Clay Mineral Changes Research Articles

Climatic evolution across oceanic anoxic event 1a derived from terrestrial palynology and clay minerals (Maestrat Basin, Spain)

AbstractStudies dealing with the response of the continental biosphere to the environmental perturbations associated with Cretaceous oceanic anoxic events (OAEs) are comparatively rare. Here, a quantitative spore-pollen record combined with clay mineral data is presented, which covers the entire early Aptian OAE 1a interval (Forcall Formation, Maestrat basin, east Spain). The well-expressed OAE 1a carbon-isotope anomaly is paralleled by changes in the clay mineral assemblage and by a stepwise decline in the normalized frequency ofClassopollispollen (produced by xerophytic Cheirolepidiaceae) with lowest contents occurring during the positive δ13C shift. In contrast,AraucariacitesandInaperturopollenitespollen show a pronounced increase in relative abundance from low background values to become a significant component of the palynological assemblage during theClassopollisminimum. The observed changes in clay minerals and pollen distribution patterns are interpreted to reflect a major change in the composition of the hinterland vegetation of the Maestrat Basin, most probably due to short-lived but pronounced climatic cooling and changes in humidity. Temperature anomalies driven by organic carbon burial and associated CO2decline have been postulated for all major Mesozoic OAEs. The palynomorph record from the Iberian Maestrat basins indicates that the climax of this cooling episode was significantly delayed in comparison to the end of organic carbon-rich deposition in the world oceans.

Clay mineralogy of the riverine sediments of Hainan Island, South China Sea: Implications for weathering and provenance

Clay mineralogy of 54 fluvial samples collected from 20 major rivers on Hainan Island are investigated in order to determine compositional changes of clay minerals and to assess the weathering processes. The clay mineral assemblages consist dominantly of kaolinite (31–66%), with a lesser abundance of chlorite (22–44%) and illite (4–33%), and a trace amount of smectite (0–15%). Fluvial sediments from the east and northwest of Hainan Island are characterized by a higher kaolinite content and illite chemical index and poorer illite crystallinity than those from southwest Hainan. Only minor smectite (mean of 7%) occurs in the sediments from west Hainan; smectite is total lacking in east Hainan. Compared with the adjacent basins, Hainan Island is characterized by moderate to intensive chemical weathering with strong hydrolysis. Our results suggest that rainfall is the principal factor controlling the intensity of chemical weathering on Hainan Island, with more intense chemical weathering occurring in eastern and northwestern Hainan. Anotherpracticalimplication of this study is that it provides a “missing” end member (Hainan Island) in the provenance discrimination study focused on the northern South China Sea (SCS). Hainan fine-grained sediments likely play an important role in providing clay minerals to the northern SCS carried by the South China Sea Warm Current (SCSWC) during the summer.

Silicon isotopes record dissolution and re-precipitation of pedogenic clay minerals in a podzolic soil chronosequence

By providing the largest part of the reactive surface area of soils, secondary minerals play a major role in terrestrial biogeochemical processes. The understanding of the mechanisms governing neo(trans-)formation of pedogenic clay minerals in soils is therefore of the utmost importance to learn how soils evolve and impact the chemistry of elements in terrestrial environments. Soil-forming processes governing the evolution of secondary aluminosilicates in Podzols are however still not fully understood. The evolution of silicon (Si) isotope signature in the clay fraction of a podzolic soil chronosequence can provide new insight into these processes, enabling to trace the source of Si in secondary aluminosilicates during podzol-forming processes characterized by the mobilization, transport and precipitation of carbon, metals and Si. The Si isotope compositions in the clay fraction (comprised of primary and secondary minerals) document an increasing light 28Si enrichment and depletion with soil age, respectively in illuvial B horizons and eluvial E horizon. The mass balance approach demonstrates that secondary minerals in the topsoil eluvial E horizons are isotopically heavier with δ30Si values increasing from −0.39 to +0.64‰ in c.a. 200years, while secondary minerals in the illuvial Bhs horizon are isotopically lighter (δ30Si=−2.31‰), compared to the original “unweathered” secondary minerals in BC horizon (δ30Si=−1.40‰). The evolution of Si isotope signatures is explained by the dissolution of pedogenic clay minerals in the topsoil, which is a source of light 28Si for the re-precipitation of new clay minerals in the subsoil. This provides consistent evidence that in strong weathering environment such as encountered in Podzols, Si released from secondary minerals is partially used to form “tertiary clay minerals” over very short time scales (ca. 300years). Our dataset demonstrates the usefulness to measure Si isotope signatures in the clay fraction to discern clay mineral changes (e.g., neoformation versus solid state transformation) during soil evolution. This offers new opportunity to better understand clay mineral genesis under environmental changes, and the short-term impact of the dissolution and re-precipitation of pedogenic clay minerals on soil fertility, soil carbon budget and elemental cycles in soil–plant systems.

