Stages Of Weathering Research Articles

Genesis and supergene weathering of tetrahedrite-(Hg) in meta-carbonate rocks: Bearing on differential mobility of priority pollutant metals

The Cu-Sb-Hg mineralization of San Giuliano Terme (Monti Pisani, Tuscany, Italy) is characterized by the widespread occurrence of deeply altered tetrahedrite-(Hg) hosted within joints and faults in the Liassic “Calcari ceroidi” Formation. Through a multi-technique approach (optical and scanning electron microscopy, electron microprobe analysis, single-crystal and powder X-ray diffraction, micro-Raman spectroscopy, X-ray fluorescence, fluid inclusion analysis), tetrahedrite-(Hg) and its alteration products have been characterized and data about its genesis and successive supergene weathering have been collected. Tetrahedrite-(Hg) from San Giuliano Terme has the empirical formula Cu9.92Ag0.02(Hg1.64Fe0.30Zn0.04)Σ1.98(Sb3.53As0.56)Σ4.09S12.95, and is found with scarce gangue minerals represented by calcite, baryte, and very rare fluorite. The mineralization formed from hydrothermal fluids with moderately high salinity (∼17.5 wt% NaClequiv.) of dominantly metamorphic origin at T ∼ 285 °C. Tetrahedrite-(Hg) is usually fully replaced by a mixture of cinnabar, roméite-group minerals, malachite, and rarely azurite. Based on the modal abundance of the mineralogical constituents and their micro-textures, four stages of supergene weathering of tetrahedrite-(Hg) have been recognized. The alteration stages reflect the progressive ingression of meteoric water into the system, with consequent oxidation of tetrahedrite-(Hg) and the introduction of Ca2+, HCO3– and H2O, as well as the progressive removal of S, Sb, and Cu. The relative proportions of the supergene minerals in the four alteration stages can be taken as a proxy for the mobility of the main chemical constituents of tetrahedrite-(Hg), three of which (Hg, Sb, and Cu) are priority pollutant metals. Mercury was found to be the least mobile element in the reconstructed geochemical process. In fact, the widespread precipitation of cinnabar in the space formerly occupied by tetrahedrite-(Hg) hinders the dispersion of Hg in the environment, sequestering it in a solid matrix.

Leachate Experiments to Evaluate Weathering of Waste Rock for Backfill Aquifers in Restored Coal Mine Pits, Powder River Basin, USA

Restoration of open-pit mines may utilize waste rock for landscape reconstruction, which can include the construction of backfill aquifers. Weathering and contaminant transport may be different in backfill aquifers compared to the surrounding aquifer because of newly available mineral surfaces and transportable nano- to micro-scale particles generated during mining. Waste rock from the Cordero Rojo open-pit coal mine in the Powder River Basin was exposed to benchtop leachate experiments for 20 weeks at temperatures of 5 °C and 20 °C. Collected leachate was analyzed for Eh, pH, specific conductance, alkalinity, and cation and anion concentrations as unfiltered and 0.45-μm and 0.2-μm filtered concentrations. During the experiment, leachate Eh and pH substantially varied during the first 55 days, which corresponds to a period of high specific conductance (>1000 µS/cm) and alkalinity (>200 mg/L). Correspondingly, anion and cation concentrations were the largest during this early weathering stage, and the filter fractions indicated multiple forms of transported elements. After this early weathering stage, column leachate evolved towards a weathering equilibrium of neutral, oxidizing, and low solute conditions indicated by positive Eh values, pH near 7, and specific conductance <500 μS/cm. This evolution was reflected in the decline and stabilization or non-detection of metal(loid) concentrations reflective of a shift to primarily bulk aluminosilicate weathering when coal- and salt-associated elements, such as arsenic, cadmium, and selenium, were not detected or at minimal concentrations. Over the course of the experiment, the solute trend of certain elements indicated particular weathering processes—cadmium and nanoparticle transport, selenium and salt dissolution, and arsenic and pyrite oxidation. The mining of overburden formations and use of the waste rock for backfill aquifers as part of landscape reconstruction will create newly available mineral surfaces and nanoparticles that will weather to produce solute concentrations not typically found in groundwater associated with the original overburden.

