Soil evolution over the Quaternary period in a semiarid climate (Segre river terraces,northeast Spain)

A macro- and micromorphologic study was done on the soils from a stepped sequence of seven dated fluvial terraces in the lower Segre river valley (Lleida, northeast Spain) under a present-day semiarid Mediterranean climate. The soils have evolved from the Holocene through the early Pleistocene, providing an excellent morphostratigraphic framework for evaluating time-dependent factors influencing soil formation in a dry and calcareous environment. Throughout the chronosequence, some properties are regularly age-related specially carbonatation in subsurface horizons. The carbonates occur mainly as micrite, and although microsparite and sparite also appear in the oldest soils, they are replaced by fine-grained calcite by dissolution–reprecipitation processes (micritization process), which is active at present. Some pedological paleofeatures as the presence of sparite and recarbonated argillans in oldest terrace can be interpreted as the reflex of climatic changes during the Quaternary. In spite of this climate variability, the soils display progressive and systematic patterns of carbonate accumulation: on the lowest terraces, the soils do not yet have secondary carbonates but in the beginning Late Pleistocene calcic horizons, with carbonate pendents, are developed; these pendents increase its thickness with age although pendent growth rates decreases from Late Pleistocene to Middle Pleistocene. In the middle of the Late Pleistocene, calcic horizons evolved to petrocalcic horizons, which increase its thickness in the Middle and specially in Early Pleistocene. The presence of calcic and petrocalcic horizons is the primary basis for soil classification. This criterion is applicable not only to the soils of the lower Segre river basin, but also to many soils throughout the semiarid Mediterranean region.     

Soils of Agricultural Terraces with Retaining Walls in the Mountains of Dagestan

Soil-archeological studies of agricultural terraces with retaining walls in the area of construction of the Gotsatlinskaya Hydroelectric Power Station in Khunzakh district of the Republic of Dagestan have been performed. The morphogenetic and chemical properties of the anthropogenic soils (Anthrosols) in different parts of the terrace complex are analyzed. It is argued that slope terracing in the mountains ensures the development of thicker soil profiles with pronounced genetic horizons. The soils of agricultural terraces store important information of the paleoenvironmental history and land use. A characteristic feature of the Anthrosols of agricultural terraces is a relatively even distribution of gravelly material of up to 5 cm in diameter in the plow layer. The soils of terraces are characterized by the high variability in their properties within the entire terrace complex and within the particular terraces.     

Properties of solonetzes on terraces of salt lakes Bulukhta and Khaki in the Caspian Lowland

A comparative assessment of pedogenetic processes in solonetzes (Calcic Gypsic Salic Solonetzes (Siltic, Albic, Cutanic, Differentic)) developing on terraces of lake depressions within the Volga–Ural interfluve of the Caspian Lowland has been performed on the basis of data on their macro- and micromorphological features and chemical, physicochemical, and physical properties. The studied soils have number of common characteristics shaped by the humus-accumulative, solonetzic, eluvial–illuvial, calcification, and gypsification processes. However, it is shown that macro- and micromorphological indicators of solonetzic processes (the development of clay–humus coatings and the character of structural units in the solonetzic (B) horizon) do not always agree with the modern physicochemical conditions of the development of this process. This is explained by differences in the degree and chemistry of the soil salinization and the depth and salinity of the groundwater. Solonetzes developing on the second terrace of Playa Khaki are distinguished by the highest water content and maximum thickness of the horizons depleted of soluble salts. They are characterized by the well-pronounced humus-accumulative process leading to the development of the light-humus (AJ) horizon. In other solonetzes, the accumulation of humus is weaker, and their topsoil part can be diagnosed as the solonetzic-eluvial (SEL) horizon. Active solodic process and illuviation of organomineral substances with the development of thick coatings and infillings in the B horizon are also typical of solonetzes on the second terrace of Playa Khaki. Micromorphological data indicate that, at present, layered clayey coatings in these soils are subjected to destruction and in situ humification owing to the active penetration of plant roots into the coatings with their further biogenic processing by the soil microfauna. The process of gleyzation (as judged from the number of Fe–Mn concentrations) is most active in solonetzes developing on the first terrace of Playa Khaki. These soils are also characterized by the highest degree of salinization with participation of toxic salts. The maximum accumulation of gypsum is typical of the heavy-textured horizons.     

