Sediment Supply Research Articles

Grain-size variability in debris flows of different runout lengths, Wenchuan, China

Debris-flow grain-size distributions (GSDs) control runout length and mobility. Wide, bimodal GSDs and those containing a higher proportion of silt and clay have been shown experimentally to increase runout length. However, the relationship between grain size and mobility has not been well established in field conditions. Here, we compared the grain-size characteristics of two debris flows with considerably different runout lengths (1.5 km vs. 8 km) to understand the role of grain size in governing runout. The two debris flows were triggered in the same rainfall event from coseismic landslide debris generated in the 2008 Wenchuan earthquake in catchments with similar lithology and topography. We compared the deposited GSDs and their spatial patterns using our rare, three-dimensional GSD datasets. Surprisingly, the proportions of each size fraction deposited by the two flows were statistically indistinguishable. The spatial pattern of grain size differed between the two flows, with evidence of inverse grading only preserved in the smaller deposit. From these observations, we can infer that the GSDs of both flows were determined by the coseismic landslide source material, and that there was little difference in the GSDs of material entrained as the flows bulked. The contrasting spatial distributions of grains indicated that different internal processes were dominant within the two flows. These findings demonstrate that where GSDs are dominated by coarse grains and are governed by similar source conditions, grain size plays a lesser role relative to sediment supply and hydrology in controlling the runout length of large catastrophic post-earthquake debris flows.

The Effect of Sediment Supply on Pool‐Riffle Morphology

AbstractDownstream width variations can generate pool‐riffle morphology under experimental conditions, in numerical simulations and natural river channels. The present understanding of how pool‐riffle morphology varies with sediment supply and caliber, however, is insufficient due to the limited range of sediment supply rates explored in previous experiments and the little attention paid to sand supply and sediment size distribution in the laboratory and in the field. We present a model of river morphodynamics that can account for the spatial variability of channel width, and we validate the model with experimental data. Model validation shows how this one‐dimensional model can capture pool‐riffle formation, growth, and equilibration with errors that are comparable with those of other 1D models of river morphodynamics. We then apply the validated model to study the effects of sediment supply rate and caliber on pool‐riffle morphology. Model results show that pool‐riffle morphology is resilient to the range of tested sediment supply (i.e., five‐fold the sediment amount, 41‐fold the sand amount and coarsening the gravel supply). Bed and water surface slopes are sensitive to all types of change of sediment supply, whereas the sensitivity of bed surface sediment grain size varies with the type of change. These findings support prior research emphasizing the role of downstream width variations for the development/maintenance of pool‐riffle morphology and can help in the restoration and recovery of pool‐riffle gravel‐bed rivers.

Gravity-detached material increases sediment supply but requires more time to transport based on laboratory experiments

Mass movement erosion on the gully sidewalls is recognized as an important erosion mode and sediment source in hilly and gully watersheds. However, the trigger of mass movement erosion and transport of gravity-detached material remain poorly understood. A series of rainfall simulation experiments were conducted on six loess gully sidewall models, with a height (1 m), three rainfall (60 mm, 48 mm and 24 mm) and two slope gradients (70° and 80°), to quantitatively explore the sensitivity factor and transport mechanisms of mass movement. Results revealed that the accumulation volume and initiation of the mass failure were significantly influenced by rainfall amount. The accumulative volume of failure events was observed to increase in a linear pattern with increasing rainfall amount. The minimum cumulative rainfalls for the initiation of mass failure on the loess gully sidewalls were approximately 43.6, 28.2 and 65.6 mm for short-duration and high-intensity, medium-duration and moderate-intensity and short-duration and moderate-intensity rainfalls, respectively. This implied that the initiation of mass failure was more prone to rainfall events with a medium-duration and moderate-intensity than those with a high intensity and short duration. Rainfall amount and initial slope gradient were the most sensitive elements driving the number and volume of the mass movement erosion. Mass movement erosion raised sediment concentration, but the eroded material was unable to be transported by runoff in a timely manner. Average sediment concentrations at the model outlet increased by 1.9–11.9 times following the occurrence of mass failures compared to those before. A low instantaneous sediment delivery ratio of 0.032 for the mass movement erosion. The experimental findings help comprehend the influence of mass movement erosion on sediment supply on the gully sidewall in the hilly and gully network, i.e. the Loess Plateau.

