Sediment Grain Research Articles

Porous Plate Method: Reduction in Local Scour around Pier-Type Structures in Multidirectional Flows

To reduce the local scour around pier-type structures, a “porous plate method” was proposed, aiming at effectiveness in multidirectional horizontal flows. The porous plates installed on the pier surface near the bed play two important roles in the reduction of the local scour. One is “breaking down or weakening” of the horseshoe vortex by a decline in vorticity. In the neighborhood (just upstream region), the local scour depth greatly decreases due to suppression of picking up sediment grains from the bed. Another is the resultant “flow regulation” in the boundary layer on the pier surface. In the downstream side, the wake separated from the pier surface behaves as “semi-homogeneous turbulence” without a Kármán vortex street, then the scour area drastically decreases.

Updated Radiative Transfer Model for Titan in the Near-infrared Wavelength Range: Validation against Huygens Atmospheric and Surface Measurements and Application to the Cassini/VIMS Observations of the Dragonfly Landing Area

We present an analysis of Titan data acquired by the Cassini Visual and Infrared Mapping Spectrometer (VIMS) at the landing site of the Dragonfly mission, using a new version of our radiative transfer model for Titan, with significant updates for the spectroscopic parameters of atmospheric gases and photochemical aerosols. Our updated radiative transfer model is validated against the in situ spectroscopic measurements of the Huygens probe during its descent and once landed. We confirm that aerosols with a fractal dimension of 2.3–2.4 provide the best fit to the observations. We apply our radiative transfer model to four VIMS data cubes over the Selk crater region including the Dragonfly landing and exploration areas, further validating our model by producing consistent aerosol population and surface albedo maps. These infrared albedo maps, further corrected from the photometry, enable us to study the Selk crater region in terms of surface composition, landscape formation, and evolution. Our results suggest that the Selk crater is in an intermediate state of degradation and that the mountainous terrains of the area (including the crater rim and ejecta) are likely to be dominated by fine grains of tholin-like sediment. This organic sediment would be transported to the lowlands (crater floor and surrounding plains), possibly with water ice particles, by rivers, and further deposited and processed to form the sand particles that feed the neighboring dune fields. These results provide information for the operational and scientific preparation of the Dragonfly mission, paving the way for future exploration of Titan’s surface composition and geology.

Radioactive parameter analysis in soil samples at the Cauvery river

Cauvery, one among the major rivers, passing through three states, namely Karnataka, Tamil Nadu and Kerala. This river is crucial for drinking water, irrigation and electricity. In India, river sand is a key component of building construction. Through a gamma ray spectrometer with a NaI doped with thallium detector, the natural radioactive elements such as uranium, thorium and potassium (238U, 232Th, 40K) are explored and analysed. This analysis was already published. As per the report of United States Department of Agriculture (USDA) sediment and sand grain size is divided into several types, which include gravel medium sand (250–500µm), fine sand (100–250 µm), very fine sand (50–100µm), silty sand (2–50µm) and clay (<2µm). The range of gravel medium sand to fine sand (>125 µm) and non-magnetic grains were separated with the help of American Society for Testing Materials standard sieve and strong electromagnet. Those two samples for each site were subjected to Gamma ray spectroscopy and analysed. Related parameters like Absorbed-Dose (Din & Dout), Annual effective dose equivalent (AEin & AEout) is computed and correlated. By comparing the results of this investigation to the global average, it can be seen that practically all radioactive parameters are under control. However, the Cauvery River, with the exception of site no 31, does not present a radioactive hazard.

