Fe Enrichment Research Articles

Porphyrin protonation induces decoupling of trace metals in petroleum

The mechanism of migration of trace metals in petroleum systems is poorly understood, which limits our understanding of organic–inorganic interactions and their application in tracing oil sources. Based on a molecular model of metalloporphyrin, numerical simulations involving density functional theory have revealed that porphyrin protonation is associated with trace-metal decoupling in petroleum. Trace metals readily form covalent bonds with weakly protonated porphyrin N to form stable compounds. However, the metals may be decoupled at lower fluid pH owing to increased N protonation, which activates the formation of ionic bonds with O2−. The released metals may then be fixed in authigenic calcite cement (ACC) reservoirs through substitution of Ca. For Mg, Mn, and Fe, the decoupling order is Mg > Fe > Mn, whereas that for the substitution of Ca is Mn > Fe > Mg, reflecting the complexity of organic–inorganic interactions and indicating the potential application of metals in fingerprinting oil sources. This case study of the southern Junggar Basin, China, revealed that Mn, Fe, and Mg enrichment of ACC may provide indications of Paleozoic, Mesozoic, and Cenozoic petroleum systems, respectively, providing a potential new approach for the tracing of oil sources in petroleum basins.

Desert dust improves the photophysiology of heat-stressed corals beyond iron

Desert dust is an important source of essential metals for marine primary productivity, especially in oligotrophic systems surrounded by deserts, such as the Red Sea. However, there are very few studies on the effects of dust on reef-building corals and none on the response of corals to heat stress. We therefore supplied dust to two coral species (Stylophora pistillata and Turbinaria reniformis) kept under control conditions (26 °C) or heat stress (32 °C). Since dust releases large amounts of iron (Fe) in seawater, among other metals, the direct effect of different forms of Fe enrichment on coral photosynthesis was also tested. First, our results show that the desert dust altered the coral metallome by increasing the content of metals that are important for coral physiology (e.g. lithium (up to 5-fold), manganese (up to 4-fold in S. pistillata), iron (up to 3-fold in S. pistillata), magnesium (up to 1.3-fold), molybdenum (up to 1.5-fold in S. pistillata)). Overall, metal enrichment improved the photosynthetic performance of corals, especially under thermal stress (e.g. Pgross (up to 2-fold), Pnet (up to 10-fold), chlorophyll (up to 1.5-fold), symbionts (up to 1.6-fold)). However, Fe exposure (ferric chloride or ferric citrate) did not directly improve photosynthesis, suggesting that it is the combination of metals released by the dust, the so-called “metal cocktail effect”, that has a positive impact on coral photophysiology. Dust also led to a decrease in Ni uptake (up to 1.4-fold in the symbionts), likely related to the nitrogen metabolism. Finally, we found that the isotopic signature of metals such as iron, zinc and copper is a good indicator of heat stress and dust exposure in corals. In conclusion, desert dust can increase coral resistance to bleaching by supplying corals with essential metals.

Low [O/Fe] Ratio in a Luminous Galaxy at the Early Cosmic Epoch (z > 10): Signature of Short Delay Time or Bright Hypernovae/Pair-instability Supernovae?

