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Rare earth elements (REEs) mobilize, fractionate, and are re-distributed during supergene processes, and thus provide a powerful tool with which to quantitatively reconstruct the effects of chemical weathering. Moreover, under certain conditions, the REEs can concentrate to levels in the regolith sufficient to form giant regolith-hosted REE deposits, that are now responsible for much of the World’s production of heavy REEs (HREEs). Understanding the supergene behavior of the REEs is an important first step towards applying the REEs as a geochemical tool and meeting the growing global demand of the REEs. Thermodynamic calculations predict that dissolution of the main REE minerals in REE-rich protoliths, namely synchysite-(Y), gadolinite-(Y), hingganite-(Y), yttrialite-(Y), allanite-(Ce), eudialyte, chevkinite-(Ce), britholite, euxenite and loparite-(Ce), should occur spontaneously during weathering. It therefore follows that a high abundance of these minerals in the protolith implies high mobility of the REEs during weathering and consequently a high potential for the discovery of economic REE resources. Dissolution of apatite is promoted by metamictization or structural distortion and could be also important at low pH. In contrast, some LREE-fluorocarbonate minerals, notably bastnasite-(Ce) and parisite-(Ce), and monazite-(Ce) are likely thermodynamically stable in acidic environments. Thus, they would be preserved in the regolith. Zircon, titanite, aeschynite, fergusonite, and xenotime-(Y) are resistant to acidic dissolution, consistent with their common occurrence as residual minerals. In the cases of the world-class regolith-hosted REE deposits in South China, the groundwater is mildly acidic to circumneutral and carbonate-rich. The REEs are consequently transported dominantly as hydrated cations and carbonate complexes, depending on the pH. The general inheritance of the REE pattern of the regolith groundwater in the clay-sorbed fraction in the regolith indicates that the REEs in regolith are scavenged from the regolith groundwater. Elemental anomalies of specific REEs in the clay-sorbed fraction are very likely caused by an anomalously high REECO3+ fraction in the corresponding regolith groundwater, suggesting a preferential uptake of the REECO3+ complexes by the clay minerals, feasibly by halloysite through intercalation as interlayer complexes. This reaction is expected to be particularly important for the sorption and enrichment of the HREEs in the regolith. Depending on the pH and carbonate concentration of the water, surface complexation on clay minerals or interlayer intercalation particularly in halloysite control the pattern of REE enrichment. Mixing of the regolith groundwater with the alkaline and carbonate-rich aquifer groundwater increases the pH and carbonate concentration and, in turn, affects the ability of the mixed water to transport the HREEs. Interplay of aqueous complexation with the regolith mineralogy significantly affects the REE fractionation and re-distribution during groundwater-regolith interaction.

Degraded water quality and environmental impacts caused by weathering of sulfide-bearing mine wastes are a legacy remaining at many historical mine sites. Release and mobilization of toxic metals (e.g., Zn and Cd) in mine drainage are often associated with weathering of primary sulfide minerals and precipitation and dissolution of secondary minerals. This study aims to couple field-scale measurements of physicochemical parameters with μm- and nm-scale mineralogical characterization to investigate sphalerite weathering and controls on Zn and Cd migration in an uncovered mine waste-rock pile. Elevated concentrations of Zn and Cd, potentially harmful to the receiving environment, were detected in waste-rock pore water and seepage. A suite of analytical techniques, including scanning electron microscopy – energy dispersive X-ray spectroscopy (SEM-EDS), scanning transmission electron microscopy (STEM) with EDS, electron microprobe analysis (EMPA), and synchrotron-based micro X-ray fluorescence (μ-XRF) mapping and micro X-ray absorption near edge structure (μ-XANES) spectroscopy were utilized in a high-resolution investigation of elemental- and secondary-mineral associations with sphalerite grains. EMPA and μ-XRF elemental maps and STEM investigations show depletion of Zn, Fe, S, and Cd, local enrichment of Cu, and distinct dissolution pits at the margins of sphalerite grains. Using μ-XANES, the speciation of solid phases containing Zn, Cu, Fe, and S indicates the dominance of primary sphalerite with microscopic inclusions of chalcopyrite, along with sparse occurrence of secondary Cu-bearing sulfides formed during weathering. These results suggest sphalerite oxidation leads to congruent dissolution without formation of distinct secondary-mineral coatings. Sphalerite weathering significantly contributes to elevated aqueous concentrations of Zn and Cd. Field-scale observations and mineralogical investigations indicate common occurrence of Fe-oxyhydroxides in the waste-rock pile. Seepage chemistry and surface complexation modeling results suggest that pH-dependent variations in reactions on the surfaces of the Fe-oxyhydroxides control aqueous concentrations of Zn and Cd, and the Zn/Cd ratio in the seepage. This work highlights the importance of understanding the mechanisms of sulfide-mineral oxidation and subsequent surface precipitation and adsorption, such that appropriate remediation action can be implemented to limit mobilization of metals to sensitive ecosystems.

Subaerial physical, chemical and biological weathering processes are significant contributors to mountain landscape development worldwide, and over long time scales. This paper reports on pseudokarst features formed by different subaerial weathering processes on a high-elevation basalt plateau surface in the Maloti–Drakensberg mountains of eastern Lesotho, southern Africa. Different mesoscale landforms identified on this plateau surface include enclosed depressions (containing seasonal pools) that are morphologically similar to karstic solutional features. Such basalt pseudokarst landforms have not been previously described. This study uses field data on depression morphometry, sediments, water chemistry and rock surface hardness to explore the varied subaerial weathering and erosion processes contributing to pseudokarst depression development. Results show that physical, chemical and biological weathering and erosion processes in combination can impact on the basalt land surface in widening and deepening these depressions. An evolutionary model for pseudokarst depression development proposes that different weathering processes in combination within the ‘critical zone’ cause changes in depression morphology, and that there are significant feedbacks between bedrock, weathering, and the development of distinctive micromorphological forms. It is likely that similar pseudokarst landforms from other locations with non-carbonate substrates have been under-reported in the literature.

International audience; AimsRare earth elements (REEs) and normalized REE patterns determined in plant and soil samples represent powerful tools to trace biogeochemical processes during weathering, soil genesis and processes in the rhizosphere, and thus publications reporting REE concentrations and normalized REE patterns in soil systems and plants are rapidly increasing.MethodsA normalized REE pattern allows for the recognition of anomalous concentrations of an individual REE. In the literature, anomalies are predominantly reported/focused for/on the redox-sensitive elements cerium (Ce) and europium (Eu) that can shift their oxidation state during interactions with organic and inorganic soil phases and the biological processes affecting their mobility in soil and uptake by plants. Thus positive Eu anomalies in plants are often interpreted as a consequence of reduction of Eu3+ to Eu2+ in the rhizosphere followed by a preferential uptake of Eu2+.ResultsDue to an analytical artefact in ICP-MS analysis, a false Eu anomaly may be reported. This can be avoided by using a barium (Ba) interference correction. We draw attention to the possibility of this problem and to being aware of its potential occurrence when Eu anomalies are reported.ConclusionsWe recommend (i) including information on how this potential problem was dealt with in the Materials and Methods section of articles and (ii) how to implement Findable Accessible Interoperable and Reusability (FAIR) guiding principles in that section (including data availability in an open repository).

Deep-seated relict permafrost was identified in borehole Udryn PIG-1 (north-eastern Poland) at depths from +450 to 357 m. In potential its extant provides an opportunity to expand the known effective realm of grain weathering. Specifically, uncertainty exists as to whether or not glacial-period frost weathering could even occur at such considerable depths, which is well outside an active-layer range (i.e., beyond the currently acknowledged domain of grain weathering). Sand deposits collected at a 410.70–396.75 m depth were subjected to grain-size analysis, then 0.5–0.8 mm quartz-grain surfaces were analysed under stereoscopic and scanning electron microscopy. The obtained results indicate that these relict-permafrost grains were both mechanically and chemically weathered. Mechanical weathering of quartz grains is identified as P- & F-type weathering. The former is associated with an increase in stress generated both by overlying ice-sheet masses and permafrost degradation. Here mechanical weathering was facilitated by the presence of well-sorted sediment, rounded or well-rounded grains, and high porosity. Its effects are microtextures such as breakage blocks and conchoidal fractures. F-type weathering is/was generated by freezing water in various sorts of cavities and cracks. Weathering is directly associated with the presence of permafrost at this depth. Additionally, chemical weathering is recorded on quartz-grain surfaces in the form of a ragged discontinuous coating. It has been proven here that weathering of quartz grains is not just a near-surface phenomenon, but also occurs deep below Earth's surface.

