Fine Clay Research Articles

Anthropogenic Hg-Au residues from placer mining compared to natural Au-Hg sources, South Island, New Zealand

ABSTRACT Amalgamation of gold (Au) with mercury (Hg) has been occurring around the world for thousands of years, and global modern uncontrolled use of the process for gold concentration is causing widespread Hg contamination. Despite the environmental significance of HgAu-amalgamation, there has been little characterisation of solid materials that escape the processes and contribute to the Hg contamination. We describe herein the morphological and compositional characteristics of solids sampled through amalgamation processes obtained from small modern active mines in New Zealand under well-confined conditions. Liquid Hg droplets resisted amalgamation because of clay coatings on gold, and finely particulate gold (especially <100 µm) was only superficially coated by HgAu-amalgam with relict liquid Hg droplets. Recovery of purified gold and liquid mercury after amalgamation was done at high temperature (>360°C) by retorting, and at room temperature with acid treatment. Acid treatment yielded variably crystalline bronze-coloured Au with ∼10% Hg, whereas retorting yielded pale yellow porous amorphous (‘sponge’) Au with <1% Hg. Most anthropogenic products are distinguishable from natural Hg-bearing materials, but some micron-scale features of retorted gold are indistinguishable from natural authigenic gold. Materials from all stages of the amalgamation process can be discharged to the environment, contributing to elevated dissolved Hg.

Classification of Shallow Subsurface Heterogeneity, using 2-D Wenner Array and Induced Polarization Methods, in Parts of Southern Ijaw, Bayelsa State, Nigeria

An integrated study, consisting of 2-D Wenner array and Induced Polarization (IP) measured at five profiles, were used to characterize the near surface heterogeneity in Southern Ijaw area of Bayelsa State. Using Abem Terrameter (SAS 1000) for both measurements, five 2-D resistivity profile lines with electrode spacing of 5.00m and electrode spread of 100.00m were employed. Computer software, RES2DINV was adopted for the interpretation of the data while Microsoft Excel software was used for plotting the IP chargeability anomaly against electrode distance. The results showed various resistivity distributions with the lowest value of 1.98Ωm and highest value 638Ωm indicating fine Clay and medium coarse sand respectively. The resistivity varies horizontally and vertically, and such that at the base it is higher than that of the topsoil except in profiles 3 and 5. Resistivity ranges for the profiles are profile 1 (5.96-175Ωm), profile 2 (1.98-495Ωm), profile 3 (46.5-638Ωm), profile 4 (20.3-187Ωm) and profile 5 (10.1-485Ωm). Positive and negative Induced Polarization (IP) chargeability were recorded in all the profiles. However, at Profile 1(NDU New site), negative IP effect was encountered throughout with range values between 0 and -450ms chargeability. This result is associated with the distribution of chargeable zones in the ground and also due to a thin chargeable layer at the surface. Few measurable negative values were also recorded at Profiles 2, 3, 4 and 5. Positive IP values were encountered in greater part of the profiles: profile 2 (0 – 80ms) profile 3 (0-3ms) profile 4 (0- 3ms) and profile 5(0-8ms). The signatures obtained from the IP effects are indicators of Clay sediment of various compositions which corroborate with, to a reasonable extent, the observation from the inverse 2-D resistivity section. The sediments observed in the study area can be classified into clay, clayey sand, fine clayey sand and medium...

Delineating Potential Groundwater Recharge Zones in the Semi‐Arid Eastern Plains of Rajasthan, India

ABSTRACTSurface and subsurface anomalies, hydrological conditions, and dynamic interactions between embedded thematic layers influence groundwater recharge potential (GRP). Conducting a GRP study plays an essential role in promoting the sustainable use of groundwater resources amid a growing population and unplanned urbanization. This study focuses on assessing GRP in the semi‐arid eastern plains of Rajasthan by delineating groundwater potential zones (GPZs) using an integrated approach involving remote sensing and geographical information system (RS‐GIS) technique and analytical hierarchy process (AHP) method. Research findings indicate that the region dominated by fine sand, silt and clay, pediment‐pediplain complex, aeolian sand sheet, higher drainage density, cambisols soil, river channels, floodplains, water bodies, soil hydraulic conductivity and higher surface wetness significantly contributed to good recharge potential in plains of the region. Additionally, lineaments, hills and valleys regulate water movement. A strong negative correlation (–0.78) between decadal‐mean‐depth fluctuation and GPZs frequency classes validates identifying high potential zones in areas with low mean‐depth fluctuation. Sensitivity analysis highlights geology and geomorphology as crucial factors. However, the study addresses potential limitations and challenges, such as data scaling and spatial resolution issues due to nonlinear pixel fusion algorithms and AHP method‐related limitations in model interpretation. The current study presents a convenient approach for improving groundwater resource management in hydrogeologically sensitive and drought‐prone regions.

