Sedimentary Processes Research Articles

Study on the regularities of flow‐sediment transport and sedimentation in the lower Yellow River

AbstractThe training effectiveness of the lower Yellow River (LYR) depends on the understanding of the regularity of flow‐sediment transport and riverbed sedimentation. The measured data of daily flow discharge and sediment transport rate at the five hydrological stations (Xiaolangdi [Xld], Huayuankou [Hyk], Gaocun [Gc], Aishan [As], and Lijin [Lj]) in the LYR during the period from 1960 to 2017 are used to investigate the regularity of flow‐sediment transport and sedimentation in the LYR. The Xld station is used as the inlet control station, and the LYR is divided into four segments using four other stations, and the whole year is divided into three periods, namely, the dry season, the flood period, and the nonflood period of the wet season. On this basis, the relationships between the sediment transport rates at the four stations (Hyk, Gc, As, and Lj) and the rates at their respective closest upstream stations are analyzed in each of the three periods. According to the incoming sediment coefficient of the Xld station, the flow and sediment processes in the three periods are classified, and the refined equations for the relationship between the sediment transport rates at the downstream station and its upstream station are established. The results show that the calculated amount and process of erosion and deposition in each period and each segment of the LYR using the equations are in good agreement with the measured values. The relationship equations established in this study can conveniently predict the amount of erosion and deposition in different periods and different segments of the LYR in the future, which is of great significance to the rapid decision of the impact of the construction and operation of hydraulic projects in the upper and middle reaches of the Yellow River on the sedimentation in the LYR.

Exploring electron backscatter diffraction analysis as a tool for understanding stromatolite: Quantitative description of Cretaceous lacustrine stromatolite reveals formative processes and high‐resolution climatic cycles

AbstractLacustrine stromatolites serve as important archives for recording environmental changes, and the detailed examination of their microfabrics is essential for understanding their formative processes and the environmental changes embedded within them. This study explored the application of Electron Backscatter Diffraction combined with Energy‐Dispersive X‐ray Spectroscopy to investigate a well‐preserved middle Cretaceous lacustrine stromatolite from south‐eastern Korea, unveiling ultra‐high‐resolution sedimentary processes that are often challenging to observe using conventional methods. Two types of microsparitic layers and one type of crystalline layer are distinguished based on their texture, crystal morphology and elemental composition. Both microsparitic layers are micrometre‐thick and are characterized by poorly co‐oriented calcite grains, but differ in their composition. Type 1 is depleted in magnesium but enriched in detrital elements such as silicon and aluminium, likely originating from the trapping and binding of detrital sediments on microbial mats during rainy seasons. In contrast, type 2 is enriched in magnesium but devoid of detrital elements, interpreted to have formed by the precipitation of calcium carbonate during dry seasons. The crystalline layers comprise fan‐shaped calcite crystals (ca 500 μm in length) with radiating internal structures, with their c‐axes oriented perpendicular to the stromatolite layers. These structures resemble those observed in some modern freshwater stromatolites, which are interpreted as imprints of cyanobacterial fascicules. While the cyclic occurrence of types 1 and 2 microsparitic layers might imply annual seasonal cycles, the less frequent crystalline layers are interpreted as a result of environmental changes occurring every 27 to 30 years. This is the first study to apply Electron Backscatter Diffraction to stromatolites, showcasing its potential in unravelling both the formative and diagenetic processes of ancient stromatolites.

Geographical factor dominates spatial patterns of potential nitrate reduction rates in coastal wetland sediments in Fujian Province, China

