Abundant Clay Minerals Research Articles

Metal-free pristine halloysite nanotubes: Electrochemically active and stable oxygen evolution reaction

Halloysite nanotubes (HNT) are naturally occurring one-dimensional porous clay minerals and have a unique chemical structure of kaolinite. The presence of hydroxyl functional groups on the surface of HNT is more suitable for O2 evolution reaction (OER). The HNT based electrocatalyst coated on Ni foam substrate shows excellent water oxidation activity with an overpotential of 287 mV to reach a current density of 10 mA cm−2 and have excellent stability in alkaline electrolyte solution over 32 h without any decay. The adsorption of OH− species occurs on the surface of HNT from the alkaline electrolyte via one-electron transfer, the metal cation underwent repeated oxidation and reduction reactions during the OER. This result outperforms many of the transition metal-based electrocatalysts. This work provides a new platform to use naturally abundant clay minerals as an anode material in fuel cell applications.

Reusable and efficient clay material for the fixed-bed neodymium recovery

Neodymium is an essential resource for the future development of clean energy. Its future supply is a global concern motivating the application of different adsorbent materials to recover neodymium from secondary sources. However, there is a lack of studies of adsorption with scale-up potential. This work aims to recuperate neodymium from aqueous solution through dynamic adsorption in a fixed-bed of expanded vermiculite, an abundant clay mineral with excellent adsorbent properties. For that, the flow rate and concentration optimization, mathematical modeling; cycles of adsorption and desorption; and the extensive characterization of the regenerated adsorbent matrix were carried out. The main findings of the study are the column high adsorption capacity 0.40 mmol/g; the effective modeling of the column by Thomas and DualSD model, being useful for scale-up purposes; the constant bed efficiency along with the cycles and the well succeed neodymium recovery (96% in the third cycle) and concentration (28.4 times). Besides that, the structural composition was maintained, attesting to the physical and chemical stability of the material. Thus, the neodymium continuous recovery from aqueous solution through successive cycles of adsorption and desorption on an expanded vermiculite fixed-bed has high potential for scale-up and rare earth rich wastewater treatment studies.

Pore Structure and Fractal Characteristics of Organic-Rich Lacustrine Shales of the Kongdian Formation, Cangdong Sag, Bohai Bay Basin

In order to examine the pore structure and reveal the fractal geometric nature of shales, a series of laboratory experiments were conducted on lacustrine shale samples cored from the Kongdian Formation. Based on the low temperature nitrogen adsorption, fluorescent thin section and field emission scanning electronic microscope, a comprehensive pore structure classification and evaluation were conducted on shale samples. Fractal dimensions D1 and D2 (with relative pressure of 0–0.45 and 0.45–1.00, respectively) were obtained from the nitrogen adsorption data using the fractal Frenkel-Halsey-Hill (FHH) method. With additional means of X-ray diffraction analysis, total organic carbon content analysis and thermal maturity analysis, the relationships between pore structure parameters, fractal dimensions, TOC content and mineral composition are presented and discussed in this paper. The results show that interparticle pores and microfractures are predominant, whereas organic matter pores are rarely found. The pore morphology is primarily featured with wide-open ends and slit-shaped structures. In terms of pore scale, mesopores and macropores are predominant. The value of fractal dimension D1 representing small pores ranges from 2.0173 to 2.4642 with an average of 2.1735. The value of D2 which represents large pores ranges from 2.3616 to 2.5981 with an average of 2.4960. These low numbers are an indication of few pore types and relatively low heterogeneity. In addition, smaller D1 values reveal that large pores have more complicated spatial structures than smaller ones. The results of correlation analysis show that: 1) D2 is correlated positively with specific surface area but negatively with average pore diameter; 2) D1 and D2 literally show no obvious relationship with mineral composition, TOC content or vitrinite reflectance (Ro); 3) both total Barrett-Joyner-Halenda (BJH) volume and specific surface area show a positive relationship with dolomite content and a negative relationship with felsic minerals content. These results demonstrate that the pore types are relatively few and dominated by mesopores, and the content of brittle minerals such as dolomite and felsic minerals control the pore structure development whilst organic matter and clay minerals have less influence due to low thermal maturity and abundance of clay minerals.

