Sediment Mixing Research Articles

Long-term coastal dynamics: The evolution of a mixed sediment mega-nourishment consisting of colliery spoil

Mega-nourishments, where large volumes of sediment are deposited on coastlines, are increasingly employed to manage shoreline erosion, yet our understanding of their long-term behaviour is limited by the fact that most current schemes are less than 15 years old. However, on the County Durham coast, 39 million m3 of coal spoil was tipped onto beaches between the late 1800s and 1993, acting as a de facto mixed sediment mega-nourishment. Our findings reveal key insights into the long-term dynamics of mega-nourishment schemes, including evidence of effective sediment dispersal around headlands into normally disconnected units of coast. Following cessation of tipping, shorelines retreated up to 12 m yr−1, with 150 m overall retreat in 12 years. Subsequently, retreat slowed but the present-day shoreline remains seaward of its 1860 position and is subject to ongoing coastal recession. We document significant fining of the deposited material in the years post deposition through abrasion and chemical breakdown. Furthermore, we show that the highest erosion rates now occur downdrift from the initial dump site, indicating that nourishment impacts migrate through time. These findings highlight the need for holistic and adaptive management approaches to mega-nourishment schemes, showing the behaviour of the nourishment to continually change in both location and magnitude as the system evolves. We demonstrate that mixed sediment mega-nourishments can be a cost-effective and durable solution to mitigate erosive losses, even in the absence of a planned approach to the location or composition of deposited sediment. Our results suggest that lessons from this historical intervention can inform the design and management of future mega-nourishment schemes, particularly in mixed sediment environments.

Geochemical Dynamics and Evolutionary Implications of Sediments at the Xingu–Amazon Rivers’ Confluence: Proxies for Mixing, Mobility and Weathering

This study investigates the geochemical characteristics and evolutionary implications of sediments at the confluence of the Xingu and Amazon Rivers. The main objective is to understand sediment mixing, mobility, and weathering processes through geochemical proxies. Samples were collected from various sections of the lower Xingu River, focusing on its interaction with the Amazon River. Analytical techniques such as X-ray diffraction (XRD), X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP-MS) were employed to analyze major and trace elements. The results reveal significant spatial variations in mineralogical and textural patterns, with sediments forming distinct groupings based on their location. The data suggest that the lower Xingu River is strongly influenced by sediment inputs from the Amazon River, particularly affecting sediment composition and chemical weathering processes. This research highlights the critical interactions between river systems and their implications for the evolution of the Amazon basin, especially regarding sediment contributions from various geological sources. Even though the Xingu River drains cratonic regions at higher elevations, the geochemistry of the bottom sediments confirms that the bedload is derived from heterogeneous sources with primarily intermediate igneous compositions and has undergone substantial recycling during river transport.

Continental-scale sediment mixing and dispersal across northern Gondwana: detrital zircon U-Pb-O-Hf isotopic evidence from the Cambro-Ordovician sandstones overlying the Arabian Shield

ABSTRACT The juvenile Neoproterozoic basement of the Arabian Shield is overlain with angular unconformity by a voluminous Cambro-Ordovician cover sequence known as the Saq Formation and Wajid Group. Provenance studies of this vast siliciclastic cover over the Saudi Arabian part of the Arabian-Nubian Shield (ANS) have to date been based solely on U-Pb zircon data and heavy minerals. We present the first combined in-situ U-Pb, δ18O and Lu-Hf isotopic data for detrital zircon from the Saq and Wajid units exposed along the northeastern margin and southern part of the Arabian Shield. U-Pb age spectra reveal prominent age peaks at ca. 0.8–0.55 Ga and 1.1–0.9 Ga with subordinate peaks at ca. 2.2–1.7 Ga and 2.7–2.5 Ga. The δ18O secular variation mirrors global compilations with Archaean zircon defining a restricted δ18O range of ca. 4.0–8.0 ‰ and younger zircon showing wide variation in δ18O up to ca. 14 ‰. The ca. 0.8–0.55 Ga age peak has the largest variation in εHf(t) with about half of all these Neoproterozoic zircon grains being juvenile (εHf(t) > 5), which are interpreted to be sourced from the juvenile terranes of the ANS. Neoproterozoic zircon with evolved εHf(t) signatures require a more distal source beyond the ANS. As extensive ca. 1.1–0.9 Ga crust is lacking in the vicinity of the ANS, the ca. 1.1–0.9 Ga age peak is interpreted to be derived from either contemporaneous orogenic belts in Central Africa or recycled from older sedimentary rocks containing these age components. Extreme variations in δ18O of post – Archaean zircon, together with the evolved εHf(t), indicate crustal thickening and increased incorporation of supracrustal material associated with collisional orogenesis. The remarkable similarities in age spectra and isotopic compositions of the Saq Formation and Wajid Group sandstones with those from other regions in northern Gondwana indicate a continental–scale homogenization and dispersion process.