Nitrate (NO3−) reduction is a key process governing the nitrogen (N) dynamics of coastal wetland sediments. Although the effects of environmental factors on the NO3− reduction mechanism in coastal wetland sediments have been examined in various studies, the effects of spatial variation in potential NO3− reduction processes in coastal wetland sediments and the factors driving geographical variation in these processes have not been widely examined. Here, we conducted research on surface sediment samples from four different vegetation types at six coastal wetland sites across two regions. We characterized potential rates of NO3− reduction processes (including denitrification (DF), anammox (ANA), and dissimilatory nitrate reduction to ammonium (DNRA)) using a15N tracer method. Additionally, we assessed the abundances of functional genes, and microbial community structure using high-throughput sequencing, and metagenomic sequencing. In six wetland sites, the contribution ranges of DF, ANA, and DNRA to NO3− reduction were 38.43%–55.69%, 31.33%–45.65%, and 5.26%–17.11%, respectively, and potential NO3− reduction was mainly driven by N removal via gaseous N (DF+ANA). Significant spatial differences were observed in the structure of bacterial and fungal microbial communities, suggesting that geographical distance has a major effect on microbial community structure. Environmental factors and Functional gene abundances were significantly related to potential NO3− reduction processes, and physicochemical properties had a stronger effect on potential NO3− reduction processes than gene abundances. Factors showing significant differences across regions were the main drivers of variation in potential NO3− reduction processes. Overall, our study showed that sediment substrates and geographical environmental factors rather than the abundance of functional genes and vegetation types were the main indicators of potential NO3− reduction activities in coastal wetlands.

Sediment Transport Mechanism and Provenance of Unconsolidated Sediments in Opak River Channel, Yogyakarta, Indonesia

This study focuses on the Opak River, which crosses administratively through two regencies, Sleman and Bantul. This research aims to reveal the sedimentation mechanism and provenance of Opak River sediment based on textural and sedimentary composition. Sediment samples were collected from ten points along the river channel, spanning from upstream to downstream. Granulometric and grain morphology analysis were conducted which the followed by QFL analysis wherein the presence of light detrital minerals (quartz, feldspar, lithic) was observed. The sediment texture of Opak River Channel generally consists of coarse-grained sand, poorly sorted, with varying degrees of roundness and sphericity, which are angular to sub-rounded and intermediate to sub-equant, respectively. Opak River sediment predominantly comprises Feldspar (20-48%), Quartz (4-17,9%) and Lithic (13,5-19,6%) which implies arkose-lithic arkose type. The sedimentation process in Opak River is mainly driven by the traction process, which is indicated by a 48-79% traction fraction on the probability log curve. Based on QFL analysis, it is inferred that the Opak River sediment originated tectonically derived from a magmatic arc setting, specifically a transitional arc subtype. The primary sediment source could have been derived from Mount Merapi with a potentially strong influence by the Oyo River, especially in the downstream of Opak River.

Exploring the alteration of environmental radioactivity in terms of compositional elements of heavy minerals in an anthropogenically affected urban river: Radiological and ecological risks assessment

This study explored the alteration of naturally occurring radioactive materials (NORMs: 226Ra (≈238U), 232Th, 40K) in an anthropogenically disrupted urban river-basin (Turag, Bangladesh) in terms of constitutional substances (Sc, Ti, V, Fe, La, Ce, Sm, Eu, Tb, Dy, Ho, Yb, Lu, Hf, Ta, W, Th, U) of heavy-minerals. Average activity concentrations of 226Ra (≈238U), 232Th, and 40K were 41.5 ± 12.9, 72.1 ± 27.1, and 639 ± 100 Bqkg−1, respectively which were relatively higher compared to crustal origin. ∑REEs, Ta, W, Th, and U were ~2 times higher compared to crustal values with Ce and Eu-anomalies. APCS-MLR and PMF receptor models were used to determine the various anthropogenic and/or geogenic sources of NORMs and elements. Layer-wise variations of NORMs and elements were observed to trace the response of sedimentary processes towards the incoming pollution load. Presence of REEs indicates moderate degree of ecological risk to aquatic biota. However, carcinogenic risk (3.84 × 10−4 Sv−1) were significantly higher than threshold limit.

Control of paleoclimate and paleoweathering on chromium contents in a non-ultramafic aquifer hosting high chromium groundwater.