Micromorphological Cryogenic Features in Meadow Podbels of Middle-Amur Lowland

Meadow podbels (dark-humus gleyic and gleypodbels in the Classification of soils of Russia) are subject to deep and prolonged freezing in the western part of their area. It is manifested in cryogenic deformations of genetic horizons as well as in thin sections. Micromorphological features of soils on permafrost are well known. and the purpose of this research was to reveal them in three profiles of meadow podbels as related to soil cryological and hydrological regimes. Unlike northern cryogenic soils. the meadow podbels have dark-humus horizons with weak cryogenic manifestations; in eluvial horizons. there are frost-created platy microstructures and numerous iron-organic nodules of any size. Specific microstructures are common in textural BT horizons: these are rounded or ellipsoidal peds with iron-organic nodules in their nuclei. and ooids: rounded aggregates with iron impregnation/segregations in their centres and circular striated b-fabric of the micromass on aggregate peripheries. Typical gley mirofeatures in the lowermost clayey horizons are well expressed. along with illuviation clay coatings. part of them being deformed. The skeleton grains and micromass re-arrangement. as well as concentric orientation of skeleton grains in the groundmass. are weak as compared to cryogenic soils with permafrost.

Characterization of sediment organic matter in the outer Yangtze River Estuary using stable isotopes, optical techniques, and FT-ICR-MS: Implications for the carbon burial mechanism

The burial of sediment organic matter (SOM) in the estuary and shelf plays an important role in the global carbon cycle. However, it is challenging to determine the source, composition, and burial of SOM in the coastal sea, especially at the molecular level. This was explored in the coastal area outside the largest Yangtze River of China with multiple techniques including elemental and stable isotopic analysis, absorption spectroscopy, fluorescence excitation-emission matrices coupled with parallel factor analysis (EEMs-PARAFAC), and ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). The end-member mixing analysis based on δ13C and δ15N showed a dominance of marine contribution (up to 70%) at most stations while the terrestrial contribution increased to >55% nearshore in summer at a high fluvial sediment flux. This was consistent with the offshore decreasing humic-like C1 and C2, humification index (HIX), %lignin-like compounds, and %CHO but increasing tryptophan-like C3, biological index (BIX), %protein-like compounds, and %CHOS from EEMs-PARAFAC and FT-ICR-MS analysis. The %clay correlated positively with SOM content, HIX, %lignin-like compounds, O/C, and modified aromaticity index (AImod) but correlated negatively with %C3, H/C, and the relative abundance of labile formulas (MLBL), while %silt showed contrasting correlations. These results indicated the fine clay sediments adsorbed more humified, aromatic, oxygenated, and terrestrial compounds that were probably more resistant to biodegradation and thus had a higher burial efficiency than those on the silty sediments. Principal component analysis based on SOM indices further revealed different characteristics of SOM in the nearshore, northern offshore, and southern offshore regions, which were probably dependent on the delivery by local current systems. Overall, these findings contributed to unraveling the source and molecular composition of SOM associated with different grain size sediments and local current delivery, which are fundamental for understanding the factors underlying carbon burial in the complex coastal environment.

Advanced multi-scale characterization of loess microstructure: Integrating μXCT and FIB-SEM for detailed fabric analysis and geotechnical implications

Loess, a Quaternary wind-blown deposit, is a problem soil that gives rise to frequent geohazards such as landslides and water-induced subsidence. The behaviour of loess is controlled by its microstructure, consisting of silt-sized skeleton particles and complex bonding structures formed by clay-sized particles. Achieving a deep understanding and precise modelling of loess behaviour necessitates comprehensive knowledge of the realistic 3D microstructure. In this paper, a correlative investigation of the 3D loess microstructure is performed using X-ray micro-computed tomography (μXCT) and focused ion beam scanning electron microscope (FIB-SEM). Details of clay structures in loess, such as clay coatings, clay bridges and clay buttresses, are visualized and characterized in 3D based on FIB-SEM images with a voxel size of 10 × 10 × 10 nm3. The clay structures exhibit a diverse degree of complexity and their impact on the mechanical properties of loess is highlighted. Statistical analysis of the skeleton particles, including size, shape and orientation, are derived from μXCT images with a voxel size of 0.7 × 0.7 × 0.7 μm3. The findings provide insights into the collapse mechanism and particle-scale modelling of loess. The combination of μXCT and FIB-SEM proves to be a powerful approach for characterizing the intricate micro-structures of loess, as well as other geomaterials.

