Alluvial Deposits Research Articles

The Chaman and Paghman active faults, west of Kabul, Afghanistan: Active tectonics, geomorphology, and evidence for rupture in the destructive 1505 earthquake

The city of Kabul, Afghanistan, lies within the Kabul Block, which is bounded by the Sarobi, Gardez and Paghman fault, the northern extension of the Chaman fault, accommodating oblique convergence between the Indian and Eurasian plates. In this paper, we describe the geologic structure and tectonic geomorphology of the northeast-striking Paghman fault and a ∼10-km-long portion of the Chaman fault using a combination of field observations and remote sensing data, and assess evidence for rupturing in the 1505 historical earthquake. The Paghman fault is predominantly a left-lateral strike-slip fault with a minor dip-slip component along the eastern margin of the Paghman Mountains. The Chaman and Paghman faults displaces Paleogene to Quaternary units with clear displacement of recent deposits. Continuous left-lateral movement of the both faults have caused stream deflection, capturing, abandonment, and finally, incision of alluvial deposits inside the Kabul Basin. We identify several stages in the alluvial fan development and displacement that were once a continuous unit displaced left-laterally as a single fan but are now incised by beheaded and offset stream channels. An approximately 30-km-long active fault trace is identified with geomorphic evidence of recent faulting and vertical offset ∼0.5–3 m, which we interpret is related to the historical 1505 earthquake in the area along the Chaman and Paghman faults. Our observations indicate significant along-strike variations in faults trace geometry. The seismic event comprises several fault segments separated by discontinuities such as stepovers. The two faults have accumulated enough elastic strain to cause a larger earthquake since the 1505 quake.

Spatial-temporal variation, source apportionment and risk assessment of lead in surface river sediments over ∼20 years of rapid industrialisation in the Pearl River Basin, China

Lead (Pb) is a highly toxic element and is not essential to the human body. Lead pollution caused by human activities and a high geological background is considered a global environmental issue. According to the China Geochemical Baseline (CGB) project, the Pearl River Basin had the highest Pb content in alluvial sediments of 30 first-level basins in China. For this reason, it is of great significance to determine the temporal and spatial variations in Pb and their influencing factors in the Pearl River Basin. In this study, 956 stream sediment samples collected in the 1980 s (early stage) and 129 river sediment samples collected from 2008 to 2010 (late stage) were used to study the background value and spatial-temporal variation characteristics of Pb in river sediments in the Pearl River Basin. The Pb source apportionment and an ecological risk assessment were also carried out. The background value of Pb (36.2 mg·kg–1) in the river sediments of the Pearl River Basin was significantly higher than that in China (22.1 mg·kg–1). The parent rocks determine the Pb background in sediments and the high Pb background areas mainly comprised carbonate rocks and acid volcanic rocks. Over 20 years of rapid industrialisation, the average Pb increased from 43.3 to 68.3 mg·kg–1 in the Pearl River Basin. The BCR analysis revealed that Pb mainly existed in the reducible phase (48 % on average) and residue phase (42 % on average). The enrichment factor and geo-accumulation index indicated that the late-stage sediments experienced more Pb pollution than the early-stage sediments. However, the risk assessment code (RAC) showed that there was a low ecological risk of Pb in the late-stage sediments. The factor analysis results for the two rounds of data were significantly different. The Pb content in early-stage sediments was closely related to Al2O3 and Zr, while Pb in the late-stage sediments was mainly related to Zn, As, Sb, Au and Hg, indicating that the increase in Pb in the later samples was mainly influenced by human activities. The Pb isotope composition of the late-stage sediments confirmed that low Pb content was mainly controlled by natural sources, while high Pb content was significantly affected by anthropogenic sources. Combining the results of spatial-temporal variation, chemical speciation and source apportionment indicated that the rapid rise of Pb in late-stage sediments in certain areas could be attributed to mining and smelting activities during the process of industrialisation over 20 years. The anthropogenic exogenous Pb could be immobilised by Fe-Mn (hydro)oxides when it entered the soil, so although there was a high background the ecological risk of Pb in river sediments was low. In the future, Pb pollution control and remediation needs to be strengthened in the Pearl River Basin to avoid the outbreak of potential ecological risks linked to Pb.