Discovery of Holocene ooid shoals in a siliciclastic delta, De Grey River, North West Shelf, Australia

AbstractOnshore and offshore site investigations along the dryland tide-dominated De Grey River delta (northwestern Australia) led to the unexpected discovery of the largest yet-known marine ooid shoals in the Indo-Pacific region. Ooids exhibit up to 60 tangential aragonitic laminae that were formed around fluvial sediment grains during the late Holocene. Covering an area &amp;gt;1250 km2, their spatial extent rivals in size individual ooid shoals from the Bahamas. Shoals appear to be spatially linked with the De Grey River, suggesting that fluvial outputs, combined with a macrotidal range, facilitated the precipitation of the ooids. Following their formation, ooids were reworked through tidal and wave processes along the delta. As a result, the delta sedimentary features, including beach ridges, mouth bars, and distributary channels, are composed of ooids.This discovery broadens the range of depositional and climatic environments in which ooids can form and demonstrates that fluvial runoff may not inhibit aragonite precipitation. Such a configuration also provides a unique analogue for ancient ooids found in association with siliciclastic grains and further indicates that the interpretation of typical siliciclastic geomorphologies from geophysical data does not preclude the presence of carbonate grains.

Characterizing Trace Metal Contamination and Partitioning in the Rivers and Sediments of Western Europe Watersheds

Adsorption and desorption processes occurring on suspended and bed sediments were studied in two datasets from western Europe watersheds (Meuse and Mosel). Copper and zinc dissolved and total concentrations, total suspended sediment concentrations, mass concentrations, and grain sizes were analyzed. Four classes of mineral particle size were determined. Grain size distribution had to be considered in order to assess the trace metal particulate phase in the water column. The partitioning coefficients of trace metals between the dissolved and particulate phases were calculated. The objective of this study was to improve the description of the processes involved in the transportation and fate of trace metals in river aquatic ecosystems. Useful data for future modelling, management and contamination assessment of river sediments were provided. As it is confirmed by a literature review, the copper and zinc partitioning coefficients calculated in this study are reliable. The knowledge related to copper and zinc (e.g., partitioning coefficients) will allow us to begin investigations into environmental modelling. This modelling will allow us to consider new sorption processes and better describe trace metal and sediment fates as well as pressure–impact relationships.

Terrestrial surface stabilisation by modern analogues of the earliest land plants: A multi-dimensional imaging study.

The evolution of the first plant-based terrestrial ecosystems in the early Palaeozoic had a profound effect on the development of soils, the architecture of sedimentary systems, and shifts in global biogeochemical cycles. In part, this was due to the evolution of complex below-ground (root-like) anchorage systems in plants, which expanded and promoted plant-mineral interactions, weathering, and resulting surface sediment stabilisation. However, little is understood about how these micro-scale processes occurred, because of a lack of in situ plant fossils in sedimentary rocks/palaeosols that exhibit these interactions. Some modern plants (e.g., liverworts, mosses, lycophytes) share key features with the earliest land plants; these include uni- or multicellular rhizoid-like anchorage systems or simple roots, and the ability to develop below-ground networks through prostrate axes, and intimate associations with fungi, making them suitable analogues. Here, we investigated cryptogamic ground covers in Iceland and New Zealand to better understand these interactions, and how they initiate the sediment stabilisation process. We employed multi-dimensional and multi-scale imaging, including scanning electron microscopy (SEM) and X-ray Computed Tomography (μCT) of non-vascular liverworts (Haplomitriopsida and complex thalloids) and mosses, with additional imaging of vascular lycopods. We find that plants interact with their substrate in multiple ways, including: (1) through the development of extensive surface coverings as mats; (2) entrapment of sediment grains within and between networks of rhizoids; (3) grain entwining and adherence by rhizoids, through mucilage secretions, biofilm-like envelopment of thalli on surface grains; and (4) through grain entrapment within upright 'leafy' structures. Significantly, μCT imaging allows us to ascertain that rhizoids are the main method for entrapment and stabilisation of soil grains in the thalloid liverworts. This information provides us with details of how the earliest land plants may have significantly influenced early Palaeozoic sedimentary system architectures, promoted in situ weathering and proto-soil development, and how these interactions diversified over time with the evolution of new plant organ systems. Further, this study highlights the importance of cryptogamic organisms in the early stages of sediment stabilisation and soil formation today.

