Intense Weathering Research Articles

Fast CO2 uptake by intense weathering of volcanic islands during interglacial stages

Fast CO2 uptake by intense weathering of volcanic islands during interglacial stages

Intense weathering attending the emergence of the SE Amazonian Craton during the Neoarchean

Sedimentological evidence and detrital zircon provenance analysis show that the Amazonian Craton, Brazil, was subjected to large-scale subaerial erosion by c. 2.7 Ga. To assess weathering conditions attending the emergence of the Amazonian Craton, we used the chemical composition of terrigenous sediments deposited in the Carajás Basin, SE Amazonian Craton, between c. 2.7 and 2.6 Ga. Results from 41 samples collected in two drill cores along 150 and 250 m thick intervals show that emerged lands have been affected by strong chemical weathering conditions, similar in intensity to those occurring in the present-day inter-tropical belt. These intense chemical weathering conditions were probably due to the conjunction of warm temperatures (potentially as high as 22 ± 3°C), abundant precipitation (mean annual precipitation estimated at 1540 ± 150 mm) and high atmospheric CO 2 content ( p CO 2 ≥ 10 times the present atmospheric level) that enhanced the chemical alteration of labile minerals. These intense weathering conditions contrast with those inferred in other cratons, which suggests that regionally contrasted climates existed during the Neoarchean.

Crystallization characteristic of sandstone under capillary salt weathering test using different salt property and temperature

This work aimed to explore the influences of different salts and temperatures on the salt weathering of sandstone in the Nankan Grotto. Capillary salt weathering tests were designed under different conditions. The geochemical, physical, and mechanical properties of sandstone were also analysed. After the tests, the electrical conductances (EC), anion concentrations, masses, P-wave velocities, and porosities of specimens increased as the test temperature was changed from 15 °C to 35 °C within individual experimental settings. Under 6% Na2SO4 + 3% NaNO3 condition, only Na2SO4 exerted crystallization pressure, which exceeded the tensile strength of Nankan sandstone (2.20 MPa). Under 3% Na2SO4 + 6% NaNO3 condition, NaNO3 crystallized at 25 °C and 35 °C, and Na2SO4 crystallized at 35 °C. Their crystallization pressures exceeded the tensile strength of Nankan sandstone. Temperature influences the physical properties of a salt solution, which determines the salt weathering intensity. Our research suggests that salt weathering issues in grottoes should be evaluated in different seasons.

Geochemistry and source area weathering of soils around Mount Bamboutos (Cameroon Volcanic Line)

<p class="MsoNormal" style="text-align: justify; text-justify: inter-ideograph; line-height: 120%; layout-grid-mode: char; mso-layout-grid-align: none; punctuation-wrap: simple; margin: 12.0pt 0cm 6.0pt 0cm;"><span lang="EN-US" style="font-size: 10.0pt; mso-bidi-font-size: 11.0pt; line-height: 120%; font-family: 'Times New Roman',serif; mso-fareast-language: ZH-CN;">This study aimed at investigating the weathering of the source area and the geochemistry of the soils around Mount Bamboutos, West Region, Cameroon. In this study, soil samples were collected from a depth of 0–40 cm. The soil samples were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). Significant SiO<sub>2</sub> (63.37–73.05 wt.%) content recalculated to an anhydrous basis and adjusted to 100% (SiO<sub>2</sub> (adj)) indicates the abundance of quartz and kaolinite in soil samples. The enrichment of Al<sub>2</sub>O<sub>3</sub> (9.98–15.12 wt.%) suggests the presence of aluminosilicate minerals such as clay minerals, muscovite, and feldspars. The considerable Fe<sub>2</sub>O<sub>3</sub> (0.01–11.04 wt.%) content relates to the mechanical erosion of ferrallitic soil or to Fe-source rock weathering. The elevated LaN/YbN levels indicate that the soils were derived from heterogeneous source rocks during weathering. The inverse correlation between SiO<sub>2</sub> and Fe<sub>2</sub>O<sub>3</sub>, MgO, TiO<sub>2</sub>, and P<sub>2</sub>O<sub>5</sub> indicates the prevalence of heavy minerals, which are likewise influenced by the relative amount of quartz. The positive Ce anomalies may result from the redox conditions. Weathering indices such as the plagioclase index of alteration (PIA: 77.03%–97.75%), Chemical Index of Weathering (CIX: 58.25%–66.83%), chemical weathering index (CIW: 91.31%–99.13%), and chemical index of alternation (CIA: 50%–70%) all signify moderate to intense weathering in the source area, which occurred in hot, humid climatic conditions. This is evidenced by the removal of labile cations (Ca, Na, and K) in relation to stable residual components (Al and Ti). The relatively high Ce anomalies in the soil samples (Ce/Ce* = 0.01 to 7.44; average 2.39) suggest intense chemical weathering.</span></p>

