Spatial Distribution Of Sediments Research Articles

Spatial distribution of sediment dissolved organic matter in oligotrophic lakes and its binding characteristics with Pb(II) and Cu(II).

Dissolved organic matter (DOM), the most active component in interstitial waters, determines the stability of heavy metals and secondary release in sediments. However, little is known about the composition and metal-binding patterns of DOM in interstitial water from oligotrophic lakes affected by different anthropogenic perturbations. Here, 18 interstitial water samples were prepared from sediments in agricultural, residential, tourist, and forest regions in an oligotrophic lake (Shengzhong Lake in Sichuan Province, China) watershed. Interstitial water quality and DOM composition, properties, and Cu(II)- and Pb(II)-binding characteristics were measured via physicochemical analysis, UV-vis spectroscopic, fluorescence excitation-emission matrix-parallel factor analysis (EEM-PARAFAC), and fluorescence titration methods. The DOM, which was produced mainly by microbial activities, had low molecular weights, humification degrees, and aromaticity. Based on EEM-PARAFAC results, the DOM was generally composed of tryptophan- (57.7%), terrestrial humic- (18.7%), microbial humic- (15.6%), and tyrosine-like (8.0%) substances. The DOM in the metal complexes was primarily composed of tryptophan-like substances, which accounted for ~42.6% of the DOM-Cu(II) complexes and ~72.0% of the DOM-Pb(II) complexes; however, microbial humic-like substances primarily contributed to the stability of DOM-Cu(II) (logKCu = 3.7-4.6) and DOM-Pb(II) (logKPb = 4.3-4.8). Water quality parameters did not significantly affect the stability of DOM-metal complexes. We demonstrated that the metal-binding patterns of DOM in interstitial water from oligotrophic lakes are highly dependent on microbial DOM composition and are affected by anthropogenic perturbations to a lesser extent.

Net Transport Patterns of Surficial Marine Sediments in the North Aegean Sea, Greece

The spatial distribution of sediments on the seafloor reflects the various dynamic processes involved in the marine realm. To analyze sediment transport patterns in the North Aegean Sea, 323 surficial samples were obtained and studied. The granulometry data revealed a diverse range of grain sizes of surficial sediments, ranging from purely sandy to clay. The predominant size classes were silt and muddy sand, followed by sandy silt and mud. However, there were very few samples that fell within the clay classes. The sorting coefficient ranged from 0.21 to 5.48, while skewness ranged from −1.09 to 1.29. The sediment transport patterns were analyzed based on the grain-size parameters (mean, sorting, and skewness). The results showed the variability of flow parameters involved in sediment distribution. River influx and longshore drift near the shoreline are the most significant factors affecting sediment transport. At the open sea, sediment distribution is mainly controlled by general water circulation patterns, especially by the outflow of low-salinity waters from the Black Sea through the Dardanelles and the Marmara Sea. The heterogeneity of sediment textural parameters across the study area suggests that seafloor sediments are further reworked in areas where water masses are highly energetic. It can be concluded that open sea water circulation controls sediment distribution patterns at the open shelf, while close to the coast, river discharge plays a key role.

Reservoir siltation and sediment characterization for reuse as construction material in a semi-arid area

Anibi S, Ellouze S, Zairi M. 2024. Reservoir siltation and sediment characterization for reuse as construction material in a semi-arid area. Lake Reserv Manage. 40:159–176. In this study, we investigated the siltation rate, evolution, and spatial distribution of sediments within the Siliana Dam reservoir, north-west Tunisia. We analyzed the geotechnical, chemical, mineralogical, and trace metal content properties of sediment samples collected from the reservoir. Additionally, we examined the potential valorization of reservoir sediments in road construction and the effects of hydrated lime treatment on their bearing characteristics. The Siliana dam reservoir is currently 50% silted up, and the sedimentation rate is approximately 1.52% per year. The sediments are mainly fine-grained, low organic with medium to high plasticity and high content of calcium carbonate. The sediments consist of calcite and quartz, with minor amounts of dolomite, hematite, and phyllosilicate minerals. Chromium, zinc, and copper contents in the sediments exceed environmental standards. The lime treatment improved the materials bearing capacity. Adding lime (5% by weight) resulted in an immediate bearing ratio of 26%, a higher ratio compared to the raw sediments. The study of the spatial and temporal evolution of sediment accumulation provides information to develop strategies for mitigating the accumulation of sediments. The sediment characterization evaluated the suitability of sediments to be used as construction materials, offering potential cost savings and contributing to informed decision-making for reservoir management.

