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The formation of 2:1 and 1:1 phyllosilicates in Fe–Si–O–H systems occurs in various geological and engineering settings; however, the identification and characterization of these minerals is very challenging due to the limited amount that is accessible, the very small particle size, and often the large degree of heterogeneity of these samples. To overcome these drawbacks, the synthesis of iron-rich phyllosilicates was attempted in this study with an initial Fe/Si molar ratio ranging from 0.50 to 2.33. The synthesis was performed at 150°C under hydrothermal conditions over a period of 7 days. Synthesis products were characterized by X-ray diffraction and fluorescence, by infrared, Raman, and Mössbauer spectroscopies, and by transmission electron microscopy. Results revealed that the stability field of the 2:1 clay mineral was wider than that of the 1:1 clay mineral. The 2:1 clay mineral was less sensitive to redox conditions compared to the 1:1 clay mineral. In addition, a heterogeneity of phases formed (iron oxides, nontronite, cronstedtite, or greenalite) was identified. [ABSTRACT FROM AUTHOR]

Sedimentary records suggest that the mid-Proterozoic (ca. 1.8–0.8 Ga) was persistently characterized by a greenhouse climate despite significantly lower solar luminosity compared to modern levels. To maintain greenhouse conditions, the partial pressure of carbon dioxide (pCO2) must have remained elevated, possibly indicative of key differences in the complexities of the carbon cycle compared to the modern. Modeling has suggested that high pCO2 was likely maintained by elevated rates of "reverse weathering:" marine authigenic clay formation, a process that consumes alkalinity and generates CO2. This process is kinetically slow in modern marine environments, yet is hypothesized to have been enhanced during the mid-Proterozoic due to the greater availability of important species for clay authigenesis such as silica and ferrous iron. This hypothesis is testable using the geological record, because enhanced reverse weathering would lead to the formation of abundant marine authigenic clays. However, the distribution of marine authigenic clays in the Proterozoic sedimentary record has not been paid sufficient attention. In this study, we report the presence of authigenic clays (glauconite and berthierine) from the Xiamaling Formation (ca. 1.4 Ga), North China. The glauconite-berthierine horizons occur as millimeter- to centimeter-thick laminae interbedded with muddy siltstone and feature detrital grains supported by the clay matrix. In places, these layers were partially reworked to form soft and cohesive intraclastic sands, suggesting a syndepositional origin. We hypothesize that marine iron cycling in the iron- and silica-rich mid-Proterozoic oceans may have facilitated the formation of authigenic iron-rich clay during the deposition of the Xiamaling Formation. The formation of iron-hydroxides on the seafloor—and the local increase in pH caused by subsequent dissimilatory iron reduction—could have resulted in the absorption of SiO2, Al(OH)3, and Fe(OH)2 to form soft, cohesive and noncrystalline Fe(OH)3-SiO2-Al(OH)3-Fe(OH)2 gels. These gels would have subsequently converted to glauconite/berthierine through aging. The transformation from glauconite-rich layers to berthierine-rich laminae was likely facilitated by a greater availability of Fe(II), and therefore higher Fe(II)/TFe and Fe/ Si ratios. We suggest that the relatively rapid formation of syndepositional, seafloor berthierine and glauconite layers in the basal Xiamaling Formation is the result of enhanced reverse weathering during this time. This study provides an important geological support for carbon cycle models that invokes enhanced reverse weathering rates in the mid-Proterozoic ocean that may have helped to maintain a high-baseline pCO2 during this time. [ABSTRACT FROM AUTHOR]

The bauxite-bearing Paleozoic weathering crust of the Kursk Magnetic Anomaly (KMA) is developed along the inter-ore schists of the ferruginous-siliceous formation of the Kursk series. In the banded iron formations, the weathering crust is represented by high-grade iron ores forming a series of deposits with bauxites. They are confined to the ridges of banded iron formations, which tower up in the relief of the Precambrian and are overlain by a thick layer of sediments. The recently obtained rock material studied with the use of precision methods enabled a significant refinement and adjustment of the existing ideas about KMA bauxites. Based on their texture, structure, and mineral composition, the following five main types were singled out: 1 – finely porous substantially boehmite, 2 – macroporous berthierine-boehmite, 3 – stony hydrohematite-berthierine-boehmite, 4 – massive berthierine-kaolinite-boehmite, 5 – pseudo-bean substantially gibbsite and berthierine-gibbsite. Mostly gibbsite varieties gravitate toward the northern part of the Belgorod ore region, while boehmite varieties are more abundantly distributed in its southern part. The main bauxite minerals are boehmite, gibbsite, berthierine, and kaolinite; the minor ones are illite, hematite (hydrohematite), quartz, goethite, chamosite, pyrite, carbonates, and accessories. They formed in several stages. In the pre-Devonian (pre-Eifel) time, an illite weathering crust formed along the inter-ore schists. Since the Givetian time, an illite-kaolinite profile has been developing due to the climate humidization and the emergence of terrestrial vegetation. Laterites with bauxite appeared in the Early Carboniferous and only in the Belgorod region of the KMA, because the latter was not blocked by the sea basin, unlike the rest of the territory. The processes superimposed on the weathering crust led to silicification and carbonation of the uppermost parts of the bauxite section.

