Silicic Research Articles

Soil carbon management and enhanced rock weathering: The separate fates of organic and inorganic carbon

AbstractSoil carbon (C) management has been promoted as one of the few readily available strategies to mitigate the rising concentration of atmospheric CO2 and its associated impacts on climate change. One of these carbon management strategies is enhanced rock weathering (ERW) which involves adding crushed silicate rocks to the soil. These rocks weather and remove atmospheric CO2 by converting it into bicarbonate in solution. The approach requires careful interpretation of the differences between soil organic carbon (SOC) and soil inorganic carbon (SIC) and their measurement, with implications for land management and C credit accounting. In this Opinion, we emphasise the distinct nature and fates of SOC and SIC, advocating for their separate management, particularly in C credit schemes. It is imperative that protocols for soil C management explicitly recognise the difference between SOC and SIC to prevent any ambiguity. Farmers should be able to claim credits for increases in SOC alongside and independently of any claim for credits for ERW (i.e. SIC). Despite the potential of ERW for C removal, we emphasise that further research is needed to improve the measurement and monitoring of SIC and to understand ERW's potential implications for SOC turnover and greenhouse gas emissions.Highlights Enhanced Rock Weathering increases dissolved inorganic carbon (bicarbonate). Soil organic carbon (SOC) may be influenced by Enhanced Rock Weathering. Carbon credit via Enhanced Rock Weathering is separate from credit linked to soil organic carbon. Soil organic matter and enhanced rock weathering both have roles to play for carbon credits.

Formation of silicic crust on early Earth and young planetary bodies in an Iceland-like setting

Four billion years ago, Earth’s surface was covered with a thick basaltic crust and, similar to other rocky planets and the Moon, parts of this basaltic crust underwent partial melting to produce silicic crust. On Earth, silicic crust grew into the continents. An analogue of a pre-subduction early Earth and rocky planetary bodies is found in Iceland, where poorly understood granitic rocks are encased in thick basaltic crust away from any active subduction zone. Here, we investigate these Icelandic granitoids to understand the mechanisms that generated the Earth’s oldest continents, and silicic rocks on Mars and Venus. New geochemical data from silicic Icelandic intrusions, show that the granitoids are formed through partial melting of the Icelandic crust, but are compositionally unlike early Earth continental material. We show that intra-crustal partial melting of basalt can potentially form silicic material on other planetary bodies but cannot produce the first continents on Earth.

Nanoscale characterization of Ediacaran microfossils from lower Doushantuo formation chert nodules

Microfossils identification, especially in very old rocks, is extremely challenging because morphological and chemical signatures of microfossils are subtle and inevitably altered with aging. Chert nodules from the Doushantuo Formation in the Yangtze Gorges area of South China have captured significant interest due to their remarkable preservation of Ediacaran microfossils. To understand the taphonomic processes leading to an exceptional preservation of microbes in these rocks, we studied the morphological and chemical features of microfossils within the lower Doushantuo Formation chert nodules down to atomic scales via advanced microscopy techniques. Our results align with previous studies, confirming that most microfossils there are preserved by silicification. Further analysis of a representative filamentous microfossil, Polytrichoides lineatus, reveals that both the cell wall (or extracellular sheath) and cytoplasm are preserved by loose aggregates of subrounded or irregular quartz grains, along with patchy organic residuals, which are distinctive from the closely packed and angular-shaped quartz grains in the non-fossil matrix of the chert nodule. The cell wall or extracellular sheath likely provided narrower spaces and more nucleation sites for silicification, resulting in smaller quartz grains (i.e., 115 ± 42 nm) compared to those formed in the cytoplasm (i.e., 1150 ± 258 nm). The permeation and precipitation of quartz grains within the cell wall or extracellular sheath could contribute to an exceptional preservation of subcellular structures. This study offers valuable insights into the preservation of microbes in the Doushantuo Formation chert nodules and even older siliceous sedimentary rocks.