The impact of sediment flux and calibre on flood risk in the Kathmandu Valley, Nepal

AbstractThis paper investigates how variations in sediment supply, grain size distribution and climate change affect channel morphology and flood inundation in the Nakkhu River, Kathmandu, Nepal. Climate change‐induced extreme rainfall is expected to increase flood intensity and frequency, causing severe flooding in the Kathmandu basin. The upper reaches of the Nakkhu River are susceptible to landslides and have been impacted by large‐scale sand mining. We simulate potential erosion and deposition scenarios along a 14 km reach of the Nakkhu River using the landscape evolution model CAESAR‐Lisflood with a 10 m digital elevation model, field‐derived sediment grain size data, daily discharge records and flood forecast models. In a series of numerical experiments, we compare riverbed profiles, cross‐sections, flood extent and flow depths for three scenarios (1.2‐, 85‐ and 1000‐year return period floods). For each scenario, the model is first run without sediment transport and then with sediment transport for three grain size distributions (GSDs) (observed average, finer and coarser). In all cases, the inclusion of sediment led to predicted floods of a larger extent than estimated without sediment. The sediment grain size distribution was found to have a significant influence on predicted river morphology and flood inundation, especially for lower magnitude, higher probability flood events. The results emphasise the importance of including sediment transport in hydrological models when predicting flood inundation in sediment‐rich rivers such as those in and around the Himalaya.

Google Earth Engine‐Based Estimation of the Spatio‐Temporal Distribution of Suspended Sediment Concentrations in a Multi‐Channel River System of the Yangtze River Basin

AbstractLowland multi‐channel alluvial river systems are highly variable in frequency and magnitude of floodplain inundation and are vulnerable to human activities such as damming. In the Yangtze River Basin, the Three Gorges Dam (TGD) has trapped >80% of upstream sediment supply, causing downstream scouring and rapid geomorphic changes in river and its floodplain lakes. Suspended sediment concentration (SSC) is widely used to monitor river morphodynamics, but traditional measurements of SSC are time consuming, costly and difficult to quantify SSC in a large spatial scale. Using Google Earth Engine and in situ observed hydrological data, we created a multiple linear regression model to map SSC in the multi‐channel system Songzi River of the Yangtze. The new SSC predictive model achieved high accuracy (R2: 0.87) and showed opposite downstream trends in SSC during peak flood years and normal flood years. For the first time, we found that in the peak flood year of 1998 the study rivers exhibit a downstream increase trend of SSC with an abrupt increase in their middle reach, while SSC in normal flood years experiences a downstream decline with minimal changes. A prominent difference in SSC is also revealed after the TGD with a reduction of 60%. Furthermore, SSC in the closely hydrologically connected lakes is more dynamic than the less connected lakes. Our study demonstrates that the proposed method enables to rapidly quantify the spatio‐temporal SSC distribution in the multi‐channel systems on the floodplain of large alluvial rivers and highlights the importance of connectivity in regulating SSC dynamics.

Steady‐State Bedrock Channel Width

AbstractThe increase in bedrock channel width and the decline in bedrock channel slope with increasing drainage area are fundamental characteristics of mountainous landscapes. Compared with slope, little is known about controls on steady‐state bedrock channel width. We model steady‐state bedrock channel width by iteratively solving models for bed and bank erosion by impacting bedload, using measurable physical parameters, including uplift rate, water discharge, sediment supply, grain size, rock strength, and bank angle. The results indicate that width is largely controlled by sediment flux, rather than water discharge. The commonly used width‐discharge scaling relation is an artifact of the covariance of sediment flux and water discharge. Scaling up from cross‐section to drainage basin scales, our model reproduces the width‐drainage area scaling relation and suggests that the scaling exponent is largely controlled by the downstream change in the fraction of total sediment supply transported as bedload.