Utilizing sentinel-1 SAR for delineation of narrow intertidal zones and habitat types in Svalbard

ABSTRACT Intertidal habitats have been significantly impacted by accelerated climate change in Arctic regions over the past few decades, particularly in Svalbard. New substrates are exposed as glacier retreat, making them accessible to benthic vegetation. Remote sensing techniques, including Sentinel-1 synthetic aperture radar (SAR) imagery and drones, provide the opportunity to acquire and study submerged habitats when they are exposed to the atmosphere during low tide. St. Jonsfjorden, Eidembukta, and Trygghamna were the three bays in Svalbard where this research was conducted. We used SAR imagery to determine relatively narrow intertidal zones, acknowledging that the spatial resolution of Sentinel-1 SAR imagery is limited to 10 m. Although this limitation posed a challenge when attempting to classify these narrow intertidal zones due to the coarse resolution of the data, we categorized the intertidal zones into three habitat types: vegetated rock, rock, and mixed sediment. The accuracy of this classification was consistently reliable, with a range of 64–78%. The classification results indicated that 25% of the total intertidal zone is composed of substrates that are suitable for macroalgae growth. It is remarkable that 80% of this substrate is vegetated. Additionally, this investigation demonstrated that vegetation is significantly absent in areas adjacent to glaciers. The magnitude of the glacier appears to influence the extent of this vegetation-free zone.

Modeling the transport and mixing of suspended sediment in ecological flows with submerged vegetation: A random displacement model-based analysis

Aquatic vegetation in rivers influences the flow structure, impacting the sediment transport in the river and further changing the ecosystem and geomorphologic evolution of the river. In this paper, an improved random displacement model (RDM) is proposed to investigate the concentration of suspended sediment (CSS) in flows with flexible submerged vegetation. Considering the effect of sediment resuspension on sediment transport, a probability model of sediment resuspension is embedded into the RDM so that the simulation process is more consistent with the natural cases. For the streamwise development of flow with flexible submerged vegetation, the flow is divided into a flow adjustment region and a fully developed region in the longitudinal direction. The vertical distributions of the flow velocity and turbulence diffusion coefficient were analyzed in these two regions, and they were incorporated into the RDM to simulate the along-flow development of the CSS. The simulated concentrations were compared with the experimental data. The mean relative errors (MREs) were below 15%, the root mean square errors (RMSEs) were below 0.20, and the Nash–Sutcliffe efficiencies (NSEs) ranged from 0.71 to 0.99, indicating that the improved RDM is plausible and reliable. In addition, the along-flow distribution of the sediment transport rate (STR) was analyzed. The rate exhibited a decreasing trend during the flow adjustment region and tended to stabilize during the fully developed region. This study provides a new way of thinking for research on sediment transport in rivers with aquatic vegetation, which is of great significance for achieving the sustainable development of river ecosystems and the optimal design of river channels.