Relatively little is known about the deep water circulation and the role of deep weathering processes on the Critical Zone (CZ) evolution. In this study, major fractures from four deep boreholes and water collected from these fractures (20–60 m of depth) were studied to improve our understanding of the deep CZ in a granitic headwater watershed (Strengbach watershed, France). Geochemical analysis indicates that chemical composition of deep water (20–60 m) is clearly different than shallow subsurface waters (0–15 m), with higher mean concentrations and a stronger spatial variability across the watershed. Reactive-transport modeling performed with the 1D KIRMAT code (KInetic of Reaction and MAss Transport) highlights the role of minor mineral dissolution (i.e. dolomite) and of longer mean transit time (100–597 yr) along fractures for explaining these differences. The obtained results also shed light on the difference of hydrogeochemical functioning between shallow subsurface system (water sampled from springs and piezometers) and deep system (deep water from borehole fractures). The shallow subsurface system (0–15 m) is characterized by a spatially relatively homogeneous water flow, high mean pore velocities, and water–rock interactions in a porous regolith, while the deep water circulation (20–60 m) behaves much more as independent systems along fractures, with low mean pore velocities, and variable mineralogy and hydrodynamic conditions. A state of chemical equilibrium can also be reached along fractures in the deep CZ for some primary minerals (biotite and K-feldspar), a feature never observed so far in the simulations of shallow subsurface water chemical composition in the Strengbach watershed. Even if the deep water exhibits higher solute concentrations, significantly lower mean pore velocities inferred in the fractured zones imply that the deep water is responsible for a very small part of the total hydrologic and weathering fluxes in the watershed. The limited role of the deep weathering processes (20–60 m) compared to the shallow subsurface processes (0–15 m) suggests an up to bottom control of the CZ evolution at a millennial timescale. Our results also indicate that the majority of fresh water available for water supply at a human timescale originates from shallow subsurface waters, as the deep water circulation is too low for being critical at a timescale relevant for societal needs in this type of geological context.

The Bukit Timah Granite (BTG) formation is widely distributed in the central and northern parts of Singapore Island. The BTG rocks in the formation vary from granite to granodiorite. Several hybrid rocks and dykes are also present in the BTG. The granite is in various states of fracturing and weathering, ranging from residual soils to intact, unweathered fresh rock. This paper presents some mechanical and physical properties of Singapore BTG rocks, based on data from the Factual Geotechnical Reports of more than 200 boreholes from Downtown Line stage II (DTL2) sites of Cashew, Hillview, Bukit Panjang and Beauty World. The variations of the parameters, including the unconfined compressive strength (UCS), the point-load strength index (Is50), the Cerchar abrasivity index (CAI), and the slake-durability index are derived from laboratory tests on samples from borelogs of different depths. The empirical correlations between the UCS and Is50 and between the CAI and the strength parameters (UCS and Is50) are derived and validated against the commonly adopted equations. Statistical information, including the average values, the standard deviations, and the coefficients of variation, are provided for these parameters. These statistics provide a useful reference for numerical simulations and future projects involving BTG rocks.

Long-term carbon cycle models are critical for understanding the levels and underlying controls of atmospheric CO2 over geological time-scales. We have refined the implementation of two important boundary conditions in carbon cycle models, namely consumption by silicate weathering and carbon degassing. Through the construction of continental flooding maps for the past 520 million years (Myrs), we have estimated exposed land area relative to the present-day (fA), and the fraction of exposed land area undergoing silicate weathering (fAW-fA). The latter is based on the amount of exposed land within the tropics (±10°) plus the northern/southern wet belts (±40-50°) relative to today, which are the prime regions for silicate weathering. We also evaluated climate gradients and potential weatherability by examining the distribution of climate-sensitive indicators. This is particularly important during and after Pangea formation, when we reduce fAW-fA during times when arid equatorial regions were present. We also estimated carbon degassing for the past 410 Myrs using the subduction flux from full-plate models as a proxy. We further used the subduction flux to scale and normalize the arc-related zircon age distribution (arc-activity), allowing us to estimate carbon degassing in much deeper time. The effect of these refined modelling parameters for weathering and degassing was then tested in the GEOCARBSULFvolc model, and the results are compared to other carbon cycle models and CO2 proxies. The use of arc-activity as a proxy for carbon degassing brings Mesozoic model estimates closer to CO2 proxy values but our models are highly sensitive to the definition of fAW-fA. Considering only variations in the land availability to weathering that occur in tropical latitudes (corrected for arid regions) and the use of our new degassing estimates leads to notably higher CO2 levels in the Mesozoic, and a better fit with the CO2 proxies.

The delivery of potentially reactive iron minerals to the marine environment exerts a major control on ocean and marine sediment biogeochemistry, including the preservation and burial of organic carbon. One aspect of the global iron cycle that has received little attention concerns the phase partitioning of iron in highly chemically-weathered sediments from (sub)tropical mountainous regions, where the sediment is commonly deposited directly onto adjacent continental margins. Here, we report the phase partitioning of particulate iron in surface seafloor sediments deposited from oxic bottom waters along the east coast of China, including the Bohai Sea, Yellow Sea and East China Sea, in addition to the continental shelf region adjacent to the (sub)tropical mountainous island of Hainan in the northern South China Sea. We document highly reactive (FeHR) to total iron (FeT) ratios for the Bohai Sea, Yellow Sea and East China Sea that are typical of global marine sediments deposited under oxic water column conditions. By contrast, FeHR/FeT ratios in Hainan offshore sediments are significantly elevated above normal oxic marine sediments. These Hainan offshore sediments display a strong positive correlation between FeHR/FeT ratios and the chemical index of alteration (CIA) weathering proxy, suggesting that the Fe speciation systematics are controlled by the intensity of chemical weathering. This observation is supported by additional geochemical data and Nd isotope analyses, which suggest a common source lithology for all the studied regions. The Hainan sediments thus document a specific scenario, whereby highly chemically weathered sediments from the mountainous Hainan region bypass the inner shore settings that commonly disproportionately trap Fe (oxyhydr)oxide minerals, depositing high concentrations of FeHR on the adjacent continental margin. Such enrichments likely aid in the preservation of organic carbon in marine sediments, suggesting that organic carbon preservation and burial may be enhanced by elevated FeHR in such settings. We also establish a set of essential criteria for potential recognition of chemical weathering-induced enrichments in FeHR/FeT ratios in ancient marine sediments.

Sedimentary rocks can release carbon dioxide (CO2) during the weathering of rock organic carbon and sulfide minerals. This sedimentary carbon could act as a feedback on Earth’s climate over millennial to geological timescales, yet the environmental controls on the CO2 release from rocks are poorly constrained. Here, we directly measure CO2 flux from weathering of sedimentary rocks over 2.5 years at the Draix-Bleone Critical Zone Observatory, France. Total CO2 fluxes approached values reported for soil respiration, with radiocarbon analysis confirming the CO2 source from rock organic carbon and carbonate. The measured CO2 fluxes varied seasonally, with summer fluxes five times larger than winter fluxes, and were positively correlated with temperature. The CO2 release from rock organic carbon oxidation increased by a factor of 2.2 when temperature increased by 10 °C. This temperature sensitivity is similar to that of degradation of recent-plant-derived organic matter in soils. Our flux measurements identify sedimentary-rock weathering as a positive feedback to warming, which may have operated throughout Earth’s history to force the surface carbon cycle. The release of carbon dioxide during oxidative weathering of sedimentary rocks acts as a positive feedback to warming, according to 2.5 years of CO2 flux measurements from the Draix-Bleone Critical Zone Observatory, France.

The Couriège prospect (French Guiana) provides key examples of the diversity of gold distribution related to supergene processes. The nature of gold in two contrasted weathering profiles is examined as a function of the weathering lithofacies. The autochthonous profile hosts weathered Au-bearing quartz veins whereas the pediment profile is enriched in free gold issued from dismantled gold-bearing quartz veins. The gold distribution is controlled by: (1) the preservation of primary gold as free gold in both transported and autochthonous horizons and as electrum inclusions in detrital pyrite; and (2) the formation of secondary gold through dissolution/precipitation processes, expressed as gold spherulites on the free gold grain surface, an Ag-depleted rim around transported free gold grains and Ag-depleted gold micro-inclusions hosted by oxidized autochthonous pyrite. Gold enrichment through supergene chemical processes remains limited within the truncated autochthonous profile. A new conceptual model is proposed for the area, defining the role of chemical and physical processes in gold endowment and accounting for the geomorphological context. The overall evolution includes (1) deep weathering and peneplenation, (2) dismantlement and transport of lateritic material and (3) the development of a latosol cover. This study highlights that gold exploration in tropical environments must consider the residual v. transported nature and the inheritance of targeted pedogenic horizons.