Rock - soil transition during weathering of rhyolite

Concentric layers of weathered materials around core-stones show the rhyolite to experience sequential, but gradational, changes in visible features, textures and mineralogy as it transforms from ‘rock’ into ‘soil’. The changes start with the opening-up of grain boundaries and micro-cracks (stage 1) followed by their dark brown staining (stage 2) and the subsequent alteration (to sericite and clay minerals) of plagioclase feldspar groundmass grains and phenocrysts (stage 3). Biotite flakes are then bleached and altered (to chlorite and clay minerals) (stage 4) before there starts alteration (to sericite and clay minerals) of groundmass alkali feldspar grains (stage 5) and finally alteration of alkali feldspar phenocrysts (stage 6). Quartz grains are not altered during these stages of weathering but disaggregate and reduce in size due to continual opening-up of grain boundaries and micro-cracks. Increasing stages of weathering are marked by decreasing dry unit weights, dry densities and uniaxial compressive strengths, but increasing apparent porosities. The transition between ‘rock’ and ‘soil’ occurs during weathering stage 6 when all plagioclase groundmass grains and phenocrysts have been altered as have been all alkali feldspar groundmass grains and most phenocrysts. Stage 6 is marked by large apparent porosities (>14%) but low values of dry unit weight (<21.90 kN/m3) and dry density (<2,232 kg/m3).

Metallogenetic process of Xunmei hydrothermal field (26°S), South Mid-Atlantic Ridge: Constraints from in-situ sulfur isotope and trace elements of sulfides

Seafloor hydrothermal sulfides at slow-spreading mid-ocean ridges (MORs) are of economic and scientific significance. The formation of newly discovered submarine hydrothermal sulfides on the South Mid-Atlantic Ridge (SMAR), particularly with respect to the fluid evolution, remains poorly understood. The Xunmei hydrothermal field is a typical volcanic dome-type hydrothermal field at 26°S on the SMAR. Based on the mineralogical zonation and assemblages, six distinct ore-forming stages were identified from low- to high-temperature stages with a seafloor weathering stage. The crystallinity of pyrite/marcasite and grain size of chalcopyrite increase gradually from the outer rim to the inner conduit of a sulfide chimney. The positive δ34SV-CDT values of pyrite/marcasite (2.1‰–8.2‰), chalcopyrite (2.5‰–5.6‰), and sphalerite (2.9‰–7.0‰) suggest 62%–91% of S was derived from the leaching of basement basalts, 9%–38% from reduction of seawater sulfate. In situ trace element data for sulfides show enrichments in Mn, Ag, Tl, and Pb in outer zones A and B, while enrichments in Se, In, and Sn in inner zones C and D, indicating an increase in precipitation temperature during chimney growth. Low pyrite Co contents, low Tl/Pb, low Sb/Pb, low Bi/Pb, high As, Ag, Cu, and Pb concentrations, suggesting that the pyrites precipitated from fluids that may have undergone supercritical phase separation during their ascent. High-temperature, Cl-depleted, vapor-rich hydrothermal fluids discharged into ambient cold seawater over multiple stages and probably evolved from low (<240 °C) to medium (∼ 263 °C) and high (∼ 317 °C) temperatures, reached a highest temperature of ∼335 °C, and then evolved to medium to low temperatures (∼ 270 °C to <240 °C) during the wanning of hydrothermal venting. The sulfur fugacity (fS2) likely evolved from a relatively low to high condition within the scope of intermediate sulfidation, and then decreased to low condition. The redox states (fO2) probably were strongly affected by seawater influx and evolved from relatively oxidized to original reduced conditions. The salinity decreased during chimney growth. Sulfide precipitation in the Xunmei hydrothermal field probably was the result of a combination of fluid-seawater mixing and phase separation. We propose a chimney growth and hydrothermal evolution models for the Xunmei hydrothermal field.

