Illuvial Clay Research Articles

Seismic slip zone characteristics in near-surface unconsolidated sediments: Low-angle reverse paleo-rupture in Central Korea

Fault materials and deformed sediments formed by coseismic rupturing events in the near-surface region show various deformation characteristics. To gain insights into rupture propagation and termination processes close to the surface, we analyzed the slip zone and deformed sediments/granite of a paleoearthquake rupture in central Korea. Here, we list our structural and mineralogical findings of the low-angle reverse rupture. (1) The slip zone mainly contains microbreccia and intercalated illuvial clay. The kaolinite-rich illuvial clays migrated downward with water, accumulate in spaces, and have a distinct texture and color. They show strong alignments and injection structures indicating that seismic slip occurred after clay infiltration in the open spaces along the pre-formed rupture. (2) The dip angle of the slip zone where it cuts unconsolidated strata tends to decrease, showing a branching geometry and termination. The slip zone changes in thickness where it goes through the different alternating sedimentary units (sands and clays) due to their physical properties. Based on these features, we conclude that the type and distribution of infilling materials in the slip zone and of surrounding materials transected by ruptures are related to the interruption and termination of the propagating rupture within the unlithified strata at near-surface depths.

Long-term quantification of the intensity of clay-sized particles transfers due to earthworm bioturbation and eluviation/illuviation in a cultivated Luvisol

As a result of the limited knowledge on eluviation/illuviation and bioturbation rates, these two processes of soil particles translocation are qualitatively described either as synergic or competing processes. Here we take the opportunity of the recent development of an image analysis procedure to quantify illuvial clay and earthworm’s porosity to quantify the intensity of illuviation and bioturbation cumulated over soil formation in a temperate cultivated Luvisol. The key objectives of the study are i) to quantify the total intensity of illuviation and bioturbation and their depth distributions and ii) to assess the possibility for bioturbation to limit or compensate the depletion of the clay-sized fraction in topsoil horizons due to eluviation. The total quantity of illuvial clay is 1,100 t.ha−1 while the estimated annual amount of clay-sized fraction translocated by eluviation is between 0.08 and 1 t ha−1 yr−1. This is comparable to the annual loss of land by water erosion (between 1 and 5 t ha−1 yr−1) or by arable erosion (3.3 t ha−1 yr−1). Eluviation/illuviation is thus a discrete and active form of soil loss. With approximately 1,900 t.ha−1 of clay-sized fraction, the amount of fine particles displaced at least once by bioturbation is higher than the one related to eluviation/illuviation. At first sight, it therefore seems possible for biological activity to compensate for vertical transfers of the clay-sized fraction by eluviation/illuviation. However, our study shows that a considerable amount of the clay-sized fraction will never be brought up by the bioturbation and will remain definitively lost for the surface horizons as bioturbation decreases non-linearly with depth. Consequently, a preventive management of the depletion of the clay-sized fraction in topsoil horizons by eluviation/illuviation should be preferred to the curative management of its consequences by bioturbation.

Litologie a paleopůdy klikovského souvrství ve vrtu 2140 01T1 Dunajovice, třebonská pánev

