Fine Deposits Research Articles

Bedform segregation and locking increase storage of natural and synthetic particles in rivers

While the ecological significance of hyporheic exchange and fine particle transport in rivers is well established, these processes are generally considered irrelevant to riverbed morphodynamics. We show that coupling between hyporheic exchange, suspended sediment deposition, and sand bedform motion strongly modulates morphodynamics and sorts bed sediments. Hyporheic exchange focuses fine-particle deposition within and below mobile bedforms, which suppresses bed mobility. However, deposited fines are also remobilized by bedform motion, providing a mechanism for segregating coarse and fine particles in the bed. Surprisingly, two distinct end states emerge from the competing interplay of bed stabilization and remobilization: a locked state in which fine particle deposition completely stabilizes the bed, and a dynamic equilibrium in which frequent remobilization sorts the bed and restores mobility. These findings demonstrate the significance of hyporheic exchange to riverbed morphodynamics and clarify how dynamic interactions between coarse and fine particles produce sedimentary patterns commonly found in rivers.

SIGNIFICANCE OF THE METALLURGICAL INDUSTRY OF AZERBAIJAN IN THE NON-OIL SECTOR, THE ROLE OF AZERGOLD CJSC IN THE ECONOMY OF THE REPUBLIC

Geological surveys carried out by the Closed Joint Stock Company (CJSC) AzerGold for the exploration of new deposits and expansion of production areas are giving positive results. For an effective assessment of reserves at the fields, AzerGold CJSC conducts intensive exploration work and drills deep wells in these fields. Since 2017, AzerGold CJSC has been mining Chovdar, Agyokhush, Tulallar, Marakh, Filizchay etc others and Jayirchay gold, as well as it carries out various works on fine metal deposits. The latest financial indicators of AzerGold CJSC give reason to say that it is a stable company. It is expected that AzerGold CJSC will react faster to the growth rates in the world markets due to the work carried out at new gold deposits and efficient use of resources. The net profit of a Closed Joint Stock Company has been growing at a higher rate over the years. AzerGold CJSC produces ingots and coins from Azerbaijani gold and silver in various historical designs. Bars and coins are currently sold in stores owned by Italdizain Group, Levata Group and SI Luxury World, which have a long history of selling premium goods. AzerGold CJSC will soon become better known in the local and international markets as a gold producer of the country. AzerGold CJSC issues bonds, increases the company's technological capabilities for gold production and strengthens production in order to bring more gold to the world market. Recent financial indicators of AzerGold CJSC give grounds to say that it is a stable company. The company's revenue, net profit and total capital of the company in 2019 increased several times compared to 2018. Keywords: AzerGold CJSC, geological exploration works, drilling works, production works, efficiency.

Fracture distribution in a folded fluvial succession: The Puig-reig anticline (south-eastern Pyrenees)

Sedimentary rocks of foreland fold-and-thrust belts typically undergo intensive fracturing as folds grow. The resulting fracture networks can present significant variations depending on the distribution of sedimentary facies and the complex structural characteristics of fold-and-thrust belts. The Puig-reig anticline, located in the south-eastern Pyrenees, mainly exposes proximal fluvial deposits in the north limb and medial fluvial deposits in the rest of the anticline. Thus, this anticline constitutes an excellent case study to investigate the main controls on the distribution of fracture networks in folded fluvial deposits, in terms of structural position and lithofacies variations. Outcrops were selected to be representative of different structural positions, from the fold hinge to its limbs, and of a variety of the main lithofacies, from proximal to medial fluvial deposits. Fracture data were acquired using the linear scanline method. The results indicate that the anticline rocks have been affected by four sets of fractures. The north limb is dominated by thick conglomerate bodies with interlayered sandstones deposited from unconfined flash floods and wide-shallow channel streams in the proximal fluvial fan, and presents large fracture spacing and low fracture intensity but relatively large fracture length and aperture. The crest and the crest-limb transition zones are mainly characterised by interlayered conglomerates, sandstones, siltstones and clays, deposited from braided channel streams and overbanks in the medial fluvial fan, and present fractures with relatively high fracture intensity and variable fracture length and aperture. The south limb, composed of channel filling sandstone layers and stable overbank fine deposits in the medial fluvial fan, is characterised by low fracture intensity and small fracture length and aperture. Based on multiple linear regression analysis, fracture intensity is mainly controlled by the structural position, bedding thickness and lithological associations, with relatively more intense fracturing in thin sandstone layers with multiple interlayers of fine deposits in the anticline crest. The fracture length mainly depends on bedding thickness and is affected lithological associations. The fracture apertures are mainly controlled by lithofacies, with relatively higher apertures affecting conglomerate bodies. The results of this study are relevant for characterising similar systems in the subsurface, where data is scarce.

