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1.
Abstract

A method to determine the contents of imogolite and Al-rich allophane (Sil Al ? 1 : 2) in volcanic ash soils was presented. The method is based on the (1) assessment of the presence of Al-rich allophane in clays by successsive extraction with dithionite-citrate and oxalate-oxalic acid, (2) trimethylsilylation of soil clay with a mixture of hexamethyldisiloxane, HCl, and isopropyl alcohol, and determination of the content of monomeric Si based on the trimethylsilyl derivative of monomeric orthosilicate anion by gas / liquid chromatography, (3) determination of the total content of imogolite and Al-rich allophane based on the content of monomeric Si from imogolite, (4) determination of the imogolite content by Thermogravimetry (TG )-Differential Thermal Analysis (DTA) based on the weight loss due to endothermic dehydroxylation with maximum values at ca. 386°C, (5) calculation of the Al-rich allophane content by subtracting the imogolite content from the total content of these minerals, and (6) evaluation of the imogolite and Al-rich allophane content of soil by multiplying clay content of soil and the two mineral content of clay. The trimethylsilylation analysis was found to be reproducible, and the estimated total amounts of two minerals in clays by this method were adequately approximated to those evaluated from the amount of Si (= Sio) extracted with oxalate-oxalic acid after extraction with dithionite-citrate. The variation in the abmldance of two minerals in the soil horizons of volcanic ash soils from the San'in region indicated that this method is suitable for the profile-study of volcanic ash soils.  相似文献   

2.
For the past ten years much work has been carried out on clay minerals of volcanic ash soils. Most investigators have reported that allophane is dominant among clay minerals of volcanic ash soils and crystallizes to halloysite or meta-halloysite with the advance of weathering (1–8). On the other hand, UCHIYAMA, MASUI and ONIKURA (1960) found that montmorillonite predominates in the clay fraction of volcanic ash soil in Kawatabi (9). Furthermore, MASUI, SHOJI and UCHIYAMA (1966) showed that the major crystalline clay minerals of volcanic ash soils in the Tohoku district are montmorillonite, vermiculite, intergradient montmorillonite-vermiculite and chlorite (10). They also showed that these minerals increase with the advance of weathering and that kaolin minerals are minor constituents.  相似文献   

3.
Texture is one of the major criterions in soil classification, probably because it has a decisive influence on soil properties. This is particularly true for volcanic ash soils. Most ashes are largely composed of sand and silt particles with little clay (11, 15). The ash weathers very rapidly (1), and clay site particles less than 2 microns in diameter occur even within a few months, as shown by Ishii at the authors' laboratory. Those clay size particles produced in the early stage of weathering are slightly weathered ones (2), and are still subject to rapid weathering, losing bases and silica under humid and well drained conditions. In consequence the clay fraction of volcanic ash soils is composed of particles which vary in degree of weathering from slightly altered glass and feldspar to true clay mineraloids and minerals. The clay fraction of younger soils as a whole is less and that of older ones is more weathered. Weathering brings a remarkable change in the properties of volcanic ash soils; for example, an inerease in soil acidity, lowering of base saturation and bulk density, or accumlation of organic matter. These changes must exert a great influence on soil fertility directly or indirectly.  相似文献   

4.
Soil properties related to soil development were measured in six profiles over approximately 180 years of soil development on recessional moraines of the Hailuogou Glacier, Sichuan of southwestern China. It is hypothesized that soil development is strictly time-dependent. Field and laboratory work indicate that as soil develops from initially coarse gravel outwash, the properties undergo a progressive physical and chemical change such that there is a considerable profile differentiation between the youngest and the oldest soils. The pH is also highly stratified; it decreases with time from 8.5 to 4.2 in the upper mineral soil and increases with depth in all profiles. Accumulation of soil organic C and N increases with time but the rates of accumulation become slower with time. Within the investigated timespan, soil C and N accumulated to a considerable level of 3.5 and 0.6 kg/m2 respectively, with mean annual rates of 28 g/m2 for carbon and 3.5 g/m2 for nitrogen. The rapid accumulation of organic C and N accelerates the processes of soil formation, but the content of organic C and N did not reach a steady-state during the observed timespan. The accumulation of soil organic matter results in increased acid production and in the chemical weathering of minerals that promote formation and translocation of the clay fraction and leaching of carbonate; it is also directly responsible for development of soil properties such as cation exchange capacity (CEC), and bulk density.  相似文献   

5.
Towada Ando soils consisted of five soils—Towada-a (1,000 years old), Towada-b (2,000 years old), Chuseri (4,000 years old), Nanbu (8,600 years old), and Ninokura soils (10,000 years Amorphous clay materials of these soils taken at different localities were studied by the combined use of selective dissolution and differential infrared spectroscopy, X-ray analysis, electron microscopy, etc.

