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Mineral and elemental distribution in soils formed on the River Niger floodplain, eastern Nigeria.

Introduction

Studies on the mineral and elemental distribution within soils provide vital information for the assessment of their genesis and behaviour. Teveldal et al. (1990) reported that, in some soils, the depth distribution of minerals in the fine fractions does not depict the correct relative stability of minerals, since physical disintegration of coarser fractions continually feeds the finer fractions with fresh materials. Also, St. Arnaud and Whiteside (1963) earlier showed that physical weathering may affect the distribution of minerals in the soils in ways that complicate the study of chemical weathering. From studies of a chronosequence of soils derived from alluvium, Harris et al. (1980) observed that the distribution of minerals in the coarse fraction reached stability earlier than the distribution in the fine fraction. Esser et al. (1992) indicated that physical weathering and mineral distribution patterns in the sand fraction of the Indiana dunes exert a significant influence on the distribution of minerals in the silt and clay fraction.

Evaluation of weathering potential in a soil should therefore include not only the clay and silt fractions but also the sand fractions (Keilen etal. 1976; Akhtar etal. 1995). To achieve this, the fractionation technique is often employed. It is very common in soil organic matter (SOM) studies and has been adapted by many researchers (Watson and Parsons 1974: Koutika etal. 1997). Others (Wilson and Logan 1976; Wilson 1976; Gudmundsson and Stahr 1981; Morras 1995) have used the technique to study distribution in cation exchange capacity (CEC) and nutrients within the soils. In Nigeria, Unamba-Oparah etal. (1987) observed that the knowledge of mineral distribution in the soils is useful for the understanding of the relationships between the minerals and the nutrient capacity of the soil. In Germany, Keilen et al. (1976) demonstrated that certain elements, mainly cations, were lost through weathering while others accumulate.

Studies on the distribution of minerals within fractions in Nigerian soils are non-existent. Available studies are mainly on the mineralogy of clay fractions and whole fine-earth fractions. The objectives of this study were to determine the occurrence, distribution, and weathering transformations of minerals in 5 floodplain soils of the River Niger. We selected 5 soils deposited at various stages on the floodplain, with the assumption that they represent an age sequence.

Materials and methods

Soils

The location, climate, and the vegetation pattern of the study area have been reported by Igwe and Stahr (2004). The characteristics of the soils used for this study are shown (Table 1). The detailed characteristics have also been discussed (Igwe and Stahr 2004). The oldest and old depositions (Table 1) represented by profiles 1 and 2 have less silt in their particle size fractions than the other profiles and arc well sorted with clay. In profiles 3, 4, and 5, less coarse sand is obtained. This phenomenon is attributed to the stage of material deposition and perhaps rapid physical weathering due to abrasion and grinding of coarse materials by the action of the river. The soil pH is generally low (3.8 4.9). Total carbon and total nitrogen are low in the soils, an indication of rapid mineralisation of SOM even under partially submerged conditions (Igwe et al. 1999). The low level of SOM in these soils is also reflected in the low CEC. This is a general problem for these soils and adjacent upland soils (Kang and Juo 1981). Most soils of the floodplain are derived from highly weathered upland soils of the river watershed. Therefore, the CEC and the major soil properties of the floodplain soils are a reflection of the sedimentary materials in which the soils have formed. The dithionite-extractable Fe ([Fe.sub.di]) of the soils especially for the profiles representing the middle, recent, and very recent depositions were generally higher than those of oldest and older depositions (Table 1).

Generally, the soils have high bulk density of 1.50 1.85 Mg in:. Structural degradation of the soil, irregular packing of the sand grains due to constant flooding and drying, reworking and sorting of the soils resulting in pedocompaction, may have been the reason for the relatively high bulk density. The soils are all described as Inceptisols in the USDA Soil Taxonomy (Soil Survey Staff 1999). Specifically. profile 1 is classified as Typic Tropaquept and profile 2 Typic Endoaquept while profile 3 is Dystric Durochrept. Profiles 4 and 5 are Aquic Eutropept and Fluventic Eutropept, respectively.

Geology

The underlying geological materials are mainly recent alluvial deposits (Orajaka 1975). These materials have been transported from the upstream of the River Niger and its tributaries. These geological materials also include those described by Ofoegbu (1985). According to him, these materials were from the Benue Trough and are mainly weathered materials from the Basement Complex. Oyawoye (1972) observed that the Basement Complex consists mainly of quartzofeldspathic migmatites and gneisses with occasional quartzites, marbles. and amphibolites.

Field study

Five profile pits were dug along depositional stages of the floodplain m such a way that the profiles were not less than 2 km from each other (Fig. 1). The 5 profiles were located in such a way that each represented the 5 depositional stages: thus, oldest, older, middle, recent. and very recent depositions were represented by profiles 1,2,3,4, and 5, respectively. The soils have developed under an aquic moisture regime and an isohyperthermic temperature regime. Most of the soils show iron oxide concentration with depth from the topsoil or directly below the topsoil. Gleysation was the dominant visible pedogenic process in the soils. The soil profiles are young and have diagnostic horizons (e.g. cambic) to qualify them as Inceptisols.

[FIGURE 1 OMITTED]

Laboratory methods

Particle size distribution of the <2-mm fractions was measured by the hydrometer method as described by Gee and Bauder (1986). Bulk density was determined by clod method (Blake and Hartge 1986). The soil pit value was measured in 1:2.5 suspensions of soil in 0.1 M KCl. Total organic carbon was determined by loss on ignition method using the LECO equipment. Dithionite-citrate-bicarbonate [Fe.sub.di], [Al.sub.di]. and [Mn.sub.di] were determined by the extraction method of Mehra and Jackson (1960). The ammonium oxalate extractable [Fe.sub.ox], [Al.sub.ox], and [Mn.sub.ox] were determined by Schlichting and Blume (1966) method.

For the determination of minerals and elemental oxides in sand, silt and clay fractions. <2-mm fractions were mechanically fractionated in deionised water with sieves after shaking for 24 h without chemical treatments. The sand fraction was separated with sieve and the silt and clay fractions were separated through a series of high-speed centrifugation. X-ray diffractometry (XRD) of fine sand and silt was determined as powder, and that of clay was determined with oriented clay specimens using the Siemens D500 diffractometer with Ni-filter and CuK[alpha]-radiation. Prior to mounting the oriented clay, subsamples were first pre-treated as follows: saturation with Mg, solvation with glycerol saturation with K, and subsequent heating of the samples to 110[degrees]C, 350[degrees]C, and 550[degrees]C. The aim was to be able to isolate the different mineral forms, because of their variable properties under different temperature regimes. The semi-quantitative evaluation of minerals in the soil fractions was determined using the computer package DIFFRAC AT V3.3 Siemens 1993. This method assumes that the available minerals in the sample sum to 100% and the individual mineral is a fraction of the total. Also in these fractions, and whole soils, oxides of elements were determined using Siemens SRS 200 X-ray fluorescence (XRF). In this method the <2.00-mm soil samples and the fractions were ground to fine powder, out of which 2.666g was weighed and further ground and mixed with 1.333g cellulose material with the trade name "Spectromelt C10 Merck'. This material acts as binding agent to the soil sample to be analysed, The sample was then transferred to tablet making machine and turned into tablet with a pressure of 30t for 5 min. The soil/cellulose sample in a ratio of 2:1 was then analysed using XRF against standards to obtain the concentration of the elements which was further converted to their oxide forms using factors. The elements determined in this manner are referred to as total elements and are expressed as oxides. These standards were of soil and rock materials of various mineralogies purchased commercially from Breitlander Eichproben und Labormaterial GmbH (Hans-Sachs-Strasse 12, D-59077 Hamm, Germany, www.breitlander.com). The standards, of which there were 50, were prepared in the same way as the soil samples and analysed with XRF using the Cr-Tube at the intensity of 50 kV and 50 mA. This method has been adapted in some other studies (Singer et al, 1998; Stahr et al. 2000). Thereafter, the output was calibrated using a Siemens computer package 'Spectra 300 V2.0' (Siemens 1993). Scanning electron microscopy (SEM) LEO 420 equipment was used to examine some quartz and feldspar grains in the silt and title sand fractions.