Using detrital zircon U[sbnd]Pb geochronology to track the provenance of Miocene sediments in the northern Pearl River Mouth Basin, South China Sea

The Late Cenozoic provenance study of the Pearl River Mouth Basin (PRMB) holds significant implications for understanding the tectonic-climatic interactions, drainage evolution, and oceanic circulation in the northern South China Sea. However, the Miocene sediment routing system remains poorly understood due to the paucity of zircon geochronological data and the effects of sediment mixing and homogenization. This study reconstructs the ancient source-to-sink system by means of detrital zircon analyses from the northern PRMB and zircon age-based mixture modeling of well-defined provenance end-members. The results disclose varied and complex source-to-sink scenarios since the Early Miocene, involving three primary contributors: the Pearl River drainage system, coastal SE China, and Taiwan Island. In combination with seismic facies and climatic proxies, the intensive addition of Precambrian zircons suggests that, during the Middle and Late Miocene, progressive drainage expansion within the Yangtze Block likely contributed to the increasing sediment supply from the western Pearl River drainage system. Furthermore, the provenance shift in the northern PRMB, as indicated by the Mesozoic ages, may reflect a response to the activation of oceanic circulation and intensification of the East Asian monsoon. Additionally, though less significant, contributions from the Hainan and Luzon Island are also observed, indicating the input of the branch of the Kuroshio Current during the Late Miocene.

Investigating sediment dynamics on a continental shelf mud patch under the influence of a macrotidal estuary: A numerical modeling analysis

Shelf mud patches represent major sinks for fine-grained particles on continental shelves, as well as for carbon and contaminants of continental origin. The West Gironde Mud Patch (WGMP) is an interesting example of such offshore marine systems as it is an active mud deposition area located offshore the Gironde estuarine mouth (France) at depths between 30 and 70 m. It is known to be the trap of fine particles coming from the estuary, but the contribution of this material to the total mass of the depocenter is poorly quantified. In addition, despite the economic and ecological issues at stake, the response of such subtidal sedimentary structure to the combination of tidal currents, waves, and river supply remain poorly understood. Thus, using a realistic 3-D hydrodynamic and mixed (mud/sand) sediment transport model, this study aims at investigating the sediment dynamics of the WGMP under different hydrometeorological conditions. The analysis of the residual fluxes at the estuarine mouth exhibited large discrepancies between the different sediment classes as well as for contrasted hydro-and meteorological conditions induced by different dominant transport mechanisms. During winter, the reinforced density gradients drive strong up-estuary baroclinic circulation at the bottom that dominates the sediment dynamics over the barotropic export of mud particles. The model also reproduced the signature of a subtidal mud accumulation area over the continental shelf around 30–40 m water depth, on the proximal side of the observed WGMP. On average over two years, 26% of the mud mass accumulating on the simulated subtidal mudflat comes from the estuary. The trapping efficiency of this mud patch is negatively correlated with the significant wave height. Moreover, due to the estuarine turbid plume being more concentrated and developed at the surface during high river discharge, the trapping efficiency of the mud body is enhanced compared to lower discharge. This study highlights the sensitivity of mud and sand fluxes to vertical and horizontal residual circulation, and points out the uncertainties associated with the simulation of short-term (i.e., years) fine particle deposits compared to long-term (i.e., centuries) sediment accumulation trends. In addition, these results show the primordial effects of both wave action and riverine sediment supply on the dynamics of such subtidal muddy structures, which raises concern about their fate facing climate change and human activities in the future.

Invasive mussels reduce community bioturbation but do not affect oxygen penetration or nutrient fluxes in organic‐poor Great Lakes sediments

Abstract Invasive zebra and quagga (dreissenid) mussels have disrupted nutrient cycling and benthic macrofauna communities in the Laurentian Great Lakes and other invaded ecosystems. Dreissenids are now the dominant benthic macroinvertebrate in the Great Lakes, replacing the formerly dominant native bioturbating amphipod Diporeia spp. Dreissenids and Diporeia interact with their environment in fundamentally different ways, and the consequences of this functional shift in benthic community structure on benthic–pelagic coupling are not well understood, particularly in unproductive offshore lake regions. To determine how functional biology and benthic community structure impact sediment mixing and biogeochemistry in low particulate organic matter (POM) lake regions, we conducted a 6‐week sediment microcosm experiment with dreissenids, Diporeia and oligochaete worms—the second most common Great Lakes benthic macroinvertebrate. We found that sediment mixing rate and depth varied significantly among the taxa. Diporeia mixed sediment the deepest and strongest, followed by oligochaetes, while dreissenids did not appreciably mix sediment. Despite these differences, we found no significant variations among treatments in sediment oxygen penetration depth, sediment respiration (oxygen uptake) or nutrient dynamics. Our results suggest that dreissenids mix sediment less than native Great Lakes taxa, but that differential mixing rates may not measurably affect nutrient and oxygen dynamics in low‐POM sediments. Therefore, mussel effects in these areas may be manifested more through direct mechanisms rather than via altered sediment geochemistry.