Sediment controls on the transition from debris flow to fluvial channels in steep mountain ranges

AbstractSteep channel networks commonly show a transition from constant‐gradient colluvial channels associated with debris flow activity to concave‐up fluvial channels downstream. The trade‐off between debris flow and fluvial erosion in steep channels remains unclear, which obscures connections among topography, tectonics, and climate in steep landscapes. Here, we analyze steep debris‐flow‐prone channels across the western United States and observe: (1) similar maximum channel gradients across a range of catchment erosion rates and geologic settings; and (2) lengthening colluvial channels with coarsening sediment cover. Following this compilation, we hypothesize that steep channel gradients are controlled by two competing thresholds of motion for bed‐sediment cover: bed failure by mass‐wasting and fluvial entrainment. We use downstream patterns in discharge, channel geometry, and sediment size to calculate discharges needed to mobilize sediment cover by both mechanisms across channels in the San Gabriel Mountains (SGM) and northern San Jacinto Mountains (NSJM) in southern California. Across steep colluvial channels in both landscapes, decadal discharges are below fluvial entrainment thresholds but above mass‐wasting entrainment thresholds for (median) sediment sizes, consistent with recent debris flows captured by repeat imagery. Colluvial channel gradient is similar despite &gt; 3× contrasts in surface sediment grain size. In concave‐up fluvial channels downstream, decadal discharges exceed fluvial entrainment thresholds, and mass‐wasting is not predicted on lower gradients. In both landscapes, fluvial channels steepen downstream compared to gradients needed to mobilize sediment cover, which we interpret to reflect downstream increases in sediment flux. Coarser sediment supply in the NSJM than the SGM increases fluvial entrainment thresholds, which increases total channel relief in the NSJM by (1) lengthening colluvial channels shaped by debris flows and (2) increasing fluvial channel gradients. Our compilation and downstream analysis show how differing sensitivity of fluvial and debris flow processes to sediment grain size impacts the relative relief of colluvial and fluvial regimes in headwater channel networks.

End-member characteristics of sediment grain size in modern Yellow River delta sediments and its environmental significance

IntroductionThe sediments of the Yellow River delta record the environmental changes in the Yellow River basin on a long time scale and are sensitive to the river diversion and sedimentary environment evolution.MethodsIn this study, cores YDC and YDG in the delta near the estuary of the Yellow River since 1976 were taken as the research object, and the parameterized end-member analysis model was used to analyze the grain-size data of the cores.ResultsThe results show that: The main sediments were silty and sand (58% and 77.9%). The grain-size parameters showed opposite changes with wide grain-size ranges and mixed sizes obviously. End member 1 (EM1) and end member 2 (EM2) were composed of clay and fine silt with fine particle sizes of 0.04 mm and 9.8 mm, respectively, and were deposited under weak hydrodynamic conditions during long-distance transport along the Yellow River. End member 3 (EM3) and end member 4 (EM4) were coarse silt with mode particle sizes of 40.14 mm and 66.89 mm, respectively. These were deposited by waves and tidal currents under strong dynamic conditions.DiscussionAccording to the channel changes and the sedimentary facies data of the modern Yellow River delta, before the Yellow River was diverted in 1996, the cores YDC and YDG were both in the estuary-front bar sedimentary environment. In 1996, the Yellow River was diverted to the Qing 8 course. Subsequently, the core YDC changed to the delta-plain sedimentary facies, and the core YDG changed to the delta-front facies. The sediment sources of the two cores changed from the Yellow River sediments to coastal sediment erosion and resuspension. The sedimentary environment changed from siltation to erosion. The results of this study are of great practical significance for estuary management and coastal engineering construction in the modern Yellow River delta and can provide a scientific basis for ecological protection and high-quality development of the Yellow River basin.

