Chemical Weathering Research Articles

The Distribution of Major Elements By Geochemical Perspective of Whole-Rock Weathering Profile at Ulie Nickel Laterite Deposit in Central Halmahera Island

Abstract As one of the world’s largest nickel (Ni) producers, Indonesia should become one of the centers determining the direction of global nickel policy and is expected to be an important source of Ni in the future. In general, Ni laterite deposits evolved with three layers from the bottommost bedrock, saprolite layers, and uppermost limonite layers, as a consequence of intense weathering processes. A common trend of Ni enrichments concentrated in the saprolite layers must be understandable for efficient exploration. This study is to investigate the geochemical characteristics of weathering profiles at Ni laterite deposits from Central Halmahera island, and to clarify the Ni enrichment processes by geochemical perspective through qualitative analyses. The complexity of Ni raw ores may challenging for ore processing in the metallurgical processes, as the reason to identify comprehensive through the different series of analytical approaches methods. The bedrock type through mineralogical analyses by XRD 2Ɵ Cu-Kα revealed that bedrock was composed of serpentine predominantly, followed by pyroxene, magnetite, and small numbers of goethite. The dominance presence of serpentine was notified with the sharp peaks (e.g., 7.4 Å) and high intensity may indicate that serpentine is the major mineral in the bedrock with high crystallinity. Furthermore, the presence of goethite may assume that bedrock already weathered in advance. Similarly, microscope observation portrayed that the bedrock predominantly evolved from serpentine, pyroxene, and magnetite, where pyroxene appeared as a single large crystal and magnetite identified with dark freckles and usually surrounding serpentine. The whole-rock geochemical characteristic through XRF leads to analyze the major elements (e.g., SiO2, MgO, Al2O3, Fe2O3, and NiO) and minor elements (TiO2, MnO, CoO, Cr2O3, Sc2O3, and V2O3) in which examined from the bedrock, rocky saprolite, earthy saprolite, transition, lower limonite, and upper limonite layers. The whole rock trends show that there are inverted trends where SiO2 and MgO typically show downward trends and depleted from the bedrock towards the upper limonite layers, compared to Fe2O3 which is enriched towards the top of profile, while Al2O3 which less characterized since in the bedrock but significantly increased particularly in the transition layer. NiO shows fluctuating trends throughout the profile where started less enriched in the bedrock but dramatically enriched further up the rocky saprolite and earthy saprolite layers with NiO 2.4 wt% and reach the peaks of Ni concentration between earthy saprolite and transition layers with NiO 3.5 wt%. Consistently, the gain and losses (τ value) from the bedrock to further up the limonite layers indicate where Fe2O3 and NiO show the positive gain correlation with (τ = 0 - 9) and (τ = 0 - 12), respectively. The major elements from the XRF result, furthermore, be able to indicate the degree of chemical weathering in which visualized by the equation of the ultramafic index alteration (UMIA). The UMIA value of the bedrock was low (3,3) and extremely increased from the saprolite layers (7.0-18.5) to limonite layers (44.4 – 83.7), assumed that the highest degree of chemical weathering was located in the limonite layers and indicate strongly altered. The geochemical trends ultimately can provide the information of the center Ni concentration processes and the highest degree of chemical weathering which is located in the saprolite layers and limonite layers, respectively, as a consequence of the mobilization major and minor elements. Keywords: Nickel; geochemical; mining; earth resources; weathering

Analysis of Bacterial Diversity In Temple Bricks Using Phenetic Numeric Taxonomy Method

Temple bricks-based constructions are known to often face various challenges, including physical, chemical, and biological weathering. Previous studies identified various biological factors contributing to brick weathering including exudate produced by microorganisms, such as bacteria. In addition, bacteria often live synergistically and antagonistically with other species, exhibiting diverse morphological and physiological traits (bacterial diversity). Various methods have been developed to explore bacterial diversity, with phenetic numerical taxonomy being the most popular. Therefore, this study aims to determine bacterial diversity on the surfaces of temple bricks using phenetic numerical taxonomy method. Bacterial isolation was carried out aseptically, followed by labeling and transferring the isolate to the laboratory for further tests. The tests carried out included morphological characterization, biochemical assays, physiological reactions, and potential enzymatic activities. Subsequently, dendrogram was constructed using MVSP (Multi-Variate Statistical Package) software with isolated grouping based on the Unweighted Pair Group Method Averages (UPGMA) algorithm. The similarity between isolates was analyzed using the Simple Matching Coefficient (SSM) similarity value. The dendrogram analysis revealed the presence of 3 clusters namely A (4 isolates), B (1 isolate), and C (2 isolates), with a similarity index of 0,543 to 0,857. Clusters A, B, and C had a similarity index of ≤0.700, indicating the occurrence of distinct species in each cluster. Based on the profile-matching results of key characters, the 7 bacterial isolates were identified as belonging to the genera Bacillus, Corynebacterium, and Mycobacterium.

