Medium Silt Fractions Research Articles

ГРАНУЛОМЕТРИЧЕСКИЙ СОСТАВ ДОННЫХ ОТЛОЖЕНИЙ ОЗЕРА АНАШКИНО (ЮГО-ЗАПАДНОЕ ПРИОНЕЖЬЕ)

The lithostratigraphy and grain-size composition of sediments in Lake Anashkino (south-western Onego area) are described. The younger, upper sediment layers showed a prevalence of very fine sand. Further down the sediment, there dominate coarse and medium silt fractions, and down from the depth of 10.03–10.16 m — medium and fine silt. The oldest sediments (at 10.19–10.20 m) feature a prevalence of very coarse and coarse silt, and further below (10.30–10.31 m) there prevail very fine sand and very coarse silt fractions. The prevalent activity in the palaeo-hydrodynamic environments in which the ancient sediments (9.96–10.31 m) were deposited was turbidite flows. Younger sediments (9.32–9.92 m) were deposited in the environment of low-velocity flows. The sediment formation pattern in Lake Anashkino during the change from a nival to a humid climate suggests there happened five shifts in dynamic water regimes.

Microplastic abundance and accumulation behavior in Lake Onego sediments: a journey from the river mouth to pelagic waters of the large boreal lake

Contamination of bottom sediments with microplastics (MPs) was first studied in Lake Onego - the second largest lake in Europe. The studied region is the most populated part of the lake watershed and covers the estuarine part of a large river (Shuya River), the Petrozavodsk Bay and the pelagic part of the lake. The mean MPs concentration in the sediment was 2188.7 ± 1164.4 pieces per kg of dry weight. It is two times higher than the same in The Baltic Sea and is comparable with highly urbanized areas of the world. Possible reasons for such a high rate of MPs accumulation in Lake Onego can be due to both the proximity to their sources and accumulation behavior. MPs spatial distribution exhibited a predictable pattern along the transsection from the river mouth to pelagic waters. Fibers were the most abundant form comparing with other fractions (61 ± 13 % of the total), however different MPs shapes prevailed in various regions. Relationship between MPs content in sediment and physical and chemical sediment characteristics was established. Fibers accumulation is related to the medium silt fraction (0.01-0.05 mm) and indicates the presence of the major accumulation zones for MPs.

Short-Term Changes of Biotite in Various Particle-Size Fractions of Podzolic Soil in a Model Field Experiment

An experiment on the transformation of test biotite of the clay fraction (<1 µm) and the medium silt fraction (5–10 µm) immersed into the AELоа horizon of podzolic soil for one or three years was performed. Partial transformation of biotite in the medium silt and clay fractions into irregular biotite–vermiculite under the modern pedogenesis conditions within one year of incubation in the AELоа horizon of podzolic soil was demonstrated. A considerable part of biotite was transformed into irregular biotite–vermiculite and biotite–vermiculite–pedogenic chlorite, and small amounts of vermiculite and pedogenic chlorite were formed after three years of incubation in the soil. Biotite transformation into expandable minerals was accompanied by the decrease in the layer charge, loss of interlayer K, and loss of Mg and Fe from the octahedral lattice. Mica transformation was most significant in the medium silt fraction: the overall decrease in the share of nonexpandable biotite layers and in the thickness of biotite crystallites after three years of incubation was more pronounced in this fraction than in the clay fraction.

Changes in the Content, Composition, and Properties of Humic Substances in Particle-Size Fractions of Soddy-Podzolic Soils under the Impact of Long-Term Drainage