Spatial and temporal distributions of clay minerals in the central Andaman Sea: Provenances and sedimentary processes over the last 42 kyr

The uplift of the Tibetan Plateau has led to the formation of the world’s largest sediment “source–sink” system in the northeastern Indian Ocean, and seafloor sediments record rich environmental and climatic information during the accumulation process, making it an ideal area to reconstruct past sedimentary processes. To reveal fine sediment provenance and climatic implications, we present a sedimentary reconstruction during the past 42 kyr based on clay mineral analyses of sediments from core ADM-159 retrieved from the central Andaman Sea. The clay minerals mainly consist of illite (I, 27%–47%) and kaolinite (K, 8%–37%) with minor smectite (S, 11%–37%) and chlorite (C, 11%–37%). Provenance analyses show that the illite-dominated clay minerals are mainly derived from terrestrial sources of detrital material input from the Irrawaddy River, indicating a primary supply of fine sediment from Myanmar terrestrial material. Considering the stable sediment provenance, S/K, S/(I+C), and the illite chemical index were chosen to reconstruct the transport pattern of the fine fraction sediment over the last 42 kyr. S/K and S/(I+C) showed relatively consistent trends over time with relatively high values at 32–25 and 15–6 ka BP, indicating a strong supply and transport capacity of fine particulate matter. In contrast, relatively low values of S/K and S/(I+C) occurred at 25–15 ka BP, indicating a relatively weak deposition process of fine sediments in the study area. The trends in S/K and S/(I+C) are roughly consistent with the variations in solar radiation. Together with the illite chemical index, these trends indicate that solar activity controlled the weathering and sedimentation of fine-grained sediments. We also found significant periodicities in our clay mineral records at 25.05 and 0.473–0.477 kyr, suggesting that the parameters of the Earth’s orbit and solar radiation were potential driving mechanisms of the changes in regional climate. Moreover, monsoon precipitation triggered by the movement of the intertropical convergence zone was another important factor controlling the supply and transport of fine particulate matter in the study area, especially the weak precipitation during the last deglacial period and the relatively strong precipitation during the Holocene, so we could draw a conclusion that precipitation during these periods had significant effects on the weathering, erosion, and transport of fine particulate terrestrial materials over the last 42 kyr.

A Paleo-Changjiang Delta Complex on the East China Sea Shelf Formed Some 30 ka Ago (at the MIS 3 Stage)

The distribution patterns of the paleo-Changjiang River deltas formed during the MIS 3 period before the last glacial maximum (LGM) contain important information about the deltaic deposits in response to climate and sea-level changes. However, so far, they are still poorly understood. Here, we reconstruct the stratigraphic and chronological framework of the deltaic system based on the analysis of 1835 km of high-resolution seismic profiles obtained from the northern East China Sea, together with a comparison with the research results from four existing boreholes and three groups of published seismic profiles from the study area. Within the strata from MIS 5 to MIS 1 that are preserved on the northern shelf of the East China Sea, we discovered a large-scale paleodeltaic complex formed during the MIS 3 period. During MIS 3, sea level dropped slowly; the paleodelta formed was large in scale and was distributed between water depths of 40 and 150 m. It is now directly exposed at the seabed at a depth of more than 100 m. The paleodelta had extended from the northwest to the southeast, with maximum thickness of the deposits around 55 m. The extensions in the east–west and south–north directions both exceeded 300 km, with a total area around 1.35 × 105 km2. Since the late Pleistocene, the tectonic structure beneath the East China Sea has been relatively stable. As such, sea-level fluctuations, sediment supply, and original topography were the main controlling factors for the development of the delta.

Analisis Pengaruh Pembangunan Detached Breakwater terhadap Perlindungan Garis Pantai di Pulau Bengkalis Menggunakan Penginderaan Jauh

The coastline is the boundary between land and sea water whose position is always changing dynamically. Changes in coastlines are caused by disturbances to sediment transport along onshore, reduced sediment supply, disturbances of buildings, and low condition of the cliffs therefore they can’t cover the waves (Ministry of Public Works and Housing, 2015). The purpose of this study is to determine the response of the coastline after the construction of detached breakwater structure on the north coast of Bengkalis Island. Sentinel-2 imagery data used in this study and then analyzed using the Digital Shorelines Analysis System (DSAS) tool. The results of the analysis show that there are have variations of the shoreline response to the structures that have been built. In the period 2016 – 2022 the coastline hase changes, both accretion and abrasion. The maximum change in the forward coastline is 189.09 meters long with an accretion rate of 30.5 meters/year. While the maximum change in the backward coastline is 144.56 meters long with an abrasion rate of 23.32 meters/year. Overall, the construction of detached breakwaters has a positive impact on the coastline, thus increasing the land area on the north coast of Bengkalis Island.
 