Abstract We present an [O/Fe] ratio of a luminous galaxy GN-z11 at z = 10.60 derived with the deep public JWST/NIRSpec data. We fit the medium-resolution grating (G140M, G235M, and G395M) data with the model spectra consisting of BPASS-stellar and Cloudy-nebular spectra in the rest-frame UV wavelength ranges with Fe absorption lines, carefully masking the other emission and absorption lines in the same manner as previous studies conducted for lower-redshift (z ∼ 2–6) galaxies with oxygen abundance measurements. We obtain an Fe-rich abundance ratio [ O / Fe ] = − 0.37 − 0.22 + 0.43 , which is confirmed with the independent deep prism data as well as by the classic 1978 index method. This [O/Fe] measurement is lower than that measured for star-forming galaxies at z ∼ 2–3. Because z = 10.60 is an early epoch after the Big Bang (∼430 Myr) and the first star formation (likely ∼200 Myr), it is difficult to produce Fe by Type Ia supernovae (SNe Ia), which requires sufficient delay time for white-dwarf formation and gas accretion. The Fe-rich abundance ratio in GN-z11 suggests that the delay time is short or that the major Fe enrichment is not accomplished by SNe Ia but by bright hypernovae (BrHNe) and/or pair-instability supernovae (PISNe), where the yield models of BrHNe and PISNe explain Fe, Ne, and O abundance ratios of GN-z11. The [O/Fe] measurement is not too low to rule out the connection between GN-z11 and globular clusters (GCs) previously suggested by the nitrogen abundance but rather supports the connection with a GC population at high [N/O] if a metal dilution process exists.

Iron redox shuttling and uptake by silicate minerals on the Namibian mud belt

Anoxic marine sediments represent an important source of bioavailable iron (Fe) to the ocean. The highest sedimentary Fe fluxes are observed in open-marine oxygen minimum zones where anoxic bottom waters are in contact with ferruginous surface sediments. Here, sedimentary Fe release, transport and re-deposition (i.e., Fe shuttling) may generate a lateral pattern of sedimentary Fe enrichment and depletion, which can be used to trace redox-related Fe mobility in the paleo-record. However, depending on the balance between terrigenous and authigenic (i.e., shuttle-related) Fe flux, the stability of bottom water redox conditions as well as post-depositional processes of mineral alteration, the sedimentary fingerprint of an Fe redox shuttle may be obscured and difficult to identify.We investigated sedimentary Fe cycling along two transects across the Namibian mud belt with variable terrigenous sedimentation (23°S < 25°S) and during two seasons with opposing bottom water redox conditions (oxic in austral winter versus anoxic to sulfidic in austral summer). On both transects, substantial benthic Fe fluxes up to −50 µmol m−2 d−1 were inferred based on pore water profiles. The magnitude of these fluxes is comparable to those reported for other open-marine oxygen minimum zones. On the transect at 23°S, Fe source areas with ferruginous surface sediments were clearly separated from Fe sink areas with highly sulfidic surface sediments. Therefore, Fe redox shuttling was reflected by a lateral pattern of reactive Fe depletion and enrichment relative to the terrigenous background sedimentation. By contrast, on the transect at 25°S, benthic Fe fluxes were temporally and spatially more variable and surface sediments were ferruginous or only weakly sulfidic. Therefore, sedimentary Fe depletion and enrichment was less pronounced at 25°S. In the Fe sink area at 23°S, hydrogen sulfide was present at the sediment surface during both sampling campaigns and solid phase data suggest that Fe sulfide minerals represented the main burial phase of reactive Fe. By contrast, at 25°S excess Fe was associated with potassium (K) rather than reduced sulfur. While a differing sediment provenance cannot be ruled out entirely, combined evidence from pore water silica profiles, K to Fe stoichiometric relationships and electron microprobe images suggest that laterally derived excess Fe was incorporated into pre-existing and/or authigenic clay minerals during early diagenesis. Iron uptake by clay minerals may be supported by frequent redox oscillations and sediment mixing preventing preservation of Fe sulfide minerals and promoting Fe and K fixation in clay minerals. The burial fluxes of excess Fe associated with sulfide minerals at 23°S and silicate minerals at 25°S were similar. Our findings thus underscore that neoformation or alteration of silicate minerals can be important processes within the low-temperature marine Fe cycle.