Clay mineral changes across the Eocene–Oligocene transition in the sedimentary sequence at Xining occurred prior to global cooling

During the Cenozoic, high-quality long-term sedimentary sequences formed in Xining basin at the northeastern margin of the Tibetan Plateau, which are characterized by alternating gypsiferous layers and reddish mudstone beds. The Tashan section was previously dated in detail by magnetostratigraphy, which yielded an age span of 16 to 35.7Ma. In this study, bulk and clay mineral assemblages and magnetic parameters of the 33.1–35.7Ma portion were analyzed using X-ray diffraction and magnetic methods to determine the behavior of the Eocene–Oligocene climate transition. Quartz, calcite, feldspar and clay fractions in sediments that are mainly derived from the surrounding catchments, gypsum and dolomite are authigenic minerals. Illite, chlorite, irregular mixed-layer illite-smectite and smectite are the four main clay-sized fractions (<2μm) in the gypsum/gypsiferous layers and the reddish mudstone beds, which suggest that no significant tectonic activity occurred in the catchment area of the Xining basin during the period of 35.7–33.1Ma. Dominant hematite, illite and gypsum in the sediments indicate that the climate was dominantly hot and dry in the Xining basin. This was controlled by a “planetary” subtropical aridity zonal pattern; the variations in gypsum, dolomite and smectite content are mainly controlled by the climate changes. The characteristics of the clay mineral assemblages suggest that warm and humid fluctuations with hot and dry conditions prevailed during ~35.7–34.1Ma in inner Asia. This changed to cold and dry conditions at ~34.1Ma and remained so from ~34.1 to 33.1Ma. Comparisons with open ocean marine records and Northern Hemisphere continental records indicate that the climate cooling in continental records occurred prior to the main drop of δ18O in foraminifera preserved in marine sediments at Oi-1 (33.545Ma). This demonstrates that the magnitude of Antarctic ice growth during the EOT was not the major contributor to inner Asian aridification, possibly due to the northward moving of subtropical highs that existed in northwest China and was induced by temperate zones moving during the late Eocene to early Oligocene.

Sorption equilibrium and kinetics of CO2 on clay minerals from subcritical to supercritical conditions: CO2 sequestration at nanoscale interfaces

CO2 sequestration in geological formations has attracted attention as a promising method to reduce anthropogenic CO2 emission. CO2 sorption at nanoscale interfaces of clay minerals were studied from subcritical to supercritical conditions because clay minerals are a constituent of various rocks such as a cap rock, reservoir rock and coal mineral matter. The sorption capacity and kinetics of CO2 on montmorillonite, illite, and sepiolite were measured by a gravimetric method. Sepiolite had the highest sorption capacity at all experimental conditions. After high CO2 pressure sorption, the desorption isotherm on montmorillonite showed significant hysteresis, but the hysteresis on illite and sepiolite was relatively weak. The excess sorption isotherms of all clay minerals showed a maximum near the critical pressure and the absolute sorption isotherms approached the saturation over the critical density value of CO2. The surface area changes of clay minerals by supercritical CO2 sorption were observed by comparing the N2 sorption isotherms between the raw material and post-experiment sample. The CO2 sorption rates on clay minerals were within a single order of magnitude (10−8 m2/s). The results at nanoscale interfaces can contribute to understanding the sorption capacity and sealing integrity of sedimentary rocks in CO2 geological storage.

