Weathering Mechanisms Research Articles

Mineralogical approach on laboratory weathering of uncontaminated Ryugu particles: Comparison with Orgueil and perspective for storage and analysis

AbstractAlthough CI chondrites are susceptible to terrestrial weathering on Earth, the specific processes are unknown. To elucidate the weathering mechanism, we conduct a laboratory experiment using pristine particles from asteroid Ryugu. Air‐exposed particles predominantly develop small‐sized euhedral Ca‐S‐rich grains (0.5–1 μm) on the particle surface and along open cracks. Both transmission electron microscopy and synchrotron‐based computed tomography combined with XRD reveal that the grains are hydrous Ca‐sulfate. Notably, this phase does not form in vacuum‐ or nitrogen‐stored particles, suggesting this result is due to laboratory weathering. We also compare the Orgueil CI chondrite with the altered Ryugu particles. Due to the weathering of pyrrhotite and dolomite, Orgueil contains a significant amount of gypsum and ferrihydrite. We suggest that mineralogical changes due to terrestrial weathering of particles returned directly from asteroid occur even after a short‐time air exposure. Consequently, conducting prompt analyses and ensuring proper storage conditions are crucial, especially to preserve the primordial features of organics and volatiles.

Quantitative analysis on the impact factors of salt weathering for sandstone grottoes along Silk Road, China

A large number of exquisite sandstone grottoes remaining along the Silk Road in Northwest China suffer from severe salt damage due to the vulnerability of the sandstone materials used and long-term continuous fluctuation of environmental conditions. Exploring the mechanism of salt weathering is crucial for the conservation of these grottoes. This study aims to quantitatively analyze the damage potential and the main impact factors of salt weathering in 14 grottoes along the Silk Road that were selected and investigated by using visual evaluation, salt analysis including thermodynamic modeling, and a comprehensive evaluation based on the entropy weight method. The results indicate that salt weathering of the sandstone grottoes is primarily characterized by efflorescences, peeling, and powdering. The overall salt content within the weathering layer typically exceeds a threshold of 1 %. Within the semi-arid area, the humidity fluctuations critical for significant volume changes in crystalline salts fall within the ranges 46–76 % and 16–30 %. In the semi-humid area, these ranges are 58–90 %, 42–50 %, and 16–30 %. A total of 14 salts can precipitate in the study area with NaCl, NaNO3, KNO3, Na2SO4·xH2O and several double salts occuring most frequently. Generally, the damage degree of sandstones grottoes in the semi-humid area is more serious than that in the semi-arid area. Through a comparison of visual inspection and more comprehensive quantitative evaluation, it has been confirmed that the salt damage is primarily influenced by the factors salt content, salt type, and environmental conditions. Furthermore, the order of influence for each factor on salt weathering can be ranked as follows: salt content > salt type > environmental conditions. This study quantitatively reveals the impact of various factors on salt weathering and proposes a method to evaluate the salt damage potential, which is of great significance for the preventive conservation of sandstone grottoes.

Experimental study on weathering mechanism of ancient bricks in Jiayuguan Wei-Jin tombs, Gansu, China

This study focuses on the ancient bricks of Wei-Jin tombs in Jiayuguan, Gansu, China, analyzing the deterioration of the bricks under the long-term influence of natural environments and human activities. Currently, the ancient bricks exhibit various degradation diseases such as cracks, exfoliation, fracture, weathering, and microbial erosion, severely affecting the integrity of the cultural relics. Through on-site investigation and characterization testing, the physical and mechanical properties, compositional elements, pore size distribution, and thermal characteristics of the ancient bricks were analyzed. Indoor simulation experiments were conducted to study the impact of different types of environmental erosion cycles (such as H2O, HCl, NaOH, Na2SO4) on the performance and structure of the ancient bricks, the patterns and causes of deterioration were also studied. The results indicate that the cyclic effects gradually transform the porosity of the ancient bricks into lateral microcracks, which continue to expand, leading to varying degrees of degradation of performance. The extent of the impact of these cycles on the properties of ancient bricks is in descending order: Na2SO4, HCl, NaOH, H2O. H2O, NaOH, HCl, Na2SO4.

