Clayey Matrix Research Articles

The Ain Dibba and Ain Kissa phosphorites, Tebessa (NE Algeria): REE depletion versus shallow, open depositional environment during the Paleocene-Eocene phosphogenesis in North Africa

The Ain Dibba and Ain Kissa phosphorites, located north of Tebessa town, NE Algeria, belong to the Upper Cretaceous-Paleocene-Eocene Afro-Arabian phosphatic province that extends from Morrocco to the Middle East. These two phosphorite showings, which were partly exploited at the beginning of the 20th century, were deposited during the Late Paleocene (Thanetian) times on the northern basin of the Kasserine Paleo-Island. Although they are not yet economically very important, the present petrological and geochemical study contribute highly to the knowledge of their critical trace and REE contents as well as the understanding of their paleo-depositional environment. Petrographic and XRD data show that these phosphorites are mainly composed of pellets, coprolites, bioclasts and rare glauconite, gypsum, quartz grains and zeolites. These constituents are cemented by calcareous, siliceous or rarely clayey matrix. The pellets and coprolites are composed mainly of cryptocrystalline carbonate fluor-apatite (CFA). The XRF and ICP-MS chemical analyses of these phosphorites, show they are not as rich as those from Kef Essenoun and Bled El Hadba southern basin, neither in P2O5 nor in REE contents. P2O5 concentrations range from 14.16 to 26.57 wt% (average = 20.24 ± 4.33 wt%, n = 15), with only one sample having 31.89 wt% P2O5, whereas ΣREE contents range from 171 to 344 ppm (average = 252 ± 69 ppm, n = 9) and, therefore, considered as moderately REE-enriched phosphorites. Ce anomaly values display a decrease from the lower to the upper phosphorite sub-layers (from −0.57 down to −0.72), suggesting an increase from relatively sub-oxic to more oxic conditions. The Eu anomalies range from 0.89 to 1.35 for Ain Dibba and from 0.93 to 1.35 for Ain Kissa phosphorites. The highest Ce/Ce∗ and lowest Eu/Eu∗ anomalies are recorded in the lower layers, often enriched in both REE and glauconite contents, whereas the lowest Ce/Ce∗ and highest Eu/Eu∗ anomalies, reflecting more oxic conditions, are characteristics of the glauconite-free and REE-poor upper layers. The gradual timewise transition from relatively sub-oxic to oxic conditions (from the lower to the upper layers) is also recorded in the redox-sensitive (Cr, Ni, V, U) trace element data. This implies that during early diagenesis, the sedimentary environment became slightly reduced, which enabled intensive uptake of both REE and some trace element (e.g., Cr, V, Ni, U) mainly from pore-water through substitution and adsorption mechanisms onto apatite and glauconite minerals. This is noticed especially in the lower phosphorite layers of both Ain Dibba and Ain Kissa deposits. In a larger scale, the Ain Dibba and Ain Kissa phosphorites show lower REE contents, lower Ce and Eu anomalies, and lower redox-sensitive trace element contents than those of the southern (Kef Essenoun and Bled El Hadba) and eastern (Tunisian) basins of the Kasserine paleo-Island. These geochemical features indicate that phosphorites from the northern basin were deposited, through upwelling current, in a more open, shallower, oxygenated and agitated environment during the Paleocene-Eocene phosphogenesis in North Africa and Middle East.

Geotechnical Characterisation of Flysch-Derived Colluvial Soils from a Pre-Alpine Slope Affected by Recurrent Landslides

