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1.
The Yithi submarine canyons,composed of four canyons less than 60 km in length,are located on the narrowest part of the East China Sea(ECS) slope.They extend from the shelf break at 160 m down to water depth of 1 500 m with an average gradient(along the canyon axis) of 3°(<1 000 m) and 0.7°(>1000 m).The sinuosity of the canyons ranges form 1.02 to 1.14 and their pathways extend radially from the shelf break to the axis of the Okinawa Trough.Structural and evolution pattern of the Yithi canyons are mainly controlled by sediment mass-movements and turbidity current and similar with that of the canyons in Ebro continental slope.The whole canyon system consists of three parts:the canyon,the channel and the fan.Slumps and slides often develop in the upper part of canyon where the water depth is less than 1000 m,and the turbidities usually developed on the fan.The scale of turbidites becomes smaller and their inner structures become more regular towards the ends of the canyons.Canyon-fans are often associated with small angle progradational reflection.Most canyon-fans and levees were transversely cut by active normal faults with NEE-SWW trending that are coupled to the modern extension of the Okinawa Trough.According to the age of formation of canyon-fans and sediments incised by canyons,we can infer that the Yithi canyons were formed since the middle the Medio-Pleistocene.  相似文献   

2.
Particle size distributions (PSDs) of bottom sediments in a coastal zone are generally multimodal due to the complexity of the dynamic environment. In this paper, bottom sediments along the deep channel of the Pearl River Estuary (PRE) are used to understand the multimodal PSDs′ characteristics and the corresponding depositional environment. The results of curve-fitting analysis indicate that the near-bottom sediments in the deep channel generally have a bimodal distribution with a fine component and a relatively coarse component. The particle size distribution of bimodal sediment samples can be expressed as the sum of two lognormal functions and the parameters for each component can be determined. At each station of the PRE, the fine component makes up less volume of the sediments and is relatively poorly sorted. The relatively coarse component, which is the major component of the sediments, is even more poorly sorted. The interrelations between the dynamics and particle size of the bottom sediment in the deep channel of the PRE have also been investigated by the field measurement and simulated data. The critical shear velocity and the shear velocity are calculated to study the stability of the deep channel. The results indicate that the critical shear velocity has a similar distribution over large part of the deep channel due to the similar particle size distribution of sediments. Based on a comparison between the critical shear velocities derived from sedimentary parameters and the shear velocities obtained by tidal currents, it is likely that the depositional area is mainly distributed in the northern part of the channel, while the southern part of the deep channel has to face higher erosion risk.  相似文献   

3.
High-resolution multichannel seismic data enables the discovery of a previous, undocumented submarine canyon(Huaguang Canyon) in the Qiongdongnan Basin, northwest South China Sea. The Huaguang Canyon with a NW orientation is 140 km in length, and 2.5 km to 5 km in width in its upper reach and 4.6 km to 9.5 km in width in its lower reach. The head of the Huaguang Canyon is close to the Xisha carbonate platform and its tail is adjacent to the central canyon. This buried submarine canyon is formed by gravity flows from the Xisha carbonate platform when the sea level dropped in the early stage of the late Miocene(~10.5 Ma). The internal architecture of the Huaguang Canyon is mainly characterized by high amplitude reflections, indicating that this ancient submarine canyon was filled with coarse-grained sediments. The sediment was principally scourced from the Xisha carbonate platform. In contrast to other buried large-scale submarine canyons(central canyon and Zhongjian Canyon) in the Qiongdongnan Basin, the Huaguang Canyon displays later formation time, smaller width and length, and single sediment supply. The coarse-grained deposits within Huaguang Canyon provide a good environment for reserving oil and gas, and the muddy fillings in Huaguang Canyon have been identified as regional caps. Therefore, Huaguang Canyon is potential area for future hydrocarbon exploration in the northwest South China Sea. Our results may contribute to a better understanding of the evolution of submarine canyons formed in carbonate environment.  相似文献   