Controls on grain-size variability in the Holocene fill of the Indus Submarine Canyon

ABSTRACT What processes control grain size and bed thickness in submarine canyon deposits? Erosive, shelf-cutting canyons contrast with accretionary basin-floor submarine fan accretionary channels because the former tightly constrain turbidity flows in deep channels. This study addresses such a deep-water depositional system in the Indus Submarine Canyon using a series of cores collected along the canyon. Grain-size analysis was conducted for turbidite and hemipelagic sediment deposited in the Holocene Indus Submarine Canyon mostly by diffuse, fine-grained turbidity currents and hemipelagic hypopycnal plumes. We investigate the links between sedimentary grain size, bedding thickness, facies, and canyon morphology. Well-sorted silt in layers mostly &amp;lt; 2 cm thick dominates the canyon. Core sites in the canyon located downstream of knickpoints have coarser, less well sorted sediments because of current acceleration in these areas and then the slowing of flows downslope. Sediments fine with increasing height above the canyon thalweg, implying deposition from a turbulent plume head. The great depth of the canyon, caused by the exceptionally wide shelf and steep slope, prevents channel overspill which controls sedimentation and channel form in submarine fans. Thalweg sediment fines down-canyon into the mid canyon, where sediment bypassing is inferred. The thickest turbidites are found in the sinuous lower canyon where the gradient shallows from ∼ 0.7° to 0.3°. However, canyon gradient has little impact on mean grain size, but does correlate with bed thickness. The active canyon channel, located in a channel belt gradually becomes less steep, more meandering, and narrower farther downstream. Sinuosity is an influence on turbidite bedding thickness but does not control grain size, in contrast to the situation in submarine-fan channel–levee complexes. Compared to the well-known, more proximal Monterey Canyon of California the grain sizes are much finer, although both systems show evidence of &amp;gt; 200 m plume heads.

East Asian hydroclimate responses to the Eocene-Oligocene transition in the Weihe Basin, central China

The Eocene-Oligocene transition (EOT) at ∼34 Ma marked a significant global cooling on Earth when the ice cover in the Antarctic was formed. How the regional hydroclimate responded to this global cooling event has been extensively investigated, but the specific processes in the Asian monsoon dominated regions are still elusive, due to the lack of independent and detailed timescales. Moreover, previous sedimentary records are mainly from the Asian interior and the influence of tectonic deformation/uplifts in northeastern Tibetan Plateau on the deposit records has not been effectively separated. Here, we present a high-resolution hydroclimate record from a fluvial-lacustrine sequence in the Weihe Basin, central China, which is dated from ∼34.9 to 31.5 Ma by a high-resolution magnetostratigraphy with age controls of mammal fossil assemblages and apatite fission track (AFT) chronometry. This record shows a remarkable hydroclimatic shift occurred at ∼33.7 Ma, as manifested by a sedimentary environment change from lakeshore to lake-delta. The associated significant changes in sediment grain size and magnetic susceptibility exhibit responses of regional drying to the EOT and the Early Oligocene Glacial Maximum (EOGM). In addition, spectral analyses of the time series of paleoenvironmental proxies reveal that the hydroclimate also varied at orbital frequencies with relatively persistent eccentricity cycles (∼100 kyr), accompanied by precession (∼20 kyr) and obliquity (∼ 40 kyr) cycles after the formation of the Antarctic ice sheet at ∼33.2 Ma. Our results suggest that the monsoon-like paleoclimate variations in the mid-latitude northern Hemisphere during the EOT were partly modulated by high-latitude temperature and insolation variations.

Seasonal variations in textural characteristics and depositional environment of foreshore sediments along Kerala Coast, India

The study investigates textural characteristics of foreshore sediment along the central Kerala coast. The selected beaches extend from Ponnani in the north to Alleppey in the south along the west coast of India. Samples were collected from foreshore zone at 22 selected locations to assess sediment grain size distribution and its seasonality. Statistical parameters such as mean (M), standard deviation (SD), skewness (Sk), and kurtosis (K) were used to evaluate the textural characteristics. The purpose of the present study was to examine the textural behaviour of coastal sediments in different seasons from November 2014 to October 2015. Textural characteristics show that the sediment samples are unimodal and bimodal with medium and fine grain sand. The standard deviation (sorting) reveals the sediment samples are very well sorted to moderately sorted with a range of 0.24 phi to 1.03 phi, while the skewness values of the sediment samples range from −0.55 phi to 0.32 phi. The CM plot depicts that the foreshore sediments are transported by tractive currents and transporting the sediments by rolling, bottom suspension with rolling. The analysis of Linear Discriminant Function (LDF) illustrates that the sediment samples are accumulated by aeolian or coastal and shallow turbulent environments.