Heterogeneous rock masses that include rhythmic alternations of marl, shale, marly limestone, sandstone, siltstone, and argillite, such as Flysch, are particularly prone to generating colluvial deposits on gentle slopes, which are often subject to failures triggered by heavy rainfall. Flysch-derived colluvial soils are made up of highly heterogeneous sediments ranging from clayey loam to rock fragments, and they have been studied more rarely than homogeneous soils. In this work, we present a geotechnical and hydraulic characterisation performed both in situ and in the laboratory on flysch-derived colluvial soils that were involved in a channelised landslide in the pre-alpine area of the Friuli Venezia Giulia region (NE Italy). The investigated soils were characterised by the average values of the grain size composition of about 25% gravel, 20% sand, 30% silt, and 25% clay. The loamy matrix presented low-to-medium values of the liquid and plastic limits, as well as of the plasticity index (LL = 40%, PL = 23%, and PI = 17%, respectively). The values of the peak friction angle for natural intact samples were 33° < ϕ’p < 38°, whereas the residual friction angle fell to 23–24° at great depths and high vertical stresses, for a prevailing silty–clayey matrix. Variable head permeability tests were performed both in situ and in the laboratory, showing that the values of the vertical and horizontal permeability were very close and in the range 1 × 10−4–1 × 10−6 m/s. The soil permeability measured in the field was generally higher than the hydraulic conductivity calculated on laboratory samples. The proposed geotechnical and hydrological characterisation of flysch-derived colluvial soils can be of fundamental importance before the use of more thorough analyses/models aimed at forecasting the possible occurrence of slope failures and evaluating the related landslide hazard. The reported geotechnical and hydraulic parameters of flysch-derived colluvial materials can represent a useful reference for rainfall infiltration modelling and slope stability analyses of colluvial covers that are subject to intense and/or prolonged precipitation. However, when facing engineering problems involving colluvial soils, particularly those coming from flysch rock masses, the intrinsic variability in their grain size composition, consistency, and plasticity characteristics is a key feature and attention should be paid to the proper assumption of the corresponding geotechnical and hydraulic parameters.

X-ray tomography applied to tsunami deposits: Optimized image processing and quantitative analysis of particle size, particle shape, and sedimentary fabric in 3D

The analysis of particle size, shape, size, and their spatial arrangement (i.e. fabric) in a sedimentary deposit plays a significant role in their interpretation in terms of transport mechanism, flow conditions, and sediment source. The present work focuses on the use of X-ray computed tomography (X-CT) to analyze tsunami deposits (core samples), as examples of complex sedimentary assemblages. A workflow of image processing is proposed to measure 3D parameters of particle size, shape, and orientation using two different software packages (Fiji-ImageJ, and IPSDK) and two different methods of image segmentation. The semi-automated method provides better segmentation quality of the tsunami deposit, as compared with the poor performance of fully-automated image segmentation. We also provide some clues to reduce the computational time. This workflow is applied to two examples of tsunami deposits on the coasts of the Algarve (1755 Lisbon tsunami, southern Portugal). Optimized processing of X-CT images gives access to detailed vertical variations of grain size, grain shape, and componentry (clayey matrix, silicates, and carbonates, including marine bioclasts), as well as information on flow directions inferred from the sedimentary fabric in 3D. High-resolution analysis of the bedforms and vertical grain size grading allows determining the flow conditions during the inundation phase of the tsunami.

Landslide hazard assessment in Yateras municipality, Cuba

The main objective of this study in the Yateras municipality was the landslide hazard zonation (LHZ). The multi-criteria decision method used by Saaty (1980) was adopted, considering the factors; slope angle, elevation, distance to rivers, distance to the fault, average annual rainfall, lithology, soil depth and soil type. The weights of the factors were determined using the Analytical Hierarchy Process (AHP), determining that average annual rainfall, lithology and soil depth obtained the highest weights in the process, being 0.24, 0.19 and 0.16 respectively. Landslide susceptibility indices were determined based on a continuous numerical scale developed for this purpose. It was found that the high and medium hazard zones corresponded to the northeast and east of the municipality. These zones are mainly made up of rocks of the ophiolitic complex, very affected structurally, which are characterized by a high density of faults and a dense hydrological network, shallow soils with a predominance of brown soils with a clayey matrix.