Amending Potassic Fertilizer with Charcoal and Sago (Metroxylon sagu) Bark Ash to Improve Potassium Availability in a Tropical Acid Soil

In Ultisols and Oxisols, potassium (K) in the soil solution is leached from the rhizosphere before it interacts with soil colloids, or exchanged with other cations at the exchange sites of the soils because of the abundance of kaolinite clay minerals. These soils are highly weathered, low in organic matter, and low in pH, but high aluminium (Al) and iron (Fe) ions. Hence, K becomes unavailable for plants, and this compromises crop production and farmers’ profitability. The pH neutralizing effects of sago (Metroxylon sagu) bark ash and the ability of charcoal to chelate Al and Fe could be utilized to improve soil pH, reduce soil acidity, and improve K availability. The objective of this study was to determine the effects of amending muriate of potash (MOP) with charcoal and sago bark ash on selected soil chemical properties in a tropical acid soil (Typic Paleudults) over 90 days in a laboratory incubation. The proportions of charcoal and sago bark ash were varied at 20%, 40%, 60%, 80%, and 100%, but the MOP was fixed at 100% of the recommended rate. Selected soil chemical properties before and after incubation were determined using standard procedures. Results revealed that co-application of the soil amendments with MOP increased soil-exchangeable K compared with conventional practice. Moreover, amending the acid soil with charcoal and sago bark ash positively enhanced the availability of other base cations and soil cation exchange capacity (CEC). This was possible because the amendments increased soil pH and reduced exchangeable acidity, exchangeable Al3+, and exchangeable Fe2+. However, there was no significant improvement in water-soluble K (WSK) in the soil with or without charcoal and sago bark over the 90 days laboratory study. The findings of this study suggested that increasing soil pH could potentially improve soil K sorption capacity. Thus, the optimum rates of charcoal and sago bark ash to increase K availability were found to be 80% charcoal with 80% sago bark ash, 60% charcoal with 60% sago bark ash, and 80% charcoal with 40% sago bark ash, because these rates improved soil-exchangeable K+ and CEC significantly, besides minimizing soil-exchangeable acidity.

Co-Application of Charcoal and Wood Ash to Improve Potassium Availability in Tropical Mineral Acid Soils

Potassium (K) is a macronutrient required by plants for energy production, enzyme activation, formation of cell wall, production of protein, and photosynthesis. However, K in the soil solution is leached from the rhizosphere before it interacts with soil colloids because of the abundance of kaolinite clay minerals in mineral acid soils such as Ultisols and Oxisols. These soils are highly weathered, low in organic matter, low in pH, but high aluminium (Al), and iron (Fe) ions. As a result, K becomes unavailable for plants, and this affects crop production and farmers’ profitability. This problem has steered the attention to the application of amendments to minimise K loss. Animal manures, plant residues, and composts applications are some of the corrective measures taken to improve the K availability in tropical acid soils. However, there is dearth of information on co-application of charcoal and wood ash as soil amendments to improve the K availability and the changes they cause to the dynamic equilibrium of K in mineral acid soils. Hence, this review discusses the dynamics, availability of K, and proposed mechanisms involved when charcoal and wood ash are used to amend tropical acid soils. The optimisation and understanding of the role of charcoal and wood ash co-application as soil amendments have potential benefits to improve the K availability and physicochemical properties of mineral acid soils.

Early diagenesis at and below Vera Rubin ridge, Gale crater, Mars

AbstractData returned by NASA’s Mars Science Laboratory Curiosity rover showed evidence for abundant secondary materials, including Fe‐oxides, phyllosilicates, and an amorphous component on and below Vera Rubin ridge in the Murray formation. We used equilibrium thermochemical modeling to test the hypothesis that altered sediments were deposited as detrital igneous grains and subsequently underwent diagenesis. Chemical compositions of the Murray formations’ altered components were calculated using data returned by the chemistry and mineralogy X‐ray diffraction instrument and the alpha particle X‐ray spectrometer on board Curiosity. Reaction of these alteration compositions with a CO2‐poor and oxidizing dilute aqueous solution was modeled at 25–100 °C, with 10–50% Fe3+/Fetot of the host rock. The modeled alteration assemblages included abundant phyllosilicates and Fe‐oxides at water‐to‐rock ratios >100. Modeled alteration abundances were directly comparable to observed abundances of hematite and clay minerals at a water‐to‐rock ratio of 10,000, for system temperatures of 50–100 °C with fluid pH ranging from 7.9 to 9.3. Modeling results suggest that the hematite–clay mineral assemblage is primarily the result of enhanced groundwater flow compared to the Sheepbed mudstone observed at Yellowknife Bay, and underwent further, localized alteration to produce the mineralogy observed by Curiosity.

