Sediment Transport Mechanisms Research Articles

Sand and dust storm trajectories from Iraq Mesopotamian flood plain to Kuwait

Although Kuwait is greatly impacted by sand and dust storms (SDS) from Southern Iraq, to date little is known about the nature of these storms. Kuwait is vulnerable to SDS trajectories from the middle Euphrates region, specifically, from two “hot spot” areas (Al-Batha and Mamlahat Al-Samawah) of 4550 km2 located 250 km from its northern border. This study explores the transboundary SDS jets originating from Southern Iraq using Moderate Resolution Imaging Spectroradiometer (MODIS) images obtained from Aqua and Terra satellites over a twelve-year period (2007–2018). Furthermore, an analysis of a 5-day diurnal variation (two days prior, the day of the SDS occurrence, and two days after) explored the hourly patterns of visibility and wind speed, as well as grain size distribution of soil samples to better understand grain size compositions and sediment transport mechanisms. Satellite images confirmed that dust storm jets originated from the “hot spot” in southern Iraq and spread over Kuwait and extended to neighboring Arab Gulf countries as far as Bahrain (900 km) and Qatar (1200 km). In general, the highest wind speed and lowest visibility values were recorded in Northern of Kuwait, with suspended dust sustained for two days following the dust storm. The largest silt and clay fractions (grains ≤63 μm) were identified at the center and west Sabkha region of the “hot spot” area. Very fine sand particles (63–250 μm) were identified within the crescent sand dunes (Barchans) and artificial sand dunes (Al-Fajr). It is recommended that sustainable rehabilitation and land restoration of the “hot spot” area will result in the elimination of the long-range transport of SDS jet streams affecting the downwind Gulf countries.

Reach‐scale changes in channel geometry and dynamics due to the coastal backwater effect: the lower Trinity River, Texas

AbstractIn this paper we use multiple field surveys spanning several decades to systematically evaluate the geomorphic consequences of a change in flow hydraulics from uniform flow to backwater flow for the lower Trinity River in east Texas, USA. Spatial changes in lateral migration rate, channel geometry, and point bar size correspond to two distinct geomorphic zones. Within the upstream uniform flow reach, the river channel is defined by fully developed point bars and a high rate of lateral channel migration. This zone transitions where the median channel bottom elevation drops below sea level. At this point flow is affected by the backwater influence of the Trinity Bay water surface elevation, as opposed to being bed slope control dominated. The change in hydraulics within the backwater zone is reflected in the channel morphology, which is characterized by smaller point bars, narrower and more symmetrical cross‐sectional channel geometry, lower channel migration rates, and little to no bend deformation or cutoffs. Studying the connection between channel geometry, river bend kinematics, sediment transport, and fluid mechanics in each zone provides a deeper understanding of the relationship between channel shape and river mechanics. © 2019 John Wiley & Sons, Ltd.

Fluvial and Eolian Sediment Mixing During Changing Climate Conditions Recorded in Holocene Andean Foreland Deposits From Argentina (31–33°S)

Continental drainage systems archive complex records of rock uplift, source area relief, precipitation, glaciation, and carbon cyclicity driven largely by tectonics and climate. Significant progress has been made in linking such external environmental forcings to the geomorphic expression of landscapes and the stratigraphic record of depositional basins in coastal and offshore areas. However, there are large uncertainties in the degree to which sediment dispersal processes can modify signals between the erosional sources and the depositional sinks. We investigate a Holocene sediment transfer zone with contrasting fluvial and eolian sediment transport mechanisms to understand how river and wind processes impact the propagation of environmental signals in continental-scale drainage systems. To quantify these processes, we employ sediment fingerprinting methods for unconsolidated sand samples (detrital zircon U-Pb geochronology), incorporate sediment mixing models, and correlate the findings with the regional geologic and geomorphic framework. Three contrasting source regions deliver sediment to the Andean foreland: volcanic rocks of the Frontal Cordillera, sedimentary rocks of the Precordillera, and metamorphic basement of the Sierras Pampeanas. Although all samples of Holocene eolian dunes accurately record sediment input from three fluvial source regions, spatial variations in U-Pb results are consistent with north-directed paleowinds, whereby river sediments from Frontal Cordillera sources are transported northward and progressively mixed with river sediments from Precordillera and Sierras Pampeanas sources. In contrast, samples of modern rivers show progressive southward (downstream) mixing along a large axial fluvial system. Sediment mixing induced by eolian transport and reworking of various sources is likely a critical, climate-modulated process in the propagation of environmental signals, potentially involving the aliasing of tectonic signals, local storage and recycling of synorogenic river sediment, and cyclical patterns of sediment starvation and delivery to distal zones of accumulation.