Sequence stratigraphy and geometry of the carbonate platform in the Longwangmiao Formation (Toyonian), Cambrian, SW China

Carbonate platforms provide important sedimentary archives for paleoceanography and recording paleoenvironments. The aim of this study was to decipher the control of platform evolution and its constraint on the chemostratigraphic correlation in the Lower Cambrian at the eastern part of the Yangtze Platform. With the petrological observation, XRD, as well as C and O isotope analysis, two third-order sequences (SQ1 and SQ2) and six fourthorder sequences (PSQ1, PSQ2, PSQ3, PSQ4, PSQ5, and PSQ6) were recognized in the Longwangmiao Formation. Thirteen lithofacies (Lf-1–Lf-13) and three facies associations (shoreface, upper offshore, and lower offshore) were identified across the proximal to distal range of the platform. The correlation between logged outcrop sections suggested that the carbonate platform evolved from a homoclinal ramp in PSQ1 to a more distally deepened geometry in PSQ2, with this evolution driven by synsedimentary fault activity. From PSQ2 to PSQ3, the geometry evolved from a ramp to a rimmed platform associated with depleted d13C values and an increasing Chemical Index of Alteration (CIA) index. Such a transition of platform geometry may be attributed to the enhanced rate of carbonate production due to intense weathering and nutrient input. The final evolution of the Eastern Yangtze Platform (PSQ4) seemed to have been driven by falling relative sea levels and resulted in the formation of a flat-topped morphology, associated with subaerial exposure and depleted in d13C (LNE2). The two final sequences recognized in outcrops, PSQ5 and PSQ6, were only recognized in the distal reaches of the deposit and were interpreted to be “missed beats” in the sense that the sea level did not transgress the platform top. This study suggests the importance of carbonate production driven by chemical weathering on the control of platform geometry and sequence stratigraphy..

Sedimentary and Early Diagenetic Responses to the Huaiyuan Movement During the Early–Middle Ordovician Transition in the Ordos Basin, North China

The early Paleozoic Huaiyuan Movement created a major unconformity in the Ordos Basin, significantly influencing sedimentation and early diagenesis in both the overlying and underlying strata near the unconformity. However, the origins of the associated dolomite and silica near this unconformity remain poorly understood. This study aims to reveal how this tectonic event controlled the Early–Middle Ordovician sedimentary environments and early diagenetic processes. The petrological and geochemical results indicate a progressive transition from a dolomitic tidal flat to an intra-platform depression, culminating in a mixed tidal flat during the Early-to-Middle Ordovician, driven by the Huaiyuan Movement. Furthermore, this movement, accompanied by intense weathering and erosion, increased the supply of marine dissolved silica (DSi) and terrestrial nutrients. Consequently, extensive tidal-edge biogenic silica accumulated, which later precipitated as siliceous-cemented dolomite during a shallow-burial stage. We propose a conceptual model of the sedimentary–early diagenetic processes in response to the Huaiyuan Movement, providing novel insights into the regional paleoenvironmental evolution across the Early–Middle Ordovician transition in the Ordos Basin.

Lithium Isotope Reveals Tight Links Between Chemical Weathering Intensity and Indian Summer Monsoon in South Asia

Abstract The relationship between catchment silicate weathering and short‐term (<104 yrs) variations in the Indian summer monsoon (ISM) remains a topic of debate. To investigate this link, we present a comprehensive analysis of lithium isotopic composition (δ7Li), neodymium isotopic composition (εNd), and chemical index of alteration (CIA) in the silicate phase of clay fractions from a sediment core retrieved from the western Bay of Bengal. The values of εNd, δ7Li and CIA range from −14.7 to −10.5, −1.7–0.1‰ and 68 to 81, respectively. A source‐corrected δ7Liclay‐source is used as a proxy for chemical weathering intensity. Our weathering records show strong correlations with the ISM on both orbital and millennial timescales. At the orbital scale, increased weathering coincides with periods of global warming and a strengthened ISM. At the millennial scale, variations in our proxies closely track global (Heinrich stadial 1) and regional (8–6 ka) events, highlighting the sensitivity of silicate weathering to climatic variability. The prevailing warm and humid climatic conditions since the last deglaciation have promoted new soil formation, thereby enhancing the chemical weathering intensity captured by the clay fraction. These findings provide compelling evidence for a tight connection between catchment‐scale silicate weathering and short‐term ISM variations, offering valuable insights into the complex interplay between earth's surface processes and regional climate dynamics.