Characteristics and Mechanism of Salt Weathering in Moist Earthen Sites: A Case Study on China’s Jinsha Earthen Site

ABSTRACT This study investigates salt weathering in the indoor, humid environment of China’s Jinsha earthen site. Methods such as digital microscope, scanning electron microscopy (SEM), ion chromatography (IC), energy dispersive spectroscopy (EDS), and laser particle size analysis were employed to collect and analyze samples from four heavily weathered walls. The sampling approach took into account differences in depth and height and prioritized the extraction from various weathering layers to unveil the attributes, causes, and mechanisms of salt weathering. The findings indicate that the Jinsha site’s eastern segment suffered salt-induced damage, such as powdering, salt crusts, and blistering, due to the presence of gypsum and magnesium sulfate. These salts were primarily sourced from groundwater. Groundwater ions ascended to the site’s surface via capillary action, instigating various forms of salt damage. Salt damage severity has a direct link to salt and moisture content. The degradation patterns can be categorized into powder and multi-layered composite deterioration, both seems related to soil particle composition. Powder deterioration tends to occur when the sand content exceeds 40%. This research proposes preservation strategies that focus on managing groundwater and conducting environmental surveillance. These measures are designed to effectively address and mitigate the risks associated with salt damage.

Mineral transformation, element transport and hydrological impact in weathering at the Bingling Temple Grottoes: Implications for weathering in alkaline environments in NW China

Alkaline environments are common in arid and semi-arid regions in northwestern China and have preserved quantities of rock heritages along the Silk Road. In contrast to the frequently reported weathering mechanism of stone heritages in acidic conditions, mineral weathering mechanism (especially the transformation mechanism of smectite) in natural alkaline environments still remains to be evaluated. To deepen the understanding of weathering in such an environment, research idea from critical zone science was applied to investigate the element transport and mineral transformation from protolith (interbedded sandstone and conglomerate) to regolith in a world cultural heritage, Bingling Temple Grottoes (BTG), in northwestern China. From geochemical and mineralogical characterizations on boreholes, excavated profiles, fractures and cliff surface, we found that dissolution of calcite, plagioclase (anorthite, albite) and K-feldspar (orthoclase) caused major elemental loss of Na, K and Ca (to aqueous solution) in the BTG, and elements of Mg and Fe mostly retained in solid materials. Characterizations on the cliff surface demonstrated higher extents of element depletion and mineral weathering and lower ultrasonic P-wave velocities in sandstone than in conglomerate, and in the bottom sandstone layers (located in the capillary zone and exposure to rain scouring) than in upper sandstone layers (located in the cave and free of precipitation). The transformation of smectite from protolith to regolith follows the sequential reactions: dehydrated smectie → bihydrated smectite → randomly interstratified illite/smectite → illite. Such transformation pathway is favored by alkaline pH and wetting–drying cycles frequently occurred at the BTG. Typical weathering patterns such as clay swelling damage, efflorescence, salt precipitation, etc., are highly-linked to seasonal changes in the hydrological process influenced by both reservoir construction and groundwater system. Our study provides more evidence for the illitization of smectite in natural alkaline environments and highlights the hydrological impacts on weathering patterns of rock grottoes.

Temporal variability and site specificity of thermomechanical weathering in a temperate climate