Morphological Computation of Dune Evolution with Equilibrium and Non‐Equilibrium Sediment‐Transport Models

AbstractThis paper presents an exploratory study that comprises the implementation and comparison of different approaches and parameterization of sediment transport mechanisms in a process‐based morphological model for simulating river dunes. The purpose of this study was to assess the underlying physical processes associated with sediment transport and dune evolution simulated by the model using two different bedload transport models: a non‐equilibrium approach considering saltation distance and an equilibrium approach with the incorporation of the effect of the local bed slope. The study comprised detailed analysis of the bed shear stress and sediment transport over a dune during time varying flows, comparing both transport models and revealing distinctive transient features of bedload transport and dune evolution. We also improved a non‐equilibrium transport model by incorporating a formulation for sediment saltation distance as a length‐scale. Using both sediment transport approaches, the morphological model was applied to replicate a large‐scale field experiment. Notably, the model yielded the quasi‐equilibrium dune feature reasonably well using either sediment‐transport formulation. However, detailed analysis of simulated spatial and temporal features of sediment transport and the dune evolution process were found to be noticeably different. Even though both sediment transport mechanisms appear to work adequately at a basic level, the major difference between the two approaches is the underlying transport process over the dunes and time‐scale of the dune evolution process.

Mechanism of sediment transport by flood and longitudinal peak discharge amplifications in the Yellow River

As the general principle of river bed evolution during the fluvial process, the channel is formed by river flows, while the movement of river flows is contained by channels. When the hyperconcentrated flood propagates along the wandering reach of the Yellow River, the peak discharge of the flood can increase along the reach. Due to the recurrence of this phenomenon, attentions have been drawn from various stakeholders, since the amplifications of flood peak can jeopardize flood control works. By analyzing the field observed data, we present our research findings of “scour during rising” and “deposit during falling” of a flood event, as well as the sediment transport mechanism with constant discharge. The bedform affects the characteristics of sediment transport and the resistance force. When the bedform is in the dynamic equilibrium state, sediment transport characteristics can be described as “the more sediment input, the more sediment output”. When the shear stress created by flow acting on bed is increasing, scour is observed on the channel bed. On the contrary, when shear stress is decreasing, deposition is observed. When the shear stress remains the same, sediment transport is in the equilibrium state. After the operation of Xiaolangdi Reservoir, due to coarsen of the bed material, the bedform resistance increased. When the flow condition changes and the bed roughness decreased abruptly, the increasing flow velocity can result in the reduction of channel storage volume. This is the main reason for the longitudinal amplifications of peak discharge in the wandering reach of the Yellow River.

Sediment Transport Mechanisms in a Lagoon with High River Discharge and Sediment Loading

The aim of this study was to investigate the sediment dynamics in the largest lagoon in Europe (Curonian Lagoon, Lithuania) through the analysis of in situ data and the application of a sediment transport model. This approach allowed to identify the propagation pathway of the riverine suspended sediments, to map erosion-accumulation zones in the lagoon and calculate the sediment budget over a 13-year-long simulation. Sampled suspended sediment concentration data are important for understanding the characteristics of the riverine and lagoon sediments, and show that the suspended organic matter plays a crucial role on the sediment dynamics for this coastal system. The numerical experiments carried out to study sediment dynamics gave satisfactory results and the possibility to get a holistic view of the system. The applied sediment transport model with a new formula for settling velocity was used to estimate the patterns of the suspended sediments and the seasonal and spatial sediment distribution in the whole river–lagoon–sea system. The numerical model also allowed understanding the sensitivity of the system to strong wind events and the presence of ice. The results reveal that during extreme storm events, more than 11.4 × 106 kg of sediments are washed out of the system. Scenarios without ice cover indicate that the lagoon would have much higher suspended sediment concentrations in the winter season comparing with the present situation with ice. The results of an analysis of a long-term (13 years) simulation demonstrate that on average, 62% of the riverine sediments are trapped inside the lagoon, with a marked spatially varying distribution of accumulation zones.

