in these coastal basins and that their presence is an indication of aridity. By transcending global sea level that occurred at the end of the Paleocene, the nonappearance of kaolinite at the Dababiya area (southern Egypt) and its richness at the Wadi Nukhul Section (Sinai, Egypt) no relationship is shown between differences in kaolinite abundance and sea level fluctuations during this period. Six units of clay mineral species were distinguished throughout this formation reflecting their evolution.

Microstructure and palygorskite neoformation in pedogenic calcretes of central Morocco

The aim of this research was the micromorphological and mineralogical characterization of calcrete outcrops located in central Morocco, with particular focus on microstructure development and palygorskite formation processes. Two study sites in the Al Haouz Plain (ca 30km west to Marrakech city) were identified, in an area dominated by Quaternary sedimentary formations including layers cemented by carbonate and widespread calcareous crusts at the surface. The calcrete samples were examined by means of polarizing microscopy from thin sections, scanning electron microscopy / energy-dispersive X-ray spectroscopy (SEM/EDX) from undisturbed samples, and X-ray diffraction (XRD) methods. The matrix of the calcrete material cementing the schist fragments composed of abundant calcite was associated mainly with palygorskite, quartz, and to a lesser extent illite/mica, feldspar, and chlorite. SEM observations indicated that palygorskite mainly occurred as fibres, fibre bundles and networks mainly grown on and/or enclosing calcite rhombohedrons. The EDX spectra of the palygorskite fibres exhibited strong silicon (Si) peaks followed by Al, Mg and Fe peaks. The EDX analysis of calcite rhombohedric crystals exhibited a strong Ca peak, followed by weak peaks of Si, Mg, Al and Fe possibly due to nearby or overlapped palygorskite crystals. One main palygorskite neoformation process was described. Palygorskite was authigenically formed (neoformed) during and after precipitation of calcite from percolating soil solutions in a near-surface setting. Peculiar sub-rounded microstructural units, here designated as pedogenic ooids/pisoids (according to the size), were determined in the matrix of the studied calcretes, associated to pendants and clay-rich rims surrounding them.

Occurrences and genesis of palygorskite/sepiolite and associated minerals in the Barzaman formation, United Arab Emirates

AbstractThe Barzaman Formation exposed in the United Arab Emirates was deposited as a series of fluvial sediment sequences lying along the western margin of the Hajar Mountains, part of the Oman–UAE ophiolite. This formation consists of a sequence of rocks dominated by variably cemented and altered conglomerates comprising calcareous siltstones and calcareous clays deposited during the Miocene to Pliocene under a humid climate. The conglomerates are composed largely of ultramafic and lesser-mafic clasts. The present study was undertaken in order to understand the occurrence and genesis of palygorskite and sepiolite in relation to the environmental changes including evaporitic and sabkha environments.Sediments were collected from two trenches and a drill hole of ∼22 m depth. Samples were analysed by optical petrograpy, X-ray diffraction and scanning electron microscopy. Pedogenesis occurred at the deeper level in well cemented conglomerate which constitutes the hard crust. Post-depositional erosion started in marine phreatic or vadose zones as shown by the neoformation of serpentine from the weathering of olivine as well as of calcite and dolomite. Neoformation of palygorskite, sepiolite, dolomite and halite occurred under evaporitic conditions on calcareous silty clay facies. Relatively hot, vadose and oxidizing environmental conditions affected the calcareous siltstone facies leading to the genesis of dolomite and palygorskite by direct precipitation from solution rich in Ca, Mg, Al, Fe and Si ions.

Factors Affecting the Occurrence of Palygorskite in Central Iranian Soils Developed on Tertiary Sediments