The abundance and distribution of dissolved Re (DRe) were determined in the freshwater part of the Krka River (Croatia), which drains a karst landscape, and in the salinity gradient of its highly stratified estuary. Due to the low DRe concentration, a batch procedure consisting of a pre-concentration step using an anion exchange resin (Dowex) and analysis of DRe in 8 M HNO3 eluate using high-resolution inductively coupled plasma mass spectrometry (HR ICP-MS) was applied. Due to potentially inconsistent recoveries, which ranged from 60 to 87%, quantification was performed using the isotope dilution technique (ID). DRe concentrations in the Krka River increased downstream, from 6.2 pM at the spring site to 11.9 pM upstream of the estuary region. Weathering of the surrounding carbonate lithology is assumed to be the source of the natural Re. Two specific anomalies were registered: a strong increase in DRe concentration due to anthropogenic input near the town of Knin (27.5 pM) and a decrease at a downstream site caused by subsurface input of freshwater from the Zrmanja River, resulting in a relatively low DRe concentration (8.5 pM). In the estuarine region, a near- conservative behavior of DRe was found in the salinity gradient of the upper surface layer, with DRe concentrations ranging from 18 to 38 pM. Anthropogenic input was suspected within the estuarine segment near the urban area, causing a small positive deviation from the conservative line. In the bottom seawater layer, a minor decrease in DRe concentration in the most upstream estuarine regions was apparent, implying weak scavenging of Re

The Central Andes of South America host the largest known lithium resources in a confined area, but the primary lithium sources of the salar deposits and the mobilisation process of lithium are still a matter of speculation. Chemical weathering at or near the surface and leaching in hydrothermal systems of the active magmatic arc are considered the two main mechanisms of Li extraction from the source rock. The lithium and strontium isotope composition of typical salar deposits offer insights into the processes on how Li brine deposits in Andean evaporites are formed. Data from the Salar de Pozuelos indicate near-surface chemical weathering in a cold and dry climate as the dominant mobilisation process of Li, with evaporation being responsible for the enrichment. The Cenozoic ignimbrites are the favoured source rock for the Li, with subordinate additions from the Palaeozoic basement. The identification of the source rocks is supported by radiogenic Nd and Pb and stable B isotope data from salar deposits. A comparison with other Li brine and salt deposits in the Altiplano-Puna Plateau and its western foothills places the Salar de Pozuelos as an endmember of Li solubilisation by chemical weathering with only minor hydrothermal mobilisation of Li., Universität Bremen (1013)

Weathering of pyrite and copper sulfide-bearing rocks produces a consistent series of iron- and copper-bearing minerals that reflect vertical and lateral geochemical changes as supergene solutions react with rock and experience loss of oxidizing capacity. Reactive host rocks, comprising feldspars, mafic minerals, chlorite, and carbonates, buffer pH values that limit copper mineral destruction, thus restricting the supergene transport of copper. Generally, rocks that have undergone well-developed hypogene or supergene hydrolysis of aluminosilicates promote copper mobility because they do not react substantially with low-pH supergene solutions generated by oxidation of pyrite and associated copper sulfides. Development of geochemical stratigraphy is characterized by physical and geochemical parameters that determine the maturity of a supergene profile, with cyclical leaching and enrichment periods critical for the production of economically significant copper accumulation. Evidence for multicycle enrichment is recorded by hematite after chalcocite, hanging zones of copper oxides that replace chalcocite, and hematitic capping overlying immature goethitic-pyritic capping. Because pyrite is the most refractory sulfide with respect to chalcocite replacement, geochemically strong supergene enrichment is independent of total copper added to protore and instead is indicated qualitatively by the degree to which chalcocite replaces pyrite. Covellite replacement of chalcopyrite indicates weak copper addition to protore and generally represents the base and lateral extent of supergene enrichment; covellite replacement of chalcocite indicates incipient copper removal by copper-impoverished supergene solutions. Exploration for, and delineation of, mature supergene enrichment profiles benefits from the recognition of paleoweathering cycles and consequent development of mature geochemical stratigraphy.

This work focused on three landslide events that have attracted significant public concern due to the associated calamities they recorded in 1945, 2017 and 2019, i.e. the Charlotte, Regent and Madina landslides, respectively. Their geology, tectonics (structural discontinuities) and geomorphology, i.e. their GTG characteristics were studied to establish links between them and the landslide events.Field surveys were conducted, particularly on the Charlotte landslide, where the identification of geological structures was impeded to an extent by its obliteration by vegetation and sediment accumulations on relatively planar sections of the landslide area. Remote sensing and GIS techniques (earth imagery and drone images) enhanced the mapping and determination of landslides’ geometric and geomorphic parameters. Laboratory analyses of rock and soil samples provided the landslides’ petrological characterisation and were used to determine the particle-size distribution in the slide-prone soil.The study indicated a change in the gabbroic rock composition, variable geomorphological characteristics, and nature/pattern and density of the discontinuities. These factors, to a large extent, determined the nature and magnitude of the rainfall-triggered landslides. Charlotte lithology slightly differed from the other two landslides and recorded higher Silica (Si) and Aluminum (Al) and lower iron (Fe) from X-Ray Fluorescence (XRF) than rocks of Regent and Madina landslides. The study also revealed only a tenuous correlation between rock composition and weathering depth. The slope angles at the landslides’ prominent scarps (depletion zone) are steep (> 45 degrees) with altitudes of approximately 270 m, 200 m and 470 m above sea level for Charlotte, Regent and Madina, respectively. Unlike the Charlotte landslide, both Regent and Madina landslides are active, but geometrically, their area, length and run-out distances have relatively high variance with a coefficient of variance equals to 1. Information derived from this work can help understand the spatial variation in landslide characteristics and develop a susceptibility map.

The magnetic properties of the loess-paleosol sequences from northern Iran provides a model for understanding pedogenic processes and their relationship to paleo-precipitation in this region. For the first time, we present diffuse reflectance spectrophotometry (DRS) analyses, color measurement analyses, and temperature-dependent susceptibility (χ-T) in argon from two late Pleistocene loess-paleosol sequences in northern Iran. Magnetic iron oxide minerals, principally magnetite, maghemite, hematite, and goethite were identified in the study sections. The results of DRS and color measurements show that a* values, the hematite to goethite ratio and the maghemite to hematite ratio, exhibit a significant positive correlation with the pedogenic process and paleosol formation and are superior to low-frequency susceptibility alone for estimating paleoprecipitation. Our data also indicates that pedogenic maghemite-magnetite formation and dissolution/reprecipitation are major contributors to the magnetic enhancement of loess-paleosol sequences and might indicate a seasonal aspect for pedogenic maghemite-magnetite formation. We propose the DRS-derived illite to chlorite ratio as a useful index for assessing the intensity of silicate mineral weathering in the northern Iranian loess-paleosol sequences. In addition, DRS can be used to discriminate between pedogenic and detrital hematite of loess-paleosol sequences. We also propose that the χ-T cooling and heating ratio model is a quantitative proxy for magnetic enhancement in soils and paleosols of loess-paleosol sequences.

Terrestrial sediment supply and its composition, aquatic productivity and coastal hydrodynamics together control the nature of organic matter (OM) that buried in ocean margins. Distinguishing their individual roles in river-dominated continental margins is challenging, but crucial for understanding (i) the regional carbon cycle in modern times and (ii) the OM burial-climate link on shorter timescales. Here we investigate the contents of total organic carbon (TOC) and total nitrogen (TN) and stable carbon isotopic composition of TOC (δ13C), along with grain size and calcium carbonate, in three short, 210Pb- and 137Cs-dated, sediment cores (DH1-1, DH3-3 and DH5-1) from the Yangtze distal mud belt in the East China Sea to delineate the spatiotemporal distribution, origin and burial flux of sedimentary OM for the last ca. 130 years. We also use selected inorganic elements (Si, Al, Ca, Na, K, Rb and Sr) and geochemical proxies derived from them (i.e. chemical index of alteration-CIA, molar Al/Si, molar K/Na, K/Rb and Rb/Sr) to elucidate the importance of detrital composition and chemical weathering on the supply, transport and burial of OM. Bulk organic geochemical and grain size data suggest a longer transport of fine sediments-laden OM, indicating the role of China Coastal Current on hydrodynamic sorting in the study area. Spatial distribution of Al/Si, K/Na, Rb/Sr and CIA in all cores corroborates the selective transport of fine-grained minerals from the Yangtze estuary to the distal mud belt. Less variable molar C/N ratios (5.6–7.7) and δ13C values (–22.4 to –21.2‰) in our cores and the results of δ13C mixing model indicate the predominance of marine OM burial over the last century in the study area. Relationships of TOC, δ13C and mean grain size and spatial evolution of δ13C along the river-mud belt continuum show that adsorption of marine OM on the Yangtze-derived fine sediments during their southward transport. Estimated mean burial fluxes of terrestrial and marine OC (0.73 ± 0.21 and 1.88 ± 0.29 Tg C yr−1) indicate that the Yangtze distal mud belt, despite covering ~18% of the shelf area, acts as a key OM sequestration center (>50%) in the East China Sea. Comparison of records of riverine OC burial and geochemical weathering and grain size proxies of our cores with East Asian winter monsoon index, and sediment and water discharges in the Yangtze River confirms that hydrodynamics associated with the winter monsoon winds-driven China Coastal Current predominantly controlled the sediment accumulation and OM burial along the mud belt before 1970s. Nonetheless, human activities especially the construction of Three Gorges Dam have reduced the burial flux of terrestrial OC from 0.93 to 0.54 Tg yr−1, significantly affecting the supply and burial of OM and thus the regional carbon cycle since 1970s.