4.
On the basis of the measurement data pertaining to waves, current, and sediment in February 2012 in the mouth bar of the Modaomen Estuary, the Soulsby formulae with an iterative method are applied to calculating bottom shear stresses (BSS) and their effect on a sediment resuspension. Swell induced BSS have been found to be the most important part of the BSS. In this study, the correlation coefficient between a wavecurrent shear stress and SSC is 0.86, and that between current shear stresses and SSC is only 0.40. The peaks of the SSC are consistent with the height and the BSS of the swell. The swell is the main mechanism for the sediment re-suspension, and the tidal current effect on sediment re-suspension is small. The peaks of the SSC are centered on the high tidal level, and the flood tide enhances the wave shear stresses and the SSC near the bottom. The critical shear stress for sediment re-suspension at the observation station is between 0.20 and 0.30 N/m2. Tidal currents are too weak to stir up the bottom sediment into the flow, but a WCI (wave-current interaction) is strong enough to re-suspend the coarse sediment.  相似文献   

5.
Multi-beam,sub-bottom and multichannel seismic data acquired from the western Nigerian continental margin are analysed and interpreted to examine the architectural characteristics of the lower parts of the submarine canyons on the margin.The presence of four canyons: Avon,Mahin,Benin,and Escravos,are confirmed from the multi-beam data map and identified as cutting across the shelf and slope areas,with morphological features ranging from axial channels,moderate to high sinuosity indices,scarps,terraces and nickpoints which are interpreted as resulting from erosional and depositional activities within and around the canyons.The Avon Canyon,in particular,is characterised by various branches and sub-branches with complex morphologies.The canyons are mostly U-shaped in these lower parts with occasional V-shapes down their courses.Their typical orientation is NE–SW.Sedimentary processes are proposed as being a major controlling factor in these canyons.Sediments appear to have been discharged directly into the canyons by rivers during the late Quaternary low sea level which allows river mouths to extend as far as the shelf edge.The current sediment supply is still primarily sourced from these rivers in the case of the Benin and Escravos Canyons,but indirectly in the case of the Avon and Mahin Canyons where the rivers discharge sediments into the lagoons and the lagoons bring the sediments on to the continental shelf before they are dispersed into the canyon heads.Ancient canyons that have long been buried underneath the Avon Canyon are identified in the multichannel seismic profile across the head of the Avon Canyon,while a number of normal faults around the walls of the Avon and Mahin Canyons are observed in the selected sub-bottom profiles.The occurrence of these faults,especially in the irregular portions of the canyon walls,suggests that they also have some effect on the canyon architecture.The formation of the canyons is attributed to the exposure of the upper marginal area to incisions from erosion during the sea level lowstand of the glacial period.The incisions are widened and lengthened by contouric currents,turbidity currents and slope failures resulting in the canyons.  相似文献   

6.
Based on the test data in dynamic water and static water, the main factors, which influence the fine sediment flocculation, are analyzed with a gray model method of correlation theory. It is shown that the main influencing factors are water temperature, settling time, salinity, grain size, sediment concentration and current velocity according to the correlation coefficients. Among them, the salinity and the sediment grain size are critical type influencing factors (CrTIF); the settling time, the sediment concentration and the velocity are continuous type influencing factors (CoTIF); and the water temperature has the characteristics of both. When the critical values of CrTIF are reached or exceeded, the fine sediments will be flocculated, but values of CrTIF will not influence the settlement strength of floes. The influence of CoTIF is continuous. The values of the CoTIF will not only influence the occurrence of flocculation but also the settlement strength of the floes.  相似文献   

7.
Based on the in-situ measurements,the impact of the marine hydrodynamics,such as wave and tide,in the rapidly deposited sediments consolidation process was studied.In the tide flat of Diaokou delta-lobe,one test pit was excavated.The seabed soils were dug and dehydrated,and then the powder of the soil was mixed with seawater to be fluid sediments.And an iron plate covered part of the test pit to cut off the effect of the marine hydrodynamics.By field-testing methods,like static cone penetration test (SPT) and vane shear test (VST),the variation of strength is measured as a function of time,and the marine hydrodynamics impact on the consolidation process of the sediments in the Yellow River estuary was studied.It is shown that the self-consolidated sediments’ strength linearly increases with the depth.In the consolidation process,in the initial,marine hydrodynamics play a decisive role,about 1.5 times as much as self-consolidated in raising the strength of the sea-bed soils,and with the extension of the depth the role of the hydrodynamics is reduced.In the continuation of the consolidation process,the trend of the surface sediments increased-strength gradually slows down under the water dynamics,while the sediments below are in opposite ways.As a result,the rapidly deposited silt presents a nonuniform consolidation state,and the crust gradually forms.The results have been referenced in studying the role of the hydrodynamics in the soil consolidation process.  相似文献   