Limited information is available on the distribution and origin of palygorskite in soils developed on Tertiary sediments as the major soil parent materials in central Iran and other Middle Eastern countries. The objectives of this study were to determine the distribution and origin of palygorskite in soils developed on Tertiary sediments, and to identify the major soil properties that influence palygorskite distribution in the soils studied. Sixteen soil profiles developed on Paleocene, Eocene, Oligocene, Oligocene-Miocene, Miocene and Pliocene sediments were studied by X-ray diffraction analysis, transmission electron microscope, and scanning electron microscopy. Physicochemical characteristics of the soils and sediments including particle size distribution, pH, electrical conductivity, organic carbon, gypsum, carbonates, and soluble Si, Ca and Mg were determined. The principal component analysis was used to establish the relationships between palygorskite and the physicochemical characteristics of the soils studied. Results showed that clay fraction of all the soils in the study area was dominated by palygorskite. The highest amount of palygorskite was found in horizons where simultaneous accumulation of both carbonates and gypsum occurred. Limited amount of palygorskite was found in salic and calcic horizons. Palygorskite seemed to be of eolian origin in the surface horizon of all the soils. Using principal component analysis, the soluble Mg/Ca ratio, pH, soluble Si and gypsum contents were identified as the most important factors affecting the distribution and genesis of palygorskite in the soils studied. Results might suggest the neoformation of palygorskite by precipitation from solutions in which evaporation fluxes were very high. However, palygorskite in soils developed on Tertiary sediments in central Iran seems to be of both inherited and pedogenic origins.

Pedogenesis and clay mineralogical investigation of soils formed on gypsiferous and calcareous materials, on a transect, southwestern Iran

This study examined pedogenesis, as well as the clay mineralogy of soil and rock samples obtained from a transect of gypsiferous and calcareous materials. The main objectives of this research were to study the relationship between clay minerals and physiographic units as well as the relative importance of key pedogenic processes in controlling clay mineralogy. Palygorskite, chlorite, illite, smectite, quartz and interstratified minerals were observed in both soil and rock samples, using XRD, TEM and EDX analyses. Illite, chlorite, and interstratified minerals are inherited largely from parent rocks. Most of the smectite is inherited from highly smectite marl formations, although some may be the product of palygorskite weathering and transformation of illite particularly at the surface horizons. Neoformation of palygorskite, as a result of calcite and gypsum precipitation, seems to be a major pathway for the occurrence of this mineral, especially on plateau physiographic units, although inheritance has less importance. Gypsiferous soils showed more pedogenic palygorskite as compared to calcareous soils. Three morphological forms of palygorskite, related to degree of weathering, were identified in the studied pedons. New great groups and subgroups of Ustepts (Aridic Gypsiustepts and Aridic–calcic Gypsiustepts) are suggested to be included in Soil Taxonomy based on the properties of some of the studied pedons. Dissolution and transport of anhydrite from outcrops, is considered the main source of pedogenic gypsum in these soils. Micromorphological studies, including thin section observations and SEM analyses indicated variable habits of gypsum crystals suggested a dynamic soil environment.

Constraints on alluvial clay mineral assemblages in semiarid regions. The Souss Wadi Basin (Morocco, Northwestern Africa)

Illite, chlorite and kaolinite, resulting directly from substratum weathering, dominate the clay assemblages recorded in altered rocks and soils of the Souss Wadi watershed. Nevertheless, the transformation and neoformation of diverse clay minerals, which is mainly controlled by changing climatic, lithological and topographic conditions, enables one to establish three distinctive source areas. High altitude, largely watered zones where chlorite is transformed into vermiculite; middle altitude drier areas where more pronounced seasonal contrast induces the transformation of chlorite into chlorite-smectite mixed layer; finally, semiarid low altitude zones with gentle slopes where the weathering of carbonate-dominated substrata, evaporation and chemical concentration result in smectite and palygorskite neoformation. These minerals, which result from transformation and neoformation, provide suitable environmental indicators and local to zonal tracers of sediment contribution. Nevertheless, the original clay mineral assemblages undergo a significant homogenisation due to the destruction of most of the transformed and neoformed minerals during fluvial transport. As a consequence, inherited clay minerals (illite, chlorite and kaolinite) usually dominate the assemblages recorded in the downstream alluvial sediments. The clay assemblages recorded in different tributary wadi alluvial deposits reflect major sediment contribution from the High-Atlas and the older alluvial plain deposits affected by intensive erosion. On the other side, Anti-Atlas contribution is lesser as a consequence of its wide tableland topography and the widespread outcropping of karstified carbonate rocks, which enhance water infiltration and preclude sediment supply.