Provenance analysis of sediments in the south-east Aegean during the Upper Quaternary: a composite approach based on bulk and clay mineralogy and geochemistry

AbstractSediments from the ST5 deep-sea bottom core collected from the south-east Aegean Sea between Symi and Tilos islands, Greece, were examined by quantitative mineralogical analysis and geochemical analysis to infer provenance and palaeoenvironmental control over sediment deposition. The mineralogical composition comprises carbonates (mainly calcite and Mg-calcite), quartz, feldspars, serpentine, amphibole and clay minerals. Chlorite is the most abundant clay mineral, whereas smectite and illite are less abundant than in the sediments in the south-west Aegean and the Cretan Sea. Semi-quantitative analysis of clay minerals from oriented clay fractions overestimates significantly the smectite content and underestimates the abundances of illite, chlorite and kaolinite. The studied sediments are enriched in MgO, Ni and Cr, which decrease in abundance with decreasing depth, following the distribution of serpentine. By contrast, the abundances of SiO2, Al2O3, Fe2O3, Na2O and K2O increase upcore. The regional S1 sapropel horizon is enriched in V and Co and has considerably greater Ba/Al ratios than the remaining sequence. The mineralogical and geochemical relationships indicate a strong ultrabasic influence, probably from the Marmaris ophiolite in the Lycian nappes. The clay mineral distribution suggests that the smectite was mainly of volcanogenic origin, the illite was supplied by the nearby landmasses of west Anatolia and the islands of Rhodes, Tilos and Symi and the contribution from the south-east Mediterranean was limited or totally lacking. The combined use of the mineralogical and geochemical analysis of bulk sediments rather than the clay fractions is not only extremely useful in tracing sediment provenance in relatively closed basins, but it also enables a more realistic assessment of the importance of water circulation patterns on sedimentation processes in such environments.

Mapping hydrocarbon microseepage prospect areas by integrated studies of ASTER processing, geochemistry and geophysical surveys in Assam-Arakan Fold Belt, NE India

Long-term microseepage of hydrocarbons creates a reducing environment in the near-surface soil and sediment cover inducing an array of diagenetic alterations such as bleaching of red beds and increasing abundance of ferrous, clay and carbonate minerals. Spectral enhancements of satellite images have effectively been used in microseepage-induced mineral mapping in arid regions. However, the present study aims to delineate microseepage-induced mineral alteration areas in Assam-Arakan Fold Belt (AAFB) in the north-eastern part of India, dominated by humid climate and heavy precipitation. The study uses an integrated approach consisting of advanced spaceborne thermal emission and reflection radiometer (ASTER) image processing, geochemistry, gravity and magnetic data. ASTER image processing involves specialized band ratios (BRs), false colour composite (FCC) and spectral angle mapping (SAM). Integration of remote sensing, geochemistry, gravity and magnetic anomaly data successfully delineates microseepage prospect areas in the basin. The study would provide important advantages in hydrocarbon exploration strategy in similar basins around the world.

Clay-mineral distribution in recent deep-sea sediments around Taiwan: Implications for sediment dispersal processes

Clay-mineralogy study of Taiwanese river-mouth sediments, recent deep-water seafloor sediments around Taiwan, along with sediments collected from the Tainan shelf edge, have been investigated to access the source and transport of detrital fine-grained sediments. We determined the clay mineralogy in both hemipelagites and turbidites in the top 50 cm of the deep-sea sediment cores to infer how sediments are dispersed through river-fed turbidity currents, hypopycnal plumes, and oceanic currents. Our results show that the clay mineral assemblages in both hemipelagites and turbidites of different provinces change gradually between two major end-members: illite+chlorite and smectite. They are predominantly sourced from Taiwan and Luzon, respectively. The relative abundances of clay minerals in turbidites and hemipelagites are quite similar in most of the cores. Therefore, we argue that the adjacent turbidites and hemipelagites of a core share common detrital clay sources. We found that smectite is relatively abundant around Taiwan, indicating that the Kuroshio Current is an important transportation system, which brings smectite from Luzon. Besides, the river-related canyon systems consist dominantly of illite and chlorite, and less smectite, indicating that the smectite brought about by the Kuroshio Current is diluted by river-fed hyperpycnal and hypopycnal flows. This also implies that flood-induced turbidity currents are efficient agents for transporting Taiwan-derived sediments into the neighboring deep-sea basins.