Depositional age and genesis of the host strata of the Shuangjianzishan Ag–Pb–Zn deposit: Implications for the Late Carboniferous magmatic–hydrothermal activities and tectonic evolution of the eastern central Asia orogenic belt

The Shuangjianzishan Ag–Pb–Zn deposit is hosted by an over 2030-m-thick succession of Late Carboniferous slate-dominated deep-water sediments. Three tuff layers interbedded with slates yield zircon U–Pb ages of 314.4 ± 2.5 Ma, 315.9 ± 3.6 Ma, and 317.9 ± 2.3 Ma. Using Monte-Carlo simulations, we constrain the maximum time span between the bottom tuff and the top tuff to no longer than 6.9 Myr at a 2σ (95.3%) confidence level. On the basis of this time span, the long-term accumulation rate of the Shuangjianzishan slates is 294 m/Myr. This accumulation rate is faster than any subduction-related accumulation rates by at least 30%; it is similar to that of fine deposits in a rift setting. The variably low δ18O of the zircons from the interbedded tuffs also suggest that a high-temperature hydrothermal alteration occurred during the generation of the low δ18O parental magma. Magmatic–hydrothermal events related to a rifting event are the most likely mechanism that caused the low δ18O signature. The chemical compositions of the slates suggest that their source rocks were very immature, probably similar to contemporary intermediate to acidic volcanic rocks. On the basis of down-well logging data, the dipping angle data are plotted with the stratigraphic depth of each stratum. The stable dipping angle of the slates also supports a sedimentation processes in an active rifting environment.

Polymer surfactant (Triton-100) assisted low cost method for preparing silver and graphene oxide modified Bi-MnOx nanocomposite for enhanced sensor and anti-microbial health care applications

Silver nanoparticles decorated on nanotubes morphology of Bismuth doped manganese oxide (Bi-MnOx) was prepared by Triton-X-100 polymer assisted precipitation process. In the second step, Ag nanoparticle with very fine particle size and graphene nanoparticle deposition by high power ultra-sonication method. Biogenic route synthesized silver nanoparticles have forms the spherical particle morphology with particle size obtained <10 nm. Polymer assisted method prepared pristine Bi-MnOx has existing in Nano- tubular morphology. The nanotube formation/nano particle incorporation has clearly confirmed by Scanning and Transmision electron microgph images. The synthesized silver nanoparticle modified Bi-MnOx composite was further tested for non-enzymatic detection of hydrogen peroxide sensor application. To exploit the biological activity of as prepared Bi-MnOx and biogenic route prepared silver quantum dot (QDs) particle and graphene oxide (GO) modified Bi-MnOx nanocomposite was further studied for gram positive and gram-negative bacterial strain. The nanoparticle dispersed Bi-MnOx could be adopted as low cost coating materials in health care smart building construction. Diffuse reflectance spectral studies are described for as prepared Ag QDs/GO doped Bi-MnOx is shown reduced band gap values (2.93 eV) than the pristine Bi-MnOx (3.17 eV) and it could be adopted for visible light photo-catalysis and antimicrobial applications.