Trapped microplastics within vertical redeposited sediment: Experimental study simulating lake and channeled river systems during resuspension events

Plastic waste and its fragments (microplastics; <5 mm) have been observed in almost all types of environments. However, the mechanisms underlying the flow and transport processes of plastics are unknown. This is particularly valid for river sediments, where complex interactions occur between particles and influence their vertical and horizontal distribution patterns. In this study, we investigated the vertical redistribution of 14 pristine microplastics (MPs) with different densities, sizes, and shapes within disturbed sediment without lateral transport (i.e., low-velocity flow). MPs were spiked into sediments (height: 8 cm) in a column with a height of 1 m (diameter: 6 cm) filled to the top with water. The sediment was perturbed by turning the column upside-down to simulate remobilization and the subsequent deposition of sediment. After the complete sedimentation of the particles, the water column was filtered and the sediment was cut into vertical sections. MPs were then extracted from the sediment using sieves and a density separation method, and were counted under a stereomicroscope. Low-density polymers were mainly recovered in the water column and at the surface of the sediment, whereas high-density polymers were found within all sediment sections. The vertical distribution of high-density polymers changes primarily with the sediment grain size. The distribution of each polymer type changes depending on the size and/or shape of the particles with complex interactions. The observed distributions were compared with the expected distributions based only on the vertical velocity formulas. Overall, the formulas used did not explain the sedimentation of a portion of low-density polymers and predicted a lower distribution in the sediment than those observed in the experiment. In conclusion, this study highlights the importance of considering MPs as multi-dimensional particles and provides clues to understand their fate in low-velocity flow systems, considering that they undergo scavenging in sediments.

A preliminary study of soft bottom benthic communities in an area affected by intense maritime traffic (Slovenian Sea, Northern Adriatic)

Maritime traffic and port activities pose several environmental and ecological problems in the marine environment. The purpose of this study was to provide baseline data for the future assessment of anthropogenic impacts related with port activities in Slovenian Sea (Northern Adriatic Sea). The macrobenthic communities near the port of Koper, as well as sites offshore were analysed. Results showed that the sites offshore were generally richer and more structured than sites inside the Port area. Those differences were explained partly by depth and sediment grain size. The ecological quality indicated by M-AMBI index resulted Good/High at all the sampling sites. However, the k-dominance curves indicated a disturbance at certain sites, in particular in the port channels. This work highlights the need for consistent monitoring programs to provide baseline data for future studies assessment of anthropogenic impacts.

Gas-saturated carbon dioxide hydrates above sub-seabed carbon sequestration site and the formation of self-sealing cap

Storing CO2 in sub-seabed sediments is a promising CO2 sequestration method to reduce atmospheric CO2 concentrations and mitigate climate change. Leaked CO2 from the sequestration site can form CO2 hydrates in the sediment and reduce the effective permeability of the sediment layer, developing a self-sealing cap above the storage site. Previous studies usually treat the CO2 hydrate layer similarly to a methane hydrate reservoir. However, unlike methane, CO2 has a larger solubility that increases significantly with depth, leading to high gas saturation levels in the sediment. Near the base of the CO2 hydrate stability zone, CO2 free gas, CO2 hydrate and dissolved CO2 coexist, and elevated surface energies of the curved surfaces of bubbles and hydrate crystals in pores shift the phase equilibria. The bubbles entrapped in the three-phase zone help to reduce the effective permeability besides accumulate CO2 hydrates. We simulate the three-phase zone in a shallow seabed using Monte Carlo methods in packed synthetic mono-dispersed spherical sediment grains, taking into account of the surface curvatures of the gas–liquid and hydrate–liquid interfaces in irregular pore spaces constrained by the sediment grains, and estimate the permeability reduction caused by entrapped CO2 bubbles. Finer sediment grains, larger geothermal gradients and shallower seawater all tend to broaden the zone, and the effective permeability in the three-phase zone can be further reduced by up to an order of magnitude than that with hydrates only. We also analyze the sensitivity of the three-phase zone due to temperature and pressure perturbations, and the results suggest possible thickness and depth variations of the zone due to cyclic temperature and sea level changes. This work demonstrates the difference between the CO2 hydrate-bearing sediment layer and the methane hydrate reservoir, and provides insight into the formation mechanism of the self-sealing cap above the sequestration sites.