Diagenesis and reservoir quality evolution of estuarine sandstones: Insights from the Cenomanian-Turonian Yolde Formation, northern Benue Trough, NE Nigeria

Estuarine sandstones often exhibit complex diagenetic pathways due to the interaction of fluvial and shallow marine processes, resulting in significant reservoir heterogeneities. The Yolde Formation is an important petroleum reservoir in the Northern Benue Trough, NE Nigeria. However, diagenetic and reservoir quality evolution of the formation are still poorly understood. This study utilizes thin-section petrography, XRD, SEM, and fluid inclusion microthermometry to analyse the composition, diagenesis, and reservoir quality of the sandstones. Results show that the sandstones are mainly arkose and subarkose in composition; they are generally well-sorted and vary in grain size from very fine-to coarse-grained. Three diagenetic stages are identified: early, middle, and late. The early stage includes feldspar dissolution, formation of kaolinite, development of clay coating, and mechanical compaction. The middle stage comprises the formation of authigenic chlorite and Fe-oxide cements. The late-stage diagenesis involves illitization of kaolinite, formation of dickite, albitization of K-feldspar, and precipitation of quartz overgrowths. The diagenetic evolution of the sandstones was strongly controlled by their compositional makeup. The feldspathic nature of the sandstones resulted in the formation of kaolinite, illite, and quartz overgrowths, through feldspar dissolution and silica supply. The inner and middle estuarine facies have inhibited the development of quartz overgrowths due to well-developed clay coatings, whereas the outer estuarine facies were well-cemented by quartz overgrowths due to lack of clay coatings. Illitic clay coatings were found to be effective in preventing quartz cementation. Fluid inclusion analysis reveals that the formation temperatures of the quartz overgrowths range from 98 °C to 135.5 °C, corresponding to burial depths ranging between 2.3 and 3.5 km. These findings would provide useful insights that would reduce the risks of exploration of the sandstones and also supplies potential input data for forward diagenetic modelling of their subsurface equivalents in similar depositional settings elsewhere.

Formation and degradation of textural pedofeatures in soils of ancient tropical coastal plains in southeastern Brazil

Textural features in soils are defined as having a distinct granulometric composition compared to the surrounding groundmass. Among these, clay coatings are found in various pedo-environments, covering a range of climatic conditions, from wetter regions to semiarid areas. This study aimed to understand how textural features in ancient coastal plain soils can reveal mechanisms of their pedogenetic evolution and how this relates to environmental transformations. Three soil profiles were studied at different points in a toposequence, representing the upper, middle, and lower thirds. The study area is located in the municipality of Seropédica, in the state of Rio de Janeiro, southeastern Brazil. Morphological, physical, chemical, mineralogical, and micromorphological analyses were conducted on the selected profiles. Acrisols, formed in free-draining conditions, were later transformed into Planosols due to base level oscillation and the percolation of brackish solutions through the soils. The pedogenetic model proposed in this study involves the following stages: i) Clay formation by in situ mineral weathering, mainly of phyllosilicates, with pseudomorphization of the structures. ii) Destruction of the pseudomorphized structures by pedoplasmation with proximal migration of clay and genesis of textural features of coating and filling. iii) Partial and episodic saturation of the base of the profile with solutions enriched in sodium of a fluvial-marine nature. iv) Dispersion of the clays, leading to the destruction of the textural features and soil micromass, accompanied by relative sand enrichment and E horizon formation. v) Local lowering of the surface and smoothing of the base of the slopes. This transformation model is unprecedented for the southeastern region of Brazil, increasing the evolutionary complexity of soil genesis in areas of ancient fluvial-marine plains.