Thermomechanical processes caused by short- and long-term temperature fluctuations are a prevalent weathering mechanism on exposed rock walls. While many authors have explored the potential for thermomechanical weathering in alpine and polar regions, few have examined the effects of seasonality on weathering in temperate climates. This is pertinent as seasonal climatic conditions may influence both short-term temperature oscillations which produce incipient fractures and diurnal-to annual-scale cycles which propagate pre-existing fractures via thermal fatigue. In this study, three rock outcrops located along the Niagara Escarpment in Hamilton, Canada were monitored to examine changes in the thermal regime at the rock surface and within pre-existing fractures over a 1-year period. Temperature was sampled in 1-min intervals, providing data at a fine temporal resolution. Our unique dataset demonstrates that the rock surface and fracture experience minute-scale temperature oscillations which magnify over time. Longer-term temperature cycles during the year are superimposed upon minute- and diurnal-scale fluctuations which likely augment weathering potential. This produces considerable thermal stress over the year which we estimate to be on the order of 18 GPa at the rock surface and 8 GPa in fractures. We also observed diurnal reversals of the temperature gradient between the rock surface and fracture which may further amplify crack propagation. Seasonality and site-specific characteristics interact to modify different components of the rockwall thermal regime. Vegetation shading has seasonal and diurnal-scale impacts on the temperature gradient between the surface and fracture, and the amplitude of daily warming and cooling cycles. Aspect has a stronger influence on minute-scale temperature oscillations. Estimates of diurnal thermal stress indicate that the thermomechanical weathering potential is seasonally variable, but highest in the spring. Our findings demonstrate that in a temperate climate, rockwall thermal regimes experience variability across the gradient of temporal scale with strong seasonal effects.

Freeze-thaw cycles drove chemical weathering and enriched sulfates in the Burns formation at Meridiani, Mars.

Sulfate-rich sedimentary rocks explored by the Opportunity rover during its 14-year surface mission at Meridiani Planum provide an invaluable window into the thousands of sulfate deposits detected on Mars via remote sensing. Existing models explaining the formation of martian sulfates can be generally described as either bottom-up, groundwater-driven playa settings or top-down icy chemical weathering environments. Here, we propose a hybrid model involving both bottom-up and top-down processes driven by freeze-thaw cycles. Freezing leads to cryo-concentration of acidic fluids from precipitations at the surface, facilitating rapid chemical weathering despite low temperatures. Cryosuction causes the upward migration of vadose water and even groundwater with dissolved ions, resulting in the accumulation of ions in near-surface environments. Evaporation precipitates salts, but leaching separates chlorides from sulfates during the thawing period. Freeze-thaw cycles, therefore, can enrich sulfates at the surface. While freeze-thaw is more commonly understood as a mechanism of physical weathering, we suggest that it is a fundamental aspect of chemical weathering on Mars.

Patterns of distribution of eluvia soils in the oil region of Tatarstan

The article is devoted to the study of eluvial deposits in the southeastern part of the Republic of Tatarstan. As a result of river erosion, a highly dissected and rugged terrain has formed here. Its characteristic elements are erosion-denudation watersheds separated by narrow river valleys and terraced slopes. According to the results of the research, it was revealed that the differences in the structure of weathering profiles in carbonate and terrigenous soil massifs are due to the structural and mineralogical features of rocks that were formed at the stage of sedimentation and subsequent diagenesis. In the central part, on the site of the upper plateau, the rocks underwent mainly physical weathering processes, on the site of the middle plateau – chemical weathering processes, on the site of the lower plateau – physical and chemical weathering processes. Such selectivity in the manifestation of hypergenic processes is due to the predominant lithotypes of sedimentary rocks composing the surfaces of the upper, middle and lower plateaus of the studied territory. Based on the conducted research, the zoning of the studied territory was performed and an engineering and geological map was built. The results obtained made it possible to understand the mechanism of weathering of carbonate and terrigenous rocks, as well as to assess the potential change in their physical and mechanical properties during the construction and operation of buildings and structures.

Regional patterns of zoning hypergenic transformations of sedimentary rocks of the middle Permian age of the Eastern Zakamye

The article is devoted to the study of eluvial deposits in the territory of the Eastern Zakamye. Due to the activity of river erosion, a highly dissected and rugged terrain has formed in this area. Its characteristic elements are erosion-denudation watersheds spaces separated by narrow river valleys and terraced slopes. According to the results of the research, it was revealed that the difference in the structure of weathering profiles in carbonate and terrigenous soil massifs is due to the structural and mineralogical features of rocks acquired at the stage of sedimentation and subsequent diagenesis. In the central part, at the upper plateau site, the rocks underwent mainly physical weathering processes, at the middle plateau site – chemical weathering processes, at the lower plateau site – physical and chemical weathering processes. Such selectivity in the manifestation of hypergenic processes is due to the predominant lithotypes of sedimentary rocks composing the upper, middle and lower plateau surfaces of the plateau of the studied territory. Based on the completed study, the zoning of the territory of the Eastern Zakamye was carried out and an engineering and geological map was built. The results obtained make it possible to understand the mechanism of weathering in carbonate and terrigenous rocks, and, consequently, to assess the potential change in the physical and mechanical properties of rocks, both during construction and during the operation of buildings and structures.