Geotechnical, microscopic and mineralogical characterization of surficial sediments nearshore the southern coast of Brazil

ABSTRACT Many important maritime projects depend on the correct characterization of surficial sediments (e.g. gas and water pipelines; dredging works; transport of sediments, and water-soil-structure interaction). However, the sampling and characterization of such sediments are very challenging due to the environmental conditions. Furthermore, the investigation often consists only of a basic granulometric analysis. In this context, this paper presents a geotechnical, mineralogical, and microscopy characterization of an offshore area on the southern coast of Brazil. Surficial samples were collected from the seabed, in water depths between 13.0 and 91.0 metres. Then, they were submitted to basic geotechnical characterization tests (size distribution by sieving and sedimentation, Atterberg limits, and basic physical properties), mineralogical analysis by X-ray diffraction tests (XRD), microscopy investigation by scanning electronic microscopy (SEM) and shear vane tests. Based on the state and index parameters of the sediments, as well as the undrained shear resistance, three main sets of sediments have been identified: group I (sands), group II (clayey sands), and group III (mixtures of sand, silt, and clay). The spatial distribution of sediments was also inferred, reflecting different deposition environments and bottom dynamics. The clay mineral quantification through XRD revealed that the predominance of 2:1 clay minerals is related to the higher plasticity found in some samples. Moreover, the presence of diatoms could explain the difference in porosity in the samples, resulting in a higher plasticity and lower shear strength.

ESTIMASI BESARAN SEDIMENTASI DI SUB DAS PAGUYAMAN YANG BERADA DI KABUPATEN GORONTALO

Paguyaman watershed is the second largest watershed in Gorontalo province with an area of 3,485.65 which is a critical watershed. There is a problem of sedimentation in the watershed causing the river flow rate to slow down. It is hoped that it can be used as an alternative to overcome siltation. The research aims to estimate the amount of sedimentation and determine the spatial distribution of sedimentation in the Paguyaman sub-watershed, the method used is the Soil and Water Assessment Tool (SWAT) model. carried out with the help of geographic information systems (GIS) with ArcGIS 10.4 software, SWAT can describe hydrological processes (sedimentation). DEM data resolution (10x10) as the main input for the DAS delineation process. Soil data, land use, soil type, determines the land unit/hydrologic response unit (HRU) of the watershed. Rainfall and climate data (temperature, average humidity, solar intensity, wind speed) obtained from stations spread over the area are integrated into SWAT to calculate sedimentation. The results of the Paguyaman watershed have a very steep slope (> 40), land use is dominated by primary and secondary dryland forest with a total area of 49511.90 with a percentage of 45.39%, Tropudults soil type; Dystropepts area of 22125.96 with a percentage of 20.28%, DAS Paguyaman has 8202 HRU's and sub-basin 475 there are 5 classifications of sedimentation quantities, namely very high sedimentation 285.25 ha, with a percentage of 0.26%, high sedimentation 87.78 ha with a percentage of 0.08%, moderate sedimentation 505.94 ha with a percentage of 0.45%, low sedimentation 3040.37 ha a percentage of 2.79% and very low sedimentation 105171.27 ha with a percentage of 96.41%.

Multi‐Year Tracing of Spatial and Temporal Dynamics of Post‐Fire Aeolian Sediment Transport Using Rare Earth Elements Provide Insights Into Grassland Management

AbstractAeolian sediment transport occurs as a function of, and with feedback to ecosystem changes and disturbances. Many desert grasslands are undergoing rapid changes in vegetation, including the encroachment of woody plants, which alters fire regimes and in turn can change the spatial and temporal patterns of aeolian sediment transport. We investigated aeolian sediment transport and spatial distribution of sediment in the surface soil for 7 years following a prescribed fire using a multiple rare earth element (REE) tracer‐based approach in a shrub‐encroached desert grassland in the northern Chihuahuan desert. Results indicate that even though the aeolian horizontal sediment mass flux increased approximately three‐fold in the first windy season in the burned areas compared to control areas, there were no significant differences after three windy seasons. The soil surface of bare microsites was the major contributor of aeolian sediments in unburned areas (87%), while the shrub microsites contributed the least (<2%) during the observation period. However, after the prescribed fire, the contribution of aeolian sediments from shrub microsites increased considerably (∼40%), indicating post‐fire microsite‐scale sediment redistribution. The findings of this study, which is the first to use multiple REE tracers for multi‐year analysis of the spatial and temporal dynamics of aeolian sediment transport, illustrate how disturbance by prescribed fire can influence aeolian processes and alters dryland soil geomorphology in which distinct soils develop over time at very fine spatial scales of individual plants.