Data analysis

The values of soil minerals and elements measured were subjected to principal component analysis using the SYSTAT on SPSS 10 computer package (SPSS 1999). This method was able to decompose many soil properties relating to kaolinite to only 5 principal components. For improved interpretation, varimax rotation was applied to the eigenvectors or loadings. The ultimate goal in rotation is to obtain some theoretically meaningful factors and if possible the simplest factor structure. Varimax rotation had the effect of reallocating variances to higher components as well as increasing the number of components order than the few components produced before rotation. Therefore, with varimax rotation, the maximum number of components is produced.

Results and discussions

Dynamics of Fe oxide

The values of [Fe.sub.di] and [Fe.sub.ox] for the soils are shown (Table 1). The [Fe.sub.di] is the crystalline plus the amorphous or poorly crystalline forms of Fe, whereas the [Fe.sub.ox] is the amorphous form. [Fe.sub.2][O.sub.3] in these various forms was prominent in these soils (Table 1 and Table 2). The dominance of crystalline forms of Fe over amorphous forms (Table 1) may have been due to the age of these soils or the age of the sediments in which these soils formed. Schwertmann and Kampf (1983) showed that crystalline iron forms are widely distributed in all climatic regions and prevail in alternating reducing and oxidising conditions such as those of the soils being studied. The mobile [Fe.sub.2+] moves to better aerated sites where it becomes oxidised to form lepidocrocite. Lepidocrocite in the soil was measured by the method of Blume and Schwertmann (1969) using [Fe.sub.ox]/[Fe.sub.di] ratio. A ratio of [less than or equal to] 0.2 may be indicative of the formation of lepidocrocite, hematite, and goethite. In these soils, the [Fe.sub.ox]/[Fe.sub.di] ratio for most fine-earth fraction was <0.2, showing the formation of any of these forms of iron oxides. The higher [Fe.sub.ox]/[Fe.sub.di] observed in profiles 1, 2, 3, and 4 suggest rapid redox process in these horizons of the 4 soils. Kodama and Schnitzer (1977) remarked that lepidocrocite, among other elements, would normally be the weathering end product under alternate reduction and oxidation conditions. The presence of lepidocrocite suggests changes in the redox conditions, such as could be associated with seasonal flooding.

The lower [Fe.sub.di]/clay ratio (Table 1) in almost all the Ap horizons of the soil profiles (except in profile 5) was speculated to be the result of long periods of waterlogging of these soils, dissolution of Fe oxides, and their eventual removal from the soil. Blume and Schwertmann (1969) reported that with a long annual wet period as is the case in the study area, the [Fe.sub.di]/clay ratio minimum occurred m the topsoil. They attributed this process to lateral removal of Fe in solution. Again, the significant positive correlation coefficients (r=0.84, 0.80) between clay, total Fe, and [Fe.sub.di], respectively, further suggested the close relationship between crystalline Fe and clay. Also, the higher [Fe.sub.di]/total Fe ratio was an indication that the soils and the parent materials were matured irrespective of the time of present sediment deposition, in these soils the sediments and the parent materials, though recent, are transported from soils that have undergone intensive weathering from the upland which explains the occurrence of advanced weathering products such as kaolinite and crystalline Fe and Al in the soils.

Table 2 presents the total elemental distribution of the soils. The Si[O.sub.2] contents are generally high in all the soils; however, lower values are obtained in profile 3, perhaps due to higher clay and lower sand contents than other soils. In this study, lower Si[O.sub.2] values were obtained in clay fractions than feldspars and quartz. This trend is reflected in the total [Fe.sub.2][O.sub.3] and MnO. In general terms the soils have high values of total [Al.sub.2][O.sub.3]. Low values of plant essential elements such as [K.sub.2]O, CaO, MgO, and [P.sub.2][O.sub.5] are prevalent in all the soils but with somewhat higher values of these elements present in the younger soils.

Sand fraction

In the coarse sand fraction, results of gleysation, plinthisation, and ferralitisation appear to be dominant in the middle and recent depositions represented by profiles 3 and 4, respectively, as shown by the high values of total [Fe.sub.2][O.sub.3] and [Al.sub.2][O.sub.3] over those of Si[O.sub.2] (Table 3). The number of Fe-nodules and concretions of these oxides observed in the soil profile support this. Apparently, the high values of Fe and Al have affected drastically the values of [Na.sub.2]O, MgO, CaO, and [P.sub.2][O.sub.5] with only [K.sub.2]O slightly higher as also confirmed in the fine-earth fractions. This situation, according to Kronberg and Fyfe (1989), has a major consequence to agriculture, especially in the tropics where nutrient reserve is low in the soil.

In the fine sand, quartz was the dominant mineral in all the soil profiles (Table 4). Apart from the middle deposition represented by profile 3, all the other soil profiles showed a high concentration of feldspar on the topsoil and/or directly below their Ap horizons. These feldspar grains are heavily weathered (Fig. 2). This suggests that the bulk of the feldspar materials in the fine sand fractions were transported and redeposited on the soils. This is because in the soils of the adjacent landscapes, Igwe et al. (1999) did not find significant quantities of feldspars as identified in these flooded soils. Huang (1989) observed that feldspars found in sedimentary environments were generally of igneous origin. In this study these feldspatic materials may have been transported from the basement complex and areas of igneous geology from the upstream of the River Niger. However, Somasiri et al. (1971) remarked that feldspars are commonly present in the silt and sand fractions of young-to-moderately developed soils. Next to the feldspars in abundance were the micas. The muscovite is thought to be inherited from the parent materials, which may be further being transformed into 2 : 1 expansible minerals in the finer fractions as weathering progresses. A number of researchers have noted these transformation processes of mica to expansible minerals and perhaps to kaolinite. Norrish (1973) showed that the transformation of K-bearing micas to expansible 2 : 1 minerals by replacement of the K with hydrated cations gave rise to vermiculite from biotite.

[FIGURE 2 OMITTED]

The dominance of Si[O.sub.2] and [Al.sub.2][O.sub.3] in the elemental oxide of the fine sand is due to the high quartz and feldspar contents observed in this fraction. Schulze (1989) classified the silicate minerals and showed that Si[O.sub.2] constituted their fundamental units. In the fine sand fraction the [K.sub.2]O values in all the profiles and perhaps the [Na.sub.2]O in profiles 2, 4, and 5 (Table 4) were greater than the other elements studied. This suggests that the mica, the expansible minerals, and the feldspars are rich in K. Mica is known to release K when it weathers, whereas vermiculite upon weathering releases exchangeable K. Huang (1989) showed that the crystalline phases of alkali feldspars stable in soils have a range of chemical compositions such as KA1[Si.sub.3][O.sub.8] or NaAl[Si.sub.3][O.sub.8].