Modeling Water Flow in Variably Saturated Porous Soils and Alluvial Sediments

The sustainable exploitation of groundwater resources is a multifaceted and complex problem, which is controlled, among many other factors and processes, by water flow in porous soils and sediments. Modeling water flow in unsaturated, non-deformable porous media is commonly based on a partial differential equation, which translates the mass conservation principle into mathematical terms. Such an equation assumes that the variation of the volumetric water content (θ) in the medium is balanced by the net flux of water flow, i.e., the divergence of specific discharge, if source/sink terms are negligible. Specific discharge is in turn related to the matric potential (h), through the non-linear Darcy–Buckingham law. The resulting equation can be rewritten in different ways, in order to express it as a partial differential equation where a single physical quantity is considered to be a dependent variable. Namely, the most common instances are the Fokker–Planck Equation (for θ), and the Richards Equation (for h). The other two forms can be given for generalized matric flux potential (Φ) and for hydraulic conductivity (K). The latter two cases are shown to limit the non-linearity to multiplicative terms for an exponential K-to-h relationship. Different types of boundary conditions are examined for the four different formalisms. Moreover, remarks given on the physico-mathematical properties of the relationships between K, h, and θ could be useful for further theoretical and practical studies.

FIELD AND MODEL RESEARCH OF THE GROUNDWATER FLOWS IN THE AREA OF THE PAKS-2 NPP CONSTRUCTION, HUNGARY

The construction of the nuclear power plant (NPP) requires conducting a large number of engineering and hydrogeological surveys, as well as assessment of the design decisions’ safety. A deep excavation pit at the Paks II NPP construction site requires execution of the cut-off wall due to extremely high groundwater saturation of the alluvial deposits. However, lithological anisotropy and the presence of dislocation zones did not allow identifying the appropriate depth for the cut-off wall construction. Unfortunately, engineering geological boreholes with a 20-meter distance between them and surface and borehole geophysical surveys could not identify the hydrogeological units. Thus, to conceptualize the hydrogeological settings, an analysis of the groundwater head distribution and the large-scale pumping tests were conducted. The interpretation of the geological data and the distinguishing of the hydrogeological units were carried out iteratively using the hydrogeological numerical model. The flow model could represent the hydraulic head distribution, the response of the lithologically heterogeneous layers to the water fluctuations in the Danube river, and the pumping tests carried out at the different depths. The results of the hydrogeological modeling revealed the aquitard to be continuous throughout the territory; however, its top’s depth changes from 30–35 to 90 m within the construction site of the Paks II NPP. This complex geometry of the aquitard is controlled by the plicated dislocation zone, which cuts the construction site in half and is revealed as the right wall of the graben.Correct hydrogeological stratification enabled us to ensure waterproof activities such as the cut-off wall construction using the hydrogeological model when excavating a deep pit for the Paks II NPP. This also minimizes the hydrodynamic impact on the closely located NPP Paks in operation.

Technological analysis of the Baboungué collections, Central African Republic: New data on the Early Stone Age macro-tools

Despite numerous sites attributed to Early Stone Age (ESA), the emergence and diversification of lithic industries in Central African Republic is still challenging for discussion. Among all these sites, those located near Baboungué village have been reported by Roger de Bayle des Hermens in the late 1960s, and provided artifacts from two localities, namely Baboungué 1 and Baboungué 2. Both sites are situated around 800 meters from Baboungué village within the Sangha River alluvial deposits. Nowadays, the lithic assemblages from Baboungué are stored at the Institut de Paléontologie Humaine, Paris, France. In this paper, we reappraise a selection of 90 pieces from both localities (Baboungué 1=26 and Baboungué 2=74), which have already been identified and classified by R. de Bayle des Hermens in “Recherches préhistoriques en République centrafricaine” (1975). He used a morphological and typological approach. We decided to apply a new technological approach on these collections. Reduction strategies (flaking and shaping) and techno-functional analysis were applied with a focus on the shaped tools and pebble tools. Even though, the classification made by R. de Bayle des Hermens is taken into consideration in our study. We introduced several new categories such as Large Flake Tools, and Trifacial Shaped Tools. We expose the unexpected diversity of Baboungué shaped tools and pebble tools both in terms of production and techno-function (structural specificities). This paper also describes for the first time the trifacial shaping strategies for Central African ESA, whereas traditional ESA bifacial shaping is absent. Finally, we question the techno-cultural and functional significance of these collections marked by robust to massive stone tools.