The main clay minerals of Towada-a soils, present-day soils, were montmorillonite-vermic-ulite chloritic intergrades and opaline silica, or these minerals and allophane in the humus horizons, and allophane in the non-humus ones. Towada-b soils overlain by the Towada-a soils showed the clay mineralogical constituents similar to those of Towada-a soils. However, allophane was one of the main clay minerals in all the humus horizons as well as non-humus ones. The main clay minerals of Chuseri soils were allophane and layer silicates consisting chiefly of chloritic intergrades and chlorite in the humus horizons, and allophane in the non-humus ones. Opaline silica was present in minor amounts in the humus horizons of Chuseri soils, but nearly absent in Nanbu and Ninokura soils.

There were remarkable differences in the clay mineralogical composition of Nanbu and Ninokura soils with differences of their environmental conditions. Allophane and imogolite Were dominant in the clay fractions of both humus and non-humus horizons of very shallowly buried Nanbu soil which was subjected to the strong leaching process. Allophane was the main clay mineral of deeply buried Nanbu and Ninokura soils which showed the absence of notable accumulation of bases and silica. On the contrary, halloysite with a small amount of siliceous amorphous material appeared in very deeply buried Nanbu and Ninokura soils where bases and silica were distinctly accumulated. The amounts of halloysite in the clay fractions were larger in the humus horizons than non-humus ones, and in Ninokura soil than Nanbu soil.

Soil age, soil organic matter, and depositional overburden of tephras were observed to be conspicuous among various factors relating to the weathering of amorphous clay materials in Towada Ando soils.  相似文献   

6.
The relationship and mechanisms among weathering processes, cation fluxes, clay mineralogy, organic matter composition and stability were studied in soils developing on basaltic material in southern Italy (Sicily). The soils were transitions between Phaeozems and Vertisols. Intense losses of the elements Na, Ca and Mg were measured indicating that weathering has occurred over a long period of time. The main weathering processes followed the sequence: amphibole, mica, volcanic glass or if ash was the primary source → smectite → interstratified smectite–kaolinite → kaolinite. Kaolinite formation was strongly related to high Al, Mg and Na losses. The good correlation between oxyhydroxides and kaolinite in the soils suggests that (macro)aggregates have formed due to physical or electrostatic interactions between the 1:1 clay minerals and oxides. The stability of organic matter was investigated with a H2O2-treatment that assumes that chemical oxidation mimics the natural oxidative processes. The ratio of C after the H2O2 treatment to the total organic C ranged from 1–28%. No correlation between clay content and organic matter (labile or stable fraction) was found. The refractory organic fraction was enriched in aliphatic compounds and did not greatly interact with the kaolinite, smectite or poorly crystalline Fe or Al phases. A part of this fraction (most probably proteins) was bound to crystalline Fe-oxides. In contrast, the oxidisable fraction showed a strong relationship with poorly crystalline oxyhydroxides and kaolinite. Surprisingly, smectite did not contribute to the stabilisation of any of the organic C fractions. The stabilisation of organic matter in the soils has, therefore, two main mechanisms: 1) the protection of labile (oxidisable with H2O2) organic matter, including also aromatic-rich compounds such as charcoal, by the formation of aggregates with oxyhydroxides and kaolinite and 2) the formation of a refractory fraction enriched in aliphatic compounds.  相似文献   

