Basaltic Soils Research Articles

Mobilization of colloidal carbon during iron reduction in basaltic soils

The transport of organic carbon (C) to deep mineral horizons in soils can lead to long-term C stabilization. In basaltic soils, C associations with short-range-ordered (SRO) minerals often lead to colloid-sized aggregates that can be dispersed and mobilized by changes in soil solution chemistry. In the montane forest region of Hawaii, basaltic soils are exposed to high rainfall and anoxic conditions that facilitate ferric (FeIII) (oxyhydr)oxide reduction. We explored the potential of iron (Fe)-reducing conditions to mobilize C by exposing the surface mineral horizons of three soils from the Island of Hawai'i (aged 0.3, 20, and 350ky) to 21days of anoxic incubation in 1:10 soil slurries. Mobilized C was quantified by fractionating the slurries into three particle-size classes (<430nm,<60nm,<2.3nm≈10kDa). In all three soils, we found Fe reduction (maximum Fe2+ (aq) concentration≈17.7±1.9mmolkg−1 soil) resulted in ~500% and ~700% increase of C in the 2.3–430nm, and <2.3nm size fractions, respectively. In addition, Fe reduction increased solution ionic strength by 127μScm−1 and generated hydroxyl ions sufficient to increase the slurry pH by one unit. We compared this to C mobilized from the slurries during a 2-h oxic incubation across a similar range of pH and ionic strength and found smaller amounts of dissolved (<2.3nm) and colloidal (2.3–430nm) C were mobilized relative to the Fe reduction treatments (p<0.05). In particular, C associated with the largest particles (60–430nm) was dispersed almost exclusively during the Fe reduction experiments, suggesting that it had been bound to Fe-oxide phases. Our experiments suggest that colloidal dispersion during Fe-reducing conditions mobilizes high concentrations of C, which may explain how C migrates to deep mineral horizons in redox dynamic soils.

Testing the Gippsland Basin zonation in northern Australia: palynostratigraphical analysis of a 23 Ma 40Ar/39Ar dated claystone from Toowoomba, southeast Queensland

The spore-pollen zonation developed for the Gippsland Basin, southeast Australia, is widely used to date Paleogene–Neogene terrestrial sediments elsewhere in Australia. Microfloras preserved in an argon-40 (40Ar)/argon-39 (39Ar) dated 23 Ma claystone on the summit of the Great Dividing Range at Toowoomba in subtropical southeast Queensland indicate the Gippsland zonation, and the parallel schemata developed for the epicontinental Murray Basin in southeastern Australia provide only a general guide to the age of Late Paleogene–Neogene sediments as far north as Queensland. The finding reiterates the need to develop regional spore-pollen palynostratigraphies for Queensland (and northern Australia) centred on Cenozoic microfloras whose geologic age can be independently verified by other dating techniques. The same microfloras, however, are reliable evidence of past vegetation and climates, in this instance that a form of Nothofagus-gymnosperm temperate rainforest was colonising basaltic soils at Toowoomba during the Oligo-Miocene transition when southeast Queensland was located c. 15° south of its present latitudial position.

The Influence of Hydrothermal Activity on the Li Isotopic Signature of Rivers Draining Volcanic Areas

We explore the geochemistry and the isotopic composition of lithium (δ7Li) of rivers draining volcanic islands (Guadeloupe, Iceland, Java, Martinique and Sao Miguel) with a specific focus on continental hydrothermal activity. Our preliminary results reveal a global-scale trend between δ7Li and the elemental ratio Li/Na in rivers draining volcanic islands. We suggest that this trend results from a mixture between waters with low δ7Li and high Li/Na, inherited from high-temperature water rock interactions, and waters with low Li/Na and high δ7Li, in which Li is controlled by the neoformation of clays during low-temperature chemical weathering in basaltic soils. This latter process can be described by a simple isotope fractionation model, consistent with reported values for isotopic fractionation factors between secondary weathering products and water.These data highlight the important potential role of continental high-temperature weathering processes on the oceanic budget of lithium.

