Clay Enrichment Research Articles

Pedological formations on old mountain geomorphological surfaces of central Spain

The chemo-morphological properties of soils on ancient landforms (quarzitic pliocene alluvial fans, pleistocene terraces), namely “rañizos”, on middle-high mountains (Eastern-Central System, Iberian Peninsula, Rio Negro, Cogolludo) were investigated. Several properties were analyzed by standard procedures. A detailed soil diagnostics and classification on “rañizos” were done, unlike those widely studied on “rañas” (similar landform), by identifying parallel pedogenetic processes in both formations. The genetic and geographic features of Alfisols, Ultisols and Inceptisols are closely related to the nature of their parent materials, based on quartzite and quartz conglomerates, sometimes with an arkosic matrix, red shale, polygenic gravels and pebbles. Soil features were determined by genuine soil-forming inherent lithological rock properties. Other driving factors were flat topography and enough soil formation time to allow intense pedogenesis. The main soil-forming processes were intense weathering, clay enrichment horizons with illuviation, red color caused by iron oxide dehydration and signs of pseudogleyzation processes. Such pedological formations can be considered endemisms; that is, “rare” soils and, up to a point, “relict”. The soil reaction is acid/slightly acid with low base saturation. Despite lying on mountains, soils are characterized by moderate-low organic matter content. Soil conditions and climate provide good vine production requirements despite acidity levels. A common feature of all Rio Negro soils is the presence of gravel (size up to 3–5 cm), which is evenly distributed on arable layers. The results can be used to assess vineyard soil use in a potential Pago (Protected Denomination of Origin) and to extend the database of vineyard soils from poorly studied Mediterranean continental mountain regions.

Deep‐water sand transfer by hyperpycnal flows, the Eocene of Spitsbergen, Arctic Norway

AbstractFlood‐generated hyperpycnal flows are dense, sediment‐laden, turbulent flows that can form long‐lived, bottom‐hugging turbidity currents, which undoubtedly transport large volumes of fine‐grained sediments into the ocean. However, their ability in transferring sand into deep‐water basins is debated. This study presents sedimentological evidence of sandy hyperpycnal flow deposits (hyperpycnites) in a series of basin floor lobe complexes associated with a progradational shelf margin in the Eocene of Spitsbergen, Arctic Norway. Four coexisting types of sediment gravity flow deposits are recognized: (i) sandy hyperpycnites deposited by quasi‐steady hyperpycnal flows; (ii) turbidites deposited by waning, surge‐type turbidity currents; (iii) hybrid event beds deposited by transitional flows; and (iv) mass transport deposits emplaced during rare slope failures. The abundance of thick‐bedded massive sandstones, frequent bed amalgamation, the distribution of hyperpycnites across the lobes and the abundance and systematic occurrence of plant‐rich hybrid event beds and associated climbing ripple cross‐laminated beds in the lobe fringes, suggest that hyperpycnal flow was the most important mechanism driving lobe progradation. Shelf‐edge positioned fluvial channels linked to the basin floor lobe complexes via deeply incised, sandstone‐filled slope channels, suggest that rivers fed directly onto the slopes where their dense, sand‐laden discharges readily generated quasi‐steady hyperpycnal flows that regularly reached the basin floor. The composite architecture and complex waxing–waning flow facies configuration of the hyperpycnites is consistent with sustained and concomitant suspension and traction deposition under fluctuating subcritical to supercritical conditions. Similar sandstone beds occur on the clinoform slopes, indicating that the hyperpycnal flows operated likewise on the slope. Plant‐rich hybrid event beds indicate transformation of initially turbulent flows by relative enrichment of clay and plant material via progressive sand deposition to such an extent that it suppressed turbulence. The multi‐faceted character of the hyperpycnites reported here, challenges traditional beliefs that hyperpycnites assumingly preserve the waxing–waning signal of single‐peaked floods.