This study presents detailed sedimentological, geochemical, and mineralogical evidence of green clay formation at the basal part of the early Maastrichtian Kallankurichchi Formation, Cauvery Basin, India. Immediately overlying a basal scree conglomerate, the highly fossiliferous Kallankurichchi Formation hosted a ∼ 3.5 m thick dark grey limestone containing abundant green clay minerals formed by the alteration of metastable framework grains. Abundant fresh to partially palagonitized sideromelane glass and occasional preservation of gas bubble structures in green clays strongly suggest a volcaniclastic source. Petrographic observations manifested primary occurrences of the green grain pseudomorphs mimicking the shape of the precursor volcanic grains. The X-Ray Diffraction analysis of the randomly oriented bulk sample and oriented, smear-mounted green clay separates identified the berthierine by the strong ∼7 Å basal spacing. The mineral chemical data of the berthierine grain pseudomorphs recorded substantial compositional variation from Mg-, Si- and Al-rich core and Fe-rich rim, characterizing the maturation of berthierine from volcaniclastic substrate through 'proto'-berthierine. Tiny berthierine flakes (1–5 μm long) grew vertically from the mineral grain boundary and feldspar cleavages, suggesting its authigenic origin. Contemporaneous tectonic events, marked by abundant slide planes, suggested continuous sagging of the basin, causing oxygen-depleted bottom water conditions. The unusual appearance of berthierine as grain pseudomorphs, rarely reported from the rock record, revealed the dissolution of metastable volcaniclastic grains in a slightly acidic, oxygen-depleted depositional environment as the primary mechanism of authigenesis. The early diagenetic calcite cementation ceased the berthierine formation, preventing compaction and transformation. • Rare occurrence of berthierine pseudomorph from the lower Maastrichtian Kallankurichchi Formation, Cauvery Basin, India. • A strong influence of tectonism and volcanism has been established facilitating authigenic green clay mineral formation. • A direct link between berthierine formation and volcanism related iron supply has been established. [ABSTRACT FROM AUTHOR]

Studying with precision methods the mineral composition of bauxites in the Kursk Magnetic Anomaly (KMA) made it possible to reevaluate the conditions of their formation. Occurring among Early Proterozoic jaspilites in the Belgorod ore region, they are confined to the upper part of the Early Carboniferous lateritic weathering profile on the biotite–muscovite schists. The northern part of the region is dominated by the pseudopisolitic gibbsite ores; the southern part, by the boehmite varieties with an inherited layered structure of parent rocks. Along with aluminum hydroxides, berthierine is a rock-forming (major) mineral in these bauxites. Previously, berthierine was attributed to the subsequent transformation of bauxites. Our data suggest the existence of two berthierine generations. The first generation represents a natural intermediate mineral related to the formation of bauxites during Fe concentration in the weathered rocks. Therefore, we can substantiate a certain stage in the evolution of bauxite formation in the Earth's history leading to the formation of Paleozoic deposits. [ABSTRACT FROM AUTHOR]

The formation conditions and stability fields of Fe-serpentines are still poorly understood in both terrestrial (natural or anthropic) and extraterrestrial environments. Knowledge of the effects of physical-chemical parameters on compositional and structural features of Fe-serpentines is lacking, and only a few thermodynamic parameters of these minerals are available in the literature. To fill these gaps, the synthesis of these minerals, while controlling all the physicochemical experimental parameters, was undertaken. Two hydrothermal syntheses were carried out at 90°C to investigate the effect of two different starting mineralogical mixtures on the nature of Fe-serpentines. The run products were identified by several analytical techniques (powder X-ray diffraction, transmission, and scanning electron microscopy). Berthierine crystals were synthesized from a starting mixture of kaolinite and metal iron. The berthierines synthesized show different morphologies and iron contents (~3–38 at.%). From a starting mineralogical mixture composed of quartz and metal iron, cronstedtite crystallizes. Most of the crystals are 1M polytypes. Magnetite is always associated with both berthierine and cronstedtite. Lepidocrocite was observed only in the experiment with kaolinite. These experimental results demonstrated that Fe enrichment in serpentines depends on the silicate precursor (kaolinite or quartz) of the starting mixture. The results are also in agreement with the geochemical equilibrium predicted by thermodynamic modeling, i.e. the formation of berthierine and cronstedtite in association with magnetite at the expense of metal iron and silicates. [ABSTRACT FROM AUTHOR]

The kaolinite-to-chlorite conversion is one of the chloritization processes that occurs in low temperature diagenetic and hydrothermal systems. The mechanism of this mineralogical transformation is still under discussion, since direct transformation, conversion via berthierine as intermediate phase or direct formation of berthierine/chlorite mix, either by dissolution-crystallization or by solid state transformation (or a combination of both), are all hypotheses put forward. In this context, each description of a kaolinite-to-chlorite conversion occurrence becomes an opportunity to shed new light and to renew this debate. Studying Carboniferous shale–crosscut by large quartz-kaolinite veins–from the mining basin of the North of France, we report therefore an uncommon kaolinite-Fe-rich chlorite assemblage. This assemblage appears as a chlorite fringe 20 µm wide along the interfaces between the shale and the quartz-kaolinite veins. All petrographical, mineralogical and chemical data suggest that the Fe-chlorite results from the interaction between the shale, providing the Fe,Mg supply, and the Si,Al-rich veins, leading to the chloritization of the kaolinite at a small scale via at least one dissolution-recrystallisation step. High-resolution observations highlight that neoformed Fe-rich chlorite contains some 7Å isochemical layers, as relict of berthierine. Therefore, we advance that the conversion takes place either through the precipitation of berthierine following by a second step involving solid state berthierine-chlorite conversion, or through the direct precipitation of a chlorite-rich/berthierine-poor mix driven by the Fe/(Fe + Mg) ratio, at low temperature and in reducing conditions. The comparison of our data with the recent literature allows to prefer the second hypothesis.