Importance of arsenic bioaccessibility in health risk assessment based on iron “Minette” rocks and related soils

Total element concentrations by themselves are not always good predictors of toxicity and are therefore not suitable for eco- and/or human toxicological risk determination. In addition, despite the growing call for harmonization, countries show significant variation in risk assessment tools, screening/background values, protocols and legal management of soils. By incorporating mobility and bioaccessibility/availability into soil risk assessments, location-specific physico-chemical and geological conditions can be considered in routinely applied general risk assessment methodologies. Minette soils and rocks are a great case in point since they often are associated with high geogenic As concentrations and consequently potential risks. Minette iron ores form the world largest Fe ore deposits since the “great oxidation”. For the first time, oral bioaccessibility during direct ingestion was assessed on Minettes from Luxembourg by applying the in vitro Solubility/Bioavailability Research Consortium (SBRC) method. Out of > 180 samples, 25 representative samples were selected providing a unique dataset which showed an average gastric bioaccessibility of ∼10% (7.8 ± 4.0 mg/kg) of the total As-concentration, with a maximum of 45% (17.9 mg/kg). Of importance is that bioaccessibility of As in Minette rocks and soils are controlled by, and can be estimated from, lithology, mineralogy and total Ca content. Soils and ooid grainstones with an iron oxide or clayey matrix, are characterized by average gastric bioaccessible As concentrations < 6 mg/kg. Gastric As bioaccessibility is highest in Fe-bearing calcite-cemented bioclastic grainstones (∼12 mg/kg). Importantly, for all samples the maximal bioaccessible As concentrations remain below the threshold from which significant adverse non-carcinogenic and/or carcinogenic health effects are expected. These new results are in strong contrast with what total As concentrations might suggest. Considering bioaccessibilities, consequently, can help to avoid disproportionate, costly and environmentally impacting risk management strategies. Furthermore, this study illustrates the importance of cross-disciplinary collaboration between geo- and health scientists.

Early Investigation of a Landslide Sliding Surface by HVSR and VES Geophysical Techniques Combined, a Case Study in Guarumales (Ecuador)

The access road to the powerhouse’s hydraulic system’s facilities in Guarumales (Azuay, Ecuador) presents a medium-sized landslide. Geophysical tests were conducted in the initial research stage, combining electrical and seismic methods. A vertical electrical sounding (VES) and horizontal to vertical spectral ratio (HVSR) survey campaign have been taken as a reference for the analysis of the landslide area. The distribution of these test points has been at three different levels along the landslide where the access road crosses it, trying to cover the area’s most extensive possible length and width. In the area, we find the geology dominated by the presence of schists, altered to different degrees and presenting blocks of material with a lower degree of alteration within colluvium formed by a clayey matrix and coarse material of the exact nature. There is also observed runoff water and groundwater in the area. The results obtained through SEV tests have allowed for defining the separation zone of the mobilized or sliding materials compared to the fixed or immobile ones (potentially, the sliding surface was marked). Using the HVSR technique, the natural vibration frequencies of the ground associated with the sliding mass (separation of seismic impedances between a two-layer model: mobile and fixed) have been determined. Previous authors proposed an empirical relationship establishing the exponential relationship, already proposed by previous authors, between sediment thickness and natural frequencies. It has been possible to determine the depth of the position of the loosely compacted sediment zone (and probably moving or mobilized) compared to that of compact materials (immobile) and thereby define the potential rupture surface.

Microstructural, Physical and Mechanical Characteristics of Adobes Reinforced with Sugarcane Bagasse

This study deals with the reuse of sugarcane bagasse in adobes in order to improve their physicomechanical properties. Mineralogical and geotechnical characterization of the soil used shows that it is composed of quartz, kaolinite and goethite and is suitable for the manufacture of adobes. Sugarcane bagasse has a rough surface and contains mainly cellulose, hemicelluloses, lignin and traces of sucrose. Microstructural studies on adobes reinforced with sugarcane bagasse have shown that their microstructure is homogeneous for additions of these fibres up 4 wt.%. It has been found that the addition of sugarcane bagasse to the clayey matrix strongly improves the mechanical properties and reduces the water absorption kinetics and thermal conductivity (mainly because of the presence of cellulose) of the adobes, linked to their microstructure. The rough surface of sugarcane bagasse and the presence of sucrose acting like glue improve its adhesion with the clayey matrix, and cracks propagation in adobes is reduced. The presence of bagasse fibres leads to the formation of hydrogen bonds between sugarcane molecules and the clayey minerals, which could explain the improvement in the physicomechanical properties. Considering the thermal conductivity results, such adobes could improve the thermal comfort in habitats, especially in arid areas.