Modeling the spatially distributed nature of subglacial sediment transport and erosion

Abstract. Glaciers expel sediment as they melt, in addition to ice and water. As a result, changing glacier dynamics and melt produce changes to glacier erosion and sediment discharge, which can impact the landscape surrounding retreating glaciers, as well as communities and ecosystems downstream. Currently, numerical models that transport subglacial sediment on sub-hourly to decadal scales are one-dimensional, usually along a glacier's flow line. Such models have proven useful in describing the formation of glacial landforms, the impact of sediment transport on glacier dynamics, and the interactions among climate, glacier dynamics, and erosion. However, these models omit the two-dimensional spatial distribution of sediment and its impact on sediment connectivity – the movement of sediment between its detachment in source areas and its deposition in sinks. Here, we present a numerical model that fulfills a need for predictive frameworks that describe subglacial sediment discharge in two spatial dimensions (x and y) over time. SUGSET_2D evolves a two-dimensional subglacial till layer in response to bedrock erosion and changing sediment transport conditions. Numerical experiments performed using an idealized alpine glacier illustrate the heterogeneity in sediment transport and bedrock erosion below the glacier. An increase in sediment discharge follows increased glacier melt, as has been documented in field observations and other numerical experiments. We also apply the model to a real alpine glacier, Griesgletscher in the Swiss Alps, where we compare outputs with annual measurements of sediment discharge. SUGSET_2D accurately reproduces the general quantities of sediment discharge and the year-to-year sediment discharge pattern measured at the glacier terminus. The model's ability to match the measured data depends on the tunable sediment grain size parameter, which controls subglacial sediment transport capacity. Smaller grain sizes allow sediment transport to occur in regions of the bed with reduced water flow and channel size, effectively increasing sediment connectivity into the main channels. The model provides the essential components of modeling subglacial sediment discharge on seasonal to decadal timescales and reveals the importance of including spatial heterogeneities in water discharge and sediment transport in both the x and y dimensions in evaluating sediment discharge.

Spatial-temporal evolution of sediment transport in the upper Yangtze River Basin considering the cumulative impacts of mega reservoirs

The intensive construction of large dams in the upper Yangtze River Basin (UYRB) has formed large-scale cascade reservoirs and obviously altered the flow regime and sediment transport of the basin. However, few studies have quantitatively described the cumulative impact of these reservoirs on sediment interception. In this study, a flow and sediment transport model that fully considers the operation processes of 24 mega reservoirs in the UYRB was established, and the spatial and temporal variations in sedimentation from 2011 to 2080 were elucidated, assuming repeated series of daily input flow discharge and sediment concentration during 2011–2020 and monthly water operation levels of 24 reservoirs during 2018–2021 as boundary conditions. The results showed an annual average sedimentation of more than 300 Mt in the UYRB during 2011–2060, which falls to 270 Mt in the period 2061–2080, and more than 80% of the sedimentation occurs in the flood season. Nearly 80% of the total sedimentation during 2010–2080 was observed in the mainstream reservoirs, especially the four mega reservoirs in the lower Jinsha River and the Three Gorges Reservoir (TGR), which accounted for 31.9% and 22.7% of the total sedimentation, respectively. The proportion of sedimentation in mainstream reservoirs will further increase with increasing operation periods. Most reservoirs in the UYRB will not reach sedimentation equilibrium by 2080, except for reservoirs in the Min River Basin. The ratio of siltation capacity to average annual sediment yield determines the percentage of residual siltation capacity of each reservoir. The operation of the cascade reservoirs in 2013–2020 had no more immediate impact on the middle and lower Yangtze River than that in 2003–2012, when the TGR started impoundment. However, the joint operation of these cascade reservoirs has changed the spatial distribution of sedimentation in the UYRB, and will lead to prolonged impacts on downstream channel erosion.