Sorting and Weathering Trends of Soil at Gale Crater, Mars: Implications for Regional Pedological Processes

AbstractDetailed soil characterization at Gale crater based on in situ observations has revealed compositional trends within soils, while the physical and chemical processes underlying the compositional trends remain to be evaluated. Here we use the grain‐morphometrical and geochemical trends across the Wentworth‐classes of 48 in situ soil targets at Gale crater to evaluate underlying pedological processes and potential chemical weathering signatures. The concentration of olivine minerals within the ∼250 to ∼500 μm size range indicates the prevalence of heavy mineral sorting in a granulometric sense in Gale soils that surpasses the possible effect of the cratering‐induced mixing processes. The extent of olivine sorting in soils varies spatially and is influenced by the targets' aeolian setting. The finest portion of Gale soils (<125 μm) is likely a mixture of allochthonous sediment, globally sourced from atmospheric suspension, and autochthonous counterparts from the weathering of local rocks, while the coarser soils (>125 μm) are mostly sourced from local rocks, with possible inputs from both the unaltered parent rock of the Stimson formation and the bedrocks that have undergone diagenetic alteration. If applicable globally, this would reinforce prior inferences that even dust‐mantled regions are geochemically heterogeneous owing to a substantial fraction of soils derived from underlying lithology. The low chemical weathering intensity and coupling of mobile elements in soils suggest localized, low pH and low water‐to‐rock ratio aqueous weathering conditions under predominantly cold and arid climates, which may occur either during post‐pedogenetic alteration in soils or during the acidic alteration of source rocks.

Erosion-weathering partitioning from paired-mineral and weathering-corrected cosmogenic nuclide approaches

Chemical weathering can bias the interpretation of cosmogenic nuclide measurements for denudation rates, because soluble minerals have shorter regolith residence times than insoluble minerals. Paired mineral measurements in target minerals with different solubility and corrections based on stream-water-derived weathering rates theoretically offer ways to mitigate these biases. Here we test these approaches in the carbonate landscapes of the Tabular Jura and Black Forest in Switzerland and Germany. We measured 26 36Cl and 10Be concentrations for catchment-average denudation rates in calcite and quartz grains, respectively, and derive weathering rates from stream water chemistry along a denudation rate gradient. In catchments with homogeneous lithology, the 10Be-36Cl paired nuclide approach predicts weathering rates that agree with stream-water derived measurements. In catchments with heterogeneous lithology, stream-water derived weathering rates were used to correct 10Be and 36Cl denudation rates. Weathering-corrected denudation rates increase by 100% for 10Be and decrease by 5% for 36Cl compared to uncorrected ones, illustrating that the magnitude of weathering correction depends on the abundance of target minerals.We find denudation rates of 50 – 100 mm/ka on the low relief carbonate-dominated Bözberg plateau and intermediate relief incised carbonate valleys of the Randen, where weathering accounts for about 75% and 50% of the denudation, respectively. Along the Bözberg plateau flanks and the mid-relief Wutach tributaries denudation rates range between 100 – 200mm/ka, with erosion and weathering each contributing about 50%. In the rapidly incising Wutach gorge, denudation rates are 300 – 500 mm/ka with less than 20% of weathering. These findings show that, similarly to crystalline rocks, the fraction of weathering in mixed sedimentary rocks inversely scales with denudation rate. Our study demonstrates that when sampling sites are chosen to ensure that target minerals are sourced from the same area, paired mineral measurements and stream-water weathering corrections can be effectively used to determine denudation and weathering rates.

Robust waterborne superhydrophobic PAI/PTFE/GO@TP anion-release coating with anti-corrosion and anti-scaling performance