The 2140 01T1 borehole sampling the Late Cretaceous non-marine strata of the Klikov Formation in the central part of the Třeboň Basin in southern Bohemia provided ~ 70 m thick alluvial succession composed of alternating sandstone and mudstone intervals that overlays deeply weathered crystalline basement. The mudstone interval in the lower part of the Klikov Formation is separated by sandy layers into several 2–4 m thick fining-upward units. The sharp-based sandy layers with fusain, carbonized stems and rip-up clasts of underlying mudstone are interpreted as avulsion deposits. They grade upwards into heterolithic sand-silt sequence and mottled massive mudstone with burrows, rhizohalos and variably developed pedogenic features. Such cyclic arrangement probably reflects autogenic processes on distal floodplain with episodic deposition and upward increasing subaerial exposition and pedogenic overprint. In the middle to upper parts of the Klikov Formation up to 6 m thick channel sandbodies with sharp erosional bases cutting into the underlying laminated sand-silt heteroliths of channel levee deposits occur. The thickness of the single-storey sandbodies corresponds usually to c. 2 m which suggests up to 3 m deep channels during bankfull discharge. The thicker multi-storey sandbodies record channel amalgamation on the alluvial ridge or shallow paleovalley fillings. The sandbodies grade upwards to massive mudstones of abandoned channel fills and floodplain deposits. These floodplain units are up to 8 m thick and consist of variegated massive mudstones interrupted by discrete up to 1 m thick fining upward layers of rippled sandstone representing crevasse splay deposits. Depositional context including preserved levee deposits, abandoned channel fillings and floodplain finegrained deposits suggests rather higher sinuosity of the formative rivers. Palaeosol profiles represent pedogenically modified floodplain fines with gradational bases and sharp erosive top surfaces. At least 10 palaeosols were identified in the measured section, forming mostly discrete profiles up to 2 m thick consisting of several B-horizons that differ in the degree of the soil structure development, colour, mottling, grain size, presence of clay hypocoatings and bioturbation index. The most common Bw horizons form lower parts of the profiles and have no or only a weakly developed angular blocky structure (ABS). The typical mottling is caused by a hierarchical system of vermicular greenish-grey reduction rhizohalos, that may be filled by silt to sand or illuviated clay hypocoatings and probably follow the original plant root system. Some patches have diffuse orange rims of iron oxides, probably represented by goethite. Mudstone of Bsst horizons displays well-developed ABS with rare wedge-shaped peds and contains a number of illuviated clay skins and redox depletions. Vertic features like fine cracks filled by sand are common, and slickensides with clay hypocoatings occur rarely. Mudstones of Bt horizons contain a number of illuviated clay hypocoatings filling root channels or interpedal cracks, while the Bss horizons exhibit well-developed ABS with slickensides and contain a number of vertical cracks filled by sandy grains. Palaeosol profiles represent mainly argillisols and vertic argillisols with transitions to argillic vertisols. Poorly developed argillic to vertic protosols are also common. Palaeosol profiles differ mainly in the degree of structural development/maturity, which is given by various lengths of exposition to similar climatic conditions. Vertical distribution of palaeosols reflects their position in the alluvial landscape with locally specific hydromorphic conditions rather than a distinct climatic trend. Most of palaeosols exhibits downprofile translocation of clay (illuviation) leading to the formation of argillic horizon, which typically develop on stabilized landscape in humid climate with seasonal moisture deficit.

Polygenesis and cementation pathways for plinthic and non-plinthic soils on the Upper Coastal Plain, South Carolina

Plinthic soils on the Upper Coastal Plain (UCP) of South Carolina are directly underlain by hard but unconsolidated older Coastal Plain sediment, as are non-plinthic soils on adjacent dissected landforms. The older deposit, called brick material, is integral to plinthite formation via perched soil water hence intensified redox conditions. Currently, few causes are known for horizon matrix cementation of these soils. Six pedons from three hillslope positions were investigated for soil uniformity, selectively dissolved Fe and Si distributions, and micromorphology. Particle-size indices and ground-penetrating radar (GPR) confirmed uniform soils and thick plinthic horizons on summit positions and a discontinuity at shoulder and backslope positions. Contrasts in GPR radar reflections corresponded to the brick material and were thought to be associated with changes in moisture contents, iron mineralogy, pore size, and clay content. Illuvial clay infillings and minute channels confirmed pedogenesis in brick material. In plinthic horizons above the brick material, excess citrate dithionite Fe (Fed) was indicated by over-bulging distributions relative to Fed/clay ratios. Water-soluble silica (Siw) may be recycled in upper sola by capillarity and leaching, move through the discontinuity, and interact with Fe throughout the solum compatible with coarse material encapsulated with Fe-enriched fine material in the brick matrix. Absolute molar contents of oxalate extractable Si (Sio) and Fe (Feo) were low throughout all pedons, however, Sio/(Feo + Sio) ratios ranged from 0.30 to 0.60 in Btvx, Btx, and 2Btx horizons to account for fragic soil properties. Nascent UCP parent material or soils evidently provided adequate constituents for plinthic soil formation. A new theory proposes UCP plinthic soils evolved simultaneously with uniform soils that do not have a water table and have Bt horizons that begin as yellowish or brownish then redden with depth. Ferricrete sourced from nearby extant landscapes may have provided detrital ironstone to the parent material mix.

Glossic planosols in the postglacial landscape of central europe: Modern polygenetic soils or subaerial palaeosols?