Mineralogy and Major Element Geochemistry of the Oligocene Barail Group Sandstones from the Sylhet Trough, Bengal Basin: Provenance and Tectonic Implications

The origin of Oligocene sediments in the Bengal Basin and associated tectonic setting remain poorly understood. This study investigates the framework mineralogy and major element geochemistry of the Barail Group sandstones from the Sylhet Trough within the Bengal Basin to clarify the provenance and tectonic history of the Oligocene. Modal analysis (Q83F7L10) and geochemical data support a classification of sublitharenite to subarkose, some with Fe enrichment. The heavy mineral assemblage is dominated by opaque minerals, followed by ultrastable minerals with zircon &gt; tourmaline &gt; rutile. The sub-angular to sub-rounded sand grains with a compositionally moderate mature nature suggest that the sediments were deposited close to the source area. The mineralogical and geochemical provenance discrimination diagram suggests contributions from felsic igneous, sedimentary/metasedimentary, and low-grade metamorphic sources, with detritus derived from the Indian craton and proto-Himalaya region. Data suggest moderate to intense chemical weathering, indicative of low relief and a sub-humid to humid climate in the source area. The tectonic analyses indicate that the Bengal Basin transitioned from a predominantly passive margin to an active tectonic margin setting during the Oligocene.

Recycling of terrigenous sediments recorded in late Permian-early Triassic Fe-rich intrusions from Yunkai Massif, South China

The origin of Fe-rich intrusion remains debatable regarding the respective role of magmatic evolution and Fe enrichment in the source. Here, we report detailed mineral and bulk-rock geochemistry of Permian-Triassic (251–250 Ma) mafic intrusions from the Tengxian area in Yunkai Massif, South China. These rocks consist of hornblende norites, show Fe-rich affinities with high FeO*(FeO* = FeOt / (FeOt + MgO) in weight ratio, >0.8, based on total iron oxide in the rock), and exhibit significant enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) but depletion in Sr and high field strength elements (HFSEs), resembling subduction-related magmas. In addition, they show remarkable features that include very high δ18O values in zircon (δ18O = 8.8–10.6 ‰) and apatite (δ18O = 8.7–10.8 ‰), and extremely enriched SrPb [e.g. 87Sr/86Sr(i) = 0.7181–0.7196, 207Pb/204Pb(i) = 15.77–15.78, 208Pb/204Pb(i) = 38.95–39.05] and nonradiogenic NdHf isotopic compositions [e.g. εNd(t) = −11.1 ~ − 10.1, εHf(t) = −8.8 ~ −7.3] in bulk rocks. These characteristics distinguish the Tengxian norites from modern arc basalts and subduction-related magmas in the Paleo-Pacific Tectonic Domain. Instead, they are isotopically similar to Cenozoic Tibetan and Mediterranean potassic to ultrapotassic rocks in the Tethys Tectonic Domain. Regardless of variable influence by orthopyroxene and plagioclase accumulation, the intrinsically low SiO2 and high FeOt and Fe/Mn ratios in these rocks were likely attributed to significant contribution of a Fe-rich mantle component such as Si-poor pyroxenite, which might have formed through crystal accumulation of mafic magmas at mantle conditions. The highly evolved Sr-Nd-Pb-Hf isotopic signatures and very high δ18O values in zircon and apatite required substantial (10–20 %) involvement of recycled crust in the mantle source. The combined mineral and bulk-rock geochemical data suggest that the parental magmas for the Tengxian norites originated from a metasomatized mantle wedge through addition of terrigenous sediment-derived melt following the subduction of Paleo-Tethys Ocean beneath the Yunkai Massif.

Study of black glaze and sauce glaze porcelains from Dangyangyu kiln during the Song and Jin Dynasties, China