7.
Surface and buried Andosols and buried Luvisols of the Nevado de Toluca Late Quaternary tephra-paleosol sequence (Central Mexico) were studied to show whether these soils present an evolutionary sequence and to determine the pedogenic mechanisms and environmental factors involved in the evolutionary process. Micromorphological observations and mineralogical composition of fine sand and clay fractions were used to detect type and succession of soil-forming process. Some of the buried Andosols, defined as “intergrade” Andosols, have a predominantly blocky structure, humus-depleted areas, redoximorphic features and thin clay coatings in Ah horizons. Clay fractions of buried Andosols contain halloysite besides amorphous components, whereas in modern Andosols, allophane is dominant. Luvisols have micro-areas with granular structure and abundant phytoliths in the groundmass of Bt horizons assumed to be the relict Andosol features. Luvisol clay fractions are dominated by halloysite and kaolinite. Primary minerals show micromorphological weathering features in all studied soils being stronger in Luvisols; however, even in Luvisols, sand fractions consist mostly of unstable volcanic silicates. We hypothesise that the studied profiles form an evolutionary sequence: Andosols–“intergrade” Andosols–Luvisols; the soil transformation is supposed to be linked to progressive crystallisation of 1:1 clay minerals. Comparing the Nevado de Toluca paleosol properties with the existing data on volcanic soil climo- and chronesequences and assessing the regional paleopedological and lacustrine records of Quaternary paleoclimates, we concluded that wet/dry climatic oscillations took place during the formation of the studied paleosols. Rapid crystallisation of 1:1 minerals occurred during dry phases, which speeded up the Andosol to Luvisol transformation and made it independent from the primary mineral weathering status. The Andosol to Luvisol transformation accelerated by climatic fluctuations is thought to be a common soil evolutionary pathway in the subtropical and tropical regions of recent volcanism, which suffered contrasting precipitation oscillations in the Quaternary.  相似文献   

8.
As a consequence of global warming, additional areas will become ice-free and subject to weathering and soil formation. The most evident soil changes in the Alps will occur in proglacial areas where young soils will continuously develop due to glacier retreat. Little is known about the initial stages of weathering and soil formation, i.e. during the first decades of soil genesis. In this study, we investigated clay minerals formation during a time span 0-150 years in the proglacial area of Morteratsch (Swiss Alps). The soils developed on granitic till and were Lithic Leptosols.Mineralogical measurements of the clay (< 2 μm) and fine silt fraction (2-32 μm) were carried out using XRD (X-ray Diffraction) and DRIFT (Diffuse Reflectance Infrared Fourier Transform). Fast formation and transformation mechanisms were measured in the clay fraction. The decreasing proportion of trioctahedral phases with time confirmed active chemical weathering. Since the start of soil formation, smectite was actively formed. Some smectite (low charge) and vermiculite (high charge) was however already present in the parent material. Main source of smectite formation was biotite, hornblende and probably plagioclase. Furthermore, irregularly and regularly interstratified clay minerals (mica-HIV or mica-vermiculite) were formed immediately after the start of moraine exposure to weathering. In addition, hydroxy-interlayered smectite (HIS) as a transitory weathering product from mica to smectite was detected. Furthermore, since the start of soil evolution, kaolinite was progressively formed. In the silt fraction, only little changes could be detected; i.e. some formation of an interstratified mica-HIV or mica-vermiculite phase.The detected clay mineral formation and transformation mechanisms within this short time span confirmed the high reactivity of freshly exposed sediments, even in a cryic environment.  相似文献   