Seedling growth rates and light requirements of subtropical rainforest trees associated with basaltic and rhyolitic soils

A trade-off between shade tolerance and growth in open conditions is widely believed to underlie the dynamics of humid forests. Little is known about how the growth versus shade tolerance trade-off interacts with other major trade-offs associated with differential adaptation to major environmental factors besides light. We asked whether the growth versus shade tolerance trade-off differed between subtropical rainforest tree assemblages native to basaltic (fertile) and rhyolitic (infertile) soils in northern New South Wales, because of the allocational costs of adaptation to low nutrient availability. Seedling relative growth rates of six basalt specialists and five rhyolite specialists were measured in a glasshouse and the minimum light requirements of each species were quantified in the field by determining the 10th percentile of juvenile tree distributions in relation to understorey light availability. A similar range of light requirements was observed in the two assemblages, and although the two fastest growing species were basalt specialists, seedling growth rates did not differ significantly between the two substrates. The overall relationship between light requirements and growth rate was weak, and there was no compelling evidence that the slope or elevation of this relationship differed between the two assemblages. Growth rates were significantly correlated, overall, with specific leaf area, and marginally with leaf area ratio. The apparent similarity of the growth versus shade tolerance trade-off in the two suites of species could reflect effects of leaf nutrient content on respiration rates; basalt specialists tended to have a smaller root mass fraction, but this may have been offset by the effects of leaf nitrogen status on respiration rates, with higher respiration rates expected on fertile basaltic soils. However, the results might also partly reflect impairment of the field performance of two basalt specialists that were heavily attacked by natural enemies.

Mapping and compositional analysis of mare basalts in the Aristarchus region of the Moon using Clementine data

The process of accurately defining and outlining mare basalt units is necessary for constraining the stratigraphy and ages of basalt units, which are used to determine the duration and the flux of lunar volcanism. We use a combination of Clementine's five-band ultraviolet/visible data and TiO2 and FeO abundance distribution maps to define homogenous mare basalt units and characterize their compositional variations (with maturity) in the Aristarchus region. With 20 groups of distinct mare basaltic soils identified using the method in this paper, six additional spectrally defined areas and five basaltic units are constructed, and their mineralogic quantization values provide new constraints on their temporal and spatial evolution. Our results indicate that the Aristarchus region has diverse basalt units and a complex history of volcanic evolution. We also demonstrate that the techniques, from which spectrally distinct mare basalts can be mapped, performed well in this study and can be confidently expanded to other mare regions of the Moon.

Curiosity at Gale Crater, Mars: Characterization and Analysis of the Rocknest Sand Shadow

The Rocknest aeolian deposit is similar to aeolian features analyzed by the Mars Exploration Rovers (MERs) Spirit and Opportunity. The fraction of sand <150 micrometers in size contains ~55% crystalline material consistent with a basaltic heritage and ~45% x-ray amorphous material. The amorphous component of Rocknest is iron-rich and silicon-poor and is the host of the volatiles (water, oxygen, sulfur dioxide, carbon dioxide, and chlorine) detected by the Sample Analysis at Mars instrument and of the fine-grained nanophase oxide component first described from basaltic soils analyzed by MERs. The similarity between soils and aeolian materials analyzed at Gusev Crater, Meridiani Planum, and Gale Crater implies locally sourced, globally similar basaltic materials or globally and regionally sourced basaltic components deposited locally at all three locations.

Analysis of Surface Materials by the Curiosity Mars Rover

Analysis of Surface Materials by the Curiosity Mars Rover

Instability investigations of basaltic soil slopes along SH-72, Maharashtra, India

Mahabaleshwar is one of the most attractive and important destinations for tourists in Maharashtra, India, which experiences frequent slope failure due to high-intensity rain and complex geological conditions. The litho unit of the area is the Deccan Trap Basalt, the most famous consecutive basaltic flows during the late Cretaceous to Tertiary periods. The area is very susceptible to weathering, different degrees of alteration, formation of soils and occurrences of bole beds in between two consecutive basaltic flows. Soil formation process in this area is one of the most influencing factors for slope failure; in addition to this, joints, sub-vertical-to-vertical slopes, heavy rainfalls, etc. also play a pivotal role in instability. These transformed soils create instability on the slopes and ultimately converge to slope failures. Five types of soils have been identified during field investigations, petrographic study and X-ray diffraction that indicate change in composition and colour variations. Geomechanical properties viz. bulk density, grain size analysis, Atterberg limit, uniaxial compressive strength, cohesion and angle of internal friction were calculated for five types of soil samples. Effects of these soils on slope stability have been depicted with the help of numerical program Slide 6.0 based on limit equilibrium method.