In oil well field production, fluids cause mechanical damage and chemical corrosion, increasing the demands on the adaptability and durability of superhydrophobic materials. For this purpose, a superhydrophobic/superoleophilic polyamideimide (PAI)/polytetrafluoroethylene (PTFE)/graphene oxide@tourmaline powder (GO@TP) anion-release coating was successfully developed using a combination of hydrothermal synthesis and spraying technology. The crosslinked network formed by the PAI and PTFE endowed the coating with exceptional mechanical durability and adhesion, maintaining a water contact angle of 151.5 ± 1.8° after enduring 800 wear cycles under 125 kPa of pressure. The homogeneous lamellar micro/-nanostructure provided a stable air barrier that shields the coating surface from contact with corrosive substances, ultimately enhancing its anti-corrosion performance. Following a 30-day soaking period, the coating demonstrated an impressive impedance modulus at low frequency, |Z|0.01 Hz value of 1011 Ω cm2. The slow release of hydroxyl anions from the tourmaline powder electrically neutralized, cations in water to form soluble salts, preventing the nucleation of the scale. The oil layer on the PAI/PTFE/GO@TP coating surface synergistically reduced water scale adhesion, resulting in only 0.23 mg/cm2 of scaling after 7 days. Moreover, the internal migration and surface arrangement of functional groups significantly improved the chemical stability and weather resistance of the coating. This study presented a feasible approach to expand the functional application of superhydrophobic coatings for anti-scaling and anti-corrosion.

Hydrochemical and Isotopic Characterization of Groundwater in the Nakivale Sub-Catchment of the Transboundary Lake Victoria Basin, Uganda

This study characterized groundwater resources for the Nakivale sub-catchment of the transboundary Victoria Basin in Uganda using classical hydrochemical and stable isotopic approaches. Groundwater in the study area is essential for domestic, agricultural, and industrial uses. As a sub-domain of the larger Victoria Basin, it also plays a crucial role in shaping the hydrological characteristics of this vital transboundary basin, both in terms of quality and quantity fronts. This makes its sustainable management and development vital. The predominant groundwater type is Ca-SO4, with other types including Ca-HCO3, Na-Cl, Na-HCO3, and Ca-Mg-SO4-Cl. Hydrochemical facies analysis highlights the importance of rock–water interactions in controlling groundwater chemistry, mainly through incongruent chemical weathering of Ca-rich plagioclase feldspars and the oxidation of sulfide minerals, such as pyrite, which are prevalent in the study area. Groundwater recharge is primarily influenced by the area’s topography, with recharge zones characterized by lineament networks, located in elevated areas. Stable isotope analyses indicate that groundwater mainly originates from local precipitation, while tritium data suggest the presence of both recent and older groundwater (likely over 20 years old). The study’s comprehensive approach and findings contribute significantly to the understanding of groundwater systems in the region, thus providing valuable insights for policymakers and stakeholders involved in water resource management and development strategies.

Iron isotope fractionation during granite weathering under different climates

Climate controls chemical weathering of silicate rocks on the transport of iron (Fe) and its isotopes from continent to the ocean, impacting the global Fe geochemical cycle. However, it's elusive if Fe isotope fractionation during silicate weathering reflects variations in climate factors. This study examines two granite-derived regolith profiles; one in Beijing (BJ), representing a temperate climate, and the other in Guangdong (GD), representing a tropical climate, to investigate their mineralogy, Fe-bearing phases, element concentrations, and Fe isotope compositions. Our results show that, despite climate differences, the two granite weathering profiles have average δ56Febulk regolith values within analytical uncertainty (0.09 ± 0.02 ‰ vs. 0.12 ± 0.04 ‰, 2SD). The δ56Febulk regolith values of temperate and tropical regolith are similar to or slightly higher than those of their respective bedrocks and remain steady along the entire weathering profile. The limited variation of Fe isotope composition in weakly weathered temperate regolith likely reflects the dissolution of primary minerals rather than the formation of secondary minerals. The Rayleigh fractionation calculations also show a Δ56Fepore solution-regolith value of ∼0 ‰ between pore solution and regolith. In contrast, in the tropical profile, despite the abundance of secondary minerals and the differences in δ56Fe values among the extracted Fe-pools exceeding 0.68 ‰, only limited Fe isotope fractionation is observed in the bulk regolith (0.01 ‰ to 0.24 ‰). These variations are likely driven by the formation of Fe oxides, relying on the atomic distribution of Fe in hematite and goethite. The linear regression analysis estimates the apparent Fe isotope fractionation factor between hematite and goethite as 0.46 ± 0.07 ‰ (Δ56Fehematite-goethite, 1SE). These findings indicate that the sensitivity of Fe isotope fractionation in bulk regolith to variations in climate factors is relatively limited. However, combined with results from other weathering profiles in different climate zones, two models suggest that changes in δ56Fe values of easily leachable and silicate-bound Fe pools are likely influenced by climate factors such as temperature and precipitation. This work advances our understanding of the Fe isotope fractionation during silicate weathering and its potential climate connection on Earth's surface.