Thermal Properties of Pressure Core Samples Recovered From Nankai Trough Wells Before and After Methane Hydrate Dissociation

AbstractThe thermal properties of methane hydrate (MH)‐bearing sediments are necessary for developing gas production technologies (e.g., gas production rate prediction). The direct thermal property measurement of a general MH reservoir is difficult because it demands an advanced coring and measuring technology. Therefore, a good thermal property value estimation model for a system containing sediment grains, water, MH, and gas is necessary. In 2018, the pressure core samples were recovered from the AT‐CW1 and AT‐CW2 wells in Nankai Trough of Japan. Using a single‐sided transient plane source method, we measure herein the thermal property values of those core samples and estimate their thermal conductivity by improving existing models. The measured thermal conductivity (λ), specific heat (ρCp), and thermal diffusivity (α) of the MH‐bearing sediments before and after MH dissociation are obtained. The de Vries model agrees well with the measured thermal conductivity values before and after the MH dissociation. For the random distribution (geometric mean) model, the difference between the estimation values and the data after the MH dissociation increases as the gas saturation Sg′ increases. In the worst case, the distribution model shows an 87.6% error, while the de Vries model yields 5.2% of the same. We propose and use an estimation method of the thermal property values in an MH reservoir, which requires classical thermophysical models and well log data. The in‐situ thermal property values can be estimated when the log data are highly accurate.

Observed correlations between the sediment grain size and the high-frequency backscattering strength.

In March 2019, Teledyne RESON and the Applied Physics Laboratory at the University of Washington conducted surveys with a calibrated multibeam echosounder at ten sites in Sequim Bay, a shallow sheltered bay in Washington State, USA. For each site, the mean grain size was obtained from a diver core sample, and estimates of the backscattering strength at frequencies ranging between 200 and 350 kHz were calculated. The correlation between the backscattering strength and the normalized grain size have been investigated for the grazing angles 45° and 75°. For 45°, a correlation consistent with previous results has been found. It demonstrates the potential for simple seabed classification.

Benthic metabolism and nutrient uptake vary with geomorphology and season in a lowland river

Meandering rivers are characterized by geomorphic units like cut banks, point bars, and thalwegs. These units arise from interactions between hydrological and geomorphological forces. However, the individual contributions of geomorphic units to whole-river metabolism or nutrient processing are unclear because these quantifications are often done at larger spatial scales. We used closed recirculating chambers to measure benthic gross primary production (GPP), respiration (R), N uptake or release, and P uptake or release at bimonthly intervals over 1 y at different geomorphic units in the Mulde River, Germany. We compared GPP, R, and nutrient processing among a cut bank, a point bar, and the thalweg at a natural meander. We also compared the cut bank of this natural meander with a cut bank fixed by riprap at a human-altered meander. In the natural meander, GPP, R, and nutrient processing rates were higher at the point bar than the cut bank or thalweg. These differences are likely related to larger sediment grain sizes that provide a more stable substrate for microbial communities. A strong interaction between geomorphic units and time for GPP and NH4+ fluxes suggested that differences in nutrient processing rates among geomorphic units were restricted to specific times during the year. Specifically, we found that the nutrient processing rates differed among geomorphic units during the summer, but not winter. Furthermore, in June and August 2017, R was 2 to 3× lower at the cut bank stabilized by riprap than at the natural cut bank. Our results demonstrate that rivers are composed of functionally distinct geomorphic units susceptible to human-induced hydromorphological degradation. However, strong interactions between space and time and large within-geomorphic unit variability propose that local drivers influence ecosystem function, suggesting that we need additional research to resolve these drivers at the scales of geomorphic units.