Numerical simulation of sediment transport in a U-shaped channel with lateral intake: Effects of intake position and diversion angle

In this work, the mechanism of sediment transport in a U-shaped channel with a lateral intake is investigated experimentally and numerically, together with the processes of sediment entry into the intake itself and formation of bed topography. Dry sediment is injected into a steady flow in a rigid channel with a bend and sediment particles are traced in time. In order to validate the numerical model, the three components of the flow velocity, as well as the sediment path in time and the diverted sediment ratios, are measured experimentally. A numerical Discrete Phase Model (DPM) is then applied to study the effect of the intake position and diversion angle on the sediment transport mechanism in the bend. The DPM has, in fact, the capability of specifying for each particle its position relative to a reference time and space and, thereby, it is used in this study to analyze the phenomenon evolution and determine the sediment particles diverted into the intake. The comparison between the experimental data and the DPM numerical results shows a good agreement. In order to investigate the mechanism of sediment transport and to evaluate the percentage of the diverted sediments, a parametric study is then conducted through the numerical model, with different positions of the outer bend of the channel, diversion angles of the lateral intake and diversion discharge ratios. The results show that the mechanism of sediment entry into the lateral intake is affected by the diversion discharge ratio. For low discharge ratios, the mechanism of sediment entry to the lateral intake only consists of continuous entrance from the upstream edge of the intake. With the increase of the discharge ratio, it consists of a continuous entrance from the downstream edge and a periodic entrance from the upstream edge of the intake. The DPM results show that, for all diversion discharge ratios, the minimum percentage of sediment entered into the lateral intake corresponds to the position of 120∘ and diversion angle equal to 50∘.

Analysis of Measured Surface Nearshore Currents Using Multiple Drifters on Anmok Beach, South Korea

Lim, H.S.; Kim, M.J.; Kim, D.H., and Lee, H.J., 2019. Analysis of measured surface nearshore currents using multiple drifters on Anmok beach, South Korea. In: Lee, J.L.; Yoon, J.-S.; Cho, W.C.; Muin, M., and Lee, J. (eds.), The 3rd International Water Safety Symposium. Journal of Coastal Research, Special Issue No. 91, pp. 46-50. Coconut Creek (Florida), ISSN 0749-0208.To understand the mechanism of sediment transport and beach erosion processes in the surf zone near the coast of the Korean Peninsula, the development of coastal erosion control technology, an R&D project supported by the Korean government, has been conducted since 2013. Anmok Beach, located on the eastern coast of the Korean Peninsula, has been studied by measuring currents and sediment transport using bottom-mounted acoustic sensors and offshore long-term wave observation since February 2015. Moreover, for measurement of surface currents, multiple Lagrangian drifters were developed and successfully deployed nine times near the surf zone and submerged breakwaters close to Kangneung northern breakwaters. The variation of the measured bottom currents was induced directly by seasonal wave height and direction, depending on the incoming waves from the NNE in winter, ENE in summer, and NE, normal to the shoreline, in the case of high waves. However, the measured surface currents were affected not only by the incoming waves in the presence of high-energy waves, but also by wind speed and direction in the presence of low-energy waves. In this study, the observed surface nearshore currents measured by small Lagrangian GPS drifters near the surf zone and submerged breakwaters at Anmok were analyzed to investigate the variability of the wave-induced currents and nearshore surface currents generated by different wave and wind environments. The drifter experiments showed that offshore surface currents in the surf zone were predominantly developed, especially by strong seaward winds that opposed the direction of the weak waves. However, onshore surface currents were developed by wave-induced currents generated by the interaction of waves from offshore accompanied by sea winds. This measurement is now used to calibrate and validate the coastal sediment modeling system for the eastern coast of the Korean Peninsula.