Micro-Topographic Controls on Rare Earth Element Accumulation and Fractionation in Weathering Profiles: Case Study of Ion-Adsorption Rare Earth Element Deposit in Hedi, Zhejiang Province, China

Ion-adsorption rare earth element (REE) deposits are a major source of REEs and are found mainly in China. The formation of such deposits is affected by a combination of endogenic and exogenic factors. This study investigated the effect of micro-topography on the REE distribution in four weathering profiles at different topographic sites on a knoll in Hedi, Zhejiang Province, China. The weathering profile and REE accumulation are both most developed at mid-slope positions of the knoll. The intensity of chemical weathering decreases in the order of mid-slope > base > summit. As weathering progressed, REE enrichment initially increased but later decreased, with a progressive increase in light/heavy REE fractionation. REE fractionation is more pronounced on the north-facing slope than on the south-facing slope. Weathering degrees and clay mineral characteristics are key factors influencing the varying REE distributions on the knoll. Water leaching and the evolution of clay minerals towards higher maturity reduce REE adsorption capacity. Clay minerals also play a significant role in REE fractionation; the abundance of these minerals and the presence of illite enable the retention of more HREEs with minimal desorption. Taking into account water content, it is inferred that hydrological conditions, modulated by the micro-topography, strongly affect the depth and extent of REE accumulation, as well as fractionation.

Quantitative reconstruction of sedimentary processes, provenance, and binary sources in Horqin Sandy Land, NE China: An integrated approach

As the largest semi-fixed dune field in China, the Horqin Sandy Land (HSL) provides a valuable opportunity to study the surface processes and paleoenvironmental evolution of drylands in the monsoon region. However, limited data and a single qualitative approach hinder our understanding of the sediment erosion and transport process of the HSL. The ability to trace and quantify sediment provenance of the HSL is increasingly needed to properly understand the source-to-sink processes, and to accurately interpret aeolian–fluvial interactions in terms of a comprehensive database and multidisciplinary approach perspective. This study integrates previously existing grain-size, heavy mineral, element geochemistry, Sr-Nd-Hf isotopic, and zircon-geochronological databases with new petrographic, TIMA automation heavy mineral data and statistical analysis. Together, the high degree of recycling of HSL severely limits the provenance identification of element fingerprints, although these elements are largely inherited from the parent rocks and are not affected by chemical weathering. The heavy minerals, Sr-Nd-Hf isotopes, and zircon U-Pb age composition together reveal that the HSL sediments are a binary mixture of the Palaeozoic-Mesozoic igneous rocks in the Great Xing’an Range (GXR) and the Precambrian metamorphic rocks in the Yanshan Mountains. The isotopic end-element mixing models, multidimensional scaling (MDS) diagrams and inverse Monte Carlo models of detrital zircon ages indicate that GXR and Yanshan Mountains account for ∼ 60 % and ∼ 40 % of the source contributions, respectively. Under the strong influence of the northwest to west winds controlled by the Mongolia-Siberian High, detrital material from the GXR is consistently transported to the interior of the dune field and intensively reworked. The Laoha River and the Yangxumu River originating from the Yanshan Mountains provide stable detrital sources for the HSL. In addition, the transverse flow of the Xilamulun River and the West Liao River has provided sufficient space and sediment for the dunes, which is conducive to the full mixing of materials inside the dune field. The sediment in the southeast of HSL shows an obvious Yanshan Mountains source dominance and a grain-size dependence. The coarse fractions (>63 μm) mainly modified from the river channel sand and alluvial plain of the Yangxumu River (∼75.8 %), while the fine fractions (<63 μm) have a strong affinity with the loess deposit of Yanshan Mountains (∼52.4 %). The fluvial-lacustrine deposits during the last glacial maximum served as a temporary transit station, providing a direct dust source for the modern dunes in the HSL region. Aeolian–fluvial interaction controls the geomorphology and landscape evolution of the HSL in the monsoon region; however, it is challenging to derive insights into the landscape evolution from studying surface samples.

Anatomy of a deep Piedmont critical zone: Evaluating hypotheses on regolith depth controls through comparison of ridge and valley boreholes

