Clay Infillings Research Articles

Polygenesis and cementation pathways for plinthic and non-plinthic soils on the Upper Coastal Plain, South Carolina

Plinthic soils on the Upper Coastal Plain (UCP) of South Carolina are directly underlain by hard but unconsolidated older Coastal Plain sediment, as are non-plinthic soils on adjacent dissected landforms. The older deposit, called brick material, is integral to plinthite formation via perched soil water hence intensified redox conditions. Currently, few causes are known for horizon matrix cementation of these soils. Six pedons from three hillslope positions were investigated for soil uniformity, selectively dissolved Fe and Si distributions, and micromorphology. Particle-size indices and ground-penetrating radar (GPR) confirmed uniform soils and thick plinthic horizons on summit positions and a discontinuity at shoulder and backslope positions. Contrasts in GPR radar reflections corresponded to the brick material and were thought to be associated with changes in moisture contents, iron mineralogy, pore size, and clay content. Illuvial clay infillings and minute channels confirmed pedogenesis in brick material. In plinthic horizons above the brick material, excess citrate dithionite Fe (Fed) was indicated by over-bulging distributions relative to Fed/clay ratios. Water-soluble silica (Siw) may be recycled in upper sola by capillarity and leaching, move through the discontinuity, and interact with Fe throughout the solum compatible with coarse material encapsulated with Fe-enriched fine material in the brick matrix. Absolute molar contents of oxalate extractable Si (Sio) and Fe (Feo) were low throughout all pedons, however, Sio/(Feo + Sio) ratios ranged from 0.30 to 0.60 in Btvx, Btx, and 2Btx horizons to account for fragic soil properties. Nascent UCP parent material or soils evidently provided adequate constituents for plinthic soil formation. A new theory proposes UCP plinthic soils evolved simultaneously with uniform soils that do not have a water table and have Bt horizons that begin as yellowish or brownish then redden with depth. Ferricrete sourced from nearby extant landscapes may have provided detrital ironstone to the parent material mix.

Vibrational spectroscopic study of three Mg–Ni mineral series in white and greenish clay infillings of the New Caledonian Ni-silicate ores

Abstract. This study presents and discusses infrared spectroscopic data of well characterised, naturally occurring trioctahedral layer silicates of the serpentine (Srp), talc (Tlc), and sepiolite (Sep) mineral groups, which are found in reactivated faults and sequences of white and green clay veins (deweylite and garnierite) of the New Caledonian Ni-silicate ores. Bands assigned to the OH stretching vibrations of these 1:1 and 2:1 layer silicates in both the fundamental and first overtone regions of mid- and near-infrared (MIR and NIR) spectra, respectively, are compared to those reported in the literature for synthetic Mg–Ni series of the Srp and Tlc mineral groups. They are also presented according to the sequences of infillings recognised in the white and green veins of the Ni-silicate ores. The study reveals that serpentine-like (SL) minerals of the first sequences of clay infillings are residues of larger crystals of serpentines (lizardite, chrysotile, and antigorite) and that the newly formed talc-like (TL) minerals and Sep are the main Ni-bearing carriers of the Ni-silicate ores. Decreasing crystal size and order in serpentine species have major effects on vibrational bands. They favour the broadening of the OH stretching bands, the degradation of the signals assigned to the interlayer OH, and the enhancement of the signal related to weakly bound water molecules. The replacement of Mg by Ni in octahedral sites of the 2:1 layer silicates (TL, Sep) of the greenish clay infillings can be traced by specific OH stretching bands related to the Mg3OH, Mg2NiOH, MgNi2OH, and Ni3OH configurations in the fundamental (MIR) and first overtone (NIR) regions of the spectra. The dominance of the Mg3OH and Ni3OH configurations with respect to mixed configurations in the Mg–Ni mineral series of the clay infillings (mostly in the dominant TL minerals) suggests that Mg and Ni segregation is related to separate Mg-rich and Ni-rich mineral phases rather than to a cationic clustering within the individual particles. This segregation of Mg and Ni in discrete mineral phases is related to Mg–Ni oscillatory zoning patterns (banded patterns) and is reproduced at the scale of the Ni-silicate ores between the white (deweylite) and greenish (garnierite) veins of the reactivated faults.