Specific features of the transformation of humic substances in particle-size fractions of drained soddy-podzolic soils were studied on a field (12 ha) of the Experimental and Educational Center of Lomonosov Moscow State University in Moscow oblast. The field had a clearly pronounced microtopography. Surface-gleyed soddy-podzolic soils (Albic Stagnic Glossic Retisols (Loamic, Aric, Ochric)) of microdepressions with excessive surface moistening and nongleyed soddy-podzolic soils (Albic Glossic Retisols (Loamic, Aric, Ochric)) of elevated positions were examined. These soils were studied before the field drainage and during 25 years after drainage works in the periods differing in conditions of humification and with due account for not only drainage works but also other factors, such as topography and agrotechnology and their joint action. The specificity of transformation of humic substances in the soils and their particle-size fractions was analyzed in the basis of data on the organic carbon content, group and fractional composition of humus, the intensity of individual stages of humification (the neoformation of humic acids and the formation of humates), and the optical density of the fractions of humic acids. The results of the study of these properties in the fine soil fractions (<50 μm) made it possible to assess the response of the clay (<1 μm) and silt (1–5, 5–10, 10–50 μm) fractions to changes in the ecological situation and the role of separate particle-size fractions in the degradation of humus under adverse impacts. Overall, a clear tendency toward worsening of the humus quality was observed in both soils during the 25-year-long period, which is related to the long-term (20 years) agricultural use of the reclaimed field without application of agrochemicals. The features of humus degradation were mainly manifested in the finest (<10 μm) fractions with a general decrease in the humus content, slowing down of the formation of humic acids and humates, and considerable loss of humic acids, including their agronomically valuable fractions HA1 and HA2. The degradation of humus quality in the clay fraction was largely due to the impact of the reclamation (drainage) factor; the degradation of humus quality in the fine and medium silt fractions was mainly due to the negative changes in the agricultural background. Among negative consequences of the worsening humus quality, the lowering of soil fertility, ecological sustainability, and productivity of agrocenoses should be noted.

Minerals in the three-component combination of agrochernozems in the Kamennaya Steppe

Properties and mineralogy of fine fractions separated from agrochernozems forming a three-component noncontrasting soil combination in the Kamennaya Steppe have been characterized. The soil cover consists of zooturbated (Haplic Chernozems (Clayic, Aric, Pachic, Calcaric)), migrational-mycelial (Haplic Chernozems (Clayic, Aric, Pachic)), and clay-illuvial (Luvic Chernozems (Clayic, Aric, Pachic)) agrochernozems. All the soils are deeply quasi-gleyed because of periodical groundwater rise. The mineralogy of the fraction <1μm includes irregular mica–smectite interstratifications, di- and trioctahedral hydromicas, imperfect kaolinite, and magnesium–iron chlorite. The profile distribution of these minerals slightly varies depending on the subtype of spot-forming soils. A uniform distribution of clay minerals is observed in zooturbated agrochernozem; a poorly manifested eluvial–illuvial distribution of the smectite phase is observed in the clay-illuvial agrochernozem. The fractions of fine (1–5 μm) and medium (5–10 μm) silt consist of quartz, micas, potassium feldspars, plagioclases, kaolinite, and chlorite. There is no dominant mineral, because the share of each mineral is lower than 35–45%. The silt fractions differ in the quartz-to-mica ratio. The medium silt fraction contains more quartz, and the fine silt fraction contains more micas.

Magnetostratigraphy and environmental magnetism in a sedimentary sequence of Miramar, Buenos Aires, Argentina

A sedimentary sequence called “Fogones de la Costa” located at 38° 17′ 35″ S, 57° 50′ 50″ W, on the coastal cliffs, south of Miramar city, was studied from geological, paleomagnetic and rock magnetic viewpoints. The stratigraphic column shows normal and reverse polarity records associated with chrons and subchrons of magnetopolarity. The younger sediments were assigned to the Brunhes Polarity Chron (<0.78 Ma) and the older sediments of the middle and lower part of the profile were assigned to Upper Matuyama (0.99–0.78 Ma), Jaramillo (1.05–0.99 Ma) and Middle Matuyama (1.78–1.05 Ma). A very short normal polarity record between cycles V and VI, at the base of the cliff, suggests the presence of a condensed record of Cobb (or Olduvai?). The oldest reverse polarity layers at the base of the profile should be related to the lower Matuyama (>1.9 Ma). On the basis of these data, the sequence should span from the Lower Pleistocene to the Holocene, and may be correlated (although partially) with the geological formations of San Andrés, Miramar, and Arroyo Seco described in coastal cliffs north of Miramar. The model of behavior of concentration parameters (κ, χ, Ms and Mr) is in agreement with that determined in other loess sections studied in northern Buenos Aires province. The values of the concentration of magnetic parameters decrease with increasing pedogenesis and weathering of the original material (loess and loess-like). This is a behavioral feature, independent of the carrier agent (wind or water). The medium silt fraction is dominant over the other grain sizes. In that fraction, the amount of magnetic minerals increases significantly. Conversely, the layers corresponding to paleochannels and paleolagoons show a decrease of magnetic minerals, the medium silt fraction also decreases, and the very fine silts and clays increase.