AbstractControls on the physical and chemical architecture of the subsurface critical zone are somewhat controversial, with multiple hypotheses proposed to account for variations in the depth of weathering between sites, and with landscape position at a site. In the Piedmont region of the Mid‐Atlantic US weathering of crystalline bedrock has been observed to extend tens of meters below the surface and groundwater in a'bow‐tie’ shape – i.e. weathering extends to lower elevations below ridges than below channels. The chemical and physical structure of a hillslope transect in the Maryland Piedmont was explored with a 45 m borehole in the ridge, as well as shallow bedrock boreholes at the toe of the slope and valley. Chemical weathering fronts were characterized using elemental abundances and mineralogical analysis. The ridge borehole did not extend deeper than the chemically and physically weathered rock. Surface and borehole geophysics and density measurements were used to characterize the weathered rock and saprolite. Na and Ca results suggest that plagioclase feldspar weathering is similar between samples collected from 45 m under the ridge and 2.2 m under the valley bottom. A narrow Fe oxidation garnet weathering front co‐insides with the transition from weathered bedrock to saprolite, suggesting that this reaction may generate initial saprolite porosity. Muscovite weathering co‐occurs with complete depletion of plagioclase a few meters above the Fe oxidation front. These nested weathering fronts in the saprolite appear to follow a subdued version of the surface topography. The location and shape of the nested saprolite weathering fronts may be controlled by the feedback between the transport of reactants and solutes and reaction‐generated porosity, consistent with the conceptual “valve” hypothesis. Differing dominant control mechanisms on deep bedrock weathering and saprolite initiating reactions may explain the thickness and structure of the critical zone at our site.

Monitoring soil salinization and waterlogging in the northeastern Nile Delta linked to shallow saline groundwater and irrigation water quality

Soil salinization and waterlogging are critical environmental issues affecting agricultural productivity and cultural heritage preservation, particularly in arid regions. This study investigated soil degradation processes in the archaeologically and agriculturally significant northeastern Nile Delta of Egypt. The objective was to assess the severity of soil degradation and identify key drivers related to water resources and soil characteristics to aid in the development of management strategies. The research employed a multi-faceted approach, including hydrochemical analyses (of groundwater, irrigation water, and soil), water quality indices calculations, statistical analyses, and satellite data. The results revealed high levels of soil salinization in the northern and central areas, with 64% of soil samples classified as strongly and very strongly saline. Soil chemistry indicated salinization sources linked to sodium chloride dominance. Satellite data from Sentinel-2 images and SRTM digital elevation data showed widespread severe waterlogging in the northern lowlands. The Irrigation Water Quality Index (IWQI) values indicated that 87.5% of irrigation water samples posed severe restrictions due to high salinity and sodium hazards, which were mismatched with the low soil permeability observed in 81% of the collected samples exhibiting clay texture and covering most of the study area. Furthermore, shallow groundwater at depths of 0.5–3 m with high salinity was detected, where total dissolved solids exceeded 20,000 mg/L, and Na-Cl water types prevailed, indicating saltwater intrusion. A strong positive correlation (r > 0.83) was found between shallow saline groundwater and soil salinity. The combination of poor irrigation water quality, shallow saline groundwater tables, and low-permeability soils created a synergistic effect that severely compromised soil health and agricultural productivity. It also posed severe risks to the structural integrity of archaeological sites and buried artifacts through accelerated physical and chemical weathering processes. This necessitates an urgent mitigation strategy to combat soil degradation in this critical area.

Land-Use Impacts on Soil Erosion: Geochemical Insights from an Urban Drinking Catchment, South-Central Chile

We investigate the influence of land use and land cover (LU/LC) changes on soil erosion and chemical weathering processes within the Nonguén watershed in the Coastal Cordillera of south-central Chile. The watershed is divided into three sub-basins, each characterized by distinct LU/LC patterns: native forest and exotic plantations. A comprehensive geochemical analysis, including trace elements and lithium (Li) isotopes, was conducted on river water and suspended sediment samples collected from streams within these sub-basins to assess how land management practices, particularly plantation activities, influence the geochemical composition of river systems. Our results show that sub-basins dominated by exotic plantations exhibit significantly higher concentrations of major and trace elements in suspended sediments compared to sub-basins dominated by native forests. The elevated trace element concentrations are primarily attributed to increased physical erosion due to forestry activities such as clear-cutting and soil disturbance, which enhance sediment mobilization. Notably, concentrations of elements such as Fe, Al, and As in plantation-dominated sub-basins are raised to ten times higher than in native-dominated sub-basins. In contrast, sub-basins with native forest cover exhibit lower levels of sediment transport and trace element mobilization, suggesting that native vegetation exerts a stabilizing effect that mitigates soil erosion. Despite the substantial differences in sediment transport and element concentrations, Li isotopic data (δ7Li) show minimal fractionation across the different LU/LC types. This indicates that land use changes impact the chemical weathering processes less compared to physical erosion. The isotopic signatures suggest that physical erosion, rather than chemical weathering, is the dominant process influencing trace element distribution in plantation-dominated areas. The study provides critical insights into how forestry practices, specifically the expansion of exotic plantations, accelerate soil degradation and affect the geochemical composition of river systems. The increased sediment loads, and trace element concentrations observed in plantation-dominated sub-basins, raise concerns about the long-term sustainability of forest management practices, particularly regarding their impacts on water quality in urban catchment areas. These results are of significant relevance for environmental management and policy, as they underscore the need for more investigation and sustainable land use strategies to minimize soil erosion and preserve water resources in regions undergoing rapid LU/LC changes.