Geomorphic evolution of the craton-derived Sone megafan in the southern Ganga plain, India: A tectono-climatic interplay

The Ganga plain neotectonics has been studied from surface and sub-surface faults, frequent geomorphic readjustment, changing sedimentation pattern, piedmont progradation, pedological variation, and frequent earthquake occurrences. However, being neotectonically stable, the peninsular region’s geomorphic changes are governed by climatic fluctuations, contributing to the Ganga plain’s sedimentation. Therefore, peripheral craton sourced marginal alluvial deposits in the Ganga basin are appropriate features to study the control of both the Himalayan tectonics and climate of core peninsular region away from their respective source areas. This study uses a process-response approach model to describe the geomorphic development of the Sone megafan, located at the marginal part of the Ganga plain to the south of the Ganga River, bordering the Indian craton.Geomorphological mapping, field investigation of the depositional features, soil profiles, and Optical Stimulated Luminescence (OSL) chronology suggest four phases of geomorphic evolution, i.e., in 22–8 Ka, 8.0 Ka–7.3 Ka, 7.3 Ka–2.4 Ka, and 2.4 Ka–0.5 Ka on the Sone megafan. The different evolutionary phases are marked by channel and floodplain abandonment and soil profile development. The megafan surface is divided into four distinct geomorphic units (OdSP – Oldest Sone Plain, OSP – Old Sone Plain, YSP – Young Sone Plain, and AFP – Active Floodplain) based on OSL ages and soil properties. Geomorphology and soil suggest a mixed climate in the source and sink area. The arid climate in the catchment contributed to the sediment production, and the humid climate promoted its transport, which resulted in the largest depositional unit of the megafan, even during the arid period in the Ganga basin. Contrast to the north of the Ganga River, no surface faults are found on the Sone megafan. However, the tectonic activity of the bounded basement faults, i.e., the East and the West Patna faults, are well pronounced in the sediment distribution and fluvial response. Tilting and twisting the fault-bounded block controls the sediment remobilization in space and time. Thus, the climatic fluctuation in the source, the sink, and the activity of the basement faults, propelled by the Himalayan tectonics, contributed to the Sone megafan’s geomorphic evolution. Two events of the Ganga River’s encroachment at the distal part of the Sone megafan were recorded (2.4 ± 0.14 and 1.3 ± 0.16 ka). The correlation between OSL ages of megafan units, climatic fluctuations in the Sone River’s catchment, and established time windows of tectonic episodes in the Ganga basin has also been investigated. As the Sone and the Gandak megafans rest on the same tectonic blocks, their tectono-geomorphic responses to the Himalayan neotectonics are similar.

A pathological lesion or a postmortem artefact? An interdisciplinary approach to deal with an interesting early medieval case

ObjectiveThis study evaluates a case of pseudopathology and the effects that postmortem taphonomic changes and environmental influences can have on bone. MaterialA skeleton of a young male from the early medieval site Staré Město, dated to the 9th–10th century CE. MethodsThe skeletal remains were subjected to detailed macroscopic and X-ray examination, and then a CT scan and XRF analysis were performed. ResultsX-ray examination of the mandible revealed unusually dense structures, whose appearance was not consistent with any known pathology. Based on the results of CT scanning, it was hypothesized that these were cavities filled with alluvial sediment. X-ray fluorescence spectrometry (XRF), focusing on the determination of the silica content, revealed a high intensity of silica in the samples of the affected area of the bone. ConclusionThe hypothesis that the inclusions were composed of waterborne sediment was supported. SignificanceAlthough it is well known that soil can infiltrate bones buried in the ground, its appearance on plain radiographs is not that commonly known. The case illustrates the usefulness of differentiating true pathologies from postmortem alterations to avoid inappropriate interpretations. LimitationsNo similar cases have been described. Suggestion for further researchIn palaeopathological evaluation, the use of multiple imaging and evaluative techniques should be implemented to differentiate pathological lesions from pseudopathology.

Mineral chemistry in apatite from heavy mineral concentrate samples as a prospecting tool for carbonatites in the Angico dos Dias region, BA/PI border, Brazil