The impact of wide-graded debris flow on sediment-trap dams in the Tibetan Plateau: an experimental study

In the Tibetan Plateau, pronounced topographical relief (steep mountains and deep valleys) coupled with intense weathering processes generates highly fragmented slope surfaces, creating debris-flow source materials with exceptionally heterogeneous grain-size distributions. These conditions frequently produce debris flows that exhibit extraordinary impact forces which cause severe damage to sediment-trap dams. Through 27 sets of flume experiments that systematically varied the particle-size distribution ( d max ), bulk density ( γ ) and flume slope ( θ ), this study investigates the impact mechanisms of wide-graded debris flows on sediment-trap dams. The results demonstrate that debris-flow interactions with sediment-trap dams occur through three distinct phases: (1) impact run-up, (2) rotational backflow and (3) depositional back-silting. Lower bulk-density flows exhibited greater run-up heights and more pronounced phase differentiation. Measured impact forces ( F ) showed an inverse relationship with bulk density ( γ ↑→ F ↓), while displaying positive correlations with both slope gradient ( θ ↑→ F ↑) and maximum particle size ( d max ↑→ F ↑). This occurs because higher- γ flows experience increased internal shear resistance, resulting in a reduction in velocity. Steeper slopes enhance kinematic energy, while larger particles generate more concentrated momentum transfer during impact. Sensitivity analysis revealed that d max exerts dominant control over impact dynamics compared to γ and θ . These findings provide critical insights for sediment-trap dam design in high-altitude debris-flow mitigation systems.

Investigating the role of rock weathering and clay mineralogy in landslide occurrences within the exposed Tertiary Formations in Rangamati area

BackgroundLandslides are a major and recurring hazard in the folded Tertiary sedimentary rock units of Southeastern Bangladesh. The mechanical strength and stability of these rocks are strongly influenced by their mineralogical composition and geochemical alteration, which can affect their susceptibility to weathering and collapse. However, the role of these factors in triggering landslides remains poorly understood.ObjectiveThis research addresses this gap by linking rock weathering intensity and clay mineral composition to landslide mechanisms in the outcropped Tertiary Formations in the Rangamati region.MethodsDetailed geological field work has been conducted on four major exposed Tertiary Formations: Dupi Tila Formation, Tipam Sandstone Formation, Boka Bil Formation, and Bhuban Formation. A comprehensive analysis of 30 landslides is carried out to evaluate the geological influence, with 22 samples (both fresh and weathered) examined using X-ray Diffraction (XRD), X-ray Fluorescence (XRF), and Scanning Electron Microscope (SEM) techniques to determine clay content and the extent of weathering. Shale percentages are estimated from outcrops as well as from wireline logs using empirical equations.ResultsThe Bhuban Formation exhibits the highest shale content, followed by the Boka bil, Dupi Tila, and Tipam Sandstone formations. Illite is identified as the dominant clay type and they are more prevalent in the older formations. Smectite is also present in varying proportions contributing significantly to landslide occurrences through its expansive properties. The Upper Marine Shale in Bokabil Formation contains the most smectite, followed by the Dupi Tila and Bhuban formations. The degree of weathering is evaluated through field observations and oxide analysis, with average Chemical Index of Alteration (CIA) values exceeding 75, indicating intense weathering in all formations, as clearly reflected in the outcrops. Four primary types of landslides: flow, fall, slide, and complex—are identified across all formations in varying proportions. Flow is predominant in formations dominated by single rock type, such as the Bhuban and Tipam Sandstone formations, while slides are more common in formations with alternating layers of sandstone and shale, such as the Boka bil and Dupi Tila formations.ConclusionThe findings highlight that higher shale volume, clay content, and CIA values significantly elevate the landslide susceptibility of geological formations, especially when these factors are compounded by primary triggers like intense rainfall and human-induced slope modifications.