Late Holocene geochemical signature of inter reef mixed sediments on the northeastern Brazilian outer shelf

The northeastern outer shelf in Brazil is a complex ecotone that holds significant information on Holocene sedimentary processes and evolution. X-ray diffraction (XRD), X-ray fluorescence (XRF), and scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) were employed to investigate bioclastic sedimentary facies and patches of relict siliciclastic sands. Radiocarbon dating (AMS) indicates that the carbonate sediments and corals formed in the past millennium. The sediment samples were divided into two groups using a multivariate analysis of XRD and XRF. The first group consists of siliciclastic materials, characterized by Si, Al, Fe, K, Zr, and Ti, and has low levels of carbonate and organic matter. The second, bioclastic and mixed facies, has a high carbonate content and exhibits elevated concentrations of Ca, Sr, and Mg, indicating authigenic processes. The EDS data revealed that the shells predominantly consisted of Cl, Cu, Al, Fe, and Ca. The terrigenous sites are detached from the coastal sources and are mainly located within the reef areas of the outer shelf. The erosion processes in these areas were inefficient to eliminate the siliciclastic sediments. This deposit trapped in inter reef sediments holds the key to understanding the timing and interactions between past coastal processes, shelf valley incision, and reef evolution during the Late Holocene transgression.

Predictive GAM seabed maps can account for defined and fuzzy boundaries to improve accuracy in a Scottish sea loch seascape

Marine seabed mapping is an important element in marine spatial and conservation planning. Recent large scale mapping programmes have greatly increased our knowledge of the seafloor, yet at finer resolutions, large gaps remain. Loch Eriboll, Scotland, is an area of conservation interest with a diverse marine environment supporting habitats and species of conservation importance. Here we test and present strategies for a predictive seabed substrata map for Loch Eriboll using drop down Stereo Baited Remote Underwater Video (SBRUV) imagery collected as part of systematic underwater survey of the Loch. A total of 216 SBRUV deployments were made across the study site in depths of 3 m–117 m, with six seabed classes identified using an adaptation of the EUNIS (European Nature Information System) hierarchical habitat classification scheme. Four statistical learning approaches were tested, we found, Generalised Additive Models (GAMs) provided the optimal balance between over- and underfitted predictions. We demonstrate the creation of a predictive substratum habitat map covering 63 km2 of seabed which predicts the probability of presence and relative proportion of substratum types. Our method enables naturally occurring edges between habitat patches to be described well, increasing the accuracy of mapping habitat boundaries when compared to categorical approaches. The predictions allow for both defined boundaries such as those between sand and rock and fuzzy boundaries seen among fine mixed sediments to exist in the same model structure. We demonstrate that SBRUV imagery can be used to generate cost effective, fine scale predictive substrata maps that can inform marine planning. The modelling procedure presented has the potential for a wide adoption by marine stakeholders and could be used to establish baselines for long term monitoring of benthic habitats and further research such as animal distribution and movement work which require detailed benthic maps.

Pore structure of the mixed sedimentary reservoir of Permian Fengcheng Formation in the Hashan area, Junggar Basin