Cobalt and nickel distribution and controlling factors in the Bushveld layered complex

The Bushveld Complex is the largest known layered intrusion in the world and has been extensively studied. However, there remains an absence of systematic investigations of cobalt (Co) and nickel (Ni) distribution at various scales. Elements Co and Ni behave varying degrees of compatibility within chromite, silicates, and sulfides, making them effective proxies for elucidating chemical competition and interaction among these minerals. This study aims to characterize Co and Ni distribution in olivine, pyroxenes, chromite, and whole rocks from different seams of the Bushveld Complex and to reveal their controlling factors. Our results indicate large variations of whole-rock Co and Ni concentrations, with a decreasing sequence of dunites (Co: 156–222 ppm; Ni: 2208–2750 ppm) > harzburgites (Co: 87.8–174 ppm; Ni: 152–2050 ppm) > pyroxenites (Co: 58.7–143 ppm; Ni: 387–1947 ppm) > norites (Co: 16.0–113 ppm; Ni: 153–646 ppm) > anorthosites (Co: 3.20–16.3 ppm; Ni: 19.7–97.2 ppm). In general, olivine has higher Ni contents (717–4496 ppm) and lower Co (105–239 ppm) than chromite (Ni: 524–1948 ppm; Co: 236–563 ppm). Pyroxenes have apparently low Co (orthopyroxene: 39.7–184 ppm; clinopyroxene: 17.2–114 ppm) and Ni contents (orthopyroxene: 224–1195 ppm; clinopyroxene: 177–831 ppm). Chromite in chromitites has lower Co content than that in other rocks. The whole-rock and mineral Co and Ni variations in the stratigraphic profile are closely related with lithology, mineral assemblages and element partition coefficients in minerals. The Co contents in the chromite and pyroxenes vary alternately with the chromitites and rock seams, with lower Co contents in ore samples than that in silicate rocks. Whole rocks and mineral separates in the Merensky Reef exhibit the highest Ni contents (whole-rock: up to 4000 ppm; orthopyroxene: 1035–1195 ppm; clinopyroxene: 730–831 ppm; chromite: 1760–1948 ppm), which are likely attributed to sulfide segregation and diffusion between sulfides and other minerals. In addition, the sulfide segregation may also be a main factor resulting in Co-Ni decoupling in pyroxenes from the Main Zone of the Bushveld Complex.

Sustainability performance of enhanced weathering across countries: A triple bottom line approach

Enhanced weathering (EW) is a promising negative emission technology involving the application of crushed silicate rocks to croplands for carbon capture. There is limited research about the broad sustainability impacts in rolling out this intervention on a large scale. This research assesses the triple bottom line sustainability of EW in eight top-emitting countries using an extended input-output model. Results indicate that overall sustainability performance of EW is influenced by each country's environmental and social metrics than the economic. Compared to developed countries (UK, France, Germany, USA), emerging economies (Brazil, Russia, India, China) show relatively lower economic sustainability due to high working hours impact but benefit from higher socio-economic contributions. Improving practices, particularly reducing emissions, energy use, labour rights and health and safety risk for silicate rock production, is vital for better sustainability outcomes.

Novel approach evaluating powdered raw and hydrothermally treated syenite as stonemeal for tropical environments: Potential effects on groundwater quality and agricultural suitability

Soluble fertilizers, particularly potash, are often prohibitively expensive or unavailable in Africa. Consequently, alternatives such as powdered silicate rocks, both raw and hydrothermally treated, are being explored as potential solutions, especially for acidic tropical soils. This study investigates the possible impacts of these rocks (syenite) on groundwater quality, which is a critical factor for agricultural activities. The powdered raw material underwent chemical and mineralogical characterization, including X-ray fluorescence and X-ray diffraction, followed by quantitative evaluation of materials by scanning electron microscopy. Both raw and 46 hydrothermally treated materials were subjected to sequential leaching cycles (1, 24, and 192 h) using deionized water, and the resulting leachates were analyzed by inductively coupled plasma atomic emission spectroscopy. Parameters such as electrical conductivity, total dissolved solids, soluble sodium percentage, sodium adsorption ratio, magnesium hazard, Kelly's ratio, and permeability index were also evaluated. Results from the 47 leachates indicated that 64 % of the samples exhibited excellent to acceptable water quality for irrigation purposes across all parameters. Conversely, 6 % to 13 % fell into the doubtful category, and 2 % to 24 % were classified as unsuitable. Consistency index and ratios of approximately 0.07 and 0.042, respectively, were determined using multi-criteria decision analysis (analytic hierarchy process: AHP), confirming the coherence of the decision and pairwise comparison matrix. The weighted coefficients for each criterion ranged from 0.06 to 0.2. Consequently, the optimal sample (Treatment 23) was identified, showing a hydrothermal temperature of 176 °C, a time of 3.9 h, a normality of 4.62, and a liquid-solid ratio of 0.24. This treatment met all high-water quality standards, including low salinity and sodium hazard, as corroborated by the US salinity laboratory and Wilcox diagrams. Furthermore, due to their nutrient release, low concentration of toxic elements, and effective buffering capacity (pH ∼ 10.6), these powdered syenites are suitable for application in acidic soils.