Iron Oxides as Major Available Interface Component in Loamy Arable Topsoils

To characterize biogeochemical interface properties in soil with respect to oxide surfaces, the contribution of weakly crystalline and crystalline oxides to soil specific surface area (SSA) of particle size fractions was determined. Three arable topsoils with intermediate to high clay content were subjected to ultrasonic dispersion and particle size fractionation. The obtained silt and clay fractions were treated with hydrogen peroxide, extracted with oxalate and dithionite and the SSA of all fractions was determined using BET-N 2 . Results show that stable microaggregates were present in the coarse and medium silt fractions of all soils that could not be dispersed physically even at the highest ultrasonic dispersion energy and were probably stabilized by organic matter and iron oxides. Iron oxides were a major contributor to the SSA of all particle size fractions and the losses of carbon after oxalate and dithionite extraction showed that a major part of the organic matter in all particle size fractions was stabilized by iron oxides, even in these clay-rich soils. Weakly crystalline oxide surface area did not increase with decreasing particle size and calculated negative surface areas for some of the fine fractions indicated that weakly crystalline oxides were present as coatings on other minerals. The results demonstrate the importance of (iron) oxides for microaggregation and stabilization of organic matter in soil. However, the actual interface provided by these oxides depends on particle size and crystallinity due to the possible occlusion of mineral surfaces by organic matter and weakly crystalline oxides. Abbreviations: OC, organic carbon; OM, organic matter; SSA, specific surface area; XRD, X-ray diffraction.

Dust deposition in the Aral Sea: implications for changes in atmospheric circulation in central Asia during the past 2000 years

We investigated mineral aerosol ( dust) deposition in the Aral Sea with intention to understand the variability of dust in central Asia and its implications for atmospheric circulation change in the late Holocene. Using an 11.12-m sediment core of the lake, we calculated bulk sediment fluxes at high time-resolution and analyzed grain-size distributions of detrital sediments. A refined age-depth model was established by combined methods of radiocarbon dating and archeological evidence. Besides, a principal component analysis (PCA) of grain-size fractions and elements (Fe, Ti, K, Ca, Sr) was used to assess the potential processes controlling detrital inputs. The results suggest that two processes are mainly relevant for the clastic input as the medium silt fractions and Ti, Fe and K are positively correlated with Component 1 (C1), and the fine size fractions (<6 μm) are positively correlated with Component 2 (C2). Taking the results of the PCA, geological backgrounds, clastic input processes into account, we propose that the medium silt fractions and, in particular, the grain-size fraction ratio (6–32 μm/2–6 μm), can serve as indicators of the variability of airborne dust in the Aral Sea region. On the contrary, the fine size fractions appear to be contributed mainly by the sheetwash processes. The bulk sediment deposition fluxes were extremely high during the Little Ice Age (LIA; AD 1400–1780), which may be related to the increased dust deposition. As indicated by the variations of grain-size ratio and Ti, the history of dust deposition in central Asia can be divided into five distinct periods, with a remarkably low deposition during AD 1–350, a moderately high value from AD 350–720, a return to relatively low level between AD 720 and AD 1400 (including the Medieval Warm Period (MWP, AD 755–1070)), an exceptionally high deposition from AD 1400 to 1940s and an abnormally low value since 1940s. The temporal variations in the dust deposition are consistent with the changes in the Siberian High (SH) and mean atmospheric temperature of the northern hemisphere during the past 2000 years, with low/high annual temperature anomalies corresponding to high/low dust supplies in the Aral Sea sediments, respectively. The variations in the fine size fraction also show a broadly similarity to a lacustrine δ 18O record in Turkey ( Jones et al., 2006), implying that there was less moisture entering western central Asia from the Mediterranean during the LIA than during the MWP.