The Permian Fengcheng Formation (P1f.) in the Hashan area, situated on the southwestern margin of the Junggar Basin, has witnessed a remarkable breakthrough in shale oil exploration in recent years with nearly 789 million tons of shale oil resources. As a unique set of mixed sedimentary shales, the Fengcheng Formation in the Hashan area is characterized by mixed sedimentation of terrigenous siliciclastic sediments, authigenic minerals, and tuffaceous materials. However, the understanding of pore characteristics in the mixed sedimentary reservoir still remains limited, prohibiting accurate estimation of the oil content and insights into oil mobility. Scanning electron microscopy (SEM), X-ray diffraction (XRD), mercury injection capillary pressure (MICP), nuclear magnetic resonance (NMR), X-Ray Computer Tomography (X-CT), and geochemical analysis were performed to investigate the pore size distribution and main controlling factors of the mixed sedimentary reservoir. Results showed that the main pore types in the mixed sedimentary reservoir are intergranular pores and dissolution pores. The pores of the P1f. mixed shales in the Hashan area were classified into II-micropores (< 25 nm), I-micropores (25–100 nm), mesopores (100–1000 nm) and macropores (> 1000 nm). In general, the mixed sedimentary rocks of P1f. formation feature few macropores but a large number of micropores and mesopores. The CS exhibits the most favourable physical properties among all lithofacies. It is concluded that the abundance and maturity of organic matter, mineral composition, sedimentary structure, and diagenesis of reservoir together impact the pore structure in the mixed sedimentary reservoirs. The maturity of organic matter and the content of tuffaceous minerals are the most significant in influencing the pore structure of P1f. shales. Overall, the pore structure of complex lithologic reservoir formed by mixed deposition and its influence on physical properties are studied, and the characteristics of the microscopic pore-throat system of the dominant lithofacies in the Hashan area are clarified, which is of great significance as a guide for the exploration and development of mixed sedimentary reservoirs in continental shale oil in China.

Geochemistry of Quaternary sediments in the northwestern South China Sea: Sediment provenance and mid-Pleistocene transition

The Quaternary sediments in the northwestern South China Sea (NW-SCS) provide valuable information about provenance, climate and sea level changes. However, the correlation between the geochemical records in marine sediments and these influencing factors remains less understood in the NW-SCS. Two wells penetrated Quaternary sediments on the shelf and shelf margin of the NW-SCS and provide an excellent dataset. In this study, the major, trace, and rare earth elements in the sediments were analyzed to reveal the Quaternary provenance changes that correlate with the climatic Middle Pleistocene transition (MPT). These results indicate that the core sediments were mainly derived from felsic source rocks and the degree of chemical weathering in the source areas is relatively low (CIA averaged at 58). The Quaternary provenance of the NW-SCS did not undergo significant changes, recording mixed sedimentation from the Red River, Hainan Island, and central Vietnamese sources. The felsic source rocks and negative Eu anomaly indicated the shelf area received sediments primarily from the Red River and Hainan Island. However, a positive Eu anomaly on the shelf margin suggests additional contributions from mafic rocks sourced from central Vietnam. During the MPT (1.3–1.4 to 0.8–0.9 Ma), the dominant periodicity of climate cycles changed from a 40 kyr obliquity cycle to a 100 kyr eccentricity cycle; the cooling climate led to a slight weaking in chemical weathering and a minor decrease in sediment supply from terrestrial sources. After the MPT, the mixed sourced sediments in the shelf and shelf margin areas of the NW-SCS likely suffered from multiple hydrodynamic forces under the influence of the Pleistocene high-frequency and high-amplitude sea level fluctuations. These climate induced changes led to significant fluctuations in element content that provide new insights into Quaternary sources and climatic events in the NW-SCS.