CO₂ sequestration and soil improvement in enhanced rock weathering: A review from an experimental perspective

AbstractEnhanced rock weathering (ERW) is an emerging negative emission technology (NET) with significant potential for mitigating climate change and improving soil health through the accelerated chemical weathering of silicate minerals. This study adopts a critical research approach to review existing ERW experiments, focusing on the mechanisms of soil improvement and CO₂ sequestration, as well as the economic costs and environmental risks associated with its large‐scale implementation. The results demonstrate that while ERW effectively enhances soil pH and provides essential nutrients for crops, its CO₂ sequestration capacity is highly dependent on variables such as soil type, rock type, application rate, and particle size. Furthermore, the economic feasibility of ERW is challenged by high costs related to mining, grinding, and transportation, and environmental risks posed by the release of heavy metals like Ni and Cr during the weathering process. Notably, significant discrepancies exist between laboratory experiments and field applications, highlighting the need for extensive in‐situ monitoring and adjustment of ERW practices. This study underscores the importance of optimizing ERW strategies to maximize CO₂ sequestration while minimizing environmental impacts. Future research should focus on long‐term field experiments, understanding secondary mineral formation, and refining the application techniques to enhance the overall efficiency and sustainability of ERW. © 2024 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Hematite U-Pb dating of Snowball Earth meltwater events

The Snowball Earth hypothesis predicts global ice cover; however, previous descriptions of Cryogenian (720-635 Ma) glacial deposits are limited to continental margins and shallow marine basins. The Tavakaiv (Tava) sandstone injectites and ridges in Colorado, USA, preserve a rare terrestrial record of Cryogenian low-latitude glaciation. Injectites, ridges, and chemically weathered crystalline rock display features characteristic of fluidization and pervasive deformation in a subglacial environment due to glacial loading, fluid overpressure, and repeated sand injection during meltwater events. In situ hematite U-Pb geochronology on hematite-quartz veins, which crosscut and are cut by Tava dikes, constrain sand injection at ~690-660 Ma. We attribute early Tava sand injection episodes to basal melting associated with rifting and geothermal heating, and later injections to meltwater generation during ~661 Ma Sturtian deglaciation. A modern analog is provided by the Ross Embayment of Antarctica, where rift-related faults border sediment-filled basins, overpressurized fluids circulate in confined aquifers below ice, and extensive preglacial topography is preserved. Field evidence and geochronology in Colorado further highlight that deep chemical weathering of Proterozoic bedrock and denudation associated with the Great Unconformity predate Cryogenian injection of fluidized sand, consistent with limited glacial erosion.

Late Miocene Uplift and Exhumation of the Lesser Himalaya Recorded by Clumped Isotope Compositions of Detrital Carbonate

AbstractThe Himalaya orogen evolved since the Eocene as the Tethyan‐, Greater‐, Lesser‐ and Sub‐Himalaya thrust sheets were uplifted and exhumed in sequence. Reconstructing the provenance of sediment in Himalayan River systems can inform on stages in the tectonic history of the orogen. Here, we analyze the oxygen, carbon and “clumped” isotope compositions of carbonate minerals from Himalayan bedrock, Ganga River sediments and Bengal Fan turbidite deposits. We demonstrate that river sediments consist of a mixture of Himalayan‐derived and authigenic calcite precipitated in the river system. The relative abundance and clumped isotope apparent temperatures of detrital calcite in turbidite deposits decreased between the Late Miocene and Pliocene, while chemical weathering intensity did not increase during this interval. Considered together, these results reflect the establishment of the Lesser Himalaya as an important carbonate sediment source for Himalayan rivers, driven by the uplift and exhumation of this thrust sheet.