Origin of clays in the interbasaltic red boles of Deccan Volcanics: Pedogenesis versus palagonitization

Red-coloured clay-rich beds (bole beds) occur at flow breaks in parts of the Deccan volcanic province (DVP). These boles in the Deccan province retain paleoenvironmental information that prevailed at the K-T boundary, including the timing of the Deccan eruption synchronous with the K-T mass extinction. This contribution assesses the origin of clays in various red boles, selected based on their field appearances, physical properties, and relation with bounding units. The saprolitic red bole, fragile red bole and grey bole capping red bole have kaolinite and smectite clay with broad 001 peaks (FWHM>0.62°). The selective dissolution of grey bole reveals the highest Alo, Sio and Feo/Fed (>3) characteristics of short-range ordered alumino-silicates and oxyhydroxide. Both red and grey boles show relative enrichment in immobile elements, indicating leaching within the incipient stage of weathering (saprolite equivalent). Clays from these boles show FeFe and AlAl segregated domains in the octahedral sheet, features characteristic of short-range ordered clay, indicative of a pedogenesis. Smectite in these boles shows Fe > 0.3 apfu with trans vacant (tv) nature, suggesting oxidizing conditions at low temperatures. The STEM-EDS of clay FIB section reveal smectite laths with multiple chemistries in each sample, indicating re-equilibrating conditions in a closed system due to fluctuating wet and dry seasons. Contrary to the above two red boles, indurated-structure less and indurated-laminated red boles have glass shards with yellowish rinds and smectite clay (FWHM<0.5°), indicating palagonitization. The cation occurrence probability in the smectite octahedral sheets of later boles has values characteristic of randomly distributed cations, suggesting a relatively higher temperature of interacting solution. We envisage two processes of clay formation in red boles: a) pedogenesis and b) palagonitization of basalt flow top and/or mafic volcanoclastic deposits.

Mechanisms leading to exceptional niobium concentration during lateritic weathering: The key role of secondary oxides

Niobium (Nb) is considered as one of the most immobile elements during supergene weathering due to its low solubility and the expected resistance of the pyrochlore mineral group (A2B2X6Y) in which Nb occupies the B site. Although the resistance of pyrochlore is challenged by direct evidence of alteration in lateritic profiles, the geochemical and mineralogical processes controlling its behavior in the critical zone remains elusive. This study uses a multiscale geochemical, mineralogical and spectroscopic approach to monitor Nb solid speciation in a thick weathering profile. The weathering of the pyrochlore-bearing core carbonatite facies from Morro dos Seis Lagos has resulted in a Fe-enriched laterite with exceptional Nb concentrations (2.91 wt% Nb2O5 on average). The preservation of the successive secondary phases (Ti-, Fe-, Ce-oxides) resulting from weathering processes along the horizons offers the opportunity to track Nb during pyrochlore alteration from the fresh parent rock to the final stages of weathering. Intense lateritization processes have led to an enrichment in Fe and Ti in the pyrochlore B-sites, resulting in the weakening of the structure and its ultimate destabilization due to weaker B-O bonds. After the release of Nb from pyrochlore, the fate of Nb is dependent on the secondary phases formed during weathering. In the lower horizons dominated by Fe oxides, goethite is the main host for Nb (1 wt% Nb2O5) due to its capacity to substitute Fe3+ for Nb5+, in contrast to hematite. In the upper horizons, where Ti oxides have formed during the reworking of the laterite, Nb5+ is preferentially incorporated into brookite and rutile (20 wt% Nb2O5), which may have formed owing to slightly acidic pH and high Nb activity during their growth. The presence of Nb in hollandite and cerianite in a vein from the manganiferous horizon involves the transport of Nb with mobile elements at the scale of the laterite. With this study, we describe a new model accounting for the formation of Nb-enriched laterites. The latter is based on the ability of Nb5+ to substitute for Fe3+, Ti4+, Ce4+ in minerals formed by lateritization processes after its release from pyrochlore. The nature of the secondary Nb-bearing oxides is dependent on the chemistry of the parent rock and the conditions of formation of the laterite. This work, evidencing the mobilization of Nb both at the scale of the mineralogical assemblage and of the entire profile questions the pervasive use of Nb as a geochemical invariant in the critical zone.