In an effort to evaluate mineral-water isotopic exchange during cyclic steam stimulation (CSS), solutions and <2 μm berthierine-dominated solids from the Clearwater Formation oil sands of Alberta, Canada were analyzed for stable isotope compositions before and after reaction in autoclaves for 1008 h at 250 °C. There was no significant change in solution δ18O and δ2H, which is consistent with the high water/mineral ratio used in the experiments. The solids showed a marked decrease in both δ18O and δ2H following the experiments. Pre-run solids have δ18O of +9.5 to +12.9‰ and δ2H of −114 to −113‰, whereas post-run solids have δ18O of −4.7 to +2.1‰ and δ2H of −147 to −128‰. Neither oxygen- nor hydrogen-isotope equilibrium was established between the solids and the solutions. Calculation suggests that oxygen-isotope exchange (44–58%) was greater between the solids and the solutions than was the case for hydrogen isotopes (23–50%). We propose that this behaviour resulted from partial inheritance of the pre-run berthierine structure during formation of the post-run smectite, chlorite-smectite and chlorite. This process confounds the use of clay mineral stable isotope compositions as a temperature indicator of in situ steam/steam condensate interaction with oil-sands reservoirs. The results also suggest an additional mechanism by which new clay minerals can be formed during CSS-related, artificial diagenesis. Image 1 • Alberta oil sands clay was reacted at 250 °C for 6 weeks in low 18O &2H solutions. • Berthierine-rich clays transformed to smectite with lower δ18O and δ2H. • Smectite and solutions are not in oxygen- and hydrogen-isotope equilibrium. • Post-reaction smectite isotopic composition is inherited partly from berthierine. [ABSTRACT FROM AUTHOR]

Abstract The Vectis Formation was deposited in a restricted lagoonal environment that periodically dried up, as indicated by the presence of desiccation surfaces. The fauna indicates that salinities fluctuated significantly during deposition, from fresh to brackish-marine. Pre-burial berthierine-rich clay replaced faecal pellets in the sediment, infilling desiccation cracks, during re-flooding of the lagoon. Concretions formed by early pyrite and apatite cementation during initial burial in lake sediment, with organic debris of fish and wood, acting as nuclei and a trigger for cementation. With subsequent partial or complete exhumation oxidation of the pyrite occurred, prior to cementation by Mn siderite. All further concretion cementation occurred within the oxic to sub-oxic diagenetic zones. Textural relationships indicate that commonly occurring baryte formedafter pyrite oxidation and represents the last diagenetic mineral phase. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various forms of chamosite and berthierine occur within Nb-Zr-REY-Ga deposits. • Chamosite and berthierine mainly derived from Fe-Mg-rich hydrothermal fluids. • Part of berthierine sourced from the alteration of precursor detrital materials. • A scenario of the transformation mechanism of clay minerals has been proposed. • The Nb-Zr-REY-Ga mineralization occurred in a low-temperature thermal condition. Clay minerals are generally used as pivotal indicators to reveal diagenetic parameters such as temperature and pH in hydrothermal ore-forming systems. Within the Late Permian Nb-Zr-REY-Ga-mineralized horizons in eastern Yunnan, the elevated enrichment of critical metals has been considered to be closely associated with abundant clay minerals. In this paper, the identification, abundance, morphology, modes of occurrence, and chemical compositions of two phyllosilicate minerals, namely chamosite (chlorite group) and berthierine (serpentine-kaolinite group) were analyzed by XRD (X-ray diffraction) and SEM-EDS (scanning electron microscopy equipped with an energy dispersive X-ray spectrometer). The results show that chamosite mainly occurs as massive and book-like aggregates, while berthierine occurs in various forms, including coarse granular, spherulitic, sheaf-like, sharp-angular, and vermicular aggregates. The modes of occurrence and scatter plots of Mg/(Mg + Fe) vs. Al/(Al + Fe + Mg) of chamosite indicate a Fe-Mg-rich siliceous hydrothermal origin. In the Al/Si-Mg/Fe diagram, analysis points for berthierine are distributed in the partially overlapping fields of hydrothermal ore, laterite/bauxite, and marine, indicating that the formation of berthierine was influenced by various geological factors. Based upon its chemistry and modes of occurrence, berthierine mainly originated by direct precipitation from Fe-Mg-rich siliceous hydrothermal fluids, but in some cases, it was derived from the replacement of precursor minerals and the in-situ alteration of volcanic fragments. A scenario of the transformation mechanism of clay minerals in the Nb-Zr-REY-Ga-rich horizons is proposed. Airborne volcanic glasses and primary minerals were initial altered in-situ into vermicular kaolinite and angular berthierine in the early diagenetic stage. Subsequently, some vermicular kaolinite and the oolitic berthierine crystallized from solutions underwent gradual illitization, and some pre-existing minerals (e.g., albite, kaolinite, and illite) were altered into berthierine, while a proportion of chamosite transformed from berthierine through an interstratified berthierine/chamosite (B/C) in the middle to late diagenetic stages. Throughout all stages of diagenesis, the chamosite, berthierine, and their intermediate phases precipitated directly from Fe-Mg-rich siliceous hydrothermal fluids. Moreover, the diagenetic temperature revealed by chamosite is from ∼200 to ∼302℃, indicating that the Nb-Zr-REY-Ga mineralization and chamosite formation occurred under low-temperature thermal alteration conditions. [ABSTRACT FROM AUTHOR]