Texturally bipartite and stagno-gleyed Planosols are becoming more commonly reported from the temperate climate zone. Although ferrolysis is widely accepted as the major process responsible for abrupt textural change in South American Planosols, clay illuviation or native lithogenic discontinuity is understood to be more important for texturally distinct profile differentiation in other regions of the world. Textural discontinuities, accompanied by seasonal water stagnation, are common in the (post)glacial landscapes of Central and Northern Europe, and extend the possibility for Planosol recognition, which has previously been considered atypical of this region. However, a unique combination of lithogenic, periglacial and pedological features has raised questions about the classification and genesis of these soils. In particular, an Eemian age for the illuvial clay (argic) horizon in loamy subsoils developed from pre-Vistulian ice-sheets has been hypothesised. Eight texturally bipartite soil profiles (sandy over loamy), located within the range of the older Saalian ice-sheet (Polish: Odra) were investigated from the Lower Silesia region (SW Poland). Abrupt changes in the relative contributions of particle size fractions, heavy minerals, rare-earth elements, rounded and semi-rounded sand grains, and clay minerals, as well as the presence of wind-polished periglacial pavements, accompanied by Late Pleistocene–Holocene optically stimulated luminescence ages for the cover sands, have confirmed the different lithogeneses of the topsoil and subsoil layers as the reason for the abrupt textural difference in the soil profiles. Macro- and micromorphological observations support the following model of Glossic Planosol development in SW Poland: (a) formation of illuvial soil (Luvisol type), including its argic horizon, during the Eemian; (b) truncation of profile (erosion of eluvial horizons) during the cold stages of the Last Glacial Maximum, followed by the formation of a periglacial pavement, soil cracking and the cryogenic reworking of the illuvial structures in the argic horizon (Marine Isotope Stage [MIS] 4–MIS 2); and (c) soil burial with wind-transported sands (during MIS 2, remodelling in the Holocene), which formed a lithological discontinuity at the top of argic horizon. During the Holocene period, the upper argic horizon has been transformed by extending the albeluvic tonguing under a humid temperate climate. Observations from SW Poland support the hypothesis that Luvic/Glossic Planosols in the older (post)glacial landscapes are polygenetic soils, in terms of both their litho- and pedogeneses, the formation of which started in the Eemian and is still active.

Soils of the coastal and lower belt of Galápagos Islands – The case of Isla Santa Fé and Isla Santa Cruz

This paper compares the development of soils in low-altitude zones of two eastern Galápagos islands having a similar composition of the volcanic rock substrate but contrasting topographical features, i.e. the small and relatively flat island of Santa Fé and the larger, mountainous, younger island of Santa Cruz. The soils of the lower, dry zone of Santa Cruz are less weathered compared to those of the higher slopes on the same island. They contain basalt-derived mineral grains, swelling 2:1 phyllosilicates, and poorly crystalline kaolinite, and they are rich in calcite features. The soils on Santa Fé, in a similar altimetric position, are less weathered, containing more weatherable basalt-derived mineral grains and a clay fraction composed of open 2:1 phyllosilicates and small amounts of mica-like components, together with likely sepiolite. Sepiolite seems to occur in part in the form of small yellowish nodules. Some soils on both islands contain significant amounts of phosphate, probably linked to populations of sea birds. Compared to the parent rock, an increase in Al, Fe, Ti and K, and a loss of Mg, Ca and Na, are observed for both islands, but this is less pronounced for Santa Fé. The observed micromorphological, mineralogical and chemical differences are explained by geomorphology and related climatological factors, since the present altitudinal setting of the soils is similar. The soils of Santa Fé receive less precipitation because the island has no central mountain chain. On both islands, the heterogeneous nature of the low-elevation soils indicates major colluvial input. Biological factors, such as nesting of seabirds and the development of phytogenic calcite, may play an important role in local soil development. Remnants of illuvial clay coatings, sometimes entrapped in calcitic features, indicate wetter conditions in the past.

Time for nonilluvial Bt horizons?

The Bt horizon is the diagnostic horizon of the Luvisolic Order in Canada. According to the Canadian System of Soil Classification (CSSC), the Bt must be formed from clay illuviation through the processes of lessivage (i.e., physical transport of clay). In a study of a Luvisol catena in the central Saskatchewan, we demonstrate that Ae/Bm horizons overlying IIBt horizons are formed in a sandy mantle overlying till (i.e., a lithological discontinuity) and that the sandy mantle contributed negligible amounts of illuvial clay despite the presence of clay skins on ped surfaces in the IIBt horizon. We extended the results of this study to the regional scale by examining sand fractions in 63 pedons of Luvisol-dominated soil associations from soil surveys in the Northern Forest Reserves (between latitudes 53°N and 55°N). Of the 63 pedons, 13 had lithological discontinuities identified in their profile description and a further 27 had discontinuities identified through shifts in the sand fractions between horizons. For the profiles with discontinuities, inherited particle size differences are a more likely cause of coarse-over-fine textural contrasts than lessivage. A regional analysis of the distribution of Luvisol-dominated associations showed distinct zonations that account, in part, for the differences in the occurrence of lithological discontinuities. Based on these results, we suggest that the criteria for Bt horizons in the CSSC should be broadened to include nonilluvial coarse-over-fine texture-contrast horizons and that the criteria for the Luvisolic order also be broadened to include these nonilluvial Bt horizons.