Low-Cost High-Performance SnO2–Cu Electrodes for Use in Direct Ethanol Fuel Cells

The high cost of Pt-based electrode materials limits the commercialization of fuel cells and their subsequent application in renewable energy production. It is thus necessary to develop economical, high-performance electrodes alongside biofuels to reduce the pollution associated with the production of energy. Tin dioxide–copper foil (SnO2–Cu) electrode materials are herein developed using an electrodeposition process. Cyclic voltammetry, chronoamperometry, and potentiodynamic polarization methods are used to electrochemically characterize the electrode materials, with the results revealing that their excellent catalytic properties result in them delivering a high current. The surface morphologies of the developed electrodes are examined using scanning electron microscopy, with the results showing that upon an increase in the deposition time, a finer deposit of SnO2 is formed on the surface of the Cu foil. Consequently, electrochemical oxidation using an enhanced surface area of the material leads to it exhibiting a high current and excellent corrosion resistance. Powder X-ray diffraction was used to confirm the successful depositing of SnO2 on the surface of Cu. The fuel cell fabricated using the SnO2–Cu electrode is promising for use in clean energy generation, as it can be prepared at low cost compared to conventionally used electrodes.

Myeloma cast nephropathy with diffuse amyloid casts without systemic amyloidosis: two cases report

BackgroundMultiple myeloma (MM) is a plasma-cell derived hematologic malignant disease. The malignant proliferating plasma cells secrete massive monoclonal immunoglobulins which lead to various pathologic types of renal injury. Myeloma cast nephropathy (MCN) is the most common histopathologic lesion with the worst renal prognosis. Rarely, the free light chains in the protein casts can form amyloid fibrils. Here, we reported two rare cases of MCN with diffuse amyloid casts.Case presentationCase 1: A 54-year-old Chinese man presented with a 4-year history of multiple myeloma, proteinuria and hematuria. He had monoclonal IgAλ plus free λ spike in both serum and urine. He had been on chemotherapy for 4 years and maintained normal serum creatinine until 11 months ago. Then, his renal function deteriorated and he went on hemodialysis 4 months before admission. Renal biopsy showed diffuse amyloid casts in the tubular lumens, without any obvious amyloid deposits in other kidney compartments or signs of extra-renal amyloidosis. The amyloid fibrils formed around mononuclear cells which were CD68 negative. According to the morphology and location, these mononuclear cells were considered as tubular epithelial cells. The patient was maintained on chemotherapy and hemodialysis. He died 8 months after renal biopsy.Case 2: A 58-year-old Chinese man presented with a one-and-a-half-year history of proteinuria and slowly rising serum creatinine. He had monoclonal IgDλ spike in both serum and urine. Amyloid casts were observed in the tubular lumens and mononuclear cells could be identified in the center of some casts. There were no amyloid deposits in other kidney compartments and no sign of systemic amyloidosis. The patient also had fine granular deposits along the tubular basement membrane with λ linear staining along tubular basement membrane suggesting light chain deposition disease. He was treated with bortezomib-based chemotherapy followed by lenalidomide-based chemotherapy and achieved very good partial remission (VGPR). After 27 months of follow-up, the patient still showed no signs of systemic amyloidosis.ConclusionsThese 2 cases of MCN with diffuse amyloid casts have different histopathologic characteristics from the usual myeloma casts and tubular epithelial cells might play important roles in the pathogenesis.

Phases of fluvial activity in loess landscapes: Findings from the Sió valley (Transdanubia, central Europe)