Delamination of smectite in river-borne suspensions at the fluvial/marine interface – An experimental study

Fine fractions (<2 μm) from smectite-rich flood-plain sediments from the Elbe and Weser rivers in Germany were treated in the laboratory with synthetic sea salt solutions at different concentrations and for different periods of time to document sheet delamination of smectite particles at the fluvial/marine interface and thus simulate changes in clay minerals at the mouth of a river. The project consisted of two steps: (1) Pilot tests were made in 0.5% salt solutions (brackish environment) showing a nearly 2-min delay of the clearing of the clayey suspensions, when the suspension was redispersed 15 and 30 min later after the first measurement. This was due to an obviously increased number of fine laminae from disintegrated smectite particles. (2) X-ray diffraction studies (XRD) of the clayey material from suspensions in 0.0, 0.5, 1.0, and 3.0% salt solutions after standing 10 min, and one and three weeks were made to document alteration reactions of smectite. An aliquot was pipetted periodically from each series, and oriented clay-mineral specimens were analyzed by XRD in air-dried, glycol- and glycerin-solvated states. The peak intensities in the XRD patterns of the clay minerals smectite, random-ordered mixed-layer illite/smectite (I–S), kaolinite, chlorite, and illite did not change in the salt-free series during the experiments. In contrast the peak intensities of smectite and I–S mineral in the air-dried and glycerin-solvated states after suspension in saline solutions decreased significantly. The d-values of the smectitic materials in the air-dried state also decreased after contact with the saline solutions, and in the glycerin-solvated state the full-width-at-half-maximum (FWHM) of the 001 smectite reflection increased by about 20%, indicating a reduction in grain size. The variations in FWHM, d-values and peak intensity of the smectitic material are assumed to be caused by an exchange of Na for Ca in the interlayer spaces and subsequent delamination of the particles along the Na-activated interlayers. Only those smectite particles in which adjacent sheets are still stabilized by the remaining Ca are preserved after contact with seawater. The experiments show that delamination of smectite and I–S mixed-layer minerals is likely to occur in the brackish environment at the mouth of a river. However, formation of these fine laminae is expected to be a transitional stage in the development of clay particle size, owing to the formation of flocs and aggregates in the higher salt concentrations of seawater.

The sedimentary legacy of a palaeo-ice stream on the shelf of the southern Bellingshausen Sea: Clues to West Antarctic glacial history during the Late Quaternary