The naturally fractured rock in the open pit slope is susceptible to irreversible damage caused by fatigue loads related to freeze-thaw weathering, blasting vibration, earthquakes and tramcar traffic. To ensure the safety of rock mass and reveal how natural fracture affects the damage modelling characteristics is of great concern. Hence, this work aims at investigating the fatigue damage evolution of rock from volumetric deformation caused by F-T and cyclic loads. The rock structural deterioration and damage accumulation were investigated as well as the stimulated natural fracture pattern. Results show the frost heaving force acted on natural fracture results in the rock volumetric changes. The damage variable expressed by volumetric strain presents a linear relationship with freeze-thaw cycles. In addition, the axial, lateral and volumetric strain of marble exposed to cyclic loads present a two-stage pattern, they first increase quickly and then get to steady and last for a long time. A new fatigue damage model was established by considering the freeze-thaw damage and mechanical damage simultaneously. The proposed coupling damage model can well describe rock damage accumulation. Moreover, the CT images further reveal the influence of the natural fracture on rock volumetric deformation and the final damage accumulation. It is suggested that the opening-mode natural fractures contribute a lot to rock freeze-thaw deformation and fatigue deformation.

The belowground architecture of the critical zone (CZ) consists of soil and rock in various stages of weathering and wetness that acts as a medium for biological growth, mediates chemical reactions, and controls partitioning of hydrologic fluxes. Hydrogeophysical imaging provides unique insights into the geometries and properties of earth materials that are present in the CZ and beyond the reach of direct observation beside sparse wellbores. An improved understanding of CZ architecture can be achieved by leveraging the geophysical measurements of the subsurface. Creating categorical models of the CZ is valuable for driving hydrologic models and comparing belowground architectures between different sites to interpret weathering processes. The CZ architecture is revealed through a novel comparison of hillslopes by applying facies classification in the elastic-electric domain driven by surface-based hydrogeophysical measurements. Three pairs of hillslopes grouped according to common geologic substrates — granite, volcanic extrusive, and glacially altered — are classified by five different hydrofacies classes to reveal the relative wetness and weathering states. The hydrofacies classifications are robust to the choice of initial mean values used in the classification and noncontemporaneous timing of geophysical data acquisition. These results will lead to improved interdisciplinary models of CZ processes at various scales and to an increased ability to predict the hydrologic timing and partitioning. Beyond the hillslope scale, this enhanced capability to compare CZ architecture can also be exploited at the catchment scale with implications for improved understanding of the link between rock weathering, hydrochemical fluxes, and landscape morphology.

The article presents and analyzes the data on ground waters of active (suprapermafrost) and hindered (subpermafrost) water exchange of geodynamically different terrains in order to prove the hydrogeological importance of their historical and tectonic characteristics. On the example of Trans-Polar Chukotka it is shown that, under suprapermafrost conditions, the ubiquitous eluvial-deluvial nappes are the most water-abundant on the terrane – a fragment of the passive continental margin, whereas they are the least water-abundant on the terrains of the active margin. Hydrogeological situation changes under subpermafrost conditions: more permeable and water-retaining rocks compose the terranes of the active margin. These differences are associated with the level of rock tectonic decompaction and, accordingly, with different intensity of weathering processes in the terrane rocks of different geodynamic origin in suprapermafrost and subpermafrost conditions. The hypergenesis zone on the terranes of the passive continental margin features coarse-grained rock weathering products accumulated in relatively calm geological and historical environments, the aggregate is sandy. The terranes of the active margin, which underwent long-term subvertical and subhorizontal displacements contain more fine-grained weathering products; the aggregate includes sandy loam and clay sand. Since the permafrost strata in both Trans-Polar Chukotka and Eastern Siberia is greater than the depth of hypergene transformations, the terranes of the active continental margin, the rocks of which were impacted by tectonic decompaction processes, mainly of a strike-slip and thrust nature, feature greater water abundance in subpermafrost conditions.

We investigated soil organic carbon (SOC) storage and the quantitative relationship between SOC and geochemical properties in tropical surface and subsurface soils, where information on various soil geochemical properties remains limited. We used soil samples from 178 sites in Indonesia, Thailand, Cameroon, and Tanzania as tropical soils and 34 sites in Japan as a comparison. The tropical soils were acidic, formed under high precipitation. We separated the soil samples into three groups based on the degree of weathering. We applied correlation and single regression analyses between SOC and geochemical properties including oxalate extractable Al and Fe (Alo + Feo), pyrophosphate extractable Al and Fe (Alp + Fep), and clay + silt. In the subsurface soils, Alo + Feo and Alp + Fep were strongly correlated with SOC (r = 0.79–0.85 and 0.58–0.85, respectively), and the quantitative relationships of SOC with these properties were similar in all the weathering groups (4–5 and 5–8, respectively). On the other hand, no strong correlation with SOC or similar quantitative relationships among the weathering groups were found for clay + silt. In the surface soils, Alo + Feo and Alp + Fep were correlated with SOC (r = 0.48–0.56 and 0.55–0.76, respectively), but the ratio of C to active Al and Fe was higher probably because of the large C input. Our results highlight the importance of Alo + Feo and Alp + Fep in SOC storage, of which the ratios to SOC are similar in each of the surface and subsurface soils regardless of the weathering degree.

To study the effect of freeze–thaw weathering damage deterioration on the strength of Huashan granite, this paper conducted a freeze–thaw (FT) cycle test on Huashan granite at − 20 to 20 °C and 0–100 cycles. Thus, the basic physical parameters change law of Huashan granite after freeze–thaw weathering are obtained. The SHPB (Split Hopkinson Pressure Bar) device was used to perform uniaxial and confining impact compression of granite, analyze the macro-mechanical test phenomena, and reveal the influence of freeze–thaw damage on rock strength. The results show that frost heave failure is the principal mechanism that causes the strength to decrease after freeze–thaw weathering. The static uniaxial compressive strength and maximum tensile strength of Huashan granite decreased by 38.4 and 21.5% after 100 FT cycles, respectively. The rate of reduction of peak stress does not necessarily grow with the increase of the number of cycles, and the average reduction rate in each phase ranges from 0.1 to 2.4%. It means that the damage accumulation of freeze–thaw weathering on rocks is not a uniformly increasing damage process. The radial restraint of confining pressure can effectively increase the peak stress of the material. When the strain rate is low, no failure occurs in the specimens due to the hoop restraint of confining pressure.

Groundwater samples were evaluated throughout Turkana County (Kenya, East Africa) while looking for drinking water sources. Some samples showed high concentrations of fluoride with values in the range of 0.15–5.87 mg/L. Almost 50% of the samples exceeded the WHO and Kenyan potable water standard guideline value of 1.5 mg/L for drinking water quality. The hydrogeochemical studies revealed that the dominant cation in water is Na+ and the dominant anion is HCO3− resulting in Na-HCO3 type of groundwater, followed by Ca/Mg-HCO3 or Na-SO4 and Na-Cl in a few cases. Speciation modelling revealed that the groundwater is undersaturated with respect to gypsum and anhydrite, mostly undersaturated with respect to fluorite (6 samples are at equilibrium), and supersaturated or at equilibrium with respect to calcite (CaCO3). Precipitation of calcite favours the dissolution of F-rich minerals in the alkaline medium. Simultaneously, groundwater is enriched with sodium and bicarbonate, probably as a result of chemical weathering of Na-feldspar. Investigated groundwater can be presumably used for drinking purposes from 17 wells, but a detailed investigation of other trace element concentrations is necessary.

Pyrochlore-group minerals are common accessory rare-metal bearing minerals in the calcite and ankerite carbonatites of the Amba Dongar complex (India). Pyrochlore from the Amba Dongar carbonatites differs from that in other Indian complexes in Ta, Zr, Ti, rare earth element (REE) and Pb contents, but is similar with respect to Ca, Ba and Sr abundances. The evolution of pyrochlore composition was studied to understand the alteration processes and the formation of late-stage pyrochlores enriched in REE and Pb. The early magmatic pyrochlore are calcio- and niobium-dominant types and were replaced by secondary cation-deficient varieties as a consequence of the action of hydrothermal fluids and supergene weathering. These processes produce changes mainly at theAsite, rarely at theBsite, and the original F is replaced by OH–groups. Calcium and Na can be extracted from the structure at the alteration stage and charge balance is achieved by the introduction of REE, Th, U, Ba or Sr. At the latest supergene stages, marginal and fractured zones of pyrochlore grains are altered to Pb-rich, Si-rich and cation-deficient hydrated varieties. The magmatic pyrochlore was crystallised in a highly alkaline environment at a high activity of Ca and at temperatures near 600°C, the alteration of pyrochlore began in a hydrothermal environment at temperatures below 350°C. The major compositional changes that are associated with the alteration are summarised by the following reactions: Ca2++ Nb5+→REE3++ Ti4+; Nb5++ Fe3+→ Ti4++ Zr4+; and 2Nb5++ Ca2+→ Ti4++ Si4++ U4+.