Conulariids of the Paraná Basin: taxonomic revisions and taphonomic insights

ABSTRACT Conulariids are extinct benthic marine cnidarians whose affinity with the phylum Cnidaria is well established. This group was studied in the Paraná basin in the early 20th century and the early 21st century. However, significant advances in the taxonomy of the group over the past decades, combined with the analysis of numerous new specimens previously unaddressed in the literature, have highlighted the need for a taxonomic revision of the group within the basin. This revision aims to clarify the actual diversity and geographic distribution of these organisms. Five species were identified in the basin: Conularia quichua Ulrich (in Steinmann & Doderlein, 1890), Paraconularia africana (Sharpe, 1856), Paraconularia ulrichana (Clarke, 1913), Reticulaconularia caetensis Guedes et al. 2023, and Reticulaconularia baini (Ulrich, 1892). New descriptions of P. ulrichana, R. baini and R. caetensis were provided, with the identification of previously unreported features in their thecae. The first formal description of R. baini in the Paraná Basin was made in the literature. Additionally, a unique feature in the theca of the species Conularia quichua was observed after intense weathering. This distinctive characteristic of Conularia quichua can assist in the taxonomic identification of heavily weathered specimens that have lost their diagnostic morphological features.

Climate change enhanced habitat diversification for the Middle Jurassic Yanliao Biota in East Asia

Abstract The Jurassic Period was characterized by the dominance of dinosaurs and the rise of early mammals, with the Yanliao Biota (ca. 167–157 Ma) in East Asia notable for its exceptional fossil preservation and diverse life forms. However, the drivers of the flourishing of the Yanliao Biota remain unclear. Here, we reconstruct the palaeoclimate and habitat characteristics of the Yanliao Biota using sedimentary facies analysis, organic carbon isotope data, palynological records, source weathering trends, and climate simulations from the Community Earth System Model (CESM 1.2.2). The studied sedimentary successions are well-constrained to the Middle Jurassic based on carbon isotope stratigraphic correlation and published tuff zircon U-Pb ages. Our findings reveal a regional climate shift in the late Bathonian, transitioning from wet to sub-humid conditions, as evidenced by an increase in gymnosperm pollen, a marked decline in coal seams, and reduced weathering intensity. Sedimentological evidence further supports a synchronous facies change from ever-wet fluvial-delta systems to seasonally active alluvial plains. This climate shift aligns with simulation results and coincides temporally with the initial flourishing of the Yanliao Biota. We propose that this shift, associated with lithospheric extension in the Yanliao region, increased landscape heterogeneity and habitat diversity, fostering biological evolution through ecological isolation and allopatric speciation, ultimately driving the diversification of the Yanliao Biota.

Solid Waste As Alternative Amendments For Acidity Correction in Dystrophic Yellow Latosol

Objective: The aim was to evaluate the effect of alternative acidity-correcting sources, derived from agro-industrial residues, applied to a dystrophic Yellow Latosol. Theoretical Framework: Soil acidity represents one of the main agricultural limitations in tropical regions due to intense weathering and base leaching. Limestone is widely used for pH correction; however, residues such as shells and eggshells have potential as sustainable alternatives. Method: Four alternative sources (oyster shell, eggshell, and crab shell) and dolomitic limestone were studied at five application rates (2, 3, 4, 5, and 6 t ha⁻¹). The experiment was conducted in a completely randomized design with a 5 × 4 factorial arrangement and three replications. After a 30-day incubation period, soil pH was analyzed.. Results and Discussion: All corrective sources significantly increased soil pH, showing linear responses with increasing doses. Oyster shell stood out, reaching a pH of 6.7 at the highest dose, due to its high calcium and magnesium carbonate content. Limestone and eggshell showed intermediate effects, while crab shell was less efficient. However, all sources were effective up to the 3 t ha⁻¹ dose. Research Implications: The data highlight the agronomic and sustainable potential of these materials. There is a possibility of reusing residues, such as oyster shells, for soil management as an alternative to limestone, which is typically sourced from mining. Originality/Value: Compared to the conventional method, oyster shell presented superior results for soil pH correction.