Characteristics of Clay Minerals in Podzols and Podzolic Soils

The clay minerals in Podzols and podzolic soils developed under coniferous forests in the Subarctic and Cool-temperate zones are characterized by the predominance of smectite and/or mica-smectite interstratified minerals in the eluvial horizons and chlorite-vermiculite intergrade in the illuvial horizons. A large amount of vermiculite is present in the eluvial horizons of some podzolic soils in the Cool-temperate zone. The illuvial horizons of these soils also contain free iron oxides such as goethite. Imogolite and allophane are present in the illuvial horizons of several soils derived from volcanic ashes. It is suggested that the critical bioclimate for the release of interlayered aluminum from the 2:1-type minerals lies between the Cool- and Warm-temperate zone. In the eluvial horizons of Podzols and podzolic soils, mica minerals and chlorite, as primary minerals, have been transformed to smectite through the pedogenic process. Based on previous studies on the structure and degradation of the dioctahedral mica minerals, it is considered that smectite is transformed from 1M-type mica minerals directly, and from 2M-type mica minerals via mica-smectite interstratifled minerals. The formation of a smectite lattice in the eluvial horizon should be a clay-mineralogical indicator of podzolization.     

Study of a toposequence for variability in micronutrients from the moist subhumid Siwalik agro-ecological subregion of Punjab

A toposequence from the moist subhumid Siwalik agro-ecological subregion ofPunjab was studied for available and total micronutrient variability. The toposequence showed the least developed soils with only an A–C horizon sequence on steep slopes and a well-developed profile with an argillic horizon on moderate slopes. The soils consist of a variety of minerals and thus belong to the mixed mineralogy class. There were higher levels of DTPA-extractable micronutrients in the surface horizon than in the subsurface horizon due to their association with organic matter through chelation and adsorption. The surface horizons have relatively lower total micronutrient contents than the subsoil horizons. Soils from moderate slopes and lower terraces showed higher total micronutrients contents in the middle horizons, suggesting some redistribution of the constituents due to the illuviation process of pedogenesis. DTPA-extractable and total micronutrients showed an irregular increasing trend from the steep slope to the lower terrace soils. The DTPA-extractable micronutrients showed relatively greater variability (8–107%) than the corresponding total micronutrient contents (2–34%), suggesting the relatively dynamic nature of the former. Variability in DTPA-extractable and total micronutrients within and among the different soils was caused by several processes involved in the differentiation ofmicronutrients. DTPA-extractable micronutrients show the influence of organic matter through the processes of chelation and adsorption, whereas total micronutrients varied due to differences in pedogenic processes of eluviation/ illuvial on different landscapes and textural variation.     

A sequence of marine terraces near Latina (Agro Pontino, central Italy)

A detailed physiographic soil survey has been carried out in the NW part of the Agro Pontino, near Latina. Four marine terraces and extensive eolian sand covers were found. The oldest marine terrace, the Latina complex, largely consists of augitic fine sands of marine-lagoonal origin. Towards the end of the transgression (of uncertain age) some minor sea level fluctuations occurred. The next marine terrace, the Minturno complex, is thought to date from the Tyrrhenian II transgression and was preceded by a major regression. This has the characteristics of a normal transgressive system, including late minor sea level fluctuations. The beachridge and lagoonal deposits are slightly tilted to the SW and are underlain by littoral gravels, most probably derived from the adjacent Latina complex through strong abrasion. Following a minor regression another marine terrace was formed (the Borgo Ermada complex). This terrace is considered to date from the Tyrrhenian III transgression, but has a regressive character, a phenomenon which can be explained by assuming a synformational tectonic tilting, some evidence for which is found. During a subsequent major regression (Würmian) eolian sands were repeatedly deposited, particularly on the Borgo Ermada complex. This was followed by the formation of a simple beachridge-lagoon system during the Holocene (the Terracina complex). The datings are based on correlation with sequences elsewhere, the two marine faunas studied give no clue as to their ages.Soil formation depends strongly on the texture of the parent materials and these relationships are indicated schematically. Soils in sands form a clear chronosequence, exhibiting an increased rubefaction and illuvial concentration of clay with age (Regosols - Arenosols - Luvisols). The distinction between the Borgo Ermada and Minturno complex is partly based on this chronosequence. Soils with a sandy albic E horizon, more or less abruptly overlying a stagnative clayey B horizon (Planosols and related soils) abound in intermediate materials of the Pleistocene terraces. The characteristically abrupt textural change was found to be due to the heterogenity of the parent material (eolian sand over loam to clay) rather than to soil formation.Some attention is paid to prehistoric artefacts, in particular Pontinian type tools and observations of BLANC on the famous site of Gniff-Gnaff are reinterpreted.     

