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Transmission electron photomicrographs. (a) Lath-like clay particles (red line) and flakes (blue line) in the same aggregate; (b) "cotton-like" clays with filamentous pore-lining (red arrows) bond in the core (yellow dashed line) composed of S and Ba; (c) "cotton-like" clays associated with elongated clays; (d) different types of morphologies of clay minerals. The yellow dashed line indicates a portion rich in Ca and P; (e) aggregation of "cotton-like" and pseudohexagonal clays. The circulated area (yellow dashed line) is composed mainly of Si and Al, comprising kaolinite; (f) detail of the pseudohexagonal kaolinite. Kln-kaolinite.

Transmission electron photomicrographs. (a) Lath-like clay particles (red line) and flakes (blue line) in the same aggregate; (b) "cotton-like" clays with filamentous pore-lining (red arrows) bond in the core (yellow dashed line) composed of S and Ba; (c) "cotton-like" clays associated with elongated clays; (d) different types of morphologies of clay minerals. The yellow dashed line indicates a portion rich in Ca and P; (e) aggregation of "cotton-like" and pseudohexagonal clays. The circulated area (yellow dashed line) is composed mainly of Si and Al, comprising kaolinite; (f) detail of the pseudohexagonal kaolinite. Kln-kaolinite.

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Mg clay minerals are usually associated with carbonates in alkaline-saline environments, precipitated from solution and/or transformation from other minerals. The aim of this research is to identify the mineralogy and geochemistry of clay minerals in different alkaline lakes in the Nhecolândia region, the southernmost region of the Pantanal wetland...

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... images of the sample from Coração lake show a large thin euhedral sheet mineral, which overlaps, probably in the basal plane, and a lenticular shape, representing a longitudinal plane or other kind of clay mineral. Different shades among the crystals were noticed, which might represent a different electric absorption pattern (Figure 8a). ...
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... thin euhedral and subhedral sheets are arranged close to lenticular crystals in the same aggregate and they exhibit different shades. Besides these characteristics, the samples have also shown irregular morphologies, as "cotton-like", with a filamentous pore lining growing up from the core of the boundaries of some material (Figure 8b). It is possible to notice crystals with thin euhedral morphologies and elongated sheets associated with a cotton-like material disposed together (Figure 8c,d), as well as rounded shapes among a cotton-like mineral, as Figure 8e shows. ...
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... these characteristics, the samples have also shown irregular morphologies, as "cotton-like", with a filamentous pore lining growing up from the core of the boundaries of some material (Figure 8b). It is possible to notice crystals with thin euhedral morphologies and elongated sheets associated with a cotton-like material disposed together (Figure 8c,d), as well as rounded shapes among a cotton-like mineral, as Figure 8e shows. Despite the different morphologies observed, in the EDX analyses of several points along the minerals, they showed similar chemical composition. ...
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... these characteristics, the samples have also shown irregular morphologies, as "cotton-like", with a filamentous pore lining growing up from the core of the boundaries of some material (Figure 8b). It is possible to notice crystals with thin euhedral morphologies and elongated sheets associated with a cotton-like material disposed together (Figure 8c,d), as well as rounded shapes among a cotton-like mineral, as Figure 8e shows. Despite the different morphologies observed, in the EDX analyses of several points along the minerals, they showed similar chemical composition. ...
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... (0.5-8.0 wt.%) and Mg (1.1-4.2 wt.%) and some other elements as Ca, Mn and Na. The "cotton-like" morphology mentioned above seems to be growing up from a barite grain in Figure 8b. The cotton-like shaped clay mineral is bound with the organic material through pore-lining or pore-bridging projections, which may indicate an authigenic clay [30]. ...
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... cotton-like shaped clay mineral is bound with the organic material through pore-lining or pore-bridging projections, which may indicate an authigenic clay [30]. In Figure 8d, the structure highlighted by the dashed line show a composition rich in P and Ca, which was not observed in any other sample and might indicate an apatite grain. In Figure 8e, the crystal surrounded by a dashed line is composed only of Si and Al, which corresponds to kaolinite. ...