A major trough (“Belgica Trough”) eroded by a palaeo-ice stream crosses the continental shelf of the southern Bellingshausen Sea (West Antarctica) and is associated with a trough mouth fan (“Belgica TMF”) on the adjacent continental slope. Previous marine geophysical and geological studies investigated the bathymetry and geomorphology of Belgica Trough and Belgica TMF, erosional and depositional processes associated with bedform formation, and the temporal and spatial changes in clay mineral provenance of subglacial and glaciomarine sediments. Here, we present multi-proxy data from sediment cores recovered from the shelf and uppermost slope in the southern Bellingshausen Sea and reconstruct the ice-sheet history since the last glacial maximum (LGM) in this poorly studied area of West Antarctica. We combined new data (physical properties, sedimentary structures, geochemical and grain-size data) with published data (shear strength, clay mineral assemblages) to refine a previous facies classification for the sediments. The multi-proxy approach allowed us to distinguish four main facies types and to assign them to the following depositional settings: 1) subglacial, 2) proximal grounding-line, 3) distal sub-ice shelf/sub-sea ice, and 4) seasonal open-marine. In the seasonal open-marine facies we found evidence for episodic current-induced winnowing of near-seabed sediments on the middle to outer shelf and at the uppermost slope during the late Holocene. In addition, we obtained data on excess 210Pb activity at three core sites and 44 AMS 14C dates from the acid-insoluble fraction of organic matter (AIO) and calcareous (micro-) fossils, respectively, at 12 sites. These chronological data enabled us to reconstruct, for the first time, the timing of the last advance and retreat of the West Antarctic Ice Sheet (WAIS) and the Antarctic Peninsula Ice Sheet (APIS) in the southern Bellingshausen Sea. We used the down-core variability in sediment provenance inferred from clay mineral changes to identify the most reliable AIO 14C ages for ice-sheet retreat. The palaeo-ice stream advanced through Belgica Trough after ∼36.0 corrected 14C ka before present (B.P.). It retreated from the outer shelf at ∼25.5 ka B.P., the middle shelf at ∼19.8 ka B.P., the inner shelf in Eltanin Bay at ∼12.3 ka B.P., and the inner shelf in Ronne Entrance at ∼6.3 ka B.P. The retreat of the WAIS and APIS occurred slowly and stepwise, and may still be in progress. This dynamical ice-sheet behaviour has to be taken into account for the interpretation of recent and the prediction of future mass-balance changes in the study area. The glacial history of the southern Bellingshausen Sea is unique when compared to other regions in West Antarctica, but some open questions regarding its chronology need to be addressed by future work.

Local environmental changes recorded by clay minerals in a karst deposit during MIS 3 (La Chauverie, SW France)

The four stratigraphic units of the Late Pleistocene (MIS 3) clay-rich deposit of La Chauverie (Charente, SW France) have been characterized for mineral composition. The lower part of this 75 cm-thick karst deposit preserves a mammal fauna typical of temperate climate, followed by an assemblage pointing to a colder phase. The clay fraction of both horizons mostly results from mineral transformations of the clays contained in the sediments of the Paleogene formation surrounding the cave. Because clay mineral properties and changes intimately depend on the physico-chemical conditions and reaction kinetics prevailing at a given time in the soils, they are highly temperature-related. Notably, changes are rapid under temperate conditions, but slow in tundra-like cold contexts. As shown by the altered inherited mica-illite, as well as by the increase of crystallinity of kaolinite particles, at La Chauverie these transformations were marked in the stratigraphically lower part of the deposit formed under temperate conditions. Conversely, as reflected by the reduction of the kaolinite/smectite ratio characterizing the sediments of the upper horizon, the pedological evolution was limited during the subsequent cold phase. Here, both illite/smectite and kaolinite/smectite mixed layers become smectite-richer than their equivalent in the Paleogene. The parallelism between paleontological evidence and mineral signature in recording a relatively rapid (millennial-scale) shift towards colder conditions suggests that clay mineral assemblages from cave deposits can be used to assess paleoclimatic and paleoenvironmental dynamics at local scale. Nonetheless, future research should test this potential tool in more appropriate, thicker deposits investigated using other independent paleobiological and geochemical indicators.

Changes in clay minerals and potassium fixation capacity as a result of release and fixation of potassium in long-term field experiments