Remediation Techniques Applied in Residual Clayey Soil (Oxisol) Contaminated by Diesel and Biodiesel

Biodegradation in residual basaltic soil contaminated by diesel fuel and biodiesel was assessed by three different techniques comprising natural attenuation, bioaugmentation, and bioventing. The soil was described in terms of its physicochemical and microbiological characteristics, showing favorable bioremediation conditions. Natural attenuation was monitored throughout the experiment. Bioaugmentation was performed using bacteria pre-selected from the soil at the concentration of ~3.0 x106 CFU mL-1. In the bioventing process, the soil was aerated during a period of 4 h a day at a pressure of 280 kPa. Bioremediation was assessed by counting the colony forming units (CFU g-1 of soil) and by degradation of contaminants using gas chromatography for 120 days. The highest microbial density was observed at 30 days in natural attenuation and at 60 days in bioaugmentation and bioventing. Biodiesel-contaminated soils had the largest microbial activity and highest degradation of carbon chains. At 120 days, bioaugmentation was the most efficient bioremediation technique, with the largest biodegradation rate for the light fraction of diesel (78.5%) and for biodiesel esters (98.6%). Bioventing was more efficient than natural attenuation for both contaminants, indicating the presence of aerobic bacteria at the analyzed soil depth.

Surface scattering properties at the Opportunity Mars rover's traverse region measured by CRISM

AbstractThe Opportunity Rover has been exploring Meridiani Planum; concurrently, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) has been collecting orbital hyperspectral data. Herein, both surface and orbital data are used to characterize surface properties at the Opportunity traverse region around Victoria crater. Results agree with previous studies, which used Opportunity's Panoramic Camera (Pancam) data, and the current study extends estimates of the Hapke single‐particle‐scattering albedo and asymmetry parameter to a greater spatial and spectral range. Results are useful for determining boundaries between surface units that otherwise look relatively uniform spectrally. This work also provides photometric functions essential for converting spectra to a single viewing geometry to yield more accurate spectral comparisons. Retrieved single‐scattering albedos range from 0.42 to 0.57 (0.5663–2.2715 micrometers) and retrieved asymmetry parameters range from −0.27 to −0.17 (moderately backscattering). Surfaces become more backscattering with increasing wavelength above 1 µm. The majority of Victoria crater's ejecta apron is more backscattering than surrounding regions, indicating a change in physical properties. Images taken when the rover traversed this unit show a cover of basaltic soil with superposed millimeter‐scale hematitic spherules. Wind streaks on the apron appear smooth (low backscatter) because basaltic sands have partly buried spherules, lessening millimeter‐scale roughness. CRISM‐derived scattering parameters also show that bedrock‐dominated surfaces are less backscattering than soil‐covered surfaces, largely due to lower areal abundance of spherules. The ability to analyze surface unit spherule cover is important because it relates to a wetter period during which spherules formed in Meridiani.

Heavy metals concentration in soils under rainfed agro-ecosystems and their relationship with soil properties and management practices

Heavy metals are governed by parent material of soils and influenced by the soil physicochemical properties and soil and crop management practices. This paper evaluates total heavy metal concentrations in rainfed soils under diverse management practices of tropical India. Vertisols (clayey soils with high shrink/swell capacity) had the highest concentrations of heavy metals. However, chromium (Cr) content was above the threshold value in Aridisol [calcium carbonate (CaCO3)]-containing soils of the arid environments with subsurface horizon development. Concentration increased at lower depths (>30 cm). Basaltic soils showed higher concentrations of nickel (Ni), copper (Cu) and manganese (Mn). Cadmium (Cd), cobalt (Co), Cu and Mn concentrations were higher in soils cultivated to cotton, whereas Cr concentration was above the threshold level of 110 mg kg−1 in food crop cultivated soils. As the specific soil surface is closely related to clay content and clay type, soil’s ability to retain heavy metals is more closely tied to the specific surface than to the soil cation exchange capacity. Higher positive correlations were found between heavy metal concentrations and clay content [Cd(r = 0.85; p ≤ 0.01); Co (r = 0.88; p ≤ 0.05); Ni (r = 0.87; p ≤ 0.01); Co (r = 0.81; p ≤ 0.05); Zn (r = 0.49; p ≤ 0.01); Cr (r = 0.80; p ≤ 0.05); Mn (r = 0.79; p ≤ 0.01)]. The amounts of nitrogen–phosphorus–potassium applied showed a positive correlation with Co and Ni (r = 0.62; p ≤ 0.05). As several soils used for growing food crops are high in Ni, Cr and Mn, the flow of these metals in soil–plant–livestock/human chain needs further attention.