The Evolution of Diagenetic Fluids and Accumulation Characteristics of Tight Sandstone Reservoir in Upper Paleozoic, Southwestern Ordos Basin

The Upper Paleozoic in the southwestern Ordos Basin has significant potential for natural gas exploration. This study investigated the diagenetic fluid evolution and hydrocarbon accumulation characteristics of He 8 section from Permian Lower Shihezi formation and Shan 1 section from Shanxi formation tight sandstone reservoirs by petrographic observation, scanning electron microscope imaging, fluid inclusion study, and laser Raman spectrum analysis. The results show that He 8 section and Shan 1 section reservoirs are mainly composed of quartz sandstone, subordinate arkose quartz sandstone, and lithic quartz sandstone, with minor lithic sandstone and lithic arkose sandstone. The major pores are intergranular dissolved pores. The main diagenetic minerals include quartz overgrowth, siliceous cement, carbonate cement, illite, montmorillonite, and mixed-layer clay minerals. The overall diagenetic features show strong compaction, multistage siliceous and calcareous cements, and abundant clay minerals, strong dissolution, and well-developed fractures. Two stages of fluid inclusions developed in the He 8 and Shan 1 sections recorded the migration and accumulation of the early-stage and late-stage natural gas, respectively. The reservoir in the study area experienced early and late diagenetic stages, and its formation was simultaneous with or after its densification. The diagenetic environment changed from alkaline to acidic and again into alkaline. There are two stages of fluid activities in the study area, namely, the early diagenetic stage corresponding to hydrocarbon generation and migration and the late diagenetic stage corresponding to hydrocarbon accumulation. This study suggests that Upper Paleozoic natural gas migrated into the reservoir in Weibei Uplift, Yishan Slope, and Tianhuan Depression tectonic units during 220-197 Ma, and the large-scale migration and accumulation occurred in these tectonic units at different times. No natural gas was generated in the west margin of the basin because the temperatures of the hydrocarbon source rocks in the Upper Paleozoic were below the gas window.

Reservoir characteristics and control mechanism of resistivity low-contrast oil pays in Chang 8 tight sandstone of Longdong West area, Ordos Basin

Log interpretation and evaluation of tight sandstone reservoir in Chang 8 Member of Longdong West area, Ordos Basin, China, are facing great challenges due to the co-development of normal oil pay and resistivity low-contrast oil pay. To better guide the exploration and development of oil resources in this area, the reservoir characteristics and control mechanism of resistivity low-contrast oil pay were studied. Firstly, the reservoirs were divided into resistivity low-contrast oil pay (RLP) and normal oil pay (NP) based on the relative value of the apparent resistivity increase rate. Then, the difference of reservoir characteristics between RLP and NP is analyzed by comparing a series of experimental data and real logging data in those two reservoir types. Finally, the control mechanism of RLP was studied from reservoir micro-factors and regional macro-factors, respectively. It is found that the chlorite and illite are the most abundant clay minerals in RLP and NP, respectively. Compared with NP reservoir, the average porosity of RLP is better, but the pore space is mainly composed of micropores, which lead to smaller average pore throat radius and poor pore structure. The high irreducible water saturation and high formation water salinity reduced the reservoir resistivity from micro-aspect. Besides, the difference of hydrocarbon expulsion capacity of source rock and the regional difference of formation water salinity controlled the distribution of RLP and NP. Comprehensive consideration of the reservoir micro-factors and regional macro-factors is important to carry out effective logging interpretation and evaluation.

Facies associations and sequence stratigraphy of the Middle-Late Eocene Pila Spi Formation in the High Folded Zone, Kurdistan Region, northeastern Iraq