We investigated to what extent soil K balances, resulting from plant off-take and K fertilizer application rates, had changed the content of illitic (10 Å) materials (as discrete illite and as illitic layers in mixed-layer minerals) in soil clay fractions. We also assessed to what extent different particle size fractions were involved in the processes. The study was performed on soil samples from five long-term agricultural experiments located on Mollisols and Inceptisols in South and Central Sweden, each having a range of K fertilizer application rates. We analysed X-ray diffraction (XRD) patterns from parallel orientated samples of the following particle size fractions: total clay (< 2 μm), fine clay (< 0.2 μm), and (at two of the sites) fine–medium silt (2–20 μm). In addition, K fixation capacity in the total fine earth (< 2 mm) was measured in order to assess changes in the number of fixation sites due to previous release or fixation of K in the field. At all sites but one, K management had measurably affected the content of the illitic components in the total clay fraction, as expressed by an ‘illite layer ratio.’ Although the content of illitic materials in phyllosilicates differed between particle size fractions, they were all altered to a similar extent by the soil K balance; i.e., the net off-take or input of K in the different fertilizer treatments. Soil K balances also affected the K fixation capacity of the soil. Overall, 8 ± 6 to 40 ± 30% of accumulated net inputs or outputs of K in the field were recovered as a change in K fixation capacity. This means that K release was reversible by K fertilization to a highly variable extent. The release of K appeared reversible in (i) two silty clays and (ii) a sandy loam developed in a parent material characterized by the occurrence of calcite. Two other soils showed evidence of irreversible loss of interlayer K from 2:1-minerals. XRD patterns and the slightly lower pH at the latter sites suggest that the occurrence of hydroxyaluminium interlayers in 2:1-minerals may have hampered K fixation in these soils. To generalize, a reversible nature of K release and fixation may be promoted if easily weatherable soil minerals are abundant.

Changes in clay minerals of vertic chernozems under the impact of different ameliorants in a model experiment

The interaction of different ameliorants and fertilizers with the solid phase of clayey vertic chernozems was studied in a model experiment. Changes in the organization and properties of the mineral mass from the plow horizon under the impact of ameliorants took place at several hierarchical levels. At the level of soil aggregates, both the disaggregation of the soil mass and the formation of agronomically valuable soil aggregates under the impact of different ameliorants were observed. The method of fractional peptization of the soil mass was applied to study the behavior of clay minerals. The specificity of the crystallochemistry of smectitic minerals and their changes under the impact of introduced substances were studied in different fractions of clay.

Clay minerals as a soil potassium reservoir: observation and quantification through X-ray diffraction

Potassium (K) is a major element for plant growth. The K+ ions fixed in soil 2:1 clay mineral interlayers contribute to plant K nutrition. Such clay minerals are most often the majority in temperate soils. Field and laboratory observations based on X-ray diffraction techniques suggest that 2:1 clay minerals behave as a K reservoir. The present work investigated this idea through data from a replicated long term fertilization experiment which allowed one to address the following questions: (1) Do fertilization treatments induce some modifications (as seen from X-ray diffraction measurements) on soil 2:1 clay mineralogy? (2) Are soil 2:1 clay mineral modifications related to soil K budget in the different plots? (3) Do fertilizer treatments modify clay Al, Si, Mg, Fe or K elemental content? (4) Are clay mineral modifications related to clay K content modifications? (5) Are clay mineral changes related to clay Al, Si, Mg or Fe content as well as those of K content? Our results showed that K fertilization treatments considered in the context of soil K budget are very significantly related to 2:1 soil clay mineralogy and clay K content. The 2:1 clay mineral modifications observed through X-ray measurements were quantitatively correlated with chemically analyzed clay K content. Clay K content modifications are independent from clay Al, Si, Mg or Fe contents. These results show that the soil chemical environment can modify interlayer site occupations (illite content) which suggests that high level accumulation of potassium can occur without any modification of the clay sheet structure. This study therefore validates the view of 2:1 clay minerals as a K reservoir easily quantifiable through X-ray observations.

Soil-plant potassium transfer: impact of plant activity on clay minerals as seen from X-ray diffraction

Potassium (K) availability influences many processes in cultivated and natural ecosystems. Several studies suggest that “non-exchangeable” K+ ions fixed in 2:1 clay mineral interlayers contribute to plant nutrition. Although depletion of these K+ ions could be observed by X-ray diffractometry, this technique has never been considered for the observation of short-term changes in illitic 2:1 clay minerals. We established in this study that new treatments of X-ray diffraction patterns allow quantification of short-term 2:1 clay mineral changes through K addition in solution and removal of interlayer K by Lolium multiflorum. Moreover, we obtained a significant relationship (r 2 = 0.95, P < 0.0001) between an indicator calculated from X-ray diffraction patterns and analyzed clay K content. X-ray diffraction should therefore be considered as an appropriate tool to follow qualitatively and quantitatively clay mineral modifications induced by soil K balance. Our results suggest that 2:1 clay minerals behave as a huge, renewable K reservoir whose theoretical capacity in fertile soils could exceed 3 t/ha. Beyond obvious agronomical implications, this new vision of soil K cycle raises ecological questions about plant inter specific competition and soil fertility. Finally, our study clearly shows that soil 2:1 clay minerals could react as quickly as a biological system.