Damage of porous building stone by sodium carbonate crystallization and the effect of crystallization modifiers

Salt crystallization is an aggressive weathering mechanism affecting porous building materials. The extensive use of Portland cement, a source of alkalis, in modern buildings and restoration interventions makes sodium carbonate salts important weathering agents. Herein, we study salt damage to a porous stone commonly used in the Andalusian built heritage (Santa Pudia limestone) due to stress generation associated with the precipitation of natron (Na2CO3·10 H2O). We performed cyclic crystallization tests combined with thermodynamic and poromechanical calculations to determine salt crystallization pressure and effective tensile stress suffered by the material. The outcome reveals that in-pore natron crystallization during cooling/evaporation generates stresses exceeding the tensile strength of the wet substrate, leading to extensive damage by fracturing and material loss. Damage is reduced using aminotris(methylenephosphonic) acid (ATMP), a common phosphonate-based crystallization modifier that induces non-damaging efflorescence growth as opposed to damaging subflorescence growth, which takes place in its absence.

The effect of weathering on drillability of dolomites

Abstract In this study, an aggregate quarry was investigated in order to understand the impact of weathering phenomenon on the drillability of dolomite stones, respectively. Samples were collected from the study area and analyzed in terms of physicomechanical tests (specific gravity, dry unit weight, uniaxial compressive strength, point load index (Is50), and Brazillian tensile strength). The drillability of the rocks was investigated using the drilling rate index method. Based on the analysis results, significant relationships were obtained between physicomechanical properties and drillability of dolomites at different weathering grades. Initial evaluations can be interpreted as an increase in the weathering degree would result in an increase in drillability. This understanding of weathering's impact on drillability is actually the main purpose of this study. This article could be a tool as regards initial evaluations of the drillability of dolomites combined with the weathering mechanism, since successful evaluations and meaningful relations were achieved.

Mesoscale Characteristics of Exceptionally Heavy Rainfall during 4–6 May 2023 in Jiangxi, China

A long-lasting rainfall event exceeding historical extremes took place in Jiangxi, China, from May 4 to 6, 2023. Because of the concentrated duration of precipitation, it led to significant water accumulation in the northern, central, and southern regions of Jiangxi. The objective of this study was to investigate the weather mechanisms underlying this extreme rainstorm in Jiangxi. By examining detailed observational data, the mesoscale weather characteristics and environmental conditions of the event can be obtained. These findings offer valuable insights for future weather forecasting and warnings. It was observed that after the Huanghuai cyclone moved eastward into the sea, the cold air on its western side shifted northward and converged with the warm, moisture-laden air mass in Hunan and Jiangxi provinces. This convergence of air masses triggered the heavy rainstorm event. The peak precipitation period occurred from midnight on May 5 to 0800 BJT on May 6. Concerning the macroscopic precipitation characteristics, multiple mesoscale convective systems (MCSs) originated in Hunan during this period and progressed eastward along the shear line toward the central part of Jiangxi. As for the microscopic precipitation features, the total precipitation amount was closely linked to the duration of heavy rain droplets. The rainfall distribution in the raindrop spectrum also served as a valuable reference for understanding the persistence and size of precipitation. The temporal pattern of the combined reflectivity echo along 27.5° N indicated that from 2000 BJT on May 5 to the early morning of May 6, there was a rapid development of a weaker MCS after passing through the Luoxiao Mountains. This development resulted in a “train effect” in the central region of Jiangxi. The presence of a 200 hPa divergence area, high vertical ascent rate, and abundant water vapor contributed to the formation of a narrow area of heavy rainstorms in central Jiangxi. Additionally, the falling area of heavy rain coincided with the front of the 500 hPa low trough. In the northern part of Jiangxi, the occurrence of heavy precipitation was influenced by the equivalent temperature front area. Favorable conditions, including water vapor, dynamics, and thermal factors, further supported the occurrence of heavy precipitation.