Pyrolysis Process for the Recycling of Cork Dust Waste from the Processing of Cork Agglomerate Caps in Lightweight Materials

This study aimed to investigate the possibility of recycling cork scraps derived from the production of agglomerated bottle caps containing organic additives (glues and adhesives) in addition to virgin wood. The study involved pyrolysis treatment followed by the use of char to obtain lightweight material prototypes. The scrap was pyrolysed in order to achieve the thermal degradation of unwanted molecules with decomposition temperatures lower than the pyrolysis temperatures, but also to achieve the reduction in mass and size of the starting material. The substitution of 15% by weight of weight-lightening agent (char from pyrolysed cork, or half char and half spent coffee grounds) into the clayey matrix made it possible to obtain lightweight aggregates with pH and conductivity values that could be exploited in an agronomic context. The substitution of clay with of 5 to 15% by weight of pyrolysed cork char in the production of specimens pressed at 25 bar and fired slowly at 1000 °C led to lightweight ceramics with particularly interesting porosity (from 41 to 68%) and bulk density (850–1600 kg/m3) values.

Microstructure, Physical and Mechanical Properties of Adobes Stabilized with Rice Husks

ABSTRACT The main objective of this study was to manufacture resistant, durable adobes having low thermal conductivity. For this purpose, a moderately plastic clayey soil from Korsimoro (Burkina Faso) was used to manufacture adobes reinforced with up to 1 wt.% of rice husks. The chemical and microstructural characteristics of the rice husks were evaluated, as were the physical, mechanical and microstructural characteristics of the adobes that were manufactured. The incorporation of rice husks in the clayey matrix increased the compressive strength of adobes and decreased their thermal conductivity. From a durability point of view, the addition of rice husks in adobes decreases the capillary absorption and improves the resistance to water erosion, due to the good adhesion of rice husks with the clayey matrix. According to standards related to building materials, adobes manufactured with at most 0.4 wt.% are suitable for the construction of resistant and durable dwellings that provide acceptable thermal comfort.

The pottery production from the Deh Dumen Bronze Age graveyard (South-Western Iran): a chemical, mineralogical and physical study

A collection of pottery vessels uncovered during the first season of excavations in the Deh Dumen Bronze Age graveyard (the second half of the third millennium BC) located in south-western Iran were studied by using chemical, mineralogical and physical techniques, with the aim to identify the pottery manufacturing process in this region. The site is located in a region of the Zagros fold and thrust belt that includes carbonate rocks and alluvial deposits. The pottery vessels found in the site present two different fabric types in their fresh surface: bright yellowish hue fabric (TYPE-1) and sandwich-like or black core fabric (TYPE-2) showing presumably different production techniques or workshops. Twenty-four samples from pottery sherds were selected and analysed by X-ray fluorescence (XRF), powder X-ray diffraction (XRD), polarized light microscopy (PLM), and field emission scanning electron microscopy (FESEM). Hydric tests were also performed. Samples were different according to their chemistry having distinguished calcium-rich and calcium-poor ceramics. Al2O3 and Fe2O3 were detected as the other main components of samples besides SiO2 and CaO. The mineralogical and textural characterisation revealed a fine-grained clayey matrix with quartz and feldspar grains in TYPE-1 potteries and large and small calcitic and clayey lumps inclusions in TYPE-2 potteries. Imprints of straw or other plants can be responsible for the higher porosity of some of the potteries. It was found that most of the potteries from the Deh Dumen graveyard were produced by means of a local and traditional pottery manufacturing technique, whilst others may have been produced in different places and transported to the graveyard as ritual offerings.