Hydrochemical Characteristics, Controlling Factors and Water Quality Evaluation of Groundwater Quality in Kono, Sierra Leone

Groundwater is a major source of drinking water and is considered an imperative component of the accessible water assets across Sierra Leone and many parts of the world. The degradation of groundwater can jeopardize drinking water availability and human health. 29 groundwater monitoring samples with 16 water quality parameters were analyzed. Descriptive statistics, Piper plots, Arc GIS spatial interpolation, Gibbs plots, ion ratio analysis, Wilcox diagram, water quality index (WQI), and entropy-weighted water quality index (EWQI) were used to investigate the hydrochemical characteristics, controlling factors and evaluate the groundwater quality in the study area. The results revealed that the groundwater mean concentration of NO3− in the mining concession was 34.00 mg/L which was above the permissible limit, Ca2+ and HCO3− are higher in the Koidu community compared to the mining concession water, indicating weakly alkaline with dominant anions and cations of HCO3− and Na+ + K+ respectively, and the hydrochemical types were mainly HCO3−·Ca2+ and HCO3− ·Na+. The order of anion concentration in groundwater was HCO3− > NO3− > SO42− > Cl− and HCO3− > SO42− > NO3− > Cl− in the mining concession and the Koidu community respectively. Cations were Ca2+ > Na+, K+ > Mg2+ > Fe²⁺, and Ca2+ > Na+ > Mg2+ > K+ > Fe²⁺ in the mining concession and the Koidu community respectively. The interpretation of WQI and EWQI analysis exhibits 55.17% excellent, 17.24% good, 20.69% medium, 6.90% very poor, and 27.59% excellent, 24.14% good, 34.48% medium, 3.45% poor, and 10.34% very poor water respectively. Most of the sampling sites display similar trends to the WQI and EWQI. The solute source of groundwater was mainly controlled by water-rock interaction, cation exchange and the weathering of silicate and carbonate rocks were jointly the main contributors to the formation of the chemical components of groundwater in the study area, among which the main controlling factors of the groundwater were leaching, precipitate concentration and anthropogenic activities, and sulfate rock and carbonate rock dissolution. The overall water quality in the study area was suitable for human consumption but was polluted to an insignificant extent by mining activities. This study provides theoretical support and a decision-making basis for developing, utilizing, and protecting water resources in the study area.

Detrital Tourmalines in the Cretaceous–Eocene Julian and Brkini Flysch Basins (SE Alps, Italy and Slovenia)

In the SE Alps, two Cretaceous–Eocene flysch basins, Julian and Brkini, filled with turbidite sediments, are present. This study novelly reports heavy mineral assemblage counts and detrital tourmaline characterization for 11 samples. It is possible to define three different groups, characterized by the presence of (1) a clinopyroxene–epidote–low-ZTR (zircon+tourmaline+rutile; 5%) sample association, (2) a high-ZTR (>48%)–garnet–apatite association and (3) a low-ZTR (<40%)–Cr-spinel–garnet association. Detrital tourmalines from both the Julian and Brkini flysch basins are rather similar in composition, associated with metapelites and metapsammites coexisting or not coexisting with an Al-saturating phase, ferric-iron-rich quartz–tourmaline rocks and calc–silicate rocks; however, their number is drastically different. In fact, even if the percentage of heavy minerals is very low and similar in both basins (0.17–1.34% in weight), in the Julian basin, the number of tourmaline crystals is much lower than that in Brkini (1–14 vs. 30–100), suggesting an important change in the provenance area. Interestingly, the presence of a high amount of tourmaline derived from ferric-iron-rich quartz–tourmaline rocks and calc–silicate rocks makes these two basins different from all the Cretaceous flysch basins of Bosnia and the Northern Dinaric zone, where these supplies are missing or very limited.