Prediction and Early Warning of Air Quality based on the LSTM-ARIMA Model

At present, China's economy is transforming from a stage of high-speed growth to a stage of high-quality development. Building an ecological civilization is an important part of the realization of the Chinese dream of national rejuvenation. Air pollution will cause harm to human health, ecological environment, social and economic aspects, and its pollution level is affected by many factors, such as PM2.5, PM10, CO, temperature, wind speed, precipitation and so on. In order to implement the party's 20th spirit, strengthen the coordinated control of pollutants, basically eliminate heavy pollution weather, improve and improve the response and disposal mechanism of heavy pollution weather, a place issued an emergency plan for pollution weather, which will strengthen monitoring and early warning, energy conservation and emission reduction, and minimize the impact of pollution weather. To explore the influencing factors of PM2.5 concentration change, more accurate prediction PM2.5 concentration and AQI index, this paper for the prediction and warning of air quality, using the daily pollutants in January 2015 to April 2023, the data of analysis of PM2.5 concentration, the importance of the top three factors PM10, average temperature, CO as auxiliary variables, to construct the LSTM-ARIMA combination model. First, LSTM was used for multi-factor prediction. In order to improve the accuracy of the prediction results, the prediction error of LSTM was then linearly corrected based on the ARIMA model, the time step was adjusted to observe the previous data, and the prediction results of the model were evaluated by root mean square error (RMSE).

Effects of biomass co-pyrolysis and herbaceous plant colonization on the transformation of tailings into soil like substrate

Enhancing soil organic matter characteristics, ameliorating physical structure, mitigating heavy metal toxicity, and hastening mineral weathering processes are crucial approaches to accomplish the transition of tailings substrate to a soil-like substrate. The incorporation of biomass co-pyrolysis and plant colonization has been established to be a significant factor in soil substrate formation and soil pollutant remediation. Despite this, there is presently an absence of research efforts aimed at synergistically utilizing these two technologies to expedite the process of mining tailings soil substrate formation. The current study aimed to investigate the underlying mechanism of geochemical changes and rapid mineral weathering during the process of transforming tailings substrate into a soil-like substrate, under the combined effects of biomass co-smoldering pyrolysis and plant colonization. The findings of this study suggest that the incorporation of smoldering pyrolysis and plant colonization induces a high-temperature effect and biological effects, which enhance the physical and chemical properties of tailings, while simultaneously accelerating the rate of mineral weathering. Notable improvements include the amelioration of extreme pH levels, nutrient enrichment, the formation of aggregates, and an increase in enzyme activity, all of which collectively demonstrate the successful attainment of tailings substrate reconstruction. Evidence of the accelerated weathering was verified by phase and surface morphology analysis using X-ray diffraction and scanning electron microscopy. Discovered corrosion and fragmentation on the surface of minerals. The weathering resulted in corrosion and fragmentation of the surface of the treated mineral. This study confirms that co-smoldering pyrolysis of biomass, combined with plant colonization, can effectively promote the transformation of tailings into soil-like substrates. This method has can effectively address the key challenges that have previously hindered sustainable development of the mining industry and provides a novel approach for ecological restoration of tailings deposits.

Investigation and analysis of ancient brick carvings of the Liuhe Pagoda in Hangzhou

AbstractThe Liuhe Pagoda in Hangzhou, China, has a large number of brick carvings from the Southern Song Dynasty (1152 ce), covering an area of 464 m2. However, the exquisite brick carvings in the Liuhe Pagoda have deteriorated due to natural weathering and a high‐humidity environment. Through laboratory analysis and on‐site nondestructive testing, the physical and chemical properties of the brick carvings of Liuhe Pagoda were investigated, and the weathering mechanism of the brick carvings was further analyzed. The brick carving of Liuhe Pagoda is composed of brick, white plastering and black coating. CaCO3 is the main component in white plastering, and the black coating on the top surface contains Chinese lacquer. The weathering products of the brick were analyzed and a trace of CaSO4.2H2O was found. In addition, the brick carvings with high water content have low Leeb hardness and severe weathering. Therefore, water and soluble salt are the main factors in weathering of the brick carvings of the Liuhe Pagoda.