Fractionation of yttrium and holmium during basaltic soil weathering

The anomalously low affinity of yttrium (Y) for iron (Fe) (oxyhydr)oxides relative to lanthanides with similar ionic radius (e.g., Ho) has been demonstrated in experiments with isolated Fe minerals and in a variety of marine systems that contain high concentrations of solid phase Fe. However, it has not previously been demonstrated to occur during soil genesis, despite the common observation that many soils become enriched in Fe over time. We hypothesized that Y would become progressively depleted in soils relative to Ho with increased weathering. Since, trivalent Y has an anomalously low Misono softness relative to other trivalent ions included in the rare earth element and yttrium group (REY3+), we also investigated whether soil REY fractionation reflects variation in Misono softness. To test this, we measured trends in total REY concentrations for Hawaiian soils derived from basaltic parent materials aged 0.3–4100ky, and measured REYs released from the same samples during short-time (3h) dissolution experiments conducted as part of a previous investigation linking dissolution with surface charge properties (Chorover et al., 2004). The chondrite-normalized Y/Ho ratios in the parent Hawaiian basalt (Chond[Y/Ho]=0.998) and continental dust (Chond[Y/Ho]=0.994) inputs are remarkably similar, and thus we can interpret deviations from Chond[Y/Ho]∼1.0 to result from soil biogeochemical processes and not source mixing. Between 0.3 and 20ky, the Chond[Y/Ho] ratio of the subsurface soils decreased from 0.96±0.07(2σ) to 0.71±0.05, and then remained unchanged across the rest of the weathering sequence. In contrast, the Chond[Y/Ho] ratio of the surface soils decreased from 0.99±0.07 to 0.76±0.05 at 150ky and then, most likely due to continued dust inputs, increased to 1.04±0.07 in the oldest soils. Analysis of the short-time dissolution experiments revealed preferential release of Y relative to Ho (and also La relative Pr) at intermediate pH where aqueous REY concentrations are governed by proton competition for adsorption sites. Proton-competition-control over REY release is bounded at high pH by the onset of colloidal dispersion—represented by the point of minimum dissolution (p.m.d.) of Al—and at low pH by the soil’s point of zero net charge (p.z.n.c.) and/or when proton-promoted dissolution of REY-containing solids, including Fe-(oxyhydr)oxides, control REY release. Results of our dissolution experiments suggest that complexation of REYs by dissolved organic matter (DOM) does not drive Y–Ho fractionation during pedogenesis, but rather may suppress it. Synthesis of these field and laboratory experiments suggests the Y/Ho ratio decreases early in soil development (<20ky) when weathering rates are high and competitive proton adsorption affects REY fractionation. Given that Fe-(oxyhydr)oxide sorbents exhibit greater affinity for Ho relative to Y, their prevalent neo-formation during incipient pedogenesis likely plays a central role in Y–Ho fractionation in these soils. Persistence of low Chond[Y/Ho] ratios in the subsurface soils even at 4100ky suggests Y–Ho fractionation continues, albeit at a slower rate, as weathering proceeds.