In the Song and Yuan Dynasties of China, numerous renowned kilns simultaneously employed black glaze and sauce glaze porcelain; however, limited research has been conducted on the differentiation of process systems and the potential existence of a transforming relationship between these two types of porcelains from the same kiln. In this study, the black glaze, sauce glaze and flambé (窑变, Yaobian) glaze porcelain from Dangyangyu kiln during the Song and Jin Dynasties were selected to compare their optical characteristics, firing and formula process via OM, LRS, SEM-EDS, XPS, DIL and EDXRF methods. The research reveals that notable distinctions exist in the glazing process between black glaze and sauce glaze porcelain; while the former demonstrates thicker glazing techniques, the latter showcases thinner glazing techniques. Sauce glaze porcelains undergo firing at high temperatures within strong reducing atmospheres and differs from black glaze in terms of their formulation processes. The sauce glaze is composed of high Al clay with a low flux content, making it a calcium-alkali glaze. On the other hand, the black glaze has a higher flux content and falls under the category of high calcium glazes. Through the investigation of flambé glaze, it was observed that despite a thicker black glaze layer does not promote Fe enrichment on the glaze surface, however, when the flux content in the glaze is lower, meanwhile accompanied by a high temperature and strong reducing atmosphere firing process, the glaze exhibits a dynamic tendency towards the formation of sauce coloration.

Macroscopic and microscopic element distribution in transition zones of GTAW Alloy 52M weld joint and its PWSCC growth behaviour

The microstructure and element distribution in the transition zone (TZ) of Alloy 52M buttering (52Mb) layer near the fusion boundary to the SA508III low alloy steel in a dissimilar metal weld joint with post-weld heat treatment (PWHT) is characterized. Two macroscopic TZs in the heat-affected zone have lower Cr and Ni contents than the bulk Alloy 52Mb. The first TZ near the fusion boundary has the lowest Cr and Ni compositions, accompanying the highest Fe content. Cr depletion and Ni enrichment along with slight Fe enrichment at the dendrite boundaries in the TZs, are more significant than those in the bulk Alloy 52Mb. The number and the maximum depth of local oxidation penetrations at the alloy-inner oxide interface based on the oxidation tests, the number and the maximum length of locally interdendritic cracks, as well as the average crack growth rate (CGR) in terms of the stress corrosion cracking (SCC) band based on the SCC tests in the first TZ are higher than those in the second TZ. The average SCC CGR is enhanced by macroscopic element dilution, while local oxidation penetration, as well as locally interdendritic SCC, are thought to be enhanced by both the macroscopic dilution of Cr in the TZs and the microscopic Cr depletion at dendrite boundaries.

Carcinogenic and Non-Carcinogenic Health Risk Evaluation of Heavy Metals in Water Sources of the Nubian Sandstone Aquifer in the El-Farafra Oasis (Egypt)

Expanding anthropogenic activities, globally and in Egypt, have increased concentrations of heavy metals in surface and ground waters. Contamination of drinking water may threaten public health. In the present study, the concentrations of 10 heavy metals were analyzed from natural springs (6) and drilled wells (10) in the Nubian Sandstone Aquifer of the El-Farafra Oasis and the White Desert National Park, Egypt. The average concentrations of heavy metals were in most cases below critical values of the WHO drinking water standard, except for Fe and Mn (average values were 495 and 107 µg·L−1, respectively). There is a surface circulation that develops within limestone (Post-Nubian Aquifer System—PNAS) and feeds the springs, while the water present in the wells (at least for the deeper ones) comes from the ferruginous sandstone (Nubian Sandstone Aquifer System—NSAS). This double circulation could account for the differences in the EC and TDS values (typical of a circulation in limestone-type aquifers for springs) and the Fe and Mn enrichment coming from the ferruginous sandstone of the NSAS. The average chronic daily intake (CDI) values for heavy metals in the study area are listed in decreasing order in the following: Fe &gt; Mn &gt; Zn &gt; Co &gt; Ni &gt; Cr &gt; As &gt; Pb &gt; Co &gt; Cd. The total hazard quotient (HQtotal = HQoral + HQdermal) and Hazard Index (HI) values calculated for different heavy metals were well below the acceptable limit, indicating no significant non-carcinogenic health risks to the residents of both areas via oral and dermal absorption of drinking water. Furthermore, the results obtained for the total risk to human health showed that oral ingestion is the major pathway. Carcinogenic risk analysis indicated that the Incremental Lifetime Cancer Risk (ILCR) values for Pb, Cd, Ni, and Cr were well below the acceptable limits.