Silt fraction

The silt fraction is also dominated by quartz followed by feldspars (Table 5). In all of the soil profiles, quartz accounts for >70% of the total minerals. The feldspar contents in the silt fraction were lower than those observed in the fine sand fraction. In most cases the mica contents are higher in the silt fractions than in the fine sand fractions. These micas are believed to be the direct physical weathering products of shales from the sediments along the River Niger. Also, mechanical breakdown of the soils by previous cultivations may be the cause of increased mica contents in the silt fraction.

In the silt fraction, the expansible and non-expansible clay minerals also begin to manifest (Table 5). The emergence of kaolinite suggests that there was a transformation process favouring 1:1 minerals. According to Fanning et al. (1989) micas serve as precursors for expansible 2:1 minerals, vermiculites, smectites, and also kaolinite by complex mineral transformation. However, White et al. (1960) indicated that this process is very slow under poor drainage. In the study area, the soils remained submerged for most of the year, whereas there is an abrupt dry period when aeration is maximum. This may be an indication that the transformation process of mica to 2 : 1 minerals was mainly during the dry periods of the year when the oxidation rate is very high in the soil.

Again, the high values of Si[O.sub.2], [Al.sub.2][O.sub.3], and total [Fe.sub.2][O.sub.3] (Table 5) show that they relate to the quartz, feldspars, and the secondary minerals. Esser et al. (1992) postulated that high values of total [Fe.sub.2][O.sub.3] over MgO suggest that the clay minerals are rich in Fe and also indicate stronger weathering. In the present study, the soils have high Al and Fe contents, followed by [K.sub.2]O with values of 2.96-3.64% in the silt fractions of all soils. This K may have come from the feldspars and or mica. Huang (1989) showed that majority of K found in clay and silt fractions resides in the K-bearing feldspars and micas. The soil solution, clay minerals, and SOM have to be continuously replenished with K through the weathering of K reserves. Somasiri et al. (1971) noted that the fraction of K from feldspar increases with increasing particle size.

Generally, the other elements MnO, MgO, CaO, and [P.sub.2][O.sub.5] were relatively low but higher in the silt fractions of profile 3. However, [Na.sub.2]O was found to have accumulated in the recent deposition represented by profile 5.

Clay fraction

The clay fraction is characterised by the dominance of kaolinite accompanied by a large proportion of expansible 2:1 minerals such as smectite, vermiculites, and the Al-hydroxide interlayered minerals (Table 6). The last of these minerals are supposed to be alteration products of micas in the soil system. Rich and Cook (1963) postulated that alteration of mica to vermiculite, including deposition of interlayered Al hydroxide, is a common process in acid soils. The pH range of these soils (3.8-5.0) is favourable for the alteration of mica. Also there is evidence that it is possible for mica to undergo transformation, giving rise to smectite in the soil. In the expansible mineral groups, the XRD results indicated that an amount of illite/smectite (HIS) intergrade does occur. In this soil, the transformation process was observed, probably because of the low pH. Aoudjit et al. (1996) showed that transformation of micas follows 2 steps. First they transform into 1-1.4-nm mixed-layered minerals and then into hydroxy-Al interlayered vermiculite. This is particularly possible in acid soils such as the ones studied.

Kaolinite content was high in all of the soils, especially in the oldest deposition and was often >40-50% of the mineral component of the soil (Table 6). It is suggested that these high kaolinite contents were an early product of weathering of minerals in these soils in which feldspar altered in the process of kaolinitisation, forming kaolinite. Bjorlykke (1989) demonstrated the possibility of this process and summarised the process as follows:

2KAl[Si.sub.3][O.sub.8] + 2[H.sup.+] + 9[H.sub.2]O [arrow right] + [Al.sub.2][Si.sub.2][O.sub.5][(OH).sub.4] + [H.sub.4]Si[O.sub. 4] + 2[K.sup.+]

The distribution of the minerals was an indication of deposition of minerals and the continuous synthesis of new ones. The environmental conditions of temperature >25[degrees]C and low pH promote the formation of kaolinite. Kittrick (1970) obtained kaolinite from smectite under acidified conditions. Soil pH was significantly negatively correlated with kaolinite (r = -0.71) but positively correlated with mica (r = 0.54). The interpretation of this relationship is that the lower the pH the more favourable the formation of kaolinite. Both the condition of soil and atmospheric environment suggested that the minerals in the clay fractions were not yet stable. This is because the clay fractions remained a collector of fragments from the coarse fractions, while at the same time pedogenic formation of minerals was a constant occurrence.

Table 6 shows that Si[O.sub.2], [Al.sub.2][O.sub.3], and [Fe.sub.2][O.sub.3] were very common and dominant over other elements in the clay fraction. This could be because these elements are mostly in the structural units of the minerals. The same could be attributed to the relatively higher [K.sub.2]O and MgO, which are components and alteration products of illite, expansible minerals, and feldspars. According to Gudmundsson and Stahr (1981), during the alteration of feldspars certain elements, particularly Na, K, Ca, and to some extent Al, were removed from the soil, leading to accumulation of Si. Although significant correlation existed between feldspar in fine sand and [K.sub.2]O and MgO in clay (r=0.50, 0.55, respectively), it was only in the oldest deposition that these relationships manifested fully. This was because profile 1 has matured and is closer to equilibrium in mineral transformation and weathering. A high (Al + Fe)/Mg ratio indicated that the vermiculite minerals are mostly the aluminum-hydroxide interlayered vermiculite. Esser (1990) and Esser et al. (1992) used this index to distinguish between the Al-hydroxide vermiculite and the non-Al-hydroxyide vermiculite. In the clay fractions, both [Na.sub.2]O and CaO and are lower in concentration than in the other fractions. This fraction is completely decalcified and depleted of Na and Ca minerals. This process is a contemporary process in the soil during the cyclic flooding and subsequent drying but is favoured by the rather fluvial materials low in these minerals.

Mineral and elemental components of fine-earth fraction affecting kaolinite clay

In view of the dominance of kaolinite over other silicate clays, principal component analysis was employed to reduce 23 variables that relate to kaolinite and other clays to 5 orthogonal components. These are variables or minerals having eigenvalues greater than unity (Table 7). These 5 components altogether accounted for 92.8% of the total variance within the variables. Component 1 explained 45.8% of the total variance and has significant loadings on Si/Al ratio, total Al, Si[O.sub.2], MgO, Ti[O.sub.2], total Fe, and loss on ignition. This first component referred mainly to the total polyvalent elements. Some of these elements (Al and Si[O.sub.2]) contribute to the structural framework of kaolinite. Component 2 explained 22.7% of the total variance and has significant loadings on [Mn.sub.di], total Mn, [Mn.sub.ox], [Fe.sub.di]/Clay ratio, and [Fe.sub.di]. The underlying properties in this component are mainly Mn and Fe oxides. The significant elements in component 3 are [Na.sub.2]O, [K.sub.2]O, Zr[O.sub.2], and CaO. This component explained 14.8% of the total variance of the variables. Component 4 explained 5.2% of the total variance and has significant loadings on [Fe.sub.ox]/[Fe.sub.di] and [Fe.sub.ox]. The major contributing variable in this component is Fe oxide. Finally, component 5 explained 4.2% of the total variance and loaded significantly on [Al.sub.ox]/[Al.sub.di] and [Al.sub.di]/total Al ratios. In this component the controlling factor is the ratio of various forms of Al.