Micromorphological evidence of pedogenesis and paleoclimatic change in the Holocene loess-paleosol in the south Qinling Mountains, China

Micromorphological investigations of loess-paleosol sequence offer the potential for understanding pedogenic and paleoclimate change at the microscopic scale. However, the micromorphological study is comparatively scarce in the south Qinling Mountains, China. Here, micromorphological analysis (coarse particles, pedofeatures and voids) in conjunction with physicochemical indexes of pedogenesis (i.e., clay content, CaCO3 and Fe2O3) were carried out from two Holocene loess profiles in the upper Hanjiang River. These results show that: (i) Paleosol is considered as strongly-developed soils on basis of much finer and rounder particles, channels, more reddish color and abundant illuvial clay coatings; (ii) Lessivage (clay formation, eluviation and illuviation), intensive carbonate eluviation and rubification were identified as the major pedogenic processes of paleosol; (iii) Comparative study with Chinese Loess Plateau (CLP) indicates that loess deposits in the south Qinling Mountains experienced a much stronger pedogenesis as evidenced by multiple generations of illuvial clay and almost completely eluviation of carbonate, which implies a warmer and wetter paleoclimate in the subtropical monsoon zone. The pedogenic differences across the Qingling Mountains are mainly controlled by regional paleoclimatic differences and provide a good response to monsoon climate change in the East Asian.

Textural features of saline-sodic soils affected by Urmia Lake in the Northwest of Iran

The increasing regression of Urmia Lake in the last 30 years has brought about the salinization and sodification of arid soils from the shoreline, which has aggravated land degradation in this area. The objective of this work was to assess the changes in the soils brought about by progressive and fast salinization of the region, and to determine the present- or past character of several textural pedofeatures. We studied the micromorphic, mineralogical and physico-chemical properties of four profiles of saline-sodic soils in the west of Urmia Lake. Most of voids in the studied horizons were mainly vesicles due to structure collapse, besides planes and channels, and their b-fabric were mainly crystallitic micritic and granostriated due to argilloturbation. The main pedofeatures were illuvial clay coatings and also their fragments in the groundmass, clay and silt coatings, calcite accumulations as nodules, infillings and coatings and redoximorphic accumulations as nodules and coatings. Owing to the arid climate and high amounts of calcium carbonate and soluble salts, the illuviation of pure clay in natric horizons probably took place during a wetter past climate during the lower Quaternary. Additionally, based on high values of exchangeable sodium, ESP and SAR, we believe that the high values of exchangeable sodium are the responsible for the structural collapse, dispersion and translocation of fine material (clay and silt) at varying distances within the soil profile. Alkalinisation is likely to proceed from evaporation of the supersaturated waters of Urmia Lake through carbonate precipitation and smectite formation, increasing ESP and changing previous argillic horizons to natric horizons. Increase of organic matter through the application or organic amendments seem to be the best strategy for their reclamation.

The undisclosed paleoclimatic record of northern mesoamerica: A pedostratigraphic approach for environmental reconstruction