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... Figure 8d, the structure highlighted by the dashed line show a composition rich in P and Ca, which was not observed in any other sample and might indicate an apatite grain. In Figure 8e, the crystal surrounded by a dashed line is composed only of Si and Al, which corresponds to kaolinite. Minerals 2020, 10, x ...
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... 5f and 7c exhibit clay crystals forming a "bridge" between quartz grains and Figure 5g shows a pore-lining morphology growing up from a core sample to form a cotton-like structure, indicating a characteristic typical of smectites [30]. The aggregates of clay minerals at Figure 7a and the subhedral and elongated shapes recognized at HRTEM images (Figure 8a-f are common in detrital clays. The different morphologies, however, do not show a specific chemical composition, demonstrating that clay crystals are comprised by distinct components. ...
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... this work, EPS have been recognized in the surface water, generally with algae and often associated with alkaline-saline lakes. The samples from the top of the sequences in these lakes showed features on SEM and TEM images that could refer to authigenic characteristics, such as the thin laminae covering quartz grains (Figure 7b), filamentous structures bridging quartz grains together (Figure 7c) and a cotton-like material involving organic nuclei (Figure 8b) and other clays (Figure 8a,e) [30,32]. ...
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... this work, EPS have been recognized in the surface water, generally with algae and often associated with alkaline-saline lakes. The samples from the top of the sequences in these lakes showed features on SEM and TEM images that could refer to authigenic characteristics, such as the thin laminae covering quartz grains (Figure 7b), filamentous structures bridging quartz grains together (Figure 7c) and a cotton-like material involving organic nuclei (Figure 8b) and other clays (Figure 8a,e) [30,32]. ...

Citations

... Although magnesium is an element that can be easily diluted by water and thus forms part of the smectite structure when the magnesium fluid interacts with the volcanic glass, an extra Mg contribution to the system is required. Smectites with high Mg-contents (like saponites and stevensites) have been associated whit alkaline lakes systems (Furquim et al., 2008;Dias et al., 2020). The enrichment of cations such as Mg and Si provided from detrital phases is usually propitiated, among other things, by the confluence of seasonal rains and intense evaporation due to long periods of drought (Meunier, 2005). ...
... Fig. 6. VI Al + Fe vs VI Mg plot for smectites, showing fields corresponding to Dioctahedral, Trioctahedral and Intermediate character (modified from Dias et al., 2020). Microanalysis were obtained by SEM-EDS (reported in Table 5). ...
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Clay mineral characterization is a valuable tool for unraveling the evolution of continental sedimentary basins. The Fiambalá basin is a foreland Andean basin located in the Southwest of the province of Catamarca (Argentina), on the flat subduction segment. In order to characterize its paleoenvironment and post-depositional evolution, petrographic, X-ray diffraction (XRD), and scanning microscopy (SEM-EDS) studies were carried out in detrital and volcaniclastic samples from the Tambería, Guanchín, and Rodados de la Puna Fms. Petrographic and XRD analyses show a predominance of phyllosilicates, quartz, plagioclase, and low proportions of feldspar and anhydrite, sporadic calcite, analcime, heulandite, and hematite. In the XRD fraction <2 μm, minerals from the smectite and illite groups dominate, with lower proportions of chlorite and kaolinite. An analyzed tuff level presents smectite solely in this fraction. The textural-compositional analyses of SEM-EDS show that illite and chlorite have a detrital origin. Their preservation would be consistent with the dominance of an arid climate in the region during the erosion and deposition of material from the source areas. The smectites are of the magnesium-rich beidellite-montmorillonite type and, together with the zeolites would be authigenic as a product of the alteration of both the volcanic material and magnesian detrital phases (chlorite and biotite), possibly under the influence of an alkaline environment related to the arid climate. From a thermal point of view, the presence of smectite throughout all stratigraphic succession allows interpreting maximum temperatures that, even in the deepest levels of the basin, inhibit the development of prograde phases (such as smectite/illite and smectite/chlorite mixed-layered) and allow the preservation of smectite. Based on the authigenic clays present in the basin, paleogeothermal gradients of between 13 and 18 °C/km (considered a fill of 4000 m thick) and between 8 and 11 °C/km (considered a fill of 6000 m thick) could be estimated.