Cr(VI) is a carcinogen with proven mutagenic and genotoxic effects. The effects of the depositional environment (e.g., paleoweathering, paleoclimate, and paleoredox condition) on Crenrichment in non-ultramafic aquifer solids are unclear. In this study, we presented the sedimentary characteristics of a borehole from a typical non-ultramafic aquifer with high Cr groundwater in Jingbian, central Ordos Basin, China. Chromium was enriched in the K1h sandstone aquifer, especially at depths of 400-500m, with the highest value of mass transport coefficient (τAl,Cr) up to 92.13% and τAl,Fe up to 33.5%. The provenance of aquifer Cr was predominantly intermediate and felsic igneous rocks with a mafic rock mixture. This mafic source was inferred from Cr-rich granodiorite and mafic/ultramafic rocks in the Yinshan (Daqingshan-Wulashan) Block, northern Ordos Basin. The Cr-rich aquifer in K1h was developed due to a moderate chemical index of alteration (CIA) (mean, 56.7) under relatively warm and humid paleoclimate, as evidenced by high CIA-temperature (CIA-Temp) (mean, 6.79°C) and paleoclimatic index values (mean, 0.40). Fe-Mn redox cycling in the oxic to suboxic environments contributed to aquifer Cr accumulation. Using path analysis, we identified that paleoclimate created favorable weathering conditions and enrichment of Fe contributed to the formation of high-Cr aquifers. The study reveals the formation of positive Cr anomalies in non-ultramafic aquifers, which is the potential source of groundwater Cr, and highlights the effects of depositional factors on Cr accumulation during aquifer deposition or early diagenesis. It can provide new insights into the natural processes of high-Cr sediments occurring in non-ultramafic aquifers.

In situ measurement of the three-dimensional distribution of labile copper in sediment pore water using a microneedle sensor with nanoporous structure

Conventional ex situ analytical methods for sediment pore water are susceptible to disruptions in the speciation equilibrium of metals due to changes in external conditions. This study introduced an innovative in situ method for detecting the three-dimensional distribution of labile copper (CuLabile) in sediment pore water with high spatial resolution using a highly stable microneedle electrochemical sensor. The sensor featured a nanoporous tip structure and embedded gold nanomaterials with excellent electrocatalytic performance. The nanoporous structure could prevent the nanomaterials from falling off because of friction during the in situ detection process in sediments. The sensor exhibited good detection performance under different salinity conditions with a detection limit of 0.2 nM. Vertical and three-dimensional distributions of CuLabile in sediment pore water were successfully obtained using the in situ microneedle sensor. The results showed that the concentration of CuLabile was in the range of 5.2–43.5 nM, with a maximum value at a depth of approximately 4 cm, while there was almost no difference in the horizontal direction of a specific sediment sample column. Furthermore, this functional sensor could be extended to the in situ detection of other labile metals in sediment pore water.

The Ironberry Plan: an Electric and Steel-making Way to Build a Science Station on Mars

This paper introduces the Ironberry Plan. This practical plan leads to the construction of a science station in the iron region of the Meridiani Planum (IRoM), Mars. It also enables the continuation of NASA’s Water Strategy, the beginning of astronomy from Mars, the landing of humans at IRoM and the beginning of continuous human habitation there. A focus of the plan is to provide abundant electricity on Mars through an intense use of local resources. The characteristic early steps of the Ironberry Plan are: 1. The robotic harvesting and processing of a superb iron ore at IRoM; 2. The use of Mars-optimized, robot-controlled steel-making and manufacture of steel parts; 3. At least for some years, a deliberate push for mutually feeding exponential growth in electricity generation, steel-making and steel manufacture, where early steel manufacture is focused on making more electrical generation equipment; 4. Using the rapidly growing power capacity and advanced robotics and processing of local sediments, the start of many more foundational activities (i.e., water liberation, sulfur-concrete construction, multi-material manufacture, agriculture and more); 5. Using 1-4, the building of a science station at IRoM while also converting excavated sediment caverns into underground, radiation protected spaces for the science station. Keywords: Ironberries, Iron Region of the Meridiani Planum (IRoM), Science Station, Abundant Electricity, Steel-making

Morphology and evolution of submarine canyons around the Zhongsha Platform, South China Sea: Implications for sedimentary processes in a modern isolated carbonate setting