Application of microwave digestion for complete dissolution of igneous silicate rock samples: A simple and quick sample preparation procedure

In the area of geochemical analyses of rock solutions, achieving a complete sample dissolution is a fundamental prerequisite for obtaining accurate, precise and reliable analytical results. The challenge posed by the presence of resistant minerals such as zircon, rutile, corundum, spinel, tourmaline, beryl, chromite, and cassiterite in different silicate rocks is a well-recognized challenge in geological studies. These minerals, due to their resilient nature, demand additional efforts to ensure complete dissolution during sample preparation. The prevailing conventional sample digestion methods require several days of laboratory work and the handling of large amounts of multiple types of acids, which also increase sample blanks. Until recently, there was a widely held belief that microwave-assisted digestion, where microwave radiation is transformed to heat, faced limitations in achieving complete dissolution of refractory minerals. This prevailing opinion led to skepticism about the applicability of microwave-assisted digestion for sample preparation of e.g. igneous rock samples containing these minerals. This study introduces a novel, universal and quick closed-vessel (pressurized) high-temperature microwave-assisted digestion method appropriate for dissolution of all major types of igneous silicate rock samples, including rocks containing refractory minerals. This streamlined and expeditious procedure, comprising three steps, requires only a total time of ∼9 h. The method proves its versatility by successfully dissolving both, mafic igneous samples (e.g., basalt) with low-content of resistant minerals, and felsic igneous samples (e.g., granite) with relatively high-content of resistant minerals. To validate the reliability of this procedure, 36 trace elements were analyzed: Li, Be, Sc, V, Cr, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Cs, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, Pb, Th and U in several geological Certified Reference Materials (CRMs). The CRMs including basalts JB-3, BCR-2, BHVO-2; andesites JA-2, AGV-2; granodiorite GSP-2; granite JG-2 and alkaline granite MGL-OShBO, were digested and analyzed using triple quadrupole Inductively Coupled-Plasma-Mass Spectrometer (ICP-QQQ). The results of the analysis demonstrate remarkable consistency, closely aligning with both certified and literature values.

The Weixi High‐silica Granitoids in the Central Sanjiang Orogenic Belt, Southwest China: Implications for Growth of the Continental Crust

AbstractHigh‐silica granitoids record the formation and evolution of the continental crust. A new intrusive complex has been recognized among silicic volcanic rocks of the Weixi arc, Southwest China. The intrusions consist of granites, granitic porphyries, and granodiorites. Zircon U‐Pb age data indicate that the Weixi granitoids formed at 248–240 Ma and were coeval with silicic volcanic rocks of the Weixi arc. The Weixi granitoids are enriched in Rb, Th, and U, depleted in Ba, Sr, Nb, Ta, and Ti, and have high light/heavy rare earth element ratios and slightly negative Eu anomalies. The Weixi granitoids have negative εNd(t) values (–9.8 to –7.8) and negative zircon εHf(t) values (–12.02 to –5.11). The geochemical and isotopic features suggest the Weixi granitoids were derived by partial melting of ancient crustal material. The Weixi granitoids and silicic volcanic rocks were derived from the same magma by crystal accumulation and melt extraction, respectively, and they record the formation of a continental arc in the central Sanjiang orogenic belt.