8.
A horizontal two- dimensional numerical model is developed for estimation of sediment transport and sea bed change around a large circular cylinder under wave action. The wave model is based on an elliptic mild slope equation. The wave-induced current by the gradient of radiation stress is considered and a depth integrated shallow water equation is applied to the calculation of the current. The mass transport velocity and the bed shear stress due to streaming are considered, which are important factors affecting the sediment transport around a structure due to waves, especially in reflective areas. Wave-current interaction is taken into account in the model for computing the bed shear stress. The model is implemented by a finite element method. The results of this model are compared with those from other methods and agree well with experimental data.  相似文献   

9.
The shelfbreak of the East China Sea lies in an area with a marked change in gradient between the continental shelf and the slope (west wall of Okinawa Trough), depth ranging from 132 to 162m with an average of about 147 m, and the width ranging from 4 to 18 km. The types of the shelfbreak differ markedly from the north to the south, having an abrupt break in the south and a gradual break in the middle and the north. Without permanent deposition of fine-grained material formed at the shelfbreak zone, it serves only as a temporary resting place for terrigenous sediments moving toward the Okinawa Trough through submarine canyons as important transport conduits.  相似文献   

10.
Organic carbon (OC) in definitely small area sediments(according to marine dimension)offthe Huanghe River Estuary is investigated in order to evaluate the feature of regional difference of physical and chemical properties in marginal sea sediments.The distributions of OC in sediments with natural grain size and the relationship with the pH,Eh,Es and Fe^3 /Fe^2 are discussed.In addition,OC decomposition rates in surfacial/subsurfacial sediments are estimated.OC concentrations range from 0.26% to 1.8%(wt)in the study area. Significant differences in OC content and in horizontal distribution as well as various trends in surfacial/subsurfacial sediments exhibit the feature of regional difference remarkably in marginal sea sediments. The complicated distribution of OC in surface sediments is due to the influence of bacterial activity and abundance, bioturbation of benthos and physical disturbance. The OC decomposition rate constant in surfacial/subsurfacial sediments ranges from 0.009 7 to 0.076 a^-1 and the relatively high values may be mainly related to bacteria that are mainly responsible for OC mineralization;meio-and macrofauna affect OC degradation both directly, through feeding on it, and indirectly through bioturbation and at the same time coarse sediments are also disadvantageous to OC preservation.In almost all the middle and bottom sediments the contents of OC decrease with the increase of deposition depth, which indicates that mineralization of OC in the middle and bottom sediments has occurred via processes like SO4^2- reduction and Fe-oxide reduction.  相似文献   

11.
This study examines the influence of a submarine canyon on the dispersal of sediments discharged by a nearby river and on the sediment movement on the inner shelf. The study area includes the head region of the Kao-ping Submarine Canyon whose landward terminus is located approximately 1 km seaward from the mouth of the Kao-ping River in southern Taiwan. Within the study area 143 surficial sediment samples were taken from the seafloor. Six hydrographic surveys along the axis of the submarine canyon were also conducted over the span of 1 yr. Three different approaches were used in the analysis of grain-size distribution pattern. They include (1) a combination of ‘filtering’ and the empirical orthogonal (eigen) function (EOF) analysis technique, (2) the McLaren Model, and (3) the ‘transport vector’ technique. The results of the three methods not only agree with one another, they also complement one another. This study reveals that the Kao-ping Submarine Canyon is relatively a stratified and statically stable environment. The hydrographic characteristics of the canyon display seasonal variability controlled primarily by the temperature field and the effluent of the Kao-ping River. The hydrographic condition and the bottom topography in the canyon suggest the propagation of internal tides during the flood season (summer) of the Kao-ping River. The submarine canyon acts as a trap and conduit for mud exchange between the Kao-ping River and offshore. Near the head of the canyon there is a region of sediment transport convergence. This region is also characterized by high mud abundance on the seafloor that coincides with the presence of high suspended sediment concentration (SSC) spots in the bottom nepheloid layer. Outside the submarine canyon on the shelf where the evidence of wave reworking is strong, the northwestward alongshore transport dominates over the southeastward transport, which is a common theme on the west coast in southern Taiwan.  相似文献   