Archaeological analogues for the lifetime prediction of the canister for spent nuclear fuel in the deep geological repository: Part I. Composition of pore water and corrosion products

AbstractThis work focuses on archaeological analogues as a way of obtaining long‐term data for assessing the lifetime of a spent nuclear fuel canister. An analysis of the environment around the excavated artefacts is presented, followed by geochemical modelling of the likely corrosion products and subsequent comparison with real phases in the corrosion layer estimated by X‐ray diffraction. A total of 16 archaeological sites with fine clay soils and the potential for long‐term flooding were evaluated. Although the soil pore solution contained high levels of silicates, no such phases with iron in the corrosion products were confirmed. Carbonate corrosion products, typical of bentonite environments, were also not observed. Although oxygen access is very limited in the environments of all sites, even low concentrations shifted the equilibrium of corrosion products formed in favour of (hydroxy)oxides.

New vertebrates from the Ituzaingó Formation (Late Miocene of Entre Ríos Province, Argentina), including first records of Leptodactylus (Amphibia, Anura) and Chelonoidis (Testudines, Cryptodira)

ABSTRACT The Late Miocene vertebrate fauna from the Entre Ríos Province, Argentina, comes from two units: the marine Paraná Formation and the Lower Member of Ituzaingó Formation (LMIF). This latter includes a lower conglomerate set, with fine quartz gravel, and clay and chalcedony clasts, and fossil remains, traditionally known as ‘Mesopotamiense’ or ‘Conglomerado osífero’. We present new fossil vertebrate remains from the LMIF at the Puerto Víboras locality (Hernandarias, Entre Ríos Province) including Leptodactylus sp. (Amphibia, Anura), Crocodylia indet. Caimaninae indet. and Paranasuchus gasparinae (Alligatoridae), Chelidae indet. (Testudines, Pleurodira), Chelonoidis sp. (Testudines, Cryptodira), Plohophorus paranensis (Cingulata, Glyptodontidae), and Macraucheniinae indet. (Macraucheniidae, Litopterna). The record of Leptodactylus sp. represents the oldest record of the genus and the first amphibian record for the Neogene of the Entre Ríos Province. The material described herein and assigned to Chelonoidis sp. allows to confirm for the first time the presence of a testudinid in the Late Miocene of the Entre Ríos Province.

Lithofacies assemblage and effects on diagenesis in lacustrine tight sandstone reservoirs: Samples from Upper Triassic Yanchang Formation, Ordos Basin, China

Lacustrine basins are rich in unconventional oil and gas resources and the heterogeneity of matrix reservoir quality seriously affects its development. Previous studies have recognized that diagenesis is the key factor affecting the heterogeneity of matrix reservoir quality, but diagenesis controlled by lithofacies assemblages is poorly studied. In this study, tight sandstones in the Triassic (Ladinian-Carnian) Chang 7 Member of Ordos Basin were taken as examples. Lithofacies, lithofacies assemblages, diagenesis evolution and distribution were investigated by casting thin section analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), fluid inclusion and carbon-oxygen isotope. The results indicate that eight lithofacies assemblages in Chang 7 exhibit variations in lithofacies, sand-mud ratio and grain size rhythm, controlling the distribution and intensity of diagenesis. Variations in average proportion of lithofacies assemblages are linked to lake level cycles. Compared to cementation, the mechanical compaction has a higher adverse effect on primary porosity of tight sandstones in Chang 7. Siltstone lithofacies show stronger compaction and cementation (mainly clay cementation), whereas fine sandstone lithofacies exhibit stronger dissolution, especially FSpc (fine sandstone with parallel or cross-bedding). Modest proportions of illite (<4%) and chlorite (<1.5%) in fine sandstones tend to form clay coatings, resisting compaction and preserving more porosity. Conversely, abundant pore-filling illite (>4%) and chlorite (>1.5%) result in a noticeable decline in porosity. Particle size and sorting affect reservoir quality by controlling compaction strength. The origin of carbonate cement in sandstones is closely related to mud-rich lithofacies within lithofacies assemblages. Carbonate cementation preferentially occurs in fine sandstones within 0.4 m from the sand-mud interface and the thickness of adjacent mud-rich lithofacies is greater than 0.1 m. Interfaces between fine sandstones serve as fluid migration pathways and bidirectional erosion, facilitated by high porosity and feldspar content. In contrast, the clay-rich matrix in siltstones acts as a barrier hindering fluid migration, creating unidirectional erosion in fine sandstones near the interfaces between siltstones and fine sandstones. Ultimately, five evolution processes linking diagenesis with lithofacies assemblages are summarized, highlighting the differential reservoir quality. This study contributes to understanding the mechanism behind diagenetic variations in tight sandstones and the reservoir evaluation. Consequently, it offers geological reference for the development of unconventional oil and gas resources in comparable lacustrine basins.