Recent high-resolution multibeam bathymetry and seismic data from the platform-top to the abyssal plain of the Zhongsha Platform allow for a detailed investigation of the morphologies, spatial distribution, and trigger mechanisms of submarine canyons, submarine landslides, and associated sedimentary features along modern isolated carbonate slopes. The newly observed Zhongsha Canyon System provides a natural laboratory for reconstructing the source-to-sink sedimentary processes in a pure carbonate setting. This study reveals that there are thirty-four submarine canyons at water depths between 300 and 4100 m on the northern and western slopes of the Zhongsha Platform. Two morphologically different submarine canyon types are identified: (1) dendritic canyons, which exhibit abundant tributaries with scallop-shaped failures at the canyon heads, and (2) linear canyons, which feature rare tributaries with elongated failures at the canyon heads. The dendritic canyons are more complex in morphology than the linear canyons as a result of the interaction among numerous tributaries. Canyon initiation and evolution pass through three phases: (1) initial stage: off-platform sediment transport and platform margin failures contribute to erosive gravity flows; (2) developmental stage: initiation and incision of submarine canyons along platform margin failures; and (3) mature stage: numerous mature canyons along the platform margin. Off-platform sediment transport, density cascading, gravity flows, monsoon currents, and deep circulation play an essential role in shaping the slope morphologies. In addition, submarine landslides are extensively observed along the entire slope of the Zhongsha Platform at water depths of 600 to 4200 m, including canyon-wall failures, slope landslides, canyon-front landslides, and slope-toe failures based on their location and genesis. These processes can steepen the platform slopes by upward retrogressive and downward progressive erosion. On a larger scale, the persistent submarine canyons and occurrence of landslides around the Zhongsha Platform contribute to the uniqueness of this landscape among modern carbonate slopes. The morphologies and evolutionary processes of Zhongsha Canyon System present significant differences from the global carbonate submarine canyons in terms of their dimensions and trigger mechanisms. The findings of this work provide novel insights into the morphological features and sedimentary processes of submarine canyons in modern isolated carbonate platform settings.

Analysis of Land Use Changes in the Sado Estuary (Portugal) from the 19th to the 21st Century, Based on Historical Maps, Fieldwork, and Remote Sensing

This study analyses land use changes in the Sado Estuary (West-Central Portugal) based on a multi-temporal analysis of 19th century cartographic data and 21st century remote sensing land use maps, updated by fieldwork. A GIS plot of land use evolution is summarized in a quantitative table. The comparison shows the changes in land use, with increasing occupation by human economic activities, including extensive agriculture and forestry, as well as localized urbanization and industrialization. The main elements of the landscape impacted by anthropogenic uses were (i) hydrography—river dams affected the flow dynamics and sedimentary processes in the estuary; (ii) vegetation—increasing agriculture and forestry reduced the area of native vegetation, which is now mostly occupied by vineyards, pine forests and cork oaks; (iii) wetlands—tidal and alluvial plains are being occupied by rice cultivation, aquaculture, industries, and ports; (iv) coastal dunes—new developments are occupying large areas of Holocene coastal dunes; and (v) natural environment—mining and dredging have affected some habitats and biodiversity. This analysis is intended to help the territorial organization of present and future economic activities, as well as to reduce environmental and social problems, thus promoting the long-term sustainability of this rapidly evolving region.

Depositional processes in a shale-dominated Devonian succession: Sedimentary facies and trace fossil integrated analysis

Fine-grained rocks have historically been interpreted as a product of the settling of fine fractions in low-energy environments. However, recent studies have suggested that in these environments, more dynamic and complex processes operate. These processes involve a much more diverse set of sedimentary processes than those previously assumed. The lithological homogeneity of clayey successions, associated with the obliteration of their primary characteristics by diagenetic and/or weathering processes, makes it difficult to interpret depositional processes and understand the paleoenvironment. To contribute to a better comprehension of the mechanisms of transport and deposition of fine-grained rocks in a siliciclastic mud-dominated succession, as well as their depositional site, the present study aims at the detailed analysis of a continuous drill core. This core contains a thick Devonian succession consisting essentially of shale from the Ponta Grossa Formation (Paraná Basin, Brazil). Throughout the analyzed succession, a wide variety of sedimentary structures have been identified, such as parallel laminations, wave-ripple cross-stratification, hummocky cross-stratification, normal grading, and gutter casts. These structures show the constant performance of high-energy flows, which are configured as important deposition and/or rework agents. The integrated analysis of facies and trace fossils has proven to be more efficient for paleoenvironmental characterization than isolated approaches. This is because facies and ichnofacies (e.g., Cruziana, with its proximal, impoverished, archetypal, and distal expressions; Skolithos and Glossifungites) can be easily correlated, facilitating the identification of facies associations. This approach not only allows for the interpretation of a shallow marine platform with a gentle slope (ramp shelf) paleoenvironment of moderate to high energy, subject to storm wave action, but also enables the identification of the particular characteristics of deposits from different sub-environments (proximal to distal offshore, offshore transition, shoreface to offshore transition, and prodelta) and their deposition mechanisms. Furthermore, the facies associations are useful for highlighting the variations formed in response to oscillations of the relative sea level and changes in sedimentary input.