Coastal compartments: the role of sediment supply and morphodynamics in a beach management context

Coastal compartments provide a hierarchical framework to manage beaches and coastal ecosystems in Australia. This study examines the individual behaviour of three adjacent beaches within Shoalhaven Bight, a secondary compartment on the south coast of New South Wales (NSW). The Shoalhaven River discharges intermittently into the northernmost of the beaches, and a fluvial component is detectable within beach and foredune sands. The distribution and orientation of headlands constrains dispersal of fluvial sediments, and results in lower wave-energy conditions further south, implying limited sand transport from one beach, or tertiary compartment, to another. Two years of monthly subaerial surveys across ten different profiles and modelled storm-wave conditions during the major storms, were used to compare the response of beach volume and shoreline position. The greatest changes in volume were observed near Shoalhaven Heads and the northern ends of Culburra and Warrain-Currarong beaches. Results indicate the distinct individual response of neighbouring beaches over the two-year period, in contrast to general trends in beach behavior that might be inferred from long-term regional monitoring programs. However, they also demonstrate the limitations of short-term observations in comparison to those longer-term studies. The NSW beach systems of are some of the best understood in the world in terms of regional behaviour, as a consequence of several decades of surveys on key beaches. However, more focused local monitoring programs may be needed to establish detailed coastal sand transport, and an understanding of intermittent delivery of fluvial sand and longshore inputs and outputs, within and between different compartments.

Sequential riparian vegetation alteration in Japanese river landscapes

Bare gravel bed channels have been a common landscape feature of the middle reaches of rivers throughout Japan. They are disappearing these days because of vegetation colonization. Vegetation coverage of the riparian zones in the midstream reaches of rivers distributed throughout Japan was investigated using aerial photo images taken in 1946, 1975, and 2010. It was then compared with hydrological and water quality records, locations of dams and weirs, residential conditions of the surrounding areas, sediment yields, and forest coverage of the upstream mountainous areas. Riparian vegetation coverage has substantially increased in the last 70 years, from nearly 0 to 30-40%. Herbaceous vegetation coverage is higher than tree coverage. The total vegetation coverage did not correlate with water quality parameters. However, vegetation coverage had a significant negative correlation with the upstream basin's sediment yield and a slight negative correlation with the maximum flood peak flow rate. It was positively correlated with the terrestrial area fraction between levees. Riparian vegetation coverage was high within the 2 km downstream of dams or weirs, intercepting sediment flows. These results indicated that the gravelly sediment supplied from the upstream and deposited in the midstream at flood time has been the major contributor to keeping the vegetation coverage low rather than flushing by flood water. Reforestation since World War II has reduced the coarse sediment supply into the midstream river channels. This reforestation, together with gravel mining and intercepting sediment flow by dams and weirs, has caused the recent increase in vegetation coverage of the riparian zones. Human intervention can affect the vegetation conditions in riparian zones by decreasing sediment supply to river channels.

Multivariate examination of the sediment-deficient southeast Australian continental shelf

Continental shelves are the most morphologically variable element within the source-to-sink system owing to the numerous processes that influence their formation. A recent multivariate analysis of a global compilation of modern continental shelf data showed that much of the variability is related to tectonic setting, the degree to which the shelf has been glaciated, and carbonate production. While these factors play first-order roles in determining the morphology of shelves, other controlling mechanisms such as siliciclastic sediment supply, wave and tidal energy, bedrock lithology, and sea-level fluctuations are not as well understood. Here, we report findings from a detailed investigation of the southeast Australian shelf that explored how sediment distribution, wave energy, and bedrock lithology influence shelf morphology. The high-resolution analysis suggests that the southeast Australian shelf has 11 distinct shelf types. No strong relationships exist between the shelf attributes or shelf type with their onshore catchments. However, a substantial section boundary correlates with a bedrock contact between the Sydney Basin in the south and the New England Orogen to the north. South of this boundary, we propose that the shelf morphology reflects transgression with low sediment supply, whereas to the north, the morphology reflects transgression with higher sediment input. Although several factors contributed to this difference in shelf morphology, we suggest that sediment distribution and retention due to the active wave climate during the most recent transgression likely played a vital role.