Trace metal evolution of the Late Cretaceous Ocean

The Cenomanian-Turonian boundary (Late Cretaceous) witnessed the last spectacular manifestation of Mesozoic Anoxic Events (OAE 2, ∼94 Ma), marked by a prominent carbon isotope excursion (CIE) and burial of organic-matter-rich sediments under high atmospheric CO2 concentrations. But the Late Cretaceous generally was a time of profound environmental change. OAE 2 was preceded by other CIEs, including the Mid-Cenomanian Event (MCE), and was punctuated by a short re‑oxygenation and cooling event (the Plenus Cold Event, PCE). Extensive previous studies, including many trace metal studies, have focused on OAE 2, but there is still debate concerning the degree of drawdown of oceanic trace metal reservoirs during OAE 2, whether this drawdown is global or local, its causes and consequences for ocean ecology. Here, we present records of eight trace metals, over about 5 Myr of the Late Cretaceous, from the Tarfaya Basin in the proto-North Atlantic. The long records from a core preserving a continuous sedimentary succession allow us to set changes occurring across OAE 2 in the broader context of Late Cretaceous, including the lead up to OAE 2. Moreover, the multiple trace metal dataset allows us to broadly investigate the oceanographic setting in the context of recent studies of multiple trace metals in modern organic-rich sediments aimed at refining the proxies.Trace metal enrichments in these organic-rich sediments are discussed on three different timescales. Firstly, comparison of these Late Cretaceous sediments with modern organic-rich sediments are consistent with deposition in an open ocean upwelling margin in the Late Cretaceous, very like the modern Peru or Namibian Margin, although the deep proto-North Atlantic was probably partially restricted. Secondly, in common with previous studies, metal/TOC ratios often show sharp drops in the early part of OAE 2. Thirdly, however, this sharp drop occurs within a framework of pseudo-cyclical variations in metal/TOC, with a period of about 143 ±19 kyr (1 SD), that is a feature of these long records well before OAE 2, including across the MCE. Different metals respond differently to the perturbation in the early part of OAE 2 itself. Simple mass balance considerations suggest that trace metal drawdown with organic carbon must be at least partially compensated by changes in the rate of chemical weathering on the continents, as previously inferred from Li and Ca isotopes. Moreover, changes in the patterns of variation between different metals, as well as covariation of metal/TOC ratios and Os isotopes, hint at changes in the pattern of chemical weathering, most prominently in the contribution of mafic rocks to the chemical weathering flux.

Lithium isotope evidence for a plumeworld ocean in the aftermath of the Marinoan snowball Earth

The snowball Earth hypothesis predicts that continental chemical weathering diminished substantially during, but rebounded strongly after, the Marinoan ice age some 635 Mya. Defrosting the planet would result in a plume of fresh glacial meltwater with a different chemical composition from underlying hypersaline seawater, generating both vertical and lateral salinity gradients. Here, we test the plumeworld hypothesis using lithium isotope compositions in the Ediacaran Doushantuo cap dolostone that accumulated in the aftermath of the Marinoan snowball Earth along a proximal-distal (nearshore-offshore) transect in South China. Our data show an overall decreasing δ7Li trend with distance from the shoreline, consistent with the variable mixing of a meltwater plume with high δ7Li (due to incongruent silicate weathering on the continent) and hypersaline seawater with low δ7Li (due to synglacial distillation). The evolution of low δ7Li of synglacial seawater, as opposed to the modern oceans with high δ7Li, was likely driven by weak continental chemical weathering coupled with strong reverse weathering on the seafloor underneath silica-rich oceans. The spatial pattern of δ7Li is also consistent with the development and then collapse of the meltwater plume that occurred at the time scale of cap dolostone accumulation. Therefore, the δ7Li data are consistent with the plumeworld hypothesis, considerably reduced chemical weathering on the continent during the Marinoan snowball Earth, and enhanced reverse weathering on the seafloor of Precambrian oceans.

MINERALOGICAL, PETROGRAPHIC, AND LITHOCHEMICAL FEATURES OF THE UPPER JURASSIC–LOWER CRETACEOUS SECTION OF THE NORDVIK PENINSULA (NORTH OF EASTERN SIBERIA)

Some intervals of the Jurassic–Cretaceous strata of the Anabar-Lena sedimentary basin have a certain oil and gas production potential, which can be realized in the synchronous offshore horizons of the adjacent territories of the Arctic shelf. Among the most representative objects in this regard are the outcrops of Upper Jurassic and Lower Cretaceous formations of the Nordvik Peninsula. The main data on the composition and structure of this section were obtained mainly at the beginning of the second half of last century. The results of complex mineralogical, petrographic, and lithochemical studies of the Urdyuk-Khaya and Paksa formations of Cape Urdyuk-Khaya of the Nordvik Peninsula presented in here enabled us to identify 10 boundaries for changing of sedimentation regimes of the paleobasin. It was found that the Urdyuk-Khaya Formation was formed mainly in the conditions of the shelf transition zone (moderate deep water) with low rates of terrigenous material intake, some depletion of oxygen in bottom waters, and a trend towards an increase in the depths of the basin. The basal stratum of the Paksa Formation was formed in offshore conditions with periodically occurring dioxic conditions in bottom waters and extremely low rates of terrigenous material intake. The overlying part of the formation was formed in various parts of offshore transition conditions with a gradual decrease in the depths of the basin, an increase in the oxygen content in the bottom layer of water, and the rate of terrigenous material intake. The main provenance area was igneous rocks of mafic, possibly intermediate composition. There was some influence of felsic igneous rocks, or ancient sedimentary rocks rich in quartz. The parent strata were subjected to moderate and severe chemical weathering, in a warm humid climate. The revealed features of the studied strata are similar to the characteristics of the same-age sediments of the lower reaches of the Anabar River, which determines their high correlation potential and allows us to judge the evolution of the western part of the Anabar-Lena basin.