SHRIMP U–Pb ages of the detrital zircons from the Cretaceous Ullyeonsan Formation, SE Korea: A small piece for stratigraphic correlation in eastern Asia

To constrain the maximum depositional age of the Ullyeonsan Formation in the Yeongyang Subbasin, southeast Korea, detrital zircon U–Pb age determination was conducted using high-resolution secondary ion mass spectrometry (HR-SIMS). The U–Pb populations of detrital zircons from the Ullyeonsan Formation show a broad range of ages from the Archean to early Cretaceous and diverse patterns depending on the temporal and spatial distribution of sedimentation. The difference in location-dependent age distribution indicates that sediments originated from adjacent areas and source rocks were exposed during the sedimentation period of the Ullyeonsan Formation. The youngest detrital zircon cluster of the Ullyeonsan Formation yields concordia age of 110.4 ± 2.5 Ma (n = 5, MSWD = 1.2), indicating the maximum depositional age. Therefore, the Ullyeonsan Formation began to be deposited from the Albian period, and the Yeongyang Subbasin started to form around the same time as the deposition of the Hayang Group in other subbasins of the Gyeongsang Basin (e.g., Miryang and Uiseong).

Sedimentary Facies and Morpho-dynamics of Sand Spit and Island Inference as Coastal River Process

Abstract This study aimed to characterize the sedimentary facies and understand the morphodynamics of the study area, and their results were correlated with various analytical methods. Different analyses such as depositional environmental, statistical, shoreline change, and grain size illustrated the temporal and spatial distribution of sediments. It has previously been claimed that current research locations are locii to fluvial landforms and are affected by fluvial processes. However, there are currently no rivers in the study region. This study was done to better understand the presence of fluvial landforms and to evaluate the previous findings. The dynamic behavior of the coast was revealed through shoreline analysis, which was done using satellite images from various years. Oceanographic parameters and longshore sediment transport play a vital role in geomorphological changes in coastal zones. According to the grain size analysis results, mean values showed that the deposits predominantlyare medium grained. The outcome discussed the spatiotemporal variations in geomorphology, sedimentation, and the function of coastal and fluvial processes on the beach of an island and a sand spit. Also highlighted was the role that wave action, fluvial currents, and tidal currents had in the long-term evolution of coastal geomorphological features such as spits, beaches, open coasts, and islands. The standard deviation signifies that the sediments are very well sorted to poorly sorted. Skewness ranges from fine skewed to strongly fine skewed and the kurtosis values show that the sediments are predominately very platykurtic which implies a low-energy environment of deposition. Four sedimentary facies (Facies A, B, C, D) have been found and facies A, B, and C may be wave-influenced deposits, but facies D may be formed by fluvial processes and contain medium to sand-sized particles. The direction of the tip area is also pointing to the south and this result concluded that the tip area is continuously growing. Thus, the results of this study revealed that sediment transport and coastal geomorphology evolution may be governed by two main processes such as the present ocean hydrodynamics and paleo fluvial processes of the study regions.

Hotspots of microplastic accumulation at the land-sea transition and their spatial heterogeneity: The Po River prodelta (Adriatic Sea)

Deltas are the locus of river-borne sediment accumulation, however, their role in sequestering plastic pollutants is still overlooked. By combining geomorphological, sedimentological, and geochemical analyses, which include time-lapse multibeam bathymetry, sediment provenance, and μFT-IR analyses, we investigate the fate of plastic particles after a river flood event providing an unprecedented documentation of the spatial distribution of sediment as well as of microplastics (MPs), including particles fibers, and phthalates (PAEs) abundances in the subaqueous delta. Overall sediments are characterized by an average of 139.7 ± 80 MPs/kg d.w., but display spatial heterogeneity of sediment and MPs accumulation: MPs are absent within the active sandy delta lobe, reflecting dilution by clastic sediment (ca. 1.3 Mm3) and sediment bypass. The highest MP concentration (625 MPs/kg d.w.) occurs in the distal reaches of the active lobe where flow energy dissipates. In addition to MPs, cellulosic fibers are relevant (of up to 3800 fibers/kg d.w.) in all the analyzed sediment samples, and dominate (94 %) with respect to synthetic polymers.Statistically significant differences in the relative concentration of fiber fragments ≤0.5 mm in size were highlighted between the active delta lobe and the migrating bedforms in the prodelta. Fibers were found to slightly follow a power law size distribution coherent with a one-dimensional fragmentation model and thus indicating the absence of a size dependent selection mechanism during burial. Multivariate statistical analysis suggests traveling distance and bottom-transport regime as the most relevant factors controlling particle distribution. Our findings suggest that subaqueous prodelta should be considered hot spots for the accumulation of MPs and associated pollutants, albeit the strong lateral heterogeneity in their abundances reflects changes in the relative influence of fluvial and marine processes.