Apatite is one of the most common minerals found in a wide variety of rocks. It has variations of minor and trace elements in its composition that allow the recognition of its host lithotype. In this study, apatite grains identified in rock samples and grains recovered from heavy mineral concentrates in the Angico dos Dias Carbonatite Complex region, located on the border between the State of Bahia and the south of the State of Piauí, Brazil, were analyzed using an electron probe microanalyzer. These concentrates come from alluvial sediments downstream of the carbonatitic body from drainage channels. Sampling was guided by regional geochemical analytical results for the chemical elements of apatite. Grains were detected in alluvial covers for up to 9.5 km downstream in all fraction including coarse sand (1.0 mm) in proximal samples and up to medium sand fractions (0.50 mm) in distal samples. The 96 analytical results on 48 apatite grains show that most have chemical signatures characteristic of metacarbonatitic lithotypes (SrO 0.88–1.7 wt%) and that some host lithotypes were affected by the substituition processes (Si + LREE (Ce+La+Nd) 0.15–0.59 apfu), which may be an alternative to metasomatic fenitization. Statistical analysis by principal component analysis (PCA) helped the visualization and interpretation of the data by constructing clusters of the different compositions of apatite. The apatite fields of carbonatitic and silicate source rocks were separated and associated with the results obtained for alluvial apatite grains, resulting in carbonatitic derivation. The results of using this prospecting tool were satisfactory. Thus, it was possible to classify and detect the sources of alluvial apatite grains relating them to the Angico dos Dias carbonatite body, in addition to proposing a new potential area for the occurrence of carbonatitic bodies northeast of the Angico dos Dias phosphate deposit.

Geocryological Structure of a Giant Spring Aufeis Glade at the Anmangynda River (Northeastern Russia)

Gigantic aufeis fields serve as indicators of water exchange processes within the permafrost zone and are important in assessing the state of the cryosphere in a changing climate. The Anmangynda aufeis, located in the upstream of the Kolyma River basin, is present in the mountainous regions of Northeast Eurasia. Recent decades have witnessed significant changes in aufeis formation patterns, necessitating a comprehensive understanding of cryospheric processes. The objective of the study, conducted in 2021–2022, was to examine the structure of the Anmangynda aufeis and its glade, aiming to understand its genesis and formation processes. The tasks included identifying above- and intra-frozen taliks, mapping groundwater (GW) discharge channels, determining permafrost base depth, and assessing ice thickness distribution. Soundings using ground-penetrating radar (GPR), capacitively coupled electrical resistivity tomography (CCERT), and the transient electromagnetic (TEM) method were employed. GW discharge channels originating from alluvial deposits and extending to the aufeis surface within river channels were identified through GPR and verified through drilling. Deep-seated sources of GW within the bedrock were inferred. CCERT data allowed us to identify large and localized frozen river taliks, from which water is forced onto the ice surface. According to the TEM data, the places of GW outlets spatially coincide with the zones interpreted as faults.

The geological evolution of the Silala River basin, Central Andes

AbstractImproved understanding of the geology and stratigraphic architecture of the Silala River basin and its evolution, reviewed here, has been important in providing scientific evidence to an international dispute between Chile and Bolivia on the nature and origin of the waters of the Silala River. The dispute was submitted in 2016 to International Court of Justice (ICJ), which issued its judgment in 2022. The Silala River has evolved within an active volcanic chain, in the western region of the Andean plateau. Various volcanic structures, at different stages of their evolution, have determined the basin's development. The first evidence of alluvial drainage associated with the Silala fluvial system appeared in the Lower Pleistocene (ca. 2.6–1.6 Ma), a record of alluvial deposits with paleoflow directions toward the Southwest and South‐Southwest. These deposits had an important role in forming a highly permeable horizon, confined between two pyroclastic deposits (the Cabana and Silala Ignimbrites) which comprise the main regional aquifer in the basin, although there are other minor locally important aquifers. The second stage in the evolution of the river system occurred in the late Upper Pleistocene‐Lower Holocene (ca. 11–8.5 ka BP), when an erosive period carved the current trans‐boundary ravine in the Silala Ignimbrite. Morphological evidence clearly shows that the ravine was carved by fluvial action. The only documented tectonic activity during the development of the Silala River basin is the Cabana reverse fault and associated normal faults, representing an East–West shortening, which occurred between 2.6 and 1.6 Ma.This article is categorized under: Science of Water > Water and Environmental Change Science of Water > Hydrological Processes Water and Life > Nature of Freshwater Ecosystems Human Water > Water Governance