Eruption of the Emeishan large igneous province and associated climate change forced intense weathering of Emeishan flood basalts and the formation of overlaying Nb-Zr-Ga-rare earth element and Y polymetallic deposits

Economically important niobium (Nb), zirconium (Zr), gallium (Ga), and rare earth element deposits (Nb-Zr-Ga-REE polymetallic deposits) are widespread in the Emeishan large igneous province (ELIP), Southwest China. These deposits are hosted in the lower part of the Xuanwei Formation, which consists mainly of lacustrine sedimentary rocks overlain directly on ELIP basalts. While the close temporospatial correlation between these deposits and ELIP basalts has been recognized for a long time, their causal link is poorly understood. We analyzed major and trace elements, Hg concentrations, and Hg isotopic compositions of the lower part of the Xuanwei Formation. At three sites, the samples studied show enrichment in Nb (34.2−500 ppm), Zr (229−4220 ppm), Ga (33.6−138 ppm), and REEs and Y (REY; 123−2670 ppm). Multiple lines of evidence based on major and trace element analysis (e.g., Al2O3/TiO2, Eu/Eu*, Nb/Yb, and REE distribution patterns) support that ELIP basalts are dominant source materials for the lower part of the Xuanwei Formation. High Hg concentrations (up to 335 ppb) and slightly negative to near-zero Δ199Hg values (−0.19‰ to 0.11‰) were observed in the samples studied, which suggests that ELIP-derived Hg entered the lower part of the Xuanwei Formation via atmospheric deposition and weathering of ELIP basalts. This study highlights the crucial role of the ELIP eruption in the metallogeny of the Nb-Zr-Ga-REY polymetallic layers in the lower part of the Xuanwei Formation and can benefit our understanding of the genesis of supergene polymetallic deposits in large igneous province regions.

Preliminary stream sediment geochemical exploration for base metals and other elements in terms of source apportionment and contamination status of Manjo and environs, Cameroon

This study seeks to evaluate stream sediments for metal exploration, pollution and ecological implications using single and cumulative pollution indices in the light of recent discoveries. The concentration of metals in stream sediments of Manjo and environs was evaluated using inductively coupled Plasma-mass spectrometry. The sediment samples exhibit high concentrations for Fe, Pb, Hg, Ga, Zn, Cr, Cu, Co, Ni, V, Sn, Ce, La, U and Th when compared with the geochemical threshold values of upper continental crust (UCC), indicating some strong anomalies for potential base metal mineralization and exploration implications. The single and cumulative pollution indices suggest sediment contamination severity and metallic pollution. Potential ecological risk index (RI: 17.682–457.791) and toxic risk index (TRI: 2.243–29.981) indicate high ecological and significant toxicity risks, suggesting biological effects of metals to sediment-dwelling organisms. Sediment quality guidelines suggest high toxicological impacts and response stress of metals (Pb, Cu, Cr and Ni) to the aquatic ecosystem flora and fauna. Natural versus anthropogenic input origins are ressponsible for sediments enrichment in base metals and metallic pollution in the study area. The sediments are sourced from mafic and quartzose sedimentary provenances and mainly deposited in a non-marine environment. In addition, the sediments are mature and display moderate to intense weathering and rich mostly in quartz. According to this research, there should be more focus on monitoring the point sources of metals entering aquatic environment from human-induced activities to abate the anthropogenic inputs. Commitment to research and the implementation of science-based strategies will be crucial in ensuring the ecological sustainability of the water sediments’ environment. More so, note is taken of the natural lithological contributions to the sediment geochemistry having implications for future mineral exploration ventures.

Assessing Silicate Catchment Dynamics of the Oplotnica River (Slovenia) Through Stable Carbon and Nitrogen Isotopes

This study investigated the sources of carbon and nitrogen in a small, silicate-dominated catchment (Oplotnica River, Pohorje, Slovenia) with two creeks, Lukanjski and Javorski, from 2012 to 2014. Additionally, carbon and nitrogen cycling in soil profiles was studied at Javorski Creek. Isotopic analyses of river water, particulates, and sediments provided a more holistic view of the sources of carbon and nitrogen, weathering contributions, and the evasion or sequestration of CO2 in the atmosphere within the catchments. The weathering of rocks, such as granodiorite and quartz diorite, influences water geochemistry. The Oplotnica River and its tributaries were characterized by the ion composition: Na+ > Ca2+ > Mg2+ > K+ and HCO3− > SO42− > Cl− > NO3−. Partial pressure of CO2 concentrations in river and creeks ranged from 1.1 to 13.4 times that of atmospheric pressure, representing a source of CO2 to the atmosphere. The carbon isotope value of dissolved inorganic carbon (δ13CDIC) ranged from − 9.8 to − 1.4‰ in river, while in the creeks, it ranged from − 26.1 to − 4.7‰, reflecting the degradation of organic matter and exchange with the atmosphere. The intensity of bicarbonate weathering for the Oplotnica River at its gauging station was 10.4 mmol/(l⋅km2⋅s), characteristic of silicate watersheds. The isotopic composition of carbon (δ13C) and nitrogen (δ15N) in river sediments reflects values typical of soil and temperate (C3) plants. This study is significant on both local and global levels, as it addresses the contribution of weathering rates and the release of CO2 to the atmosphere from small silicate watersheds.