Studies on reservoir quality associated to chlorites in turbidites are quite rare and in recent studies on that topic, chlorite is generally a minor mineral. Moreover chlorite coatings are generally described for their major role in porosity preservation by preventing from quartz cement overgrowths, and only few studies describe their role in reducing permeability when present in excess in the reservoir. The objective of this study is therefore to focus on the material sourcing deep sea turbidites and its impact on the chlorite petrographic/mineralogical characteristics and abundance, and the resulting current reservoir quality. This study focuses on Lower Cretaceous Agat Formation (Måløy Slope, Norwegian North Sea) hosting two reservoirs of contrasted quality. It is based on drill-hole to micrometer scale investigations using QEMSCAN mapping, scanning electron microscopy equipped with an energy dispersive spectrometer, X-ray diffraction, and FEG SEM observation of ultrathin sections. Chlorite of Ib polytype, inherited from berthierine precursor, is observed in both reservoirs. Its homogeneous composition suggests that the geochemical controls of chloritization are similar for the two reservoirs. Grain replacing chlorite, clay replacing chlorite and chlorite coatings are observed in both reservoirs but the grain coatings present different textural configurations. In the upper reservoir, the clay coating is dominated by chlorite platelets whose growth is controlled by geometrical selection. In the lower reservoir, the chlorite coating differs by an additional inner part consisting of a diagenetic-recrystallized clay coat. The preburial material consists of ferric illite (± glauconitic pelloids). The illite morphology is considered to be inherited from an earlier supergene vermiculitization of phyllosilicates in saprolites. As ferrous iron dominates in berthierine/chlorite, a change in redox conditions is needed for Fe illite-berthierine transformation that could be linked to bacteria activity. These results provide a better understanding of the diagenetic process and influence of the material provenance in the evolution of the reservoir properties. • Crystal-chemistry, textural properties and origin of chlorite coating in turbidites formations. • Crystal-chemistry of green "glauconitic" clays. • Dual origin hypothesis for Fe-bearing clays (Fe-illite, glauconite) in the sedimentary material. • Contribution of hinterland weathering profiles of plutonic rocks under tropical climate to the source material of sediments. [ABSTRACT FROM AUTHOR]

Berthierine and chamosite are iron-rich clay minerals that share similar chemical compositions. Berthierine forms at low temperature (25-45 °C) during early diagenesis and may transfer to chamosite at temperatures of ≥70 °C. Because the formation of berthierine and chamosite requires significant amount of Fe2+ supply, their presence in marine sediments is often used as a mineral proxy for ferruginous conditions in porewater. Recent studies reveal that the Precambrian oceans were characterized by pervasive ferruginous water-column conditions that may favor the formation of iron-rich clay minerals like berthierine and chamosite. To evaluate if ferruginous water-column conditions in the Precambrian ocean played a role on iron-rich clay mineral formation, we conducted an integrated petrographic, mineralogical, and geochemical study on the chamosite -and glauconite-bearing strata of the Mesoproterozoic Xiamaling Formation (~1.40-1.35 Ga) in North China. Petrographic, XRD, SEM, and EDS analyses show that the chamosites of the Xiamaling Formation was transferred from glauconite, with berthierine as an intermediate mineral phase during early diagenesis. Geochemical analyses indicate that a complete transformation from glauconite-dominated to chamosite-dominated end-members (samples) requires an addition of a large amount of Fe (16.9 wt%), Mg (2.4 wt%), and a small amount of Al (1.4 wt%), but a simultaneous release of Si (11.8 wt%) and K (6.0 wt%). Considering that the glauconite- and chamosite-bearing strata are devoid of iron-rich detrital minerals (e.g., biotite and iron oxides) and lack evidence of hydrothermal alteration, the required Fe2+ for glauconite-berthierine-chamosite transformation was most likely from Fe2+-rich (ferruginous) seawater, which may have promoted glauconite-berthierine transformation at the very early diagenetic stage when Fe2+ exchange between porewater and seawater was still available. This interpretation is consistent with the high FeHR/FeT (but low Fepy/FeHR), Fe/Al, and V/Al ratios from the hosting strata that support ferruginous depositional environments. Because most Precambrian strata have passed the oil window temperature (>50-150 °C), the preservation of berthierine would be rare and chamosite should be the representative iron-rich clay mineral. Thus, the abundance of chamosite in fine-grained, marine siliciclastic sediments may be used as a mineral indicator of ferruginous water-column conditions. [ABSTRACT FROM AUTHOR]