Experimental Investigations of Combined Flow Sediment Transport

Abstract In shallow marine environments gravity-driven currents (e.g., hyperpycnal flows) often traverse surface wave fields, and the resulting complex flows are key mechanisms for offshore sediment transport. Our laboratory experiments illustrate how surface waves alter sediment transport in gravity-driven density currents. The addition of a wave field to a gravity-driven current resulted in a 7–8.5% increase in the downslope transport of the deposit volume. Additionally, oscillatory velocities recorded at downslope locations in surface-wave-altered turbidity currents were larger than wave-field velocities measured at the same location without a turbidity current. These observations indicate that surface waves alter turbidity currents in a longitudinally complex manner whereby the influence of oscillatory currents is transported downslope within the body of the turbidity current. These effects were observed in a conservative case: the maximum orbital velocities of the wave field were an order of magnitude less than the maximum unidirectional velocities of the current. We predict that if the velocities of the wave field and the current were sub-equal, a plausible scenario for hyperpycnal flows in near-shore, deltaic, and proximal shelf environments, these effects would be substantially more effective. This work has significant implications for modeling offshore sediment transport in shallow marine environments and for interpreting the deposits of such flows, most notably that the presence or absence of combined-flow ripples might not indicate whether the current was deposited above or beneath wave base.

Regularity of sediment transport and sedimentation during floods in the lower Yellow River, China

The flood season is the main period of flow, sediment transport, and sedimentation in the lower Yellow River (LYR). Within the flood season, most of the flow, sediment transport, and sedimentation occurs during flood events. Because of the importance of floods in forming riverbeds in the LYR, the regularity of sediment transport and sedimentation during floods in the LYR was studied. Measured daily discharge and sediment transport rate data for the LYR from 1960 to 2006 were used. A total of 299 floods were selected; these floods had a complete evolution of the flood process from the Xiaolangdi to the Lijin hydrological stations. For five hydrological stations (Xiaolangdi, Huayuankou, Gaocun, Aishan, and Lijin), a correlation was first established for floods of different magnitudes between the average sediment transport rate at a given station and the average sediment concentration at the closest upstream station. The results showed that the sediment transport rate at the downstream station was strongly correlated with the inflow (upstream station) sediment concentration during a flood event. A relation then was established between sedimentation in the LYR and the average sediment concentration at the Xiaolangdi station during a flood event. From this relation, the critical sediment concentrations were obtained for absolute erosion, sedimentation equilibrium, and absolute deposition during floods of different magnitudes in the LYR. The results of the current study contribute to a better understanding of the mechanisms of sediment transport and the regularity of sedimentation in the LYR during floods, and provide technical support to guide the joint operation of reservoirs and the regulation of the LYR.

A 4,500‐Year‐Long Record of Southern Rocky Mountain Dust Deposition

AbstractDust emissions from southwestern North America (Southwest) impact human health and water resources. Whereas a growing network of regional dust reconstructions characterizes the long‐term natural variability of dustiness in the Southwest, short‐term fluctuations remain unexplored. We present a 4.5‐millennia near‐annual record of dust mass accumulation rates from the southern Rocky Mountains, CO. Using microscanning X‐ray fluorescence and a geochemical end‐member mixing model, the record confirms dust increased with human disturbance beginning around 1880 CE, reversing a long‐term decreasing trend potentially related to changes in effective moisture, wind, and vegetation. However, increases in dust mass accumulation rates do not correspond to years or periods of drought, as characterized by tree rings. This result suggests sediment supply and transport mechanisms have a strong influence on dust deposition. The record shows the Southwest is naturally prone to dustiness; however, human disturbances have a large influence on dust emissions, which can be mitigated by changing land use.