CARACTERIZAÇÃO QUÍMICA E MINERALÓGICA DOS SUSPENSATOS DOS RIOS PURUS E JURUÁ NO ESTADO DO ACRE

The state of Acre, located in the southwest of the Brazilian Amazon, is drained by two large river basins, the Purus and Juruá rivers, which have their sources on the sub-Andean slopes of Peru and cross the state in a path almost parallel to each other and a southwest-northeast direction. They are meandering rivers, with a large amount of suspended sediment (suspended solids or load materials), which gives them their white or muddy color, in addition to transporting a lot of silty-sandy sediments by traction, forming significant beach bodies (pointed bars). The geological terrains drained by these rivers are made up of rocks from the Solimões Formation and sediments from the Alluvial Terraces. The present work sought to characterize the granulometry, mineralogy and chemical composition of suspensions from rivers in the State of Acre. These were subjected to granulometric analysis, mineral identification using X-ray diffraction (XRD) and scanning electron microscopy (SEM/SED) and total chemical analysis of trace elements. The highest concentration of suspended solids was found in the central part of the State both during the flood and dry periods, while the lowest are in the Moa and Paraná dos Mouras rivers. They are predominantly made up of silt with little fine sand and clay, averaging 12 microns. Mineralogically, they are made up of quartz, mica, smectite, illite, kaolinite, as well as albite and K-feldspar. These are sediments rich in SiO2 (55.69% +/- 3.89%), Al2O3 (18.68% +/- 1.76%), Fe2O3 (5.89% +/- 0.41%), with significant K2O values ​​(1, 93% +/- 0.07%), MgO (1.17% +/- 0.22%), Na2O (0.41% +/- 0.06%), in addition to TiO2 (0.85% +/- 0.10%). The values ​​of P2O5 (0.10% +/- 0.014%), CaO (0.14% +/- 0.17%) and MnO (0.10% +/- 0.021%) are at crustal levels. In terms of trace elements Rb, Sr, Cs, Ba, Th, U, Zr, Hf, Y, Nb, Cr, Co, Ni, Cu, Sc and V, are the elements that presented the highest concentrations. The average concentrations of these elements in the suspended materials when compared with beach sediments show enrichment in Al2O3, Fe2O3, MnO, MgO, Rb, Cs, Sc, and V. On the other hand, with the upper earth’s crust they show enrichment in Cs, Y, Cr, Co, Ni, Cu, Sc and V and with post-Archaean Australian shales only slightly enriched in Y. The presence of clay minerals (smectite, illite and kaolinite) and feldspars (albite and K-feldspars) are responsible for the high concentrations not only Al2O3 and Fe2O3, but also K2O, MgO and Na2O. The mineralogical and chemical composition shown by these suspensions, in addition to their granulometry, contribute to fertilizing both the floodplains (“varzeas”) as well as the beaches exposed by the rivers during the dry period, which are intensely cultivated with corn (Zea-mays) and beans (Vigna unguiculata (L) Walp) by riverside dwellers.

OS MINERAIS PESADOS E IDADES DE ZIRCÕES DOS SEDIMENTOS DE PRAIAS (BARRAS EM PONTAL) DOS RIOS PURUS E ACRE NO ESTADO DO ACRE (BRASIL)