Calculation of oil saturation in clay-rich shale reservoirs: A case study of Qing 1 Member of Cretaceous Qingshankou Formation in Gulong Sag, Songliao Basin, NE China

The targeted reservoir, which is referred as the first member of Cretaceous Qingshankou Formation in Gulong Sag, Songliao Basin, NE China, is characterized by the enrichment of clay and lamellation fractures. Aiming at the technical challenge of determining oil saturation of such reservoir, nano-pores were accurately described and located through focused ion beam scanning electron microscopy and quantitative evaluation of minerals by scanning electron microscopy based on Simandoux model, to construct a 4D digital core frame. Electrical parameters of the shale reservoir were determined by finite element simulation, and the oil saturation calculation method suitable for shale was proposed. Comparison between the results from this method with that from real core test and 2D nuclear magnetic log shows that the absolute errors meet the requirements of the current reserve specification in China for clay-rich shale reservoir. Comparison analysis of multiple wells shows that the oil saturation values calculated by this method of several points vertically in single wells and multiple wells on the plane are in agreement with the test results of core samples and the regional deposition pattern, proving the accuracy and applicability of the method model.

The Impact of Fly Ashes from Thermal Conversion of Sewage Sludge on Properties of Natural Building Materials on the Example of Clay

The reduction of carbon dioxide emissions, introduced by the European Union, opened the possibility of conducting experimental works on a new generation of materials—ecological and environmentally friendly ones. Such materials include those which combine raw natural resources with waste subject to disposal. The objective of the performed investigations was an assessment of the influence of fly ashes on selected parameters of building materials. The paper proposes a method of the enrichment of clay with fly ash, which would lead to the neutralization of heavy metals in the burnt matrix, possible oxidation of organic substances present in the ashes, or the destruction of pathogens, as well as an increase of the resistance of the clay ceramics to low temperatures. Clay samples were prepared with the addition of the fly ash from three sewage treatment plants. The experiments encompassed investigations of physical and chemical properties of the fly ash, as well as bending strength tests of the beam-shaped samples heated at temperatures of 20, 300, 500, and 700 °C. The beam halves, resulting from the destruction of the samples during these tests, served for testing the compressive strength. The collected results allowed a comparison of the properties of the samples. The obtained test results confirm the possibility of manufacturing a product modified with the fly ash from the thermal treatment of sewage sludge. The obtained compressive strength of the samples amounted 0.3–2.6 MPa.

Effect of Clay Mineralogy and Soil Organic Carbon in Aggregates under Straw Incorporation

The interaction between soil organic carbon (SOC) and clay minerals is a critical mechanism for retaining SOC and protecting soil fertility and long-term agricultural sustainability. The SOC composition and minerals speciation in clay fractions (<2 μm) within soil aggregates under straw removed (T) and straw incorporation (TS) conditions were analyzed by X-ray diffraction, Fourier transform infrared spectra and X-ray photoelectron spectroscopy. The TS treatment promoted enrichment of clay in aggregates. The TS increased the contents of SOC (27.0–86.6%), poorly crystalline Fe oxide (Feo), and activity of Fe oxides (Feo/Fed); whereas, it reduced the concentrations of free Fe oxide (Fed) in the clay fractions within aggregates. Straw incorporation promoted the accumulation of aromatic-C and carboxylic-C in the clay fraction within aggregates. The relative amount of hydroxy-interlayered vermiculite, aliphatic-C, and alcohol-C in the clay fractions within the macroaggregates was higher than that microaggregates, whereas the relative amounts of illite, kaolinite, Fe(III), and aromatic-C had a reverse tendency. The hydroxy-interlayered vermiculite in clay fractions showed positive correlation with the amounts of C–C(H) (r = 0.93) and C–O (r = 0.96 *, p < 0.05). The concentration of Feo and Feo/Fed ratio was positively correlated with the amounts of C=C and C(O)O content in clay within aggregates. Long-term straw incorporation induced transformation of clay minerals and Fe oxide, which was selectively stabilized straw-derived organic compounds in clay fractions within soil aggregates.

Origin and Enrichment of Vanadium in the Lower Cambrian Black Shales, South China.