Ligand-Induced Atomically Segregation-Tunable Alloy Nanoprobes for Enhanced Magnetic Resonance Imaging.

Bimetallic iron-noble metal alloy nanoparticles have emerged as promising contrast agents for magnetic resonance imaging (MRI) due to their biocompatibility and facile control over the element distribution. However, the inherent surface energy discrepancy between iron and noble metal often leads to Fe atom segregation within the nanoparticle, resulting in limited iron-water molecule interactions and, consequently, diminished relaxometric performance. In this study, we present the development of a class of ligand-induced atomically segregation-tunable alloy nanoprobes (STAN) composed of bimetallic iron-gold nanoparticles. By manipulating the oxidation state of Fe on the particle surface through varying molar ratios of oleic acid and oleylamine ligands, we successfully achieve surface Fe enrichment. Under the application of a 9 T MRI system, the optimized STAN formulation, characterized by a surface Fe content of 60.1 at %, exhibits an impressive r1 value of 2.28 mM-1·s-1, along with a low r2/r1 ratio of 6.2. This exceptional performance allows for the clear visualization of hepatic tumors as small as 0.7 mm in diameter in vivo, highlighting the immense potential of STAN as a next-generation contrast agent for highly sensitive MR imaging.

Contrasting effects of increasing dissolved iron on photosynthesis and O2 availability in the gastric cavity of two Mediterranean corals.

Iron (Fe) plays a fundamental role in coral symbiosis, supporting photosynthesis, respiration, and many important enzymatic reactions. However, the extent to which corals are limited by Fe and their metabolic responses to inorganic Fe enrichment remains to be understood. We used respirometry, variable chlorophyll fluorescence, and O2 microsensors to investigate the impact of increasing Fe(III) concentrations (20, 50, and 100 nM) on the photosynthetic capacity of two Mediterranean coral species, Cladocora caespitosa and Oculina patagonica. While the bioavailability of inorganic Fe can rapidly decrease, we nevertheless observed significant physiological effects at all Fe concentrations. In C. caespitosa, exposure to 50 nM Fe(III) increased rates of respiration and photosynthesis, while the relative electron transport rate (rETR(II)) decreased at higher Fe(III) exposure (100 nM). In contrast, O. patagonica reduced respiration, photosynthesis rates, and maximum PSII quantum yield (Fv/Fm) across all iron enrichments. Both corals exhibited increased hypoxia (<50µmol O2 L-1) within their gastric cavity at night when exposed to 50 and 100 nM Fe(III), leading to increased polyp contraction time and reduced O2 exchange with the surrounding water. Our results indicate that C. caespitosa, but not O.patagonica, might be limited in Fe for achieving maximal photosynthetic efficiency. Understanding the multifaceted role of iron in corals' health and their response to environmental change is crucial for effective coral conservation.

Changes in Growth and Heavy Metal and Phenolic Compound Accumulation in Buddleja cordata Cell Suspension Culture under Cu, Fe, Mn, and Zn Enrichment.

Buddleja cordata cell suspension cultures could be used as a tool for investigating the capabilities of this species to tolerate heavy metals (HMs) and for assessing the effects of HMs on the accumulation of phenolic compounds in this species. It grows in a wide range of habitats in Mexico, including ultramafic soils, and mobilizes some HMs in the soil. The mobilization of these HMs has been associated with phenolic substances. In addition, this species is used in Mexican traditional medicine. In the present study, a B. cordata cell suspension culture was grown for 18 days in a culture medium enriched with Cu (0.03-0.25 mM), Fe (0.25-1.5 mM), Mn (0.5-3.0 mM), or Zn (0.5-2.0 mM) to determine the effects of these HMs on growth and HM accumulation. We also assessed the effects of the HMs on phenolic compound accumulation after 1 and 18 days of HM exposure. Cells were able to grow at almost all tested HM concentrations and accumulated significant amounts of each HM. The highest accumulation levels were as follows: 1160 mg Cu kg-1, 6845 mg Fe kg-1, 3770 mg Mn kg-1, and 6581 mg Zn kg-1. Phenolic compound accumulation was affected by the HM exposure time and corresponded to each HM and its concentration. Future research should analyze whole plants to determine the capabilities of Buddleja cordata to accumulate abnormally high amounts of HM and to evaluate the physiological impact of changes in the accumulation of phenolic compounds.