The Purus River and its largest tributary, the Acre River, originate in Peru and constitute the main drainage system for the northeast and southeast portions of the State of Acre. These rivers and their smaller tributaries develop their beds over the Solimões Formation (Miocene to Pliocene-Late) and form a broad dendritic drainage pattern. During the rainy season, due to the high rainfall in the region and the low resistance of the drained rocks, these rivers mobilize a large volume of sediment, which is deposited mainly during the dry season, forming beaches (pointed bars), predominantly composed of fine sand, silt and clay. To investigate the probable primary sources of these sediments and their possible geographic locations, a mineralogical and morphological study of their heavy minerals and a geochronological analysis of their detrital zircons were used. Heavy minerals were extracted from fractions between 0.062-0.125 and 0.125-0.250. The transparent ones were investigated using a petrographic microscope and the opaque non-magnetic ones, together with the lithic fragments using a Scanning Electron Microscope (SEM/SED). In descending order, the main transparent heavy minerals of the Purus River are epidote (19%), kyanite (17%), zircon (14.5%), andalusite (8%), tourmaline (7.4%) and sillimanite (5 .5%), in addition to these, in amounts less than 5%, staurolite, garnet, apatite, amphibole, chlorite, muscovite, biotite, anatase, pyroxene and cassiterite occur. With similar content and different proportions, the assemblage of heavy minerals from the Acre River consists of andalusite (22.5%), kyanite (22.5%), zircon (12%), epidote (8%), sillimanite (5%) and tourmaline (5%), its accessories are: garnet muscovite, chlorite, apatite, amphibole, biotite, staurolite, titanite, anatase, serpentine and rutile. The non-magnetic opaque minerals of both rivers were shown to be predominantly formed by ilmenite, and the ages obtained in the zircons varied from 180 Ma to 3000 Ma, with great frequency in the intervals between 200-400 Ma and 900-1200 Ma.

Comprehensive analysis of fine particle migration and swelling: Impacts of salinity, pH, and temperature

About 70% of the world's oil production comes from reservoirs with loose reservoir rock. The looseness of the reservoir rock causes fine particles to move during production. Additionally, there are different types of clays in the reservoir, which have the possibility of swelling in addition to migration. Migration and swelling of fine particles result in increased permeability reduction and formation damage. Identifying the migration and swelling mechanisms of fine particles can prevent the migration and swelling of fine particles in the porous media. As a result, it prevented production reduction and excess production costs and increased the EOR process's efficiency. Salinity, pH, and water temperature changes can significantly affect fine migration and swelling. This research investigates a laboratory's parameters affecting injection water, such as salinity, pH, and temperature. Due to the precision in analyzing the results and a better understanding of the mechanisms, synthetic cores containing fine particles and clays were used. The permeability, turbidity, electron microscope images, and pH data showed that the change in salinity, pH, and temperature disturbs the balance between the rock's surface and fine particles. With the decrease of salinity below the critical concentration of salt, permeability reduction and turbidity were observed. In this case, the dominant mechanism was the migration of fine and clay particles. When the pH of the injection fluid increased, the permeability reduction increased, the turbidity decreased, and the predominant mechanism was the swelling of fine particles. An increase in temperature also caused an increase in permeability reduction and turbidity. The mechanisms of migration and swelling were supposed to be simultaneous with the temperature rise.

Geochemical insights of arsenic mobilization into the aquifers of Punjab, Pakistan

It is well known that groundwater arsenic (As) contamination affects million(s) of people throughout the Indus flood plain, Pakistan. In this study, groundwater (n = 96) and drilled borehole samples (n = 87 sediments of 12 boreholes) were collected to investigate geochemical proxy-indicators for As release into groundwater across floodplains of the Indus Basin. The mean dissolved (μg/L) and sedimentary As concentrations (mg/kg) showed significant association in all studied areas viz.; lower reaches of Indus flood plain area (71 and 12.7), upper flood plain areas (33.7 and 7.2), and Thal desert areas (5.3 and 4.7) and are indicative of Basin-scale geogenic As contamination. As contamination in aquifer sediments is dependent on various geochemical factors including particle size (3–4-fold higher As levels in fine clay particles than in fine-coarse sand), sediment types (3-fold higher As in Holocene sediments of floodplain areas vs Pleistocene/Quaternary sediments in the Thal desert) with varying proportion of Al-Fe-Mn oxides/hydroxides. The total organic carbon (TOC) of cored aquifer sediments yielded low TOC content (mean = 0.13 %), which indicates that organic carbon is not a major driver (with a few exceptions) of As mobilization in the Indus Basin. Alkaline pH, high dissolved sulfate and other water quality parameters indicate pH-induced As leaching and the dominance of oxidizing conditions in the aquifers of upper flood plain areas of Punjab, Pakistan while at the lower reaches of the Indus flood plain and alluvial pockets along the rivers with elevated flood-driven dissolved organic carbon (exhibiting high dissolved Mn and Fe and a wide range of redox conditions). Furthermore, we also identified that paired dissolved AsMn values (instead of AsFe) may serve as a geochemical marker of a range of redox conditions throughout Indus flood plains.

