Initial Weathering Research Articles

Structural characteristics and physicomechanical properties of bamboo scrimber composite during natural weathering

Bamboo-based composite materials used outdoors are exposed to diverse natural climates, necessitating an understanding of their surface, physical, and mechanical properties for long-term use. This study evaluated changes in chemical composition, surface color, microstructure, and physicomechanical attributes of bamboo scrimber composite (BSC) manufactured from heat-treated moso bamboo bundles and phenol formaldehyde resin. Over two years of weathering, photodegradation affects bamboo and phenol formaldehyde resin, especially lignin, causing surface discoloration and cracking. Initial weathering stages reduced the width swelling rate, thickness swelling rate, and shear strength of BSC. Despite this, two-year weathered BSC meets the Chinese GB/T 30364-2013 standard for outdoor flooring and exhibits strong weather resistance.

Geochemical evolution along regional groundwater flow in a semi-arid closed basin using a multi-tracing approach

Groundwater is the main source for domestic drinking water supply, irrigation, and industrial activities in Zacatecas in central Mexico, a good example for numerous semiarid regions worldwide, however, there is insufficient information about characterization and evolution of the baseline water quality to create hydrogeological conceptual models, fundamentals for the future planning of new sources of groundwater supply for the population, especially under ongoing global climate change conditions. By a multi-method analysis that included geological, geophysical, hydrochemical and isotopic tools this investigation allowed the identification of: a) local flows, represented by shallow groundwater and shallow wells, hosted over basin fill sediments with low average temperatures (≈ 23.3 °C), variation in water types related to anthropogenic activities, low trace elements concentrations, δ18O and δ2H signatures indicating surface water and tritium being present in this system, b) intermediate flows (25 °C), identified in wells with depths of 100 to 200 m, water circulating through the basin fill sediments and the sequence of volcanic rocks characterized by intermediate concentrations of trace elements, and groundwater ages calculated for this system vary from 1,000 to 6,000 years, c) regional flows in volcanic rocks, characterized by groundwater from wells with depths of more than 200 m, high temperatures (up to 31.5 °C) and elevated concentrations of trace elements. The δ18O and δ2H signals are more homogenous and the 14C residence times for this flow system are greater than 8,000 years, and d) regional flows in Cretaceous rocks, with depths greater than 400 m, the highest temperatures (≈ 43.7 °C) and intermediate concentrations of trace elements. The δ18O and δ2H signals are homogenous and δ13C can widely be associated with carbonate shales. The hydrogeochemical evolution has been documented along a 62 km flow line to develop a robust conceptual model, reflecting the water–rock interaction in the system. Physicochemical parameters, as well as major and trace element concentrations, reflect a distinct evolution according to the flow paths and their increase is generally proportional to the residence time. Likewise, processes of dissolution of feldspars and some clay minerals from initial weathering in the basin fill sediments, as well as devitrification of the glassy matrix in the volcanic rocks are taking place in the evolution of the system.The results obtained through the analysis of water–rock interaction in this research can be applied to other semi-arid regions with geogenically impacted aquifers, due to the geological and climatic similarity with numerous volcano-sedimentary basins around the world.

Tracing the source and transport of Hg during pedogenesis in strongly weathered tropical soil using Hg isotopes