International audience; The Oligocene-Miocene boundary Asian climatic reorganization linked to the northward migration of the East Asian monsoon into subtropical China is a potentially important but poorly constrained atmospheric CO2 consumption process. Here, we performed a first-order estimate of the CO2 consumption induced by silicate chemical weathering and organic carbon burial in subtropical China related to this climatic reorganization. Our results show that an increase in long-term CO2 consumption by silicate weathering varies from 0.06×1012 to 0.87×1012 mol yr−1 depending on erosion flux reconstructions, with an ~50% contribution of Mg-silicate weathering since the late Oligocene. The organic carbon burial flux is approximately 25% of the contemporary CO2 consumption by silicate weathering. The results highlight the significant role of weathering of the Mg-rich upper continental crust in East China, which would contribute to the rapid decline in atmospheric CO2 during the late Oligocene and the Neogene rise in the seawater Mg content. If this climatic reorganization was mainly induced by the Tibetan Plateau uplift, our study suggests that the growth of the Himalayan-Tibetan Plateau can lead to indirect modification of the global carbon and magnesium cycles by changing the regional hydrological cycle in areas of East Asia that are tectonically less active.

Ultrasonic pulse velocity (UPV) measurement has previously been determined to be a good proxy for rock weathering intensity. As such, it has the potential to be useful for the establishment of rela...

Quaternary sediments of the Haji Arab River catchment located in Qazvin Plain, northwestern Iran, were studied in terms of sedimentology and geochemistry to determine the sedimentary environment and rock weathering. Discrimination diagrams show that the source rock of these sediments is granite and their tectonic setting is the active continental margin. These rocks show a negative Eu anomaly and a high ratio of light rare earth elements to heavy rare earth elements, suggesting that these sediments are originated due to the weathering of felsic rocks. Regarding the descending trend of chemical index of weathering, chemical index of alteration values, and the increase in coarse-grained particles, it was concluded that the sediments from the depth of 6 to 2.6 m formed under arid and high-energy conditions; however, this trend for sediments from 2.6 m depth to surface changes slightly toward semi-humid up to semiarid climate. Hence, it can be stated that the conditions of sedimentation environments in the Haji Arab basin are not constant at least in the Upper Holocene (Schmidt et al. in Holocene, 2011. https://doi.org/10.1177/0959683610385961 ) and this has led to changes in river sedimentation. These results indicate the changes in river regime conditions probably because of the changes in weather conditions during the Quaternary.

Ecosystem nutrient economies are commonly studied from the perspective of primary productivity in relation to nutrient availability, but a plant-specific view limits our ability to predict broader-scale patterns related to nutrient economics, such as ecosystem carbon turnover and storage controlled by soil microbial communities. Viewing nutrient economics from the heterotrophic decomposer community perspective can provide an additional perspective on ecosystem nutrient economics. We used microbial investment in extracellular enzyme production and ecoenzymatic stoichiometry theory as a conceptual framework to study nutrient economics in forest soils of the Northeast United States. Two years after experimentally increasing soil pH and phosphorus availability to offset the effects of chronic acid and nitrogen deposition, we found that belowground microbial communities were consistently investing more energy into phosphorus acquisition relative to nitrogen, in both space and time, suggesting that ecosystem demand for phosphorus might be high relative to nitrogen. Moreover, soil age and weathering, quantified by comparing glaciated vs non-glaciated regions, might not be useful predictors of nutrient economics in these forest systems. This study offers important insight into controls on ecosystem nutrient dynamics and soil microbial resource investment, information that can inform efforts to model soil microbial interactions and ecosystem carbon dynamics.

Varved clay deposits from ice-dammed lakes are a particularly important and broadly applied raw material used for the production of high-quality ceramics (red bricks, roof tiles, etc.), but the mineralogy and geochemistry of these sediments are not fully understood. The aim of the present study was to determine the chemical and mineralogical composition of ice-dammed lake sediments of the Lębork deposit. Major-element analysis of the compositions of selected samples from the ice-dammed lake clays was performed by X-ray fluorescence (XRF) and trace elements were determined by inductively coupled plasma-mass spectrometry. The mineralogical composition of clay samples was determined by X-ray diffraction (XRD). Analyses of the chemical composition of the ice-dammed lake clays of the Lębork deposit showed that the dominant component was SiO2 with a mean content of 56.13 wt.%; the second most abundant component was Al2O3, with a mean content for the entire deposit of 11.61 wt.%. Analysis by ICP-MS indicated the presence of rare earth elements (REE), e.g. cerium, neodymium, lanthanum, and praseodymium; their mean contents are: 56.9, 27.0, 26.3, and 7.3 ppm, respectively. Mineralogical analysis of the varved clays identified quartz, muscovite, calcite, and clay minerals – illite, kaolinite, and montmorillonite. The material filling the Lębork basin is characterized by small lateral and vertical variability in chemical composition. The results of the present study may be of considerable importance in determining the parent igneous, metamorphic, and sedimentary rocks, the weathering products of which supplied material to the ice-dammed lake, as well as in determining the mechanisms and character of the sedimentation process itself.

The red beds in Zhejiang province of China host the highest concentration of Danxia arched rock shelters in the world, just as the Colorado Plateau in the western USA hosts the world’s largest concentration of natural arches and bridges. This study investigated the geological background of the arched rock shelters and compared them to the natural arches and bridges, based on field study and a literature review. It was found that Zhejiang arched rock shelters differ from Colorado Plateau natural arches and bridges in geometry and formation mechanism. Statistical geometric data on arch geometry shows that Danxia arched rock shelters in Zhejiang tend to be relatively flat. They are relatively low features with long spans, and great depth. The natural arches and bridges on the Colorado Plateau are similar to each other, but the bridges are larger than the arches. The geometric differences between the arched landforms could be attributed to their different geologic history and to their different formation mechanisms. The arched rock shelters in Zhejiang are formed by differential weathering between sandstone and conglomerate due to moisture-induced tensile stresses. In contrast, natural arches on the Colorado Plateau are closely related to the Salt Valley anticline, vertical tectonic fractures, and horizontal discontinuities in rock fins. The Colorado Plateau natural bridges were formed by river erosion.

River hydrogeochemistry offers necessary guidance for effective water environmental management. However, the influence of cascade reservoirs on river hydrogeochemistry remains unknown. In this study, the Jinsha River, the headwaters of the Yangtze River of China, was selected to investigate the spatiotemporal variations of hydrogeochemistry after the construction of six cascade reservoirs. Major ions, total dissolved solids, electrical conductivity, and pH values of sampled water in the upper natural reaches and lower reservoir-regulated reaches were analyzed in both flood and dry seasons. The results of Piper diagram and Gibbs plots showed that the hydrogeochemistry of the Jinsha River was naturally controlled by both evaporation-crystallization and carbonate weathering processes, but it was also artificially affected by reservoirs. The impoundment of cascade reservoirs affected the hydrodynamic condition of the river. The river flow in the flood season was reduced by approximately 24.5%, altering the proportions of water sources and leading to notable hydrogeochemical alterations in reservoir-regulated reaches. Conversely, river hydrogeochemistry generally remained unchanged in the dry season, owing to the insignificant effect of cascade reservoirs on river flow. In contrast to what has been observed in previous studies of individual reservoirs, the cumulative influence of cascade reservoirs on the Jinsha River flow regime did not cause abrupt hydrogeochemical changes between the upstream and downstream areas of each reservoir. Moreover, the water quality assessments revealed that the impoundment of cascade reservoirs improved downstream irrigational water quality, with lower Na+ ratio values in the flood season. This study provides the earliest evaluation of cascade reservoir influence on the hydrogeochemistry of the Jinsha River. The findings of this study can be used as a reference for scientific guidelines for future environmental management of cascade reservoirs in large rivers.