... The low levels of SiO 2 verified in the profiles P2 and P3, in function of the processes of dissolution of silicates in alkaline medium, also contributed to the reduction of the ki and kr ratios, mainly in the superficial horizons (Dias et al., 2020;Furquim et al., 2010a;Oliveira et al., 2021). The dissolution of silicates in an alkaline medium also contributes to the accumulation of amorphous silica and the formation of cemented horizons such as Ortstein (Furquim et al., 2010a;Schiavo et al., 2012Schiavo et al., , 2020. ...
... As for mineralogy, through the analysis of DRX patterns, it appears that the predominance of micas, smectites, calcite and kaolinite and even quartz in the clay fraction are controlled by different processes of transport, transformation and neoformation (Coringa et al., 2012(Coringa et al., , 2014Dias et al., 2020;Furquim et al., 2008Furquim et al., , 2010bOliveira Junior et al., 2017;Oliveira et al., 2021). The minerals come from sediments from surrounding geological formations (Coringa et al., 2012;Oliveira Junior et al., 2017;Oliveira et al., 2021). ...
... The minerals come from sediments from surrounding geological formations (Coringa et al., 2012;Oliveira Junior et al., 2017;Oliveira et al., 2021). The intense process of evapotranspiration of the saline lagoon water promotes the precipitation of Ca, Mg and K and consequent participation in autigenic mineral phases, such as carbonates, smectites and probably micas around the saline (Barbiéro et al., 2002;Dias et al., 2020;Furquim et al., 2010b). ...
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The Nhecolândia region is formed by sandy sediments, coming mainly from the Taquari river basin, with soil sodification and the accumulation of organic matter in the subsurface being the main pedogenic processes observed in this environment. This research aimed to study the genesis of soils with spodic features in the subsurface horizons in an alkaline environment in the saline lagoons of the Pantanal of the State of Mato Grosso do Sul, Brazil. Three trenches were excavated, and the soils were morphologically described and classified according to Brazilian Soil of Classification System in Espodossolos and WRB in Arenosols. In addition, deformed samples from all soil horizons were sampled and used in physical, chemical, mineralogical and micromorphological analyses. In all profiles, the sandy texture predominates (sand ≥879 g kg⁻¹) the colors vary from light olive-brown on the surface horizons to grayish-brown-very dark on the subsurface horizons, with hues ranging from 2.5Y to 5Y. In the profiles, the occurrence of the E horizon was observed, followed by the subsurface horizon with cementation, forming ortstein. The profiles showed high pH values (6.8–10.2), electrical conductivity (EC) > 4 dS m⁻¹, and high saturation for Na⁺ (up to 60.6%), characterizing them as saline-sodic soils. In the soils around the saline lagoon, it was observed the accumulation of Fe (Fe2O3), Al (Al2O3) and dissolved organic carbon (DOC) in the horizons with spodic features. Among the humic substances, the humin fraction presented the highest levels, mainly in the B horizons, with variations from 0.1 to 6.2 g kg⁻¹. In the thin sheets, coatings and fillings were observed, consisting of organo-ferruginous colloidal material of brown to opaque color with monomorphic characteristics, covering and binding the quartz grains. Alkaline soil conditions in saline lakes contribute to the dissolution of clay minerals and surface organic matter, and later, to the dispersion of dissolved organic compounds together with Al2O3, Fe2O3, and amorphous silica, forming subsurface horizons rich in organic matter, Al, neoformed clay minerals and ortstein cemented horizons.
... The few published studies about the mineralogy of Pantanal use material from the sub-regions of north Pantanal (Coringa et al. 2012(Coringa et al. , 2014Couto et al., 2017;Olivera Junior et al. 2017. In south Pantanal a few studies have been carried out in the sub-region of Nhecolândia; although they are very specific to saline soils with a sandy texture (Schiavo et al., 2012;Barbiero et al. 2008Barbiero et al. , 2016Barbiero et al. , 2016Furquim et al. 2008Furquim et al. , 2010aFurquim et al. , 2010bFurquim et al. , 2017Furquim et al. , 2010aFurquim et al. , 2017McGlue et al., 2017;Dias et al., 2020;Andrade et al., 2020). However, in other sub-regions of south Pantanal, there are soils formed by felsic and carbonate minerals, which present a morphology with a prismatic structure, hard consistency when dry, plastic and sticky when wet, a vertic character and elevated fertility. ...