Taphonomic analysis of the exceptional preservation of early bird feathers during the early Cretaceous period in Northeast China

Fossil soft tissues contain important and irreplaceable information on life evolution, and on the comprehensive understanding of the nature of Mesozoic ecosystems. Compared to other fossil soft tissues, Jehol Biota feathers are more commonly reported. However, taphonomic analysis of these feathers is lacking. Here, five Jehol Biota specimens of early bird Sapeornis chaoyangensis with differently preserved feathers were selected. One specimen, STM 15-36, has a complete set of extraordinarily preserved feathers. An interesting consequence was revealed by their host sediment Zr/Rb analysis that specimen STM 15-36 possesses the coarsest sediment grain size but the best-preserved feathers. More geochemical analyses of host sediments, including organic carbon isotopes and major elements, were conducted to restore the paleoenvironment during those Sapeornis’ burial. The result mainly shows that the paleoclimate when Sapeornis STM 15-36 was buried is warmer and wetter than those of the other four; STM 15-36 host sediment has a pure terrestrial-derived organic input, while the others are aquatic algae. In addition, redox-sensitive trace elements analysis indicates the lake bottom-water preserved Sapeornis STM 15-36 is anoxic and restricted, being more oxygen-depleted than those of the other four. Therefore, the transportation and burial of Sapeornis STM 15-36 were preliminarily inferred as: the carcass of Sapeornis STM 15-36 was transported rapidly into the lake by a short and strong rain flush, and then was buried quickly by the accompanying terrestrial debris; the subsequent anoxic and restricted burial environment inhibited bioturbation and hydrodynamic disturbance on Sapeornis STM 15-36 and its host sediments, allowing its whole set of feathers to be delicately preserved. This finding provides a valuable case study on understanding the taphonomy of fossil soft tissues’ exceptional preservation in Jehol Biota.

Numerical Simulation on the Local Scour Processing and Influencing Factors of Submarine Pipeline

To investigate the different influencing characteristics of local scour around submarine pipelines, hydrodynamic and sediment transport two-dimensional models based on Flow-3D are used to numerically simulate the local scour around the pipeline under steady currents. An RNG k-ε turbulence model is applied to simulate the turbulent flow field around the pipeline. The instantaneous shear stress of the bed surface is taken as the starting and transporting conditions of the sediment. The simulation results of the equilibrium scour depth and terrain around the pipeline are verified with the previous experimental results, which perform with good agreement. Then, the numerical simulation method is applied to investigate the local scour process around the pipeline. The results show that shear stress is the main driving force of scour around a pipeline. The velocity, sediment grain size, pipeline diameter, and the initial gap between the pipeline and the seabed, significantly affects submarine pipeline equilibrium scour depth and terrain in varying degrees.

On the occurrence of low concentration hyperpycnal river plumes in a small mountainous river-canyon system

This study aimed to understand the mechanisms controlling the formation of hyperpycnal river plumes in small mountainous rivers. The suspended sediment concentration (SSC) and grain size distribution in the Gaoping River were obtained by field observations and used as the basis for numerical simulations. The SSC of the Gaoping River during Typhoon Soudelor was lower than 20 g/L according to the real-time SSC estimated using the calibration curve between turbidity and SSC. The calculated median grain size of the suspended sediments was 15.15 μm, which indicated that the silt accounted for a large proportion of the flow. The observed grain-size distribution and SSC were incorporated into a numerical model to examine the conditions under which hyperpycnal river plumes occur. The model results revealed a three-dimensional process near the river mouth: cross-canyon currents converge near the head of the canyon, and the topography of the submarine canyon further confines the path and width of the hyperpycnal river plume. The descending plume continues to move through the steep slope of the submarine canyon. In addition, the simulation results showed that the SSC of the hyperpycnal river plumes increases as the grain size of riverine sediment decreases. However, if the sediment grain size is smaller than 8 μm, most of the suspended sediment remains on the sea surface in a surface plume.