9.
Background, Aims, and Scope  Hydroxy interlayered vermiculite (HIV) and vermiculite are commonly referred to as 1.4 nm minerals. In the subtropical soils of central China, the concentration of vermiculites decreased while that of HIVs increased gradually from north to south as the intensity of soil formation or eluviation increases in the same direction. The cutans in these soils closely interact with air, roots, microbes, water and dissolved ions in soils. Cutans may therefore be expected to exert an important influence on the formation of 1.4 nm minerals relative to the matrix soils. However, little is known about the transformation of 1.4 nm minerals in Alfisols in central China. Here, we investigate the compositional differences of 1.4 nm minerals in cutans and matrix soils, and the probable transformation of vermiculite to HIV or vice versa when sodium citrate and sodium acetate are added to matrix Alfisols. Methods  Cutans and matrix soils were separated from three soils in the northern subtropical zone in China. The samples were analyzed for Fe, Mn, exchangeable cations, organic matter(O.M.), pH, and clay minerals. To 10 mL of matrix soil, suspensions containing about 250 mg (oven-dry weight) of clay was added with 5 mL of 0.4 mol/dm3 or 2 mol/dm3 of sodium citrate or sodium acetate solution and 5 mL of 0.2 mol/dm3 mixed solutions of CaCl2, Mg(NO3)2 and KCl. After its pH was adjusted to 6.0, the mixture was ‘incubated’ for 120 or 210 days (more than one season or half a year) during which period it was shaken for 1 hour every day. The clay mineral composition of the samples was determined after incubation. Results  Both vermiculites and HIVs were present in matrix soils, but only vermiculties were detected in cutans. The addition of organic ligands (citrate and acetate) promoted the transformation of HIV to vermiculite. This transformation was obvious for the matrix soils that had been incubated with 0.5 mol/dm3 sodium citrate for 210 days while sodium acetate was less effective in this regard. The promoting effect of organic ligands is dependent on type and concentration as well as incubation time. This would suggest the reverse transformation occurred in the formation of cutans compared with a vermiculite-to-HIV transformation in the subtropical soils of central China from north to south. Discussion  The position and environment of cutans in the B horizon together with the pH, organic matter and exchangeable base status in cutans seem conducive to the co-existence of vermiculite and HIV in the soils, but only vermiculite is found in cutans. The transformation of HIV to vermiculite in incubation experiments could be divided into two steps: 1) Cheluviation of organic matter to the interlayer hydroxy-aluminums from HIVs. 2) Rebasification of hydrated cations into the interlayers of vermiculites. Conclusions  The clay minerals in cutans can interact with organic ligands and nutrient elements excreted by roots. Under conditions of frequent wetting and drying and high pH, and when the concentrations of exchangeable bases, iron-manganese oxides, clays, and organic matter are high, the exchangeable cations can be incorporated into the interlayers of HIV, thereby promoting the partial transformation of HIV to vermiculite in rhizosphere soils. Recommendations and Perspectives  Cutan is at the interface of material and energy exchange involved in physical, chemical and biochemical reactions in the rhizosphere. These factors strongly affect the compositions of cutans. HIVs in (upper or adjacent) matrix soils may transform to vermiculites during cutan formation in these special soil environments. ESS-Submission Editor: Jizheng (Jim) He (jzhe@rcees.ac.cn)  相似文献   

10.
Andr Eger  Allan Hewitt 《CATENA》2008,75(3):297-307
This study focuses on soils in a mountainous catchment area located in the eastern part of the Southern Alps, South Island, New Zealand. The objective was to check the soils for non- or poorly crystalline constituents (metal organic complexes, short-range-order minerals) and if there is a relationship between pedogenesis and aspect and more recent landscape history. The morphology of the soils indicates brown soils (dystric cambisols, dystrudepts) with only few signs of podsolisation. In contrast, selected chemical properties of the soils reveal very strong weathering and leaching. Feo/Fed ratios are high and exceeding 0.6 in almost every soil horizon. Oxalate-extractable aluminium and silicon show prominent peaks in the lower subsoil horizons with 1.76–2.52% Alo and up to 0.68% for Sio on southern aspects. This is considerably higher than the values measured for soils on northern aspects (0.59% to 1.07% Alo, max. 0.26% Sio). This aspect relationship is also applying to phosphate retention reaching values of more than 90% on southern aspects and not more than 70% for northern aspects. Additionally, significant movement of organic matter in soils on southern aspects is evident by measurements of organic carbon and pyrophosphate-extractable Al and Fe. Thus soil formation can be regarded as more advanced on southern aspects. Allophane in association with organic matter can be considered as an important constituent in southern aspect subsoils being responsible for the typical andic properties. Metal-humus complexes and ferrihydrite are of subordinate significance. Considering the actual soil forming conditions under scrub-grassland (esp. soil acidity), it is unlikely that weathering and leaching is still strong enough today to allow significant podsolisation and the formation of short-range-order minerals. Under consideration of existing soil data from other studies it is proposed that these components and the podsolisation features are relicts caused by more acidic conditions under former forest cover which supported a stronger weathering and leaching.  相似文献   