12.
We investigated Oceanographer Canyon, which is on the southeastern margin of Georges Bank, during a series of fourteen dives in the “Alvin” and “Nekton Gamma” submersibles. We have integrated our observations with the results of previous geological and biological studies of Georges Bank and its submarine canyons. Fossiliferous sedimentary rocks collected from outcrops in Oceanographer Canyon indicate that the Cretaceous—Tertiary boundary is at 950 m below sea level at about 40°16′N where at least 300 m of Upper Cretaceous strata are exposed; Santonian beds are more than 100 m thick and are the oldest rocks collected from the canyon. Quaternary silty clay, deposited most probably during the late Wisconsin Glaciation, veneers the canyon walls in many places, and lithologically similar strata are present beneath the adjacent outer shelf and slope. Where exposed, the Quaternary clay is commonly burrowed by benthic organisms that cause extensive erosion of the canyon walls, especially in the depth zone (100–1300 m) inhabited by red crabs (Geryon) and/or jonah crabs (Cancer). Bioerosion is minimal on high, near-vertical cliffs of sedimentary rock, in areas of continual sediment movement, and where the sea floor is paved by gravel. A thin layer of rippled, unconsolidated silt and sand is commonly present on the canyon walls and in the axis; ripple orientation is most commonly transverse to the canyon axis and slip-faces point downcanyon. Shelf sediments are transported from Georges Bank over the eastern rim and into Oceanographer Canyon by the southwest drift and storm currents; tidal currents and internal waves move the sediment downcanyon along the walls and axis. Large erratic boulders and gravel pavements on the eastern rim are ice-rafted glacial debris of probable late Wisconsinan age; modern submarine currents prevent burial of the gravel deposits. The dominant canyon megafauna segregates naturally into three faunal depth zones (133–299 m; 300–1099 m; 1100–1860 m) that correlate with similar zones previously established for the continental slope epibenthos. Faunal diversity is highest on gravelly sea floors at shallow and middle depths. The benthic fauna and the fishes derive both food and shelter by burrowing into the sea floor. In contrast to the nearby outer shelf and upper slope, Oceanographer Canyon has not been extensively exploited by the fishing industry, and the canyon ecosystem probably is relatively unaltered.  相似文献   

13.
Based upon 2D seismic data, this study confirms the presence of a complex deep-water sedimentary system within the Pliocene-Quaternary strata on the northwestern lower slope of the Northwest Sub-Basin, South China Sea. It consists of submarine canyons, mass-wasting deposits, contourite channels and sheeted drifts. Alongslope aligned erosive features are observed on the eastern upper gentle slopes (<1.2° above 1,500 m), where a V-shaped downslope canyon presents an apparent ENE migration, indicating a related bottom current within the eastward South China Sea Intermediate Water Circulation. Contourite sheeted drifts are also generated on the eastern gentle slopes (~1.5° in average), below 2,100 m water depth though, referring to a wide unfocused bottom current, which might be related to the South China Sea Deep Water Circulation. Mass wasting deposits (predominantly slides and slumps) and submarine canyons developed on steeper slopes (>2°), where weaker alongslope currents are probably dominated by downslope depositional processes on these unstable slopes. The NNW–SSE oriented slope morphology changes from a three-stepped terraced outline (I–II–III) east of the investigated area, into a two-stepped terraced (I–II) outline in the middle, and into a unitary steep slope (II) in the west, which is consistent with the slope steepening towards the west. Such morphological changes may have possibly led to a westward simplification of composite deep-water sedimentary systems, from a depositional complex of contourite depositional systems, mass-wasting deposits and canyons, on the one hand, to only sliding and canyon deposits on the other hand.  相似文献   