Pedogenic and early diagenetic processes in Palaeogene alluvial fan and lacustrine deposits from the Sado Basin (S Portugal)

The Palaeogene deposits of the Sado Basin were deposited in a continental basin that shows a typical pattern with alluvial fans system in the margins of the basin, passing towards distal areas of mudflat facies where, in some areas, the installation of shallow water bodies favoured the development of palustrine conditions. The deposits of this basin vary form coarse conglomerates and sandstones to palustrine carbonates. These sediments were affected by pedogenesis and early diagenetic processes that promoted important modifications on their primary features. These modifications have been studied by the analyses of four profiles, developed on proximal, middle and distal fan deposits and the fourth one on lacustrine deposits. The overall analyses of the sedimentological, pedogenic, diagenetic features and their relationships indicate that three main processes took place throughout the basin: soil formation, palygorskite neoformation and dolomitization. Soil formation processes led to illuviation of clays and carbonate precipitation mostly around roots. Pedogenic carbonates increase towards distal areas, whereas hydromorphic features are present throughout the basin. Palygorskite neoformation was partially diagenetic, being maximum in proximal areas and palustrine deposits. This neoformation is attributed to the percolation of alkaline Mg-rich soil and groundwaters through smectitic-rich sediments, promoting important clay transformation. Dolomitization was an early diagenetic process that occurred mainly in carbonate-rich deposits of distal and lacustrine environments, as a result of the increasing Mg/Ca ratio of the percolating groundwaters. In all these processes there has been a close spatial and temporal interplay between pedogenesis and diagenesis, driven by the chemistry of soil particles and groundwaters.

Micromorphological and geochemical characterization of Tertiary ‘freshwater carbonates’ locally preserved north of the edge of the Miocene Molasse Basin (SW Germany)

Miocene carbonates intercalated in a deposit of Upper Freshwater Molasse (Middle Miocene), exposed in a limestone quarry at Heidenheim-Mergelstetten (Germany), were analysed geochemically and micromorphologically. The heavy minerals (fine sand) and clay minerals confirm the sedimentary interpretation of the formation as a sequence of Paleogene soil residues overlain by younger Neogene soil horizons developed in sediments of the Upper Freshwater Molasse (OSM). The supposed continental origin of the massive, bedded, pisolitic limestone and white, chalky, columnar limestone indicated by terrestrial gastropods, is confirmed by analysis of stable carbon and oxygen isotopes. The microfacies show the characteristics of terrestrial carbonates: pisoids, nodules and pedodes. Nevertheless, the occurrence of intraclasts, reworking features, grey/black concretions, indications of swampy conditions, and carbonate enrichment restricted to the depression area cannot be explained by terrestrial pedogenetic processes. Cathodoluminescence suggests the meteoric character of the sparitic cements, which could be differentiated into three phases of cementation corresponding to conditions during lake regression and subsequent transgression. X-ray diffraction, differential thermal and transmission electron microscope analysis of the ammonium acetate insoluble residue of the carbonates indicate neoformation of palygorskite within the pisolitic limestone. Si and Al for formation of palygorskite were probably supplied by degradation of clay minerals (illite) under alkaline conditions. Mg was externally supplied to the system. The results suggest formation of the Miocene carbonates in a marsh or shallow ephemeral lake environment with repeated superimpositions of pedogenetic processes.