Soil is one of the largest reservoirs and re-emission sources of mercury (Hg) on Earth’s surface. The accumulation and remobilization of Hg during pedogenesis affect how Hg is transported from terrestrial to aquatic environment and biota, but these processes are poorly understood. Here we present Hg concentration and isotope ratios of soil and bedrock samples from a latosol profile formed through intense weathering of Cenozoic basalts in Zhanjiang, Guangdong Province, China, to trace the sources, transport and transformation processes of Hg during pedogenesis, and to gain insights on the potential impact of tropical soils on global Hg cycling. The entire soil profile shows negative δ202Hg (−2.97‰ ± 0.08‰ to −2.54‰ ± 0.08‰) and negative Δ199Hg (−0.68‰ ± 0.04‰ to −0.43‰ ± 0.04‰), with a gradual downward positive shift of Δ199Hg below 35 cm. An isotopic mixing model based on Δ199Hg suggests a dominant Hg input from atmospheric Hg (HgAtm) and limited contribution (<36%) of geogenic Hg (HgGeo) from the bedrock. The strongly negative Δ199Hg throughout the latosol profile suggests that HgAtm was likely subject to substantial photoreduction on soil surface and migrated downward after incorporation into soils. Moreover, there is a distinct positive shift of δ202Hg alongside a rapid decrease of HgGeo from the bedrock to the weakly weathered basalt, indicating a substantial loss of HgGeo with the preferential release of lighter isotopes during the initial weathering, likely due to the dissolution of primary minerals. In addition, the δ202Hg shows a negative correlation with soil pH at some horizons, attributable to the isotopic fractionation during Hg(II) speciation change in soil solution and the selective complexation/adsorption of different Hg(II) species onto mineral surfaces, which are affected by surface charge properties and thus soil pH. Overall, our results provide direct evidence for the accumulation and downward migration of HgAtm in tropical soils during pedogenesis, as well as the loss of HgGeo during the weathering of bedrock, which may serve as an underappreciated source of Hg in tropical regions and have a potential impact on the Hg isotope signatures in aquatic environments.

Mobile evaporite enhances the cycle of physical–chemical erosion in badlands

Abstract. Chemical weathering driven by physical erosion is a natural process that strongly affects chemical and solid matter budgets at the Earth's surface. However, the influence of extreme climatic erosion on chemical weathering dynamics is poorly understood. Badland landscapes formed in highly erodible substrates have the potential to respond to individual events on scales that are rapid enough for direct observation. Here, we assess the geochemical and grain-size composition of suspended sediment and riverine chemistry measurements collected from two catchments during the 2017 Nesat and Haitang typhoons in southwestern (SW) Taiwan. During the typhoons, the Na+ concentration covaried with suspended sediment concentration (SSC), which we attributed to sodium-induced deflocculation. Evaporite weathering at peak rainfall is succeeded by peak silicate weathering at maximum discharge. Overall, our observations suggest that initial weathering of near-surface evaporite enhances the physical erosion of silicate rock during extreme rainfall events.

Weathering of Viamão granodiorite, south Brazil: Part 2 – Initial porosity of un-weathered rock controls porosity development in the critical zone

The development of porosity during rock weathering is a key process controlling nutrients release, water holding capacity available for plants and water flow. Here we used X-ray Computed Tomography (XRCT) and 14C PolyMethylMethAcrylate (PMMA) autoradiography to show how cracks are created and enlarged during initial weathering stages (saprock and saprolite) of granodiorite in southern Brazil (Viamão - RS). The physical evolution is characterized by imaging the pore network, using 14C-PMMA and XRCT methods. Combined with bulk porosity measurements, they highlight the increase in porosity with the degree of weathering (un-weathered rock Φ = 1.66 %, saprolite Φ = 11.7 %). This increase is related to the joint increase of the density of the cracks (un-weathered rock D = 0.28 mm−1, saprolite D = 0.94 mm−1) and of the average opening of the microcracks (un-weathered rock w = 2.4 µm, saprolite w = 3.9 µm) and macrocracks (un-weathered rock w = 176 µm, saprolite w = 400 µm). However, these average crack openings do not account for the variability of the openings that govern the flows, characterized here by specific distribution ranging from the submicrometre to the centimetre scale.The results highlight that the pore network of the un-weathered rock plays a key role in the initial stages or incipient weathering. The density and aperture and cracks increase following the subcritical cracking concept and new pores are formed by chemo-mechanical processes. The presence/absence of initial fractures in the regolith is certainly a key parameter controlling the weathering of different rock types (mafic vs felsic).

Natural weathering of spruce wood chemically modified by re‐used ε‐caprolactone solution

AbstractIncreasing environmental pressures over the last few years have led to attention for non‐biocide treatments in the wood protection field. The ε‐caprolactone modification of wood by substitution or blocking of hydroxyl groups with hydrophobic poly(ε‐caprolactone) (PCL) is one of the novel modification methods developed in recent years. In this study, ring‐opening polymerisation of ε‐caprolactone in wood cell walls was evaluated by the third and sixth re‐use of recovered monomer and by oven‐curing method. Spruce samples were modified by re‐used ε‐caprolactone and exposed to the natural weathering agents for 12 months. After weathering, the colour change, surface roughness measurements, and macroscopic and ultra‐microscopic observations revealed that the modified wood had better surface properties than reference wood. Fourier‐transform infrared (FTIR) analysis proved that PCL could be found on the weathered surface up to the sixth month, but very little amount was detected on the surfaces with a longer weathering period. The results clearly showed that the efficiency of PCL modification with re‐use of the monomer solution was sufficient during the initial weathering periods, but efficiency was reduced after a prolonged exposure period.