Floristic and vegetation structure of a grassland plant community on shallow basalt in southern Brazil

Few studies have adequately described the floristic and structural features of natural grasslands associated with shallow basalt soils in southern Brazil. This study was carried out on natural grazing land used for livestock production in the municipality of Santana do Livramento, in the Campanha region of the state of Rio Grande do Sul, Brazil. The aim of the study was to describe the floristic and structural diversity of the area. The floristic list obtained comprises 229 plant taxa from 40 botanical families, with a predominance of the families Poaceae (62), Asteraceae (28), Fabaceae (16) and Cyperaceae (12). The estimated diversity and evenness in the community were 3.00 and 0.874, respectively. Bare soil and rock outcrops accounted for 19.3% of the area, resulting in limited forage availability. Multivariate analysis revealed two well-defined groups among the sampling units. One group showed a high degree of internal aggregation, associated with deep soils, and was characterized by the presence of tussocks, whereas the other was less aggregate and was characterized by prostrate species growing on shallow soil. Ordination analysis indicated a gradient of moisture and of soil depth in the study area, resulting in different vegetation patterns. These patterns were analogous to the vegetation physiognomies described for Uruguayan grasslands. Overall, the grassland community studied is similar to others found throughout southern Brazil, although it harbors more winter forage species. In addition, the rare grass Paspalum indecorum Mez is locally dominant in some patches, behaving similarly to P. notatum Fl., a widespread grass that dominates extensive grassland areas in southern Brazil.

Modelización de una explotación ganadera extensiva criadora en basalto

Los modelos de simulación pueden ser considerados como herramientas de aprendizaje –según la idea del «simulador de vuelo»– donde los usuarios se beneficiarían por experimentar con situaciones posibles, más aún si son construidos en forma participativa con los potenciales interesados. El Instituto Plan Agropecuario (IPA) desarrolló un modelo para representar a una explotación ganadera criadora extensiva sobre un suelo representativo de basalto: el MEGanE (Modelo de una Explotación Ganadera Extensiva). Los resultados de la simulación, tanto fitotécnicos como zootécnicos muestran gran coherencia con resultados de investigación nacional. Asimismo, el MEGanE pudo reproducir una situación de crisis forrajera conocida, con resultados coherentes a una realidad posible. El MEGanE fue diseñado para transmitir conceptos, con términos de fácil comprensión por los usuarios.

Dark material on Vesta from the infall of carbonaceous volatile-rich material

Localized dark and bright materials, often with extremely different albedos, were recently found on Vesta's surface. The range of albedos is among the largest observed on Solar System rocky bodies. These dark materials, often associated with craters, appear in ejecta and crater walls, and their pyroxene absorption strengths are correlated with material brightness. It was tentatively suggested that the dark material on Vesta could be either exogenic, from carbon-rich, low-velocity impactors, or endogenic, from freshly exposed mafic material or impact melt, created or exposed by impacts. Here we report Vesta spectra and images and use them to derive and interpret the properties of the 'pure' dark and bright materials. We argue that the dark material is mainly from infall of hydrated carbonaceous material (like that found in a major class of meteorites and some comet surfaces), whereas the bright material is the uncontaminated indigenous Vesta basaltic soil. Dark material from low-albedo impactors is diffused over time through the Vestan regolith by impact mixing, creating broader, diffuse darker regions and finally Vesta's background surface material. This is consistent with howardite-eucrite-diogenite meteorites coming from Vesta.

Chromium isotope fractionation during oxidative weathering—Implications from the study of a Paleoproterozoic (ca. 1.9 Ga) paleosol, Schreiber Beach, Ontario, Canada