11.
Abstract

Properties and classification of four selected volcanic ash soils from Abashiri, Hokkaido were studied and the transition of Andisols to Mollisols was discussed. Two of the four pedons (Brown Andosol and Cumulic Andosol)1 showed morphological, clay mineralogical, physical, and chemical properties common to most Andisols in Japan. However, the properties of the other two pedons (Acid Brown Forest soil and Brown Forest soil)1 were considerably different from those of common Andisols in Japan. It was found that the changes in the andic soil properties or transition of Andisols to Mollisols was closely related to the progression of clay weathering, mainly the transformation of noncrystalline clay materials to halloysite. One of the four pedons (Brown Forest soil)1had the clay fraction dominated by halloysite from the uppermost horizon down to the bottom of the profile and satisfied both andic and mollic requirements. Thus we concluded that the pedon is a transitional soil between Andisols and Mollisols and that the transition is closely related to the duration of surface weathering under relatively weak leaching conditions. The four pedons were classified according to the Andisol Proposal (Leamy et al. 1988, New Zealand Soil Bureau) as follows:

Pedon 1: Medial, amorphic (allophane/imogolite), frigid Typic Hapludand (Brown Andosol).1 Pedon 2: Medial, amorphic (allophane/imogolite), frigid Typic Melanudand (Cumulic Andosol).1 Pedon 3: Medial, amorphic (allophane/ imogolite), over kandic, frigid Typic Melanudand (Acid Brown Forest soil).1 Pedon 4: Medial, kandic, frigid Typic Hapludand (Brown Forest soil).1  相似文献   

12.
A comparison was made between two soil climosequences on north- and south-facing slopes in northern Italy to determine the influence of slope aspect on soil processes. The climosequences span an elevational gradient ranging from moderate (1200 m a.s.l.) to high alpine (2420 m a.s.l.) climate zones on surfaces having an age of about 15 000 years. The soils were investigated with respect to organic C, oxalate and dithionite extractable Fe, Al and Si, elemental losses (Ca, Mg, K, Na, Fe, Al, Si, Mn) and clay minerals. The stocks of soil org. C as well as of oxalate-extractable Fe and Al was greatest in the subalpine zone near the timberline. There are no clear differences in organic C content between the soils on north- and south-facing sites. Fe-oxalate and to a lesser extent Alo-stocks were, however, greater on north-facing sites, indicating that weathering is greater there. Eluviation and illuviation of Al and Fe within the soil profile, typical for podzolisation, was more distinctly expressed on the N slopes. The probability of ITM (Imogolite-type-material) formation in the soil seemed to be greater on south-facing sites. On the north-facing sites, element leaching was most intense in the subalpine zone close to the timberline while on the south-facing sites this was only the case for the base cations. The N slopes exhibited higher leaching of elements which generally indicates a higher weathering intensity. On south-facing sites, typical podzolisation processes were measurable only above 2000 m a.s.l. The development of smectites is also a reflection of the weathering intensity; smectite was discernible in the surface horizon at all sites on N slopes but the highest amount was detected in the sub-alpine climate zone. For the south-facing sites only in the alpine climate zone could smectite be detected. Higher temperatures and an increased number of freeze-thaw cycles on south-facing slopes should theoretically enhance rates of chemical weathering. This could, however, not be confirmed with our measurements. The degree of chemical weathering increases from the south- to the north-facing sites that are characterised by lower temperatures, lower evapotranspiration and consequently by a higher humidity. Although precipitation in Alpine regions is abundant, the availability and flux of water through the soil is the prime factor in weathering intensity.  相似文献   

13.
Major weathering sequences in soils are well established; however, knowledge on rates of mineral transformations remains unknown, because it is often difficult to date precisely soil processes. This work was carried out on soils developed on recent (< 188 y) sand dunes on the W coast of Oléron Island (France). The coast has been protected against marine and wind erosion by constructing five consecutives barriers close to the coastline since 1820 (1820, 1864, 1876, 1889, 1948) defining the maximum age of the soil parent material, as before the areas between the barriers were under water. Soils on the older dunes have low clay content (> 94% of sand) and exhibit a bleached E horizon that overlies a yellowish brown B horizon. The process responsible for their formation is podzolization promoted by the high permeability of the material and complexing organic matter produced by coniferous vegetation. Initial mineralogy of C horizons is homogenous and constituted of chlorite, illite, illite/smectite mixed‐layer minerals, and kaolinite, quartz, calcite (≈ 8% related to shell fragments), and feldspars. The initial clay‐mineral assemblage of the E horizons is dominated by illite (well‐crystallized WCI and poorly crystallized PCI) and chlorite. With progressive podzolization, poorly crystallized illite is first transformed to illite/smectite mixed‐layer minerals and in a further step into smectite. In addition, transformation of well‐crystallized illite leads to formation of ordered illite/smectite mixed‐layer minerals in the E horizons, which is not commonly described in soils. In the B horizons, illite/smectite mixed‐layer minerals are present with traces of smectite, as well as Al and Fe oxi‐hydroxides as revealed by DCB and oxalate chemical extractions. This chronosequence illustrates that over short distances and short time (< 188 y) intense mineral weathering and soil development occur. Major clay‐mineral changes occur between 132 and 188 y in agreement with development of the pine forest producing acidic litter.  相似文献   