Palygorskite-cemented crusts (palycretes) in Southern Portugal

In the Oriola depression of Southern Portugal near the town of Evora, field examinations revealed the presence of Tertiary sedimentary deposits that had the consistency of duricrusts. These duricrusts, occurring close to the land surface, were examined in the field as well as in the laboratory, with the objective of establishing their composition and formation. Micromorphological examinations showed that the duricrusts were composed of clasts of fine sand to fine gravel sizes cemented together by a matrix dominated by either palygorskite or carbonate. The matrix : clasts ratio varied from about 1 : 3 when the cement was carbonate, to 3 : 1 or higher when the matrix was palygorskite. Occasionally the ratio in the latter was even higher. The clasts consisted of quartz, feldspar, and some Mg-rich metamorphic minerals. The palygorskite matrix fibres were arranged in mats within which they had parallel orientation. The mats or ‘domains’, which had a length of 15–25 □m and a width of about 40 □m, showed random orientation. In analogy to the term ‘calcrete’ the term ‘palycrete’ is used for the palygorskite duricrusts. The palycrete, of an average thickness of 0.5 m, frequently rested directly on the Hercynian basement rocks, and was covered by a recent solum. In the B horizons of the solum, the palygorskite appeared to undergo recent weathering and transformation into smectite. The duricrusts were proposed to have formed by authigenic calcite or palygorskite, which filled the interstices between clastic particles that had been deposited on Hercynian basement rocks following their peneplanation in the early Tertiary. The proposed environment of deposition and formation was that of an intermittent playa-lake in a semi-arid, seasonal climate, where strong evaporative processes had been active. Alteration and weathering of the mafic minerals contained in some of the clasts, in addition to interstitial solutions rich in Si and Mg, had created the chemical environment required for palygorskite neoformation. From the state of weathering–disintegration of the palygorskite in the soils formed on the palycrete, it is inferred that the environment for palygorskite neoformation had ceased to exist after palycrete formation.

Evidence of a Precursor in the Neoformation of Palygorskite — New Data by Analytical Electron Microscopy

AbstractThe rocks of the palygorskite deposit at Bercimuel (Segovia, Spain) have been studied by transmission electron microscopy and microanalysis. These rocks correspond to the zone of convergence of two alluvial fan systems that have filled the small basin of the River Riaza and would originally have been composed of illite and quartz silts. Among the accumulations of palygorskite it is possible to observe surrounded particles of micromicas that have undergone dissolution and opening thereby giving rise to disordered illite-smectite mixed-layer clays. This process continued up to the individualization of structural relics formed of units of 1–5 layers. At the same time, the chemical composition was modified with a loss of K and Al and a relative increase in Si and Mg, progressively evolving towards the composition of palygorskite. The paleogeographic position of the deposits, and the climatic conditions (arid environment), appear to be the dominant factors in the neoformation of palygorskite by alteration of the original sediments. The basic mineralogical process could be referred to as ‘early diagenesis’ in the formation of calcretes.

Pedogenic palygorskite and dolomite in a late Neogene sedimentary succession, northwestern Transvaal, South Africa

A detailed field survey identified a late Neogene sedimentary succession which accumulated in ephemeral palaeolakes on the edge of the Kalahari Basin in the northwest of Transvaal Province, South Africa. Palygorskite and dolomite formed along lake margins which fluctuated between lacustrine and dry-land conditions. The sedimentary sequence presented an opportunity to investigate the interrelationships between these minerals and study their possible modes of formation, either by lacustrine sedimentation or pedogenic processes. Clay mineralogy, transmission and scanning electron microscopy and geochemical analysis revealed an increase in magnesium-enriched minerals, palygorskite and dolomite, within the pedogenically altered marginal lacustrine sediments. Field relationships showed that the dolomite is a replacive phase within the decomposing palygorskite, although the scanning electron micrographs do not display such unequivocal evidence for a direct replacive relationship. They suggest rather that the dolomite forms by neoformation from soil solutions, which included decomposition products released by the breakdown of the palygorskite. Seen in a regional context, subaerial pedogenic processes acted on marginal lacustrine sediments and resulted in the decomposition of smectite and neoformation of palygorskite. A change in climate to drier conditions encouraged the formation of calcrete in surrounding areas which increased the magnesium/calcium ratio in groundwaters. This increase was supplemented by evaporative concentration during the desiccation of the lacustrine environment. The high magnesium concentration led to the formation of the dolomite-rich dolocrete. This interpretive model is a means by which existing genetic models for calcareous pedocretes and those models that define the concentration of magnesium in groundwater and saline lacustrine environments can be combined. The pedogenic mineral relationships described are suggested as useful palaeoenvironmental indicators for the late Neogene/early Pleistocene of southern Africa.