Model for calcite spherulite formation in organic, clay-rich, lacustrine carbonate shales (Barbalha Formation, Aptian, Araripe Basin, NE Brazil)

The formation of carbonate spherulites, recognized as part of the South-Atlantic Pre-Salt reservoir rocks, remains enigmatic. Well-chosen analogues provide insights into depositional and diagenetic conditions and the biotic versus abiotic processes that might influence or even control spherulite growth. Radial fibrous calcite spherulites of the Batateira beds in the Barbalha Formation (Aptian, Araripe, NE Brazil) formed mainly in organic and clay-rich laminite layers as nodules that grew around different nuclei, now represented by, amongst others, micrite and apatite ostracods. They vertically alternate with clays, but also carbonate laminites, which locally also contain spherulites. Characterization of the organic matter content of spherulitites (petrography, total organic carbon, vitrinite reflectance, stable isotopes) reveals TOC's of up to 30% related to the presence of mainly oil-prone alginite next to huminite, inertinite, sporinites and zooclasts. The complex mixture of clays, dominantly autogenic mixed layered illite-montmorrilonite, which alternate with lacustrine carbonates and evaporites, is diagnostic for lakes in a semi-arid environment. The occurrence of gypsum, calcitic alveolar honeycomb spherulite textures, preferential concentration of pyrite at the spherulite-matrix contact and inward spherulite perforations suggest bacterial activity under shallow and evaporitic syn-depositional conditions. Although the Barbalha spherulites formed chemically-driven in a viscous matrix, the microbial influence, mainly as lamalginite in the clayey matrix, is undeniable. The mixed organic-silicate gel catalyzed calcite spherulite formation. The Barbalha spherulites consequently illustrate the complementary influence of clays, organic matter and evaporitic syn-sedimentary conditions.

Mineralogy and geochemistry of a bauxite-bearing lateritic profile supporting the identification of its parent rocks in the domain of the huge Carajás iron deposits, Brazil

A bauxite-bearing lateritic profile, developed along a borehole within the supergenic Fe-deposits of the Carajás Mineral Province in Brazil, is investigated after its textural aspects, mineralogy, and geochemistry. Petrographic studies, XRD mineralogical analysis, SEM-EDS, and whole-rock chemistry were used to study selected samples. The 156 m depth borehole is composed of basaltic andesite at the substratum and an overlying lateritic profile well-structured in distinct horizons, from base to top composed of: a saprolite, with rock relicts within a clayey matrix of mainly vermiculite and kaolinite; a clayey horizon dominated by kaolinite; a bauxitic horizon with gibbsite as the main phase; a ferruginous crust mainly composed of hematite and goethite. XRD mineralogical quantifications indirectly confirmed the chemistry of Si, Al, Fe, and Ti, as the most abundant elements in the lateritic horizons. Statistical factor analysis of the whole chemistry and mass balance calculations showed groups of elements arranged according to their enrichment or depletion character in the distinct horizons. Si, Ca, Na, and K are leached out to the top of the profile following the destabilization of their carrier mineral phases feldspar, hornblende, and clinochlore, whereas Al, Fe, and Ti are enriched to the upper horizons, respectively in the structure of gibbsite, hematite/goethite, and anatase. The basaltic andesite at the substratum has its parental affinity confirmed after textural changes, REE normalized patterns, and Zr/Ti ratios throughout the profile, nevertheless, parent rock variations are expected. The studied lateritic profile is comparable to most of the bauxite-bearing laterites in the Amazon region, except for its unparalleled 22 m thick Fe-rich bauxitic horizon and absence of a truncating clay cover on the top of the profile. The lateritic sequence was probably formed during the Paleocene-Eocene bauxitization event that reached the Amazon region and survived as a complete unaltered fossil lateritic profile through the time.

Improvement of water resistance and thermal comfort of earth renders by cow dung: an ancestral practice of Burkina Faso

The main objective of this study was to improve some properties (physical, mechanical, hydric and thermal) of earth renders amended by cow dung, as such amendment is an ancestral practice in Burkina Faso. For this purpose, raw clayey material from Kôdeni (in western Burkina Faso), mainly composed of kaolinite (62 wt.%), quartz (31 wt.%) and goethite (2 wt.%) and having adequate geotechnical properties was used to elaborate earth renders reinforced with up to 6 wt.% of cow dung. The cow dung studied was mainly made up of small vegetable fibres, clayey minerals and quartz consumed by cows. Cow dung incorporation limits the spread of cracks and hardens the material thanks to the good adhesion of cow dung to the clayey matrix, which is linked to the rough surface of fibres contained in cow dung. The presence of cow dung in an earth render influences its mineralogy through the formation of insoluble amine silicate (Si(OH)4. 4NH3). This compound is formed during the reaction between fermented cow dung with mainly fine crushed quartz and feebly kaolinite in basic medium. The molecule formed links isolated raw material particles through free electronic doublets on the oxygen atoms and especially on the nitrogen atoms. The consequence of this effect is an improvement of the microstructural, physical and mechanical properties of earth renders. In particular, their thermal conductivity is reduced as the fibres present in the composite materials are rich in cellulose (molecule with thermally insulating properties), and their resistance to abrasion and to water is good. The earth renders elaborated in this way help to provide water resistant housing with good thermal comfort.