To obtain the relationship between kaolinite and these components, the variables defining each component were extracted. These components defining variables (CDV) are those variables with the highest loading on each component. In this study the CDV are Si/Al, [Mn.sub.di], [Na.sub.2]O, [Fe.sub.ox]/[Fe.sub.di], and [Al.sub.di]/total Al (Table 7). These CDVs were used to develop a multiple regression equation model using the kaolinite as Y, while the CDVs are X1, X2, X3, X4, and X5. The relationship between the kaolinite and the 5 CDVs may be expressed as follows:

Kaolinite = 53.408 - 9.504([Al.sub.di]/total Al) - 1.275([Fe.sub.ox]/[Fe.sub.di]) - 14.903([Na.sub.2]O) - 23.450([Mn.sub.di]) + 0.445(Si/Al) ([R.sup. 2] = 0.83; s.e. = 2.04)

Conclusions

The soils are low in pH, organic matter, and exchangeable cations. The Fe oxide in these soils were assumed to have been in suspension of floodwater, attached to clay particles, and subsequently deposited. They are mainly found in concretions and as coatings. This was manifested by the high values of [Fe.sub.2][O.sub.3] in coarse sand fractions of profiles 3 and 4. The prominence of feldspar in the fine sand fractions is a result of the physical weathering in these soils breaking large materials into finer ones, thereby releasing feldspar.

In both silt and clay fractions there were transformation processes leading to transformation of mica into illite and expansible minerals. A very significant input into the mineral pool of the silt and clay fractions was from the sand fractions and other coarse materials such as feldspars. Finally kaolinite is inherited from upland soils or formed from clay and feldspar. Gleying with enrichment of Fe and Mn was best documented in profile 3. As a result of the nature of the formation of these soils, the finer soil fractions will remain very unstable as long as there is constant supply of weathering products.

Principal component analysis has reduced the 23 mineral elements to 5 main components that explain >92.8% of the total variance of the component. The main component defining variables (CDVs) are Si/Al, [Mn.sub.di], [Na.sub.2]O, [Fe.sub.ox]/[Fe.sub.di] and [Al.sub.di]/total Al.
Table 1. Profile distribution of soil characteristics

BD, bulk density (Mg/[m.sup.3]); CEC, cation exchange capacity
(cmol/kg); Ct, organic carbon (%); T.Al, total aluminum; [Fe.sub.di],
[Al.sub.di] [Mn.sub.di], dithionithe-extractable Fe, Al, and Mn;
[Fe.sub.ox], [Al.sub.ox], [Mn.sub.ox], oxalate-extractable Fe, Al,
and Mn; T, trace

 Depth Clay Silt Sand BD Ct pH CEC [Fe.sub.di]
 (cm) (%) KCl

 Profile 1. Oldest

 0-15 12 8 80 1.53 2.11 4.0 2.8 4.82
 15-30 20 6 74 1.11 0.76 3.9 3.5 8.84
 30-60 30 6 64 1.40 0.76 3.9 6.0 15.61
 60-93 22 4 74 1.62 0.32 3.9 6.9 15.40
 93-130 20 4 76 1.31 0.32 3.8 3.9 10.13

 Profile 2. Older

 0-16 14 4 82 1.54 1.32 4.0 3.4 4.87
 16-37 18 6 76 1.34 1.08 4.0 5.7 10.02
 37-64 18 4 78 1.68 0.32 4.1 5.5 12.53
 64-108 16 4 80 1.38 0.24 4.1 5.4 15.22
108-175 6 2 92 1.87 0.12 4.2 2.5 5.14

 Profile 3. Middle

 0-12 26 14 60 1.70 1.52 4.3 3.8 14.12
 12-27 34 10 56 1.54 0.68 4.4 3.0 52.63
 27-60 32 10 58 1.38 0.40 4.4 3.0 59.07
 60-80 34 12 54 1.50 0.28 4.2 4.1 57.72
 80-125 36 14 50 1.81 0.32 4.1 6.1 48.30

 Profile 4. Recent

 0-20 18 20 62 1.33 1.52 4.8 6.2 12.96
 20-43 24 16 60 1.66 0.56 4.1 6.9 33.14
 43-79 24 16 60 1.38 0.32 4.1 8.0 26.69
 79-106 20 14 66 1.79 0.12 4.1 6.8 20.65
106-160 24 10 66 1.63 0.20 4.1 6.7 21.09

 Profile 5. Very recent

 0-23 12 18 70 1.78 1.12 4.9 6.1 13.13
 23-56 22 18 60 1.85 0.92 4.1 8.2 22.16
 56-84 22 20 58 1.84 0.12 4.2 7.8 24.66
 84-123 24 18 58 1.78 0.52 4.5 9.4 21.64
123-170 16 16 68 1.85 0.28 4.7 6.7 17.05

 Depth [Al.sub.di] [Mn.sub.di] [Fe.sub.ox] [Al.sub.ox]
 (cm) (g/kg)

 Profile 1. Oldest

 0-15 1.12 0.01 2.35 1.79
 15-30 2.20 0.01 3.21 1.11
 30-60 4.86 0.01 2.87 2.17
 60-93 2.70 0.01 3.30 1.30
 93-130 2.80 0.01 2.50 1.19

 Profile 2. Older

 0-16 1.09 0.07 3.24 1.45
 16-37 1.80 0.02 3.38 1.74
 37-64 1.43 0.01 1.72 0.83
 64-108 1.34 0.01 1.06 0.50
108-175 0.90 0.02 0.77 0.29

 Profile 3. Middle

 0-12 2.88 0.24 13.70 2.26
 12-27 2.60 1.17 7.56 1.42
 27-60 3.28 1.95 7.13 1.45
 60-80 3.65 2.01 4.83 1.47
 80-125 2.58 0.46 2.89 1.12

 Profile 4. Recent

 0-20 0.98 0.42 2.57 0.94
 20-43 2.48 0.67 2.47 1.60
 43-79 2.02 0.52 1.86 1.44
 79-106 1.21 0.59 1.70 1.03
106-160 1.79 0.30 1.11 0.85

 Profile 5. Very recent

 0-23 1.07 0.57 3.00 0.65
 23-56 2.02 0.44 6.76 1.95
 56-84 2.11 0.65 6.91 1.45
 84-123 1.61 0.45 6.41 1.13
123-170 0.76 0.42 4.27 0.79

 Depth [Mn.sub.ox] Si/ [Fe.sub.di]/ [Fe.sub.di]/
 (cm) Al Clay T.Fe

 Profile 1. Oldest

 0-15 0.009 8.20 0.04 0.43
 15-30 0.006 5.80 0.04 0.52
 30-60 0.003 3.27 0.05 0.46
 60-93 Nd 5.36 0.07 0.93
 93-130 0.001 6.47 0.05 0.79

 Profile 2. Older

 0-16 0.055 5.34 0.04 0.28
 16-37 0.012 4.91 0.06 0.48
 37-64 0.005 4.96 0.07 0.57
 64-108 0.004 5.07 0.10 0.63
108-175 0.009 10.99 0.09 0.65

 Profile 3. Middle

 0-12 0.313 3.60 0.02 0.10
 12-27 0.730 2.99 0.16 0.93
 27-60 1.600 2.59 0.19 0.97
 60-80 1.328 2.47 0.17 0.97
 80-125 0.278 2.70 0.13 0.93