Color change and surface chemistry of nano cerium-oxide treated wood after accelerated weathering

Doğal biyolojik polimer olan ahşap malzemenin, diğer yapı malzemelerine kıyasla önemli avantajları bulunmaktadır. Ancak ahşap malzeme, dış ortam koşullarında dayanıklı bir yapıya sahip olmadığı için mutlaka emprenye edilerek veya çeşitli üst yüzey işlemleri yapılarak kullanılmalıdır. Bu çalışmada, sarıçam (Pinus sylvestris L.) örnekleri %0,1; %0,2; %0,5; %0,7; %1; %2; %3; %4 ve %5 konsantrasyonda nano seryum oksit (CeO2) ile muamele edilmiş ve örneklerin hızlandırılmış yaşlandırma testi sonrasında renk değişimi ile yüzey kimyasındaki değişim araştırılmıştır. Hızlandırılmış yaşlandırma testine maruz bırakılan örneklerde başlangıçtan sonra 2, 4, 6, 8, 12, 16, 20, 24, 48, 72, 96, 120, 144 ve 168 saatte renk ve yüzey kimyasındaki değişim belirlenmiştir. Seryum oksidin etkinliği aynı konsantrasyon değerlerinde hazırlanan Tanalith-E çözeltisi ile muamele edilen örnekler ile kıyaslanmıştır. Böylece, seryum oksidin dış ortama maruz kalan ahşap malzemenin yüzey özelliklerinin iyileştirilmesinde, referans maddeye kıyasla kullanılabilirliği değerlendirilmiştir. Çalışma sonucunda, seryum oksit ve Tanalith-E ile muamele edilen örneklerde kontrol örneklerine kıyasla yüzey özellikleri korunmuştur. Araştırılan yüzey özelliklerindeki değişim en fazla, yaşlandırma testinin ilk saatlerinde gözlenmiş, seryum oksidin bakır bazlı emprenye maddesine (Tanalith-E) benzer sonuçlar verdiği bulunmuştur.

Fates of petroleum during the deepwater horizon oil spill: A chemistry perspective

We describe the initial bulk and compound specific composition of the liquid oil spilled during the Deepwater Horizon (DwH) disaster. The emphasis is on the target hydrocarbon compounds typically found in highest concentrations and on those of concern from a toxicological perspective (i.e., the target normal alkanes and isoprenoids, and PAHs on U.S. Environmental Protection Agency’s (EPA) priority list with their alkyl homolog compounds), and/or those relevant for forensic fingerprinting of spill residues (i.e., sulfur containing PAHs and biomarker compounds). Weathering changed the oil’s composition in various environmental compartments. These compositional changes and potential environmental impacts of the remaining weathered residues are presented in this paper. Biodegradation occurred in both surface and subsurface environments while photooxidation primarily modified and removed hydrocarbons in floating oil slicks. The volatile, soluble and highly labile C1 to C10 hydrocarbons were rapidly degraded in the water column and/or emitted to the atmosphere (evaporation). The semi-volatile hydrocarbons (labile C10 to C25) that remained in the water column and floating oil on the water’s surface were lost from oil residues during weathering. The heavy nonvolatile and insoluble hydrocarbons (recalcitrant C25+) were least affected by initial weathering processes in 2010. The composition of the residual oil fraction in surface floating oil was further altered by the addition of oil soluble oxy hydrocarbons produced from photooxidation. During 2011 and 2012 the resulting highly insoluble recalcitrant C25+ oily residues remained on the shorelines, bottom sediments, or bound to suspended particulates in the water column, with detectable residues mostly returning to near pre-spill levels by 2015 to 2020. Some recalcitrant oil residues can still be found at various locations, including some coastal environments (e.g., marshes), or deep-water sediments, at very low levels, ten years after the spill.