Aridisols in the Southern Permian Basin of Lithuania: a key to understanding clay cement distribution

The change from fossil to geothermal energy supply includes the necessity to re-evaluate gas reservoirs in the Southern Permian Basin of NW Europe, as higher permeability reservoirs are needed for the exploitation of geothermal energy than natural gas. A key reservoir risk in Permian sandstones in the Southern Permian Basin is the presence of clay cement. The distribution of the clay cement is not properly understood. The negative effect can be attributed to complex grain coatings formed by tangential clay directly around the detrital grains followed by authigenic clay rim cement, both being genetically related. This study presents new results on the origin of the tangential and the authigenic clay. The Southern Permian Basin in Lithuania was a marginal area of the basin with low accommodation rates and extensive aridisol development. Here, sandstones of the Perloja Formation contain abundant clayey matrix in the form of grain and void coatings. The limited burial depth of a few hundreds of metres ensured that the original internal fabric and mineralogy of the clay coatings remained well preserved. Thin section microscopy revealed that the clay coatings are cutans that formed by post-depositional mechanical infiltration (illuviation) of suspensions of clay minerals, iron hydroxides and some clay to silt-sized quartz. Other pedogenic features are the development of nodular calcrete, rootlets, and of infiltrated clay. Aridisols were recurrently eroded by fluvial or aeolian activity causing wide-scale dispersion of siliciclastic grains with more or less complete clay cutans and also carbonate (calcrete) clasts in certain stratigraphic intervals.

An archaeometric study of early Copper Age pottery from a cave in Romania

AbstractEarly Copper Age pottery sherds discovered in a cave within the crystalline dolomites of the Southern Carpathians (Romania) were investigated by polarized light optical microscopy (OM), X-ray powder diffraction (XRPD) and electron microprobe analysis (EMPA) to obtain information on the pottery production in the Copper Age in the territory of present-day Romania. Microscopically, the clayey matrix of the ceramic body is highly birefringent or consists of low-birefringent and isotropic parts mixed together, containing fragments of quartz, muscovite, alkali feldspar, plagioclase, biotite, chlorite, heavy minerals and metamorphic and magmatic rocks, as well as an opaque material. The EMPA data revealed an Fe-rich illite-like matrix and helped to identify the mineral nature of the inclusions. Local pottery production in bonfires or surface clamps is envisaged. Miocene illitic clays may have been used as raw materials, mixed with a small amount of sandy temper. The thermal changes revealed by OM, the modification of the XRPD peaks and the EMPA data suggest firing temperatures of between 800 and 850°C.

Microstructures of Building Materials from Huaca De La Luna, Peru

ABSTRACT The microstructures of building materials from the archaeological complex of Huaca de la Luna on the northern coast of Peru is assessed for the first time by a multiscale approach. The multiscale microstructural characterization used laboratory techniques including optical microscopy, scanning electron microscopy, X-ray microtomography, and both gas and powder pycnometry. Optical microscopy revealed the presence of organic matter and shell fragments and X-ray microtomography showed differences in the sizes and connectivity of pores. The BET (N2 gas adsorption) specific surface areas showed greater presence of clayey matrix in the mortars. No significant differences among mortars and brick fragments mineralogy were detected by X-ray diffraction, so the larger amount of fine binding matrix in the mortars suggests that they were produced blending raw material with different grain sizes. The aim of this study is to provide data that can be used for a better understanding of the Moche culture, its construction techniques, and to support conservation strategies of the archaeological heritage.