The distribution of octahedral cations in the two component layers of a 7 Å-14 Å interstratified mineral with a bulk chemical composition (Fe2+4.12Mg0.07Mn0.01Al1.69□0.11)(Si2.56Al1.44)O10(OH)8 was investigated using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) in combination with the image simulations. In the 14 Å component layers, comparison between the observed and simulated images revealed that the M4 sites of the interlayer sheets were occupied preferentially by Al together with a small amount of Fe; the other M1, M2 and M3 sites were occupied by dominant Fe and residual Al in equal proportions. Two types of octahedral sheets with disordered and ordered cation distributions were recognized in the 7 Å component layers. The two types of sheets were similar to the octahedral sheet of the 2:1 layer and the interlayer sheet in the 14 Å layer above, respectively. Irregular vertical stacking and lateral contact of the different component layers in structure and chemistry characterized the interstratification, which may be caused by rapid precipitation and accretion of the component layers in hydrothermal environments. [ABSTRACT FROM AUTHOR]

• Seven continental and basinal sedimentary facies associations in Ediacaran of Baltica. • Hot and humid Ediacaran climate on Baltica. • Mineral authigenesis widespread in both proximal and distal environments. • Tropical, disoxic conditions in the Ediacaran indicated by berthierine. • Marine oxic conditions in the Cambrian indicated by glauconite. Mineralogical and geochemical compositions of mudstones were used for untangling provenance and climatic signals preserved in the upper Ediacaran - lower Cambrian strata from the western part of the East European Craton (ECC). Quantitative mineralogy and geochemistry data were obtained for 735 argillaceous rock samples from 71 wells and outcrops and compared with the analyses of Proterozoic palaeosols from the same area. Additionally, sedimentological analyses of well-preserved cores were performed to reconstruct predominant Ediacaran and early Cambrian environments. Seven major facies associations were distinguished and interpreted as both continental and basinal in nature. Terrestrial environments include weathering crust, alluvial fans, and associated interlobe areas, fluvial channels, floodplains, and lakes. Transitional environments are represented by tidal lithofacies, whereas central bay and upper offshore facies associations are typical of distal deposits. The central basin area is interpreted as an estuary opening toward the east, while a separate basin developed in Podillya. Provenance heavily influenced the mineralogical and geochemical characteristics of the sediments and affected derived weathering indices. The change from mafic to felsic sources in the western ECC is evident towards the Cambrian. All geochemical and newly introduced mineralogical weathering indices show advanced kaolinite-type weathering, evidence of a hot and humid climate during this interval. Based on these indices, mudstones are weathered to a greater extent than palaeosols. This observation is interpreted as resulting from the redeposition of highly weathered topsoils, combined with additional weathering on-route to the basin. Mineral authigenesis (berthierine, pyrite, goethite, fluorapatite, and carbonates) was particularly intensive in the terrestrial interlobe areas. Berthierine is common in most environments, which reflects the reaction of kaolinite with iron oxides, mediated by microorganisms, in shallow dysoxic tropical waters, with high lateritic sediment input. Marine, more oxic conditions in the Cambrian are indicated by a pervasive appearance of glauconite. [ABSTRACT FROM AUTHOR]

Chemical reactions between oil-sands and injected steam or steam condensate during cyclic steam stimulation (CSS), commonly used to mobilize heavy oil and bitumen, result in decomposition of pre-existing minerals and formation of new phases including clay minerals. These changes can reduce reservoir permeability and limit hydrocarbon recovery. In this study, the chemical and stable isotope compositions of berthierine and smectitic clay minerals contained in pre- and post-steam Clearwater Formation oil-sands from Cold Lake, Alberta were analyzed to investigate how these phases were affected by CSS. Berthierine abundance in the injection-zone decreased after steaming whereas the abundance of smectitic clay minerals increased. Pre- and post-steam berthierine exhibited the same range of chemical compositions, while those of pre- and post-steam smectitic clay minerals commonly differed. Some post-steam smectitic clay minerals from the steam injection-zone, in particular, contain significantly more Fe and Si but less Al than pre-steam samples. It is proposed that that berthierine contributed to the formation of new smectitic clay minerals during CCS through partial inheritance of the berthierine 1:1 structure. This inheritance model approximates the unique chemical compositions of the post-steam smectitic clay minerals. The model also helps to explain the incomplete oxygen and hydrogen isotope exchange between injection fluids and smectitic clay minerals formed during CSS. • Steaming of Clearwater Formation oil-sands decreased (increased) berthierine (smectite) abundances. • Post-steam smectite contains more Fe and Si but less Al than pre-steam smectite. • New smectite partially inherited the berthierine structure. • Berthierine inheritance explains incomplete O- and H-isotope exchange of new smectite. [ABSTRACT FROM AUTHOR]