Soil chronosequences in Israel

Chronosequences of Israel soils are summarized. Soil development in the coastal plain is related to the time of the dune deposits while those of the inland valley is related to the formation of the sedimentological terraces. Soil development in the mountains is related to the features and stability of the slope.The properties of young soils resemble those of the parent material. With advancing development the soils are affected by various processes, among them also the accretion of aeolian dust. Leaching is significant already at early stages; in some cases like Hamra and Terra-rossa soils the leaching stage is more advanced in earlier stages than in the final stage of soil development.In advanced stages of soil development the effect of the underlying rock on soil properties is reduced. At the final stage soils on moderate relief in the same climatic zone on different bedrocks resemble each other. This is attributed mainly to the effect of the aeolian dust accretion. The final stage of soil development on moderate relief consists of Grumusols in the northern parts of Israel, grumic dark Brown soils in the semi-arid parts of central Israel, loessial light Brown clay loam and loessial Serozems in the arid parts of the northern Negev and Regs in the extremely arid areas of the Southern Negev and Sinai. Petrocalcic horizons are developed on slopes and terraces where the rate of soil erosion equals that of accumulation of aeolian dust. The formation of petrogypsic horizons in the extremely arid zones is restricted to areas where erosion is negligible.The final stages of soil development exhibit a clear climatic zonality. This zonality differs from the soil zonality in the USSR and the USA due to the special features of dust accretion on the soils of Israel.     

Chrono-toposequences of soils on the river terraces in Transylvania (Romania)

A sequence of surface soil profiles and buried soils described on the 4th, 3rd, 2nd and 1st terraces of different rivers in Transylvania is presented as part of an attempt to perform a paleopedologic interpretation of the dominant soil types of this area. Excepting the first terrace, the described soils were formed from Pleistocene slopewash deposits of Würm, or possibly of Riss age, which overlay alluvial terrace deposits. On the basis of fossil animal remains, periglacial cryostructures, prehistoric artifacts (Coţofeni culture of the transition period from the Neolithic to the Bronze Age) and Scythian graves an approximate age of different soil horizons, as well as the polycyclic nature of soils was established. There is no essential difference between a Würmian buried soil horizon and the argic Bt horizon of the surface soils; moreover, in some cases, the buried paleosols become the Bt horizon itself of the surface soils, through the thinning of the overlying deposits. Even if the possibility of formation of the argic Bt horizons during the postglacial until the end of Neolithic, cannot be excluded, from the presented situations it seems that these horizons in the Transylvanian Basin are Würmian relics, formed in the periglacial interstadials. In most of the cases Bt horizon has nothing in common genetically with the topsoil.     

Parent material influence on soil distribution and genesis in a Paleudult and Kandiudult complex,southeastern USA

Parent materials greatly influence soil development and the distribution of soils on the southeastern US Coastal Plain. We examined the physical, chemical, and mineralogical properties of 11 pedons in a 1-ha plot on the Upper Coastal Plain of Georgia, USA. Uniformity of parent materials was assessed by sand grain size characteristics. The soils have sandy epipedons of variable thickness and argillic horizons of variable texture. Six of the pedons also have kandic horizons. They are classified (US Soil Taxonomy) in Psammentic, Grossarenic, Arenic, and Typic subgroups of Paleudults and Kandiudults. Loamy pedons possess argillic horizons with two distinct increases in clay and greater differences between eluvial and illuvial horizons than sandy pedons. The upper boundary of the argillic horizon is approximately parallel to the present geomorphic surface, suggesting that it is associated with the contemporary surface. Discontinuities, identified by changes in sand grain size ratios and plots of the third (skewness) and fourth (kurtosis) moments of sand grain distribution, roughly correspond to the bottom of the solum. Our data suggest that there are both eolian and fluvial components in the solum, whereas subjacent horizons are completely derived from fluvial deposits. Sandier pedons have greater gibbsite/kaolinite ratios, possibly because greater permeability has enhanced leaching and Si loss. Our data suggest parent materials largely control soil distribution over this plot.     