Impact of Anthropogenic Activities on Sedimentary Records in the Lingdingyang Estuary of the Pearl River Delta, China

High-intensity anthropogenic activities have greatly altered the estuarine-shelf depositional processes of sediments, and the intensity and frequency of the impacts of human interventions have far exceeded the natural development of estuarine systems. Since the reform and opening up, human activities such as dams, sand mining, channel dredging, and reclamation have already caused anomalous changes in the dynamical–sedimentary–geomorphological processes of the Lingdingyang Estuary (LE). Analyzing the impact of high-intensity anthropogenic activities on sedimentary processes and the hydrodynamic environment through sedimentary records can provide a scientific basis for predicting the evolution of the estuary and the sustainable development of the Guangdong–Hongkong–Macao Greater Bay Area. The aims of this study are to reveal the impact of varying intensity human activities across different periods on depositional pattern and conduct a preliminary investigation into the spatial differences in sedimentary characteristic attributed to human activities. Two cores (LD11 and LD13) located in the LE were selected for continuous scanning of high-resolution XRF, grain size, and 210Pbex dating tests, and scrutinized with the previous studies of the historical process of human activities in the LE. The results show the following: (1) The abrupt alterations in 210Pbex, geochemical indices, and grain size in LD13 happened in close proximity to the 95 cm layer, suggesting a shift in the sedimentary environment during 1994. (2) In the context of the continuous reduction in water and sediment flux into the LE after 1994, the large-scale and high-intensity human activities like sand mining, channel dredging, and reclamation are responsible for the sedimentation rate increase rather than decrease, the coarsening of sediment fractions, the frequent fluctuations in Zr/Rb, Zr/Al, Sr/Fe, and Sr/Al ratios, and the increase in anomalous extremes. (3) Sedimentary records found in locations varying in anthropogenic intensities differ greatly. Compared with the nearshore siltation area, the grain size composition in the channel area is noticeably coarser and exhibits a wider range of grain size variations. The 210Pbex is strongly perturbed and the vertical distribution is disturbed; the phenomenon of multiple inversions from the surface downwards is shown, making it impossible to carry out sedimentation rate and dating analysis, and the geochemical indicators have changed drastically without any obvious pattern. The evidence of the human activities can be retrieved in the sedimentary record of the estuary and provide a different angle to examine the impacts of the human activities.

Proposal for New Method for Calculating Sedimentation Process Efficiency in Water Treatment Plants.

An important aspect of water treatment is removing fine-grain materials from water. Due to the properties of fine-grain materials, they are difficult to remove from water. During the sedimentation process, which takes place in settling tanks, such materials are removed. The sedimentation process is often accompanied by coagulation and flocculation processes, which form aggregates of particles (flocs) from the fine-grained material particles in a suspension (non-grainy suspension). This kind of suspension (consisting of aggregates of particles or flocs) shows a different behaviour when falling compared with classic grainy suspensions. The main goal and novelty of this article are to propose (and test) a modification of the often used Stokes' formula with the addition of fractal geometry into the calculation of the terminal velocity of free-falling particles in order to overcome Stokes' formula's limitation, thus obtaining the sedimentation process efficiency. Because of this fractal modification, it is possible to use the simple and elegant Stokes' formula in order to calculate better the terminal velocity of non-grainy particles-aggregates or flocs-and thus obtain the sedimentation efficiency for the whole range of suspensions, both non-grainy and grainy. The results obtained in this article show that the sedimentation process efficiency calculated by using the modified formula based on the fractal geometry morphology of particles (the proposed fractal method) describes and agrees more with the data from the experiment than the sedimentation efficiency calculated only based on particle size (classic method).