The Lower Cambrian black shales of the Sansui vanadium deposits, located in South China, host a thin accumulation of Ni, Mo, V, and platinum group of elements (PGE). However, among them, the origin of V-bearing deposits remains controversial. To characterize the enrichment process of V-bearing deposits, samples of the mineralized layer and surrounding rocks from the Sansui area, South China, were investigated through bulk geochemical analysis and scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses. There is a consistency in the change curves of Mo, Ni, and V from the Sansui V deposits, but the contents of elements show a great difference. This means the strong similarities in the metal sources but a difference in enrichment factors of Mo, Ni, and V. The presence of the tuff and the barite layer in the Sansui V deposits indicates that the formation of the associated V deposits was closely related to either a volcanic or hydrothermal activity. Analysis of geochemistry and sedimentation suggests a hydrothermal source of the metals, where the mineralization of V is related to clay and organic matter. Phosphorus nodules were observed at all sites of black shale V deposits in early Cambrian and were most likely related to the upwelling currents during the depositional period. The comparison with the Ni–Mo deposits highlights a stronger enrichment of clay in the V deposits. The V deposits are located in the lower part of the continental slope. Both organic matter and clay minerals are abundant in the Sansui deposits. However, the isomorphism of V–Al is promoted by the hydrothermal activity and suggests that the origin of V deposits is a multistage process.

Experimental investigation of water sensitivity effects on microscale mechanical behavior of shale

Drilling and multi-stage hydraulic fracturing bring a large amount of water into clay-bearing shale reservoirs, which may lead to attenuation of fracturing effects and wellbore instability. However, a thorough understanding of changes in shale micromechanics and corresponding mechanisms when exposed to water remains unclear. In this work, samples were selected based on clay enrichment. Subsequently, the contact resonance (CR) technique based on atomic force microscopy (AFM) was performed to characterize the micromechanics of shales after exposure to water. Visual phenomena provided by environmental scanning electron microscopy (ESEM) assisted to explain the underlying mechanisms. It was found that the hydration effect lowered both the storage modulus and stiffness of samples, but with different contributions from brittle minerals and clay, as well as variations depending on bedding plane orientation. Due to the difference in composition, the investigated terrestrial shale material exhibited stronger water sensitivity and anisotropy, with a general decrease of 15%–25% in storage modulus, compared with variations of -5%–15% in modulus of marine shale samples. Moreover, microscopic observation experiments revealed that the reduction of capillary force and the interlaminar swelling of clay particles might have been active after water adsorption, which led to the decreases of modulus and stiffness values. However, the swelling-caused confining effect or void space closure during the water imbibition process might have offset this weakening effect and even increased storage modulus. At mesoscale , excessive shrinkage caused the growth of micro-cracks, which in turn significantly attenuated overall mechanical properties. • Comparison of clay composition between terrestrial and marine shale based on clay enrichment. • AFM contact resonance method to characterize the micromechanical properties of shale before and after water adsorption. • Investigation of mechanisms of microscale mechanical changes in hydration and dehydration processes.

The Use of Various Rainfall Simulators in the Determination of the Driving Forces of Changes in Sediment Concentration and Clay Enrichment

Soil erosion is a complex, destructive process that endangers food security in many parts of the world; thus, its investigation is a key issue. While the measurement of interrill erosion is a necessity, the methods used to carry it out vary greatly, and the comparison of the results is often difficult. The present study aimed to examine the results of two rainfall simulators, testing their sensitivity to different environmental conditions. Plot-scale nozzle type rainfall simulation experiments were conducted on the same regosol under both field and laboratory conditions to compare the dominant driving factors of runoff and soil loss. In the course of the experiments, high-intensity rainfall, various slope gradients, and different soil surface states (moisture content, roughness, and crust state) were chosen as the response parameters, and their driving factors were sought. In terms of the overall erosion process, the runoff, and soil loss properties, we found an agreement between the simulators. However, in the field (a 6 m2 plot), the sediment concentration was related to the soil conditions and therefore its hydrological properties, whereas in the laboratory (a 0.5 m2 plot), slope steepness and rainfall intensity were the main driving factors. This, in turn, indicates that the design of a rainfall simulator may affect the results of the research it is intended for, even if the differences occasioned by various designs may be of a low order.