The role of iron-bearing minerals for the deep weathering of a hydrothermally altered plutonic rock in semi-arid climate (Chilean Coastal Cordillera)

Weathering is a fundamental process that controls the development of Earth's surface by the formation of erodible material and the release of mineral-bound nutrients. Weathering at depth has been predominantly studied in humid environments, where fluid flow sets mineralogical transformations, whereas (semi-)arid regions were barely investigated in this respect. In many studies the weathering of iron-bearing minerals was shown to play a major role for the advance of weathering at depth. Weathering of iron-bearing minerals is often superimposed on factors that precondition rocks for weathering such as hydrothermal alteration and fracturing by tectonic stress. The low degree of water-rock interactions in (semi-)arid climates offers the opportunity to single out the preconditioning factors and explore the role of iron-bearing minerals for weathering in detail. To this end the interactions of tectonic fracturing, hydrothermal alteration and weathering were investigated in a deep, weakly weathered profile of plutonic rock in a semi-arid region (Santa Gracia, Northern Chile). The profile was recovered by an 87-m-deep drill core and a 2-m-deep soil pit which were used to investigate the mineral composition, magnetic susceptibility, geochemical gradients, and Fe redox-state.Non-cemented fractures of tectonic origin were identified as pathways for the transport of fluids and reagents to depth that are fuelling the initial weathering reactions. Previous hydrothermal fluids mainly migrated along the same fractures and altered the properties of the original bedrock. Therefore, the weathering features along fractures depend on the preconditioning by hydrothermal alteration and tectonic stress which affected the vicinity of these fractures. From the fracture surfaces, water and O2 diffuse into the rock and initiate oxidation and dissolution-reprecipitation reactions. Our study shows that the transformation of iron-bearing silicates (especially biotite) to Fe(III) (oxyhydr)oxides and clay minerals is the dominant weathering-promoting process as it produces stress which leads to micro-fracturing of the rock and finally to the formation of saprolite.Deciphering the links between tectonic fracturing, hydrothermal alteration, and weathering-induced fracturing by iron-bearing silicates in semi-arid settings provides unique insights into the controls of deep weathering in regions with limited fluid flow.

Weathering and pedogenesis of the late Pleistocene and Holocene aeolian loess-paleosol sections in the Yellow River source area, NE Tibetan Plateau

The aeolian loess-paleosol sections on the northeast Tibetan Plateau (NETP) are a valuable source of paleoclimatic information because of their geographical location. In this study, two late Pleistocene–Holocene aeolian loess-paleosol sections were identified based on detailed field investigations in the Maqu reach in the Yellow River source area on the NETP. A robust chronostratigraphic framework for these two sections was established using AMS 14C dating, optically stimulated luminescence (OSL) dating, Bacon age-depth modelling and stratigraphic correlation. Measurements of magnetic susceptibility, hygroscopic water, loss-on-ignition, grain-size, micromorphology, and chemical element analysis suggest that most stratigraphic units in these aeolian loess-paleosol sections are in weak weathering and pedogenesis, whereas the mid-Holocene paleosol approaches to the moderate weathering and pedogenesis, and the sediments are in initial weathering stage of Na+ and Ca2+ leaching is dominated by plagioclase weathering. The main pedogenesis in the mid-Holocene paleosol is calcification process. In terms of intensity of weathering and pedogenesis, the stratigraphic units can be ordered as follows: paleosol > modern soil > transitional loess > aeolian loess. Multi-index comparison shows that the local climatic evolution during the late Pleistocene–Holocene was closely related to the evolution of the East Asian summer monsoon (EASM) and the Westerlies. Overall, the results provide a foundation for further exploration of the pedogenic and paleoclimatic evolution on the NETP.