14.
Y. He  D.C. Li  B. Velde  C.M. Huang  G.L. Zhang 《Geoderma》2008,148(2):206-212
A soil chronosequence consisting of six profiles formed on quartz tholeiite basalt ranging in age from 10,000 years to 1. 8 Million years (My) was studied here. Soil clays were identified using XRD diffractogram decomposition methods for samples obtained from the A and C horizons of profiles. The results showed that kaolinite minerals dominated in all the clay fractions. Gibbsite was prominent in the C horizons in the soils from older rocks. Clays in the A horizon of relatively young soils showed an initial stage of illite formation, followed by smectite mixed layer minerals (illite-smectites and then vermiculite-illite) and finally by vermiculite. The initial presence of illite is interesting as there is no magmatic micaceous or phyllosilicate phase in these basalts and the formation of illite we attribute to a secondary process, probably created by alkali transport by plant materials. The change in 2:1 clay mineralogy reflects the overall change in Si/Al ratios in the soils over longer periods of weathering. In all cases gibbsite is more abundant in the C horizons than the A horizons. The difference in gibbsite content between the A and C horizons we attribute to plant transport of siliceous phytolite material to the surface. Continued high rainfall over long periods of time removed the alkali faster than the plants could bring it to the surface, which led to continuous lowering of 2:1 minerals from younger to older in the soil chronosequence. Nevertheless a 2:1, silica-rich mineral persists in the clay assemblages although in very minor amounts.  相似文献   

15.
The clay mineralogy of 22 samples of the Ap horizons of Ando soils was determined by a combination of methods. Of these samples, 15 did and 7 did not contain allophane and imogolite. Opaline silica was found in 4 samples, whereas aluminum—humus complexes, iron oxides and layer silicates were found in all samples. The presence of allophane and imogolite and the absence of opaline silica in a few Ap horizons was related to mixing of A1 horizons and subsoils by cultivation and to lower supplies of organic matter relative to the amounts of aluminum released from volcanic ash by weathering. The contents of 2:1 and 2:1:1 layer silicates and their intergrades were larger in soils in which quartz predominated in fine fractions. It was inferred that aluminum bound with humus and in allophane-like constituents, rather than aluminum in allophane and imogolite, is important in reactions with phosphate and fluoride.  相似文献   

16.
The published and author’s data on soil-forming conditions, morphology, substance composition and physicochemical properties, total chemical and mineralogical composition, and micromorphology of mountain-meadow soils of the Western Caucasus Range are analyzed. On the basis of the analytical data obtained, the transformation of minerals and features of chemical element profile patterns developed in the course of soil formation are characterized. The main processes accompanying the transformation of mineral and organic parts of the soil mass and migration of soil-formation products are described. Soil formation is shown to be accompanied by two major elementary soil processes developing with participation of soil biota: humus accumulation and clay formation. Ways to improve the classification of mountain-meadow soils are proposed.  相似文献   

17.
The early stage of weathering / soil formation processes from new volcanic mudflow (new lahar materials) brought from Mt. Pinatubo was examined. For this purpose, comparative studies on the physical / chemical characteristics of the new lahar materials and soils formed by the deposition of old lahar materials were conducted. Original soils contained less coarse sand, more silt, and clay than the new lahar materials. Increase in the clay content of the original soils reflected the progression of weathering. The occurrence of a higher leaching process of Fe, Ca, and Mg and of a moderate accumulation of organic matter in the original soils was suggested, based on the differences in the soil elemental composition and chemical properties. Values of base saturation and phosphate absorption coefficient (PAC) of the new lahar materials were 388% and 44, while those of all the original soils ranged 15–160% and 55–894, respectively. With the progression of weathering, the PAC value tended to increase gradually while the base saturation value decreased abruptly under the environmental conditions prevailing in the Philippines.  相似文献   