Discovery of supergene REE-fluorocarbonate minerals in weathered spheres of Xiajialing regolith-hosted rare earth element deposit in Xiangshan, Jiangxi Province, South China

The Xiangshan ore field is developing not only a volcanic-related hydrothermal U deposit, but also a regolith-hosted rare earth elements (REE) deposit in the middle of the volcanic rock basin, where the spheroidal weathering layer has the highest REE content. Weathered spheres may play an important role in REE mineralization. To explore the enrichment and migration processes of REE in weathered spheres at different weathering stages, the mineralogy and geochemistry of the bedrock and weathered spheres with different weathering degrees of Xiajialing REE deposits were investigated. Results showed that the REE+Y concentration was 270–310 ppm in bedrock and 372–2377 ppm in weathered spheres, respectively. With an increase in weathering, the REE+Y content increased and then decreased, and the maximum value was observed in the core of the moderately weathered sphere sample. A large number of supergene REE-fluorocarbonate minerals were discovered in the weathered spheres (particularly in samples with a high REE content), and were mainly distributed in biotite and plagioclase. The REE2O3 (including Y2O3) content of the supergene REE minerals was 69.04–80.89 wt%. The supergene REE minerals were enriched in La2O3 (21.69–25.95 wt%), Nd2O3 (12.13–23.58 wt%), and Y2O3 (2.74–14.27 wt%), but lacked Ce2O3 (<1 wt%), and contained a certain amount of F (2.66–6.23 wt%). The Raman spectra of the supergene REE-fluorocarbonate showed several bands at 272, 741, 1103, and 3100–3700 cm−1. These results indicate that REE are adsorbed on clay minerals that were formed by weathering of biotite and plagioclase; thus, the concentrations of REE around the clays were extremely high and may have exceeded the solubility product (Ksp) of the REE-fluorocarbonate, which contributed to the supergene REE-fluorocarbonate deposits. The formation of supergene REE-fluorocarbonate minerals may be one of the most important causes of the extreme enrichment of REE in some weathered sphere samples. However, the supergene mineral is easily weathered and would dissolved with weathering proceeding, leading to a decrease in the REE content in the sphere samples that have experienced relatively strong weathering. The supergene REE-fluorocarbonate may be an important intermediate product in the formation of the Xijialing regolith-hosted REE deposit.

The effect of weathering on the variation of geotechnical properties of a granitic rock from Chile

The effect of rock weathering on geotechnical parameters can become substantial in geotechnical design. The weathering degree (WD) has usually been divided into five levels from fresh rock to completely weathered rock. In this study, the above five WDs are adopted to analyse the variation of several regularly used geotechnical properties. To that aim, a series of laboratory tests on a Chilean granitic rock in different stages of weathering was carried out. The results of the tests have been analysed by normalizing each geotechnical parameter with respect to the value obtained for slightly weathered samples instead of for fresh rock samples as is usually adopted. In this way, it was found that the unconfined compressive strength reduces steadily and considerably with each WD, as has been previously reported. Conversely, the modulus of deformation and P-wave velocity tend to stabilize the rate of reduction for highly and completely weathered rock samples, which does not agree with the trend and higher rate reductions found by other researchers. This stabilization reduction rate with WD was also found for compaction density, friction angle and Poisson's ratio.

Geochemistry of Weathering Cover and the Main Influencing Factors in Karst Area of Guilin, Southwest China

The chemical weathering of carbonate rocks is the main form of interaction between earth spheres in the karst critical zone. The karst weathering cover, which is composed by residua from carbonate rocks weathering, contains important information about the climate environment and material cycle. We present the chemical composition of weathering covers in karst area of Guilin, Guangxi province, analyze their weathering process and strength, and compare them with the other weathering covers in other karst area in China, including Yunnan, Guizhou, Hunan, and Qinghai Tibet Plateau. The results showed: (1) the chemical composition of Guilin weathering covers were similar to that of carbonate weathering covers in other areas of China, and had the common characteristics of uniform distribution of chemical composition in the profile and obvious enrichment of Fe, Al and trace elements. During the formation of carbonate weathering cover and the residua, the rapid dissolution of Ca and Mg had an important impact on the migration and enrichment of other elements. (2) The chemical index of alteration (CIA) of carbonate weathering covers in Guilin and other karst areas of China was much larger than that in the upper crust (UCC) (60.13), which showed strong chemical weathering characteristics of the humid and hot climate. (3) The weathering process of carbonate rock was different from that of silicate and loess. In the early stage of carbonate rock weathering, soluble components (calcite and dolomite) had been rapidly dissolved and leached. All the carbonate weathering residua was measured to be in the stage of K2O weathering and Al2O3 increasing. Therefore, the weathering degree of carbonate weathering cover was mainly determined by the leaching of K2O and the increase of Al2O3. As a result, there was no correlation between CIA and Na/K (molar ratio), but was a significant negative correlation between CIA and K/Al (molar ratio) in the carbonate weathering cover. (4) The CIA values of weathering residua and carbonate weathering cover in southern China were negatively correlated with latitude, reflecting the influence of climate factors. From the influence of lithology, the chemical compositions of parent rock can affect the CIA of weathering cover, and the content of insoluble matter in carbonate rock was negatively correlated with CIA. From the influence of topography, the CIA value of weathering residua decreased from the high to the low position and from the shallow to the deep part of the profile.