Evolution of sandy shores under the combined impact of global climate change and anthropogenic activities in Shandong Peninsula, East China

Most sandy shores (SSs) are currently experiencing erosion to various degrees due to the combined impact of increasing climate change and human activities. In order to reveal the evolution of the SSs in the Shandong Peninsula (SP), shoreline and elevation changing data are obtained from 29 SSs and results show that most (27 of 29) of the SSs exhibited erosion. The length of the SSs has decreased by 241.4 km from 2010 to 2020, and the average shoreline recession rate was found to be 1.0 m/a and the downward erosion rate was in the range of 0.05 to 0.10 m/a. Climate change-induced sea level rise has a smaller effect on the erosion in the short term and the construction of massive coastal engineering structures has become a major cause of local coastal erosion. The coastal erosion rate caused by river damming and sand mining in the early years has abated and reduced seaward sediment transport induced by the expansion of the built-up area has become a new factor of coastal erosion. In the past decade, the 672 km2 net increase in land area mainly originated from human activities, has occupied the original space for hydrodynamic energy dissipation, which has severely disrupted the balance between sediment supply and the hydrodynamic environment and the system then rebalance itself by eroding unprotected SSs. Therefore, with the increase in hydrodynamic forces caused by climate change and the scarcity of sediment supply caused by human activities, continued erosion is expected to occur in the SSs.

Gravitational resedimentation as a fundamental process in filling fjords: Lessons from outcrops from a late Palaeozoic fjord in Namibia

AbstractThe stratigraphic architecture of fjords is complicated due to the delicate interplay between ice dynamics, sediment supply, relative sea‐level fluctuations and slope failures. Glaciogenic sediment is prone to failure and to be carried downslope to the fjord floor through the entire spectrum of mass movements and subaqueous density flows, as the unstable paraglacial submarine landscape moves towards stability. Palaeofjords formed by Gondwanan glaciers during the late Palaeozoic Ice Age contain a compelling record of gravitational resedimentation in fjord depositional systems. This paper showcases the geomorphology and depositional history of a glacial cycle in the Orutanda fjord in north‐western Namibia as an example of an overdeepened fjord basin fill dominated by products of subaqueous gravitational processes. During glaciation, the Orutanda glacier carved a 20 km long by 3.7 km wide glacial trough that embodies an overdeepened basin. Ice thickness during terminal glacial occupation of the fjord is estimated to had been up to 200 m based on the fjord geomorphology. The progressive retreat of the tidewater glacier, concomitant with marine flooding, increased accommodation space in the overdeepened basin during deglaciation. During this stage, proglacial sedimentation through iceberg rafting and settling of turbid plumes was outpaced by intense paraglacial downslope resedimentation of glacially‐transported debris. Successive failures from the fjord walls and downslope resedimentation resulted in coalescing debrite–turbidite lobes on the fjord floor. Slide deposits, composed entirely of deformed debrites and turbidites, indicate that these resedimented facies were prone to renewed mass wasting. As the Orutanda glacier melted, the fjord experienced the axial progradation of a fjord‐head delta registered only by turbidites and slide deposits derived from its collapse. The Orutanda fjord sheds light on the relevance of paraglacial mass wasting in overprinting glaciogenic deposits. This insight is key to understanding the role of glaciers versus non‐glacial processes in producing the glacial deep‐time record.

Paleoproterozoic, Mesoproterozoic, and Paleozoic sedimentary successions of the Southwestern Amazonian craton: geochemistry, provenance, and post-sedimentary events

The Amazonian Craton is home to many Statherian to Calymmian taphrogenesis events that evolved over Large Igneous Provinces. The NW-SE faults on the Western Amazonian Igneous Belt (1.82–1.74Ga) and their reactivations, which facilitated the deposition of the Beneficente Group (1.76–1.60Ga), Prainha Formation (1.46Ga), and Alto Tapajós Group (Silurian-Devonian), are associated with these events in the southwest Amazonian Craton. Mineralogical composition, whole-rocks geochemistry, and Nd-Sr-Pb isotopic data show that the three sedimentary successions originated in the provinces of Rondônia-Juruena and Tapajós Parima, particularly during two rift stages. Beneficente Group deposition is associated with Paleoproterozoic Rift 1, while the Prainha Formation represents the post-rift 1, and Alto Tapajós Group deposition is associated with Paleozoic Rift 2. In addition, the Prainha Formation also received sediment supply from the Sunsás Province. These three sedimentary successions have an intrinsic relationship with the reworking of the local basement and their own reworking that occurred from the Paleoproterozoic to the Paleozoic. Autochthonous reworking, particularly in the Colíder and Beneficente groups, is demonstrated by Ti-magnetite grains, volcanic and arenite fragments in the Prainha Formation sublitharenite, and by angular microcline grains, high Au content, a Pb whole-rock isochron yielding the 1.796±0.096Ga age, and by vs 1/Rb relationship in Alto Tapajós Group. and flat REE patterns and some positive Eu anomalies in the Prainha Formation and Alto Tapajós Group record the influence of the mafic rocks of the Mata-Matá suite. A Pb-Pb whole-rock isochron allowed hydrothermal activity recognition at 1.32Ga in the Vila do Carmo Formation. This event was ratified by positive Eu/Eu* (1.3–1.43), Ce/Ce* (1.24–2.84), and Gd/Gd*(~1.5) anomalies. Finally, Nd model ages, geochemistry, and Sr isotopes allow for correlating the local basement and the overlaying sedimentary successions along the Columbia and Gondwana boundaries.