Facies analysis and sequence stratigraphy of the Pila Spi Formation (Middle-Late Eocene) was studied from two outcrop sections (Bekhma and Gomaspan) within the High Folded Zone, Iraqi Kurdistan Region. The formation consists of light brown dolomitic, crystallized, chalky, limestones, and dolostone, alternating with multicolored marl and marly limestones. Chert nodules are present in the upper part of the formation. The petrographic analysis was based on 65 thin sections, and the results showed that the carbonate rocks are partially dolomitized. The distinguished bioclasts consist of benthic and planktonic foraminifera, micro-gastropods, calcispheres, ostracods, pelecypods, and bryozoans. Non-skeletal grains such as peloids, intraclasts, and extraclasts were also observed. X-ray diffraction analysis revealed that abundant clay minerals are palygorskite with the rare existence of chlorite. Non-clay minerals include dolomite, calcite, and quartz with low pyrite contents. According to field observations, four different lithofacies were recognized. They are dolomitic limestone, chalky limestone, marl-marly limestone, and cherty limestone. Based on detailed microfacies analysis of limestones, four main microfacies and eleven submicrofacies types are observed. These microfacies are subdivided into two groups of facies associations; they are semi-restricted and open lagoon. The results of stable carbon and oxygen isotopes of the studied carbonate samples show negative values of δ18O, and this indicates that the seawater was warm with lower salinity. However the positive δ13C values reflect the deposition of organic-rich sediments with transgression of the sea and deepening of the basin. Two third-order depositional sequences are observed. Each of them is subdivided into a TST and HST, reflecting the transgression and stillstands of the relative sea level during Middle-Late Eocene.

Determination of slope susceptibility in hydrothermally altered rocks region with a case study in wonotirto district, blitar regency, east java province, indonesia

The significance of slope susceptibility study in hydrothermally altered area is to determine which area that geological landslide hazard is potentially occurred. This study is aimed to develop a geological hazard map based on overlaying of slope data and types of hydrothermal alteration, with the case study in Wonotirto district, Blitar regency, East Java province. Wonotirto district lies on a high topographic terrain covered up by hydrothermally altered volcanic rocks. To achieve these aims, this study was performed a suite of research methods, which are conducted through four work stages including geological mapping and slope observation, sampling, laboratory analysis and data interpretation. Slope data measurement is based on DEM data and verified in the field. Laboratory analyses consist of petrography, XRD (X-Ray Diffraction) and geomechanical properties analysis for the representative samples. The hydrothermal alteration occurred in study area consists of 4 (four) alteration types i.e. silicification, advanced argillic, argillic and propylitic alteration. Overlaying of slope data, geomechanical properties of rocks and the provided alteration map by using ArcGIS software leads the determination of slope susceptibility of the area. The area covered by extensive argillic-altered rocks shows highest slope susceptibility. On the map, the high slope susceptibility places on the northernmost sector of the study area. Meanwhile, the moderate slope susceptibility area occupies the central part of the map and the southernmost part has the lower slope susceptibility. Argillic altered rocks contain abundant clay minerals such as smectite and illite. Smectite, particularly, is a clay mineral type which has high swelling potential index. The abundantly presence of the clay minerals in the altered rocks may trigger the formation of geological landslide failure/hazard in the region.

Persistent Provenance of South Asian Monsoon‐Induced Silicate Weathering Over the Past 27 Million Years

AbstractThe development of the South Asian monsoon (SAM) and Himalaya‐Tibetan Plateau uplift were closely intertwined with some studies suggesting that uplift initiated the monsoon whereas others link tectonics with monsoon‐controlled exhumation. Silicate weathering controls atmospheric CO2 on geological timescales resulting in a large potential for monsoon strength and the Himalayan orogeny to influence global climate but detailed records of SAM‐induced weathering on million year (Myr) timescales are lacking. Here, we present radiogenic Sr, Nd, and Pb isotope compositions of clay minerals produced by silicate weathering and transported to the central Bay of Bengal. The radiogenic isotope data exhibit a relatively small range and demonstrate a remarkably consistent mixture of sources dominated by Himalayan rocks and the Indo‐Burman ranges, which consist of sediments derived from the Himalayas. This suggests that the spatial pattern of regional weathering, which today is highest in the regions of strongest monsoon rains, has persisted in a similar form for the last 27 Myrs. A pronounced increase in primary clay mineral abundance (from 9% to 22%) coincident with global cooling 13.9 Myrs ago points to a shift in the weathering regime given that the clay provenance did not change dramatically. Relatively weaker chemical weathering intensity during the mid and late Miocene cooling suggests increased aridity and changes in the large scale atmospheric circulation in the SAM domain. The establishment of the dry winter monsoon season during the mid and late Miocene may have caused this shift in the weathering regime and can reconcile much of the contrasting evidence for SAM initiation.