Geochemical and mineralogical characterization of the arsenic-, iron-, and sulfur-rich mining waste dumps near Kaňk, Czech Republic

The role of secondary minerals in controlling the migration of arsenic and selected metals (Cu, Pb, Zn) has been investigated in voluminous mining waste dumps at Kaňk (northern part of the Kutná Hora ore district, Czech Republic). These wastes initially contained a large amount of Fe sulfides and arsenopyrite and have been exposed to atmosphere for approximately 500 years. The long-term weathering under acidic conditions caused dissolution of almost all sulfides and significant alteration of primary silicate minerals, producing deeply weathered As-, Fe-, and S-rich waste material (As: 13 g kg−1; Fe: 74 g kg−1; S: 44 g kg−1) with large proportion of clayey matrix filling the space between rock fragments. Detailed mineralogical investigation (powder X-ray diffraction, electron microprobe, Raman spectroscopy) and sequential extraction revealed that arsenic in these wastes is principally stored in reactive but not highly soluble minerals such as poorly-crystalline Fe (oxyhydr)oxides, bukovskýite, and X-ray amorphous hydrated ferric arsenate (HFA). Lesser fraction of As is contained in schwertmannite and less reactive scorodite, jarosite, and well-crystalline Fe (oxyhydr)oxides (especially goethite). Fe (oxyhydr)oxides also appear to be the main reservoirs of Cu and Zn; Pb is principally stored in jarosite. Acidic pore waters (pH ≈ 2.8) collected after rainfall events contain much Al (113 mg L−1), As (2.5 mg L−1), Ca (500 mg L−1), Cu (24 mg L−1), Fe (58 mg L−1), Si (44 mg L−1), SO42− (2170 mg L−1) and Zn (16 mg L−1). Geochemical modeling revealed that most of these elements (Al, Ca, Cu, SO42−, Zn) are controlled by ephemeral Al-Ca-Cu-Zn sulfates (e.g. gypsum, aluminite), which form at the surface of the waste dumps as a result of evaporation of pore solutions during dry seasons. Despite the fact that bukovskýite and other interesting Fe(III) (sulfo)arsenate minerals store a major part of As in the mining wastes, geochemical modeling supported the notion that mobility of As and Fe is controlled by the unspectacular poorly-crystalline As-bearing Fe (oxyhydr)oxides. The data show that the Fe(III) (oxyhydr)oxides, (sulfo)arsenates and hydroxysulfates in the 500-year-old mining waste dump retain arsenic efficiently but not completely. Monitoring wells installed at the site before our research recorded up to 1440 mg L−1 As in shallow groundwater. They argue, however, that this aquifer is disconnected from the larger groundwater bodies at the site and hence does not represent arsenic accumulation of environmental concern.

Controls on diagenesis and dolomitization of peritidal facies, Early Cretaceous Lower Edwards Group, central Texas, USA

The Early Cretaceous Fort Terrett Formation of Mason County, central Texas, is a succession of subtidal to peritidal mud-dominated facies with minor intervals of bioclastic packstone–grainstone, rudist floatstone, and interbedded chert nodules. The strata conformably overlie the Hensel Formation, which was deposited unconformably on Precambrian basement. The Hensel Formation also contains a significant percentage of dolomite, precipitated within a fine-grained clayey matrix. The Hensel and Fort Terrett Formations were deposited during a transgressive episode, which provided the conditions for the extensive shallow-water Comanche carbonate platform. Siliciclastic and carbonate sediments were deposited along the coastal margin in subtidal, intertidal to supratidal areas. Previous dolomitization models have suggested that high permeability layers are required for dolomitizing brines to flow through a carbonate succession. Although, interparticle porosity in muddy tidal-flat successions can be significant, it has a limited flow capacity. However, interconnected fenestral porosity can allow sufficient fluid flow to move dolomitizing fluids more efficiently through the succession. Thus, it is hypothesized that interconnected fenestral porosity could have had a significant impact on permeability within this muddy succession and provided the pathways and conduits for Mg-rich brines. Four types of dolomite are recognized in the Fort Terrett succession. Three of these dolomite types formed largely by replacement and they occur throughout the succession. Features such as crystal size, crystal face geometry and zonation reflect the progressive development and recrystallization of the dolomite types. Only type 4 dolomite formed as a cement in void spaces during a late diagenetic stage. The direction of the dolomitizing fluid movement is difficult to determine, but it was likely downward in this case, controlled by a density-head driving-mechanism generated by dense hypersaline fluids from an evaporating lagoon.