Visible Light Communication System for Offshore Wind Turbine Foundation Scour Early Warning Monitoring

Offshore wind farms have a superior wind source to terrestrial wind farms, but they also face more severe environmental conditions such as severe storms, typhoons, and sea waves. Scour leads to the excavation of sediments around the foundations of structures, reducing the safe capacity of the structures. The phenomenon of pier scour is extremely complex because of the combined effects of the vortex system involving time-dependent flow patterns and sediment transport mechanisms. A real-time scour monitoring system can improve the safety of structures and afford cost-effective operations by preventing premature or unnecessary maintenance. This paper proposes an on-site scour monitoring system using visible light communication (VLC) modules for offshore wind turbine installations. A flume experiment revealed that the system was highly sensitive and accurate in monitoring seabed scour processes. This arrayed-VLC sensory system, proposed in this paper, has considerable potential for safety monitoring and also can contribute to improving the accuracy of empirical scour formulas for sustainable maintenance in the life cycle of offshore structures.

Ground-penetrating radar and electrical resistivity tomography reveal a deep stratigraphic sequence at Mochena Borago Rockshelter, southwestern Ethiopia

Archaeological sites in rockshelter environments have long been noted to provide excellent preservation of cultural and stratigraphic deposits, encapsulating the past occupational history of inhabitants over time. Such sites in eastern Africa have shed light on the behavior of Homo sapiens during critical landmarks in evolutionary history. Mochena Borago is a large rockshelter located in southwest Ethiopia. The site contains a dense accumulation of flaked stone artifacts deposited in archaeological horizons that span Marine Isotope Stage 3 (MIS 3), a period where securely-dated sites are limited in the archaeological record. In this study, we present the results of a ground penetrating radar (GPR) and electrical resistivity tomography (ERT) survey. Due to complexities in the interpretation of sedimentary deposits observed in non-contiguous excavation areas, geophysical surveys were collected to image vertical and lateral variations in stratigraphy and depth to the basement as a proxy for total sediment thickness. Data were interpreted based on eleven distinct GPR facies, where three main facies are highlighted as they relate to irregular, erosional and depositional sedimentary processes. The facies describe mechanisms for sediment transport into the shelter as well as post-depositional processes. Geophysical data also indicate the presence of laterally extensive subsurface unconformities and evidence of a structured basement that has controlled sedimentary deposition over time. We conclude that the GPR and ERT data acquired at Mochena Borago illuminate subsurface stratigraphic boundaries, and aid in the interpretation of sedimentary packages across the site.

Estimating sediment yield at Kaduna watershed, Nigeria using soil and water assessment tool (SWAT) model

Over the years, sedimentation has posed a great danger to the storage capacity of hydropower reservoirs. Good understanding of the transport system and hydrological processes in the dam is very crucial to its sustainability. Under optimal functionality, the Shiroro dam in Northern Nigeria can generate ∼600 MW, which is ideally sufficient to power about 404,000 household. Unfortunately, there have not been reliable monitoring measures to assess yield in the upstream, where sediments are sourced into the dam. In this study, we applied the Soil and Water Assessment Tool (SWAT) to predict the hydrological processes, the sediment transport mechanism and sediment yield between 1990 and 2018 in Kaduna watershed (32,124 km2) located upstream of the dam. The model was calibrated and validated using observed flow and suspended sediment concentration (SSC) data. Performance evaluation of the model was achieved statistically using Nash-Sutcliffe (NS), coefficient of determination (r2) and percentage of observed data (p-factor). SWAT model evaluation using NS (0.71), r2 (0.80) and p-factors of 0.86 suggests that the model performed satisfactorily for streamflow and sediment yield predictions. The model identified the threshold depth of water (GWQMN.gw) and base flow (ALPHA_BF.gw) as the most sensitive parameters for streamflow and sediment yield estimation in the watershed. Our finding showed that an estimated suspended sediment yield of about 84.1 t/ha/yr was deposited within the period under study. Basins 67, 71 and 62 have erosion prone area with the highest sediment values of 79.4, 75.1 and 73.8 t/h respectively. Best management practice is highly recommended for the dam sustainability, because of the proximity of erosion-prone basins to the dam.