MINERALOGICAL AND PHYSICO-CHEMICAL CHARACTERISATION OF CLAY MATERIALS FROM KWILU-NGONGO (Kongo-Central, DR Congo)

Clay materials collected from two sites (Camp-Beton and Kwilu-Bricks) in the Kwilu-Ngongo region located between 5°30’0’’S and 14°40’60’’E, in the Kongo Central province (DRC), Ten samples selected and subjected to mineralogical, physico-chemical and geotechnical studies with a view to their characterization. Mineralogical analysis by X-ray diffraction made it possible to identify the following minerals: quartz, feldpasth, iron oxide and simple clay minerals including kaolinite. In addition to this kaolinite we also find illite, chlorite and vermiculite. The partical size analysis led to the differentiation of three fractions including: the fine clay fraction, the silty fraction and the sandy fraction. As for the Atterberg Limits, the plasticity Limit ranges from 17 to 30% while the average plasticity index is 13 %. Chemical analyzes made it possible to identify the major oxides elements below: SiO2, Al2O3, TiO2, Fe2O3, K2O, Na2O and MgO.

Impact of sediment provenance and depositional setting on chlorite content in Cretaceous turbiditic sandstones, Norway

AbstractChlorite minerals, mainly in the form of clay coats, play a critical role in determining the reservoir quality of siliciclastic rocks. They can positively influence reservoir quality by preserving porosity during deep burial, but they can also play a negative role by reducing permeability through pore filling. The main aim of this research is to determine the optimal conditions for chlorite growth in sedimentary basins. This study investigates the Lower Cretaceous turbidite sandstone of the Agat Formation in the North Sea. We used a source‐to‐sink approach to investigate the impact of sediment source composition, chemical weathering and depositional environment on chlorite formation. Understanding the interplay between these processes can help refine exploration and exploitation strategies, optimise hydrocarbon recovery, and reduce exploration risks. Representative samples from two hydrocarbon fields (the Duva and Agat fields) were investigated using petrography, geochemistry, heavy mineral identification and quantification, and U–Pb geochronology of detrital zircons. Our results show a strong heterogeneity in the sediment provenance between the two turbidite systems. In the Duva field, the sandstone is derived from a mixture of mafic and felsic sources, producing Fe‐rich sediments. Intense chemical weathering generates fine fraction materials rich in kaolinite, vermiculite, and hydroxy‐interlayered clays, which are transported into shallow marine settings. Subsequent interaction with seawater results in the formation of glauconitic materials, Fe‐illite, and phosphatic concretions. These Fe‐rich materials are remobilised into deep marine settings, providing precursors for the development of authigenic Fe‐clays such as berthierine and chlorite. Conversely, in the Agat field, the sandstone is predominantly sourced from felsic rocks that underwent low chemical weathering, producing sediment rich in quartz and feldspar with a low amount of clays. With few Fe‐rich materials transported into the basin, the development of chlorite in the Agat field was less pervasive. Basin configuration and depositional environment exerted additional control on chlorite distribution. In the confined turbidite system (e.g. Duva field), chlorite is typically found as coating, whereas in less confined turbidite systems (e.g. Agat field) chlorite shows complex distribution related to depositional environment and dewatering processes. Our findings demonstrate the importance of considering the entire sediment routing system, from source to sink, when predicting chlorite occurrence and its impact on reservoir quality in deep marine settings. This integrated approach can guide exploration and development efforts in deepwater clastic reservoirs.

Evolution of reservoir quality related to clay coating overgrowths in tight sandstone in the fluvial facies of the southeastern Sichuan Basin