The effect of organic matter on the difference between particle-size distribution data obtained by the sedimentometric and laser diffraction methods

Particle-size distribution in dispersed sediments, soils, atmospheric dust, and other natural objects is their fundamental characteristic. The methods of sedimentometry (the pipette method) and laser diffraction have been applied to study particle-size distribution in a typical chernozem of Kursk oblast from the Alekhin Central Chernozemic Reserve. The content of the clay fraction as determined by the method of laser diffraction is three to five times lower than the clay content determined by the traditional pipette method. One of the reasons for such a great difference in the results obtained by two different methods is related to the low density of the solid phase of the particles of soil organic matter that have the size corresponding to the fine and medium silt fractions. Owing to this, they fall into the category of the clay fraction during the traditional sedimentometric analysis. The initially water-stable aggregates of 0.25–0.5 mm in size are subjected to several stages of their breakdown under the impact of ultrasonic dispersion with the detachment of small particles from their surface layers. The remaining aggregates have different resistance to ultrasonic treatment. After the long-term ultrasonic dispersion, the most stable microaggregates still exist in the soil mass. These microaggregates may only be decomposed to elementary soil particles after the addition of sodium pyrophosphate.

Mineralogical composition of silt fractions and its transformation under the impact of different cenoses in model lysimeters

A lysimetric experiment has made it possible to trace changes in the fine and medium silt fractions of soils developing from the noncalcareous mantle loam under typical phytocenoses of the southern taiga zone during a 33-year-long period. The silt fractions were separated by the Gorbunov method, and their mineralogical composition was analyzed by X-ray diffractometry. The fine silt fraction consists of quartz, kaolinite, chlorite, hydromica, smectite, and feldspars. The medium silt fraction consists of quartz, kaolinite, mica, and feldspars. In both fractions, the content of feldspars in the upper horizons has increased in comparison with the initial parent material due to the physical disintegration of coarser fractions. The chemical decomposition of mica has been registered in the layer of 10–30 cm. In lysimeters under artificially planted mixed forest cenoses, acidic hydrolysis may take place at this depth. Cryogenic processes play an important role in the soil formation at the early stages.

The role of time versus climate in the formation of deep soils of the Apennine fringe of the Po Valley, Italy

Two very deep, red soils on a loess-mantled fluvial terrace of the Trebbia River in northern Italy were sampled and analyzed to determine their history and pedologic significance. Magnetostratigraphy confirms that the upper part of the terrace gravel and all of the 4-m-thick loess cover is normally magnetized and therefore less than about 780,000 yr. Artifacts collected from the oldest loess suggest an age of about 400,000 yr for the inception of loess deposition in this area. The soil horizons in loess dominantly have argillic or albic character, with redoximorphic features that include mottles, glossic tongues, and zones of ferromanganese concretions. Soil colors become progressively redder with depth in the loess cover and are most red, a 2.5 YR color hue, in the top of the terrace gravel. The upper horizons in gravel have abundant ghosts of completely weathered marl and sandstone. Rubification and weathering of stones diminishes with depth to fresh, slightly carbonate enriched parent material at 12 m. The heavy mineral composition of the sand fraction suggests minor discontinuities in loess-derived horizons. Abundance of opaque heavy minerals and picotite, which are resistant to weathering, increases from the soil surface to the base of the loess, is highest in the upper part of the terrace gravel, and decreases from there to the C horizon in gravel. Depth functions of major elements to Si in the medium silt fraction (10–30 μm) indicate a downward increase in degree of decalcification and of dissolution of primary minerals. Micromorphology adds detail to the interpretation of these complex soils: yellow complex ferriargillans are present in almost all horizons; they are rare at the top of the sequence in loess and become progressively more abundant with depth, reaching a maximum in the upper 3 m of the gravel and then decreasing with further depth to 12 m. We interpret this peak in abundance of yellow cutans to result from long continued clay illuviation to this depth from a succession of eluvial zones in the aggrading loessial sequence above. Distinctive red, hematite-rich argillans are abundant only in the upper horizons in the gravel. The red argillans relate to initial development of the soil in gravel, because they are included as pedorelicts in the deepest loess layer, where they are embedded in the yellow argillans. Stratigraphic and pedologic evidence indicates that these soils began forming in terrace gravel for perhaps 300,000 yr during the early middle Pleistocene. From this relict core these soils continued developing, both downward by continuing deep decalcification and argilluviation and upward as a sequence of wet Alfisols developed in a succession of loess layers that began aggrading about 400,000 yr ago. A paleoclimatic record can be perceived weakly in these soils, mainly by thick horizons of FeMn nodules that mark boundaries between episodes of loess deposition that took place during glacial cold phases. Paleofeatures from one unit to another are similar in kind and intensity, indicating a degree of continuity of a basic set of pedogenic processes, principally declcification, argilluviation, and redoximorphism. These soils can be regarded as Vetusols because a single dominant set of pedogenic features are represented in all parts of these soils and deeper parts of these aggrading super profiles have never been isolated from continuing pedogenic change to the present.