The use of domestic raw materials for the production of chamotte glass melting pots with a capacity of 500 and 700 l

The possibility of a complete replacement of imported raw materials with domestic while maintaining the quality of large-sized ceramic pots and the optical glass obtained in them is considered. Imported raw materials (prosyanovsky kaolin and watch-yar clay) are characterized by high ductility, low sintering temperature, and low iron content. As an alternative to these materials, in this work, Latnian clay and Elena's kaolin are considered. The sintering temperature was established, which provides the necessary properties of the refractory (1350-1400 °C). The effectiveness of enrichment of Latnian clay has been shown: a decrease in the content of SiO 2 to the level of its content in the Elena's enriched kaolin, an increase in the content of Al 2 O 3 . Ill. 4. Ref. 2. Tab. 4.

Enrichment of clay from Vitoria da Conquista (Brazil) for applications in cosmetics

Abstract A clay sample, off-green color, from Vitoria da Conquista, northeastern Brazil was size fractionated by dispersion and centrifugation. Three different grain-size fractions with different colors (pink, red and light green) were then isolated. The aim was to characterize the physical and chemical properties of the raw clay and the resulting grain-size fractions in order to evaluate their use in cosmetic products. X-ray diffraction, Attenuated Total Reflectance - Fourier Transformed Infrared, scanning electron microscopy, X-ray fluorescence spectroscopy, inductively coupled plasma-atomic emission spectrometry, cation exchange capacity measurements, oil absorption and swelling capacity, plastic and apparent viscosities and microbiological tests were used to characterize the samples. The grain-size fractions are composed of smectite and kaolinite, without the presence of Si-polymorphs (α-quartz or cristobalite), and showed attractive colors, good swelling capacity, good oil absorption, microbiological safety and chemical inertia. These characteristics make these samples potentially interesting for applications in pharmaceuticals and cosmetics.

Soil and onsite nutrient conservation potential of aromatic grasses at field scale under a shifting cultivated, degraded catchment in Eastern Ghats, India

Land degradation due to soil erosion is a global problem, especially on cultivated hill slopes. Economically important aromatic grasses can protect degraded hill slopes more effectively than field crops, but little information is available on their performance. This study quantifies runoff, sediment yield, enrichment ratios of soil and nutrients, and sediment-associated organic carbon and nutrients losses under three aromatic grass species: citronella (Cymbopogon nardus), lemon (Cymbopogon flexuosus), and palmarosa (Cymbopogon martini), compared with a traditional field crop, finger millet (Eleusine coracana) grown at three land slopes (4%, 8%, and 12%). It was observed that the degree of slope and type of grass both significantly influenced runoff generation. Runoff and sediment yield (SY) were significantly higher at 12% slope than at 8% and 4% slopes. Relation between rainfall and runoff were significant for all the grass species (p < 0.05). Palmarosa, lemon, and citronella grass reduced the SY by 10, 54, and 60%, respectively, over finger millet. SY was also significantly related to rainfall for all the treatments (p < 0.05). The threshold runoff values to produce SY were higher for aromatic grasses compared to finger millet. Enrichment of clay, silt, sand, soil organic carbon (SOC), available nitrogen (N), phosphorus (P) and potassium (K) in the sediment were not significantly different between slopes but differed significantly between aromatic grasses and finger millet. Sediment associated nutrient load varied inversely with SY mainly because of the nutrient dissolution effect of high runoff volume. Annual loss of SOC and nutrients varied from 84.7–156.8 kg ha-1 y-1 for SOC, 4.38–9.18 kg ha-1 y-1 for available N, 0.35–0.75 kg ha-1 y-1 for available P, and 2.22–5.22 kg ha-1 y-1 for available K, with the lowest values for citronella and highest for finger millet. The study found that the aromatic grasses have greater environmental conservation values than finger millet on steep degraded land.