Textural characteristics and sediment transport dynamics of the sandstones of the Nkporo group, Southern Anambra Basin (Nigeria): evidence for the upper cretaceous sea-level lowstand

The Anambra sedimentary basin is one of the major inland basins in Nigeria. It covers an area of approximately 30,000 square kilometres and is named after the Anambra River, which traverses the basin. The geology of the basin is characterized by a complex sequence of sedimentary rocks that record a long history of deposition and tectonic activity. Detailed and systematic field investigation of its rock sequences exposed at Leru junction and adjoining localities revealed five dominant lithologic units consisting of massive sandstone facies, argillaceous sandstone facies, fissile black shale and mudstone facies, planar and ripple laminated sandstone facies, and massive and pebbly sandstone facies. The area is dominated by transgressive facies characterized by alternating sequences of thinly and parallel laminated fissile black shales, mudstones, and argillaceous sandstones overlain by regressive deposits dominated by massive and partly pebbly sandstones. The transgressive sequences perhaps represented shelf mud sedimentation that was probably interrupted by episodic influxes of sands rich in argillaceous materials transported down the shelf probably by shoreface waves or gravity-driven flows, while the regressive facies may have probably been emplaced by liquefied sand flows of the frontal slope of an advancing mouth bar. The erosion of the shelf deposits by the pebbly sandstones possibly reflected seaward migration of shallow distributary channels during sea-level low stand. Thus, facies transition from argillaceous sandstones to massive and pebbly sandstones within the continental shelf perhaps signified a fall in the relative sea level possibly triggered by the erosion of the shelf or perhaps a high rate of sediment supply.

Using lake sediments to assess the long-term impacts of anthropogenic activity in tropical river deltas.

Tropical river deltas, and the social-ecological systems they sustain, are changing rapidly due to anthropogenic activity and climatic change. Baseline data to inform sustainable management options for resilient deltas is urgently needed and palaeolimnology (reconstructing past conditions from lake or wetland deposits) can provide crucial long-term perspectives needed to identify drivers and rates of change. We review how palaeolimnology can be a valuable tool for resource managers using three current issues facing tropical delta regions: hydrology and sediment supply, salinisation and nutrient pollution. The unique ability of palaeolimnological methods to untangle multiple stressors is also discussed. We demonstrate how palaeolimnology has been used to understand each of these issues, in other aquatic environments, to be incorporated into policy. Palaeolimnology is a key tool to understanding how anthropogenic influences interact with other environmental stressors, providing policymakers and resource managers with a 'big picture' view and possible holistic solutions that can be implemented.

Types and sedimentary genesis of barriers and interlayers in the composite turbidite sand bodies of a deep-water canyon: A case study of the Central Canyon in the Qiongdongnan Basin