Assessment of the effect of short-term weathering on the molecular-level chemical composition of crude oils in contact with aquatic environments.

Multiple studies have focused on the effect of long-term weathering processes on oils after spill events, without considering the chemical compositional changes occurring shortly after the release of oil into the environment. Therefore, the present study provides a broad chemical characterization for understanding of the changes occurring in the chemical compositions of intermediate (°API = 27.0) and heavy (°API = 20.9) oils from the Sergipe-Alagoas basin submitted to two simulated situations, one under marine conditions and the other in a riverine environment. Samples of the oils were collected during the first 72 h of contact with the simulated environments, followed by evaluation of their chemical compositions. SARA fractionation was used to isolate the resins, which were characterized at the molecular level by UHRMS. The evaporation process was highlighted, with the GC-FID chromatographic profiles showing the disappearance of compounds from n-C10 until n-C16, as well as changes in the weathering indexes and pristane + n-C17/phytane + n-C18 ratios for the crude oils submitted to the riverine conditions. Analysis of the resins fraction showed that basic polar compounds underwent little or no alterations during the early stages of weathering. The marine environment was shown to be much less oxidative than the riverine environment. For both environments, a feature highlighted was an increase of acidic oxygenated compounds with the increase of weathering, especially for the crude oil with °API = 27.0.

Bone weathering in an Atlantic environment: preliminary results of the Global Weathering Project in Spain

Weathering constitutes one of the most investigated taphonomic processes for understanding the formation of archaeological and palaeontological assemblages. Despite being studied for decades through numerous monitoring experiments, no homogeneous methodology exists to compare the results obtained in different regions and climates. Here, we present the protocols and the preliminary results of an experimental research started four years ago in a coastal and inland location within the Cantabrian Region (northern Spain) to assess the influence of the weathering process in an Atlantic climate. This experiment allows evaluation of the preservation of faunal assemblages in regional open-air sites throughout the Middle and Upper Palaeolithic. We conduct this experiment within the Global Weathering Project of the International Council for Archaeozoologists (ICAZ), an international network of archaeozoologists and taphonomists who coordinates the same experiment worldwide. The experiment planned to last 18 years consists on recording the weathering stages suffered on the cow ribs disposed on the surface of a fenced enclosure under the protection of a cage, separated from the soil by a neutral inorganic substrate and close to a weather station where the temperature, humidity, rainfall, wind and sun exposure values are daily recorded.

The contribution of abiotic markers in interpreting the taphonomic weathering of Homiphoca long-bones from Langebaanweg, South Africa

We examine weathering on early Pliocene Homiphoca capensis long-bones discovered in deposits from Langebaanweg (West Coast Fossil Park) coastal site, Western Cape, South Africa. Thus far, taphonomic research of phocid seal remains retrieved from ‘E’ Quarry have focused on biotic markers. The abiotic taphonomic study is limited and reliant upon the Weathering Series classified by Behrensmeyer; the current weathering base stages do not, however, reflect the abiotic weathering progression we found preserved in a sample of 653 Homiphoca long-bones. Utilizing Behrensmeyer's definition for early weathering stages (0 and 1), we recognized five new substages within the palaeoenvironment of ‘E’ Quarry and applied them to the Homiphoca long-bones. We suggest that this contribution could be applied to other fossil assemblages with a view to addressing some current biases and furthering understanding of depositional histories.