THE DITCH OF THE 17th CENTURY FOR MOORING BOATS IN THE VOZNESENSKYI MONASTERY NEAR DUBNO: CONSTRUCTION AND MATERIALS

Archaeological research carried out on Dubovets Island in 2022 made it possible to discover and study part of the ditch for mooring boats. The rich collection of materials with a wide range of categories was obtained from the ditches fill due to the fact that it accumulated the garbage and kitchen waste. At a certain point in time, a lot of fish were scaled near it which resulted in a continuous layer of scales. Judging by surface observations, this ditch stretched from the edge of the floodplain, i.e. the former pond bank, to the place where monastery-related objects were concentrated on the top of the hill, some of which were uncovered by excavations. Position and structure of the ditch indicate that it was used as a canal for launching and mooring of boats, which was a quite appropriate engineering solution in the conditions of a changing water levels in the pond and coastal reeds. The regular rows of stakes are the remains of protective wooden structures that strengthened the sandy sides of the ditch, apparently by weaving thin wood between them. The mixed sediments of layer 6 are traces of their destruction during the operation of the ditch. The analysis of archaeological materials from the ditch fill layers indicates that it was used during the 17th and 18th centuries. Object 83 is an important addition to the spatial and planning reconstruction of the monastery territory. It also serves as an example of an archaeological study of a peculiar technical structure that is not often discovered. Obviously, such ditches were built for residential complexes in the past where there was a need and the opportunity to attract the necessary labor. Ostriv Dubovets, as evidenced by the plans of the 17th and 18th centuries, was located near one of the riverbeds of the Ikva, which was more clearly visible during the period of low water in the pond. During the flood season, especially in spring, the valley between the island and the town was completely flooded. Thus, the water level near the island was not constant throughout the year, which made it impossible to arrange a simple berth. In addition, Ostriv Dubovets had a very gentle and elongated coastline, which was flooded for different lengths throughout the year. Therefore, for the convenience of embarkation and debarkation people, as well as loading and unloading boats on a dry section of the island’s shore, the construction of the discovered ditch was a necessary and original solution.

Modelling of Granular Sediment Transport in Steady Flow over a Mobile Sloped Bed

This paper introduces a three-layer system, proposing a comprehensive model of granular mixture transport over a mobile sloped bed in a steady flow. This system, consisting of the bottom, contact, and upper zones, provides complete, continuous sediment velocity and concentration vertical profiles. The aim of this study is to develop and experimentally verify this model for sediment transport over a bottom locally sloping in line with or opposite the direction of sediment flow. The model considers gravity’s effect on sediment transport in the bottom (dense) layer when the component of gravity parallel to the bottom acts together with shear stresses associated with water flow. This is a crucial factor often overlooked in previous studies. This effect causes an increase in velocity in the mobile sublayer of the dense layer and significantly affects the vertical distributions of velocity and concentration above this layer. The proposed shear variation due to the interaction between fractions and an intensive sediment mixing and sorting process over a mobile sloped bed adds to the novelty of our approach. The data sets used for the model’s validation cover various conditions, including slopes, grain diameters, densities, and grain mobility conditions, from incipient motion to a fully mobilized bed. This extensive validation process instils confidence in the theoretical description and its applicability to real-world scenarios in the design of hydraulic infrastructure, such as dams, barrages, bridges, and irrigation, and flood control systems.

Extent and biogeochemical impact of Skolithos piperock in the lower Cambrian Zabriskie Quartzite (California, USA)

The advent of bioturbation in the early Paleozoic and the subsequent intensification of sediment mixing by benthic animals dramatically altered marine ecosystems and biogeochemical cycling. However, the timing and pace of the transition to ubiquitous well-bioturbated sediments in the uppermost seafloor remain under debate. Skolithos ‘piperock’, a classic Cambrian ichnofabric composed of densely packed vertical burrows, has often been invoked as evidence for an early ramping up of infaunalization and intense sediment disruption, but its biogeochemical impact has not been quantitatively explored in this context. Here, we relate high-resolution sedimentological and bioturbation data from 182 m of the Zabriskie Quartzite of the Death Valley region of California—a locality known for hosting piperock—to a new numerical three-dimensional diagenetic model to investigate the effect of Skolithos on sediment oxygen penetration and organic carbon remineralization. Our modeling indicates that increasing Skolithos burrow density substantially expands the local oxic zone and, in contrast with other modes of bioturbation, can also result in decreased sulfur oxidation. However, our field data indicate true ‘piperock’ is relatively scarce in the Zabriskie Quartzite, even among horizons that are of identical lithology to those containing piperock and that house individual Skolithos burrows. This suggests that, in the Zabriskie and potentially other Cambrian piperock-bearing units, the broader impact of piperock on seafloor ecology, chemistry, and sediment properties may have been restricted in scope.

Geobiology: Machine learning puts bioturbation on the map

Bioturbation, the mixing of sediment through the actions of organisms, is a crucial ecosystem engineering process that controls biogeochemical cycles and helps structure marine ecosystems. Machine learning is helping to develop global maps of the intensity and depth of bioturbation.