 Profile 4. Recent

 0-20 0.198 4.94 0.07 0.54
 20-43 0.123 3.70 0.14 0.79
 43-79 0.208 3.86 0.11 0.72
 79-106 0.223 4.17 0.10 0.58
106-160 0.040 4.05 0.09 0.70

 Profile 5. Very recent

 0-23 0.250 4.79 0.11 0.52
 23-56 0.230 3.21 0.10 0.54
 56-84 0.322 2.97 0.11 0.57
 84-123 0.260 2.95 0.09 0.54
123-170 0.117 3.89 0.11 0.53

 Depth [Fe.sub.ox]/ [Al.sub.ox]/ [Al.sub.di]/
 (cm) [Fe.sub.di]/ [Al.sub.di]/ T.Al

 Profile 1. Oldest

 0-15 0.49 1.60 0.03
 15-30 0.36 0.51 0.04
 30-60 0.18 0.45 0.05
 60-93 0.21 0.48 0.04
 93-130 0.25 0.43 0.05

 Profile 2. Older

 0-16 0.67 1.33 0.02
 16-37 0.34 0.97 0.03
 37-64 0.14 0.58 0.02
 64-108 0.07 0.37 0.02
108-175 0.15 0.03 0.28

 Profile 3. Middle

 0-12 3.33 0.78 0.04
 12-27 0.14 0.55 0.03
 27-60 0.12 0.44 0.03
 60-80 0.08 0.40 0.04
 80-125 0.06 0.43 0.03

 Profile 4. Recent

 0-20 0.20 0.96 0.02
 20-43 0.07 0.65 0.03
 43-79 0.07 0.71 0.03
 79-106 0.08 0.85 0.02
106-160 0.05 0.48 0.02

 Profile 5. Very recent

 0-23 0.23 0.61 0.02
 23-56 0.31 0.97 0.02
 56-84 0.28 0.69 0.02
 84-123 0.30 0.70 0.02
123-170 0.25 1.04 0.01

Table 2. Total elemental distributions (%) in the fine-earth fractions
of the representative profiles

LOI, Loss on ignition

 [P.sub.2] [Al.sub.2]
Horizon Depth (cm) [Na.sub.2]O MgO [O.sub.5] [O.sub.3]

 Profile 1. Oldest

Ap 0-15 0.13 0.40 0.07 8.30
Bg1 15-30 0.12 0.49 0.06 11.17
Bg2 30-60 0.09 0.75 0.07 17.40
Bg3 60-93 0.09 0.45 0.05 11.64
BCg 93-130 0.08 0.38 0.04 9.92

 Profile 2. Older

Ap 0-16 0.52 0.57 0.10 11.45
Bg1 16-37 0.52 0.59 0.07 12.50
Bg2 37-64 0.58 0.60 0.06 12.52
Bg3 64-108 0.67 0.57 0.05 12.00
Cg 108-175 0.41 0.30 0.06 6.13

 Profile 3. Middle

Ap 0-12 0.42 0.91 0.22 15.33
Bg1 12-27 0.35 1.03 0.26 17.06
Bg2 27-60 0.32 1.09 0.25 18.68
Bg3 60-80 0.27 1.11 0.20 19.57
Bg4 80-125 0.32 1.03 0.16 18.42

 Profile 4. Recent

Ap 0-20 0.73 0.70 0.16 12.24
Bg1 20-43 0.52 0.91 0.13 15.00
Bg2 43-79 0.59 0.86 0.11 14.71
Bg3 79-106 0.66 0.78 0.11 13.77
Bg4 106-160 0.66 0.83 0.10 14.20

 Profile 5. Very recent

Ap 0-23 0.89 0.77 0.12 12.43
AB 23-56 0.62 1.04 0.23 17.13
Bg1 56-84 0.57 1.12 0.26 17.64
Bg2 84-123 0.69 1.12 0.17 18.22
Bg3 123-170 0.81 0.98 0.12 15.18

Horizon Si[O.sub.2] [K.sub.2]O CaO Ti[O.sub.2] MnO

 Profile 1. Oldest

Ap 79.63 1.30 0.13 0.67 0.01
Bg1 76.49 1.27 0.14 0.85 0.01
Bg2 64.40 1.39 0.15 1.23 0.02
Bg3 73.98 1.02 0.10 0.62 0.01
BCg 75.62 1.03 0.09 0.52 0.01

 Profile 2. Older

Ap 70.36 2.55 0.39 1.16 0.04
Bg1 71.12 2.56 0.36 1.24 0.03
Bg2 71.02 2.75 0.37 1.33 0.02
Bg3 73.96 2.84 0.43 1.21 0.02
Cg 86.41 1.69 0.28 0.49 0.01

 Profile 3. Middle

Ap 62.48 2.56 0.42 1.64 0.08
Bg1 57.69 2.41 0.43 1.68 0.17
Bg2 54.86 2.37 0.44 1.72 0.31
Bg3 54.71 2.21 0.39 1.73 0.33
Bg4 56.41 2.12 0.39 1.57 0.11

 Profile 4. Recent

Ap 68.44 3.16 0.61 1.32 0.07
Bg1 62.87 2.87 0.41 1.65 0.09
Bg2 64.41 2.97 0.44 1.43 0.07
Bg3 65.68 2.98 0.47 1.29 0.08
Bg4 67.44 2.98 0.48 1.22 0.04

 Profile 5. Very recent

Ap 67.69 3.13 0.85 1.16 0.08
AB 61.97 2.74 0.70 1.46 0.08
Bg1 60.06 2.71 0.82 1.48 0.09
Bg2 60.72 2.86 0.80 1.51 0.07
Bg3 66.07 3.00 0.84 1.32 0.05

 [Fe.sub.2]
Horizon [O.sub.3] Zr[O.sub.2] LOI

 Profile 1. Oldest

Ap 1.59 0.04 7.7
Bg1 2.45 0.04 6.9
Bg2 4.84 0.04 9.6
Bg3 2.37 0.03 9.6
BCg 1.85 0.03 9.8

 Profile 2. Older

Ap 2.49 0.11 9.8
Bg1 3.00 0.11 7.9
Bg2 3.14 0.11 7.5
Bg3 3.44 0.11 4.8
Cg 1.13 0.09 3.6

 Profile 3. Middle

Ap 6.11 0.06 9.8
Bg1 8.23 0.05 10.6
Bg2 8.68 0.05 11.2
Bg3 8.48 0.04 11.0
Bg4 7.49 0.05 11.9

 Profile 4. Recent

Ap 3.46 0.11 9.6
Bg1 5.98 0.09 9.5
Bg2 5.31 0.10 9.0
Bg3 5.12 0.11 8.9
Bg4 4.33 0.12 7.6

 Profile 5. Very recent

Ap 3.64 0.14 9.1
AB 5.83 0.10 8.1
Bg1 6.16 0.09 10.3
Bg2 5.75 0.09 8.0
Bg3 4.62 0.11 6.3

Table 3. Chemical composition (%) of some coarse sand fractions from
selected profiles

There are no data for profiles 2 and 5; LOI, loss on ignition

 [Al.sub.2] [Fe.sub.2]
Horizon Si[O.sub.2] [O.sub.3] [O.sub.3] MnO [Na.sub.2]O

 Profile 1. Oldest

Ap 86.77 2.40 9.60 -- 0.07
Bg1 87.17 2.15 8.41 -- 0.06
Bg2 n.d. n.d. n.d. n.d. n.d.
Bg3 87.21 3.61 6.70 -- 0.08
BCg 87.58 1.68 9.27 -- 0.03