The contribution of termite mounds to landscape‐scale variation in vegetation in a West African national park

AbstractQuestionsTermite mounds are important sources of local‐scale soil heterogeneity and thereby affect savanna vegetation. Studies contrasting mound and savanna vegetation usually neglect variation between savanna types. We aim to answer the following questions: (1) is mound vegetation consistently different from the surrounding savanna vegetation at landscape scale; (2) is mound vegetation homogeneous across different savanna types; and (3) are differences between mound and savanna vegetation influenced more by nutrient accumulation or clay enrichment in mounds?LocationPendjari National Park, northern Benin.MethodsWe analysed the vegetation in 59 pairs of mound and savanna plots in four savanna types. We examined if mounds differed in community composition between savanna types, and from savanna plots using ordinations, and tested for correlations between community composition and soil parameters. We identified characteristic plant species for mounds in each savanna type using the IndVal method. Finally, we evaluated the relative importance of different soil parameters for differences in vegetation between mound and savanna plots using projection to latent structures regression (PLSR).ResultsThere were clear differences between savanna types for both savanna and mound plant communities, and in each savanna type, clear differences emerged between mound and savanna vegetation. Community differences correlated with differences in soil parameters in all cases. We identified ten characteristic plant species for mounds, with little overlap between characteristic species from different savanna types. Across savanna types, 63% of the variation in mound – savanna vegetation contrast was explained by variation in nine soil parameters, most importantly clay content.ConclusionEven at the landscape scale, the influence of mounds on vegetation depends on habitat context. Thus, local mound vegetation patterns can only be understood considering the influence of different soil parameters in each savanna type. However, enrichment of clay and macronutrients together explain the largest part of the differences between mound and savanna vegetation. Further variation in vegetation composition among mounds is likely driven by biotic interactions and spatial distribution of mounds.

Regional stratigraphy, elemental chemostratigraphy, and organic richness of the Niobrara Member of the Mancos Shale, Piceance Basin, Colorado

The elemental chemostratigraphy of the Upper Cretaceous Niobrara Member of the Mancos Shale shows that six chemostratigraphic zones can be identified in the Piceance Basin, Colorado, based on geochemical data. Chemostratigraphic correlations of nine wells spaced 20 mi (∼32 km) apart closely match lithostratigraphic correlations made using gamma-ray and deep-resistivity wireline logs. Lithologic interpretations made from wireline logs indicate that the Niobrara Member and equivalent strata consist primarily of interbedded calcareous shale and shaley limestone facies that increase in thickness to the northwest in the basin. The geochemical data suggest that during deposition of the Niobrara Member, anoxia and calcium enrichment increased to the east of the basin, whereas terrestrial input and clay enrichment increased to the northwest. Element crossplots suggest that a large part of the silicon is detrital and that the Niobrara Member becomes an increasingly more clastic than carbonate system to the west and northwest. The Δlog R–derived total organic carbon (TOC) calculated using a sonic-resistivity overlay analysis technique shows that the Niobrara Member comprises organic-rich and organic-poor deposits. Average TOC values range between 1 wt. % (in organic-poor deposits) and 2.37 wt. % (in organic-rich deposits), with higher TOC values recorded in the southern and eastern parts of the basin. Relative-rock brittleness estimates from element and TOC data show the stratigraphic variability of alternating ductile (TOC rich, Ca and Si/Al poor) and brittle (TOC poor, Ca and Si/Al rich) intervals for the Niobrara Member.

How Irrigation Affects Soil Erosion Estimates of RUSLE2

RUSLE2 is a robust and computationally efficient conservation planning tool that estimates soil, climate, and land management effects on sheet and rill erosion and sediment delivery from hillslopes, and also estimates the size distribution and clay enrichment of sediment delivered to the channel system. In the U.S.A., RUSLE2 is supported by extensive databases maintained by the USDA-Natural Resources Conservation Service. Examples are presented of how input climate, soil and management descriptions might be built outside the U.S.A. using data from Uruguay. In addition to average annual erosion and sediment delivery, recent enhancements give RUSLE2 the ability to predict a representative runoff event sequence for a particular location, soil, management, and user-specified return period that can be coupled with a channel erosion and routing model.