Knowledge about the evolution of rivers planforms in loess landscapes of Europe is incomplete. While there are studies on river evolution conducted in loess areas of central and western Europe, the area of Transdanubia (Hungary) remains poorly recognized. Our research work extends previous findings by studying a unique example of alluvial fill maintaining a sedimentary record of river planforms from the Late Pleistocene to the modern times (the Sió Valley, Hungary). The main goal was to determine the main fluvial phases shaping the valley floor. Our study was based on geological, geophysical and remote sensing methods supported by AMS radiocarbon and OSL dating. Three fluvial phases were identified: the formation of large-scale meanders in the Late Peniglacial, transition to an anabranching pattern ~18000 cal. BP, and formation of small-scale meanders ~12700 cal. BP. Their traces are present in the sedimentary record of other rivers evolving in loess landscapes, however, their appearance differs in the timing and type of river planform changes. Phase I was marked by large-scale meanders in the Great Hungarian Plain and Transdanubia, and braided rivers in western Europe. Phase II, marked by transitions to anabranching planforms, or periods of meander cutoffs, appeared first in the Late Pleniglacial in isolated valleys of Transdanubia and northern part of the Pannonian basin. The latest appearance of this phase took place in western Europe owing to a cooler climate and sparse vegetation compared to Transdanubia and Great Hungarian Plain. Phase III, marked by transitions from anabranching rivers to small-scale meanders, started in the Sió valley in conditions of sediment deficit causing river bed incision. Aggradation appeared owing to anthropogenic influence starting ~7000 cal. BP. Its maximum occurred 3000–4000 cal. BP. This triggered phase III in western Europe, and increased deposition of fines, resulting in flow discontinuation in some valleys of Transdanubia.

Flow–Sediment Turbulent Ejections: Interaction between Surface and Subsurface Flow in Gravel-Bed Contaminated by Fine Sediment

Several researchers have studied turbulent structures, such as ejections, sweeps, and outwards and inwards interactions in flumes, where the streamwise velocity dominates over vertical and transversal velocities. However, this research presents an experimental study in which there are ejections associated with the interchange between surface and subsurface water, where the vertical velocity dominates over the streamwise component. The experiment is related to a surface alluvial stream that is polluted with fine sediment, which is percolated into the bed. The subsurface flow is modified by a lower permeability associated with the fine sediment and emerges to the surface current. Quasi-steady ejections are produced that drag fine sediment into the surface flow. Particle image velocimetry (PIV) measured the velocity field before and after the ejection. The velocity data were analyzed by scatter plots, power spectra, and wavelet analysis of turbulent fluctuations, finding changes in the distribution of turbulence interactions with and without the presence of fine deposits. The flow sediment ejection changes the patterns of turbulent structures and the distribution of the turbulence interactions that have been reported in open channels without subsurface flows.

Onshore barrier affects sediment deposition in a subtropical mudflat

Onshore barrier in the intertidal area is reported to influence coastal geomorphology, sediment dynamics, and erosion and accretion processes. The present study describes sediment texture and deposition pattern, and shore profile of a tidal mudflat located in the Kutubdia Island of Bangladesh. A physical barrier in the form of concrete ring structure was placed on the mudflat of experimental site and the control site was 50 m away without any barrier. The texture of sediment was mostly medium silt (45.3%) in leeward side (= the side facing away from the tide/wave action) of the barrier. Whereas, coarse silt was dominant in the control (35.2%) and seaward side (31.2%), followed by medium silt (25.1% and 29.0%, respectively). The proportion of fine sand was higher in the control (18.4%) and seaward side (16.1%) than that of the leeward side (6.1%). Because of the barrier, there was noticeable sedimentation on mudflat as demonstrated by increased elevation of shore profile in the leeward side, 23.3 cm vs. 3.6 cm in the control. Sediment deposition was, however, varied due to susceptibility to erosion depending on grain size distribution, e.g. the fine deposits had greater erodibility than the sandy deposits. These results suggest that barrier on mudflat could bring a positive change to the sediment profiling and shore morphology, and thus help stabilizing the eroding shoreline.

Tectono-sedimentary characteristics in the area with distributed normal faults: Lower Cretaceous Prosopis Formation in the northern slope of Bongor Basin, Chad