Microbial reduction of Fe(III) in the Fithian and Muloorina illites: Contrasting extents and rates of bioreduction

AbstractShewanella putrefaciens CN32 reduces Fe(III) within two illites which have different properties: the Fithian bulk fraction and the &lt;0.2 µm fraction of Muloorina. The Fithian illite contained 4.6% (w/w) total Fe, 81% of which was Fe(III). It was dominated by illite with some jarosite (∼32% of the total Fe(III)) and goethite (11% of the total Fe(III)). The Muloorina illite was pure and contained 9.2% Fe, 93% of which was Fe(III). Illite suspensions were buffered at pH 7 and were inoculated with CN32 cells with lactate as the electron donor. Select treatments included anthraquinone-2,6-disulfonate (AQDS) as an electron shuttle. Bioproduction of Fe(II) was determined by ferrozine analysis. The unreduced and bioreduced solids were characterized by Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy. The extent of Fe(III) reduction in the bulk Fithian illite was enhanced by the presence of AQDS (73%) with complete reduction of jarosite and goethite and partial reduction of illite. Mössbauer spectroscopy and chemical extraction determined that 21–25% of illite-associated Fe(III) was bioreduced. The extent of bioreduction was less in the absence of AQDS (63%) and only jarosite was completely reduced with partial reduction of goethite and illite. The XRD and TEM data revealed no significant illite dissolution or biogenic minerals, suggesting that illite was reduced in the solid state and biogenic Fe(II) from jarosite and goethite was either released to aqueous solution or adsorbed onto residual solid surfaces. In contrast, only 1% of the structural Fe(III) in Muloorina illite was bioreduced. The difference in the extent and rate of bioreduction between the two illites was probably due to the difference in layer charge and the total structural Fe content between the Fithian illite (0.56 per formula) and Muloorina illite (0.87). There may be other factors contributing to the observed differences, such as expandability, surface area and the arrangements of Fe in the octahedral sheets. The results of this study have important implications for predicting microbe-induced physical and chemical changes of clay minerals in soils and sediments.

Regional trends in clay mineral fluxes to the Queensland margin and ties to middle Miocene global cooling

Three ODP sites located on the Marion Plateau, Northeast Australian margin, were investigated for clay mineral and bulk mineralogy changes through the early to middle Miocene. Kaolinite to smectite (K/S) ratios, as well as mass accumulation rates of clays, point to a marked decrease in accumulation of smectite associated with an increase in accumulation of kaolinite starting at ∼ 15.6 Ma, followed by a second increase in accumulation of kaolinite at ∼ 13.2 Ma. Both of these increases are correlative to an increase in the calcite to detritus ratio. Comparison of our record with published precipitation proxies from continental Queensland indicates that increases in kaolinite did not correspond to more intense tropical-humid conditions, but instead to periods of greater aridity. Three mechanisms are explored to explain the temporal trends in clay on the Marion Plateau: sea-level changes, changes in oceanic currents, and denudation of the Australian continent followed by reworking and eolian transport of clays. Though low mass accumulation rates of kaolinite are compatible with a possible contribution of eolian material after 14 Ma, when Australia became more arid, the lateral distribution of kaolinite along slope indicates mainly fluvial input for all clays and thus rules out this mechanism as well as oceanic current transport as the main controls behind clay accumulation on the plateau. We propose a model explaining the good correlation between long-term sea-level fall, decrease in smectite accumulation, increase in kaolinite accumulation and increase in carbonate input to the distal slope locations. We hypothesize that during low sea level and thus periods of drier continental climate in Queensland, early Miocene kaolinite-rich lacustrine deposits were being reworked, and that the progradation of the heterozoan carbonate platforms towards the basin center favored input of carbonate to the distal slope sites. The major find of our study is that increase kaolinite fluxes on the Queensland margin during the early and middle Miocene did not reflect the establishment of a tropical climate, and this stresses that care must be taken when reconstructing Australian climate based on deep-sea clay records alone.