Transformations of 2:1 phyllosilicates in 41-year-old soils under oak and pine

The large, unconfined lysimeters at the San Dimas Experimental Forest, in southern California, provide a unique setting in which to study decade-scale vegetation effects on mineral weathering. We investigated the 2:1 phyllosilicate mineralogy of lysimeter soils under 41-year-old monocultures of scrub oak (Quercus dumosa Nutt.) and Coulter pine (Pinus coulteri B. Don), and compared the results to archived original fill material. X-ray diffraction showed that mica increased relative to vermiculite in the clay and medium silt fractions of A horizons under both oak and pine, compared to the archived original fill material. The increase, however, was far greater under oak than under pine. No mineralogical differences were observed in the subsurface horizons of either oak or pine, compared to archived material. Nonexchangeable K increased by 23% in the clay fraction of the oak A horizon, and increased by 5% in the clay fraction of the A horizons under pine, relative to archived parent material. Strong evidence supports biocycling as the basis for observed decade-scale mineral transformations. We conclude that the return of K to the soil surface through litter decomposition, and subsequent fixation by vermiculite, resulted in increased mica contents in A horizons. More K may have been fixed by vermiculite in the oak A horizon compared to pine due to greater K concentration in the oak litter pool; earthworm-mediated mineralization of K from organic matter under oak; and presence of fewer roots at the surface under oak, and, consequently, less plant removal of K from the A horizon.

Occluded Mica in Hydroxy-Interlayered Vermiculite Grains from a Highly-Weathered Soil

AbstractHydroxy-interlayered vermiculite (HIV) is a ubiquitous phyllosilicate in the &lt;0.05-mm fraction of sandy soils on the U.S. southeastern coastal plain. Extensive areas of soils with abundant HIV (i.e., peninsular Florida) have no detectable mica; yet the coarseness, platy habit, and nonexchangeable K associated with HIV grains suggest a mica precursor. The objectives of this study were: (1) to probe for mica zones (1.0-nm) within HIV grains, using high-resolution transmission electron microscopy (HRTEM), and (2) to determine intragrain elemental distributions via electron microprobe analysis (EMA). HIV grains from a Quartzipsamment medium-silt fraction, which contained no detectable mica by X-ray diffraction (XRD), were concentrated via high-density liquid separation. EMA transects and X-ray dot maps showed zonation or trends of K depletion near edges of some grains, with K2O contents ranging from trace levels to &gt;40 g kg-1. Elemental oxide data indicated a dioctahedral phyllosilicate structure, with some octahedral substitution of Fe and Mg for Al. Intermittent 1.0-nm lattice-fringe images obtained by HRTEM supported the presence of mica zones within grains. There were no detectable 1.4-nm fringes, despite the dominance of a 1.4-nm XRD peak, indicating the instability of the HIV specimen under the electron beam. Results support a transformational link between mica and HIV in these soils. Rapid incursion and polymerization of Al following loss of K from mica may limit the extent of the vermiculite intermediate. The latter idea is consistent with the paucity of vermiculite in Florida soils. Traces of occluded mica may be the last remnants of the precursor grain. A sand-sized mica precursor would likely have weathered in place during the period when colloidal components such as kaolinite illuviated to deeper zones. Thus, the transformation product (HIV) would comprise a significant proportion of the &lt;0.05-mm fraction persisting in sandy eluvial horizons.

Influence of long-term fertilization with farmyard manure on soil organic matter: Characteristics of particle-size fractions