Initial carbonate weathering is linked with vegetation development along a 127-year glacial retreat chronosequence in the subtropical high mountainous Hailuogou region (SW China)

AimsThe retreat of glaciers is exposing new terrains to primary plant succession around the globe. To improve the understanding of vegetation development along a glacier retreat chronosequence, we (i) evaluated a possible link between base metal (Ca, Mg, K, Na) supply and vegetation establishment, (ii) determined the rates of the establishment of soil and plant base metal stocks, and (iii) estimated the size of the main base metal fluxes.MethodsWe determined base metal stocks in the soil organic layer, the mineral topsoil (0–10 cm), and in leaves/needles, trunk, bark, branches and roots of the dominating shrub and tree species and estimated fluxes of atmospheric deposition, plant uptake and leaching losses along the 127-yr Hailuogou chronosequence.ResultsTotal ecosystem Ca and Mg stocks decreased along the chronosequence, while those of K and Na were unrelated with ecosystem age. Fortyfour and 30% of the initial stocks of Ca and Mg, respectively, were leached during the first 47 years, at rates of 130 ± 10.6 g m−2 year−1 Ca and 35 ± 3.1 g m−2 year−1 Mg. The organic layer accumulated at a mean rate of 288 g m−2 year−1 providing a bioavailable base metal stock, which was especially important for K cycling.ConclusionsWe suggest that the initial high Ca bioavailability because of a moderately alkaline soil pH and carbonate depletion in 47 years, together with the dissolution of easily-weatherable silicates providing enough Mg and K to the pioneer vegetation, contributed to the establishment of the mature forest in ca. 80 years.

Experimental investigation of the effect of quenching cycles on the physico-chemical properties of granites

In this study, the physicochemical properties of granitic rocks subjected to quenching cycles were studied experimentally. Four granites of similar mineralogy but with different degrees of initial weathering (porosity between 1 and 6%) were slowly preheated at two peak temperatures (200 and 400 °C) and then quenched 35 times.To study the effect of thermal cycling on the physical properties, non-destructive tests were used such as water porosity, capillary water absorption tests, P- and S- wave propagation velocities, nuclear magnetic resonance relaxometry, and X-ray micro-tomography. Chemical analysis of the granites was performed using X-ray fluorescence, which provided information on the major and trace elements. Water-granite interactions were followed using inductive plasma mass spectrometry (ICP-MS).The variation of all the measured parameters indicates the creation of cracks with thermal fatigue. The porosity, water uptake, size, and volume of cracks increased while P- and S- wave velocity and Young's modulus decreased. At 200 °C, the changes were progressive up to ten cycles, from which the stress threshold was reached and only small readjustments took place. At 400 °C, the greatest damage was observed during the first five cycles. These changes were a direct consequence of the propagation of the microcracks induced by the strong gradient during the quenching tests. For both temperatures, the changes depended on the initial weathering conditions of the granites. Initially, weathered granites showed crack development or crack closure during quenching, meanwhile the damage on the sound rocks was characterized by the creation of intragranular microcracks.The analysis of the experimental fluids showed enrichment in K, Na and Ca in the solution as consequence of the dissolution of K-feldspar, plagioclase and the degradation of mica and clays, independently of the physical and mechanical modifications.

Rate limitations of nano-scale weathering front advance in the slow-eroding Sri Lankan Highlands

In the Sri Lankan Highlands denudation and chemical weathering represent the low-end member in global weathering rates. Here we report on the causes for these low rates in corestones from a highly weathered saprolite profile. By using electron microprobe and transmission electron microscopy (TEM) analyses, we investigated weathering reactions, and derived rates of pyroxene and biotite oxidation. High-resolution TEM analyses on primary minerals showed that the initial weathering products are non-crystalline and that these form the precursors of secondary minerals (kaolinite and smectite). The dissolution of primary minerals is characterised by sharp reaction fronts in the absence of chemical gradients, hence, dissolution can best be described by a dissolution – reprecipitation process. The first observable weathering reaction is the oxidation of structural Fe(II) in pyroxene and biotite. This oxidation is restricted to distinct zones within the minerals without the formation of oxidized layers. While the oxidation is not accompanied by chemical changes, the oxidation of structural Fe(II) in biotite may cause lattice distortion. Pyroxene and biotite oxidation rates were calculated at the corestone-scale by using the gradient of bulk rock Fe(II)/Fetotal ratios, assuming that oxidation is coupled to the weathering front advance rate. At the mineral-scale, oxidation rates were calculated by using gradients of in situ Fe(II)/Fe(III) ratios measured with electron energy-loss spectroscopy (EELS) within the minerals assuming a coupled oxidation-cation diffusion process. The mineral-scale oxidation rates are significantly higher, log Ominin situ = −11 molmin m−2 s−1, than corestone-scale oxidation rates, log Omin = −13 to −15 mol m−2 s−1. We explain the difference to result from the fact that corestone-scale rates average the oxidation over the entire mineral surface. Because at the corestone-scale pyroxene oxidation rates are also similar to dissolution rates, we infer that oxidation preconditions Fe(II)- bearing primary silicate minerals to weathering. However, although oxidation is initiating chemical weathering in this setting and is limited by the supply of O2, overall conversion of bedrock to saprolite is driven by the formation of porosity by fracture formation during this reaction, which allows for fluid transport and subsequent plagioclase weathering. We conclude that in compact bedrock nm- to µm-scale fracture- and porosity generation are the processes that drive weathering in tectonically quiescent regions. They are also the processes at depth that couple the weathering zone with processes at its surface. Finally, the formation of secondary surface layers at the nm-scale is essential in controlling the equilibrium in the local weathering environment and hence mineral dissolution. These layers are likely also those that control isotope fractionation in the weathering zone.