Spatial sedimentation and plant captured sediment within seagrass patches

Habitat degradation in coastal ecosystems has resulted in the fragmentation of coastal aquatic vegetation and compromised their role in supplying essential ecological services such as trapping sediment or sequestering carbon. Fragmentation has changed seagrass architecture by decreasing the density of the canopy or engendering small patches of vegetated areas. This study aims to quantify the role different patch sizes of vegetation with different canopy densities have in the spatial distribution of sediment within a patch. To this aim, two canopy densities, four different patch lengths, and two wave frequencies were considered. The amounts of sediment deposited onto the bed, captured by plant leaves, remaining in suspension within the canopy, and remaining in suspension above the canopy were used to understand the impact hydrodynamics has on sediment distribution patterns within seagrass patches. In all the cases studied, patches reduced the suspended sediment concentrations, increased the capture of particles in the leaves, and increased the sedimentation rates to the bed. For the lowest wave frequency studied (0.5 Hz), the sediment deposited to the bottom was enhanced at canopy edges, resulting in spatial heterogeneous sedimentation patterns. Therefore, restoration and preservation of coastal aquatic vegetation landscapes can help face future climate change scenarios where an increase in sedimentation can help mitigate predicted sea level rise in coastal areas.

Numerical simulation of failure properties of interbedded hydrate-bearing sediment and their implications on field exploitation

Marine natural gas hydrate is widely accepted as a promising substitute energy resource, whereas geotechnical responses of hydrate-bearing sediments (HBS) are crucial for the safe development of natural gas hydrate. The hydrate spatial distribution in sediments is multitype and present different coalescence degrees, its distribution pattern significantly influences the failure behavior of HBS, but the mechanics behind this influence is unclear. Numerical simulations are of great importance in revealing such mechanics. In this paper, a series of numerical simulations, using a modified Mohr–Coulomb (MC) model, were performed to analyze the deformation mechanisms of HBS when the hydrate was laminarly distributed in its host sediment. Considering the vertical heterogeneity of the hydrate distribution, the vertical-laminar hydrate distribution samples were simplified as interbedded samples. The interbedded HBS specimens consisted of three layers: the middle layer with relatively lower hydrate saturation; and the upper and lower layers with relatively high hydrate saturation. Interbedded samples with different hydrate saturations, depressurization ratios, and thickness ratios were designed to analyze their mechanical behaviors. The results indicated that in both the hydrate saturation and thickness ratio of the interbedded samples, the plastic yield area first occurred in the lower hydrate saturation layer; the failure mechanism was mainly determined by the strength of the lower hydrate saturation layer. In addition, the shear failure behavior of the HBS was controlled by the hydrate saturation difference between the middle and upper layers. With a smaller hydrate saturation difference between the middle and upper layers, the samples were more likely to experience shear failure. In the thickness ratio samples, the HBS changed from brittle to ductile failure with an increase in the thickness of the lower hydrate saturation layer. Under different depressurization amplitudes, the larger compression and shear yield zones were mainly confined in the upper layer. This study provides a theoretical framework for controlling the strength-weakening mechanism during natural gas development, which can be used to guide reservoirs characterization, the selection of depressurization schemes, and decomposition zones monitoring.

Spatial distribution of microplastics pollution in sediments and surface waters of the Aras River and reservoir: An international river in Northwestern Iran