Neoformation of Palygorskite in a Southern New Mexico Aridisol

AbstractPalygorskite is the dominant clay mineral in a petrocalcic horizon of the Rotura soil series (a coarse‐loamy, mixed, thermic, Typic Haplargid), a soil of middle Pleistocene age in southern New Mexico. The purpose of this study was to determine if palygorskite is eolian in origin, inherited from its alluvial parent material, or neoformed in the soil. The origin of palygorskite was determined by examining clay mineral distribution, soil‐water extract chemistry, and palygorskite fiber morphology. An eolian origin of palygorskite is unlikely because it is absent in upper soil horizons and no palygorskite was captured in dust traps during a 10‐yr study. An inherited origin is also unlikely because palygorskite is not an inherent component of Rio Grande alluvium. Scanning electron microscopy revealed that delicate palygorskite fibers radiate perpendicularly into pore spaces, which indicates neoformation. The petrocalcic horizon may foster palygorskite neoformation because it is the site of high Mg content and abundant sand‐ and silt‐grain dissolution.

Relationship of Clay Minerals to Depositional Environment in the Non-Marine Eocene Pontils Group, Se Ebro Basin (Spain)

ABSTRACT The Eocene sequence along the central part of the SE margin of the Tertiary Ebro Basin (Igualada area) consists of alternating marine and non-marine deposits up to 2000 m thick. Non-marine conditions persisted through the Cuisian--early Bartonian (early-middle Eocene) and resulted in the deposition of the Pontils Group (up to 900 m thick). During the late Bartonian--early Priabonian (late Eocene), marine environments prevailed in this area, leading to the deposition of the Santa Maria Group. Paleoenvironmental interpretations of the Pontils Group were obtained from sedimentology data of an earlier study. The nonmarine environments recorded in this group are: alluvial fans, flood plains, mudflats, playa-lakes, and shallow freshwater lakes. X-ray diffraction, TEM, SEM, EDX, and chemical analyses of mudstones and marls from the Pontils Group indicate that the diverse environments also can be distinguished from one another on the basis of the clay-mineral content. Illite is present in all samples of the Pontils Group. Palygorskite, with minor amounts of illite and sometimes chlorite, is the dominant clay mineral in flood plain and mud flat sediments. Palygorskite is also predominant in sabkha, playa-lake and carbonate-lagoonal sediments. This clay mineral is absent in sediments from fresh, organic-rich lakes. Kaolinite is relatively abundant in mudstones from the organic-rich lakes. Smectite is relatively abundant in the sediments from subaqueous environments but is almost always absent from the sediments which were subjected to subaerial exposure and water-table oscillations such as flood plain and mudflat deposits. According to these clay-mineral distribution trends, the organic-rich lacustrine, lagoonal, and marine sediments preserve the detrital clay-minerals. The original detrital assemblages were mostly formed by illite, associated with chlorite, kaolinite and subordinate smectite. In the environments which underwent repeated flooding and desiccation, chlorite and smectite were eventually eliminated and palygorskite was formed. Microscopic observation suggests that palygorskite was formed in mudflats and flood-plains mainly by the transformation of smectite and/or illite in a Mg-rich environment. In the sabkha facies, the abundance of palygorskite, frequently associated with smectite, dolomite, and chert, suggests palygorskite neoformation in a Si- and Mg-rich environment.

Mineralogy of Saudi Arabian Soils: Central Alluvial Basins

AbstractThese investigations were conducted to provide basic soil chemical, physical, and mineralogical data for an area of Saudi Arabia that had not been studied and for which greatly increased agricultural development is anticipated. Fourteen soils were collected from two arid interior basin areas of Saudi Arabia. The silt and clay mineralogy was studied using x‐ray diffraction, differential thermal analysis, and electron microscopy. Quantitative estimation of clay‐sized minerals was based on a combination of chemical and x‐ray diffraction techniques. The calcareous soils of the central basins show minimal profile development. Particle‐size classes range from sandy‐skeletal to fine silty. Soils with shallow water tables are saline with large SAR values. The clay minerals in soils of the basins are primarily inherited. Soils developed in alluvium from mixed igneous rocks have clay fractions in which smectite > mica > kaolinite > chlorite, palygorskite, vermiculite. Soils formed from Permian sedimentary rocks have kaolinitic clay fractions. It is postulated that the central basins do not receive sufficient Si inputs for palygorskite neoformation and it is though that palygorskite is detrital, originating from easternregion Tertiary rocks. The soil clays of the central hasins have greater smectite contents than those of the kaolinitic western highland soils and palygorskite‐rich eastern‐region soils.