Clay illuviation in Red Mediterranean soils

Theories regarding pedogenesis in Red Mediterranean soils have undergone several stages of development. The concept of clay illuviation in these soils was not a part of early theories and it is not yet unanimously accepted as a leading soil forming process. A methodology is presented for studying the illuviation of clay in these soils emphasizing typology of textural features and fabrics. The problem of age determination is also addressed, through the use of radiometric dates and correlation with archaeological artifacts. Clay illuviation in Red Mediterranean soils under present day environmental conditions suggests that it occurs presently only on humid and sub-humid margins of the Mediterranean basin. Elsewhere illuvial clay accumulations are inherited from Interglacial periods. Red Mediterranean soils during glacial periods were eroded, colluviated, aggraded with aeolian dust, calcitic fraction of which was redistributed in form of calcitic features and eventually were affected by water logging. An example of water logging of Red Mediterranean soils (Mamora, Morocco) which took place during the last Glacial cycle, consists of yellow illuvial clays accompanied by a yellowing of the ground mass. During earlier cycles water logging resulted in whitish grey stains in which hydromorphic textural features were deposited.     

Vertical distribution of low molecular weight aliphatic carboxylic acids in some forest soils of Japan

Low molecular weight organic acids are widespread and reactive in soils, but their distribution among mineral horizons is uncertain. We investigated the distribution of low molecular weight aliphatic carboxylic acids (LACAs) in three Japanese forest soils, two Acid Brown Forest soils and one Podzolic soil. The total LACAs ranged from 207.3 to 411.8 μmol kg^–1 and were abundant in the lower horizons as well as in the surface horizons of these soils. The illuvial horizons of the Podzolic soil were rich in adsorbed oxalic acid and citric acid. Total LACAs were similar in the two subtypes of Brown Forest soils derived from different parent materials but formed under similar vegetation and climate, and were larger than that in the Podzolic soil. Among the volatile LACAs, formic acid and acetic acid dominated the moist horizons containing much organic material, whereas the non-volatile LACAs, the most abundant being oxalic acid and citric acid, increased in the subsurface horizons. The distribution of water-soluble LACAs in the Brown Forest soil profiles was closely correlated with soil acidity.     

The effect of industrial aerial pollution on the composition of soil solutions in podzols

The composition of soil solutions is a sensitive indicator of the technogenic transformation of podzols of the Kola Peninsula under the impact of aerial pollution. The soil solutions have been obtained using Rhizon vacuum samplers. A sharp rise in the concentrations of heavy metals and sulfates is registered in the solutions from polluted soils. The leaching of organic substances, potassium, sodium, calcium, magnesium, manganese, and zinc from the litter horizons of polluted soils considerably increases. The ratios between the element concentrations in solutions from the litter horizons to those from the illuvial horizons become narrower, which suggests that the litter has partly lost its barrier function.     

Soil genesis along a chronosequence on marine terraces in eastern Taiwan

Soil chronosequences developed on elevated marine terraces are ideal for studying changes in soil-forming processes with time. The coastal range of eastern Taiwan is a product of active arc–continent collision. Vertisols, Mollisols and Entisols are generally found on the different levels of marine terraces herein, but no detailed investigations of soil chronosequence have been conducted by integrating field morphology, physio-chemical characterization, micromorphology and mass-balance interpretations. Five soil pedons were selected on the three marine terraces including Tt-1 and Tt-2 pedons (Typic Hapluderts) on the first higher level with the oldest soil age (9–10 ka), Tt-3 (Vertic Hapludolls) and Tt-4 pedons (Typic Hapludolls) on the second intermediate level (5–6 ka), and Tt-5 pedon (Typic Udipsamments) on the third lower level with the youngest soil age (≤ 3.5 ka). The morphological characteristics showed that strongly developed angular blocky structures, pressure faces and slickensides are more common in higher terrace soils than in lower terrace soils. In this study, depth to C horizon, solum thickness, and thickness of the clay-enriched zone increase with relative terrace age. Although only one to two profiles per terrace were characterized, the following soil analytical characterizations increase with time: the degree of sand grains weathering, pH (H₂O), organic carbon, CEC, contents of Fe_d, Fe_o and Mn_d. Based on X-ray diffraction analysis of the clay-size fraction, soils on all terraces have a mixed mineralogy. Mica, smectite, and kaolinite have slightly increased with increasing terrace age. Furthermore, the dominant processes identified with mass-balance analysis include loss of bases (Ca and Mg), iron, and clay with time. The soil properties, including analytical and mineralogical characterizations, which do not have notable changes with time are primarily due to relatively young soil age (< 10 ka).     