Microplastics (MPs) in freshwater environments have been recognized as one of the important sources of plastic contamination in marine ecosystems. Reducing the amount and spatial distribution of MPs reaching the sea through accumulation behind dams remains unclear. In this study we analyzed the spatial distribution of sediment and surface water MPs in the Aras Dam and from nineteen upstream and downstream locations of the Dam in the Aras River. The MPs abundance ranged from 32 to 528 items/kg dry weight (mean 217.8 ± 132.6) and 1 to 43 items/m3 (mean 12.8 ± 10.5) in the sediment and surface water stations, respectively. MPs abundance in surface waters collected within the Dam reservoir was significantly higher than those found either upstream or downstream (P < 0.05). For sediments, reservoir MPs concentration was generally higher than upstream and downstream, although their differences were not significant. High MPs concentration was observed in the vicinity of urban areas. Moreover, MPs abundance was positively correlated with total organic carbon (TOC) and clay content (P < 0.01). GAM analysis revealed that clay is the most important variable with lowest Akaike information criterion (AIC) and explained 61.3 % of deviance (R-sq.(adj) = 0.344) in MPs abundance. MP particles ranged from 0.1 to 5 mm in size and were dominated by fibers (53.5 %), black color (24 %) and PE polymer (36.6 %). Our results highlight the high MPs distribution in the Aras River and demonstrate that they accumulate in the surface waters behind the Dam. Consequently, the fate and effects of MPs in international rivers is one of the most politicized issues between countries with a common boundary and therefore needs joint management policies that help mitigate this insidious problem.

Experimental study of erosion by waves on the lakeshore of lateritic soils

Many countries use hydropower as their main source of power generation. One of the factors responsible for erosion in hydroelectric reservoir margins is the action of wind-induced waves, which increases sedimentation and reduces their storage capacity. Despite potential economic and environmental damages, research into wave erosion processes on reservoir margins are found mainly in cohesive soils from cold regions. Research on erosion by waves of cohesive soils from savannah regions, which are commonly found in tropical reservoirs, is incipient; studies evaluating breaking and non-breaking wave conditions on this type of erosion are especially important. This work presents the results from 18 water wave channel experiments which were conducted to investigate the erosional processes by waves on lateritic soils, under breaking wave and non-breaking wave conditions, as well as determining the spatial distribution of the resulting sediments. Lateritic soil samples were placed on the wave channel and different conditions were tested. Wave frequencies varied from 0.272 to 0.999 Hz on four different beach slope angles of 22.50, 30.00, 45.00, and 60.00 degrees. In 80% of the tests, the erosion rate varied positively in a nonlinear form with the increase of the accumulated wave power. However, when the waves broke, erosion rate sometimes varied negatively and the sediment production tended to be reduced. High precision 3D surveys showed a good agreement between the maximum depth of the eroded surfaces and the power increase of the waves. The average roughness of the samples increased in 90% of the tests. The spatial distribution of sediments and their grain size distributions were also investigated. The waves’ driving forces were incapable of transporting the sediments away from their source of origin and, therefore, were not able to change the natural distributions of the grains with the simulated conditions.

Mechanical behaviors of hydrate-bearing sediment with different cementation spatial distributions at microscales

SummaryUnlike the conceptual models, the natural hydrate spatial distribution in sediments is multitype and presents different coalescence degrees. In this study, we present pore-scale triaxial test results for hydrate-bearing sediments with different hydrate spatial distributions for the first time. It shows that the specimen with a more dispersed hydrate distribution yields later and exhibits larger peak strength. Correspondingly, the localized deformation develops more slowly, and the shear band is steeper and thinner. The cementation failure in the specimen with a more dispersed hydrate distribution develops more slowly. However, the changing rate of the pore space characteristic does not seem to be affected by the hydrate spatial distribution. Moreover, the specimen with a more dispersed hydrate distribution has a larger hydrate-sand interfacial area, and further axial loading would increase it rapidly firstly, and then the increasing rate would be slowed down since the cementation structure failure.

Mechanical Behaviors of Hydrate-Bearing Sediment with Different Cementation Spatial Distributions: Insight from Pore Scale

Unlike the conceptual models based on idealistic assumptions, the natural hydrate spatial distribution in sediments is multitype and presents different coalescence degrees, which could greatly influence its geomechanical behavior. In this study, we present pore-scale triaxial test results for hydrate-bearing sediments with different hydrate spatial distributions for the first time. The results show that both specimens exhibit strain-softening, and the specimen in which the hydrate present a dispersed distribution yields later and shows a larger peak strength and weaker strain-softening. The localized deformation of the specimen in which the hydrates present a dispersed distribution develops slower, and the shear band is steeper and thinner. During the shearing process, the cementation failure in the specimen which the hydrate present a dispersed distribution develops faster. However, the changing rate of the pore space characteristic seems to not be affected by the hydrate spatial distribution. Moreover, the specimen in which the hydrate present a dispersed distribution has a larger hydrate-sand interfacial area. Along with the axial loading, the hydrate-sand interfacial area would increase rapidly and even straighten. Further loading would lead to the complete failure of the hydrate-cemented structure, which would lead to the slowing of the increase in the hydrate-sand interfacial area.