How Irrigation Affects Soil Erosion Estimates of RUSLE2

RUSLE2 is a robust and computationally efficient conservation planning tool that estimates soil, climate, and land management effects on sheet and rill erosion and sediment delivery from hillslopes, and also estimates the size distribution and clay enrichment of sediment delivered to the channel system. In the U.S.A., RUSLE2 is supported by extensive databases maintained by the USDA-Natural Resources Conservation Service. Examples are presented of how input climate, soil and management descriptions might be built outside the U.S.A. using data from Uruguay. In addition to average annual erosion and sediment delivery, recent enhancements give RUSLE2 the ability to predict a representative runoff event sequence for a particular location, soil, management, and user-specified return period that can be coupled with a channel erosion and routing model.

Effects of slope orientation on pedogenesis of altimontane soils from the Brazilian semi-arid region (Baturité massif, Ceará)

Given the importance of climate conditions for the development of soils, studies on climosequences are a valuable tool to predict the influence of climate change on weathering rates and on soil formation processes. The Baturite massif, a humid enclave located in the Brazilian semi-arid region, has unique characteristics that cause a disproportional distribution of rainfall: the eastern and northern slopes receive more than 1,600 mm/year of rainfall, whereas the southern and western slopes have semi-arid characteristics with rainfall of less than 600 mm/year. Eight soil profiles were selected to investigate the influence of these distinct climates on soil formation. To achieve this, physical, chemical, morphological, mineralogical and micromorphological data were determined and analyzed. In the humid slope predominate soil processes include melanization, brunification, intense leaching, acidification and alitization, with intensified weathering in higher altitudes. In contrast, the environment in the dry slope favored the occurrence of soils with a higher base status, high-activity clays, low Al saturation and bisialitization processes coexisting with monosialitization, mainly in the soils located at lower altitudes. Micromorphological data indicate that clay illuviation is not the main process responsible for the enrichment of clay in the subsurface horizons. The contrasting environmental conditions with different mineralogical composition seem to be an important indicator of weathering intensity and pedoenvironmental conditions.

A Micromorphological Assessment of Anthropogenic Features in Pre-Columbian French Guiana Dark Soils (FGDS): First Results

In order to document site formation processes at microscale and to characterise pre-Columbian French Guiana dark soils (FGDS), micromorphology was performed on three sites. For the first time it was possible (i) to microscopically characterise pre-Columbian Anthrosols in different physical contexts and (ii), to identify anthropogenic features associated with past human occupation. Microfeatures of the Holocene alluvial terrace of the lower Maroni River witnessed (i) several episodes of clay enrichment and/or redistribution, (ii) seasonal waterlogging, and (iii), post-depositional biological activity. Clay en- richment and organic matter inputs together with biological activity processes might have alternated, probably in relation to vegetal cover and/or anthropogenic activities. On top of the alluvial terrace, bio- turbated dark layers are enriched in fine brown organic matter and charcoals. Cumulic soil development was favoured when successive sediment inputs due to episodic flooding and/or overland flow was pos- sible (Chemin Saint Louis site). On a lateritic hill, under rainforest, at the MC87 ring-ditched mountain (Montagnes Couronnees or Crowned Mountain), microscale identification of yellowish unburnt oxic B horizon aggregates together with anthropogenic features related to fire such as charcoals and burnt soil fragments (rubefied and dark brown aggregates) stress that lateritic soil acted as support for activities in the enclosure, and as reworked material in the ditch. These components could result from clearance for settlement, agricultural management and cultivation, or domestic activities. The obtained results allow first comparisons to be drawn between pre-Columbian FGDS and Brazilian dark earths (BDE). Except a similarity in colour, the former is revealed to be less rich in anthropogenic components with an absence of phosphatic elements such as bones.