HYDROCARBON CONTAMINATION IMPACT ON SANDY SOILS WITHIN THE DZUNBAYAN OIL FIELD (EASTERN MONGOLIA)

The data are presented on the particle-size distribution, content of hydrocarbons, n-alkanes in their composition and the number of microorganisms in the soils of Dzunbayan oil production area (Mongolia, the Eastern Gobi desert steppe). The soils studied are characterized by the dominance of sand and fluid fraction (99.50–99.8%) with particles of 2–20 μm. The soils show alkaline reaction (pH 8.2–8.7), they are slightly saline in the control areas and highly saline (water extract salinity 0.13–2.34‰) near the production well. The content of petroleum hydrocarbons (HC) in soils of the study area varied from 9 to 60 mg/kg, with a maximum near the well. The study of the molecular composition of n-alkanes revealed the dominance of long-chain homologues (66.3–79.2% of the total n-alkanes), occurring at various stages of physicochemical and microbiological weathering. According to a number of features, the microbial community of soils is characterized by a high degree of adaptation to the conditions of the arid zone, salinity, and high pH values; at the same time, these conditions limit the development of typical representatives of soil microbiocenoses, i.e., actinomycetes and, to a greater extent, microscopic fungi. The total number of heterotrophic bacteria (HBGs) in the studied soil samples varied within 1.22–3.49 million CFU/g of soil. The proportion of oil-oxidizing bacteria (NOB) was 12.6–18.9% OBA, which corresponded to the high adaptive capacity of the community to hydrocarbons. Specific climatic conditions, features of soil composition, as well as oil with a predominance of heavy paraffin fractions of the Dzunbayan deposit, characterize the low potential ability of soils to self-purify under the oil pollution.

Petrographic Studies of a Part of East Coast Bauxite Deposits, Odisha, Eastern India and Implication on their Genesis

Abstract The East coast bauxite deposits of Odisha are well known in the mineral map of India. Some such deposits exposed at Nunapaimali, Sasubohumali and Baphlimali overlying khondalite of the Precambrian Eastern Ghats belt have been studied in respect of petrology, mineralogy and microstructure with a view to find out their genetic evolution. Bore hole samples from two former deposits and mine profile samples from Baphlimali revealed a good profile differentiation, in terms of three horizontal zones of variable thickness, which in descending order are: 1 to 29m laterite zone, 2 to 28m bauxite zone, 9 to 36m saprolite zone, comprising of lithomarge and partially lateritised khondalite [PLK] developed over host khondalite. Petrographic and mineralogical difference between these three zones, brought out through optical microscopy and XRD studies, further confirms the differentiation. Genetic evolution of bauxite is interpreted from the study of a large number of samples and results are collated from the photomicrographs appended in the paper. The authigenic bauxitisation was brought about by gradual dissociation of Al-silicate to Al-hydroxide minerals through different weathering cycles as indicated from their microstructural manifestations and mineral assemblages. Primary gibbsite is formed in the initial stage of weathering directly from Al-silicate minerals. Advanced stage of prolonged weathering converts the Al-silicate to kaolinite and then to secondary gibbsite. Grain size enlargement and recrystallisation showing mosaic habit, grain boundary migration and grain orientation are the outcome of digenesis. The weathering / lateritisation process continues, resulting in colloidal precipitation of gibbsite from pore water of lateritic residuum and is in progress even in recent period The Fe-oxide phases, represented by goethite and hematite are youngest in the paragenesis, and formed due to solution, precipitation and dehydration. Iron is mostly contributed by almandine garnet present in the host khohdalite. During chemical leaching, Fe gets released from garnet and occur either as FeOOH along its fractures or fill the weak planes / inter-granular space as secondary goethite. The goethite dehydrates to hematite during digenesis. Goethitisation and limonitisation particularly in the laterite zone are the results of supergene alteration.