Early Triassic Silicic Volcanics of South China: Petrogenesis and Constraints on the Geodynamic Evolution of the Paleo‐Tethys Ocean Region

AbstractThe only occurrence of Lower Triassic silicic volcanic rocks within the South China Block is in the Qinzhou Bay area of Guangxi Province. LA‐ICP‐MS zircon U‐Pb dating reveals that volcanic rocks of the Beisi and Banba formations formed between 248.8 ± 1.6 and 246.5 ± 1.3 Ma, coeval with peraluminous granites of the Qinzhou Bay Granitic Complex. The studied rhyolites and dacites are characterized by high SiO2, K2O, and Al2O3, and low MgO, CaO, and P2O5 contents and are classified as high‐K calc‐alkaline S‐type rocks, with A/CNK = 0.98–1.19. The volcanic rocks are depleted in high field strength elements, e.g., Nb, Ta, Ti, and P, and enriched in large ion lithophile elements, e.g., Rb, K, Sr, and Ba. Although the analyzed volcanic rocks have extremely enriched zircon Hf isotopic compositions (εHf(t) = –29.1 to –6.9), source discrimination indicators and high calculated Ti‐in‐zircon temperatures (798–835°C) reveal that magma derived from enriched lithospheric mantle not only provided a heat source for anatectic melting of the metasedimentary protoliths but was also an endmember component of the S‐type silicic magma. The studied early Triassic volcanics are inferred to have formed immediately before closure of the Paleo‐Tethys Ocean in this region, as the associated subduction would have generated an extensional setting in which the mantle‐derived upwelling and volcanic activity occurred.

The Aguas Zarcas carbonaceous chondrite meteorite: Brecciation and aqueous alteration on the parent body

AbstractCM chondrites are samples from primitive water‐rich asteroids that formed early in the solar system; many record evidence for silicate rock–liquid water interaction. Many CM chondrites also exhibit well‐developed fine‐grained rims (FGRs) that surround major components, including chondrules and refractory inclusions. Previous studies have shown that Aguas Zarcas, a CM2 chondrite fall recovered in 2019, is a breccia consisting of several lithologies. Here, we present a study of Aguas Zarcas using optical microscopy, scanning electron microscopy, and electron probe microanalysis, focusing on brecciation and aqueous alteration on the parent body. We observed two lithologies within our sample, separated by a distinct textural and chemical boundary. The first lithology has a higher chondrule abundance (“chondrule‐rich”) and significantly larger FGRs compared to the second lithology (“chondrule‐poor”), even for similarly sized chondrules. We observed clear compositional differences between the two lithologies and more multilayered FGRs in the chondrule‐rich lithology. We determined that the chondrule‐rich lithology is less altered (petrologic type 2.7–2.8) and displays larger FGRs to chondrule ratios compared to the more altered chondrule‐poor lithology (petrologic type 2.5–2.6). These observations are contrary to previous models that predict aqueous alteration as a cause of FGR formation in the parent body. Our observed differences in Mg and Fe distribution in the lithology matrices alongside variable FGR thickness suggest distinct formation environments. We propose that the Aguas Zarcas parent body was subjected to several minor and major brecciation events that mixed different materials with variable degrees of aqueous alteration together, in agreement with previous studies.

Dry masonry mixtures based on siliceous opal-cristobalite rocks for clinker bricks

Clinker bricks have always attracted consumers with their high physical and mechanical characteristics: strength, dense structure, frost resistance, low water absorption values. In recent years, enterprises producing ceramic materials have begun to look for the opportunity to produce these products in Russia. With increased demand for clinker bricks, a technology has emerged for creating large-sized clinker stones which feature increased voids – 60-80%, an average density of 450-700 kg/m3 and thermal conductivity of 0.8-0.11 W/(m·°C), and a compressive strength of 10-30 MPa. The use of such wall products in construction projects predetermines specific building mixtures for masonry work that would meet the required values for strength, water absorption, vapor permeability and, at the same time, would have reduced thermal conductivity characteristics. To develop such masonry mortars, it is necessary to select the grain composition of quartz sand for building mixtures to ensure structural strength indicators. Thus, the research aims at finding lightweight aggregate and increasing porosity in order to improve the heat-shielding properties of clinker brick masonry and clinker high-hollow large-sized blocks.