This study reports detailed stable Cr, Sm–Nd and Rb–Sr isotope data for a ca. 1.9Ga old subaerial weathering profile at Schreiber Beach, Ontario, Canada, from which detailed major and trace element signatures and δ18O values were previously reported. The weathering profile developed on Neoarchean (∼2.7Ga) pillow basalts and is unconformably overlain by the Paleoproterozoic (∼1.88Ga) Gunflint Chert and basal conglomerates. This stratigraphy suggests that the basalts were uplifted and subaerially weathered prior to deposition of the Gunflint Formation.The aim was to investigate the behaviour of chromium during ancient weathering processes and to contribute to the question whether or not stable isotope fractionation accompanied the release of chromium from the weathering rocks at times when atmospheric oxygen was supposedly high enough (in a period following the Great Oxygenation Event (GOE) ∼2.45Ga ago and prior to the deposition of the Gunflint cherts at ∼1.82Ga). These iron-rich cherts belong to one of the last regionally extensive banded iron formations (BIFs) deposited before the ∼1 billion year-long Mesoproterozoic period during which a drastic change in ocean chemistry prevented deposition of BIFs.The gradual textural, mineralogical, and geochemical changes from unweathered basalts to strongly weathered hematite-bearing basalts with increasing stratigraphic height are associated with shifts in the chromium isotope compositions. The δ53Cr value of unweathered pillow basalt cores (−0.19±0.02‰, 2σ) is within the range of mantle inventory values, whereas weathered brown to green basalts (soils), exhibiting up to 30% lower Cr concentrations compared to unweathered pillow cores, are isotopically lighter (δ53Cr=−0.35±0.11‰). In contrast, red, hematite-rich basalts and hyaloclastites underlying the brown to green basaltic soils, with the highest δ18O enrichment in the profile, are isotopically heavier (δ53Cr=+0.05±0.15‰). Rb–Sr isotope data of weathered basalts define a correlation line with a slope corresponding to an age of 1574±24Ma (MSWD=13) which we interpret to reflect a diagenetic event accompanied by alkaline metasomatism during subsidence/burial of the Gunflint basin. The non-correlation of K enrichment factors with δ53Cr, δ18O and other major and trace elements in the weathered rocks indicates that alkaline metasomatism did not affect the geochemical signatures produced during in situ subaerial weathering. Instead, correlations between δ53Cr and δ18O, and between δ53Cr, Ce/Ce*, U and V, indicate coupled mobilization of the redox sensitive elements during oxidative processes and their partial re-deposition at depth from high δ18O freshwaters. Partial re-precipitation of heavy Cr at depth can be explained on the basis of the weak positive correlation between δ53Cr and Fe enrichment factors; it is seen as a consequence of the reduction of mobile Cr(VI) and co-precipitation as mixed Fe(III)–Cr(III) oxhydroxides during contemporaneous oxidation of the Fe2+-bearing groundwaters at depth, a process similar to the one governing the deposition of most Precambrian BIFs. Redistribution of certain elements during the weathering process, in this case REEs, is furthermore indicated by a correlation line in a Sm–Nd isochron diagram defined by the Schreiber Beach data with a slope corresponding to an age of 1.93±0.19Ga (MSWD=26), an age which is compatible with the direct geological constraints for the timing of the paleosol formation at this locality.An oxidative atmosphere at ∼1.9Ga, as implied by the results from the Schreiber profile, is furthermore supported by positively fractioned Cr isotopes (δ53Cr from +0.06 to +0.39‰) recorded in the iron-rich Gunflint Cherts directly above the palaeo-weathered horizons at Schreiber Beach. These values are interpreted to stem from a positively fractionated shallow seawater chromium composition at ∼1.88Ga, potentially reflecting a continental run-off characterized by positive δ53Cr, and are in accordance with Cr isotope signatures in worldwide BIFs (including the Gunflint Iron Formation).Our results show the potential of Cr isotope studies on ancient paleosols to untangle the presence of oxidative weathering processes, making this isotope system a viable and important tracer for the reconstruction of surface oxygenation in Earth's history.

Application of planetary analog mechanical properties to subsurface geological investigations

Investigations of the mechanical properties of planetary analog materials are of great importance to improve future mission success and to enhance our understanding of the history and evolution of planetary surfaces and subsurfaces. Determining the stratigraphy of the subsurface using drills and penetrometers implies knowing the mechanical properties of the regolith. Therefore, we investigated the mechanical properties of Martian regolith analogs (JSC Mars-1 and an unaltered basaltic soil from Mojave desert). Penetration force is dependent on the bearing capacity factor (Nq) and the angle of internal friction which is found to be function of the level of compaction and increases with relative density. The bearing capacity factor (Nq) showed an exponential trend with the angle of internal friction. For Mojave soil, (Nq) increased from 64 to 338 with φ increasing from 32 to 41.3° while (Nq) increased from 161 to 3347 with φ increasing from 39.4 to 54.7° for JSC Mars-1. Based on estimation of the bearing capacity factor and the angle of internal friction, we predicted the force of penetration under the Martian gravity using a 1.2cm diameter penetrometer. Under a bulk density of 1240 and 1500kgm−3 in JSC Mars-1 and Mojave soil, 460 and 200N is the estimated force to reach a depth of about 20cm deep. Based on this investigation, distinguishing between different regolith layers on the subsurface of Mars is possible and observable using penetration force.