Characteristics of major and trace elements in surface sediments of the Makran Accretionary Prism, Pakistan and their implications for natural gas hydrates

To accurately identify the natural gas hydrates (NGH) in the sea area of the Makran Accretionary Prism, Pakistan, this paper presents the testing and analysis of major and trace elements in sediment samples taken from two stations (S2 and S3) in the area by the China Geological Survey. As shown by testing results, all major elements are slightly different in content between the two stations except SiO2 and CaO. This also applies to the trace elements that include Sr and Ba primarily and Cr, Ni and Zn secondarily. It can be concluded in this study that the tectonic setting of the Makran Accretionary Prism is dominated by oceanic island arc and that provenance of the Makran Accretionary Prism is dominated by felsic igneous provenance, which is at the initial weathering stage and mainly consists of granodiorite. Besides terrigenous detritus, there are sediments possibly originating from Makran-Bela Ophiolite from the northwestern part and Murray Ridge igneous rocks from the southeastern part. The V/Cr, Ni/Co, and V/(V+Ni) ratios indicate that sediments of the two stations are in an oxidation-suboxidation environment. However, the authors infer that the sedimentary environment of the sediments 3.0 m below the seafloor tends to be gradually transformed into a reduction environment by comparison with the Qiongdongnan Basin in the South China Sea where NGH has been discovered. The sediments in the Makran Accretionary Prism are rich in organic matter, with total organic carbon (TOC) content greater than 1%. According to comprehensive research, the organic matter in the sediments mainly originates from marine algae and has high TOC content, which is favorable for the formation of NGH.

Nanopore Formation and Structural Changes in Black Shale During the Initial Weathering Stage: A Longmaxi Formation Profile in Northwestern Hunan, China.

Understanding the controls on composition changes and porosity evolution in the critical zone of shale remains a major challenge. The aim of the present study is to develop a model of the changes in mineral compositions, chemical compositions and nanopore formation in shale during the initial weathering stage. To understand these processes, we selected a Silurian shale profile rich in pyrite and organic matter located in South China. Based on X-ray diffraction (XRD) and bulk elemental data, the variations in mineralogical and chemical compositions with depth were studied. To characterize the full pore size spectrum and to gain insight into the nature of secondary pores and their relationship with weathering, nuclear magnetic resonance (NMR) measurements and petrographic observations were combined with scanning electron microscopy (SEM) imaging. The results show that Al and K are enriched slightly, while Ca and Na are depleted in the upper part of the weathering profile. Si, Mn and Ti are relatively stable from the bottom to the top of the profile. Quartz, feldspar, mica, illite and chlorite are the main minerals in the parent rock, and they are relatively stable along the profile. The rock density gradually decreases from 2.6 g/cm³ to 2.1 g/cm³ from the bottom to the top, and the color of the shales changes from black to grayish yellow, but no secondary minerals are detected. The chemical weathering of black shale is dominated by the oxidation of pyrite and organic matter, giving rise to color variation and nanopore formation. The increase in interparticle pores at the nanometer-micron scale is initiated by the dissolution of easily weathered components such as organic matter and pyrite. The removal of clay minerals and tiny particles by groundwater seepage may be the main cause of porosity enhancement during the initial weathering stage. This study suggests that nanoporosity may play an important role in the process of fluid-rock interaction within black shale during the initial weathering stage.