... These characteristics contributed to the formation of illite/smectite minerals with some differences in relation to profiles P1 and P2. The high levels of MgO and the low levels of Al 2 O 3 identified in the EDS suggest the formation of Fe Mg-smectites trioctahedral in this profile (Furquim et al., 2010a;Oliveira Junior et al., 2019;Dias et al., 2020). The activity of the high clay fraction in the ABk horizon of the P3 profile, much higher than the clay activity of the other profiles, is probably the result of the formation of trioctahedral smectites. ...
... The chemical characteristics of water from rivers and/or underground sources, with high pH rich in cations such as Na + , Ca 2+ K + and Mg 2+ associated with soil solution with low levels of Fe 3+ , Fe 2+ and Al 3+ , favor the formation of silicates rich in Mg such as the trioctahedral Mg-smectite (Barbiero et al., 2016;Oliveira Junior et al., 2019;Dias et al., 2020;Furquim et al., 2021). Furquim et al. (2008Furquim et al. ( , 2010a proposed the hypothesis of authigenic Mg-smectite formation by chemical precipitation directly from the lake and not by the recrystallization of a clay precursor. ...
Article
The genesis of clays in Pantanal soils is influenced by parent material, water seasonality and elevated temperatures, resulting in soils with attributes not so common in other tropical regions. This research aimed to study the genesis of minerals in the clay fraction present in three soil profiles developed from carbonate sediments in Pantanal of the State of Mato Grosso do Sul, Brazil. Three trenches were excavated, and the soils were morphologically described and classified according to WRB in Chernozem (profiles P1 and P3) and Gleysol (P2). In addition, deformed samples from all soil horizons were sampled and used in physical, chemical, and mineralogical analyses. Clay fraction obtained from the diagnostic subsurface horizons of the profiles was submitted to identification of the mineral phases using X-ray diffraction, morphological analysis in a scanning electron microscope and microchemical analysis using energy dispersive X-ray spectroscopy. In the three profiles, the presence of interlayered minerals of kaolinite-smectite and illite-smectite; quartz and calcite in profile P3, was confirmed in the clay fraction. The clays from the three profiles presented high levels of SiO2 (ranging from 35.4 to 56.7%). The clays from profiles P1 and P2 presented high levels of Al2O3 (P1 = 24.6% and P2 = 15.2%), Fe2O3 (P1 = 14.0% and P2 = 11.8%), which suggests the formation of dioctahedral clay and illite rich in Fe. The high levels of MgO (11.1%) and Fe2O3 (7.2%) in clays of the P3 profile indicated the presence of trioctahedral Mg-smectite and illite rich in Fe. In the studied soils, the condition of moderate to imperfect drainage, water from the water table rich in cations and the alkaline environments of soils, constitutes the principal factor responsible for the current dynamics of neoformation of dioctahedral illite rich in Fe and trioctahedral Mg-smectite and dissolution of kaolinite.
... One of the papers focuses on inclusions remaining from a high P metamorphism in rocks affected by a complex metamorphic history, which includes prograde as well as retrograde processes [59]; another [60], with garnet nucleation and growth, which record the initial steps of dehydration within the subduction zone. Two of them present mineral transformations in the smectite-illite system during diagenesis, either of chemical [61] or burial [28] origins, and a third the incorporation of B, coming from the transformation of organic matter, into the illitic tetrahedral layers [62]. The last one [63] uses the clay transformations and related parameters to Minerals 2020, 10, 879 3 of 7 establish the pressure/temperature conditions in a key region for the interpretation of the Eurasia-Africa collision in Cenozoic times. ...