Space Weathering of Genesis Mission Solar-wind Collectors with Inferences for Weathering on Airless Bodies

Samples from the Genesis Solar Wind Sample Return (NASA Discovery 5) are a unique opportunity to study the initial stages of space weathering, i.e., the physical and chemical effects of solar-wind irradiation. Arrays of collectors containing multiple materials were each exposed to a different solar-wind regime (fast, slow, bulk, or coronal mass ejection) at the L1 point for long durations (years). Materials exposed to the solar wind included metals, semiconductors, and insulators. Although the time of exposure was obviously short relative to samples having extraterrestrial origins, optical properties, surface chemical properties, and matrix structure have changed in many collectors due to exposure to solar wind. The thickness of amorphous zones, where present, appears to correspond with the depth of the peak of the solar-wind H distribution in each regime. Damage from high-energy particles was negligible because the collectors were 700 μm or less in thickness and shielded from the back by the spacecraft. Micrometeorite impacts and sputtering were also negligible because of the short exposure times. Our current results are preliminary: We hope future workers will extend this study both to support Genesis characterization efforts and to further understand space-weathering processes on a geologic timescale.

The Development of Limestone Weathering Rind in a Proglacial Environment of the Hallstätter Glacier

The contemporary retreat of glaciers results in the development of glacial forelands which constitute excellent areas for studies on the initial stages of weathering. This research concentrates on weathering rinds developed on glacially abraded Dachstein limestone surfaces (Eastern Alps) liberated from glacial ice since LIA (mid-19th century). We performed measurements of rock surface micro-roughness and strength (Schmidt hammer), spectral reflectance, and petrographic and microbiological analyses in SEM. There was a time-dependent increase in micro-roughness, decrease in rock strength and decrease in spectral reflectivity, but only within visual light. Rock surfaces on older sites reflected infrared radiation significantly better than younger ones. SEM analysis revealed that angular micro-structures inherited from glacial abrasion dominated in younger sites, eventually giving way to more rounded micro-structures. The structure of rock (micrite versus spar, phlogopite veinlets, etc.) plays a significant role. On older sites, microorganisms were detected within the studied weathering rinds, which probably results in better infrared reflectivity. We advocate the potential role of microorganisms (mainly heterotrophic) in the dissolution of limestone, and the role of cyanobacteria in the formation of the secondary porous limestone layer (extracellular biomineralization).

Weathering assessment approach for building sandstone using hyperspectral imaging technique

Weathering is one of the most common causes of building sandstone damage. The evolution of building sandstone in various weathering behaviors is critical for research. An intelligent assessment approach for classifying weathering degree of building sandstone in a humid environment is presented in this study. This synthesis method relates to three parts: microscopic observation of weathering characteristics, hyperspectral acquisition of weathered samples, and machine learning technology for a classification model. At first, weathering process is divided into initial weathered stage, accelerated weathered stage, and stable weathered stage according to the causes and mechanisms of weathering. Secondly, a novel classification method of weathering degree is proposed based on the weathering stage. Then, the mapping relationship between microscopic characteristics and hyperspectral image of shedding samples can be established in the visible and near-infrared spectral ranges (400–1000 nm) according to the change law of spectral absorption feature. Next, the spectral data of building sandstone with different weathering degrees are classified using Random Forest model. Furthermore, the hyperparameters of Random Forest model are optimized by Gray Wolf Optimizer algorithm for better performance. The trained model is finally applied to evaluate the weathering degree of large-scale sandstone walls quantitatively. The whole weathering assessment process is worth recommending for diagnosing and monitoring the building sandstone.

Environmental implication of geochemical record in the Arctic Ny-Ålesund glacial sediment, Svalbard (Norway)

Glacial sediments as an important end member of the global dust system, could indicate changes in global climate, aerosols sources, ocean elements, and productivity. With global warming, ice caps shrinking and glaciers retreat at high latitudes have attracted concern. To understand the response of glacier to environment and climate in modern high latitude ice-marginal environments, this paper investigated glacial sediments in the Ny-Ålesund region of the Arctic and clarified the response of polar environmental to global changes through geochemical characteristics of glacial sediments. The results showed that: 1) main factors affecting the elements distribution of the Ny-Ålesund glacial sediments were thought as soil formation, bedrock and weathering, and biological activity; 2) variations of SiO2/Al2O3 and SiO2/Al2O3 + Fe2O3, indicating low weathering of the soil. The ratio of Na2O/K2O indicating a weak chemical weathering, was negatively correlated to the CIA. With the average CIA of Ny-Ålesund glacial sediments for main minerals of quartz, feldspar, and muscovite as well as dolomite and calcite 50.13, which implied glacial sediments at the early stage of chemical weathering and depletion of Ca and Na; 3) the separating effect of stones and soils by stone circle formation due to thermal conductivity and frost heave makes sediments in stone circle have lower chemical weathering with only two main minerals, albite and quartz; 4) changes of carbonate content in sediments with glacier front retreating in different period implied that weathering rate of calcite averagely reached an estimate of 0.0792%wt/year in glacier A. The succession of vegetation made biological weathering become an important driving force for carbonate leaching from glacial sediments. These results and data provide scientifically significant archive for future global change studies.