Berthierine as the only authigenic Fe-rich clay mineral occurs in an oil-bearing, glauconite-rich sandstone (Paleocene Heimdal Member of the Lista Formation, Danish North Sea). Based on the results of thin section, transmission and scanning electron microscopy, five different morphological types of berthierine were identified: (1) mainly as grain-coatings partly together with authigenic quartz covering detrital grains, (2) as pore-filling clay in open pores, (3) small crystals in transformed glauconite grains, (4) small crystals associated with siderite in layers of mica/micaceous glauconite, and (5) as elongated crystals in siderite concretions. Although different in occurrence, all berthierine types investigated by microprobe analysis are of similar chemical composition, suggesting similar precipitation conditions. Investigations by transmission electron microscopy reveal that fine berthierine crystals display straight parallel layers with a typical lattice fringe spacing of 0.7 nm, and that their occurrence is intimately connected to oil phases in pore space. Partly, berthierine textures resemble mineralized oil–water emulsions. Berthierine is more abundant in the oil leg than in the water leg, but occurs especially abundant at the oil–water contact. The coexistence of berthierine together with quartz overgrowth, but also its appearance in glauconite indicates that berthierine formed in situ and that it is a product of glauconite dissolution. Berthierine formation is coupled to the reduction of aqueous Fe 3+ into Fe 2+ derived from glauconite dissolution, and is related to fluid–rock interactions triggered by oil degradation which occurred in the oil-filled zone and at the oil–water contact. The biomarker parameters pristane/ n -C 17 and phytane/ n -C 18 indicate an increased extent of oil degradation at the oil–water contact. On the one hand, soluble oil degradation products (methane, carbon dioxide, and hydrogen) changed the hydrogeochemical conditions (such as pH, pe, alkalinity, etc.), and controlled dissolution of glauconite (and feldspar). On the other hand, the changed hydrogeochemical conditions led to berthierine and quartz precipitation in water-wet reservoir intervals. [ABSTRACT FROM AUTHOR]

Berthierine formation reduces the permeability of the glauconitic reservoir sandstones in the Siri oilfield (Danish North Sea), and is therefore a considerable production factor. A new hydrogeochemical batch model that is based on thermodynamics of chemical equilibrium was developed to identify the processes which activated and controlled berthierine formation. A good match has been achieved between the mineralogical alteration features observed in the Siri field and the results of the batch modeling. This match points to the validity of the modeling mechanisms for berthierine formation. Based on the identified mechanisms, the modeling enables to quantify the mass conversion of hydrogeochemical processes in glauconite-bearing and berthierine-forming water–rock–gas systems. The modeling results reveal that intense berthierine formation in the Siri field resulted from in situ glauconite alteration within a more or less closed system due to hydrocarbon degradation-driven water–rock–gas interactions. This process is accompanied by formation of secondary SiO 2(s) and potassium mica. Precipitation of iron-bearing carbonates is prevented by berthierine formation, although the glauconitic sandstones are rich in iron and carbonate species. Moreover, such systems are brought to disequilibrium by the release of reducing and acidic agents originating from oil degradation, and undergo long-term, diffusion-dominated mass fluxes instead of advective mass fluxes. [ABSTRACT FROM AUTHOR]

Berthierine was proven as one of the most important products of glauconite alteration in the Siri oilfield (Danish North Sea). However, there is an ongoing debate regarding the main product of glauconite dissolution: siderite, berthierine, or berthierine as a precursor of siderite and/or magnesium-bearing carbonate. In order to investigate the consequences of glauconite dissolution in view of thermodynamic admissibility and the resulting CO 2 -sequestering capacity, a hydrogeochemical model, which is based on thermodynamics of chemical equilibrium, was developed. Calculating various modeling scenarios helps to conclude on the pH-E H conditions of glauconite dissolution as well as of berthierine formation and dissolution in generic, aqueous systems under elevated temperature-pressure conditions. Our modeling results highlight that carbonate formation cannot be triggered exclusively by CO 2 addition into glauconitic sandstones. The injection of pure CO 2 into glauconitic sandstones leads to acidic and anoxic oxidizing conditions under which glauconite remains stable. To intensify glauconite alteration by CO 2 injection, glauconitic sandstones have to be in contact with degradable organic matter, or, alternatively, reducing agents have to be co-injected with CO 2 . Sufficient electron transfer to ferric iron bound in glauconite is the ultimate control for intense glauconite alteration and for subsequent berthierine precipitation. Once formed, berthierine remains stable over a broad pH range and is not transformed to any carbonate under reducing conditions. Thus, CO 2 injection into glauconitic sandstones under reducing conditions mainly leads to formation of berthierine instead of iron- and magnesium-carbonates. However, hydrogeochemical conditions in the subsurface can affect CO 2 sequestration via glauconite dissolution and the resulting carbonate formation, including the pH-E H conditions, the chemical composition of glauconite, and the overall mineralogical composition of glauconitic sandstones. [ABSTRACT FROM AUTHOR]