Static load tests are vital to assess the genuine behaviour of piles to substantiate the geotechnical design parameters and construction approaches. A load testing program was undertaken to determine the working capacity, skin friction, and settlement of drilled shafts in Simsima limestone, the predominant foundation stratum in Doha, Qatar. The weathering profile of the Simsima limestone is complex with the degree of weathering likely to increase with depth. This paper presents the performance of three preliminary instrumented bored cast-in-situ test piles (Type 1, Type 2 and Type 3) by Bi-directional static load test (BDSLT) using sacrificial hydraulic jacks, socketed in the weathering zones of Simsima limestone formation in Lusail FIFA World Cup 2022 stadium project, Qatar. The test piles were instrumented with vibrating wire strain gauge technology and were load tested using the BDSLT loading method to determine the pile-rock interactions within the various weathering zones of Simsima limestone. The unit shaft friction values obtained from the load test are compared with the initial design values. Results indicate that the skin friction was increased from values reported before pile load testing and was used for the optimization of pile design. BDSLT method with strain gauge instrumentation is a modern tool in value engineering of pile design to provide accurate information to the Qatar infrastructure foundation industry.

As the dominant macrofauna in many soils, earthworms play a significant role in mineral weathering and nutrient release from mineral structures into available forms for root uptake. Phlogopite is a trioctahedral micaceous mineral that can be weathered to other minerals through release of its interlayer potassium (K). In this study, we investigated the effect of earthworm activities and associated microbial communities on phlogopite weathering during the production of phlogopite-enriched vermicompost with different quantities of phlogopite added. An experiment was run under laboratory conditions using three levels of phlogopite (0, 20% and 40% by weight) in triplicates. Each Petri dish contained 20 g of a mixture of cow manure and phlogopite, and vermicomposting process was performed by inoculation of eight Eisenia foetida earthworms. Changes in clay mineralogy and C/N ratio in each dish were assessed at days 0, 45, 90, 135, and 180 during vermicomposting. The results indicated that phlogopite was partially weathered to vermiculite and interstratified mica-vermiculite during the vermicomposting process. The rate of weathering was higher during the early stages of vermicomposting (the first 90 d). The weathering of phlogopite was influenced considerably by the activity of earthworms and associated microbial communities during the organic matter transformation process. At the early stages of the process, the weathering rate for different levels of phlogopite was not significantly different, but over time it accelerated steadily, and the difference increased.

Ocean anoxic events (OAE) are characterized by increased organic content of marine sediment on a global scale with accompanying positive excursions in sedimentary organic and inorganic δ 13C values. To sustain the increased C exports and burial required to explain the C isotope excursion, increased supplies of nutrients to the oceans are often invoked during ocean anoxic events. The potential source of nutrients in these events is investigated in this study for Oceanic Anoxic Event 2, which spans the Cenomanian-Turonian boundary. Massive eruptions of one or more Large Igneous Provinces (LIPs) are the proposed trigger for OAE 2. The global warming associated with volcanogenic loading of carbon dioxide to the atmosphere has been associated with increased continental weathering rates during OAE 2, and by extension, enhanced nutrient supplies to the oceans. Seawater interactions with hot basalts at LIP eruption sites can further deliver ferrous iron and other reduced metals to seawater that can stimulate increased productivity in surface waters and increased oxygen demand in deep waters. The relative importance of continental and submarine weathering drivers of expanding ocean anoxia during OAE 2 are difficult to disentangle. In this paper, a box model of the marine Sr cycle is used to constrain the timing and relative magnitudes of changes in the continental weathering and hydrothermal Sr fluxes to the oceans during OAE 2 using a new high-resolution record of seawater 87Sr/86Sr ratios preserved in a marl-limestone succession from the Iona-1 core collected from the Eagle Ford Formation in Texas. The results show that seawater 87Sr/86Sr ratios change synchronously with Os isotope evidence for the onset of massive LIP volcanism 60 kyr before the positive C isotope excursion that traditionally marks the onset of OAE 2. The higher temporal resolution of the seawater Sr isotope record presented in this study warrants a detailed quantitative analysis of the changes in continental weathering and hydrothermal Sr inputs to the oceans during OAE 2. Using an ocean Sr box model, it is found that increasing the continental weathering Sr flux by ∼1.8-times captures the change in seawater 87Sr/86Sr recorded in the Iona-1 core. The increase in the continental weathering flux is smaller than the threefold increase estimated by studies of seawater Ca isotope changes during OAE 2, suggesting that hydrothermal forcing may have played a larger role in the development of ocean anoxic events than previously considered

The Kumtag meteorite strewn field was found in the Kumtag desert, 132 km south of Hami city in the Xinjiang province, China. It is an ellipse of 2.5 × 7.9 km, with a long axis extending along the northeast-southwest direction. The largest individual meteorite of the strewn field weighs about 10 kg; the smallest individual has a mass of only 27 g. In total, more than 100 individuals with a total mass of more than 180 kg were collected. The location and the distribution of the fragments suggest that the Kumtag meteoroid entered the atmosphere in the direction Northeast-Southwest. All meteorites collected in this strewn field are samples from the same unique meteorite shower. The Kumtag meteorite is an H5 ordinary chondrite with a shock stage S2, and a weathering grade W2. The cosmic ray exposure age of Kumtag is 6.7 ± 0.8 Ma, which is rather typical for H chondrites and which indicates that Kumtag was derived from the massive impact event on its parent body ~7 Ma ago. A significant amount of He has been lost during certain unknown processe(s) before the Kumtag meteorite was ejected from its parent body.

In geological history, volcanism is closely related to the deposition of many black shales. However, the specific mechanism between volcanism and the deposition of black shales is still unclear. The black shales developed in the Chang 7 Member of the Yanchang Formation in the Ordos Basin are considered the most important hydrocarbon source rocks in Central China. The shales are deposited by frequent volcanic activities and preserved by extremely rich volcanic ash layers, making them an excellent example when investigating the influence of volcanism on the deposition of black shales. In this paper, petrographic, mineralogical, and geochemical analyses of three typical tuff and black shale segments of the Chang 7 Member were carried out. The productivity indicators [total organic carbon (TOC), P/Al, Ni/Al, and Cu/Al], redox indicators (V/Al, Mo/Al, U/Al and U/Th), and clastic influx indicators (Ti/Al and ƩREE) of the shales basically increased together in the longitudinal direction, and a relatively good positive correlation existed between P/Al, Ni/Al, Cu/Al, V/Al, Mo/Al, U/Al, U/Th, Ti/Al, ƩREE, and TOC. This finding indicated that the development of the Chang 7 black shales is the result of a combination of high primary productivity, anoxic conditions, and increased clastic influx. Considering that increased clastic influx may dilute organic matter, many phosphate nodules represented high productivity above the volcanic ash layers, and anoxic conditions are likely to be the result of a large amount of organic matter degradation indicated by the covariations of TOC versus P/Al and TOC versus Ba/Al. Therefore, the Chang 7 black shales in this study may be mainly controlled by the increased primary productivity. In addition, compared with the Weathering Index of Parker of background shales (not the contact clip or tuff layer), that of the black shales was significantly reduced after tuff deposition. On the contrary, the clastic influx indicators, redox indicators, productivity indicators of black shales significantly increased. This finding suggested that a series of environmental effects, such as enhanced weathering of terrestrial sources, increased clastic influx, anoxic water, and productivity bloom, was likely caused by volcanic activity. Considering that hydrothermal activity at the same time as volcanism may not cause productivity bloom, the nutrients (P/Al and Fe/Al) of the Chang 7 tuffs were significantly depleted, and the total sulfur content of black shales was much higher than that in ordinary freshwater sedimentation. Therefore, this paper reviewed and proposed the volcanism hypothesis model of the Chang 7 black shales. Volcanism generates large amounts of SO2 and volcanic ash. SO2 forms large areas of acid rain and accelerates terrigenous weathering with an increase in the lake land-based sources of debris and nutrient supply, while volcanic ash is decomposed and releases nutrients. These phenomena lead to biological productivity bloom and massive accumulation of organic matter, which in turn results in lake water anoxia and the eventual formation of black shales.

Both surface and underground rocks in nature often undergo repeated drying and wetting. The dry-wet cycle is a weathering effect that includes physical and chemical processes, which has varying degrees of degradation effects on the physical and mechanical properties of rocks. This paper analyzes and discusses this kind of rock degradation based on the existing literature data. First, the deterioration degree of various physical and mechanical properties (including density, P-wave velocity, porosity, static and dynamic compressive/tensile strength, and fracture toughness) is summarized as the number of dry-wet cycles increases. Secondly, the possible degradation mechanism of the dry-wet cycle is explained in terms of clay mineral swelling, solute migration, and microcrack evolution. Then, the damage constitutive model of the rock after cyclic dry-wet treatment is introduced. Finally, the issues that need to be studied in the future are put forward.