Late Carboniferous–Early Permian sedimentary–tectonic evolution in the eastern Qaidam Basin, Western China: Insight into the zircon U–Pb geochronology of ash-fall tuffs and sandstones

The Late Carboniferous–Early Permian period is a significant transitional phase within the late Paleozoic ice age and to investigate the sedimentary–tectonic evolution of the Qaidam Basin in this period is crucial for comprehensively understanding the tectonic history of the northeastern Paleo-Tethys Ocean and the related response to energy and mineral resources. This paper focuses on the Carboniferous–Permian strata of the Wanggaxiu-Dongdagou outcrop that was taken to represent the southern Oulongbruk terrane in the eastern Qaidam Basin. We determined the ages of tuff interbeds within the Zhabusagaxiu Formation originally identified as the upper Carboniferous and obtained the crystallization age spectra of detrital zircon grains from Carboniferous to lower Permian sandstones using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) isotope geochemical techniques. The origin of the volcanic ash and the sedimentary–tectonic evolution in this period were analyzed. The results indicate that the original Zhabusagaxiu Formation can be divided into two chronostratigraphic units: the upper Carboniferous Zhabusagaxiu Formation and the lower Permian. The earliest age obtained from tuffaceous layers within the dark shale interval is 297.8 ± 3.0 Ma (mean square weighted deviation (MSWD) = 0.87), which suggests a stratigraphic boundary between the Carboniferous and Permian periods. Detrital zircons from Carboniferous–Permian samples in the southern Oulongbruk terrane predominantly originated from the Qaidam block-North Qaidam ultrahigh-pressure belt continental island arc to the south. The ultrahigh-pressure belt had a significantly increased contribution to the detrital source supply system from the Late Carboniferous to Early Permian, while the Qaidam block experienced frequent volcanic eruptions from 298 to 293 Ma, dispersing volcanic ash only northward to the Oulongbruk back-arc basin and the Zongwulong Trough. The upper Carboniferous Zhabusagaxiu Formation was marked by siliceous clastic rock–carbonate rock interbedding in an epicontinental sea, while the lower Permian was characterized by shallow to bathyal marine shelf to subaqueous sedimentation. The Early Permian transgression potentially represents the largest transgression during the late Paleozoic ice age, indicating an enriched hydrocarbon-generating interval.

Soil management practices can contribute to net carbon neutrality in California

Stabilizing climate requires reducing greenhouse gas (GHG) emissions and storing atmospheric carbon dioxide (CO2) in land or ocean systems. Soil management practices can reduce GHG emissions or sequester atmospheric CO2 into inorganic and organic forms. However, whether soil carbon strategies represent a viable and impactful climate mitigation pathway is uncertain. A specific question concerns the role that land-management practices and soil amendments can play in realizing California’s ambition for carbon neutrality by 2045. Here we examine the carbon flux impacts of soil conservation (i.e., compost, reduced tillage, cover crop) and enhanced silicate rock weathering (EW) practices at different areal extents of implementation in cropland, grassland, and savanna in California under two climate change cases. We show that with implementation areas of 15% or 50% of private cultivated land, grassland, and savanna in California, soil conservation practices alone can contribute 1.40.72.1 % ( −1.8−0.9−2.7 Mt CO2eq y−1) and 4.62.36.9 % ( −6.0−3.0−8.9 Mt CO2eq y−1) of the additional emissions reduction needed (beyond previous targets) to meet the 2045 net neutrality goal (−129.3 Mt CO2eq y−1), respectively, on an average annual basis, including climate uncertainty. Including EW in these scenarios increases the total contributions of management practices to 4.12.55.6 % ( −5.2−3.2−7.3 Mt CO2eq y−1) and 13.58.218.6 % ( −17.5−10.7−24.2 Mt CO2eq y−1), respectively, of this reduction. This highlights that the extent of implementation area is a major factor in determining benefits and that EW has the potential to make a real contribution to net reduction targets. Results are similar across climate cases, indicating that contemporary field data can be used to make future projections. With EW there remains mechanistic uncertainties, however, such as rock dissolution rate and environmental controls on weathering products, which require additional field research to improve understanding of the technological efficacy of this approach for California’s 2045 carbon neutrality goal.