Deep-water oil and gas is currently the hot spot and difficulty of global oil and gas exploration, and the complex flow process inside the turbidite channels of deep-water canyons makes it difficult to characterize reservoir structures, identify barriers and interlayers and clarify the spatial distribution laws of reservoirs, which restricts the development of deep-water oil and gas. Taking the Central Canyon of the Qiongdongnan Basin as an example, this paper identifies and characterizes the barriers and interlayers of composite channel scale by means of seismic sedimentology, based on three-dimensional seismic and core data. Then, based on the turbidite filling process, barriers and interlayers are classified, and their genesis and control factors are analyzed. Finally, a development model of deep-water barriers and interlayers is established based on the quantitative analysis of sediment transportation system parameters. And the following research results are obtained. First, based on sedimentary genesis, barriers and interlayers are classified into four types, namely mudstone interlayers of lateral (aggradational) turbidite channel genesis (type A), mudstone interlayers of fine-grained turbidite channel genesis (type B), barriers of hemipelagic deep-water sediment genesis (type C), and calcareous petrophysical interlayers (type D). Second, based on the filling stage, barriers and interlayers are divided into four combination sequences, i.e., the initial canyon formation stage with strong sediment supply conditions (type A + type C and type B+ type C), the initial canyon formation stage with weak sediment supply conditions (type B + type C), the stable canyon development/late reworking stage with strong sediment supply conditions (types A + type D), and the stable canyon development/late reworking stage with weak sediment supply conditions (type D). Third, the development types and combination sequences of barriers and interlayers are controlled by the change of sediment transportation volume and terrain slope in the canyon. In the initial canyon formation stage, there is sufficient space for the development of turbidite, and the development of thin barriers and interlayers is controlled by sediment dischage volume, while the development of thick barriers and interlayers is controlled by terrain slope change. In the stable canyon development/late reworking stage, turbidite undergoes superimposed development and overbank. The sediment supply is the primary control factor of barrier and interlayer thickness, and the terrain slope change is the secondary factor. In conclusion, the development model of barriers and interlayers can be used to describe and predict the reservoir structure models under the same sedimentary background and provides a technical support for the exploration and development of deep-water oil and gas.

Degradation of a Foreland River After the Wenchuan Earthquake, China: A Combined Effect of Weirs, Sediment Supply, and Sediment Mining

AbstractSince the 2008 Wenchuan (Ms. 8.0) Earthquake, the foreland rivers of the Longmen Mountains have suffered from significant bed degradation, among which the Shi‐ting River has experienced the largest local degradation of more than 20 m in 7 years. Potential reasons of the dramatic degradation include: (a) sediment disconnectivity due to in‐channel weirs; (b) the mobilization effect on gravel of an increased sand supply as a result of earthquake‐induced landslides; and (c) sediment extraction due to intensive mining. In this paper, we study the complex interaction among the above‐mentioned factors in the Shi‐ting River, using a one‐dimensional river morphodynamic model. Simulation results show that in‐channel weirs can reduce bedload transport and lead to bed degradation that is proportional to weir height. When coupled with additional sand supply, the weirs preferentially trap gravel and deliver sand, augmenting the downstream mobility of gravel and thus the degradation. For the Shi‐ting River, the simulated bed degradation agrees well with the observation when an annual sediment mining of 16 million tons is implemented in the simulation, along with the effects of in‐channel weirs and sand supply. The contribution of sediment mining is one order of magnitude larger than the coupling effect of weirs and sand supply. Both the simulation and observation show that the largest bed degradation occurs downstream of the Renmin Weir, due to the large spatial interval between the Renmin Weir and the next grade control structure.

Sedimentary evolution of the western North Yellow Sea mud patch: A Holocene perspective

The western North Yellow Sea mud patch has a unique location, abundant sediment supply and a complex sedimentary environment. Reconstructing its sedimentary evolution is crucial for a comprehensive understanding of source to sink process in the North Yellow Sea. Using core W03 collected from the mud patch, this study unravels its Holocene history through analysis of sedimentology, mineralogy and micropalaeontology. The results indicate that core W03 can be divided into three depositional units (DU). DU3 (538-461 cm) is composed of earthy yellow clayey silt and characterized by a hard layer. It was formed in the near-coast environment between 10.3 and 9.8 cal kyr BP, a hiatus period between Melt Water Pulse 1B and 1C events. DU2 (460-341 cm) was formed during the period of 9.8–6.5 cal kyr BP. As sea level rose, the westward retreat of the Yellow River mouth caused the transportation of Yellow River-derived sediment over longer distances, leading to an increase in flaky minerals. The rising sea level also induced a shift towards a reducing environment in the western North Yellow Sea. DU1 (340-0 cm) was formed after 6.5 cal kyr BP. During this period, the study area remained in a shelf shallow sea environment characterized by relatively strong chemical hydrolysis and reducing conditions. The intensification of the Yellow Sea Warm Current and an increase in Yellow River sediment transported to the sea led to an obvious increase in sedimentation rate after 2.3 cal kyr BP.