Weathering Products of a Dismantled Variscan Basement. Minero-Chemical Proxies to Insight on Cretaceous Palaeogeography and Late Neogene Palaeoclimate of Sardinia (Italy)

This study compares, for the first time, the mineralogy and geochemistry of two residual-clay deposits in NW Sardinia (Nurra district) that formed at different times in tropical and sub-tropical climates. Both deposits represent palaeosols with deep-weathered residual profiles and overlie Mesozoic carbonate rocks that were deposited on the south European palaeomargin. The older alterite is Cenomanian–Turonian in age and grades upward into a horizon of karstic bauxite, whereas the younger unit occurs within alluvial deposits of Late Neogene age. The Cretaceous palaeosol represents the precursor of the overlying bauxite and formed from unknown sedimentary parent rocks. In contrast, the Messinian weathering products formed by alluvium that was sourced from the Variscan metamorphic basement. Chemical Index of Alteration values, REE fractionation index values, and the results of R-mode factorial analysis suggest a common initial weathering path and a common precursor for the deposits. However, the latter stages of weathering of the Cretaceous palaeosols resulted in lateritic alteration and bauxite production, whereas weathering of the Late Neogene, palaeosols produced 2:1 clay minerals under less extreme conditions. Comparison of these residual products constrains the parental material and weathering trends and allows insight into the relationship between palaeoclimate and regional/local palaeogeography of southern Europe during Upper Cretaceous and during Messinian.

Geochemical and mineralogical features of karst bauxite deposits from the Alborz zone (Northern Iran): Implications for conditions of formation, behavior of trace and rare earth elements and parental affinity

The present study focuses on three outcrops of Upper Permian to Lower Jurassic karst bauxite deposits in the Alborz zone, north of Iran. The deposits occur as sharp semi-continuous lenses within the Upper Permian Ruteh Formation (Gheshlagh) and the Upper Triassic Elika Formation (Siahrudbar and Separdeh) carbonate rocks. Textural characteristics such as pelitomorphic matrix, local ooidic-pisoidic, fluidal, and clastic textures indicate authigenic-allothigenic origins. Mineralogically, kaolinite, boehmite, goethite, and hematite in the Gheshlagh, diaspore, hematite, and kaolinite in the Siahrudbar, and kaolinite, hematite, goethite, diaspore, siderite, and chamosite in the Separdeh deposits are the main phases. The distribution patterns of major elements normalized to the upper continental crust (UCC) depict enrichments of Al, Fe, and Ti in all three deposits. The three deposits are variably enriched in transition trace elements (Cr, Ni, Co, V), U, Th, and high field strength elements (Ga, Hf, Zr, Nb, Y) relative to UCC. The studied bauxites have average concentrations of rare earth elements (ΣREE, La-Lu) between 305.97 and 373.69 ppm. Geochemical data reveal progressive enrichment of REE and an intense (LREE/HREE)N fractionation toward the lower parts of the profile in the Separdeh deposit due to the alkaline conditions of the carbonate bedrock, and irregular distribution patterns at the Gheshlagh and Siahrudbar deposits due to water level and pH fluctuations. The positive Ce anomalies at Separdeh and Siahrudbar suggest oxidizing conditions in the upper parts of the profiles. At Gheshlagh, the negative to nil Ce anomalies reflect low intensity of oxidation. Based on previous geochemical analysis data, the Upper Permian basalts in the Gheshlagh, and the Upper Triassic basalts in the Separdeh and Siahrudbar areas were the most likely source materials. The local uplift of the Permian-Upper Triassic series led to the formation of karstic topography filled with materials derived from weathering of the basaltic rocks under humid tropical paleoclimate. The initial weathering converted the source rocks to kaolinitic soils characterized by the enrichment of Al, Fe, and Ti. Then, they were transferred to the karstic depressions and sinkholes and underwent in situ leaching and desilicification bringing about a relatively higher ore grade. The overall field and petrographic evidence demonstrate that these deposits were formed in shallow and swampy environments. In the eastern part of the Alborz zone (at Siahrudbar and Gheshlagh), better drainage conditions have enhanced the quality of ores.