The neutralization of strongly alkaline pH conditions and acceleration of mineral weathering in alkaline Fe ore tailings have been identified as key prerequisites for eco-engineering tailings-soil formation for sustainable mine site rehabilitation. Acidithiobacillus ferrooxidans has great potential in neutralizing alkaline pH and accelerating primary mineral weathering in the tailings but little information is available. This study aimed to investigate the colonization of A. ferrooxidans in alkaline Fe ore tailings and its role in elemental sulfur (S0) oxidation, tailings neutralization, and Fe-bearing mineral weathering through a microcosm experiment. The effects of biological S0 oxidation on the weathering of alkaline Fe ore tailings were examined via various microspectroscopic analyses. It is found that (1) the A. ferrooxidans inoculum combined with the S0 amendment rapidly neutralized the alkaline Fe ore tailings; (2) A. ferrooxidans activities induced Fe-bearing primary mineral (e.g., biotite) weathering and secondary mineral (e.g., ferrihydrite and jarosite) formation; and (3) the association between bacterial cells and tailings minerals were likely facilitated by extracellular polymeric substances (EPS). The behavior and biogeochemical functionality of A. ferrooxidans in the tailings provide a fundamental basis for developing microbial-based technologies toward eco-engineering soil formation in Fe ore tailings.

Magnetic susceptibility (MS) as a fast, non-destructive, and reasonable technique is very useful in soil genesis and evolution studies. The MS of soils along a climolithotoposequence in Jazmoorian Watershed was studied in the present research and the vertical distribution of MS in the representative pedons affected by soil forming factors (parent material, climate and relief) was also investigated. Rock pediment, mantled pediment, piedmont plain, alluvial fan, and playa geomorphic positions with two igneous (gabbro, diorite, granite, and andesite) and sedimentary (limestone, conglomerate and playa deposits) parent materials were selected. Thirteen representative pedons which best reflected the variations of soil forming factors were studied. Results of the study showed that the maximum (877.8 × 10−8 m3 kg−1) and the minimum (5.2 × 10−8 m3 kg−1) low frequency (χlf) MS were respectively determined in the soils formed on igneous and sedimentary parent materials. The χlf values were increased with depth in soils affected by igneous parent material, but the opposite trend was found in soils with a sedimentary origin. The activity ratio of Feo/Fed in xeric and aridic moisture regimes were 0.03 and 0.09, respectively. Meanwhile, MS value in surface soil of pedon 2 (with xeric moisture regime) is lower than its parent material which is a support for the higher weathering of this soil due to higher moisture compared to pedon 5 with an aridic moisture regime. Decreasing evolution trend of soils on igneous parent material was in the order of alluvial fan < piedmont plain < mantled pediment, but in the soils on sedimentary parent material was in the order of playa < rock pediment < mantled pediment < alluvial fan. Results of the study clearly showed that the soil χlf values changed with variations in climate, parent material, and topography.

The coupling between chemical weathering (including silicate, carbonate and pyrite weathering) and physical erosion is of high interest in active mountain belts. Participation of pyrite weathering which, results in CO2 emission to the atmosphere, also is of great research attention. Nevertheless, the responses of the (de-)couplings to landslide and typhoon are unclear. We used records of riverine TDS (total dissolved solids) and TSS (total suspended solids) with high-frequency sampling during typhoons to estimate chemical denudation rates of silicate (CDRsil), carbonate (CDRcarb), pyrite (CDRpyrite) and physical denudation rates (PDR) in two adjacent catchments, eastern Taiwan. Results show that the CDRsil in the two catchments is approx. 10-fold higher than the global mean, whereas the CDRcarb, CDRpyrite and PDR are over 15-fold higher than the global averages. Landslides likely elevate carbonate and sulfate dissolution, and streamflow is a kinetic control on the CDRs. Among CDRs, CDRsil remains constant with various landslides and typhoons. Yet, CDRcarb and CDRpyrite rapidly respond to typhoons and then contribute more CO2 emission. In sum, landslides expose fresh minerals to enhance chemical weathering; typhoons, which transport the dissolved solids within a short time and prompt new rainwater for weathering, are also dominant agents. We demonstrate the importance of dynamic partitioning of sulfuric and carbonic acid on silicate weathering for quantitative estimation of weathering-associated CO2 budget in active mountain belts.

We report detailed chemical and isotopic data from a subglacial siliceous deposit on andesitic bedrock recently exposed by glacier retreat. Whereas a single

Heavy metal(loid) (Cd, Co, Cr, Ni, Cu, Zn, Pb, V, Tl, and As) and Pb isotope compositions of two black shale weathering profiles were determined to investigate the geochemical behaviors of these toxic elements during black shale weathering and the heavy metal(loid) contamination and source apportionment of Pb in black shale-associated soils. Black shale has higher heavy metal(loid) concentrations than the upper continental crust and the worldwide average shale. In contrast, the surface soils have much higher heavy metal(loid) concentrations than the profile soils. The heavy metal(loid) concentrations in black shale-associated soils are higher than the Chinese and worldwide soil background values, except for Co and Pb. Black shale-associated soils, especially the surface soils, have higher average concentrations of As, Cd, Cr, Ni, Cu, and Zn than Chinese, Dutch, and Canadian soil guidelines. The enrichment factor (EF) and geoaccumulation index (Igeo) values indicate various degrees of heavy metal(loid) contamination in these soils, particularly for the heavy metals Cd, Tl, and V and metalloid As. Co and Pb contamination in these soils is not a current concern. According to the mass transfer coefficient (τTa,j) values, Cd, Co, Ni, and Zn show overall losses, and other metals (Cr, Cu, Pb, and V) exhibit different behavior in the studied black shale weathering profiles. Based on a simple binary Pb isotopic mixing model, black shale is the dominant contributor to the Pb in black shale-associated soils (70.5–91.1% to profile soils and 81.2–88.8% to surface soils), and vehicle exhaust contributes less (8.9–29.5%) to the Pb in profile soils. Vehicle exhaust can exert an impact on the Pb isotopic evolution at depth intervals of 60–80 cm below the soil surface.

The riparian zone is a river-land ecotone, and its environmental conditions have a significant effect on the river ecosystem and population health. In this study, As, Cu, Cr, Cd, Mn, Fe, Ni, Pb, and Zn in the topsoils of urban riparian zones in a subtropical city in southeast China were quantitatively estimated by inductively coupled plasma-optical emission spectrometry. The geoaccumulation index and health risk evaluation model were adopted to assess the accumulation characteristic and health risk of residents' exposure to metals. Principle component analysis was used to determine the source of metals. The results showed that the mean contents of metals (except Fe) were higher than the soil background value, but none of the metal contents exceeded the mass limit of environmental quality standards. The order of the geoaccumulation index was Cd > Mn > Cu > Cr > Pb > Zn > As > Ni > Fe. The contamination level of Cd was classified as slight, whereas the other metals did not contribute to pollution. The spatial distribution of metals in the riparian zone was compatible with the pattern of functional zones in the adjacent urban areas, where levels of Cr, Cd, Fe, Mn, and Ni were higher in commercial areas, as were Pb and Zn in under-construction land and As in residential and industrial areas. Carcinogenic risks of Cr, As, and Pb were acceptable. The hazard index indicated no significant noncarcinogenic risks from any metals. However, noncarcinogenic risks of metals other than Mn were higher for children than for adults, and the primary exposure route of metal into the human body was ingestion for children and inhalation for adults. Principle component analysis indicated that the primary sources of Cr, Ni, Mn, Cu, and Fe were pedogenic processes and mineral weathering, whereas Zn, As, Pb, and Cd mainly originated from anthropogenic sources, specifically, Zn from transportation emission, Pb from transportation emission and industry waste, As from coal combustion and residential waste, and Cd from pigments/paint used in commercial buildings, urban greening, consumer waste, and transportation emission.

Tafoni are a type of cavernous weathering features widespread in different climate zones around the world, but their origin has not been fully understood. Little attention was paid on tafoni in conglomerates. Danxiashan UNESCO Global Geopark, located within the subtropic humid region of South China, has a landscape of large tafoni that occur on cliffs of red conglomerates. Both the Dinosaur Rock and Pagoda Peak of the geopark were selected to investigate the formation mechanisms of tafoni in conglomerates. During the field investigation, the size, rock hardness, and the external and internal meteorology of tafoni were measured and tested. The texture and composition of rock samples were observed, and the ion chromatography experiments were performed as well. Results show that tafoni have well ellipsoidal openings. Clasts of the conglomerates are largely sub-rounded and poorly sorted, and the cement is dominantly composed of calcite and iron oxide. The hardness of the lips is almost equal to that of the columns, and both are slightly higher than the backwalls. Compared with the external intense environmental changes, the interior of the tafoni is characterized by smaller temperature and relative humidity ranges and windless condition. Therefore, the porous and permeable conglomerates provide favorable lithology for tafoni development, and the micro-environment within the caverns is conducive to improving water utilization efficiency and enhancing salt weathering. The salts mainly consist of sulfates and nitrates, which might be derived from frequent raining, water evaporation and red beds as well. Consequently, tafoni are the result of the synergistic effects by multiple factors, rather than a single mechanism.