Hydrogeological characterization of the Silala River catchment

AbstractThis article reviews hydrogeological studies carried out between 2016 and 2018 in the Silala River basin, a catchment shared by Chile and Bolivia. These were conducted in the context of the Case Concerning the Status and Use of the Waters of the Silala River, submitted to the International Court of Justice in 2016, and contributed to multidisciplinary science to demonstrate that this system is an international watercourse. In 2016, the hydrogeological understanding of the Silala River basin was poor. The studies reviewed here filled many knowledge gaps, providing a solid hydrogeological baseline, and establishing new monitoring infrastructure to collect relevant aquifer data. The most important hydrogeological units were identified as the fluvial deposits, alluvial deposits, and the Cabana ignimbrite. The latter is highly heterogeneous, weathered and fractured, and exhibits a high permeability. It is the most important unit in terms of productivity, and is the major regional aquifer providing spring flows to Bolivian wetlands and groundwater flow across the international border. The studies provided a preliminary understanding of the main aquifers in Chile and their properties, which underpinned the development of a robust hydrogeological conceptual model of the system, reviewed elsewhere in this special issue. Subsequent refinements are also summarized. This work confirmed that both surface water and groundwater flows from Bolivia to Chile, and thus confirms the status of the Silala River as an international watercourse and provided the basis for a basin‐scale groundwater numerical model, used to investigate the impact of wetland channelization on surface water/groundwater partitioning.This article is categorized under: Science of Water > Hydrological Processes

Hydrological modeling of the Silala River basin. 2. Validation of hydrological fluxes with contemporary data

AbstractA companion paper in this Special Issue reviewed the development of a hydrological model of the Silala River basin, using long‐term data (1969–1992) to determine the basin's water balance and plausible groundwater recharge scenarios. In the context of a remote river basin with limited in situ data, this article reviews the potential of in situ and remotely collected data, available for a relatively short period (2018–2019), to validate various aspects of the hydrological model performance. These include the spatiotemporal evolution of snow cover areal fraction (SCF), actual evapotranspiration (ETa) in the basin's extensive alluvial deposits, and wetland ETa. The observed SCF dynamics are well represented by the model at annual and monthly timescales, with monthly mean simulated SCF biases between −5.6% and 8%. At daily timescales, the model successfully captures snowstorm occurrence, although there are limitations on snow spatial patterning. Simulated ETa over alluvial deposits agrees with in situ observations during periods of high ETa, although the simulated values underestimate site‐specific observations during low ETa periods, due to the presence of lateral subsurface flows. In the wetlands, satellite‐based ETa estimates follow the seasonal pattern of in situ observations, but with values ~50% higher than those determined from elevation‐corrected eddy‐covariance (EC) measurements. Nonetheless, this difference is within the expected precision of the remote sensing method. Although based on a limited period, the validation results are encouraging, and demonstrate the utility of satellite tools and limited period in situ data for watersheds with scarce long‐term data.This article is categorized under: Science of Water > Hydrological Processes

Influence of the 2020 Seismic Hazard Update on Residential Losses in Greater Montreal, Canada

Greater Montreal is situated in a region with moderate seismic activity and rests on soft ground deposits from the ancient Champlain Sea, as well as more recent alluvial deposits from the Saint Lawrence River. These deposits have the potential to amplify seismic waves, as demonstrated by past strong, and recent weak, earthquakes. Studies based on the 2015 National Seismic Hazard Model (SHM5) had estimated losses to residential buildings at 2% of their value for an event with a return period of 2475 years. In 2020, the seismic hazard model was updated (SHM6), resulting in more severe hazards for eastern Canada. This paper aims to quantify the impact of these changes on losses to residential buildings in Greater Montreal. Our exposure database includes population and buildings at the scale of dissemination areas (500–1000 inhabitants). Buildings are classified by occupancy and construction type and grouped into three building code levels based on year of construction. The value of buildings is obtained from property-valuation rolls and the content value is derived from insurance data. Damage and losses are calculated using Hazus software developed for FEMA. Losses are shown to be 53% higher than the SHM5 estimates.

The Great Boundary Fault in the Indo-Gangetic foreland basin: A geomorphological perspective