Continental weathering and climatic changes inferred from clay mineralogy and paired carbon isotopes across the early to middle Toarcian in the Paris Basin

Lower Toarcian strata (Lower Jurassic) have been extensively studied with a view to understanding the oceanographic, climatic and biological processes that drove the Earth's system into an Oceanic Anoxic Event (OAE). For this time period, the evolution of the European marine seaways is now relatively well constrained owing to multiple geochemical studies, but investigations regarding climatic trends in the continental realm remain sparse. In the present study, we test the clay mineralogy as a continental climate-sensitive proxy in the well-documented Sancerre core (southern Paris Basin). We compare variations in the kaolinite content with pCO2 fluctuations (derived from paired carbon isotopes; ∆13C=δ13Ccarb−δ13Corg), taking advantage of the detailed chemostratigraphic, palaeoenvironmental and sequence stratigraphy frameworks established for this core material. The results indicate a substantial decrease in kaolinite abundance at the end of the Pliensbachian, which is compatible with a long-term diminution in continental weathering and an inferred temperature decrease. The early Toarcian, prior to the carbon cycle perturbation and deposition of black shale facies, remained relatively cold with minima in both the proportion of kaolinite and reconstructed pCO2. The mineralogical and geochemical responses across the prominent negative carbon isotope excursion (CIE) itself are not univocal. The first of four steps that compose the negative limb of the CIE at Sancerre is associated with decreased kaolinite and pCO2, and increased carbonate oxygen isotope ratios. Taken together, these trends are compatible with a transient cooling phase immediately preceding the onset of black shale deposition. Conversely, the subsequent steps are marked by substantial enrichment in kaolinite that matches increased osmium isotope ratios measured in Yorkshire, providing compelling evidence for rapid increases in continental weathering and riverine runoff forced by intensification of greenhouse conditions during the CIE. Relaxation in the intensity of continental weathering, as suggested by resumed low kaolinite abundance is seen immediately after the cessation of CO2 input (after the fourth step of the CIE). The interval spanning the upper portion of the early Toarcian and the middle Toarcian records a subsequent long-term increase in the proportion of kaolinite synchronous with significant clay enrichment of the sediment. Continued greenhouse conditions, even after the recovery from the carbon isotope perturbation and “regional” black shale deposition, are likely related to sustained CO2 emission by Karoo–Ferrar volcanism through the considered interval.

Distribution and classification of soils with clay-enriched horizons in the USA

In Soil Taxonomy three diagnostic subsurface horizons reflect clay enrichment: the argillic, kandic, and natric horizons. Clay illuviation is recognized in Soil Taxonomy at some level in 10 of the 12 orders, including the order (Alfisols, Ultisols), suborder (Aridisols), great group (Aridisols, Gelisols, Mollisols, Oxisols, Vertisols), and subgroup (Andisols, Aridisols, Inceptisols, Mollisols, Oxisols, Spodosols). Forty-four percent of the soil series in the USA contain taxonomically defined clay-enriched horizons. However, many other soils contain Bt horizons that do not qualify as an argillic or related horizons. Several soil-forming factors are important in their development, including udic and ustic soil climates, lithological discontinuities, parent materials enriched in carbonate-free clays and coarse fragments, well-drained conditions, backslopes rather than eroding shoulders, and a time interval of >2000yr or more. The genesis of argillic, kandic, and natric horizons is also dependent on electrolyte concentration, the amount and distribution of precipitation, clay charge, and microfabric.

Ediacaran Gaskiers Glaciation of Newfoundland reconsidered

Newly discovered palaeosols in the Gaskiers Formation of Newfoundland provide a new perspective on its palaeoenvironment, and are evidence that it was not a deep submarine tillite, nor an anoxic deep-sea floor, nor a ‘cap carbonate’ from extreme geochemical perturbation of the global ocean. Discovery of oxidized palaeosols and re-evaluation of sedimentary facies and stratigraphic relationships now suggest reinterpretation as a coastal plain with glacial moraines in the forearc basin of a continental volcanic arc, like modern Japan. Ediacaran palaeosols of the Gaskiers Formation lack large root traces, but show soil profile differentiation (clay enrichment and depletion of alkali and alkaline earth elements at the expense of feldspar and rock fragments) and diagnostic soil structures (blocky peds, argillans, sepic plasmic fabric). These palaeosols are evidence of a humid temperate climate and marked marine regression accompanying the Gaskiers Glaciation of the early Ediacaran (580 Ma). Geochemical weathering trends in the palaeosols, especially phosphorus depletion, are characteristic of biologically active soils. Ediacaran microbial earth ecoystems may have been responsible for filamentous disruption of bedding in the palaeosols.