Geochemistry, Petrology and Tectonic Settings of Dolerite Dykes of Ranipet District, Northern part of Southern Granulite Terrain, Tamil Nadu, India

&#x0D; &#x0D; &#x0D; The dolerite dykes and their associated rock are collected from the Ranipet district which is located in the northern part of the Southern Granulite Terrain and South of the Dharwar craton. The major dyke in the Ranipet district shows WSW-ENE trending dykes intruded the hornblende-biotite gneiss with gabbroic diorite and granite gneiss. The dolerite in this region shows typical dolerite composition with high alteration like chloritization and sericitization. Mineralogically, the rock shows laths of plagioclase, anhedral to euhedral clinopyroxene with basal cleavage, and quartz minerals. The opaque minerals ilmenite and magnetite crystals interstice the major minerals and it has altered boundaries. Texturally, the rock shows subophitic and intermediate gabbroic texture (granular texture). TAS diagram shows that the dykes plot in the basalt, basalt andesitic, and rhyolitic field (highly sericitized dolerite). The host and other associated rocks plot within the sub-alkaline field. The bivariate plot for the studied dolerite shows a positive correlation with SiO2, CaO, Na2O, K2O, and P2O5 and a negative correlation with TiO2, Fe2O, and Al2O3. The AFM and Jensen plots show that the dolerites samples plot in the tholeiitic field with Fe enrichment and a High Fe tholeiitic character respectively. The primitive mantle diagram shows the depletion of Nb, P, and Ti showing possible interaction of crust during the emplacement. The Chondrite normalized plot for the dolerite shows enrichment of LREE and Slight depletion of HREEs indicates OIB character. Tectonically, the dolerites formed emplaced in the continental and alkaline arc OIB settings with E-MORB affinity.&#x0D; &#x0D; &#x0D;

An assessment of the impact of traditional rice cooking practice and eating habits on arsenic and iron transfer into the food chain of smallholders of Indo-Gangetic plain of South-Asia: Using AMMI and Monte-Carlo simulation model

The current study was designed to investigate the consequences of rice cooking and soaking of cooked rice (CR) with or without arsenic (As) contaminated water on As and Fe (iron) transfer to the human body along with associated health risk assessment using additive main-effects and multiplicative interaction (AMMI) and Monte Carlo Simulation model. In comparison to raw rice, As content in cooked rice (CR) and soaked cooked rice (SCR) enhanced significantly (at p < 0.05 level), regardless of rice cultivars and locations (at p < 0.05 level) due to the use of As-rich water for cooking and soaking purposes. Whereas As content in CR and SCR was reduced significantly due to the use of As-free water for cooking and soaking purposes. The use of As-free water (AFW) also enhanced the Fe content in CR. The overnight soaking of rice invariably enhanced the Fe content despite the use of As-contaminated water in SCR however, comparatively in lesser amount than As-free rice. In the studied area, due to consumption of As-rich CR and SCR children are more vulnerable to health hazards than adults. Consumption of SCR (prepared with AFW) could be an effective method to minimize As transmission and Fe enrichment among consumers.