This article presents the results of a research on paleosols formation conditions in the Aguascalientes Valley, northern Mesoamerica, where paleoenvironmental reconstructions have been scarce. Records of environmental and climatic changes, as well as the alteration of the landscape are expressed in the memory of the soil. Soil micromorphology is the most efficient method to identify these changes. In paleosols, micromorphological features reflecting a certain soil forming process can be related to environments in which those processes took place. Paleoenvironmental reconstruction of the region consisted in identifying pedofeatures and other present soil attributes, grouping features into pedogenic facies under constant environmental conditions, examining the groundmass in order to detect features caused by erosion or sedimentation, and finally establishing a hierarchy between the different pedogenic facies, including erosional and sedimentary features if necessary. Specific statistical data analysis disclosed stratigraphical relationships. The results we obtained, such as illuvial clay coatings, redoximorphic nodules, and hypocoatings, revealed the most representative pedofeatures that developed under humid climate. Under a semiarid climate, representative pedofeatures that were revealed included micritic coatings and hypocoatings. A paleosol with ferruginous nodules and hypocoatings in groundmass, and at least one phase of dusty and high-birefringence yellow clay illuviation is proposed as stratigraphic marker for this area of the Aguascalientes Valley. Evidence indicates the sequence of events in the area was: (i) a large period of humid climate; (ii) a short period of climate change, from humid to semiarid, followed by subhumid; and (iii) a large period of semiarid climate, including the current one. The paleosols of the Aguascalientes Valley to a large extent preserve major trends in history and provide further evidence to define the 11 phases of stability (pedogenesis) in 8 cycles and to detect the interlayer phases of instability (sediment transport/deposition).

Laser-based 3D microscopic gauging of soil aggregate coating thickness and volume

In structured soils, clay-organic coatings are spatially distributed along macropore surfaces. Information on thickness and volume of coating material is essential for macropore-matrix mass exchange of water and solutes. However, their determination is difficult and fraught with uncertainty due to irregular shapes of macropore surfaces. The objective of this study was to test the use of a three-dimensional (3D) confocal laser scanning microscope for gauging soil macropore coatings. For this test, coating material was manually separated from the surface of intact soil clods (5 cm edge length) sampled from Bt horizons (with illuvial clay) of till-derived and loess-derived Haplic Luvisols. The resulting coating thicknesses ranged between approx. 0.1 and 0.5 mm and volumes between 0.057 and 2.9 mm3 with mean densities of 1.96 g cm−3 for loess-derived and 2.67 g cm−3 for till-derived coatings. The 3D laser microscopic method yielded data based on micro-topographic information. The key benefits of the 3D confocal laser scanning microscope are the information on the mm-scale spatial distribution of coating thickness and bulk density. These additional parameters of the clod surface or aggregate micro-topography can be useful for improved quantification of accessibility of sorption surfaces and for describing macropore-matrix mass transfer of reactive solutes.

Morphogenesis and quantification of the pore space in a tephra-palaeosol sequence in Tlaxcala, central Mexico

Tepetates are indurated subsoil horizons developed in tephra-derived materials in various parts of the Trans-Mexican Volcanic Belt. The term ‘tepetate’ includes fragipans, duripans, pedosediments and saprolites, derived from vitric rhyolitic tuff, Pleistocene volcanic ashes or pyroclastic flows. All soils with tepetates are at high risk of erosion and so they have been intensively studied for decades. The tepetates are common in Tlaxcala State of central Mexico, being formed under Ustic Isomesic soil climate. The aim of this investigation was to characterise the pore space of fragipan-type tepetates and the role of clay components in their formation. We studied porosity of tepetate from a tephra-palaeosol sequence in the north of Tlaxcala State, in undisturbed soil samples. Observations of pore space were made in 2D and 3D by analysing microscope images of thin sections and cross-sectional images from a computed tomography scanner. In the thin sections we also identified and described clay illuvial pedofeatures. Micromorphological observations showed two main pore types. Small rounded pores had a homogeneous distribution and were probably formed before the clay illuviation process that took place in a palaeosol formed on the tepetate material. The distribution pattern of the small pores in the studied tepetate was similar to that in the fragic horizon, which was probably formed by a hydro-consolidation process. Large crack-pores were formed during the palaeosol formation. Later these large pores were filled by illuvial clay coatings and so we conclude that each tepetate was part of the set of Bt horizons in the palaeosols of Luvisol type.

Paleosols and their sedimentary setting in the Old Red succession of Podolia, Ukraine