The Structure of the Net Alongshore Sediment Transport in the Eastern Gulf of Gdansk

The published schemes of the net alongshore sediment transport near the eastern coast of Gdansk Bay have been systematized. Considerable discrepancies have been identified in the structure and localization of the convergence zones of opposite currents. The results of station-based measurements of bottom currents near the Strait of Baltiysk at depths of 6–16 m were used to show that, at winds >6 m/s, the alongshore currents run along the alongshore wind component. The morphodynamic accumulation (filling of the entry corner and abrasion in the shadow zone of the obstacle) and abrasion (orientation of the abrasion depression at the extreme end of the harbor moles) criteria are discussed. The abrasion criterion is shown to work better than the accumulation criterion in determining the net sediment transport in the coastal reaches with a normal or near-normal approach angle of the wave energy flow toward the shore. The specific features of the mechanism of sediment transport from south to north, by-passing Baltiisk harbor moles, from the abrasion to accumulation shore segments are given. Two schemes of the opposite Vistula and Sambian alongshore sediment flows are proposed: before the construction of the entry harbor moles in the Baltic Strait with a vast migration zone near the northern end of the Vistula Spit and after the construction of these moles, which has narrowed this zone and shifted its southern boundary northward toward the moles.

Numerical simulations of the 2004 Indian Ocean tsunami deposits' thicknesses and emplacements

Abstract. After more than a decade of recurring tsunamis, identification of tsunami deposits, a part of hazard characterization, still remains a challenging task that is not fully understood. The lack of sufficient monitoring equipment and rare tsunami frequency are among the primary obstacles that limit our fundamental understanding of sediment transport mechanisms during a tsunami. The use of numerical simulations to study tsunami-induced sediment transport was rare in Indonesia until the 2004 Indian Ocean tsunami. This study aims to couple two hydrodynamic numerical models in order to reproduce tsunami-induced sediment deposits, i.e., their locations and thicknesses. Numerical simulations were performed using the Cornell Multi-grid Coupled Tsunami (COMCOT) model and Delft3D. This study reconstructed tsunami wave propagation from its source using COMCOT, which was later combined with Delft3D to map the location of the tsunami deposits and calculate their thicknesses. Two-dimensional horizontal (2-DH) models were used as part of both simulation packages. Four sediment transport formulae were used in the simulations, namely van Rijn 1993, Engelund–Hansen 1967, Meyer-Peter–Mueller (MPM) 1948, and Soulsby 1997. Lhoong, in the Aceh Besar District, located approximately 60 km southwest of Banda Aceh, was selected as the study area. Field data collected in 2015 and 2016 validated the forward modeling techniques adopted in this study. However, agreements between numerical simulations and field observations were more robust using data collected in 2005, i.e., just months after the tsunami (Jaffe et al., 2006). We conducted pit (trench) tests at select locations to obtain tsunami deposit thickness and grain size distributions. The resulting numerical simulations are useful when estimating the locations and the thicknesses of the tsunami deposits. The agreement between the field data and the numerical simulations is reasonable despite a trend that overestimates the field observations.

3D stratigraphic forward modeling of an ancient transgressive barrier system: A case study of accuracy and sensitivity

Accuracy of geological modeling and understanding of the controlling parameters in sedimentary systems evolution are challenges in both academy and industry. Uncertainty in the prediction of spatial and temporal facies distributions and difficulties in quantitative analysis of controlling parameters are current challenges. To increase geological model certainty and sedimentary process understanding, computational modeling has evolved exponentially during the last 50 years. In this study, 3D stratigraphic forward modeling technique is used to simulate an ancient transgressive barrier system of southern Brazil, deposited during the Lower Permian in the Paraná Basin, upper part of the Rio Bonito Formation. In the study area, the depositional systems are part of a large transgressive cycle that includes fluvial-estuarine facies at the base and barrier-lagoon deposits (associated with the development of salt marshes) at the top. Throughout the region, offshore strata cover the barrier-lagoon facies. The simulation successfully represented the retrograde evolution of the coastal barrier system, with longshore currents as the main transport mechanism of sediments. The evolution of the barrier system started with upper shoreface deposits overlying the lagoon system facies in the south. Later, lower shoreface sediments covered upper shoreface deposits. Then, shoreline migration continued landward. Finally, offshore transition deposits covered all previous deposits. Simulations and tests of controlling parameters allowed an adjustment to actual thickness and lithologies up to 83%. These simulations allowed for the analysis of model sensitivity, in particular to the influence of parameters that control sedimentary evolution. The main controlling parameter was sediment supply (volume and composition), followed by time step. Initial bathymetry and sediment velocity had less of an impact.