Influence of high‐strain deformation on major element mobility in garnet: Nanoscale evidence from atom probe tomography

AbstractGarnet is a common rock‐forming mineral that occurs in a variety of rock types and over a wide range of pressure (P)–temperature (T) conditions in the Earth's lithosphere. Because garnet is considered a high‐strength mineral stable across an extensive range of conditions (1–25 GPa, &lt;300–2000°C), it is generally accepted that garnets can retain their microstructures and chemical composition during deformation and metamorphism. Therefore, garnet is commonly used as a geothermobarometer and geochronometer to provide P–T and timing constraints on tectonic events. Herein, we study garnet from an eclogite facies mylonite (central Australia) to investigate the mechanisms of element mobility during high‐strain deformation under relatively dry, lower crustal conditions. Electron backscatter diffraction (EBSD) and electron channelling contrast imaging (ECCI) reveal evidence of crystal plasticity associated with brittle deformation in the form of heterogeneous misorientation patterns and low‐angle grain boundaries developed over length scales of 20–50 μm in the rims of garnet porphyroclasts. Atom probe tomography (APT) analysis of a low‐angle grain boundary within a highly strained portion of a clast shows Ca enrichment and Mg depletion along dislocations, whereas APT data along the rim of a mostly undeformed clast reveal a homogeneous distribution of garnet major components in the specimen matrix with the exception of Ca, Fe and Mg enrichment within a healed microfracture. The above‐mentioned results suggest that under relatively dry conditions, crystal plasticity enhances bulk element mobility via pipe diffusion, highlighting the importance of deformation‐induced microstructures on element mobility, with important implications for the robust and reliable use of garnet as a petrological tool.

Origin of Redbeds in the Neoproterozoic Socheong Formation and Their Relation to the Dashigou Large Igneous Province

During the latest Mesoproterozoic–Early Neoproterozoic era, extensional regimes generated a number of sedimentary basins in various regions in the Sino-Korean Craton. Mantle-plume emplacements are widely recognized in the sedimentary strata as mafic dikes and sills of the Dashigou Large Igneous Province (LIP). The occurrence of Fe-rich redbeds is first reported in the Neoproterozoic Socheong Formation of the Sangwon Supergroup in the Pyeongnam Basin. Their geochemical and mineralogical characteristics indicate basin-wide Fe enrichment due to hydrothermal fluid input. The episodic yet repetitive hydrothermal injection into the basin generated short-lived anoxia, recorded as greenish-gray coloration in the ferruginous beds. This hydrothermal fluid was likely sourced from the mafic igneous activities involved in the Dashigou LIP. The redbeds can be utilized as key beds for intra- or inter-basinal stratigraphic correlation and to study the negative carbon isotope excursions that occurred in the genetically related basins in the region (e.g., the Sangwon, Xu-Huai, and Dalian basins).

Responses of phytoplankton communities to N, P, Fe enrichments in wet season of tropical reservoirs in southern China: A case study of Dashahe Reservoir, Guangdong Province

Responses of phytoplankton communities to N, P, Fe enrichments in wet season of tropical reservoirs in southern China: A case study of Dashahe Reservoir, Guangdong Province

Simplification of the pretreatment method for phosphate oxygen isotope measurement in phosphogypsum leachate

The stacking of phosphogypsum has caused considerable phosphorus pollution in water bodies near phosphogypsum yards through surface runoff and underground infiltration. The phosphate oxygen isotope (δ18Op) tracing method has served as a valuable tool for tracing phosphorus pollution in water. However, the existing δ18Op enrichment and purification methods are complex, costly, and inefficient for phosphate recovery, particularly for phosphogypsum leachate with complex compositions. Herein, a simplified and optimized pretreatment method for δ18Op measurement in phosphogypsum leachate was developed. Zirconium/polyvinyl alcohol (Zr/PVA) gel beads showed good selectivity for phosphate enrichment from water at different initial phosphate concentrations with appropriate Zr/PVA dosage. The optimal enrichment pH value was <7, and the concentrated phosphate on the Zr/PVA gel beads could be effectively eluted in an alkaline environment. Compared with the traditional Fe or Mg coprecipitation enrichment methods, impurities in the solution showed no obvious adverse effects on the phosphate enrichment process. Further, the phosphate solution eluted from the Zr/PVA gel beads was purified by a simple adjustment of the pH instead of cation exchange in the traditional purification process. Magnesium ions in the solution could be completely removed when the pH ranged from 3.17 to 6.15, and the phosphate recovery rate could reach 98.66% when the eluent pH was 5.02. Fourier-transform infrared spectroscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy revealed that similar to traditional pretreatment method, the proposed method can obtain high-purity Ag3PO4 solids for δ18OP measurement and no isotope fractionation of δ18OP was observed. Therefore, this study provides a promising and reliable pretreatment method for δ18OP measurement, especially in complex phosphogypsum leachate.