Phosphatization in the São Pedro and São Paulo Archipelago (SPSPA), Equatorial Atlantic, Brazil: Insights from guano leaching and chemical weathering

This research explores the phosphatization process in the São Pedro and São Paulo Archipelago (SPSPA), located in the Equatorial Atlantic, by analyzing the geochemical interactions between guano coatings and the underlying rocks. The study also examines the geochemical characteristics of the substrates, assessing the behavior of major, minor, trace, and rare earth elements, and determines the degree of weathering degradation of guano crusts, speleothems, peridotites and carbonate sedimentary rocks affected by environmental factors as rain, wind and halmyrolysis. The distribution of chemical elements in water-soluble, adsorbed, acid-extractable/exchangeable, readily acid and reducible, acid oxidizable, and residual phases were investigated. The principal findings of this method show that elevated Na levels are leached in water-soluble fractions, thereby highlighting the occurrence of rapid and active geochemical cycling, which is influenced by seawater. In contrast, in more acidic environments (pH close 4.8 to 2.0), considerable amounts of macroelements like P, Fe, Mg, Al, and Mn are found in association with remaining phases, indicating a slower and more incremental geochemical cycle of mature guano in the input and output systems of these nutrients in the archipelago. The mineralogy, as indicated by the presence of mafic minerals such as olivine, augite, and Cr-spinel, as well as phosphates including fluorapatite, collinsite, and spheniscidite, also supports this finding. The findings underscore the complex interplay between biological activities and geochemical processes, which influence the elemental dynamics in the phosphate-rich rocks of the SPSPA at depth. This study not only enhances our understanding of phosphatization processes but also offers important insights into the sustainable management of marine resources in environmentally sensitive areas. The research underscores the necessity of considering biological and environmental variables when examining geochemical cycles, particularly in regions exhibiting distinctive geological and biological interactions that challenge the prevailing models, such as those identified in the ASPSP.

Geochemical and mineralogical analysis of low-grade metamorphic rocks and their response to shallow landslide occurrence in Central Nepal

BackgroundThe weathering intensity and geochemical properties of a rock contribute to shallow landslide occurrences. This study aims to establish the role of rock weathering in shallow slope instability in low-grade metamorphic rocks of the Lesser Himalaya region of central Nepal. The rocks of the Kuncha Formation, which consist of phyllites, metasandstones, and gritty phyllites are characterized by the formation of shallow landslides. Field characterization of the rock mass within the landslide body, along with petrographic observations, clay mineral analysis, and major bulk geochemistry were adopted to establish a relationship between rock weathering and landslide occurrence.ResultsThe landslides distributed within the Kuncha Formation in the study area are debris-related slides and falls, rock falls, and complex slides. Microscopic petrographic observation of rock from the landslide area revealed well-developed microcracks and intergranular microfractures within the weathered samples, which suggests extensive disintegration and physical alteration. Kinematic analysis of the landslide slope revealed that discontinuities and bedding planes also affected the failure of the slope. The occurrence of neo-formed clay minerals and the conversion of biotite-muscovite to vermiculite, kaolinite, and mixed-layer clays indicate chemical weathering. The CIA ranges between 71 and 80 for the rock samples and between 72 and 84 for the soil samples, signifying moderate to extreme weathering effects. The higher values of PIA and CIW reveal K-feldspar and plagioclase alteration to clay minerals by weathering and alteration. CIA-LOI plots reveal significant relationships corresponding to weathering effects.ConclusionThe transition of rock from a fresh to a moderately weathered state and the development of clay minerals and major discontinuities played a crucial role in shallow landslide occurrence. The weakened physical properties of the rock mass due to weathering coupled with unfavorable joints and fracture conditions have led to instability of the hillslopes in the study area. It was observed that one of the driving factors that drives slopes to erosion and landslides is weathering. The dominant occurrence of landslides in the weathered rock domain within the study area validates the occurrence of landslides and weathering interconnections.