Experimental study on evolution of lacustrine shallow-water delta

In the process of delta evolution, the flow regime and sediment transport change with the development of topography. Flow is the dynamic factor of shaping topography, while sediment scouring and silting is the direct cause of topography formation, and they are constrained and influenced by topographic changes simultaneously. In order to explore rules of water and sediment movement and topographic sedimentation of delta under microscale conditions, we studied the phenomena, rules and evolution mechanism of flow movement, sediment transport, particle sorting, topographic sedimentation, and flow path generation, merger and recombination under microscale conditions from the perspective of physical experiment. The influence of different external conditions on lacustrine shallow-water delta evolution and the self-organization of delta evolution are studied through comparative experiments under the condition of distinct sediment supplied rates or lake levels and repeatability experiments under the same conditions. Some rules of flow movement, sediment transport and topographic sedimentation such as characteristics of each stage during the process of evolution of lacustrine shallow-water delta, the periodic change of flow regime and the prediction model, the characteristics of sedimentary morphology under different conditions, and the influence of stochastic factors on delta evolution are summarized. The experiments suggest coupled linkage of interaction of water and sediment, self-organization of flow path evolution and the equilibrium tendency of delta structure under the action of coupling interaction of multiple factors of water, sediment and topographic sedimentation.

Sediment transport mechanisms from the slopes and canyons to the deep basins south of Crete Island (southeast Mediterranean)

Sediment transport processes from the slopes to the deep basins were studied in the southern Cretan margin (Eastern Mediterranean) by means of swath bathymetry, seismic reflection (airgun) profiling, and gravity coring. Mud/silt turbidites, developed in structureless or laminated patterns, appear to dominate the continental slope and the 2700–3600-m deep depressions of Samaria, Messara, and Gortys. These deposits are the result of successive mass transport events and turbidity currents. Over-steepening caused by strike–slip shearing associated with extensional tectonic activity in the shallow crustal levels, shaking due to significant seismic activity, and the presence of weak sediment layers are responsible for frequent triggering of slope failures and the subsequent formation of turbidity currents on the Gavdos slope. On the Cretan slope, sediments channeled as turbidity currents through canyons proved to be the major delivery mechanism, together with debris flows. Subordinate contributions of hemipelagic sediments occur only in the Messara basin. Moreover, steep non-incised slope areas and slope-confined canyons of the Gavdos slope were found to provide comparable sediment contribution with the fluvially connected canyons of the Cretan slope.

A sequence stratigraphic model for the organic-rich Upper Devonian Duvernay Formation, Alberta, Canada

The Upper Devonian Duvernay Formation of western Canada is a prolific source rock that in recent years has become an important exploration target for shale gas and oil. We present a sequence stratigraphic model for the Duvernay Formation that characterizes relationships between sea level, basin circulation, lithofacies distribution, and mechanisms for sediment transport and organic-enrichment. The study demonstrates lateral and stratigraphic variability in the character of sequence stratigraphic surfaces and systems tracts and interprets this variability in the context of sea level cycles at varying time scales. Correlation of 24 core descriptions to a network of 759 wells with wireline logs led to the creation of a basin-scale sequence stratigraphic framework.Three 3rd order depositional sequences are identified; the middle sequence straddles a 2nd order maximum flooding surface. Each systems tract shows unique trends in lithofacies, rock properties, and wireline character. Transgressive systems tracts are characterized by the increasingly widespread deposition of clay-poor, siliceous, organic-rich mudstones in the basin, resulting from decreased clastic and carbonate input, concentration of pelagic organic matter and siliceous radiolaria, and low oxygen concentrations in basin center bottom waters. Highstand systems tracts are characterized by sustained radiolarian input and increases in carbonate sediment due to shedding of carbonate detritus during aggradation and progradation of platform margins and reefs. Lowstand systems tracts are more clastic-rich and organic-poor. Near reef complexes, coarse carbonates locally mark the base of the lowstand systems tract. Bottom currents reworked mud- and silt-sized material in toe-of-slope locations and contributed to slope-parallel progradation during regression.