Mineralogy and precipitation control on saprolite lithium isotopes during intensive weathering of basalt

Abstract The fractionation of lithium (Li) isotopes in saprolites under intense weathering conditions, particularly in relation to precipitation and mineral types, remains a crucial yet complex aspect of geochemical studies. This study reports Li isotope compositions from saprolites and unaltered bedrock within a basalt weathering profile on Hainan Island, China, a region known for its high rainfall and low dust levels. We observe that Li concentrations in weathering products (ranging from 2.36 μg g−1 to 10.65 μg g−1) are generally higher than that in the unaltered bedrock (6.54 μg g−1). Correspondingly, the δ7Li values of these products vary from −9.3 ‰ to +7.4 ‰ typically lower than that in unaltered bedrock (+4.3 ‰). Our findings suggest the impact of rainwater Li on saprolite Li isotopes is not by a straightforward mixture of rainwater and bedrock, but rather modulated through the adsorption and desorption processes involving secondary minerals. Notably, the δ7Li values in saprolites correlate with the proportion of specific secondary minerals; saprolite δ7Li values rise with increased kaolin minerals and drop with more iron and aluminum oxide/hydroxide minerals. Integrating these results with previous studies on suspended sediment leaching, we propose that the higher dissolved δ7Li values in basaltic catchments, compared to granitic ones, are due to a greater abundance of Fe-Al (hydro)oxides in basaltic catchments. This mineralogical control on saprolite Li isotopes also implies a potential explanation for the observed variations in river δ7Li values under different precipitation regimes, influenced by diverse secondary minerals in riverine suspended loads.

Development Characteristics of Natural Fractures in Metamorphic Basement Reservoirs and Their Impacts on Reservoir Performance: A Case Study from the Bozhong Depression, Bohai Sea Area, Eastern China

Archaean metamorphic basement reservoirs, characterized by the development of natural fractures, constitute the primary target for oil and gas exploration in the Bozhong Depression, Bohai Bay Basin, Eastern China. Based on analyses of geophysical image logs, cores, scanning electron microscopy (SEM), and laboratory measurements, tectonic fractures are identified as the dominant type of natural fracture. Their development is primarily controlled by lithology, weathering intensity, and faulting. Fractures preferentially develop in metamorphic rocks with low plastic mineral content and are positively correlated with weathering intensity. Fracture orientations are predominantly parallel or subparallel to fault strikes, while localized stress perturbations induced by faulting significantly increase fracture density. Open fractures, constituting more than 60% of the total reservoir porosity, serve as both primary storage spaces and dominant fluid flow conduits, fundamentally governing reservoir quality. Consequently, spatial heterogeneity in fracture distribution drives distinct vertical zonation within the reservoir. The lithological units are ranked by fracture development potential (in descending order): leptynite, migmatitic granite, gneiss, cataclasite, diorite-porphyrite, and diabase. Diabase represents the lower threshold for effective reservoir formation, whereas overlying lithologies may function as reservoirs under favorable conditions. The large-scale compressional orogeny during the Indosinian period marked the primary phase of tectonic fracture formation. Subsequent uplift and inversion during the Yanshanian period further modified and overlaid the Indosinian structures. These structures are characterized by strong strike-slip strain, resulting in a series of conjugate shear fractures. During the Himalayan period, preexisting fractures were primarily reactivated, significantly influencing fracture effectiveness. The development model of the fracture network system in the metamorphic basement reservoirs of the study area is determined by a coupling mechanism of dominant lithology and multiphase fracturing. The spatial network reservoir system, under the control of multistage structure and weathering, is key to the formation of large-scale effective reservoirs in the metamorphic basement.