 Profile 3. Middle

Ap 68.34 7.80 18.52 0.15 0.30
Bg1 64.54 7.83 22.09 0.35 0.25
Bg2 57.86 10.70 24.69 0.95 0.30
Bg3 50.35 12.76 29.39 1.09 0.25
Bg4 57.12 10.38 26.31 0.63 0.31

 Profile 4. Recent

Ap n.d. n.d. n.d. n.d. n.d.
Bg1 n.d. n.d. n.d. n.d. n.d.
Bg2 58.67 11.98 21.21 0.49 0.70
Bg3 56.07 12.25 23.69 0.41 0.66
Bg4 55.00 10.93 26.44 0.22 0.74

Horizon [K.sub.2]O MgO Ti[O.sub.2] Zr[O.sub.2] CaO

 Profile 1. Oldest

Ap 0.78 0.12 0.11 0.01 0.04
Bg1 0.86 0.11 0.08 0.01 0.03
Bg2 n.d. n.d. n.d. n.d. n.d.
Bg3 1.03 0.17 0.15 0.01 0.08
BCg 0.89 0.08 0.04 0.01 0.02

 Profile 3. Middle

Ap 1.68 0.40 0.68 0.03 0.28
Bg1 1.53 0.39 0.62 0.02 0.24
Bg2 1.82 0.59 0.93 0.02 0.28
Bg3 1.67 0.71 1.16 0.02 0.28
Bg4 1.65 0.56 0.09 0.03 0.25

 Profile 4. Recent

Ap n.d. n.d. n.d. n.d. n.d.
Bg1 n.d. n.d. n.d. n.d. n.d.
Bg2 2.51 0.63 1.18 0.08 0.43
Bg3 2.41 0.66 1.18 0.07 0.41
Bg4 2.38 0.59 1.08 0.08 0.47

 [P.sub.2]
Horizon [O.sub.5] LOI

 Profile 1. Oldest

Ap 0.03 0.07
Bg1 0.01 1.11
Bg2 n.d. n.d.
Bg3 0.02 0.94
BCg 0.01 0.39

 Profile 3. Middle

Ap 0.47 1.35
Bg1 0.61 1.55
Bg2 0.66 1.20
Bg3 0.64 1.68
Bg4 0.57 1.30

 Profile 4. Recent

Ap n.d. n.d.
Bg1 n.d. n.d.
Bg2 0.32 1.80
Bg3 0.37 1.82
Bg4 0.45 1.62

n.d., Not determined; --, below detection level.

Table 4. Mineralogical and chemical composition (%) of the fine sand
fractions

Exp., Expansible minerals (vermiculite, smectite, Al-interlayered
vermiculite); mica, muscovite; LOI, loss on ignition

Horizon Quartz Felds. Mica Exp. Kaolin Si[O.sub.2]

 Profile 1. Oldest

Ap 77 21 2 n.d. n.d. 75.89
Bg1 92 7 1 n.d. n.d. 80.46
Bg2 93 7 n.d. n.d. n.d. 79.83
Bg3 90 10 n.d. n.d. n.d. 83.67
BCg 93 6 1 n.d. n.d. 84.74

 Profile 2. Older

Ap 71 29 n.d. n.d. n.d. 78.13
Bg1 73 27 n.d. n.d. n.d. 80.47
Bg2 82 18 n.d. n.d. n.d. 82.85
Bg3 82 18 n.d. n.d. n.d. 79.74
Cg 82 18 n.d. n.d. n.d. 81.88

 Profile 3. Middle

Ap 92 8 n.d. n.d. n.d. 82.03
Bg1 85 14 1 n.d. n.d. 69.25
Bg2 82 17 1 n.d. n.d. 64.85
Bg3 85 15 n.d. n.d. n.d. 61.65
Bg4 84 16 n.d. n.d. n.d. 72.51

 Profile 4. Recent

Ap 64 35 1 n.d. n.d. 74.71
Bg1 76 27 2 n.d. n.d. 75.97
Bg2 77 22 1 n.d. n.d. 77.65
Bg3 85 15 n.d. n.d. n.d. 79.50
Bg4 78 22 n.d. n.d. n.d. 77.46

 Profile 5. Very recent

Ap 79 20 1 n.d. n.d. 77.76
AB 73 27 1 n.d. n.d. 77.65
Bg1 78 21 1 n.d. n.d. 78.30
Bg2 77 23 n.d. n.d. n.d. 80.38
Bg3 84 16 n.d. n.d. n.d. 84.74

 [Al.sub.2] [Fe.sub.2]
Horizon [O.sub.3] [O.sub.3] MnO [Na.sub.2]O [K.sub.2]O

 Profile 1. Oldest

Ap 2.86 0.44 0.01 0.17 1.33
Bg1 3.12 0.57 0.01 0.23 1.36
Bg2 2.95 0.40 0.01 0.23 1.41
Bg3 3.03 0.43 0.01 0.24 1.36
BCg 2.68 0.39 0.01 0.19 1.24

 Profile 2. Older

Ap 6.70 0.67 0.01 0.89 2.76
Bg1 6.89 0.66 0.01 1.05 2.90
Bg2 7.22 0.70 0.01 1.19 3.02
Bg3 8.02 0.79 0.01 1.41 3.27
Cg 7.18 0.98 0.02 1.12 2.59

 Profile 3. Middle

Ap 7.47 3.57 0.04 0.94 2.51
Bg1 9.32 12.97 0.38 0.69 2.24
Bg2 11.36 15.35 1.02 0.71 2.30
Bg3 12.13 15.98 1.31 0.61 2.21
Bg4 10.01 11.07 0.31 0.91 2.62

 Profile 4. Recent

Ap 8.42 1.00 0.02 1.23 3.65
Bg1 8.37 2.34 0.04 1.15 3.63
Bg2 9.31 2.05 0.04 1.34 3.64
Bg3 9.02 1.50 0.03 1.42 3.69
Bg4 9.25 1.84 0.02 1.37 3.57

 Profile 5. Very recent

Ap 9.11 1.00 0.02 1.56 3.46
AB 9.66 1.08 0.03 1.66 3.63
Bg1 9.73 1.22 0.03 1.75 3.75
Bg2 8.98 1.00 0.02 1.65 3.53
Bg3 10.44 0.96 0.02 2.03 3.51

 [P.sub.2]
Horizon MgO Ti[O.sub.2] Zr[O.sub.2] CaO [O.sub.5] LOI

 Profile 1. Oldest

Ap 0.11 0.40 0.07 0.16 0.02 2.4
Bg1 0.12 0.40 0.06 0.16 0.02 2.0
Bg2 0.10 0.31 0.05 0.15 0.01 1.2
Bg3 0.11 0.43 0.08 0.15 0.01 1.6
BCg 0.11 0.40 0.06 0.15 0.01 3.2

 Profile 2. Older

Ap 0.19 0.37 0.04 0.47 0.03 2.1
Bg1 0.20 0.36 0.04 0.48 0.02 2.5
Bg2 0.21 0.36 0.03 0.54 0.01 1.7
Bg3 0.24 0.35 0.03 0.62 0.02 0.8
Cg 0.26 0.65 0.12 0.54 0.03 0.6

 Profile 3. Middle

Ap 0.21 0.40 0.03 0.45 0.19 2.1
Bg1 0.37 0.63 0.02 0.41 0.63 1.9
Bg2 0.52 0.85 0.03 0.46 0.60 2.5
Bg3 0.56 0.91 0.02 0.39 0.51 1.6
Bg4 0.39 0.60 0.02 0.49 0.36 1.4

 Profile 4. Recent

Ap 0.24 0.31 0.02 0.65 0.05 0.9
Bg1 0.24 0.34 0.01 0.58 0.07 0.7
Bg2 0.35 0.37 0.02 0.60 0.05 0.8
Bg3 0.31 0.31 0.01 0.63 0.04 1.1
Bg4 0.38 0.40 0.02 0.64 0.05 1.3

 Profile 5. Very recent

Ap 0.29 0.42 0.04 0.89 0.03 0.8
AB 0.32 0.38 0.03 0.87 0.04 0.9
Bg1 0.40 0.38 0.02 0.93 0.05 1.2
Bg2 0.29 0.41 0.03 0.90 0.03 0.8
Bg3 0.34 0.40 0.03 0.90 0.02 --

n.d., Not detected.