Integrated use of well and geophysical data for constructing 3D geological models in shallow aquifers: a case study at the Tymbakion basin, Crete, Greece

3D geological models increase our understanding of the subsurface structures and the spatial distribution of sediment’s properties. The models can be applied in different aspects of geology and assist in reaching to more robust conclusions. In this study, a methodology for constructing a 3D geological model of the Tymbakion basin, Crete, Greece, is presented. The model is based on a dense array of newly acquired Transient Electromagnetics measurements (TEM), legacy Vertical Electrical Soundings (VES), and well data that cover an area of approximately 35 km2 and 500 m in depth. The model is representative of the Plio-Quaternary section, which hosts the Tymbakion shallow aquifer. The study area is one of the main agricultural sites of Greece with touristic activity. The model reveals the existence of 12 faults, which are not observed on the surface, and provides the lithological and resistivity distribution on the subsurface. The importance of the model relies in the fact that it gives a better insight into the hydrogeological setting of the shallow aquifer and the problems related to the intensive water exploitation during the last decades.

The sediment distribution characteristics and transport pattern in the eastern China seas

As one of the most important margin seas around the west Pacific, the eastern China seas are important sink for terrigenous materials and forms multiple geology structures. So research the composition and spatial distribution of sediments could help us to understand the dynamics mechanism of the marine sedimentary environment, further to comprehend the land-sea interaction process. Based on high spatial resolution sediment survey in the eastern China seas, the distribution diagram of the sediment types was compiled to reveal the space regularities of sediment. In this study, the Principal Component Analysis (PCA) method was used to identify the controlling factors that are the main controls of the sediment distribution in the study area, which revealed three factors (F1, F2 and –F1) representing grain size categories of >5.75φ, 4.25–5.75φ and 1.50–3.00φ, respectively. F1 represents fine sediments (>5.75φ), -F1 represents coarse sediments (1.50–3.00φ), and F2 represents intermediate-sized sediments (4.25–5.75φ). The sediment transport patterns of the different grain size categories in the eastern China seas are discussed in the context of a comprehensive analysis of sediment grain size composition, material sources, flow patterns, and other factors. The results show that fine-grained sediments represent a “distant” sink of terrigenous material that formed in a stable and low-energy sedimentary environment. The coarse sediment deposits were formed in the late Pleistocene when the hydrodynamic conditions were relatively strong, and the intermediate-sized sediments were distributed in an area with a high concentration of suspension representative of mid-strength hydrodynamic conditions.

Astronomical forcing of the Paleogene coal-bearing hydrocarbon source rocks of the East China Sea Shelf Basin

The Paleogene coal-bearing deposits (Pinghu Formation) of the Xihu Depression form the most productive hydrocarbon source in the East China Sea Shelf Basin. Due to the lack of reliable magnetostratigraphic, paleontologic and geochemical/isotope data, these source rocks are still poorly dated. The absence of a robust time frame results in many disputes on the age and duration of the Pinghu Formation and hampers a thorough understanding of its sedimentary evolution. Here, we study the cyclic changes in the depositional environment that can be retrieved from seismic interpretation and sequence stratigraphic analyses of well log data (e.g., stacking patterns, logging, and lithofacies changes). We recognize one second-order sequence, three third-order sequences and 12 fourth-order parasequences. Next, we construct a floating astronomical time scale by using power spectra and evolutionary fast Fourier transformation analysis on the gamma-ray data. Wavelength variations in the gamma-ray spectra show similar ratios as the astronomically-forced Milankovitch cycles (i.e., eccentricity, obliquity and precession). The filtered long and short orbital eccentricity cycles show a good match with the La2010d astronomical target curve, allowing to create an independent time frame based on cyclostratigraphy. Our floating astronomical time scale provides new numerical age constraints for the Pinghu Formation, resulting in a total duration of ~4.95 Myr. A re-analysis of the available age data indicates that the sequence stratigraphic framework of the Pinghu Formation is best constrained to the early Oligocene, instead of the previously assumed late Eocene. Our study highlights that astronomical interpretation of sequence stratigraphic analyses is an excellent method to estimate the duration of sedimentary successions in boreholes and adds to a better understanding of the temporal and spatial sediment distribution patterns in the East China Sea Shelf Basin.