Chemical characterization of heavy minerals and stream sediment of Betare-Oya gold district and implications for gold mineralization

Stream sediment geochemical survey was carried out in Boyo, situated in Betare-Oya gold district. The study was aimed to determine the primary source of gold, mineralogy of heavy mineral concentrate, provenance, weathering conditions and tectonic setting. Samples were collected by panning and analyzed using inductively coupled plasma mass spectrometry. Heavy minerals present in concentrates include gold, zircon and magnetite and the grains count of gold is 15–37, the grains vary in size from 0.125–1 mm, suggesting nugget effect. They exhibit sub-angular and angular shapes, indicating they were proximal to the source. Sediments reveal enrichment in Au (8440- > 10000 ppb), Mn (250–350 ppm), Hg (40–560 ppm), Th (186- > 200 ppm), Y (67.5–117 ppm), large ion lithophile elements, rare earth element (REE: 1684.9–2382.6 ppm) and depletion in Fe2O3 (1.08–2.25 wt.%), Nb (0.4–1.6 ppm), Mo (0.03–0.21 ppm), high field strength elements. REE patterns show LREE enrichment (LaN/SmN = 1.06–1.24) relative to HREE (GdN/YbN = 2.20–9.29), negative Eu anomaly (Eu/Eu* = 0.24–0.31) and positive Ce anomaly. Factors 1, 4 and 5 point to the presence of granitic rocks and indicate a lithologic control. Factor 2, 3 and 6 were inferred as the mineralization factors, while the elements Bi, Pb, Sb, Sn and Zn serve as pathfinders for Au. The paragenesis Bi-Pb-Sb-Sn-Zn represents a barren sulphidation event with respect to Au. Sediments were sourced from mafic igneous provenance. Sediments were immature, had undergone intense weathering, were transported a short distance, and were deposited in a passive margin under oxidizing conditions.

Weathering profile of completely weathered rock from the Dullstroom Formation, South Africa

This study investigates the weathering profile of completely weathered rock derived from the Dullstroom Formation in South Africa. The research emphasizes the significance of the soil-rock interface, particularly the transition between completely weathered rock and residual soil, in understanding mechanical, chemical, and hydraulic behaviours. Field sampling and laboratory analyses, including particle size distribution, Atterberg limits, X-ray fluorescence (XRF), X-ray diffraction (XRD), and X-ray Computed Tomography (XRCT), were conducted. XRCT proved invaluable in visualizing pore geometry, density contrasts, and the persistence of relict rock structures in three dimensions. The findings highlight how structural prominence decreases with increasing weathering intensity, influencing compressibility and porosity. The compressibility of the material correlates better with chemical weathering indices than traditional geotechnical parameters like void ratio or dry density. These insights contribute to the geotechnical characterization of weathered rock profiles and propose structural prominence as a novel parameter for evaluating mechanical behaviour across weathering stages.

Geochemical—Mineralogical Constraints on the Provenance of Sediment Supplied From South African River Catchments Draining Into the Southwestern Indian Ocean

Abstract This study utilizes the radiogenic isotopes of neodymium (Nd) and strontium (Sr) measured in river mud —which serves as a proxy for the suspended load—to examine how source‐rock lithology and weathering intensity impact the composition of material delivered to marine sediments along the Southeast African continental margin. Sediments were sampled from 22 river catchments between Durban and Cape Town in South Africa. Two distinct endmembers (i.e., geographical source areas) characterizing the regional river systems were identified. According to endmember modeling, rivers of the Eastern Cape drain soils weathered of the Karoo Supergroup and Drakensberg basalts (87Sr/86Sr of 0.74049 and εNd of −8.53), whereas rivers of the Southern Cape drain the Cape Supergroup, exhibiting more radiogenic 87Sr/86Sr ratios (0.74596) and unradiogenic εNd values (−10.09). River sediments from the Karoo Supergroup are finer‐grained compared to those from the Cape Supergroup. We analyzed clay mineralogy and two grain size fractions (<2 μm; 2–32 μm) from co‐registered samples, and the results suggest that the spatial variability in the 87Sr/86Sr values is due to the lower degree of chemical weathering of silicate rocks and increased illite abundances toward the south, which a simple mixing model can explain. Kaolinite abundance decreased from Northeast to Southwest within South African coastal river catchments. In contrast, illite abundances increased due to diminished chemical weathering in the southern regions driven by the weaker rainfall regime. As demonstrated in this study, combining geochemical tools provides a reliable foundation for provenance studies of offshore marine sediment studies.