Table 5. Mineralogical and chemical composition (%) of the silt
faction (0.002-0.05 mm)

Exp., expansible minerals (vermiculite, smectite, Al-interlayered
vermiculite); mica, muscovite; LOI, loss on ignition

Horizon Quartz Feldsp. Mica Exp Kaolin Si[O.sub.2]

 Profile 1. Oldest

Ap 79 15 3 2 1 75.15
Bg1 87 9 3 1 n.d. 78.93
Bg2 88 5 4 2 n.d. 79.51
Bg3 89 6 2 2 1 70.89
BCg 93 3 2 2 n.d. 71.66

 Profile 2. Older

Ap 85 12 1 1 1 74.96
Bg1 72 25 2 1 n.d. 76.91
Bg2 83 13 2 2 n.d. 75.97
Bg3 87 8 3 1 1 76.28
Cg 86 10 2 1 1 75.30

 Profile 3. Middle

Ap 84 10 4 1 1 70.56
Bg1 86 6 6 1 1 69.31
Bg2 86 8 4 1 1 67.66
Bg3 78 12 4 1 5 66.94
Bg4 91 2 4 2 1 71.90

 Profile 4. Recent

Ap 90 5 2 2 1 71.15
Bg1 84 9 4 2 1 72.40
Bg2 86 8 3 2 1 69.82
Bg3 86 7 4 1 2 70.17
Bg4 83 10 3 2 2 70.86

 Profile 5. Very recent

Ap 79 11 6 1 3 69.50
AB 80 10 4 3 3 69.71
Bg1 83 8 4 2 3 67.43
Bg2 78 13 4 2 3 68.21
Bg3 71 22 2 2 3 68.00

 [Al.sub.2] [Fe.sub.2]
Horizon [O.sub.3] [O.sub.3] MnO [Na.sub.2]O [K.sub.2]O

 Profile 1. Oldest

Ap 9.90 1.71 0.02 0.40 2.97
Bg1 6.64 1.39 0.02 0.49 3.24
Bg2 7.48 1.72 0.02 0.52 3.33
Bg3 13.09 4.52 0.02 0.34 2.96
BCg 10.36 3.05 0.02 0.40 3.30

 Profile 2. Older

Ap 8.83 1.52 0.03 0.74 3.14
Bg1 7.31 1.18 0.02 0.76 3.20
Bg2 7.26 1.09 0.02 0.82 3.21
Bg3 8.07 1.62 0.02 0.86 3.26
Cg 7.47 1.59 0.03 0.79 3.05

 Profile 3. Middle

Ap 11.27 2.96 0.05 0.92 3.55
Bg1 10.56 4.47 0.15 0.89 3.64
Bg2 11.99 5.28 0.29 0.84 3.60
Bg3 11.62 4.90 0.32 0.84 3.58
Bg4 9.87 3.02 0.06 0.91 3.56

 Profile 4. Recent

Ap 8.42 1.80 0.04 0.85 3.39
Bg1 9.63 2.36 0.04 0.88 3.55
Bg2 10.05 2.75 0.05 0.81 3.41
Bg3 8.31 2.09 0.04 0.90 3.37
Bg4 7.32 1.64 0.03 0.84 3.32

 Profile 5. Very recent

Ap 9.10 2.21 0.05 1.02 3.35
AB 9.33 2.37 0.05 1.06 3.45
Bg1 10.65 2.80 0.05 1.04 3.52
Bg2 12.70 3.25 0.06 1.08 3.51
Bg3 10.19 2.89 0.05 1.02 3.45

 [P.sub.2]
Horizon MgO Ti[O.sub.2] Zr[O.sub.2] CaO [O.sub.5] LOI

 Profile 1. Oldest

Ap 0.41 1.37 0.12 0.30 0.06 5.2
Bg1 0.22 1.14 0.15 0.31 0.03 5.6
Bg2 0.31 1.29 0.15 0.28 0.02 1.9
Bg3 0.45 1.32 0.14 0.29 0.05 1.9
BCg 0.33 1.10 0.13 0.33 0.05 6.4

 Profile 2. Older

Ap 0.36 1.25 0.17 0.44 0.05 3.2
Bg1 0.25 1.06 0.17 0.47 0.02 4.3
Bg2 0.24 1.03 0.17 0.49 0.02 6.1
Bg3 0.34 1.14 0.16 0.51 0.03 5.4
Cg 0.35 0.87 0.20 0.59 0.07 1.5

 Profile 3. Middle

Ap 0.50 1.57 0.11 0.50 0.12 3.2
Bg1 0.44 1.62 0.10 0.51 0.17 8.1
Bg2 0.52 1.64 0.09 0.47 0.18 4.2
Bg3 0.55 1.62 0.09 0.42 0.14 7.5
Bg4 0.42 1.54 0.14 0.50 0.09 5.2

 Profile 4. Recent

Ap 0.37 1.21 0.15 0.57 0.07 2.3
Bg1 0.42 1.54 0.14 0.50 0.05 5.2
Bg2 0.58 1.36 0.17 0.51 0.06 2.1
Bg3 0.41 1.09 0.17 0.56 0.05 2.6
Bg4 0.33 1.06 0.20 0.61 0.04 1.5

 Profile 5. Very recent

Ap 0.45 1.27 0.21 0.84 0.07 2.4
AB 0.49 1.20 0.17 0.79 0.09 2.1
Bg1 0.63 1.30 0.14 0.85 0.10 2.6
Bg2 0.84 1.53 0.15 0.77 0.10 2.1
Bg3 0.68 1.42 0.19 0.82 0.07 3.1

n.d., Not detected.