High resolution luminescence and radiocarbon dating of Holocene Aeolian silt (loess) in west Greenland

Loess–palaeosol sequences serve as valuable archives of changes in climate and atmospheric mineral dust deposition. However, little work has been conducted on Holocene loess in the Arctic, despite the sensitivity of this region to climate changes. Aeolian silt/loess profiles in the ice-free region of western Greenland near Kangerlussuaq were sampled to develop a robust age framework using both luminescence and bulk organic matter radiocarbon dating. Radiocarbon ages generally show consistent age increases with depth but are likely offset to younger ages due to sediment mixing in the upper 10–20 cm of the profiles. Quartz OSL signals exhibit insensitivity, while low-temperature infrared stimulated luminescence performed at 50 °C (IR50) and the post-IR IRSL at 180 °C (pIRIR180) signals of polymineral fine grain revealed a consistent natural inherited dose of approximately 5 Gy for pIRIR180 and an unbleachable residual of around 2 Gy for IR50, with substantial fading rates in the latter. This led to a notable age overestimation when compared with bulk organic matter radiocarbon ages. To develop an appropriate dating approach, we evaluated the differential bleaching rates of feldspar IR50 and pIRIR180 signals, and corrected for modern inherited doses. Radiocarbon ages measured on the bulk organic carbon oxidised at 400 °C (LT 14C) increased very consistently with depth, allowing calculation of accumulation rates. The presence of the atmospheric radiocarbon bomb signal at depth indicated down-mixing of surface material into the profile, which caused negative (younger) age offsets. The offset-corrected radiocarbon-based age-depth model could be compared to the luminescence results.We show that a combination of LT 14C with polymineral pIRIR180 dating allows the development of age models for these deposits. This multi-chronological approach reveals that loess accumulation in the region was initiated around 4 ka, probably consisting of two main phases of loess accumulation at 4–3 ka and <1 ka. The initial phase matches the proposed onset of aeolian sand activity in the wider region, but post-dates local ice retreat by c. 3 kyr. The more recent phase of accumulation also matches the timing of increased sand accumulation in the region and likely coincides with Neoglacial to Little Ice Age ice advances, or even enhanced dust activity in the last decades.

Sezonowa i przestrzenna zmienność jakości wody w systemie jezior Lumina-Rosu w delcie Dunaju w Rumunii

The main aim of the present scientific paper is to assess water quality of the surface water of various lakes located in the Lumina-Rosu interdistributary depression, Danube Delta, Romania. As specific objectives, the paper considered to spot the main potential sources of contamination and their environmental impacts on aquatic ecosystems. Equally, the purpose of the article is to emphasize the importance of monitoring the water quality of the Danube Delta, for preserving these unique natural water resources and their ecosystem services (fresh water, biodiversity, flood control, recreation, nutrient cycling, fishing and other traditional activities, ecotourism). Surface water samples collected from several control sections situated on the main tributaries and canals, as well as from lakes were investigated physically (To - C, EC - μS/cm, TDS - mg/L, turbidity - NTU units, TSS - mg/L) and chemically (pH - units, DO - mg/L, N-NO2- - mg/L, N-NO3- - mg/L, P-PO43-- mg/L, Chla - mg/L, SiO2 - mg/L, TOC - mg/L, SO42- - mg/L, S2- - mg/L, H2S - mg/L and synthetic detergents - mg/L). Generally, the hydro-physical-chemical characteristics and water quality assessment of the surface waters of the lakes manifest the combined effect of both processes occurred in the catchment (weathering, sediment supply and transport), as well as the in situ lake processes (photosynthesis, sediment mixing, biogeochemical cycling, evaporation, eutrophication, productivity changes). Overall, the physical and chemical characteristics of the sampling sites investigated at high waters of the Danube are quite similar to those measured at low waters. The differences that mainly occurred within the lakes are more related to the limnological variables and the local environmental conditions. Anyway, a significant seasonal variation was noticed in the lakes, during the dry period, when different physical and chemical characteristics appeared to be influenced by high air temperature, lack of precipitation, low water level regime, low dissolved oxygen level regime, all related to climate change effects etc. Moreover, the anthropogenic factor that left its mark on some physical-chemical characteristics of water should not be omitted either. However, the results obtained within this study did not show such alarming values as might have dangerous effects on the investigated aquatic environments. The water quality information within this case study may be used for improving the understanding of the water quality issues and to better coordinate and plan for future monitoring activities in and around the Danube Delta environment. The results will contribute to updating the existing database with relevant information for a sustainable future of the Danube Delta and in similar areas that are subjected to such environmental challenges.