New outcrops at the Cerro Matoso open-pit nickel mine permitted to sample sediments found on top of the peridotites to study the textural relationships and composition of phyllosilicates that make up what we propose is a deep marine succession. The appearance and color of mounds and tabular layers divided them into two lithofacies formed by green claystone and black mudstone. The chemical, mineralogical, and petrographic analysis allowed the identification of berthierine and greenalite as the main components of the clay fraction of these rocks. Both phyllosilicates show sharp peaks in the X-ray diffractometry (XRD) diagrams, which show a high degree of "crystallinity". These peaks are produced when the phyllosilicates are formed under ideal conditions of temperature, alkaline pH, and reducing environments, which differ from the supergene and oxidizing environments in which they are now found. The fossiliferous content, in which bivalves, gastropods, and polychaetes predominate, together with the fissured and brecciated textures in the sediments, accompanied by a network of microcracks and open ducts are indicative of marine environments with fluid exhalation that can be related to hydrothermal systems and serpentinization of ultramafic rocks. This work allows us to redefine some units previously described as part of the lateritic profile of Cerro Matoso, i.e., ¨black saprolite and ¨canga mona¨ and to report what would be the first discovery of fauna associated with hydrothermal vents hosted in mantle rocks that were posteriorly accreted during the Cretaceous to the continent. These were recently exposed to humid tropical environmental conditions, where they developed weathering lateritic profiles. • Reducing conditions and high temperatures instead of oxidizing environments are identified during the formation of clays at the top of the Cerro Matoso peridotites. • Fossiliferous evidence helps to support ocean-deep environments in the Cerro Matoso sediments. • Units previously considered as alteration products of ultramafic rocks are redefined as deep-marine sediments (black mudstone and green claystone). • The findings coincide with the serpentinization processes that mantle rocks undergo in ocean ridges and that can host hydrothermal systems and associated fauna. • Evidence of fauna associated with hydrothermal vents is reported, and it would be the first reported in Colombia. [ABSTRACT FROM AUTHOR]

In the context of radioactive waste repository in geological formation, kaolinite-metallic iron interaction in chlorine solution was conducted in batch experiments, under anoxic conditions at 90 °C during 9 months. After a mineralogical characterization at a global scale, products were analyzed at the micrometer and nanometer scales by X-ray absorption spectroscopic techniques (XAS and STXM). Absorption at Al, Si and Fe edges was investigated to have a complete overview of the distribution and status of constituting elements. Whereas Si K-edge results do not evidence significant evolution of silicon status, investigations at Al K-edge and Fe L-edges demonstrate variations at aggregate and particle scales of Al:Al and Fe:Fe ratios. Spectroscopic data evidence the systematic crystallization of Fe-serpentines onto the remaining particles of kaolinite and the absence of pure species (kaolinite or Fe-serpentines). Combination of spatially resolved spectroscopic analyses and TEM-EDXS elemental distribution aims to calculate unit cell formulae of Fe-serpentines layers and abundance of each species in mixed particles. For most of the investigated particles, results reveal that the variations of particles composition are directly linked to the relative contributions of kaolinite and Fe-berthierine in mixed particles. However, for some particles, microscale investigations evidence crystallization of two other Fe-serpentines species, devoid of aluminum, cronstedtite and greenalite. [ABSTRACT FROM AUTHOR]

Interactions between metallic iron and clay minerals have been extensively studied under low-temperature anoxic conditions owing to their potential impact on the long-term safety of high-level nuclear waste disposal in deep geological repositories. To complement the studies investigating the destabilization mechanisms and rates of various initial clay minerals, the prediction of the storage long-term performance requires a comprehensive characterization of the reaction products. The Fe-rich 1:1 phyllosilicates resulting from interactions at 80 °C and in the absence of O2 between metallic iron and smectites with contrasting compositions are thus characterized chemically and structurally using various experimental techniques (X-ray and electron diffractions, infrared, energy-dispersive, and electron energy loss spectroscopies, and high-resolution electron microscopy). Cronstedtite and odinite are the two Fe-rich 1:1 phyllosilicates formed under the experimental conditions investigated, both species differing from their relative contents and the average valence state of structural Fe. No parental link has been evidenced between the two minerals despite their contrasting crystal morphologies and thermodynamical predictions. The formation of the 1:1 phyllosilicates apparently results from the destabilization of the initial smectite through the formation of an intermediate gel. [ABSTRACT FROM AUTHOR]

Abstract: The Claiborne Group (Eocene) in North East Texas consists of clayey sandstones and mudrocks, both with variable proportions of dark green to brown clay pellets deposited in a marginal to open marine setting on the Gulf Coast margin. The composition of concretionary carbonate and clay pellets, from 5 localities, has been investigated using a wide variety of analytical techniques. Our palaeontological, sedimentological, C/S and stable isotope data support an interpretation of marginal marine facies with limited freshwater input, for the Claiborne Group. Dark green (mature) pellets are predominantly associated with transgressive, bioturbated, marine sediments. From the Weches Formation through to the youngest Crockett Formation there is a trend from pellets composed mostly of dark green serpentine-rich mixed layer clay to those of mostly brown (immature) nontronite-rich mixed layer clay. The serpentine is intermediate between odinite and berthierine and may have been originally odinite that has undergone partial transformation to berthierine. Pellet maturity apparently corresponds with the degree of winnowing and sedimentation rate. It does not appear to correspond with global temperature fluctuations, though the serpentine-rich rather than glauconite-rich composition may do. Siderite cement, mostly in the form of concretions, post-dates the iron-rich clay pellets and pre-dates calcite cement. Carbonate and apatite concretions show a wide range of mineral cement textures, reflecting variation in sedimentary environment and early diagenetic processes. Based on water temperatures derived from verneriacardia bivalves a precipitation temperature of 20°C is assumed for the concretionary siderite. Using this temperature we surmise that the siderite precipitated from marine pore waters with intermittent meteoric water mixing. [Copyright &y& Elsevier]