Quartz grain microtextures of Holocene sebkhas sediments in southeast Tunisia: Implications for sedimentary processes and depositional environments

Detrital quartz grains extracted from sebkha sediments in southeastern Tunisia underwent scanning electron microscopy analysis to identify sediment sources and assess the influence of the saline environment on the grains. Core sediments collected from Sebkha el Melah and Sebkha Mhabeul cover the last 5000 and 2000 BP, respectively. The uppermost Unit III, present in both cores, exhibits two distinct facies based on the mechanical microtextures of its quartz grains. The aeolian facies sediments are characterized by quartz grains with rounded outlines, upturned plates, and crescentic percussion marks. In contrast, the fluvial facies sediments are associated with quartz grains featuring subangular outlines, v-shaped percussion cracks, conchoidal fractures. Observations on the quartz grains of the sebkhas suggest multiple transportation and processing events, indicating long-distance transport and rapid deposition rates. The majority of quartz grains appear to originate from the surrounding terrain, reflecting the dynamic geological history of the region. This study delves into the connection between microtexture variations on quartz grain surfaces and specific historical climatic conditions in the sebkhas. By examining geochemical variations along the cores, facies with elevated salt concentrations corresponding to warmer periods reveal extensively weathered quartz grains. This substantial chemical alteration is evident through microtextures such as oriented etch pits, anastomosed dissolution networks and solution crevasses. The profound dissolution has significantly impacted the quartz lattice, resulting in the decomposition of the grains and the formation of "cauliflower" or "spongy" shapes, erasing prior microtextures. Conversely, during less warm periods, quartz dissolution was less severe, thereby preserving microtextures.Sand grain surfaces are notably sensitive to both transport processes and variations in the physicochemical environment. In the hypersaline and confined environments of sebkhas in southeastern Tunisia, potent post-sedimentary processes can obliterate and obscure the original microtextures recorded on grains from previous environments due to highly fluctuating physicochemical conditions.

TECHNOLOGICAL COMPLICATIONS (FORMATION DAMAGE) DURING CO2 INJECTION FOR ENHANCED OIL RECOVERY. Part 1. GEOCHEMICAL PROCESSES INVOLVING ROCK MINERALS, CHANGE OF PETROPHYSICAL AND GEOMECHANICAL ROCK PROPERTIES

Decrease in permeability, porosity, change in wettability of oil-bearing formations during field development are defined by a general term - formation damage, which occur at various stages of field development, including drilling, production, application of enhanced oil recovery methods, well stimulation technologies with acid compositions, hydraulic fracturing and well workover. Reservoir damage leads to a reduction in the oil and gas content of reservoirs and in the economic efficiency of operation. In this regard, it is important to understand and prevent formation damage based on experimental and analytical methods, the applicationof which will minimize damage to the oil and gas bearing reservoir. The review considers anthropogenic processes that cause damage to oil and gas reservoir when CO2 is injected by various methods to enhance oil recovery. The processes of interaction of CO2 with formation rock are considered in detail. The main geochemical transformations of rock minerals are given, which lead to changes in the structure of pore space, permeability and porosity, decrease of geomechanical properties. Secondary sedimentation processes and risks of rock particles removal into the borehole are discussed.

Unravelling controls on multi‐source‐to‐sink systems: A stratigraphic forward model of the early–middle Cenozoic of the SW Barents Sea