... One of the papers focuses on inclusions remaining from a high P metamorphism in rocks affected by a complex metamorphic history, which includes prograde as well as retrograde processes [59]; another [60], with garnet nucleation and growth, which record the initial steps of dehydration within the subduction zone. Two of them present mineral transformations in the smectite-illite system during diagenesis, either of chemical [61] or burial [28] origins, and a third the incorporation of B, coming from the transformation of organic matter, into the illitic tetrahedral layers [62]. The last one [63] uses the clay transformations and related parameters to establish the pressure/temperature conditions in a key region for the interpretation of the Eurasia-Africa collision in Cenozoic times. ...
... The work by Armstrong and co-authors presents a study of the clay mineralogy of sediments from several lakes from the Nhecolândia region [61], the southernmost region of the Pantanal Wetland (Brazil). Sediment samples were analyzed by X-ray diffraction and fluorescence as well as scanning and transmission electron microscopy, together with the geochemical characterization of the lake waters, including in situ determination of pH, EC, and TDS. ...
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Rocks affected by pressure–temperature conditions in the transitional field between diagenesis and low-grade metamorphism make up large domains of the Earth’s upper continental and oceanic crust [...]
Article
The Codó Formation is an Aptian marine-influenced lacustrine depositional system in the Parnaíba Basin (Brazil). This unit is an important sedimentary succession because of the high organic matter content and for being an ancient analog for the depositional systems of the Brazilian Pre-salt interval. However, mineralogical and lithogeochemical studies have not been sufficiently carried out on the Codó Formation, which hinders detailed sedimentological knowledge. We report new mineralogical and lithogeochemical data that allow a better understanding of the environmental, climatic, and provenance evolution of the Codó deposits. Mineralogical and lithogeochemical studies were performed on 50 lutite samples collected from the 1-UN-32-PI core and 13 outcrop lutite samples obtained from sites close to the Grajaú and Imperatriz regions. A magnesium-sulfate-rich shallow alkaline hypersaline lake was identified in the lower Codó Formation based on the identification of a clay mineral assemblage composed of authigenic saponite and detrital illite. Hydrothermal processes were interpreted as the magnesium source of this alkaline lake. A salinity-alteration event was identified at the upper limit of the alkaline lake and was interpreted as the first marine ingression in the Codó Formation. This event changed the lake's pH from alkaline to acid, inhibiting the formation of Mg-smectites, and changing its hydrochemical conditions, originating a marine-influenced sulfate-rich acid saline/hypersaline sabkha. This facies succession coincides with a clay mineral assemblage composed of detrital montmorillonite, illite and kaolinite. A regional paleoclimate humidification process was identified from the sabkha to a lagoon facies succession in the upper Codó Formation. This last succession reveals the marine-dominated interval of the Codó Formation and coincides with a clay mineral assemblage composed of detrital kaolinite, montmorillonite and illite. Based on lithogeochemical data, a common post-Archean intermediate source area was also interpreted for these three environments.
Article
Carbonate deposits and sedimentary records from lake in southern Patagonia provide an excellent contribution in the regional environmental register. Laguna Timone maar crater is situated in the Pali Aike Volcanic Field, a Quaternary volcano-tectonic complex in southern Patagonia and represent one of hundreds of “pools” of brines developed after explosive volcanic eruptions in a periglacial environment. The lake constitutes an endorheic hydrological system where processes leading to carbonate precipitation under extreme physicochemical conditions and biological influences can be explored. Laguna Timone is recharged by groundwater and sporadic episodes of precipitation (ca. 200 mm per year). The strong winds regimes are responsible for high evaporation rates in this area. Carbonate precipitation was studied in microbialites fragments of tufa deposits and carbonate crust located in the edge of lake. The mineralogy of both is composed by calcite … The clay fraction of sediment that underlying carbonates was characterized. HRTEM analysis shows that authigenic smectites has influence on calcite crystals precipitation. The positive δ¹⁸O values (2.28‰) in the crust are associated to evaporation processes. In contrast, the δ¹⁸O values (-6.52‰) in the microbialites shows meteoric and/or groundwater influences. The δ¹³C (-0.43 ‰ to 2.50 ‰) values indicate physico-chemical and biochemical processes controlling the precipitation. The carbonate precipitation involves the interrelations of hydrogeological properties, climate and biological influences. Laguna Timone provides a natural laboratory for understanding of mineral precipitation processes that register continuous climatic and environmental archives