A new method for determining weathering rates in weathering pits

AbstractDetermining the rates of rock weathering is difficult because, firstly, the weathering rate of rocks is usually so slow that it is difficult to measure; secondly, it is also difficult to determine the start time and duration of weathering. The Shanxi River Valley in Fujian, China dried up after a reservoir was built upstream in 1959, and became a stone quarry site. Quarrying ceased in 1977, so a large amount of quarry wastes with artificially excavated surfaces were left in the valley. The concave‐upward curved rocky surface, broken by manual excavation, easily contains rainwater in its central part, which was easily weathered into a more concave surface. Plaster mould casting was performed in situ on such a concave surface of an excavated stone rock in the valley and scanned with a high‐precision 3D scanner to obtain 3D data of the concave‐upward rock surface and its more concave middle part, which was considered as an initial weathering pit. The 3D model provided an in‐depth understanding of the initial formation process of weathering pits, indicating that: (1) the average weathering rate of a weathering pit is 10.8 ± 0.49 cm ka−1; (2) weathering pits are generally formed by standing water in depressions on a flat near‐horizontal rock surface due to weathering actions involving water; (3) the deepening rate of a weathering pit is about four times greater than that of the surrounding area; (4) the growth of a weathering pit can begin in some small concavities on the flat rock surface without pre‐existing depressions and gradually expands; (5) a weathering pit is generally wider than deep or with a flat bottom due to expansion with a lateral weathering rate that is greater than that of the vertical, and the lamination of the host rock is not necessary for the formation of flat‐floored weathering pits. © 2020 John Wiley &amp; Sons, Ltd.

An attempt to determine the behavior of metals and their dependent thermodynamic saturation states in the groundwater along mountain front and riparian zone

A study was employed to evaluate the probable sources of heavy metal in the groundwater along the mountain front (MF) and riparian zone (RZ) using statistical techniques. 53 samples have been collected and analyzed for major ions and 16 heavy metals like Li, Be, Al, Ti, Cr, Fe, Mn, Cu, Cd, Zn, Ga, Rb, Sr, Cs, Ba and Pb. Samples along MF exceeded the permissible limits for metals like Li, Ti, Al, Cr, Fe, Sr, Cd, Ba and Pb with a maximum concentration of 30.10, 42,823, 378, 74.53, 30,801, 5970, 10.88, 1052.69 and 4458, respectively (WHO in Guidelines for drinking-water quality, First adendum to third ed., Recommendations, vol 1. WHO, Geneva 2006 and WHO in Guidelines for drinking-water quality (4th ed.). http://www.whqlibdoc.who.int/publications/2011/9789241548151_eng.pdf 2011). However, samples along the RZ exceeds the prescribed limits for the same metals as MF except Ba. Specific metals in groundwater like Cr, Cu, Ti, Mn and Pb, reflect anthropogenic signatures (agrochemicals and urban sewage); however, other metals are due to natural process, i.e., leaching of underlying rocks. Thus, both MF and RZ aquifers are highly influenced by the recharge from natural process, agricultural return flow and urban sewage. High saturation index of gibbsite is noted along the MF and it reveals the stages of initial weathering and predominance recharge zones as compared to RZ.

Morphological Transformation of Silver Nanoparticles from Commercial Products: Modeling from Product Incorporation, Weathering through Use Scenarios, and Leaching into Wastewater.

There is increasing interest in the environmental fate and effects of engineered nanomaterials due to their ubiquitous use in consumer products. In particular, given the mounting evidence that dramatic transformations can occur to a nanomaterial throughout its product lifecycle, the appropriateness of using pristine nanomaterials in environmental testing is being questioned. Using a combination of transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-mass spectrometry (ICP-MS), this work examines the morphological and compositional effects of conditions mimicking a typical lifecycle of a nano-enabled product, from the production of the silver nanoparticle (AgNP)-laden textiles, through its use, laundering, and then finally, its leaching and incubation in the wastewater collection system. These simulated weathering conditions showed evidence for the transformation of AgNPs into AgCl and Ag2S. Incubation in raw wastewater had the most dramatic effect on the AgNPs in terms of transformation, no matter what initial weathering was applied to the NPs prior to incubation. However, despite extensive transformation noted, AgNPs were still present within all the samples after the use scenarios.