Three types of paleosols have been recognized in the red siliciclastic Podolian Old Red succession in Ukraine – gleyed/calcic and calcic vertisols, and calcic protosols. Both types of vertisols are characterized by the occurrence of pedogenic nodules, an illuvial clay horizon and slickensides. They have a pseudo-anticlinal and gilgai microrelief, which document the intensive swelling and shrinking of soils in semi-arid to sub-humid (monsoonal) climates with seasonal precipitation. Moreover, the gleyed/calcic vertisols contain rhizoliths with yellow-brownish/gray depletion zones and barite accumulations in the topsoil, which suggest the development of gleying processes and reduction conditions in water-logged soils. Spectral Gamma-Ray (SGR) measurements document a high content of potassium in the vertisols. XRD analysis shows the monotonous composition of the soils with the domination of quartz, illite, chlorite, mica, and with some admixture of illite-smectite mixed layers. The SGR measurements have revealed Th-enrichment being the effect of rainwater-induced downward transport of small grains of Th-bearing heavy minerals into the cracks and micropores during wet seasons. The calcic protosols are characterized by the accumulation of calcite nodules, small and irregularly dispersed within the matrix. They represent less mature, multi-storey, stacked paleosols in contrast to the mature vertisols.The variability of paleosol maturity has allowed the recognition of the relative distance to the fluvial channel. Less mature calcic protosols indicate formation during short-term episodes of landscape stability, interrupted by rapid aggradation of mud after flood events. These vertically stacked paleosols are typical of proximal floodplains. By contrast, both types of vertisols were formed on distal floodplains and their occurrence is associated with a lower frequency and thickness of crevasse splays and sheetflow deposits. They document stable and long-term weathering processes. The sedimentological investigations have revealed the fluvial architecture of the pedogenized Old Red succession in Podolia.

The Precious Opal Deposit At Wegel Tena, Ethiopia: FormationViaSuccessive Pedogenesis Events

Abstract Since its discovery in 2008, the opal deposit in the Wegel Tena area of Ethiopia, located within an Oligocene ignimbritic trap, has become a major provider of precious opal. This study provides new field evidence and laboratory results that reinforce the pedogenetic model for gem opal formation. In the eight mines investigated, opal occurs in lenticular horizons within an unwelded ignimbrite bed. Moreover, several deposits are superimposed in the sequence, indicating that gem opal formation occurred several times in the same place. We observed that, in contrast to the other beds, the opal-bearing horizons are strongly weathered: volcanic glass is altered to smectite, rocks with a granular microstructure are apparent, and cavities are covered by illuvial clays. These features are typical of pedogenetic processes. Plant fossils in the opals reveal a well preserved cellular structure composed of chalcedony. These observations are consistent over all the mines, supporting the pedogenetic model for precious opal formation in the Wegel Tena area.

How fast are soil-forming processes in Quaternary sediments of a tropical floodplain? A case study in southeast Brazil

Floodplains are depositional features of a channel valley associated with a specific climatic and hydrologic regime of a drainage basin. In tropical conditions, sediments can be quickly weathered by soil-forming processes and tend to obliterate pre-existing sedimentary structures. Therefore, the objective of many studies on floodplains is to identify and discuss such sedimentary features, mostly those related to the morphology of channel deposits. Additionally, a qualitative approach to identify aspects of pedological evolution in these environments has been attempted in few studies. The purpose of this study was to interpret the intensity and the time of alluvial sediment weathering by pedogenetic processes in tropical humid conditions. Soil profiles were analyzed in different environments of deposition in the Pardo River floodplain (southeast Brazil) by accounting for sedimentary facies and pedological features supported by multi proxy data provided from geochemistry, macro- and micromorphology, grain size, total carbon, total nitrogen, 13C isotopic analysis and 14C/OSL (optically stimulated luminescence) dating. Based on the results, we identified that pedogenetic features and soil horizon distributions were closely related to sediment architecture, grain size and position in the floodplain. In the Pardo floodplain, Fluvic Gleysols (Loamic and Clayic) with moderately to strongly developed structures were identified in overbank fine sediments. Fluvic Cambisols (Clayic) were found in abandoned paleomeanders, Fluvic Cambisols (Loamic) in sandy scrollbars, Gleyic Acrisols (Clayic, Cutanic, Differentic) in channel deposits, which presented a 130-cm-thick Bt horizon with illuvial clay coatings, and Histosols (Fluvic) with high contents of total carbon (11.9% and 26.8% in histic horizons) in small-scale avulsive systems. Deposits were dated to between 35,000 and 700years BP. 13C isotopic data revealed a trend toward enriched values in older samples (−14.21‰) in which C4 plants dominated and a relative impoverishment of the values in more recent samples (−26.9‰ to −27.9‰). This result was consistent with the tendency of the distribution of C3 plants to increase over that of C4 plants, favored by the warmer and wetter climate since the Upper Holocene. In this study, a Fluvic Gleysol profile of <1000years and a Fluvic Cambisol of <700years were identified. Nevertheless, our primary contribution is to highlight that soil evolution in this specific situation could be more efficient than expected. Moreover, to provide consistent analyses in future studies, tools from both sedimentology and pedology are essential.