Formation mechanism of high-quality Palaeogene “compositional mixing” reservoirs in lacustrine rift basins: A case from the offshore Bohai Bay Basin, China

Mixed siliciclastic-carbonate reservoirs are currently considered a unique type of reservoir for hydrocarbon exploration. However, to date, research on “compositional mixing”, an important type of mixed sediment, remains relatively scarce. In recent years, significant breakthroughs in hydrocarbon exploration have been achieved in compositional mixing deposits, which are found within a lacustrine setting of the offshore Bohai Bay Basin in China. Despite the lack of systematic studies on their formation mechanisms, these discoveries are insightful case for understanding compositional mixing reservoirs (CMRs). In this study, an interdisciplinary approach that integrates petrographic analysis, cathodoluminescence analysis, reservoir characterization, and high-pressure mercury injection tests from drilled wells, cores, and thin sections, is employed to elucidate the characteristics of CMRs and the factors controlling reservoir modifications. Our findings reveal that compositional mixing deposits predominantly occurred with fan delta systems adjacent to uplifts. Two distinct reservoir types, namely, mixed slide deposits and mixed sandy debris flow deposits, were formed by coexistence of fan delta front siliciclastics with shallow-water biota (carbonate components). A comparative analysis of reservoir properties suggests that CMRs are of equivalent or superior quality to fan delta systems, challenging existing paradigms. This superiority is attributed to two primary factors: (1) the unique internal texture of compositional variations significantly influences subsequent diagenesis, leading to the extensive development of selective dissolution porosity and a reduction of clay cementation; and (2) distinctive early diagenetic events, including micrite envelopes and early dolomitization, markedly enhance the reservoirs’ resistance to compaction. In contrast, fan delta deposits lacking carbonate components do not undergo selective dissolution and their siliciclastic composition facilitates clay cementation. This study offers novel insights and a model for understanding the formation mechanism of CMRs, providing implications for future global petroleum exploration in mixed sediment reservoirs.

Quantification of the provenance contribution and sedimentary mixing effect of sediments in the Yellow River Basin, China

Quantifying the source contributions of sediments in large fluvial systems with active wind erosion problems has crucial implications for understanding morphological evolution and ecological progression in the Earth system. Much effort have been focused on characterizing sediments of the Yellow River, but quantitation of the sediment source proportions at the basin-wide scale is lacking. To this end, the research aims to quantitatively elucidate the potential source contributions of sediments in the Yellow River based on geochemical characteristics and sediment fingerprinting technique, in order to identify sedimentary mixing effect and propose sustainable development strategies. In total, samples of four source groups (n = 107) and target floodplain sediments (n = 61) were collected and tested for elemental composition, grain size, magnetic susceptibility, and quartz grain microtextures. The results indicated that the optimal tracer combination was determined as P, Zn, and Ca. The average contributions of the “Tibetan Plateau”, “Sandy deserts-Loess Plateau”, “Loess Plateau”, and “Loess Plateau-Qinling Mountains” source groups to the target sediments were 23.0 %, 21.5 %, 31.6 %, and 23.9 %, respectively. The accuracy of source apportionments was supported by the goodness of fit (GOF) and virtual mixtures tests. Meanwhile, large amounts of debris from surrounding mountains was transported to the Loess Plateau through fluvial processes and ultimately mixed with aeolian deposits, leading to sedimentary mixing effect. To maintain water balance and minimize erosion risk, the drought-resistant perennial planting and moderate grazing were recommended. The findings are instrumental in promoting soil and water conservation and disclosing fluvial and aeolian interaction on a global scale.