The influence of more than 100 years of fertilization with farmyard manure on soil organic matter in comparison to unfertilized soil was studied in particle-size fractions using elemental (C and N) analyses and pyrolysis-field ionization mass spectrometry. Distinct differences in C and N concentrations and distribution and in the quality of organic matter between the size fractions and the fertilization treatments were observed. Clay-associated C and N were relatively higher in the unfertilized treatment, whereas the application of farmyard manure preferentially increased soil organic matter associated with the fine and medium silt fractions. Pyrolysis-field ionization mass spectrometry of soil fractions <20 μm showed increasing values for lignin monomers and dimers and fatty acids with larger equivalent diameters, whereas the proportion of N compounds, mono- and polysaccharides and phenolics decreased in the larger size fractions. Sand fractions were particularly rich in lignin fragments, mono- and polysaccharides, and alkanes/alkenes. These relationships seemed to be independent of management practices. In the same size fractions of the different treatments, however, a higher relative abundance of N-compounds, mono- and polysaccharides, phenolics, lignin monomers, and alkanes/alkenes was observed in the unfertilized variant. Lignin dimers and fatty acids were more abundant in the farmyard manure treatment. Both trends together imply that soil enrichment in organic matter due to the application of farmyard manure largely reflects an increase in lignin building blocks and partly reflects an increase in lipids such as fatty acids in the silt fractions. Therefore these constituents are of particular importance in assessing the positive effects of farmyard manure on soil fertility.

THE EXTRACTION OF ORGANIC MATTER FROM SELECTED SOILS AND PARTICLE SIZE FRACTIONS WITH 0.5 M NaOH AND 0.1 M Na4P2O7 SOLUTIONS

Organic matter (OM) in the Bainsville and Melfort soils, and in coarse clay and medium silt fractions separated from these soils, was extracted under N2 with 0.5 M NaOH and unadjusted 0.1 M Na4P2O7 solutions. pH ranges of the soils and fractions in contact for 24 h with 0.5 M NaOH and 0.1 M Na4P2O7 solutions extended from 12.2 to 12.6 and 9.0 to 9.4, respectively. Slightly greater proportions of the soil-carbon were extracted by 0.5 M NaOH than by 0.1 M Na4P2O7 solution. The differences, however, did not appear to be significant and may vary from soil to soil. The efficiency of extraction and the characteristics of the extracted materials were assessed on humic acids (HAs), which were isolated from the extracts. From the Bainsville soil and fractions, 0.1 M Na4P2O7 solution extracted more high-molecular weight and more deeply colored HAs than did 0.5 M NaOH solution. But HAs extracted from the Melfort soil and fractions had similar molecular weights and colours. 13C NMR spectra showed that HAs extracted by 0.1 M Na4P2O7 solution tended to be more aromatic than HAs extracted by 0.5 M NaOH solution. Well defined solid-state 13C NMR spectra of HAs, containing up to 69.0% ash, could be recorded. Unadjusted 0.1 M Na4P2O7 solution under N2 was found to be an attractive alternative to 0.5 M NaOH solution as an extractant for soil OM. Key words: Humic acids, E4:E6 ratios, IR spectra, 13C NMR spectra, aromaticity

AUTHIGENIC MINERAL FORMATION BY SOLODIZATION

Mineralogical and micromorphological examination of Solodized Solonetz pedons show the presence of both crystalline and non-crystalline authigenic minerals in the Ae horizons and the solodized zones of the columnar Bnt horizons. A zeolite mineral with the characteristics of clinoptilolite was detected in the coarse clay (1.0–2.0 μm) separates and was the mineral species dominant in the &lt; 2.35 specific gravity separates of the fine (2.0–5.0 μm) and medium (5.0–20.0 μm) silt fractions. Measurement of pH (1.0 M NaF) of whole soil samples from the solodized zone of these pedons indicated the presence of high levels of active aluminum. Treatment with acid ammonium oxalate and hot 0.5 M KOH indicated that the poorly crystalline material was composed predominantly of silicon, aluminum and iron. Differential FT-IR analyses of these clay fractions before and after the chemical extractions indicated that components of this phase have characteristics reported for both opaline silica and allophane. Key words: Authigenic, clinoptilolite, solodization, allophane, smectite, opaline silica

Chemisch-mineralogische und mikromorphologische untersuchung einer eutrophen (Ramann-) braunerde des Budapester Hügellandes