Tracing multiple resedimentation on an isolated karstified plateau: The bauxite-bearing Miocene red clay of the Southern Bakony Mountains, Hungary

The Vöröstó (=Red Lake) Formation, located in the Southern Bakony Mountains and the Balaton Highlands (Hungary), is a red, clayey continental assemblage containing hard, up to fist-sized bauxite pebbles, occurring in a large apparent stratigraphic gap between underlying karstified Triassic carbonates and mid’ Miocene to Quaternary cover. The origin and the exact stratigraphic position of the assemblage have been controversial for a long time. In this study, petrographic observations on the bauxite pebbles revealed common features with Cretaceous bauxite deposits known in the region, whereas heavy mineral composition of the red clay matrix is similar to those known from the Eocene bauxite horizon of the region. Single grain zircon U–Pb ages obtained from the bauxite pebbles and their red clayey matrix show similar late Archean to Jurassic age components. Additionally, Cenozoic U–Pb ages are well represented in the mostly euhedral zircon crystals separated from the red clays, whereas this volcanogenic contribution completely missing from the bauxite pebbles. SEM morphology and related EDX chemical analysis of clay minerals indicate polygenetic, detrital origin for the red clays. The main source material of the bauxite bearing Vöröstó Formation is most probably local Cretaceous and Eocene bauxite deposits exposed during the middle-late Miocene. These tropical weathering products were partly decomposed and degraded, but dilution by siliciclastic contribution is negligible. We suggest a transport mechanism dominated by local redeposition of mostly pelitic and allitic material through seasonal muddy debris flows within a karstic landscape.

Accumulation of Pesticides in Anaerobic Clayey Till‐Controls and Implications for Groundwater

AbstractPesticide residuals after point‐source pesticide spills in clay‐rich aquitards may potentially affect underlying groundwater for many decades due to slow release of accumulated pollution in the clayey matrix material of the aquitard. In this study, we evaluated factors behind different degrees of accumulation of phenoxy acids (MCPP, dichlorprop, 2,4‐D MCPA) and triazines (simazine and terbutylazine) observed in an old pesticide pollution described by Jørgensen et al. (2016a, this issue). By using leaching experiments, it was shown that a zone of maximum concentrations of MCPP and dichlorprop (mg/L) observed by Jørgensen et al. (2016a, this issue) represented accumulated potentially mobile pollution in anaerobic, however largely immobile pore water of the clayey matrix in the upper few meters of the unoxidized aquitard zone. By using sorption experiments, we determined 9 to16 times higher mobility by diffusion and flow for the phenoxy acids (R = 1 to 2) than for the triazines (R = 9 to 16) in the clayey matrix material of the aquitard. This indicated that more rapid and greater accumulation could occur for the phenoxy acids in the clayey matrix than for the triazines. In contrast, the relative mobility of the phenoxy acids and triazines was much closer in sand‐filled fractures and thin sand layers/lamina in the clay, suggesting that the migration of the same compounds along these textural preferential flow paths into the underlying aquifer was less different. Despite that a greater mass had originally been spilled of 2,4‐D and MCPA having similar mobility as the accumulated MCPP and dichlorprop, these compounds were not accumulated in the zone of maximum concentrations. It is suggested that the controls, which initially allowed for the observed separate accumulation of MCPP and dichlorprop as a zone of maximum pollution, were due to the combination of high persistence and high mobility for these specific pesticides in the clayey till matrix material of the aquitard. The investigation showed that over time the initial high concentrations of the accumulated phenoxy acids (MCPP, dichlorprop) transformed into high concentrations of related mobile degradation products (e.g., 4‐CPP and 2‐CPP), which extended the total time of groundwater pollution beyond the disappearance of the original phenoxyacids.