Based on an integrated database (e.g., core observations, well logs, and seismic data), the characteristics of depositional systems, as well as the response to tectonics, are systemically delineated in the Prosopis Formation of the Lower Cretaceous at Bongor Basin, Chad. The tectonic setting of this study area experienced multiple, active sub-basins with narrow-spaced intra-basinal normal faults. The multiple normal faults formed in the initial rifted stage leading to the development of a corridor-shaped basin consisting of small-scale sub-basins. As this basin is attracting increased attention due to further hydrocarbon exploration, deciphering the process of sediment partition, especially in the initial rifted stage, would provide a further understanding of the tectono-sedimentary evolution in lacustrine rift basins. Based on core observations, well logs, and three-dimensional seismic data, fan-delta and sub-lacustrine-fan depositional systems are widely developed in this area. Two depositional systems (e.g., fan-delta and sub-lacustrine-fan) and three categories of slope break belts (single-faulted, step-faulted, and flexure types) have been identified. Overall, during the initial rifted stage, the formation of multiple normal faults mainly dominates the geomorphology and sediment supplies that generate the spatio-temporal features of depositional systems in semi-closed lacustrine basins. Climatic perturbations, furthermore, regulated the composition of sediments (coarse versus fine deposits). For the economic perspective, this study highlights the significance of fault systems in further hydrocarbon exploration during the initial rifted stage of lacustrine basins.

Froude supercritical flow processes and sedimentary structures: New insights from experiments with a wide range of grain sizes

AbstractRecognition of Froude supercritical flow deposits in environments that range from rivers to the ocean floor has triggered a surge of interest in their flow processes, bedforms and sedimentary structures. Interpreting these supercritical flow deposits is especially important because they often represent the most powerful flows in the geological record. Insights from experiments are key to reconstruct palaeo‐flow processes from the sedimentary record. So far, all experimentally produced supercritical flow deposits are of a narrow grain‐size range (fine to medium sand), while deposits in the rock record often consist of a much wider grain‐size distribution. This paper presents results of supercritical‐flow experiments with a grain‐size distribution from clay to gravel. These experiments show that cyclic step instabilities can produce more complex and a larger variety of sedimentary structures than the previously suggested backsets and ‘scour and fill’ structures. The sedimentary structures are composed of irregular lenses, mounds and wedges with backsets and foresets, as well as undulating planar to low‐angle upstream and downstream dipping laminae. The experiments also demonstrate that the Froude number is not the only control on the sedimentary structures formed by supercritical‐flow processes. Additional controls include the size and migration rate of the hydraulic jump and the substrate cohesion. This study further demonstrates that Froude supercritical flow promotes suspension transport of all grain sizes, including gravels. Surprisingly, it was observed that all grain sizes were rapidly deposited just downstream of hydraulic jumps, including silt and clay. These results expand the range of dynamic mud deposition into supercritical‐flow conditions, where local transient shear stress reduction rather than overall flow waning conditions allow for deposition of fines. Comparison of the experimental deposits with outcrop datasets composed of conglomerates to mudstones, shows significant similarities and highlights the role of hydraulic jumps, rather than overall flow condition changes, in producing lithologically and geometrically complex stratigraphy.

Numerical Simulation Study of Fines Migration Impacts on an Early Water Drainage Period in Undersaturated Coal Seam Gas Reservoirs

Coal fines migration exerts negative impacts on early water drainage of undersaturated coal seam gas (CSG) reservoirs. The complicated migration process results in ineffective and inaccurate forecast of coal fines production. Hence, a robust modelling tool is required to include the mechanisms of fines migration and to predict their impacts on rock and production. In this paper, fines migration in coal is categorized into three stages: generation, migration, and deposition processes. The corresponding models for different stages are established, including (1) a fines generation model, (2) the maximum fines-carrying concentration model and deviation factor of the modified Darcy model, (3) a fines deposition model, and (4) a dynamic permeability and porosity model. The above models are coupled with a water flow model, solved numerically using the finite difference method. Then, two dewatering strategies, including fast and moderate depressurization, are compared using the proposed models to study their effects on coal properties and following production. Finally, the production history of a CSG well in the Qinshui Basin, China, is utilized for history matching in a field case study. The simulation results indicate that new fines will be generated in a fast depressurization process and the water rate decline reduces the cleat permeability significantly. The newly generated fines can enhance the permeability temporarily, but they will block the flow channels and bring serious damage to the permeability when the water rate declines. The moderate depressurization strategy can produce the coal fines in a continuous mode, and the formation damage induced by fines deposition can be reduced to the acceptable level, which is the more reliable way to maintain well productivity. In addition, multiple well shut-in can trigger the irreversible fines deposition, reduce the permeability, and decrease the production rate.