Identifying active faults in alluvial plains with varying sedimentation rates, erosion, and extensive anthropogenic modifications is challenging. In tectonically active foreland basins, tectonics outweighs other controlling factors and produces a set of key fluvial geomorphic markers that are critical for precisely locating active faults. This study employs several key tectonic fluvial morphometric parameters, seismically induced soft-sediment deformation structures (SSDS) as seismites, and the displaced rocks of the Siwalik mountains to mark the surface positions of a buried basement fault system, namely the Great Boundary Fault (GBF) beneath the alluvial cover of the Indo-Gangetic foreland basin.The Great Boundary Fault (GBF) is a NE-SW trending, oblique-slip, branching reverse basement fault running from peninsular India to the Sub-Himalayas. About 400 km length of its NE segment is buried under thick sediments of the Indo-Gangetic foreland basin. This fault's surfaceward propagation deforms the overlying sediments via a network of subsidiary faults, resulting in 20 km wide broad fault zones. The extreme flatness of the Ganga plain conceals the primary faulting evidence but tectonic fluvial geomorphic signatures, the SSDS, and the laterally displaced Siwalik rocks, including south-verging thrusts at the frontal Himalayas, provide collective evidence of neotectonic activity along both fault branches. The primary objectives of this study are to characterise the GBF's buried segment in the Ganga plain through the geomorphic signatures and SSDS, to elucidate its extension up to the Main Boundary Thrust (MBT), and to understand the surfaceward propagation mechanism of its reverse faults through the alluvial-fills.Tectonic geomorphic parameters such as sinuosity spectra and knickpoints were analysed using ArcGIS and Matlab. Meander scar mapping was carried out using Google Earth Pro and Landsat imagery within ArcGIS to characterise the pattern of avulsions and adjustments of the floodplain linked to the tilting directions of the fault blocks.Fourteen prominent knickpoints of 4 to ≥6 m height were derived from the river profiles across the fault zone. Rivers on the up-thrown block possessed low sinuosity (as low as 1.1), whilst those on the down-thrown block had higher sinuosities (up to 3.1), indicating active uplift and rapid subsidence. The deflection of multiple river courses (Ganga, Ramganga, Burhiganga, Sot, Pangaili, and Deoha) and the presence of asymmetrical meander-belts demonstrate an eastward tilting of the tectonic block. The occurrence of liquefaction-induced SSDS close to the GBF corroborates its recent seismogenic nature. Field observation suggests these SSDS are likely related to the Usawan paleo-earthquake (estimated magnitude of 6.5–7.2), epicentered near the GBF. Based on the geometry and the venting characteristics, a new type of SSDS has been recognized, and the term “liquefaction vents” has been proposed for it. Their association with the other types of SSDS that are characteristically formed by >6.5 magnitude earthquakes suggests it is the minimum magnitude of earthquake required for the formation of liquefaction vents. The regional seismic record suggests a significant number of both large and moderate earthquakes around this fault.Finally, we synthesise the results to propose a growth model for the propagation of reverse faulting from the underlying basement bedrock through to the alluvial sediments and the surface of the Ganga plain.

Subcretion of altered oceanic crust beneath the SW São Francisco Craton, Brazil – A stable isotope study on diamonds and their inclusions

The presence of diamonds of lherzolitic, eclogitic and websteritic paragenesis in proximal alluvial deposits on the southwestern edge of the São Francisco Craton documents the incorporation of subducted oceanic crust and associated metasomatism through slab dehydration fluids affecting the local SCLM. To better constrain the subduction-association of diamond substrates and metasomatic events, we conducted a combined study of the δ13C-δ15N-[N] characteristics of 81 diamonds and the δ18O values of four of their eclogitic garnet inclusions. Diamond carbon isotope compositions range from −25.5 to +0.5‰, with 13C-depleted diamonds (≤ −7‰) being exclusively of eclogitic/websteritic paragenesis while the 13C-enriched (≥ −2‰) tail of the distribution is related to diamonds with lherzolitic inclusions. Nitrogen isotope values range from −14.2 to +25.5‰, with about half of the values being positive. A general absence of coherent trends in δ13C-δ15N-[N] across growth zones implies that diamond formation did not occur under fluid-limited conditions. Instead, the observed heterogeneity in carbon and nitrogen isotope compositions reflects contributions of distinct source reservoirs hosted in both altered oceanic crust and Earth's mantle. Nitrogen contents peak around a δ15N value of −3.5‰, indicating that more N-rich fluids, presumably representing a primitive endmember composition, have a mantle-like δ15N signature. While positive and negative δ15N values occur equally near the δ13C mantle value (−5 ± 2‰), 13C-depleted diamonds have nitrogen isotope compositions skewed towards positive values.13C depletion and 15N enrichment is a signature of biogenic carbonates/organic matter and low-T clays in uppermost, basaltic sections of oceanic crust that experienced low-temperature seawater alteration prior to subduction. Correspondingly, the oxygen isotope compositions of eclogitic garnet inclusions fall in a restricted range between +5.5‰ to +7.0‰. For three of the four samples, the stable isotope signatures of inclusions and host diamonds display perfect agreement, with the intensity of seawater alteration signatures, in the form of garnet inclusion 18O enrichment and host diamond 13C depletion and 15N enrichment, increasing together. For the fourth sample, the δ18O signature of the garnet inclusion (+5.5‰) and δ13C-δ15N signatures of the diamond host (−25 and + 19‰, respectively) are decoupled. While the mantle-like δ18O signature indicates a diamond substrate derived from deeper levels in oceanic crust (e.g., deep sheeted dikes), the diamond-forming fluids must have originated from sources that originally resided near the sea water interface. A viable mode of mixing such disparate isotopic signatures is the interaction of diamond-forming fluids derived from shallow oceanic crust altered at low-temperatures with eclogitized substrates originally formed in deeper levels of oceanic crust. This process likely occurred during diamond formation in a tectonic subduction mélange, which juxtaposes deeper and shallower levels of oceanic crust. In the lithospheric mantle above the subcreted oceanic slab, the elevated carbon isotope and highly variable nitrogen isotope compositions of diamonds formed in lherzolitic substrates likely relate to devolatilization and/or melting of principally oceanic sediments containing marine carbonates and clays and subsequent mixing with mantle-derived volatile components. In combination, our diamond and inclusion stable isotope data provide insight into multiple processes that promote diamond formation both inside subducted slabs accreted to the São Francisco cratonic keel and in adjacent subcontinental lithospheric mantle.