Mineralogy and Element Geochemistry of Oil Shales in the Lower Cretaceous Qingshankou Formation of the Southern Songliao Basin, Northeast China: Implications of Provenance, Tectonic Setting, and Paleoenvironment

Songliao Basin is a large Mesozoic oil shale-bearing basin in the northeast of China, where multiple layers of oil shales and mudstones developed in the first member of the Qingshankou Formation (K2qn1). Mineralogy and geochemical data were used to reveal the provenance and tectonic setting of the sediments; furthermore, the differences in the paleoenvironment between mudstones and oil shales as well as between different oil shale layers were revealed. Core observation shows that oil shales are light brown with horizontal bedding, while mudstones are dark gray with a massive structure. X-ray diffraction data revealed abundant clay minerals and a certain amount of syngenetic pyrite in the oil shales, indicating that oil shale forms in a reducing water environment. The element ratios revealed that the parent rocks were mostly felsic volcanic rocks, and the discriminant diagrams indicated that the tectonic setting was of a continental island arc. The paleoenvironment and the genetic mechanism of oil shales are revealed by geochemical data, and the oil shales and mudstones were deposited under warm-humid paleoclimate, salty brackish, and strong reducing water environments. The geochemical curves show four high and low change cycles in the column, which means that the oil shale layers have a higher organic matter content than the mudstone layers because of the higher primary productivity, more saline water environments, and stronger reducing conditions. From the lower layer 1 to the upper layer 4 of oil shales, the extent of the warm-humid climate gradually weakened, whereas the salinity of the water environment gradually increased.

Coupling of diagenetic alterations and mechanical properties of Lower Permian siliciclastic sandstones: a pilot study

Initial detrital composition and authigenic alterations during diagenesis of three sandstone types are related to their mechanical properties. Sandstones were prepared for geotechnical standard tests [density, uniaxial compressive strength (UCS), Young’s modulus (E), strain at failure (ε)] and thin sections for petrographic analyses (point counting). UCS ranges from 3 to 62 MPa and positively correlates with density (1.75–2.35 g/cm3) and E (0.3–12.7 GPa). Optical porosity is controlling these mechanical parameters and was linked to diagenetic alterations. Diagenetic alterations affecting porosity reduction are the abundance of clay minerals, and the intensity of mechanical and chemical compaction. The latter is controlled by clay mineral coatings on contacts between detrital grains, and the occurrence of authigenic quartz and dolomite. Horizontal contact lengths of grains normalized to their respective particle diameter (effective contact ratio, ECR) and porosity are identified as a control on the mechanical properties UCS and E, reflected by the rock strength index SR. The results of this pilot study suggest that SR is able to predict UCS and E based on petrographic information obtained from the studied samples. These results enhance the understanding of the coupling between mineralogy and geomechanics and highlight the impact of diagenesis on geomechanical behavior.

Mechanical Properties and Microscopic Geological Features under Uniaxial Compression in Tight Reservoir

In this study, to investigate the mechanical properties and microscopic geological features, a series of uniaxial compression, petrophysical properties, X-ray diffraction, elements, and conductivity tests were conducted. The results indicate that quartz and plagioclase are essential minerals determining Upper Triassic sandstone compositions, while quartz plays a dominant role in the Lower Permian sandstones. Due to microcracks, the relationships between porosity and permeability of Upper Triassic sandstones are better than those of Lower Permian sandstones. Observations have shown that silicon and aluminum are the main elements of those rocks. The rocks which have large porosity and permeability have a strong capacity of anticompression resistance. There are good consistencies between the mechanical behavior and the high proportion of rigid minerals. Similarly, the rocks which have abundant silicon and aluminum could better support the structural integrity of rocks. High pore structure heterogeneity and abundant clay minerals have positive influence on the mechanical resistance. Shales have distinct plastic deformation features when compared with the sandstones.

Preservation of erniettomorph fossils in clay-rich siliciclastic deposits from the Ediacaran Wood Canyon Formation, Nevada: Ediacaran preservation in sandstone beds