AbstractSource‐to‐sink dynamics are subjected to complex interactions between erosion, sediment transfer and deposition, particularly in an evolving tectonic and climatic setting. Here we use stratigraphic forward modelling (SFM) to predict the basin‐fill architecture of a multi‐source‐to‐sink system based on a state‐of‐the‐art numerical approach. The modelling processes consider key source‐to‐sink parameters such as water discharge, sediment load and grain size to simulate various sedimentary processes and transport mechanisms reflecting the dynamic interplay between erosion in the catchment area, subsidence, deposition and filling of the basin. The Cenozoic succession along the SW Barents Shelf margin provides a key area to examine controls on source‐to‐sink systems along a transform margin that developed during the opening of the North Atlantic when Greenland and Eurasian plates were separated (ca. 55 Ma onwards). Moreover, the gradual cooling which culminated in major glaciations in the northern hemisphere during the Quaternary (ca. 2.7 Ma), has affected the spatio‐temporal evolution of the sediment routing along the western Barents Shelf margin. This study aims to characterize the relative importance of different source areas within the source‐to‐sink framework through SFM. In the early Eocene, the SW Barents Shelf experienced a relatively equal sediment delivery from three principal source areas: (i) Greenland to the north, (ii) the Stappen High to the east, representing a local source terrain, and (iii) a major southern source (Fennoscandia). In the middle Eocene, our best‐fit modelling scenario suggests that the northern and the local eastern sources dominated over the southern source, collectively supplying large amounts of sand into the basin as evidenced by the submarine fans in Sørvestsnaget Basin. In the Oligocene (ca. 33 Ma) and Miocene (ca. 23 Ma), significant amounts of sediments were sourced from the east due to shelf‐wide uplift. Finally, this study highlights the dynamic nature and controls of sediment transfer in multi‐source‐to‐sink systems and demonstrates the potential of SFM to unravel tectonic and climatic signals in the stratigraphic record.

Initiation and evolution of an epicontinental shelf‐slope margin in an actively contracting deep‐water basin: The Eocene Aínsa Basin, southern Pyrenees (Spain)

AbstractThe shelf‐slope margin is a geomorphic zone with a change in gradient between subaqueous shelves and slopes, which extends towards the submarine basin‐floor. It is important because it partitions distinct sedimentary and biogenic processes between the shallow and deep‐water realms. The initiation of a shelf‐slope profile from pre‐existing conditions, and the evolution of shelf margins in space and time has been the focus of numerous studies, particularly from seismic data sets on passive margins, although markedly less‐so from active tectonic settings. This study documents the initiation and evolution of a shelf‐slope margin in the well‐studied Eocene Aínsa Basin (Spanish Pyrenees) through the segmentation of a mixed carbonate‐siliciclastic ramp via contractional tectonics and differential subsidence. The basinward propagation of a series of thrusts through the ramp allowed the maintenance of shallow‐water, predominantly carbonate sedimentation on their uplifted hanging wall anticlines. Conversely, the deepened foot wall synclines became muddy slope environments, and their axes became the main loci of siliciclastic turbidity current bypass and deposition. The deflection of turbidity currents around uplifted areas towards the synclinal lows allowed for the continuation of carbonate production at the bathymetric highs, which kept pace with subsidence. The interface between shallow‐ and deep‐water sedimentation (i.e. the shelf‐slope margin) was an erosional and composite submarine scarp surface generated by several phases of large‐scale mass wasting of the aggrading shelf carbonates, and healing by onlap of slope turbidites against the scarp. Continued thrust propagation and basin deepening led to the progressive headward degradation of the surfaces, resulting in an apparent retrogradation of the shelf‐slope margin and onlapping slope deposits. This model for the tectonically controlled conversion of a submarine ramp into a shelf‐slope profile contrasts with conventional models that consider shelf‐slope margins to be inherently progradational after initiation. This study also challenges the notion that large‐scale degradational surfaces and thick successions of submarine landslides are inherently diagnostic of canyons and their fill.

Provenance of clay-sized detrital sediments in the North Sea and the Skagerrak region based on radiogenic Nd-Sr-Hf isotopes and clay mineral compositions: assessing the impact of coastal and seabed erosion