A powerful tool for assessing distribution and fate of potentially toxic metals (PTMs) in soils: integration of laser ablation spectrometry (LA-ICP-MS) on thin sections with soil micromorphology and geochemistry.

The dynamic behavior and inherent spatial heterogeneity, at different hierarchic levels, of the soil system often make the spatial distribution of potentially toxic metals (PTMs) quite complex and difficult to assess correctly. This work demonstrates that the application of laser ablation spectrometry (LA-ICP-MS) to soil thin sections constitutes an ancillary powerful tool to well-established analytical methods for tracing the behavior and fate of potential soil contaminants at the microsite level. It allowed to discriminate the contribution of PTMs in distinct soil sub-components, such as parent rock fragments, neoformed, clay-enriched or humified matrix, and specific pedogenetic features of illuvial origin (unstained or iron-stained clay coatings) even at very low contents. PTMs were analyzed in three soil profiles located in the Muravera area (Sardinia, Italy), where several, now abandoned mines were exploited. Recurrent trends of increase of many PTMs from rock to pedogenic matrix and to illuvial clay coatings, traced by LA-ICP-MS compositional data, revealed a pedogenetic control on metal fractionation and distribution, based on adsorption properties of clay minerals, iron oxyhydroxides or organic matter, and downprofile illuviation processes. The main PTMs patterns coupled with SEM-EDS analyses suggest that heavy metal-bearing mineral grains were sourced from the mine plants, in addition to the natural sedimentary input. The interplay between soil-forming processes and geomorphic dynamics significantly contributed to the PTMs spatial distribution detected in the different pedogenetic horizons and soil features.

Development of a novel image analysis procedure to quantify biological porosity and illuvial clay in large soil thin sections

Among other driving forces, climate change may lead to significant modifications of soil properties through variations of the intensity and dynamics of a number of soil processes including the especially sensitive and ubiquitous processes of bioturbation and illuviation. Progress toward the quantification of these processes needs to be made as a first step in order to ascertain or predict the impact of climate change. In this study, we develop, and validate through an exhaustive accuracy assessment, a digital 2D image analysis method adapted to large soil thin sections, leading to the quantification, characterization and classification of pores and illuvial clay features considered diagnostic of bioturbation and illuviation, respectively. The need to consider large soil thin sections (14 x 6 cm) stems from observations that areas from 684 mm2 to more than 5 000 mm2 are needed to obtain representative measurements of fragments of illuvial clay (papules) and porosity associated with earthworms respectively. Whereas the soil heterogeneity in thin sections of such a large size prohibits the use of classical global and colorimetric image analysis procedures, we succeeded to quantify and characterize the porosity and illuvial clay features with accuracies as high as 96% for porosity and 92% for illuvial clay by carefully considering different levels of soil organization from aggregates to individual illuvial clay features. Quantification of the size and the shape of pores and of illuvial clay features makes it possible to develop morphological classifications distinguishing pores of biological origin (earthworms or roots) from others, or clay coatings and infillings from papules. All these data are particularly useful to better characterize underlying soil processes. Results suggest that the proposed methodology provides an accurate and representative quantification of biological porosity and illuvial clay features in large thin sections. We argue that the use of this approach could be extended to study and quantify bioturbation and illuviation intensities at the profile scale.

Sedimentary environment and paleosols of middle Miocene fluvial and lacustrine sediments in central Japan: Implications for paleoclimate interpretations

Sedimentary facies analysis and description of paleosols were carried out for the middle Miocene Tokiguchi Porcelain Clay Formation (PCF) in central Japan in order to interpret the soil-forming environments during a long hiatus in the Japanese Islands. The sedimentary facies suggests that deposition occurred mainly in a lacustrine environment, with minor channel-fill and debris-flow deposits associated with alluvial fan environments. The coarse-grained sediments, which are inferred to have been deposited in channel-bar and debris-flow deposits, are present only in the marginal area of the sedimentary basin. Mature paleosols are identified in the Tokiguchi PCF, characterized by illuviated clay, identifiable soil horizons including Bt horizons and many in situ plant fossils, and are then similar to Ultisols. Most tree trunk fossils, however, were preserved by burial beneath debris-flow deposits. Most of paleosols formed on lacustrine deposits and were covered by lacustrine clay and silt deposits, without intervening coarse-grained deposits, such as flood-flow deposits. This change of sedimentary facies indicates a dramatic change of hydrologic environment, from stagnant water to entirely desiccated conditions, promoting weathering and soil formation. The relationship between sedimentary facies and Pedotypes, consequently, implies the repetition of specific events, i.e., submergence and emergence of lake bottom, most likely due to formation and drainage of a dammed lake. These isolated events and development of mature paleosols might suggest specific characteristics of middle Miocene weathering conditions, such as seasonally heavy rainfall and/or warm climatic conditions in the Japanese Islands.