Folded calcite cracks in noncalcareous shales: a window into shale diagenesis and hydrothermal influence

ABSTRACT Shale diagenesis is not well understood, and cracks in shale contain important information about diagenetic conditions. The way these cracks open reveals physical changes in the sediment, and the infilling minerals provide insight into the chemical conditions of the formation water. Typically, the authigenic minerals filling the folded cracks are consistent with the chemical composition of the host rocks. For example, folded calcite cracks are found in limestone. This paper, however, focuses on a set of folded calcite cracks in noncalcareous black shales. The goal is to improve our understanding of shale diagenesis by deciphering the origins of these cracks. The cracks are sinuously to ptygmatically folded in a vertical view and weakly sinuous on the bedding plane. They are filled with calcite, bitumen, pyrite, or a combination of them. Evidence of bioturbation and low redox-sensitive trace-element ratios suggest suboxic to oxic depositional conditions of the shale. The cracks were likely opened by gas expansion in unconsolidated mud. The main mineral filling the cracks, calcite, was sourced from hydrothermal fluid that passed through the underlying dolomite. Hydrothermal influences are indicated by the presence of bornite and microcrystalline pyrite in the cracks, as well as Fe and Mn enrichment in the host sediments. Hydrothermal activity can also explain the presence of buddingtonite, an ammonium feldspar in the shale. The results of this study suggest that folded cracks filled by minerals, gradually narrowing towards the top, and lacking internal detrital matrix are likely formed during early diagenesis. The inconsistency between the chemical compositions of the infilling material and the host sediment requires further exploration to identify the source. Hydrothermal fluid passing through the underlying dolomite may be the source of folded calcite cracks in noncalcareous sedimentary rocks. These cracks resemble molar-tooth structures (MTS), which are sinuous cracks filled with microcrystalline calcite mostly found in Precambrian limestone and calcareous shales. If these cracks are indeed MTS, they may be an exception to the age and host-rock lithology constraints of MTS.

Mechanism of arsenic accumulation in sediments of the northern China: Insight from provenance, weathering processes and paleoenvironmental changes

Fluctuations in sedimentary As burial have been reported throughout geological timescales, but detailed weathering pathways governed by climatic evolution are poorly understood. To this end, we reconstructed various climatic stages utilizing lithologies, geochemical indicators, and dating data and illustrated the physical–chemical pathways that affect As accumulation and release. The results revealed six climate changes. The climatic evolution was a consequence of the relative intensities of the East Asian summer monsoon (EASM) and East Asian winter monsoon (EAWM). Higher sedimentary As, Fe, and Feclay concentrations are observed in the cold-arid climates and suggest As accumulation occurred due to strong physical erosion. Moreover, correlations between Feclay and clay minerals indicate favorable clay minerals during cold-arid climates (e.g., illite, chlorite, and illite–smectite mixed layer) enhanced the accumulation of Fe-rich clay minerals and then As burial. In warm-humid climates, intense biogeochemical processes prevailed and contributed to crystalline Fe enrichment, which might accelerate As release. This analysis shows climate shifts alter solid As partitioning in sedimentary basins and potentially result in significant impacts with respect to global As contamination.