The equatorial tropics house some of the earliest rock art yet known, and it is weathering at an alarming rate. Here we present evidence for haloclasty (salt crystallisation) from Pleistocene-aged rock art panels at 11 sites in the Maros-Pangkep limestone karsts of southern Sulawesi. We show how quickly rock art panels have degraded in recent decades, contending that climate-catalysed salt efflorescence is responsible for increasing exfoliation of the limestone cave surfaces that house the ~ 45 to 20-thousand-year-old paintings. These artworks are located in the world’s most atmospherically dynamic region, the Australasian monsoon domain. The rising frequency and severity of El Niño-induced droughts from anthropogenic climate change (that is, higher ambient temperatures and more consecutive dry days), combined with seasonal moisture injected via monsoonal rains retained as standing water in the rice fields and aquaculture ponds of the region, increasingly provide ideal conditions for evaporation and haloclasty, accelerating rock art deterioration.

Clay minerals are intermediate products generated during soil development, and their neoformation and transformation are closely related to pedogenesis. Here we aimed at identifying the difference in the clay mineral composition of upland soils derived from different parent materials and different soil-forming environments and exploring the importance of clay mineral composition in pedogenesis and soil taxonomy. We sampled 60 soil B horizons in Hunan Province of subtropical China by digging soils derived from granite (GR), slate and shale (SS), Quaternary red clay (QRC), limestone (LS), and sandstone (SDS). The clay mineral composition and its correlation with parent materials, elevation, micro-topography, and pedogenic processes were investigated using X-ray diffraction and Pearson’s correlation analysis. The clay mineral was dominated by kaolinite, followed by 2:1-type minerals (illite and vermiculite), and a small fraction of mixed-layer minerals. The composition of soil clay minerals varied with parent materials. Kaolinite was predominant in soils derived from GR and LS; mixed-layer minerals prevailed in QRC, whereas illite and vermiculite were prevalent in SDS. In addition, elevation and micro-climate could also explain the variations in clay mineral composition. Increase in elevation was associated with decreased 1:1 clay mineral content and increased 2:1 clay mineral content, especially in soils developed from LS. The composition and content of clay minerals indicated that Ferrosols, Ultisols, and Acrisols had undergone intense weathering; Primosols, Entisols, and Leptosols were characterised by weak weathering, and Plinthic Ali-Udic Cambosols, Plinthudults, and Plinthosols were characterised by strong redox status. This study suggests that clay mineral composition is related to the parent material, climate, and micro-topography, and that it can serve as an indicator of pedogenesis and soil type in subtropical China.

Because of the alkaline nature and high calcium content of cements in general, they serve as a CO 2 -absorbing agent through carbonation processes, resembling silicate weathering in nature. This carbon uptake capacity of cements could abate some of the CO 2 emitted during their production. Given the scale of cement production worldwide (4.10 Gt in 2019), a life-cycle assessment is necessary to determine the actual net carbon impacts of this industry. We adopted a comprehensive analytical model to estimate the amount of CO 2 that had been absorbed from 1930 to 2019 in four types of cement materials, including concrete, mortar, construction waste, and cement kiln dust (CKD). In addition, the process CO 2 emission during the same period based on the same datasets was also estimated. The results show that 21.02 Gt CO 2 (95 % confidence interval, CI: 18.01–24.41 Gt CO 2 ) had been absorbed in the cements produced from 1930 to 2019, with the 2019 annual figure mounting up to 0.89 Gt CO 2 yr −1 (95 % CI: 0.76–1.06 Gt CO 2 ). The cumulative uptake is equivalent to approximately 55 % of the process emission based on our estimation. In particular, China's dominant position in cement production or consumption in recent decades also gives rise to its uptake being the greatest, with a cumulative sink of 6.21 Gt CO 2 (95 % CI: 4.59–8.32 Gt CO 2 ) since 1930. Among the four types of cement materials, mortar is estimated to be the greatest contributor (approximately 59 %) to the total uptake. Potentially, our cement emission and uptake estimation system can be updated annually and modified when necessary for future low-carbon transitions in the cement industry. All the data described in this study, including the Monte Carlo uncertainty analysis results, are accessible at https://doi.org/10.5281/zenodo.4459729 (Wang et al., 2021).

Cut slope surfaces are affected by excavation activities and weathering agents. Disturbances on the surface can penetrate down to a certain depth. Slope stability analyses made on the cut slopes can reveal unsatisfactory results unless the disturbance depth is determined. Moreover, false designs ignoring the shear strength parameter differences of inner and surface sections of the slopes can affect the safety of the highways. Disturbance thickness due to blasting effect is already presented in the literature; however, the mechanical excavation is still unknown. In this study the effect of mechanical excavation on disturbance thickness is investigated by using 54 cut slopes selected from Western Black Sea Region of Turkey. According to UCS results, the strength values of the undisturbed zones are found to be two times higher than the disturbed zones. The disturbance depths formed by excavation and weathering are found to be changing between 0.05 and 0.50 m on the cut slopes. Regarding the height (H) of the slopes, disturbance thickness is found to be affecting the slope up to 0.06 H which is lower than the blasting effect. It is recommended that this thickness should be taken into consideration when assigning the disturbance factor (D) and used to prevent stability problems of the cut slopes.

Research subject. The study investigates the distribution of phosphorus (as percentages of P2O5 and P) and 4 phosphorus modules introduced by the authors - phosphorus-titanium FTM (P2O5/TiO2), phosphorus-calcium FCM (P2O5/CaO), phos-phorus-iron FIM (P2O5/Fe2O3) and phosphorus-general-iron FGiM (P2O5/(Fe2O3 + FeO)) - in the main types of sedimentary rocks, such as psammites, pelites, carbonates, silicites, in volcanic-sedimentary rocks (tuffoids), as well as in soils, sediments and such specific rocks as nodules and weathering crusts. Methods. On the basis of a large data bank (several tens of thousands of silicate analyses), new clarks of phosphorus were calculated. Clark estimates were based on average median contents for all the above-mentioned rock groups. For the first time, lithochemistry methods were successfully applied to characterize the composition of phosphorites. Correlation analysis was used to identify forms of phosphorus in rocks. Only the most reliable linear correlation coefficients of phosphorus and phosphorus modules with rock-forming components were considered significant - with a significance level no greater than 0.01 and 0.05.Results and conclusions. In some cases, new estimates of clarks differed markedly from the estimates of our predecessors. For a number of objects, clarks were determined for the first time. Interpretation of the revealed relationships allowed us to identify the following main correlations and corresponding forms of phosphorus in sedimentary rocks and their analogues (soils and sediments): positive correlation with CaO - phosphorus in the form of accessory apatite or francolite dominated; positive correlation with Fe2O3 - phosphorus sorbed on iron hydroxides dominates; positive correlation with MgO - phosphorus dominated in the composition of smectite or chlorite, initially sorbed on the clay substance of precipitation; positive correlation with TiO2 - phosphate sorbed on leucoxene, dominates. Thus, in addition to the previously known calcium and iron hydroxide, a titanium geochemical barrier for phosphorus was first identified.

Previous exploration missions have revealed Mars as a potential candidate for the existence of extraterrestrial life. If life could have existed beneath the Martian subsurface, biosignatures would have been preserved in iron-rich minerals. Prior investigations of terrestrial biosignatures and metabolic processes of geological analogues would be beneficial for identifying past metabolic processes on Mars, particularly morphological and chemical signatures indicative of past life, where biological components could potentially be denatured following continued exposure to extreme conditions. The objective of the research was to find potential implications for Martian subsurface life by characterizing morphological, mineralogical and microbial signatures of hematite deposits, both hematite rock and related soil samples, collected from Highland Complex of Sri Lanka. Rock samples examined through scanning electron microscopy-energy dispersive X-ray (SEM-EDX) spectroscopy. Analysis showed globular and spherical growth layers nucleated by bacteria. EDX results showed a higher iron to oxygen ratio in nuclei colonies compared to growth layers, which indicated a compositional variation due to microbial interaction. X-ray diffraction analysis of the hematite samples revealed variations in chemical composition along the vertical soil profile, with the top surface soil layer being particularly enriched with Fe2O3, suggesting internal dissolution of hematite through weathering. Furthermore, inductively coupled plasma-mass spectrometry analyses carried out on both rock and soil samples showed a possible indication of microbially induced mineral-weathering, particularly release of trapped trace metals in the parent rock. Microbial diversity analysis using 16S rRNA gene sequencing revealed that the rock sample was dominated byActinobacteriaandProteobacteria, specifically, members of iron-metabolizing bacterial genera, includingMycobacterium,Arthrobacter,Amycolatopsis,NocardiaandPedomicrobium. These results suggest that morphological and biogeochemical clues derived from studying the role of bacterial activity in hematite weathering and precipitation processes can be implemented as potential comparative tools to interpret similar processes that could have occurred on early Mars.