A multi-disciplinary perspective on habitat preferences among dinosaurs in a Cretaceous Arctic greenhouse world, North Slope, Alaska (Prince Creek Formation: lower Maastrichtian)

The Prince Creek Formation of northern Alaska is the most abundant source of polar dinosaur remains in the world, and now, corroborating data from this well-studied rock unit allow for making inferences about the paleoecological preferences for these extinct polar animals. The rock unit records high-latitude, alluvial sedimentation and soil formation on a low-gradient, muddy coastal plain. Compound and cumulative andic Entisols and Inceptisols formed on levees, point bars, crevasse splays, and along the margins of floodplain lakes, ponds, and swamps. Abundant organic matter, carbonaceous root traces, Fe-oxide depletion coatings, and zoned peds indicate periodic waterlogging, anoxia, and gleying, consistent with a high water table. In contrast, Fe-oxide mottles, ferruginous and manganiferous segregations, bioturbation, and less common illuvial clay coatings indicate recurring oxidation and periodic drying out of some soils. An integrated reconstruction of pedogenic processes and biota suggests that this ancient Arctic coastal plain was influenced by seasonally fluctuating water table levels and floods, and in distal areas, marine waters. Four of the five bonebeds in this study are from more distal areas, represented by lower delta plain facies, while the fifth bonebed is from a more proximal part of the basin, represented by a somewhat better drained coastal plain facies.Bonebeds in the distal areas are dominated by Edmontosaurus sp. while the more proximal bonebed is dominated by the remains of the ceratopsian Pachyrhinosaurus perotorum. The distribution of these bonebeds, sedimentological facies, paleosols, and biota suggests that Pachyrhinosaurus may have preferred more upland environments while Edmontosaurus preferred lowland, deltaic environments. This distribution may be the result of physiological adaptation to the pronounced seasonality provided by polar terrestrial ecosystems. In contrast to a preferred habitat distribution of these large herbivores, the large predatory dinosaur Nanuqsaurus hoglundi seems to have had a more ubiquitous distribution across the landscape.

Micromorphological investigations of the Late Quaternary loess–paleosol sequences of the Kashmir Valley, India

The loess–paleosol sequences of the Karewa Group preserve a valuable repository of the Late Quaternary climatic changes and the landscape evolution history of the Karewa Basin of Kashmir Valley in their lithological and pedogenic records. Three representative loess–paleosol sections at Shankerpora (SP), Khan Sahib (KS) and Pattan (PT) localities were chosen for detailed lithostratigraphic fieldwork and micromorphological observations of thin sections. Lithostratigraphic analysis revealed lateral and vertical variation in thickness and number of paleosol profiles from south-west to north-west of the Karewa Basin suggesting the availability of land-surface for periodic loess deposition. The SP section is marked by 6 (SP-S6, S7, S8, S9, S10, S12), KS section by 3 (KS-S2, S4, S5) and PT section by 2 (PT-S1, S3) thick mature paleosol profiles. Theses paleosols have well developed ‘Ah’ and ‘Btk’ horizons representing prolonged land-surface stability when pedogenic processes outpace loess deposition. On the other hand comparatively thin to thick paleosol profiles represent weak to moderate pedogenic maturity indicating short stratigraphic breaks with rapid loess deposition. Micromorphological observations of thin sections suggested that clay illuviation and CaCO3 accumulation have operated within the paleosol profiles. CaCO3 features are often associated with clay coatings suggesting decalcification of carbonates followed by clay illuviation. Pedogenic CaCO3 probably resulted from the precipitation of the soil solution near the average depth of wetting front. The pedogenic CaCO3, illuvial clay, mottles, iron manganese features, pedal microstructure and blocky aggregates reveal variation in the pedogenic maturity among and within the loess–paleosol sections. The morphological (both micro- and macro-morphological) attributes of loess–paleosols suggest variation of climatic conditions during the Late Quaternary period in the Karewa Basin of Kashmir Valley, India.