Genesis and classification of carbonate soils in the State of Rio de Janeiro, Brazil

Carbonate rocks occur in Brazil under diverse climatic and environmental conditions, and therefore are of great importance for pedological studies. The northwest region of the State of Rio de Janeiro, Brazil, is composed of calc-silicate rocks and marbles that occur under tropical climate with a long period of water deficit, which provides conditions for peculiar pedogenesis. The objective of this study was to characterize the attributes of soils formed from carbonate materials and to understand the role of the main factors and processes in pedogenesis, as well as to provide information to the WRB (World Reference Base for Soil Resources) to improve carbonate soils classification. A toposequence was selected in the municipality of Italva, RJ, Brazil, with six profiles being described and sampled. All profiles presented median CaCO3 equivalent contents, high base saturation with the predominance of Ca+2 and Mg+2, and high activity clay. The absence of effervescence and low CaO/MgO ratio obtained by acid digestion suggest the dolomitic nature of the carbonates. Pedogenic carbonates were amorphous, since no XRD peaks were found. The high Mg+2 concentration provided by the parent material increases the dispersion of clays and favors clay illuviation, which is manifested in the micromorphology through a large amount of clay infillings and coatings. Four profiles on the highest part of the landscape were classified as Kastanozems (Mollisols), the footslope profile as Fluvisol (Inceptisol), and the toeslope profile as Vertisol. The mineralogy of the Vertisol's clay fraction was predominantly composed of kaolinite interstratified with 2:1 phyllosilicates, mainly illite. Acid digestion can complete the analysis of the CaCO3 equivalent content by quantifying CaO and MgO concentration in fine earth samples, presenting the potential to distinguish the Dolomitic/Calcaric qualifiers. The recognition of Dolomitic/Calcaric qualifiers for the Kastanozem reference soil groups is suggested, considering that the carbonate present in the calcic horizon may be diverse.

Swelling capacity of mixed talc-like/stevensite layers in white/green clay infillings (“deweylite”/ “garnierite”) from serpentine veins of faulted peridotites, New Caledonia

AbstractWhite (Mg-rich) and green (Ni-rich) clay infillings (“deweylite”/ “garnierite”) found in serpentine veins of faulted peridotite formations from New Caledonia consist of an intimate mixture of fine-grained and poorly ordered 1:1 and 2:1 layer silicates, commonly referred to as non-expandable serpentine-like (SL) and talc-like (TL) minerals. New data on the swelling and shrinking capacity of these layer silicates were gathered from X-ray diffraction (XRD) after saturation of the clay fractions with different cations (Ca2+, Li+, K+), ethylene glycol (EG) solvation, and heat treatments. Simultaneously, layer charge distribution and vacancy density, respectively, were investigated by FTIR spectroscopy on NH4-saturated clay fractions and XRD on Li-saturated clay fractions before and after heating (Hofmann Klemen treatment). Five clay infillings, with dominant 2:1 layer silicates and variable Ni contents, were selected for this study, from a large set of veinlets, according to their swelling capacity. The crystal chemistry of these samples was characterized by FTIR spectroscopy and bulk chemical analyses.The swelling ability of the clay infillings is attributed to the 2:1 layer silicates. It does not seem to be affected by the relative fraction of Mg and Ni in their octahedral sheets. In XRD patterns, the swelling ability is reflected by slight shifts of the basal reflection of the 2:1 layer silicates toward low angles for bulk samples and by splitting of the peak into two contributions for clay fractions saturated with Ca (or Li) and solvated with EG. The split increases with the swelling capacity of the sample. It originates mainly from octahedral-layer charge generated by vacant sites. Such results lead us to consider the 2:1 layer silicates of the infillings as an intimate mixture of non-expandable (TL) and expandable (stevensite) phases. In agreement with previous studies that suggested a contribution of hydrothermal processes in the alteration of serpentine species into 2:1 layer silicates, we propose that the proportion of expandable phases in the clay infillings (or vacancy sites in the octahedral sheets of the 2:1 layer silicates) could be used as an efficient means for assessing the temperature of their formation. Clay infillings mostly made of stevensite would have formed at ambient temperatures, whereas those consisting mainly of non-expandable TL would have formed at higher temperatures.