Author(s): Hall, JG; Smith, EF; Tamura, N; Fakra, SC; Bosak, T | Abstract: Three-dimensionally preserved Ediacaran fossils occur globally within sandstone beds. Sandy siliciclastic deposits of the Ediacaran Wood Canyon Formation (WCF) in the Montgomery Mountains, Nevada, contain two fossil morphologies with similar shapes and sizes: one exhibits mm-scale ridges and a distinct lower boundary and the other is devoid of these diagnostic features. We interpret these as taphomorphs of erniettomorphs, soft-bodied organisms with uncertain taxonomic affinities. We explore the cast-and-mould preservation of both taphomorphs by petrography, Raman spectroscopy, X-ray fluorescence microprobe and X-ray diffraction. All fossils and the surrounding sedimentary matrix contain quartz grains, iron-rich chlorite and muscovite. The ridged fossils contain about 70% larger quartz grains compared to the ridgeless taphomorph, indicating a lower abundance of clay minerals in the ridged fossil. Chlorite and muscovite likely originated from smectite and kaolinite precursors that underwent lower greenschist facies metamorphism. Kaolinite and smectite are inferred to have been abundant in sediments around the ridged fossil, which enabled the preservation of a continuous, distinct, clay- and kerogen-rich bottom boundary. The prevalence of quartz in the ridged fossils of the WCF and in erniettomorphs from other localities also suggests a role for this mineral in three-dimensional preservation of erniettomorphs in sandstone and siltstone deposits.

Correction to: Eco-friendly removal of hexavalent chromium from aqueous solution using natural clay mineral: activation and modification effects

Inexpensive and naturally abundant clay mineral is investigated as a non-toxic and environmentally friendly adsorbent. The clay adsorbent prepared from natural clay (NC) by drying and milling then treated with diluted HCl before calcination to 600 °C. The structural and morphological properties of this modified clay are investigated by Fourier-transform infrared spectroscopy and scanning electron microscope. NC and modified clay at 600 °C (MC600) were applied for hexavalent chromium, Cr(VI), removal from aqueous media via batch adsorption facility. According to the experimental results, the adsorption capacity for chromium removal was calculated (14.3 mg g−1) with a removal efficiency reached to 66% after 90 min of equilibrium time. The sorption matrix indicated that Cr(VI) removal is following the pseudo-second order kinetic model. The experimental data are well fitted with Freundlich isotherm model and the adsorption process is suggested to follow a chemisorption and favourable uptake. The clay reusability was also tested and the outcomes suggested that MC600 had good potential as an economic adsorbent for chromium removal from contaminated water. According to this finding, modified NC is an effective adsorbent for direct Cr(VI) removal from aqueous media and the clay material is signified as an efficient treatment technology can also be adapted to heavy metal removal in wastewater treatment applications and could replace the commercially available adsorbents.

Element enrichment/depletion during faulting in shale-rich surface exposures of the 2008 Wenchuan earthquake (Mw 7.9) and implications for coseismic temperature

The coseismic frictional temperature is increasingly recognised as an important factor for the transformation mechanism in shallow crustal faulting. We report changes in the mineralogical and geochemical compositions across the fault zone in the Shaba (SB) exposure of the 2008 Wenchuan earthquake (Mw 7.9), which contained the maximum value of vertical displacement and cut through shale-rich strata by the principal slip surface. Assuming Yb to be an immobile trace element, with respect to those in the adjacent damaged zone and wall rocks, Li, Rb, Cs and most light rare earth elements (LREE) exhibited marked enrichments of 143%, 247%, 475% and >60%, respectively; and a 40% depletion of Sr and <5% depletion of most heavy rare earth elements (HREE) was found, responding to mineralogical transformation such as alteration and dissolution of feldspar and formation of abundant clay minerals. In addition, heterogeneous adsorption of clay minerals could result in fractionation between and within LREE and HREE as well as negative Eu anomalies and positive Ce anomalies. The element enrichment/depletion model of the northern segment of the Yingxiu–Beichuan (YX–BC) fault zone was quite different from the middle/southern segments characterising faults in carbonate and granitic rocks. Through model calculation, the calculated trace element compositions (Li, Rb, Sr, Cs, Ba, La, Sm and Pb) of the fault gouge were obtained at 250 °C, 300 °C and 350 °C, and were produced by frictional heating. By comparing with the observed values, we suggest that high temperatures derived from frictional heating or due to buffering of the slip zone temperature by evaporation of pore water during the earthquake within the principal slip surface in the northern segment of the YX–BC fault zone may not have existed. Mechanical crushing and chemical alteration (not under high-temperature conditions) within the fault zone during the coseismic stage may result in mass removal and element enrichment/depletion. KEY POINTS Mineralogical and geochemical compositions were reported in the Shaba exposure of the 2008 Wenchuan earthquake. Li, Rb, Cs and most LREE exhibited marked enrichments in the fault gouge. Fractionation between and within LREE and HREE, negative Eu anomalies and positive Ce anomalies occur in the fault gouge. High temperatures may not have existed within the principal slip surface of the northern segment of the YX–BC fault zone.