Interpretation of Conventional Reciprocal Method (CRM) refraction data for identification of subsoil structure in the tourism area at Batu Kuda Bandung

The purpose of this study is to identify the subsurface geological structure by using the seismic refraction method in the Wana area of Batu Kuda tourism using Seismic Data Interpretation Refractive Conventional Reciprocal Method (CRM) which aims to produce a GUI. Data obtained in the form of wave propagation time as time forward and time reverse, from the travel time of the wave and distance and time geophone analysis. From the results of the data interpretation, the velocity of P wave propagation in the medium and depth is obtained in 2 layers. In the first layer obtained a velocity value of 628.98 m / s with the depth of the first layer ranged from 0 m - 8.73 m and the seismic wave velocity in the second layer was 1228.99 m / s with the depth of the second layer ranged from 8.73 m - 20 m. Based on the 2D model the distribution pattern of velocity values, it can be indicated that the first layer is the latosol soil layer containing sand, gravel, fine sediment and clay. The second layer contains fine deposits, sandstone, gravel, sand, fine sand (silt), clay and clay. These materials as a result of the process of the eruption of an undefined young volcano.

The role of fines transport in low salinity waterflooding and hybrid recovery processes

Low Salinity Waterflooding (LSW) is a promising technology for improving oil recovery in secondary and tertiary stages over the conventional waterflooding (HSW). As widely reported in the literature, this emerging recovery approach has relatively low operating costs and is more environmentally-friendly than conventional Enhanced Oil Recovery (EOR) methods. In fact, LSW is a multi-physics recovery process; however, most of the previous studies focused on wettability modification as the sole mechanism for the incremental oil recovery by LSW. Unfortunately, these studies often ignored other crucial factors that importantly affect the performance of LSW, e.g., fines transport under a low salinity injection environment.This paper introduces a robust modeling workflow to capture important recovery mechanisms occurred in LSW by integrating fines migration, wettability alteration, and geochemistry. The results showed that fines transport including fines deposition, fines migration, and fines plugging plays an important role in LSW process. Fines plugging by LSW can cause formation damage, but it also can be used as a mobility control agent. The LSW model equipped with fines transport shows an excellent agreement for incremental oil recovery and pressure drop against laboratory coreflooding. Finally, a novel concept of hybrid low salinity assisted gas flooding was proposed to overcome the existing technical challenges associated with the conventional CO2 flooding.

Buffer effect on identifying transient streambed hydraulic conductivity with inversion of flood wave responses

Determination of streambed hydraulic conductivity (Ksb) and its variations over time are critical for quantifying exchange fluxes between surface water and groundwater. Previous studies have used flood wave response techniques (FRT) to determine Ksb or its transience, excluding the streambed storage effect, thus the estimated Ksb may not be reliable. In this study, after improving a previous FRT by substituting the gradient descent algorithm with an advanced and robust optimization method, trust region reflective algorithm, we have analyzed the influence of streambed storage effect on the estimation of time-dependent Ksb through successive inversion of flood wave responses. The study shows that the streambed storage effect is not important for identifying the transience in the hydraulic properties of a relatively thin streambed (e.g., several or dozens of centimeters). But significant under-estimation (1–2 orders of magnitude) can be seen because of neglecting the streambed storage effect. It is particularly true for a stream-confined aquifer system if the streambed is composed of fine deposits (e.g., silt, clay) with a thicker thickness greater than 1 m corresponding to low permeability but high storativity, and the aquifer is characterized by relatively low permeability (e.g., roughly 0.1–10 m d−1) and relatively low storativity (roughly 1E-5 m−1) (e.g., dense fine sands). The new method in which streambed storage effect is incorporated, can provide more reliable estimations of time-dependent Ksb for a stream-confined aquifer system, and it has been successfully applied to estimate the time-dependent Ksb of a reach of the Arkansas River, Kansas, USA.