In spite of the fact that Ramann's concept of Braunerde was extensively used throughout the world, some pedogenic processes and soil properties which are important for the formation and existence of Brown Forest Soils (eutrophic brown earths) are still not well known. Hence, a soil was investigated which was classified as a “Braunerde” by Ramann in 1909. The main question was, whether there might be soil constituents such as inorganic amorphous substances (allophanes) which are able to stabilize the brown-earth fabric, or to inhibit clay migration. From chemical data as well as from the magnitude of the pH-dependent CEC, it was deduced that there are no appreciable amounts of allophanes within the soil. The fabric, however, seems to be stabilized by colloid-chemical flocculation of the clay particles caused by large amounts of carbonates and silicates deposited with the parent material (loess). The decalcified solum is still rich in silicates, especially sand and coarse-silt-sized micas and feldspars (60–200 and 20–60 μm fractions, respectively). Since - in comparison - loesses and loess-derived soils of the Central German mountain region contain less silicates, mainly in fine and medium silt fractions (2–6 and 6–20 μm diameter, respectively), the coarser-grained silicates were assumed to be important for maintaining the Ca 2+ and Mg 2+ saturation of the soil by continuous weathering and thus stabilizing the brown-earth fabric. Although the soil is saturated predominantly with Ca 2+ and Mg 2+ ions, clay migration proceeds within the upper horizons. This was shown by calculation of the amounts of clay formed by breakdown of micas originally present in the parent material (“clay formation balance”), as well as by micromorphological studies. Furthermore, micromorphological studies and x-ray diffraction data gave some evidence for the migration of preferably finest grained montmorillonitic clays (smectites) penetrated by organic substances (humus). This kind of “selective clay migration” was assumed to be caused by high Ca 2+ (or Mg 2+) concentrations in soil solution required for flocculation of humus-penetrated (humus-coated) smectites. From the occurrence of these “humus-smectites” the possibility was assumed that the soil studied has been developed from a former Chernozem type. Quantitatively, clay migration does not reach the amounts of clay formation (breakdown of micas) accompanied by precipitation of iron oxides on mineral surfaces (“Verbraunung”). Thus, the soil profile visually and macromorphologically clearly exhibits the features of brown earths. On the other hand, however, some clay migration was observed. Hence, the soil was classified as a “brown earth with some clay migration” (“schwach durchschlämmte Braunerde”). Judging from the results of the “clay formation balance” an appreciable pedogenic (autigenic) clay formation from weathering products of feldspars was excluded for the soil studied.

Clay Mineralogy and Weathering of a Red-Yellow Podzolic Soil from Quartz Mica Schist in the Alabama Piedmont

AbstractMineralogical and chemical properties of Madison soil derived from quartz mica schist reflected the degree of weathering. The Madison soil had sandy surface horizons and clayey B horizons. The clay in surface horizons contained more mica than clay in the subsoils; a maximum of about 40 per cent mica in the coarse clay of surface horizons. Intergradient chlorite-vermiculite was present in appreciable quantities in clays of surface horizons. The presence in the whole soil of B2 horizons of about 15 per cent gibbsite and 12 per cent free iron oxides indicated a high degree of weathering. Kaolinite and gibbsite increased with depth and were the major clay minerals in all clay fractions in the lower portion of the profiles. Kaolinite and gibbsite also were important accessory minerals of the coarse and medium silt fractions and increased in percentage with depth. The B3 horizons had much of the morphology of the schist. Results indicated a high weathering intensity in the subsoil and leaching of weathering products.

A Study of the Origin and Distribution of Loess in Southern Indiana

AbstractSoil profile studies were made along two traverses extending from the Wabash River in a southeasterly direction across southern Indiana for the purpose of determining the distribution of loess in this area. The variation in thickness of the loess mantle with distance from the Wabash River, the assumed source, was measured, and equations of the curves showing the relationship were calculated. X‐ray diffraction studies were made of the medium and fine silt fractions of the A2 horizon of 10 profiles along the southern traverse. The ratio of the quartz/feldspar intensities was determined using sodium fluoride as an internal standard. The calcium, sodium, and potassium content of the medium silt fractions of these 10 horizons was determined by flame photometry. The equation for the curve fitted to points plotted along the northern traverse was Y = 122 − 47 log X, where Y is the depth of the loess in inches and X is the distance from the Wabash River in miles. The equation for the southern traverse was Y = 125 − 53 log X. The X‐ray diffraction studies indicate that the quartz/feldspar ratio may be used as an index of weathering. The correlation coefficients for the relationship between the quartz/feldspar ratio and distance from the Wabash River were 0.95 and 0.96 for the medium and fine silts, respectively. The results of the chemical determinations substantiated the findings of the X‐ray diffraction studies. It is concluded that loess was transported across southern Indiana for a distance of about 90 miles.