Genesis of an atypical Podzol in the Iberian Range: micromorphological characterization

A podzol has been described in the Iberian Range (Moncayo Natural Park), which may represent the southernmost example in Europe. The fact that it occurs at the podzol distribution limit makes its morphology atypical. The aim of this work is to identify the components and formation processes of the soil, and to determine if the processes are active or paleo-processes by a micromorphological approach. The study podzol is located in the top of a northern hillside (30% of slope), at 1600 m altitude on quartzitic sandstones, under Scots pine (<em>Pinus sylvestris</em>) with an udic moisture regime and a frigid temperature regime. We found opaque, orthic iron oxide nodules at the base of the profile (Bhs1), which is related to a current oxidation-reduction process; silt caps are also observed on the coarse elements, pedofeatures evidencing the cryoturbation process, probably also current processes. In the Bhs2 horizon, coatings and micro-laminated clay infillings are identified that are interspersed with fine silts in the holes. Many of these coatings are fragmented and mixed with the basal mass of the soil, indicating that they are paleofeature, possibly prior to the current podzolization.

An alternative model for the formation of hydrous Mg/Ni layer silicates (“deweylite”/“garnierite”) in faulted peridotites of New Caledonia: II. Petrography and chemistry of white and green clay infillings

An alternative model for the formation of hydrous Mg/Ni layer silicates (“deweylite”/“garnierite”) in faulted peridotites of New Caledonia: II. Petrography and chemistry of white and green clay infillings

Porosity and genesis of clay in gneiss saprolites: The relevance of saprolithology to whole regolith pedology

Weakening of the rock texture in a saprolite by weathering and further pedoplasmation results in the formation of a porous network and neoformed clays, which are the initial stages of pedogenesis, but the saprolite is likely the least studied compartment of the regolith. In this paper, the genesis of clays and their associated pore system was studied in gneiss saprolites. We investigated the saprolites of three regoliths in the Atlantic Forest Biome in northeast Brazil and used optical and electron microscopy to depict the clay–pore morphology. To assess the mobility of clays, we also determined the amounts of water–dispersible and total clay. The total chemical composition (SiO2, Al2O3, Fe2O3, CaO, MgO, Na2O, K2O, TiO2 and P2O5), exchangeable cations (Al+3, Ca+2, Mg+2, K+ and Na+), available P, capacity for saprolites to exchange cations and secondary forms of iron (Fed and Feo) were also measured. Micromorphological analyses showed that the most frequent pore types were channels and fissures. Channels occurred in the more weathered saprolite layers, which were identified according to the weathering indexes, and the clay–sized minerals found in the saprolite were illite, kaolinite, iron oxides, feldspar and quartz. The weathering of biotite and green hornblende formed an Fe–rich clay, and the weathering of feldspars formed an Al–rich clay. Secondary clays were accumulated at the mineral surfaces, pseudomorphs, clay infillings and clay coatings. The clay coatings are formed by two layers, i.e., the first clay layer was formed by an Fe–rich clay, and the second layer was formed by an Al–rich clay. Peculiar features named “doughnut–shaped holdfasts” were described in the clay cutans. The capacity for saprolites to exchange cations was similar to that in the shallower soils, which was environmentally relevant to the adsorption of plant nutrients, e.g., Ca+2, Mg+2 and K+, and potentially toxic elements, e.g., Al+3.

Genesis and evolution of the fragipan in Albeluvisols in the Precarpathians in Ukraine

The fragipan (Bx) is a subsurface soil horizon restricting the penetration of roots and infiltration of water due to its high bulk density, low total porosity, and discontinuous voids (so-called closed box system). Additionally, the pan is characterized by a hard or very hard consistence when dry, but brittle when moist. The genesis and evolution of the fragipan have been the subject of many research studies, and numerous theories and models concerning these issues can be found in the literature. The principal aims of this study were to: 1) explain the genesis of the fragipan in Albeluvisols in the Precarpathians in Ukraine, basing on micromorphological studies and quantitative mineral composition analyses and 2) propose a model of pan formation and evolution under moderately humid climate conditions. The abundance of clay coatings and clay infillings as well as iron–clay cutans within the studied fragipan indicates that the formation of the pan is related to the translocation of colloids (clay minerals and iron hydroxides) from upper soil horizons. This leads to the filling of voids in the Btx horizon and a decrease in the porosity and hydraulic conductivity of the pan. The enrichment of the fragipan in clay minerals (especially in swelling clay minerals) is responsible for the subsequent degradation of the pan due to wetting and drying, leading to the swelling and shrinking of soil material. The occurrence of many Fe–Mn nodules and a mottled color indicates cyclical wetting and drying within the studied fragipan. In effect, vertical cracks are formed, which serve as pathways for water infiltrating down the soil profile. The water washes out weathering products (iron oxides and clay minerals) from soil material adjacent to the cracks. This leads to the formation and development of bleached tongues along the vertical cracks, which penetrate the fragipan.