Table 6. Mineralogical and chemical composition (%) of the clay faction
(<0.002 mm)

HExp., hemi expansible minerals (vermiculite,
Al-interlayered vermiculite); LOI, loss on ignition

 [Al.sub.2]
Horizon Illite HExp Smect Kaolin Si[O.sub.2] [O.sub.3]

 Profile 1. Oldest

Ap 4 26 18 52 48.77 25.41
Bg1 4 26 17 53 47.01 26.73
Bg2 4 23 20 53 45.28 27.10
Bg3 3 26 17 54 47.08 28.95
BCg 2 26 15 57 46.26 27.01

 Profile 2. Older

Ap 2 36 15 47 49.75 23.94
Bg1 3 27 22 48 46.65 25.26
Bg2 4 24 22 50 48.30 24.49
Bg3 5 23 22 50 46.19 23.39
Cg 5 19 27 49 45.56 25.45

 Profile 3. Middle

Ap 6 25 21 48 47.36 24.79
Bg1 6 18 30 46 45.08 24.03
Bg2 7 16 29 48 46.86 23.73
Bg3 5 20 29 46 46.90 23.61
Bg4 5 13 37 45 47.71 24.02

 Profile 4. Recent

Ap 5 30 22 43 46.02 21.01
Bg1 5 18 32 45 45.83 23.02
Bg2 5 15 35 45 46.22 23.75
Bg3 6 15 34 45 45.57 23.22
Bg4 5 10 40 45 45.82 23.55

 Profile 5. Very recent

Ap 6 21 35 38 42.78 21.58
AB 5 17 36 42 44.29 23.10
Bg1 4 16 37 43 42.51 24.39
Bg2 6 13 38 43 44.89 23.65
Bg3 5 11 42 42 45.21 22.96

 [Fe.sub.2]
Horizon [O.sub.3] MnO [Na.sub.2]O [K.sub.2]O MgO

 Profile 1. Oldest

Ap 7.71 0.03 0.03 1.23 1.08
Bg1 8.52 0.03 0.01 1.09 1.05
Bg2 9.50 0.02 n.d. 1.04 1.04
Bg3 8.75 0.02 n.d. 0.89 1.04
BCg 8.66 0.02 n.d. 0.91 1.01

 Profile 2. Older

Ap 7.90 0.08 0.11 1.52 1.29
Bg1 8.97 0.04 0.08 1.44 1.25
Bg2 9.21 0.03 0.12 1.62 1.26
Bg3 11.59 0.03 0.14 1.57 1.20
Cg 8.70 0.04 0.18 1.37 1.19

 Profile 3. Middle

Ap 9.92 0.11 0.08 1.78 1.41
Bg1 10.72 0.13 0.06 1.63 1.41
Bg2 9.78 0.14 0.10 1.68 1.43
Bg3 9.05 0.15 0.08 1.53 1.39
Bg4 8.79 0.05 0.06 1.46 1.34

 Profile 4. Recent

Ap 10.36 0.16 0.10 1.90 1.59
Bg1 10.56 0.08 0.08 1.58 1.45
Bg2 10.18 0.07 0.08 1.63 1.45
Bg3 10.12 0.10 0.13 1.46 1.36
Bg4 9.13 0.04 0.15 1.32 1.38

 Profile 5. Very recent

Ap 11.96 0.21 0.09 1.70 1.65
AB 11.16 0.09 0.05 1.26 1.37
Bg1 11.30 0.09 0.06 1.22 1.33
Bg2 11.97 0.09 0.09 1.42 1.48
Bg3 11.24 0.08 0.05 1.42 1.49

 [P.sub.2]
Horizon Ti[O.sub.2] Zr[O.sub.2] CaO [O.sub.5] LOI

 Profile 1. Oldest

Ap 1.79 0.02 0.18 0.17 19.2
Bg1 1.86 0.02 0.24 0.13 18.7
Bg2 1.78 0.02 0.19 0.10 22.6
Bg3 1.59 0.02 0.15 0.10 18.2
BCg 1.56 0.02 0.13 0.10 10.3

 Profile 2. Older

Ap 2.01 0.03 0.25 0.23 19.3
Bg1 2.11 0.02 0.13 0.16 17.5
Bg2 2.31 0.03 0.12 0.13 16.2
Bg3 2.20 0.02 0.27 0.13 14.8
Cg 1.93 0.02 0.22 0.21 12.4

 Profile 3. Middle

Ap 2.08 0.02 0.46 0.28 18.2
Bg1 1.96 0.02 0.51 0.27 17.4
Bg2 2.01 0.02 0.51 0.22 17.0
Bg3 1.95 0.02 0.45 0.16 16.5
Bg4 1.89 0.02 0.40 0.14 14.3

 Profile 4. Recent

Ap 2.08 0.02 0.62 0.44 18.1
Bg1 2.10 0.02 0.25 0.21 17.3
Bg2 2.17 0.02 0.21 0.18 12.6
Bg3 2.10 0.02 0.14 0.17 13.7
Bg4 1.94 0.02 0.12 0.15 16.4

 Profile 5. Very recent

Ap 1.90 0.02 0.80 0.32 18.8
AB 1.79 0.02 0.52 0.34 18.4
Bg1 1.74 0.02 0.82 0.38 19.2
Bg2 1.86 0.02 0.79 0.27 16.1
Bg3 1.88 0.02 0.82 0.23 14.3

n.d., Not detected.

Table 7. Principal component analysis of soil minerals and
elements after varimax rotation using kaolinite component
Abbreviations follow those described on Table 1

Soil Component
properties 1 2 3 4 5

Si/Al -0.897 -0.225 -0.205 0.051 0.248
Total Al 0.882 0.410 0.115 0.028 -0.028
Si[O.sub.2] -0.789 -0.572 -0.145 -0.025 -0.073
MgO 0.760 0.475 0.371 0.107 -0.009
Ti[O.sub.2] 0.747 0.426 0.377 0.111 -0.097
Total Fe 0.746 0.628 0.110 0.047 0.059
LOI 0.733 0.514 -0.276 0.259 -0.014
[Mn.sub.di] 0.321 0.927 0.078 -0.020 0.005
[Mn.sub.ox] 0.342 0.922 0.008 0.056 0.012
Total Mn 0.185 0.903 -0.025 0.004 -0.011
[Fe.sub.di]/clay 0.305 0.790 0.214 -0.402 0.152
[Fe.sub.di] 0.537 0.787 -0.073 -0.198 0.086
[Fe.sub.di]/total Fe 0.194 0.613 -0.306 -0.546 0.257
[Na.sub.2]O 0.038 -0.065 0.986 -0.070 -0.053
[K.sub.2]O 0.259 0.097 0.913 -0.040 -0.130
Zr[O.sub.2] -0.134 -0.229 0.912 -0.130 -0.072
CaO 0.267 0.151 0.884 0.117 -0.007
[Al.sub.di] 0.632 0.180 -0.668 0.029 0.178
[Fe.sub.ox]/[Fe.sub.di] -0.085 -0.274 -0.085 0.909 -0.184
[Fe.sub.ox] 0.483 0.233 0.0006 0.775 0.094
[Al.sub.ox] 0.487 -0.008 -0.432 0.561 -0.325
[Al.sub.ox]/[Al.sub.di] -0.158 -0.131 0.196 0.407 -0.825
[Al.sub.di]/total Al -0.530 0.025 -0.153 0.062 0.764
Eigenvalue 10.9 5.5 3.6 1.3 1.0
% Variance 45.8 22.7 14.8 5.2 4.2
Cumul. variance % 45.8 68.5 83.3 88.6 92.8


Acknowledgments

The authors are grateful to the Alexander von Humboldt-Foundation of Germany for the Fellowship award within the framework of the Georg Forster Research Fellowship to one of the authors (C.A.I.). The hospitality of the Soil Mineralogy group, Institut fur Bodenkunde, Universitat Hohenheim, Stuttgart, Germany is appreciated.

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Manuscript received 5 April 2004, accepted 26 October 2004

C. A. Igwe (A,C), M. Zarei (B), and K. Stahr (B)

(A) Department of Soil Science, University of Nigeria, Nsukka, Nigeria.

(B) Institut fur Bodenkunde und Standortslehre (310), Universitat Hohenheim, D-70593 Stuttgart, Germany.

(C) Corresponding author. Email: charigwe1@hotmail.com
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