Nitrate stimulated microbial and viral activity and the subsequent influence on uranium mobility in sedimentary systems

Mobilization of naturally-occurring uranium(U) has been recognized to give rise to geogenic U groundwater contamination in aquifers. In addition to carbonate ligand complexation, nitrate has been demonstrated to play a role in controlling U mobility by altering uranium solubility through redox reactions. Nitrate is a common anthropogenic contaminant often prevalent at high concentrations in alluvial aquifers overlaying managed land. Alluvial deposition processes that form these aquifers create a lithologically heterogeneous subsurface with defined contacts between sands, silts, and clays. This leads to deposition of organic carbon and accumulation of reduced metals/radionuclides, including U(IV), in the finer grained silts and clays. The addition of high nitrate porewater into uranium-bearing alluvial aquifer silt sediments stimulated a nitrate reducing microbial community capable of catalyzing U(IV) oxidation and mobilization of U into porewaters. However, metadata from an aquifer wide study and a subsequent experiment revealed that this result is concentration dependent. Low concentrations of nitrate bearing pore-water added into organic-rich, uranium bearing sediments and resulted in a decrease in dissolved U(VI), consistent with reduction. XANES analysis of sediments supported U(VI) reduction with the precipitation of U(IV). U(VI) reduction activity occurred concurrent with an increase in dissolved organic carbon (DOC) and cell and virus abundance and activity. Metagenome assembled genomes from the microbial community revealed the metabolic potential indicating complex carbon degradation, fermentation, mineralization as well as the potential for anaerobic respiration of nitrate, metal/radionuclides, and sulfate. The virome recovered from the samples indicated a change in viral community in response to nitrate amendments and viral-encoded carbohydrate active enzymes were upregulated indicating a coupled response of both viral and microbial community regulating nitrate stimulated carbon biogeochemical cycling. These data together suggest that the addition of an electron acceptor in to organic carbon reduced sediments stimulates not only microbial but also viral activity leading to upregulation of genes associated with carbon biogeochemical cycling in sedimentary systems. While genes associated with metal oxidation are observed, net reduction of uranium prevails leading to uranium immobilization at low nitrate concentrations. Thus together these data indicate a tipping point whereby the influx of nitrate into the reduced environment can influence uranium mobility in DOC and carbon cycling supporting microbial activity and reducing conditions subsurface systems.

Typification of hydrogeological conditions in mineral deposits by system analysis method

The paper presents a non-standard approach to the typification of mineral deposits in Eastern Siberia (Russia) according to hydrogeological conditions under insufficiency and unevenness of the initial information. The most rational way to solve this problem at initial research stages is to identify a number of easily determined indirect indicators that determine the selection of sites promising for drilling hydrogeological wells. The author uses the method of system analysis including two main stages of analysis and synthesis, which result in the typification of the objects under study in accordance with the assigned tasks. The developed methodology is used for various purposes: structural hydrogeological zoning of the Ilim-Lena plateau with associated main iron ore deposits of Eastern Siberia, typification of alluvial deposits of the Lena gold ore region according to the complexity degree of engineering hydrogeological conditions, identification of the sites with high water abundance in the oil and gas fields of Eastern Siberia.