18.
Gibbsite is usually considered as end product of weathering in tropical environments with potentially high leaching rates. However, there are also hints towards gibbsite formation in initial stages of weathering in different climates. This study reports on a systematic approach based on soil forming factors in order to research the conditions of gibbsite formation in northern Thailand highlands. Therefore, three major study sites were chosen, which differ with respect to parent rock, relief, climate and vegetation. The results show that gibbsite is common in soils of the area. Reasons for its occurrence in soils are manifold. It can be a heritage of the parent rock, a result of initial weathering under free draining conditions or an accumulation under intense chemical weathering caused by high rainfall. Especially the investigation in granite and gneiss areas with a high share of primary minerals indicates that gibbsite can be an early and direct transformation without intermediates from micas and feldspars if free drainage is assured. With progressing soil genesis clay formation reduces drainage and favours kaolinite formation. Only sites with extremely high rainfall and low evaporation (high elevations in northern Thailand) show again a dominance of gibbsite in the clay fraction throughout the whole soil profile.  相似文献   

19.
Purpose

Clay minerals significantly affect the physical, chemical, and biological processes of soils. They undergo spontaneous modification and transformation depending to the climatic conditions. Information concerning the compositions and transformation of clay minerals in nanoparticle colloids (NPs) (25–100 nm) is severely lacking. Studying clay mineral transformation is important approach to understand soil formation. This study was conducted to determine the transformation sequence of clay minerals in several zonal soil NPs.

Materials and methods

Four soils (Haplustalf, Alf-1; Hapludalf, Alf-2; Hapludults, Ult-1 and Ult-2) were collected from B horizons developed under three different climatic zones of China. Alf-1 (36° 05′ N and 117° 24′ E) was located under a warm temperate zone and Alf-2 (30° 38′ N and 115° 26′ E), Ult-1 (29° 13′ N and 113° 46′ E), and Ult-2 (19° 27′ N and 109° 17′ E) under a subtropical zone. The clay particles (<?2000 nm) (CPs) and nanoparticles (25–100 nm) (NPs) of tested soils were separated. The element composition of CPs and NPs was identified by microwave digestion method. The mineralogy and chemical bonding of clay minerals were studied by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR).

Results and discussion

With decreasing latitude, NPs and CPs showed that the molar ratio of SiO2 to Al2O3 trends to diminish, indicating the phenomenon of desilication and allitization in the tested soils. XRD analysis revealed that the main clay mineral of Alf-1 NPs was illite, followed by vermiculite, kaolinite, and kaolinite interstratified minerals (KIMs). The clay minerals of Alf-2, Ult-1, and Ult-2 NPs were dominated by kaolinite (and KIMs), followed by illite, with a little content of hydroxyl-interlayered vermiculite (HIV) in Ult-1 NPs and trace content of gibbsite in Ult-2 NPs. With decreasing latitude, vermiculite and HIV decreased in NPs. When compared to CPs, smectite as well as illite-vermiculite mix-layer mineral (I-V) and illite-HIV mix-layer mineral (I-HIV) were not detected in NPs. The analysis of d060 region by XRD showed that with decreasing latitude, the main clay minerals in NPs were dioctahedral minerals (e.g., illite or kaolinite). These clay minerals resulted from the transformation of trioctahedral minerals in CPs. The disappearance of 2:1 swelling minerals and trioctahedral minerals showed that the NPs were more susceptible to weathering than CPs.

Conclusions

With decreasing latitude, the transformation of clay minerals followed the sequence of illite?→?HIV?→?kaolinite?→?gibbsite in tested NPs.

  相似文献   

20.
Since its first discovery in 1962 (24, 25), imogolite has been known to occur widely in ando-sols from subfrigid to temperate to tropical regions(1, 2, 3, 6, 7, 9, 14) and, peculiarly as gel films, in certain weathered pumice beds of Japan (11, 23). Its morphology and chemical and mineralogical properties have been investigated fairly well and the investigations have reached the 'stage where its structural models can be hypothesized (13, 16, 19, 20, 26). Relatively little attention has been paid, however, to the mechanism of its formation and to its genetic relationship to other clay minerals(18). Elucidation of these points will be very important in establishing imogolite as a member of weathering sequence in soils, and for this to be done will be needed much more extensive study of its distribution, clay mineral suits associated, environmental conditions in soils, etc.  相似文献   

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