Fungal organic acid uptake of mineral-derived K is dependent on distance from carbon hotspot.

Fungal species are foundational members of soil ecosystems with vital contributions that support interspecies resource translocation. The minute details of these biogeochemical processes are poorly investigated. Here, we addressed this knowledge gap by probing fungal growth in a novel mineral-doped soil micromodel platform using spatially-resolved imaging methodologies. We found that fungi uptake K from K-rich minerals using organic acids exuded in a distance-dependent manner from a carbon-rich hotspot. While identification of specific mechanisms within soil remains challenging, our findings demonstrate the significance of reduced complexity platforms such as the mineral-doped micromodel in probing biogeochemical processes. These findings provide visualization into hyphal uptake and transport of mineral-derived nutrients in a resource-limited environment.

Microscopic weathering mechanisms of subflorescence and crust patterns in the Nankan Grotto, northern Sichuan, China

The mineralogy, geochemical mass balance, sulfur isotope, and micro-structure of the sandstone in the Nankan Grotto were analyzed to explore the weathering mechanisms of the subflorescence and crust patterns. The results revealed that the mineralogical compositions of the rock samples from the subflorescence and crust sites were quartz, feldspar, calcite, and clay minerals. The calcite content was much higher in the crust site than that in the subflorescence site. Based on the microscopic petrographic evidence, the crystallization stress of the thenardite and calcite and the swelling/shrinking stress of the clay minerals led to the detachment of the outer rock layer, after which subflorescence became visible on the newly exposed surface. Solution migration carried Ca2+ from the interior of the rock to the surface, where it combined with CO32− and SO42− to produce gypsum and calcite on the surface during the drying process, resulting in the formation of the crust. Therefore, the mineralogical composition (especially the calcite content) laid the foundation for the distinct development of the subflorescence and crust. In addition, the microstructure and external environment influenced the amount and location of salt crystallization, eventually leading to thenardite crystallizing within the rock in the subflorescence site while the gypsum precipitated on the surface as a crust. The sulfur isotope analysis revealed that the sulfur in the subflorescence and crust sites was most likely derived from detergents and from the combustion of oil and natural gas. Our research revealed the microscopic weathering mechanisms of the subflorescence and crust patterns in the Nankan Grotto, providing insights on salt weathering mechanisms for stone heritage sites around the world.

Fluoride Contamination of Groundwater in a Coastal Region- A Growing Environmental Pollution Threat

<p>The research work's main objective is to correctly examine and find out the proper hydro-geochemistry of groundwater during the dry and wet seasons and hence evaluate it’s quality in India, Tamil Nadu state's Thirukkazhukundram Block. Data from two seasons-the "Pre-monsoon" in August 2016 and the "Post- monsoon" in February 2017-have just been used to do subjective assessments of the chemical composition of the underground water. The results of a thorough geochemical investigation of the subsurface zone are given. Gibbs emphasizes that the majority of samples in both seasons are dominated by evaporation and weathering mechanism sector. The majority of the sample's mixed water type is interpreted hydro-chemically in accordance with Piper's classification. According to the Wilcox diagram, the majority of PRM and POM samples fall into the group of "very good to good and good to permissible." The USSL diagram shows that just 23% of the samples for the C1-S1 type were collected during POM. 23% samples align under C2-S1 during PRM and 57% fall under C2-S1 during POM for. It was noted that 67% and 20% of the samples accounted under C3-S1type respectively, for POM and PRM. The C4-S1type is in PRM only, as of 13% of the samples. The irrigation quality of the groundwater samples showed that they were basically suitable for the very same purpose. Fluoride contamination in groundwater has nowadays become a slowly creeping issue in the study area. Steps need to be taken promptly to avert the resulting human health hazard on account of this pollution, in due course of time. Using ArcGIS 10.0, the groundwater quality chart was produced. Using inverse distance weighting, the regional distribution of groundwater quality measurements was interpolated. The findings of this study highlight the significance of creating techniques for managing aquifer systems.</p>