The origin of Ordovician siliceous rocks and their deposition settings in the Northwest Tarim Basin, NW China

The siliceous rocks are well developed in Northwest Tarim Basin, which plays an important role in indicating its forming environment. In order to determine the origin of siliceous rock and its deposition settings, the paper studies the petrographic and geochemical characteristics of siliceous rock in well KP 1 and outcrops in Northwest Tarim Basin based on core observation, microscopic section identification and analysis of major and trace elements and rare earth elements. The Ordovician siliceous rocks of Northwest Tarim Basin are mainly developed in the middle and upper Penglaiba Formation and the bottom of the Yingshan Formation. Three types of cherts are identified, including cryptocrystalline silica, microcrystalline quartz and fibrous chalcedony depending on the mineral morphology. The terrigenous source is best evidenced by the high Ti (160∼310 ppm) and Al (1300∼3180 ppm), and positive δ30Si (0.9–3.6‰). Whereas, hydrothermal processes can be inferred from relative high content of V, Ni, Sr, Mo and Ba, and no obvious Ce and Eu anomaly. The chert of well KP 1 and Kuluxi profile is deposited in continental-margin settings, which is evidenced by its Al2O3/(Al2O3 + Fe2O3) (0.58–0.94, average of 0.81) and its Lan/Cen ratio (0.76–1.02, average of 0.93). The continental-margin settings are also evidenced by the close relation between silicification and dolomitization. Silicification is commonly well developed where dolomitization occurs, because the dolomitization mainly occurs in the regression background, where provides more terrigenous source silica to the sea water and results in more silicification. This study highlights the origin of Ordovician siliceous rocks and the outcome from this new contribution may provide useful guidelines for hydrocarbon exploration in the basin and other global analogues.

Hydrogeochemical process and coal mining-motivated effect on the hydrochemistry for the groundwater system in mining area of Western China

The Jurassic coalfield in the mining area of western China exhibits a multi-layered groundwater system. However, it is subject to an arid and semi-arid climate with limited water resources. Consequently, the ecological environment is highly vulnerable, and the chemistry and quality of groundwater may be influenced by multiple factors. This study systematically the coal mining-motivated effect on the hydrochemistry and water quality of the groundwater system, using the Caojiatan Coal Mine as a case study. The analysis incorporates a combination of the self-organizing maps (SOM), entropy-weighted water quality index (EWQI), and traditional hydrochemical analysis methods. After coal mining, there was an increase in the proportion of HCO3-Ca and HCO3-Mg in the groundwater samples of J2z, J2y4, and J2y5. The groundwater is controlled by cation exchange as a whole. The J2y4 and above groundwater is influenced by both the dissolution of carbonate and silicate rocks before coal mining. After coal mining, the Quaternary and J2a groundwater in the western wing is primarily influenced by the dissolution of carbonate rocks; the J2z, J2y4 and J2y5 groundwater is primarily governed by the dissolution of silicate rocks and the oxidation of FeS2; the J2y3 and below groundwater is primarily controlled by the dissolution of evaporate rocks. The resulting dilution effect after coal mining and the implementation of measures for the discharge of treated mine water make the groundwater quality of the J2y4 and higher aquifers tend to be better. The research findings serve as a valuable reference for promoting the sustainable development and protection of groundwater resources not only in the study area but also in other coal mines.

Homoplasy rather than intergeneric hybridisation explains mammillose leaf cells in Schistidium mammillosum sp. nov. (Grimmiaceae)

We present a peculiar new species in the Grimmiaceae, Schistidium mammillosum, which is distinct in having mammillose leaf cells and pluristratose lamina. These features are rare in mosses but shared by a few Grimmia species including sympatric G. alpestris. Sporophyte characteristics of the new taxon, in contrast, indicated a species of Schistidium and suggested a possible intergeneric hybrid origin. Nuclear ITS and plastid rps4‒trnF sequence data consistently resolved the new taxon within species of Schistidium, thus contradicting the hybridogenic hypothesis. We suggest that the shared feature of mammillose cells evolved independently in the two genera in adaptation to similar environmental conditions, possibly prolonged snow cover. Supported by morphological similarity, our phylogenetic analyses indicate a sister relationship of S. mammillosum and S. marginale in the Confertum clade. Schistidium mammillosum colonises siliceous rocks in the alpine and nival zone and is to date known from the French Alps and a single locality in Switzerland.