Vegetation Effects on Pedogenetic Forms of Iron and Aluminium and Mineralogical Properties of Basaltic Soils in the Southern Guinea Savanna of Nigeria

This study investigates the effects of vegetation particularly fast growing exotic species like Tectona grandis on the Newer Basalt of the Jos Plateau. In particular it determines the effects exotic tree species have on the pedogenetic forms of Fe and Al and mineralogical properties of the basaltic soils age. Soil samples were determined at the depth of 0 &#8211; 30cm and 30 &#8211; 60cm under plantation of four different ages and subjected to standard laboratory analysis. The citrate bicarbonate dithionite (CBD) extractable Fe and Al slightly decreased with aging plantation, which was ascribed to the inhibitory effects of organic matter on the crystallization of Fe and Al. Similarly the active Fe value was less than unity, which implied increased crystalline forms of Fe and Al oxides are as a result of weathering intensity. Mineralogical results indicated that the soils under the fallow and 11 year old plantation had the dominance of magnetites, while those under 21 year old plantation had mixed mineralogy, consisting of magnetites, biotites and montmorillonites. The older plantations (31 and 36 year old) were dominated by kaolinites and traces of haematites and goethites. The trend suggested an increased level of pedogenesis with aging plantations. Increase in crystalline forms of Fe and Al, kaolinites, traces of haematite and goethite concludes that Tectona grandis deteriorates soil properties over time.

Lithium, magnesium and silicon isotope behaviour accompanying weathering in a basaltic soil and pore water profile in Iceland

This study presents lithium, magnesium and silicon isotope ratios from pore waters and soils from a well-characterised Histic Andosol in south-west Iceland. The soil δ7Li composition ranges between values slightly lighter than basalt, to those that are much heavier (−1.1‰ to +26.8‰), and are possibly influenced by sea salt. In contrast, precipitation-corrected dissolved (pore water) δ7Li values (1.8–10.0‰) appear to reflect preferential adsorption of 6Li onto secondary minerals, where allophane supersaturation results in high δ7Li values. Conversely low δ7Li together with high [Li] are probably due to destabilisation of allophane at low pH, and thus desorption of Li. When compared to Icelandic river values, it would appear that soil pore waters reflect an intermediate isotope composition between basalts and river waters. Precipitation corrected pore water Mg isotope ratios (δ26Mg) range between −0.46‰ and −0.12‰, and correlate with the amount of heavy Mg adsorbed onto the soil exchange complex. Silicon isotopes in the soils are isotopically lighter (δ30Si=−0.91‰ to −0.53‰) than basalt (−0.29‰), whereas pore waters are heavier (+0.13‰ to +1.03‰). Soil δ30Si values show a clear evolution between unweathered basalt and a hypothetical isotopically light endmember representing secondary minerals. Dissolved Si isotopes also respond to chemical weathering processes, and show that isotopically heavy δ30Si corresponds to high cation fluxes and high secondary mineral formation. However, comparison of all these proposed isotopic weathering tracers suggests that they respond differently to the same chemical weathering conditions. This indicates a differing behaviour during secondary mineral neoformation or adsorption depending on whether the incorporated element is a major or trace constituent. In turn, this behaviour can potentially yield important information on secondary mineral behaviour and destabilisation, and thus on the chemical weathering processes.

Study on Deformation Characteristics of Dark-Brown Weathered Basalt Soil in Guizhou

There is the dark-brown weathered basalt soil widely distributed along the slope surface of highway in Guizhou and its settlement is obvious under rainfall, which threatens the slope stability, while due to insufficient systematic study on its deformation characteristics, it hinders the highway’s construction in this region.The influence of its water content and dry density is studied by the standard consolidation test both of undisturbed soil and remolded soil under different water content and dry density conditions and its compression coefficient and rebound index are obtained, which provides a reference for slope stability analysis.