Thermal loading of smectite-rich rocks: Natural processes vs. laboratory experiments

Changes of physico-chemical properties of smectite-rich rocks (used as an engineered barrier in the nuclear waste repository) are studied. Two different genetic types of clays are evaluated—bentonite representing the residual weathering type and sedimentary montmorillonite-rich clay. Cation exchange capacity and specific surface area were determined for bulk samples (after heating experiments) and results were compared to a natural analogue (Ishirini deposit, Libya). Structural changes of clay minerals were studied using XRD, TG and DTA. Two main transformation processes (illitization and kaolinization) of smectite-rich rocks followed by deterioration of physico-chemical properties were observed after heat treatment. Cation exchange capacity drops significantly with increasing temperature and so does S micro. However, S BET values increased when heat treatment was applied.

Preliminary evaluation of PAH sorptive changes in soil by Soxhlet extraction

This study was conducted to evaluate the influence of sorbent modification by synthetic, chemical/thermal weathering on the sorptive behavior of polycyclic aromatic hydrocarbons (PAHs). A clean sandy-clay-loam soil was subjected to Soxhlet extraction and PAH sorptive phenomena were evaluated based on quantity and quality changes in soil organic matter (SOM) and clay minerals. Critical changes in sorption capacity were found to depend on the initial PAH concentrations. Above 7 mg/l, weathering increased the PAH in comparison to that of unmodified soil, whereas it decreased when applied below this concentration. Similarly, less PAH was desorbed from the altered soil when PAH was applied above 7 mg/l. Therefore, when PAH was applied below 7 mg/l, quantitative reduction of sorbent amount (i.e., SOM and clay minerals) by soil weathering governed PAH sorptive behavior. However, when the PAH was applied above the critical limit, qualitative modifications in the sorbents facilitated an opposite trend. Sorbent swelling, removal of competing compounds, and possible changes in surface characteristics by Soxhlet extraction, together with increased concentration gradient effects were factors that resulted in dissimilar PAH sorptive phenomena, pivoting at the critical concentration.

Clay Mineral Changes in the Morrow Experimental Plots, University of Illinois

AbstractThe clay mineralogy of soil samples from the Morrow Plot Experiment (University of Illinois, Urbana Campus) was investigated. Analysis of soil samples taken at various intervals between 1913 and 1996 indicates that there is a significant influence of cropping method on the clay minerals in the soils. Curve decomposition methods were used to identify and follow the evolution of the different clay minerals: mica, illite and two randomly mixed-layered illite-smectite phases. The most striking difference is seen for continuous corn and corn-oats-hay rotations. Little change in clay mineralogy is seen in the rotation plot while a significant loss of illitic material from different phases was noted for the continuous-corn cultivation plots. Use of NPK fertilizer since 1955 appears to restore the clay mineralogy in continuous-corn cropping compared to that of the 1913 samples. From these data it appears that the I-S minerals play the role of a K buffer, becoming K-poor when the soil cannot furnish enough K from mineral reserves of detrital phases and K-rich when the soil is able to release enough K to enter into the I-S minerals, where it is available during a growing season, for plant growth.