As a result of silicate overgrowth, clay coatings influence the evolution of reservoir quality during diagenesis. Most studies indicate coatings can resist compaction and inhibit cementation, thus preserving primary porosity and serving as one of the primary controlling factors for improving reservoir quality. However, some research suggests clay coatings have insufficient hardness to resist compaction and could potentially block pore throats and prevent fluid flow within the sandstone, negatively affects reservoir quality. Therefore, to address whether coatings are positive to reservoir evolution, this study employs polarized light microscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and porosity-permeability testing to investigate the characteristics of clay coatings within the fluvial facies sandstone of the Xiashaximiao Formation. The microscopy reveals abundant clay coatings were found, mainly in lithic-arenite with 30%–45% feldspar and rock fragments. The underlying Lianggaoshan Formation locally exhibits interbedded siltstones with volcanic rock fragments, providing material sources for the clay coatings formation. SEM and EDX analyses indicate two predominant forms of clay coatings: single-layer (primarily chlorite) and double-layer (inner smectite/illite, outer ferroan chlorite). Single-layer overgrowths primarily consist of thin layers of chlorite (5–15 μm), whereas double-layer overgrowths consist of a thin inner zone (1–5 μm) covering the grain surface and a thicker outer zone (10–20 μm) covering the inner zone, demonstrating characteristics indicative of multi-stage growth. Porosity-permeability testing results the sandstone samples have <10% porosity, which are typically tight sandstones, but those with clay coatings have higher porosity. Nevertheless, sandstones with double-layer overgrowths exhibit lower permeability relative to those with single-layer overgrowths or without overgrowths. Therefore, based on the integration of morphological and physical properties of silicate overgrowths, it is proposed the efficiency of clay coatings in resisting compaction, inhibiting cementation, and preserving primary porosity increases with the number of growth stages, layers, and thickness, which in turn depends on the abundance of source materials. Single-layer coatings facilitate fluid migration, whereas thicker double-layer overgrowths are prone to occluding narrow pore throats, thereby restricting fluid mobility. Consequently, this study establishes a model for the multi-stage evolution of clay coatings overgrowths, elucidating the varying fluid migration behaviors across different stages and providing a more detailed investigation of the implication of clay coatings on reservoir quality, thus offering new theoretical insights into diagenesis and the evolution of tight sandstone reservoirs.

Spatio-temporal characterisation of local scour around a circular bridge pier in cohesive soil with different clay/silt ratio

This paper presents new data on scour around a vertical pier in cohesive soils. It specifically focuses on the temporal evolution of local scour hole around the pier with increasing the clay/silt ratio content. Series of flume tests were performed using soil mixtures made with 85% fine sand and 15% fines. The fines fraction used in the soil mixtures includes silt, kaolinite clay, and various combinations of both with different proportions. The water velocity during the tests was kept constant and slightly above the erosion critical velocity of the fine sand used in the mixtures. A 3D laser scanner was employed to continuously record the geometry of the scour hole. Results show that increasing the Kaolinite clay in the fine fraction reduces significantly the scour. The mixture with a range around 7.5–10% of kaolinite clay fines content provides the threshold composition for cohesive soil behaviour effect in scouring process, recognized through scour pattern change. As the clay content increases, notable reductions are observed in the dimensions of the scour hole. Furthermore, the temporal evolution of maximum scour depth measured in flume was in agreement with the results from SRICOS-EFA (Scour Rate in COhesive Soil - Erosion Function Apparatus) method.

Numerical simulation and experimental study on seafloor sampling of an anchor-type mud collector based on SPH-FEM coupling method

Marine sediments are important for research in scientific fields such as marine geology, environmental testing of waters, marine biology and seabed resource exploration. Among them, mud miner is an important way to obtain sediments. However, due to the complexity of the marine environment, the seabed sampling operation is a relatively difficult and complicated project. The structural design of the sampler, the operation mode, and the interaction between the sampler and the sediment affect the sampling effect, which leads to the low efficiency of the sampler operation. In order to investigate the main factors affecting the drag force of the sampler during seafloor sampling, this paper takes a simple and portable anchor-type mud collector surface sediment sampler as a study. This paper introduces the mechanical structure and working principle of an anchor-type mud collector, establishes a mechanical model of the mud collector seafloor sampling process and derives the main factors affecting the dragging force: internal friction angle; the horizontal angle of the bi-directional shaft rod; undercut angle [Formula: see text] of bottom cover and dragging speed. A FEM-SPH method based on the coupling of the finite element method (FEM) and the smooth particle hydrodynamics method (SPH) was proposed to simulate the dynamic process of mud collector subsea sampling, and the mechanical data of fine sand and clay were obtained through land-based experiments. Based on the comparison between experimental data and numerical simulation data, the simulation validity of the FEM-SPH method was verified. The results show that the drag force of the clay was greater than that of the fine sand in the experiment of cutting the lower cover of the mud collector into the fine sand and clay, the internal friction angle of the clay is greater than that of the fine sand; with the increase in horizontal inclination angle and the decrease in undercut angle, the dragging force gradually increased; The dragging speed ranged from 0.2 to 0.6 m/s, with an increase in the mass of clay and fine sand collected with increasing speed, resulting in a gradual increase in dragging force. This paper provides a new method to study the force of the mud collector, provides a theoretical method to reduce the intensity and difficulty of manual work in the sampling process and increase the efficiency of sampling.