The Skagerrak basin represents the main sink area for fine-grained sediment in the North Sea region and constitutes a natural deposition center for sediments that are supplied from the Atlantic, the Baltic Sea and the surrounding continental margins and coasts. However, the exact sources and their proportional contributions to the North Sea sediments and to the Skagerrak deposits are not well understood. To trace the predominant sources of the sediment and to gain a better understanding of the sedimentary processes in the North Sea and the Skagerrak basin, radiogenic Sr, Nd, and Hf isotope signatures and clay mineral compositions of the detrital clay fraction of surface sediment samples from the North Sea, the Scandinavian margins and the Baltic Sea were measured. The results indicate that the major source for Skagerrak clay-size sediments is the northern North Sea but Scandinavia as well as the southern North Sea including the southern England coast also contribute material. Seabed and coastal erosion in the northern North Sea are enhanced by the inflowing Atlantic Currents, which provide the Skagerrak with high amounts of clay size sediments. In contrast, the southern North Sea, the Baltic Sea and mid-European rivers such as Weser, Elbe and Ems are only minor contributors. As Skagerrak deposits are dominated by clay sized material (up to 60%), the reconstructed sediment processes in this study deviate from findings in previous sediment budget studies, which were based on both clay and silt fraction and indicated predominant influences from the southern North Sea. These results highlight that coastal and seabed erosion in the North Sea is a previously underestimated source of fine-grained sediments for depocenters in the entire North Sea. With regard to climate change, the global sea-level rise will likely enhance erosional processes and can therefore significantly influence the sediment budget of the entire North Sea.

Runoff and sediment effect of the soil-water conservation measures in a typical river basin of the Loess Plateau

Soil erosion and sediment transport processes, which are intimately connected with hydrological processes, strongly affect land surface morphology and earth system dynamics. Over the past 60 years, intensive Soil-Water Conservation (SWC) measures implemented on the Loess Plateau have significantly reduced sediment load and concurrently exacerbated runoff declines, while the quantitative evaluation of the effects of SWC measures remains challenging. This study develops a sediment module which simulates the hillslope and in-stream sediment processes, and then incorporates the module into a Geomorphology-Based Ecohydrological Model (GBEHM). Besides, the model also couples with an explicit representation of different types of SWC measures, including both Hillslope SWC (HSWC) and River-network SWC (RSWC) measures. The newly developed hydro-sediment model is then applied to the Kuye River basin, a typical river basin on the Loess Plateau, and used for quantifying the effects of SWC measures on river discharge and sediment load during 1982–2019. Compared with Period 1 (1982–2000), the river discharge decreased by 48.7% in Period 2 (2001–2019), while the sediment load experienced a more substantial decrease of 95.3% between the two periods. Based on the numerical experiment results, HSWC and RSWC contributed to 25.4% (58 million m3/yr) and 28.9% (66 million m3/yr) of the annual runoff decline, as well as 58.1% (36 million t/yr) and 33.9% (21 million t/yr) of the annual sediment load reduction between the two periods, respectively. Besides, HSWC plays an increasingly important role in sediment reduction in recent years due to check dam silting. The model developed in this research is useful to evaluate the multi-faceted effects of existing SWC measures and to help with future SWC planning and policymaking.

Homologous recombination and gene-specific selection co-shape the vertical nucleotide diversity of mangrove sediment microbial populations.

Mangrove sediments host a diverse array of microbial populations and are characterized by high heterogeneity along their vertical depths. However, the genetic diversity within these populations is largely unknown, hindering our understanding of their adaptive evolution across the sediment depths. To elucidate their genetic diversity, we utilized metagenome sequencing to identify 16 high-frequency microbial populations comprised of two archaea and 14 bacteria from mangrove sediment cores (0-100 cm, with 10 depths) in Qi'ao Island, China. Our analysis of the genome-wide genetic variation revealed extensive nucleotide diversity in the microbial populations. The genes involved in the transport and the energy metabolism displayed a high nucleotide diversity (HND; 0.0045-0.0195; an indicator of shared minor alleles with the microbial populations). By tracking the processes of homologous recombination, we found that each microbial population was subjected to different purification selection levels at different depths (44.12% genes). This selection resulted in significant differences in synonymous/non-synonymous mutation ratio between 0-20 and 20-100 cm layers, indicating the adaptive evolutionary process of microbial populations. Furthermore, our assessment of differentiation in the allele frequencies between these two layers showed that the functional genes involved in the metabolic processes of amino acids or cofactors were highly differential in more than half of them. Together, we showed that the nucleotide diversity of microbial populations was shaped by homologous recombination and gene-specific selection, finally resulting in the stratified differentiation occurring between 0-20 and 20-100 cm. These results enhance our cognition of the microbial adaptation mechanisms to vertical environmental changes during the sedimentation process of coastal blue carbon ecosystems.