Rapid laminated clastic alluviation associated with increased Little Ice Age flooding co-driven by climate variability and historic land-use in the middle Severn catchment, UK

The analysis of exceptionally well-preserved visible clastic laminations in deep alluvial sediments at Kempsey, Worcestershire (UK), allows a new high-resolution analysis of late-Holocene flood-history in the largest UK catchment, as well as local human response. At the sample site over 4.5 m of sandy-silt overbank-alluvium accumulated on the floodplain and optically stimulated luminescence (OSL) dating of the upper 2.25 m demonstrates accretion from the late 14th century CE onwards. Sub-centimetre to centimetre resolution multi-proxy sediment analysis (loss on ignition, magnetic susceptibility, particle size, ITRAX and portable XRF) demonstrate clear variations in depositional history over the last millennium due to channel stability. Between c. 1380 and 1550 CE overbank sedimentation was driven by lower energy flood events, with negligible effect from climatic conditions during the Spörer Minimum (1460–1550 CE). After c. 1550 CE the magnitude of flooding events increased and by c. 1610 CE, the start of the visible sub-centimetre laminations, the accumulation rate regularly exceeded 3 mm year−1, which increased to 4.5 mm year−1 between c. 1690 and 1710 CE, and 3 and 3.5 mm year−1 between c. 1790 and 1840 CE before alluviation was altered by an embankment. The greatest extent of coarse overbank deposition and increased accumulation rate occur concurrently with periods of climatic instability associated with the Maunder (1645–1715 CE) and Dalton (1790–1820 CE) Minima, the periods of largest historical floods and during the intensification of arable cultivation across the middle Severn catchment. This data correlates well with other sites in the catchment suggesting that these are basin-wide forcing-responses. We also present evidence that this catchment-wide hydro-geomorphological history had local effects in shifting the geographical focus of an important settlement away from its historic floodplain edge location – which can be viewed as an adaptation to the flood risk.

Groundwater potentiality in hard-rock terrain of southern Saudi Arabia using electrical resistivity tomography approach

To detect groundwater-bearing zones in southern Saudi Arabia, 10 profiles of 2D electrical have been constructed resistivity tomography at five selected sites. The collected data were corrected and processed using the RES2DINV software. The results demonstrated that site-1 contains two groundwater-bearing zones; the first zone is situated 13 m beneath the ground surface, while the depth of the second zone varies from 4 m to 15 m. A promising 15-m-deep groundwater-bearing zone was identified at site 2. The groundwater-bearing zones exhibit depths of 40, 10, and 10 m at sites 3, 4, and 5, respectively. The detected groundwater-bearing zones are notably shallow, with a depth of 20 m below the ground surface and with lateral extension up to 200 m. These aquifers prevail in the alluvial deposits, where the weathered/fractured or fresh basement rocks underlying these aquifers. Moreover, rainfall recharges these unconfined aquifers, as evidenced by the increasing water levels along the main Wadi channels flow during rainy seasons. Sites 2, 3, and 5 are considered as groundwater-bearing sources with high potential. Because this unconfined aquifer can be swiftly replenished by the 300–360 mm of annual rainfall in the southern Saudi lowlands, it is a promising area for groundwater supply for future urbanization plans and agricultural projects in neighboring areas.

Estimating Groundwater Flow Velocity in Shallow Volcanic Aquifers of the Ethiopian Highlands Using a Geospatial Technique

The shallow volcanic aquifer is the major rural water supply source in the Ethiopian highlands. A significant number of hand pump wells in these aquifers experience a rapid decline in yield and poor performance within a short period of time after construction. Hence, reliable estimation of groundwater flow velocity is important to understand groundwater flow dynamics, aquifer responses to stresses and to optimize the sustainable management of groundwater resources. Here, we propose the geospatial technique using four essential input raster maps (groundwater elevation head, transmissivity, effective porosity and saturated thickness) to investigate groundwater flow velocity magnitude and direction in the shallow volcanic aquifers of the Ethiopian highlands. The results indicated that the high groundwater flow velocity in the Mecha site, ranging up to 47 m/day, was observed in the fractured scoraceous basalts. The Ejere site showed groundwater flow velocity not exceeding 7 m/day in the fractured basaltic aquifer and alluvial deposits. In the Sodo site, the groundwater flow velocity was observed to exceed 22 m/day in the fractured basaltic and rhyolitic aquifers affected by geological structures. The Abeshege site has a higher groundwater flow velocity of up to 195 m/day in the highly weathered and fractured basaltic aquifer. In all study sites, aquifers with less fractured basalt, trachyte, rhyolite, welded pyroclastic, and lacustrine deposits exhibited lower groundwater flow velocity values. The groundwater flow velocity directions in all study sites are similar to the groundwater elevation head, which signifies the local and regional groundwater flow directions. This work can be helpful in shallow groundwater resource development and management for rural water supply.