Paleoceanographic significance of sediment color on western North Atlantic drifts: I. Origin of color

Reflectance spectra collected during ODP Leg 172 were used in concert with solid phase iron chemistry, carbonate content, and organic carbon content measurements to evaluate the agents responsible for setting the color in sediments. Factor analysis has proved a valuable and rapid technique to detect the local and regional primary factors that influence sediment color. On the western North Atlantic drifts, sediment color is the result of primary mineralogy as well as diagenetic changes. Sediment lightness is controlled by the carbonate content while the hue is primarily due to the presence of hematite and Fe 2+/Fe 3+ changes in clay minerals. Hematite, most likely derived from the Permo-Carboniferous red beds of the Canadian Maritimes, is differentially preserved at various sites due to differences in reductive diagenesis and dilution by other sedimentary components. Various intensities for diagenesis result from changes in organic carbon content, sedimentation rates, and H 2S production via anaerobic methane oxidation. Iron monosulfides occur extensively at all high sedimentation sites especially in glacial periods suggesting increased high terrigenous flux and/or increased reactive iron flux in glacials.

Clay mineral transformations in soils affected by fluorine and depletion of organic matter within a time span of 24 years

Data on soil chemistry and especially on clay mineral changes are presented, which were obtained from a soil monitoring site in a forested ecosystem near Möhlin (north-western part of Switzerland) in a time span of 24 years (1969–1993). The development in soil chemistry and clay mineralogy with respect to time was compared in two soil horizons at depths of 0–5 cm and 30–35 cm. A striking feature of the chemical changes observed in the soil was the distinct decrease of soil organic matter in the subsoil during the investigation period. These changes are most presumably due to past pollution of the area with F caused by a nearby aluminium industry. The observed decomposition of organic matter strongly influenced the behaviour of major and minor chemical constituents of the soil. In the subsoil, mica was intensively weathered and contributed, therefore, to the formation of smectites. The significant decrease in chlorites also traces the formation of smectite back to the weathering of chlorite. Al removal from the interlayers seemed to be enhanced by dissolved F and especially by organic complexing agents, which must have been present in the soil solution during this period of organic matter decomposition in the soil. Vermiculitic compounds had substantial changes towards lower content only in the topsoil, while minerals, such as interstratified chlorite/HIS, remained more or less unaffected. We conclude that the decomposition of organic matter and to a certain extent also changes in the acidity within the time span 1969–1993 have led to, or initiated, a kind of weathering, which has similarities to podzolisation. Due to the decrease in exchangeable F, the process of desalumination has additionally been enhanced by fluorine. Usually, mineralogical changes—under oxic environmental surrounding conditions—are believed to be a long-term process. Our investigation, however, clearly shows that significant clay mineral alterations may occur within relatively short periods of time.

Diagenesis of Upper Jurassic Concretions from the Antarctic Peninsula

ABSTRACT Early-diagenetic calcite concretions are widespread in mudstone-tuff sequences deposited in Late Jurassic oxygen-deficient basins of the Antarctic Peninsula. Although obscured or destroyed in host rocks, original components and sedimentary structures are well preserved in concretions, in spite of significant mineralogical and geochemical change during growth. Early diagenesis led to a rapid and almost total variation in the mineralogy within the concretions, independently of the original host lithologies. Siliceous particles were replaced by chlorite and zeolites in suboxic, alkaline, and moderately reducing conditions on the sea floor and in the first centimeters of burial. These conditions also led to localized early formation of phosphate concretions. Pyrite developed subsequently because of high sulfide abundance in the sulfate reduction zone. Most calcite precipitation took place in the lower part of the sulfate reduction zone in a strongly alkaline environment where sulfide content had been lowered by pyrite precipitation. In this stage, the remaining siliceous elements were dissolved or replaced by calcite. Later diagenetic changes include enlargement of zeolites, minor changes in clay minerals, and the formation of calcite veins. The wide range of 13C values in cement and vein calcite (-1.47o/oo and -20.23o/oo PDB) is explained by mixed carbon sources from organic matter oxidation and dissolution of calcareous shells. The low 18O of calcite (-2.34o/oo to -19.72o/oo PDB) is the result of recrystallization in contact with high-temperature diagenetic or hydrothermal fluids flushed through micro-fractures in the concretions, which also produced extensive vein formation.