Hydrochemical characterization and comprehensive water quality assessment of groundwater within the main stream area of Yishu River.

To gain a comprehensive understanding of the hydrochemical characteristics, controlling factors, and water quality of groundwater in the main stream area of Yishu River (MSYR), a study was conducted using water quality data collected during both the dry and wet seasons. Through statistical analysis, hydrochemical methods, fuzzy comprehensive evaluation, and health risk evaluation modeling, the water chemical characteristics of the main stream area of Yishu River were studied, and the water quality of the area was comprehensively evaluated. The findings indicate that HCO3- and Ca2+ are the predominant anions and cations in the MSYR during the dry and wet seasons, respectively. Moreover, anion concentration in groundwater follows HCO3- > SO42- > NO3- > Cl-, while cations are ranked as Ca2+ > Na+ > Mg2+ > K+. Overall, the groundwater manifests as weakly alkaline and is predominantly classified as hard-fresh water. During the wet season, there is greater groundwater leaching and filtration, with rock and soil materials more readily transferred to groundwater, and the concentrations of main chemical components in groundwater are higher than those during the dry season, and the hydrochemical types are primarily characterized as HCO3-Ca·Mg and SO4·Cl-Ca·Mg types. These results also suggest that the chemical composition of the groundwater in the MSYR is influenced mainly by water-rock interaction. The primary ions originate from the dissolution of silicate rock and carbonate rock minerals, while cation exchange plays a critical role in the hydrogeochemical process. Groundwater in the MSYR is classified mostly as class II water, indicating that it is generally of good quality. However, areas with high levels of class IV and V water are present locally, and NO3- concentration is a crucial factor affecting groundwater quality. In the wet season, more groundwater and stronger mobility lead to greater mobility of NO3- and wider diffusion. Therefore, the risk evaluation model shows that nitrate health risk index is higher in the wet season than it is in the dry season, with children being more vulnerable to health risks than adults. To study groundwater in this area, its hydrochemical characteristics, water quality, and health risk assessment are of great practical significance for ensuring water safety for residents and stable development of social economy.

Contribution of carbonate-derived dissolved inorganic carbon into autochthonous particulate organic carbon in two small temperate Korean rivers (Geum and Seomjin)

In this study, we estimated the contributions of carbonate mineral weathering to dissolved inorganic carbon (DIC) and carbonate-derived DIC to autochthonous particulate organic carbon (POC) in two temperate Korean rivers. We combined stoichiometric and stable carbon isotopic approaches to calculate the contribution of autochthonous POC, considering diverse riverine DIC sources. We collected surface water samples from May 2016 to May 2018 and analyzed the major ion composition of rivers along with the concentrations and stable carbon isotopes of DIC. Our estimates showed that the relative abundances of carbonate mineral weathering (0.41 ± 0.11 in the Geum River and 0.43 ± 0.07 in the Seomjin River) were only slightly lower than those of silicate mineral weathering (0.59 ± 0.1 in the Geum River and 0.57 ± 0.07 in the Seomjin River). The resulting percentage contributions of DIC derived from the carbonate mineral weathering to riverine autochthonous POC, if we consider the additional DIC sources of atmospheric and soil-derived CO2, were 10 ± 3 % in the Geum River and 2 ± 1 % in the Seomjin River. The calculated annual fluxes of carbonate-derived DIC for 2016–2018 were 23.2 ± 0.3 Gg C yr−1 in the Geum River and 1.1 ± 0.4 Gg C yr−1 in the Seomjin River. Moreover, the calculated annual fluxes of carbonate-derived POC were 3.6 ± 0.5 Gg C yr−1 in the Geum River and 0.1 ± 0.7 Gg C yr−1 in the Seomjin River. Accordingly, our study provides the first insight into the contribution of carbonate-derived DIC to riverine autochthonous POC in small temperate Korean river systems, dominated by silicate rocks.