Particle-size distribution patterns in Vertisols and vertic soils of Russia

Five variants of the distribution of clay (<0.001 mm) and physical clay (<0.01 mm) fractions along the vertical profiles of Vertisols (slitozems) and vertic soils (slitic subtypes of different soil types) from the European part of Russia are distinguished: (1) accumulative, (2) even, (3) regressive, (4) with a maximum in the middle-profile horizon and with their approximately equal contents in the upper and the lower horizons, and (5) eluvial–illuvial. These distribution patterns are related to the lithological specificity of sedimentation and formation of parent materials composed of swelling clays of different geneses and ages. Solonetzic, eluvial- gley, and solodic processes contribute to the development of the eluvial–illuvial and, partly, regressive variants of clay distribution. All the five variants with a predominance of the even distribution pattern can be found in Vertisols. Most of Vertisols in the European part of Russia have a medium clayey or a heavy clayey texture in the entire profile. The regressive distribution pattern is typical of the group of vertic soils. In the upper horizons of Vertisols, where slickensides do not form, the texture is usually heavier than that in the analogous horizons of vertic soils. The middle-profile and lower horizons with slickensides have similar statistical distributions of particle-size fractions in Vertisols proper and in vertic soils. However, in Vertisols, a tendency for a more frequent occurrence of the soils with a higher content of the clay fraction and with a higher portion of this fraction in the physical clay fraction is observed (as compared with the vertic soils).     

梯田地形形态特征及其综合数字分类研究

梯田地形具有独特的平面和剖面形态特征,而现有梯田地形分类无法准确反映梯田地形的平面形态特征,导致其难以满足未来构建梯田地形数值模拟模型的需求.以黄土高原旱梯田地形为切入点,对梯田地形的总体特征、平面和剖面形态特征及几何量测特征进行深入研究,提出了基于梯田平面形态特征的梯田地形分类,并在结合现有梯田地形分类的基础上,构建出梯田地形综合数字分类.与传统梯田地形分类相比,该分类综合考虑梯田的总体特征和平面及剖面形态,能更好地反映梯田独特的形态特征和几何量测特征.研究结果为未来构建梯田地形数值模拟模型奠定了坚实基础,对于探讨利用DEM实现梯田地形的有效数字表达与分析具有重要理论意义.     

A DUNE CATENA ON THE CLAY PLAINS OF THE WEST CENTRAL GEZIRA, REPUBLIC OF THE SUDAN

Fixed dunes occupy 400 000 acres in the west central Gezira. Isolated dunes occur sporadically through the central Gezira, and trend NW from Sennar on the Blue Nile to El Geteina on the White Nile. They probably originated as channel deposits laid down by former distributaries of the Blue Nile. Minor aeolian re-sorting took place, and was followed by plant colonization and dune stabilization. Erosion of the dunes is locally active, resulting in exposure of the underlying clays. The catena comprises leached sands (Psammustents) on the dune crests and illuvial loams and clays (Orthustents) in the swales. Swale soils contain pedogenetic and relict lacustrine carbonate. The catena is often superimposed upon former soils, resulting in polygenetic profiles.     

Soil genesis along a chronosequence on marine terraces in eastern Taiwan

Soil chronosequences developed on elevated marine terraces are ideal for studying changes in soil-forming processes with time. The coastal range of eastern Taiwan is a product of active arc–continent collision. Vertisols, Mollisols and Entisols are generally found on the different levels of marine terraces herein, but no detailed investigations of soil chronosequence have been conducted by integrating field morphology, physio-chemical characterization, micromorphology and mass-balance interpretations. Five soil pedons were selected on the three marine terraces including Tt-1 and Tt-2 pedons (Typic Hapluderts) on the first higher level with the oldest soil age (9–10 ka), Tt-3 (Vertic Hapludolls) and Tt-4 pedons (Typic Hapludolls) on the second intermediate level (5–6 ka), and Tt-5 pedon (Typic Udipsamments) on the third lower level with the youngest soil age (≤ 3.5 ka). The morphological characteristics showed that strongly developed angular blocky structures, pressure faces and slickensides are more common in higher terrace soils than in lower terrace soils. In this study, depth to C horizon, solum thickness, and thickness of the clay-enriched zone increase with relative terrace age. Although only one to two profiles per terrace were characterized, the following soil analytical characterizations increase with time: the degree of sand grains weathering, pH (H₂O), organic carbon, CEC, contents of Fe_d, Fe_o and Mn_d. Based on X-ray diffraction analysis of the clay-size fraction, soils on all terraces have a mixed mineralogy. Mica, smectite, and kaolinite have slightly increased with increasing terrace age. Furthermore, the dominant processes identified with mass-balance analysis include loss of bases (Ca and Mg), iron, and clay with time. The soil properties, including analytical and mineralogical characterizations, which do not have notable changes with time are primarily due to relatively young soil age (< 10 ka).     