Improved collection of rooftop micrometeorites through optimized extraction methods: The Budel collection

AbstractThe scientific value of micrometeorites collected from deep‐sea sediments or glacial deposits can be limited by poorly constrained accumulation times or severe alteration, coupled with a complex infrastructure of sampling expeditions. Collecting micrometeorites from rooftops has recently become a feasible alternative, but extraction methods have not been optimized or standardized to date. Here, we show that existing methods for the recovery of melted cosmic spherules (CSs) can be strongly improved by using a sequence of mineral separation techniques, including shape separation with an asymmetric vibrator and heavy liquid density separation with overflow centrifuges. We retrieved 1006 micrometeorites from the gutter of a barn in Budel, the Netherlands. Particle diameters are 80–515 μm, with the major mode at 130 μm and a slope exponent of −4.88. Differences in size distributions among various types of CSs indicate a multi‐source influx, with CS textures controlled by their parent body's mineralogy and orbital parameters. Repeated sampling of the rooftop after accumulation times of 959 and 333 days allows for a time‐integrated global mass flux estimate of 472 t year−1. This estimate is notably higher than previous rooftop‐based estimates but is still severely affected by micrometeorite loss from the gutter through drainage. The mass flux peaks at an equivalent particle diameter of ~200 μm. The Budel collection is the first rooftop collection to contain abundant vitreous micrometeorites and include the coarse‐grained S‐type CS class. Unmelted and I‐type micrometeorites remain difficult to extract from rooftop samples. Vitreous micrometeorites display various stages of weathering, showing that severe alteration of glass can progress at a faster rate in populated regions than previously assumed. This study demonstrates that methodological adjustments can drastically increase the scientific potential of rooftop micrometeorite collections.

Tectono-geomorphic evolution of an alluvial fan along the Dauki fault system, Bengal Basin, Bangladesh: remote sensing and pedogenic approach

ABSTRACT Late Quaternary landform evolution of the Karnajhora fan and its adjacent areas of the mid northern Bengal Basin, Bangladesh have been studied using remote sensing and pedogenic approach. Based on pedogenic characteristics, different soil-geomorphic units can be arranged according to their maturity as Hill > Distal Fan > Mid Fan > Proximal Fan. Soil-geomorphic units are further grouped into a three member soil-chronoassociation and approximated inferred ages are QGSK1 < 1 ka; QGSK2 < 3–4 ka; and QGSK3 > 27 ka. The weakly developed youngest member QGSK1 and the moderately developed member QGSK2 represents inceptisols at fersiallitisation weathering stage. While the oldest QGSK3 member represents alfisols and show relict nature and at the initial phase of ferrugination weathering stage. Neotectonics controls the configuration of the local catena. Paleoclimate and base-level fluctuations have also played significant roles in the development of soils and landforms of the study area. The parent materials of Member QGSK3 were deposited during 80–27 ka. Since the beginning of deposition of QGSK3 soils till the Last Glacial Maximum (LGM~18 ka), the climatic conditions gradually changed from warmer-moist to cooler-drier, and the area might experienced dominantly channel incision with minor aggradation. During this period, the land between the Jamalpur Terrace and Susang Hills might be eroded and washed away while the Sherpur Terrace survived as a remnant terrace. After the LGM, the climate changed from a cooler-dry condition to warmer-moist condition and the present Holocene floodplain started to develop. The parent materials of QGSK2 and QGSK1 members then started to deposit by the paleo-Karnajhora synchronously with the old Brahmaputra River. As the Karnajhora River presently shifted toward east, soils of QGSK2 member are not presently affected and are relatively better developed compared to QGSK1 member soils.