Abstract: The karstic system in Aïn Khamouda (Central Tunisia) has been briefly exploited for its Pb–Zn mineralization in the first 20years of the 20th century. Since then, little work has been dedicated to this system, apart from some detailed mineralogical studies. Here we place the Aïn Khamouda karsts in their regional geological framework, which is marked by the presence of large basinal-scale MVT Pb–Zn deposit (e.g. at the Djebel Chambi, ∼10km to the south of the study area). The karsts are deepening along faults in Turonian–Coniacian limestone (the Douleb Fm), under a Tortonian sandy cover (the Beglia sand) that is withdrawn within the karst infilling. This makes a Tortonian or post-Tortonian age for the karstification likely, as for other comparable karsts located to the northwest of the study area, in the Algerian Constantinois. In Aïn Khamouda, the mineralization sequence is a variant of the classical gypsum→iron oxide→silicates sequence, with some specific characteristics inherited from the regional Pb–Zn background: a 7Å Zn-clay (berthierine) has been identified, mixed with halloysite, and calamine minerals (hemimorphite, smithsonite) are found in voids and fractures within the karstic system. Undersaturated meteoric fluids flowing downward meet pre-existing or recently formed base metals sulphides, in the subsurface. In the Aïn Khamouda area, the downward deepening of karsts along major regional faults brings meteoric fluids in contact with base metal sulphides. The oxidation of base metals sulphides results in the release of sulphuric acid, which also accounts for an increased karstification. Late processes occurring in the Beglia sand appear to be complex, though somewhat anecdotic in terms of volumes. They essentially consist in recurring cycles of reduction (among which biochemical reduction of galena) and oxidation (including the formation of jarosite). The study area offers the opportunity to investigate (1) a karstic system where deepening caves meet pre-existing base metal sulphides, and (2) the consequences this specific setting has, in terms of minerals found within the karst: presence of Zn-bearing clays (berthierine), formation of calamine minerals, minor cycling of lead in the late phases. [Copyright &y& Elsevier]

Abstract: The Hermod sand of the Stine Segments, Siri Field, Danish North Sea, displays large permeability variations (1–600mD). These permeability variations represent horizontal layering in the reservoir, largely formed by diagenetic processes. They have a significant impact on reservoir performance, because horizontal producers in fairly thin reservoirs (∼30m) are protected against bottom-water influx and can produce water-free for long periods of time. This paper presents the results of a detailed multidisciplinary study where the observed variation in permeability can be explained by two main diagenetic phases: silica, as opal cement and microquartz, and berthierine, a serpentine mineral that is closely related to chlorite. Opal/microquartz and berthierine cements dominate in separate parts of the reservoir bodies. Opal/microquartz cemented sands have high permeability (typically 500–600mD). Berthierine cement has a different growth pattern in the oil and water zones, resulting in intermediate permeability in the oil zone (typically 50–100mD) and very low permeability in the water zone (typically 1–10mD). [Copyright &y& Elsevier]

Berthierine-rich ooidal ironstone occurs within carbonaceous shale in the lower part of the Late Palaeocene-Middle Eocene Subathu Formation in Dogadda, Uttarakhand Himalaya. Berthierine/chamosite occurs both as ooids and as matrix. Ooids are spherical with 1-2 mm diameter and have concentric layer structure around a nucleus. Quartz is coarse-grained and occurs as embayed grains. Carbonate phase is absent in the ooids. Berthierine and chamosite assemblage indicates a temperature of ∼130-160°C of burial diagenesis for Dogadda ironstone. The lithological association, distinct mineralogy and texture suggest that the mineralogy of the Dogadda ooidal ironstone is in situ, formed in a shallow-marine environment under conditions of low net sediment accumulation. Dogadda ooidal ironstones, along with coeval ash beds in the foreland basin are useful in stratigraphic correlation. [ABSTRACT FROM AUTHOR]

The precipitation of iron-rich clay minerals has been reported in various geologic environments. However, large quantities of these minerals are not widely accessible to study their thermodynamic properties and thus improve our understanding of these particular geological systems. To obtain sufficient amount of iron-rich minerals, their synthesis can be foreseen. A design of experiments and surface response methodology was used in this study to find optimum synthesis conditions for these clay minerals. Three parameters were considered: quantity of OH−, synthesis time and temperature. The quantity of OH− had the largest influence on the synthesis result. The amount of 2:1 type clay mineral with respect to 1:1 type clay mineral increased with OH/Fe molar ratio. Time and temperature had less significant impact on the synthesis outcome, yet the formation of 2:1 type phase was favored at short synthesis time (1 day) and high temperature (160 °C). The findings suggested that the kinetic of 2:1 type clay mineral phase formation with respect to 1:1 type phase was faster, yet the precipitation was strongly dependent on the availability of the reactants. • The use of design of experiments and surface response methodology for the study of clay mineral synthesis. • The type of clay mineral synthesized depends on the availability of the reactants and the reaction kinetic. • The quantity and availability of OH− strongly governs the synthesis outcome with respect to the obtained clay mineral type. [ABSTRACT FROM AUTHOR]