Structure and function of bacterial communities in ageing soils: Insights from the Mendocino ecological staircase

The ecological staircase of Mendocino (California, USA) is characterized by a succession of uplifted marine terraces that are derived from the same mineralogical parent material but have different ages, levels of fertility, and types of vegetation, from grassland in the youngest and most fertile terrace to a pygmy forest in the older terraces. Such conditions present a unique opportunity to determine how the structure, abundance, and function of bacterial communities vary with soil fertility along this natural chronosequence. Pyrosequencing analysis of 16S rRNA gene amplicons revealed that Acidobacteria, Proteobacteria, Actinobacteria, and Bacteroidetes were the most abundantly represented phyla. Bacteroidetes, Firmicutes, Verrucomicrobia were significantly enriched in the grasslands, while the less fertile forested terraces showed higher abundance of Acidobacteria Gp2 and Alphaproteobacteria. The pygmy forest soil harboured significantly more Actinobacteria and OP10 than the non-pygmy forest. Between samples from different terraces, the structure of the bacterial community clearly correlated with soil characteristics. Notably, the number of operational taxonomic units was greater in the fertile terrace, as was the density of culturable bacterial populations. Functional characterization of the soil culturable bacteria from the pygmy and non-pygmy forest terraces revealed that the soil bacteria from the non-pygmy terrace were significantly more effective in solubilizing minerals and more abundant than in the pygmy terrace. Our results provide new information on bacterial community structure as a function of soil age, land cover and fertility, which improve our understanding of soil evolution.     

Clay illuviation and calcium carbonate accumulation along a precipitation gradient in Kansas

One of the significant features of loess-derived soils in Kansas is the occurrence of clay-rich subsurface horizons above a layer enriched with pedogenic carbonates. In order to examine the extent of clay increase and pedogenic carbonate enrichment in a precipitation gradient, ten soil profiles from three different precipitation regions were studied using micromorphological and mineralogical techniques. The precipitation gradient was divided into three groups: 400–550 mm, 550–750 mm, and 750–1100 mm regions. The objectives were to (1) understand the cause of clay orientation in clay-rich horizons (2) investigate the reasons for the clay increase, and (3) observe the interaction of clay and pedogenic carbonate accumulation features along a precipitation gradient in Kansas. Although clay films were identified in the field for soils in the 400–550 mm regions, illuvial clay films were not observed in thin section analysis. The clay accumulations mostly occurred as grain coatings. The rest of the clay accumulations observed were very thin, striated, and mostly associated with voids. The argillic horizons had a granostriated b-fabric, which indicates stress orientation of micromass caused by high shrink–swell activity. Thick and continuous illuvial coatings were observed in the buried horizons of paleosols. In the other two regions where precipitation exceeds 550 mm, illuvial clay coatings with strong orientation were observed along with thin and striated stress-oriented clay. Both types of clay orientations exceeded 1% of the cross-sectional area for the thin section. Although illuvial clay features and pedogenic carbonates were observed in all soils at approximately the same depth, complete obliteration of clay coatings was not observed in these horizons. In-situ weathering of biotite was one of the reasons for the clay increase in all soil profiles. In all soils studied, the clay increase and cause of clay orientation cannot be attributed to a single genetic process or event. Both illuviation and shrink–swell activity were involved in the orientation of clay. Although orientation of clay and pedogenic carbonates were observed in all soils at approximately the same depth, the decomposition of clay coatings was not observed in these horizons.     

辽宁省白浆化土壤中白土层的特征及其形成

本文以辽宁省浑河在不同历史时期形成的阶地上的黄土状物质发育的土壤为研究对象,通过对剖面形态学特征、基本理化性质和母质均一性判定等研究,探讨了浑河三级阶地白浆化土壤的白土层特征及其形成机制。结果显示:(1)土壤粉粒中的稳定元素钛与锆分析结果表明在三级阶地上的21-003、21-009、07和21-076剖面和二级阶地上的21-001、21-200、03和04剖面的母质均一;(2)由于土体发育程度不同,一级阶地土体中无淀积层;二级阶地土体中有淀积层且无白土层,尚未出现白浆化现象;三级阶地土体中淀积层和白浆化现象明显,出现了白土层,其形成以黏粒的机械淋溶和潴育淋溶为主;三级阶地上土壤比二级阶地和一级阶地发育时间长,但尚未达到漂白层的标准。