Spatial and temporal variations of geochemical processes and toxicity of water, sediments, and suspended solids in Sibuti River Estuary, NW Borneo

A comprehensive geochemical study was conducted in the Sibuti River estuary by considering water, suspended solids (SS), and sediment samples from 36 stations during southwest monsoon (SWM) and northeast monsoon (NEM). In this study, the distribution of in situ parameters, major ions, nutrients, trace metals, and isotopes (δD, δ18O) were analyzed in water samples, whereas sediments and SS were studied for trace metals. The distribution revealed that suspended solids were the major carrier of Cd, Zn, and Mn, whereas sediments worked as a major source of Co, Cr, Ba, Se, Cu, and Pb. Na-Cl water type and ion exchange dominated the lower part of the estuary during both seasons. However, the mixed mechanism of Ca–Cl, Ca–Mg–Cl, and higher weathering indicated reverse ion exchange in the intermediate and upper parts of the estuary. Isotopic signatures of δD and δ18O in estuarine water indicate that the precipitation over the Limbang area dominates during SWM, whereas higher evaporation was confirmed during NEM. The factor analysis revealed that seawater influence in the estuary majority controlled the water chemistry irrespective of seasons. Major ions were mainly regulated by the tidal influence during the low flow time of the river (SWM), whereas the mixing mechanism of weathering and seawater controlled the concentrations during NEM. Nutrients such as NO3, SO42−, NH3, and NH4+ mainly originated from the agricultural fields and nitrification along with ammonification were responsible for the recycling of such nutrients. Trace metals except Cd were found to be geogenic in nature and originating mainly from the oxidation of pyrites present in the sandstone and mudstones of the Sibuti Formation. Redox condition was catalyzed by microorganisms near the river mouth, whereas Al-oxyhydroxides and Fe-oxyhydroxides complexes in the intermediate and upper part under oxygenated conditions controlled the absorption of metals. Overall, the estuary was found to be absorptive in nature due to ideal pH conditions and was confirmed by the saturation index (SI) of minerals.

Impact of natural weathering on source rocks: ESI FT-ICR MS evidence from Triassic Chang 7 outcrop profile in Tongchuan City, Southern Ordos Basin (China)

Atmospheric, water, and biological interactions with source rocks exposed at or near the surface due to tectonic uplift can result in both the loss of quantity and variability in the chemical composition of organic matter (OM) in source rocks during natural weathering, especially in extractable organic matter (EOM). Most of the research work on weathering has focused on characterization of the changes of saturated and aromatic hydrocarbon fractions in EOM at molecular level. However, few studies have reported how weathering affects polar compounds in EOM. In this work, a series of source rock samples with varying degrees of weathering were obtained from the Yishicun Profile of Triassic Chang 7 member in Tongchuan City of the Ordos Basin, providing an opportunity to study the weathering mechanisms of EOM in weathered source rocks. Gas chromatography-mass (GC-MS) and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) were used to analyze the chemical composition and variations in the characteristics of EOM. Asphaltenes, resin fractions, and the slightly oxygenated heteroatomic species (O1–O3) identified by positive- and negative-ion ESI showed a clearly pronounced enrichment trend during weathering due to the oxidation of saturated and aromatic hydrocarbons (biodegradation and photo-oxidation). While saturated, aromatic fractions and the highly oxygenated heteroatomic species (O5–O6) showed a declining trend. Additionally, it was also observed that the highly oxygenated heteroatomic species with low carbon number (CN) showed a more significant loss trend than their high CN counterparts during weathering. This may be due to depletion by surface water leaching due to the high water solubility of these compounds. Therefore, both the oxidation and surface water leaching can play important roles in regulating the OM chemical composition of source rocks during natural weathering.