Application of a Low Heat Input Deposition Process for Refurbishment of Worn PM Forming Dies Using Fe-Ni Based Filler Metal

Abstract Refurbishment of worn Dies is an interesting research area which also has high economic benefit. Material which is used in PM dies for compacting powders are high carbon steel which have very low weldabilitis. Due to the high hardness, high carbon content and martensitic microstructure, these Dies are very sensitive to the thermal shock produced from fusion welding. For successfully refurbishing the worn Dies, Fine spark deposition was used for deposition of a new layer on the cold work 1.2436 steel. Different heat inputs were used for deposition of nickel based material and finally microstructure and HAZ were studied. Results show the HAZ area is very narrow, free from cracks and HAZ microstructure is similar to the base metal. GTAW welding using same filler metal induced many cracks in HAZ of weld which is detrimental to the refurbished Die performance. Results show increasing heat input in Fine spark deposition can results in crack formation in HAZ even if the weld pool does not occurred in base metal. However these cracks are much smaller than those occurred in GTAW.

Respostas dos padrões de sedimentação e hipersalinidade na cobertura vegetal de planície estuarina sob influência da semiaridez

Esta pesquisa analisa a influência das variações espaciais da salinidade intersticial e granulometria dos sedimentos na cobertura vegetal do estuário do Rio Apodi-Mossoró (RN). Foram distribuídos 10 pontos amostrais para identificar a salinidade e granulometria dos sedimentos; os mapas temáticos da cobertura vegetal foram elaborados através de técnicas de processamento de imagens LandSat 8. O trecho da foz (pontos 1-2) apresentou domínio das frações arenosas; nos demais pontos predominam sedimentos siltosos. Da foz ao ponto 5, de salinidade &lt; 50 ‰, estão os trechos mais extensos de manguezal. Todavia, os pontos 3, 6, 7, 8, 9 e 10 apresentaram elevada salinidade, com cobertura vegetal típicas de apicuns/salgados e solos expostos. Portanto, os depósitos de finos favorecem a retenção de sais, contribuindo para hipersalinidade, que se torna principal fator limitante ao desenvolvimento do manguezal.

Hydro-mechanical analysis of rainfall-induced fines migration process within unsaturated soils

Seepage-induced fines migration under rainfall infiltration is a main cause leading to shallow failures in loose colluvial slopes. To describe the full process of fines migration within unsaturated soils during rainfall infiltration and the associated hydro-mechanical behaviors, a seepage-erosion-deformation coupled formulation is proposed in this paper. The governing equations proposed are implemented into a finite element code and used to investigate the influences of skeleton deformation on the rainfall infiltration process through unsaturated soil columns. The numerical results were presented in detail for a better understanding of the rainfall-induced fines migration process within unsaturated soils. Further, the obtained results are integrated into an infinite slope model for slope stability analysis. The results show that, the skeleton deformation will affect the rainfall infiltration rate and hence the timing of slope failures; meanwhile their influences are more evident if the fines deposition process is taken into account. Moreover, the slope stability could be reduced gradually due to the soil strength loss along with loss of fine particles. Therefore, particular attentions should be paid to analyzing the stability of soil slopes susceptible to internal erosion.

Paleoenvironments and human occupation in the El Bolsón Valley of northwest Argentina (province of Catamarca, dept. of Belén)

Using an interdisciplinary perspective that integrates archaeological, geomorphological, and palynological data, this work analyzes the relationship between environmental changes and cultural landscapes in the El Bolsón Valley in the province of Catamarca, Argentina. The palynological and sedimentological studies took place using a sediment core extracted from a seasonal lake, while the geomorphological studies made use of stratified fluvial deposits. The palynological sequence indicates that wetter conditions existed at 6400calBP, but that this wetness decreased to create the current more arid conditions along with increases in anthropogenic disturbance. There is also evidence for intense processes of sediment accumulation and erosion, including changes in the uses of space by human populations as recorded for the last 2000years in fine deposits from the valley floor. The present work also makes an effort to insert this local history into its broader context, in order to contribute to existing knowledge regarding late Holocene changes at the regional level.