Origin of reversible cementation and brittleness of the fragipan horizon in Albeluvisols of the Carpathian Foothills, Poland

Abstract Fragipan horizon is a natural, subsurface soil layer exhibiting higher bulk density and lower porosity in comparison with the overlying horizons significantly restricting infiltration of water and root penetration. In contrast to hard and cemented horizons (e.g. duripan), clods of the fragipan horizon (Btx) slake or fracture immediately when placed in water. The most interesting issue concerning genesis and properties of the fragipan horizon is its reversible cementation, i.e. very hard consistence in dry state and brittle consistence in moist state. The main objective of the present study was to explain and improve the understanding of the specific consistence of the fragipan horizon in moderately humid climate on the example of Albeluvisols of the Carpathian Foothills in Poland basing on mineral and chemical composition of bridges linking coarse soil material. Quantitative X-ray diffraction shows that the studied fragipan horizon contains high concentration of swelling clay minerals. Soil material from the fragipan horizon exhibits numerous clay and iron–clay coatings and clay infillings indicating translocation of colloidal clay and iron oxides from overlying horizons. In addition, bridges between coarse grains of the soil material occur. The fragipan cementing material is composed mainly of SiO2, Al2O3, and Fe2O3 with lower concentration of K2O, MgO, CaO, and Na2O. The chemical composition of bridges within the pan is similar to that of clay coatings and clay infillings suggesting that clay minerals are major bonding agents and are responsible for brittleness and more friable consistence of the pan in the moist state. Additionally, free iron, aluminium, and silica may play some role in specific cementation of the investigated fragipan horizon but these elements are not main bonding agents.

Near‐surface paleosols in coastal sands at the outlet of Hadera stream (Israel) in the light of archeology and luminescence chronology

AbstractCatenary changes, archeology, micromorphology, and magnetic mineralogy of paleosols in coastal sands, Israel, were investigated under chronostratigraphic control by available luminescence datings from adjacent sites. At the outlet of Hadera stream, eolianites (Hebrew: “kurkar”) underlie paleosols with Epipaleolithic (approx. 17–20 ky) artifacts at the top and occasional Mousterian (>40 ky) artifacts in the subsoil. The optically stimulated–luminescence/infrared stimulated–luminescence (OSL/IRSL) dates (>50–12 ky) from adjacent sites roughly agree with the archeological findings. The paleosols show a magnetically depleted Vertisol superimposed on a magnetically enhanced cumulative Chromic Luvisol (WRB) (USDA: Rhodoxeralf, Israeli class.: Hamra). The latter contain approx. 0.25 mm thick, isotropic clay infillings distinctly separated from the soil matrix. These infillings are tentatively interpreted as the result of strong environmental disturbances, such as surface desiccation, subsequent waterlogging, and enhanced dust deposition, presumably at the time of the Last Glacial Maximum. In addition to the massive accumulation of eolian dust, diverse pedogeomorphic changes lagging in time from the onset of climatic deterioration may have taken place in coastal settings. Recurrent desiccation cracks may have exposed subsurface materials repeatedly to sunlight, consequently resetting the luminescence signal. The eolianite sequences are thus distinct from loess/paleosol sequences from temperate climates and have to be treated more rigorously at a site‐specific level.

Stable isotope study in a weakly developed paleosol horizon in the Quaternary Vár-hegy travertine (Budapest, Hungary)

The intraformational paleosol and calcareous muddy cavity fills interbedded in the travertine of the Var-hegy (Castle Hill) in Budapest were analyzed for carbon and oxygen isotope compositions and compared with the isotope compositions of the host travertine. Microscopic investigations of these layers indicate mechanical reworking of the travertine and mixing with the allothigenic siliciclastic material. Micromorphological features, e.g. needle-fiber calcite, carbonate hypocoatings around pores, ferruginous precipitations and clay infillings in the paleosol and cavity fills indicate that in situ pedogenic processes were active in both layers. The presence of ferrihydrite in the A horizon of the paleosol also supports pedogenic alteration. The stable carbon and oxygen isotope compositions of bulk carbonate of paleosol and cavity fills (d13C= -0.6 to 2.1‰ and d 18O= -16.7 to -12.9‰) are very close to the compositions of the host travertine (d 13C=1.1 to 2.1‰ and d 18O = -17.7 to -13.7‰,) and differ from the...