14.
海底峡谷是陆源沉积物向深海运移的主要通道,也是陆架/陆坡区重要的地貌单元。随着多波束测深技术的发展,如何快速而准确地从海量数据中识别并提取海底峡谷的特征要素,是一个亟待解决的重要热点问题。文中根据海底峡谷谷底下切、谷壁高而陡等地形特征,基于水文分析法和坡度分析等原理,通过ArcGIS中的数据建模工具建立了一种从数字高程模型(DEM)数据快速识别和提取海底峡谷特征要素的方法。以南海北部陆坡神狐峡谷区为例进行算例分析,结果表明,该方法在快速了解海底峡谷的发育位置和特征要素等方面是可行的,并可以获得峡谷头尾部水深、轴线长度、峡谷范围等特征信息。为获得该方法适用于研究区的最优参数组,文中讨论分析了峡谷形态、重分类阈值及数据分辨率等影响峡谷识别的因素。结果分析表明,峡谷形态会在一定程度上影响识别结果的准确性,但不影响对峡谷的总体了解;零值汇流累积量重分类阈值和DEM数据的空间分辨率是影响峡谷识别结果准确度的两个重要因素,在神狐峡谷群区,空间分辨率200 m且重分类阈值0.4时,海底峡谷识别和特征要素提取效果最佳。  相似文献   

15.
16.
The results of field studies of the beach dynamics and the continental slope (over the depth range from 0 to 5 m) of the Anapa spit barrier that were carried out in 2002–2005 using ten lateral profiles are presented. The analysis of the location of the submarine ridges based on the data of 1992 up to a depth of 11 m has shown that the configuration thereof facilitates the transport of sediments to the southeast, thus bypassing Cape Anapa. No resultant accumulation of beach-forming sediments on the southeastern flank of the spit barrier occurs within the submarine slope bordering the high coast, thus provoking the active erosion of the town beach over the last 25–30 years. The main reasons for this are the tectonic deformation of the coastal region and the submarine slope between the harbor and the central part of the town beach, as well as the change in the azimuth orientation of the resultant waves from 135° in the 1960s–1970s to 210° over the past decade. The relatively stable coast and the regions of intense erosion of the accumulative body of the Anapa spit barrier were revealed on the basis of the measurements and the analysis of the topographic data.  相似文献   

17.
海底峡谷在全球陆缘广泛分布,是浅海沉积物向深海运移的主要通道,对于理解深海浊流触发机制、深海沉积物的搬运模式、深海扇的发育历史和深海油气资源勘探等均具有重要意义。本文基于高分辨率高精度的多波束测深数据,首次对南海东北部海底峡谷体系进行了研究,精细刻画了高屏海底峡谷、澎湖海底峡谷、台湾浅滩南海底峡谷和东沙海底峡谷等4条大型海底峡谷的地貌特征并分析其发育控制因素。海底坡度、构造运动、海山与海丘是影响南海东北部峡谷群走向与特征的重要因素,其中,海底坡度对于峡谷上游多分支与“V”字特征有显著的控制作用;构造运动是控制高屏海底峡谷走向的因素,澎湖海底峡谷的走向则与菲律宾海板块与欧亚板块碰撞有关,东沙海底峡谷的走向则与东沙运动相关,台湾浅滩南海底峡谷上段受NW向断裂构造的控制;海山的阻挡作用造成峡谷局部走向和特征改变。海底峡谷群输送大量陆源沉积物到深海盆并形成大面积的沉积物波,海山和沉积物波的发育导致东沙海底峡谷下段“回春”和转向。  相似文献   

18.
High-resolution and high-density 2-D multichannel seismic data, combined with high-precision multibeam bathymetric map, are utilized to investigate the characteristics and distribution of submarine landslides in the middle of the northern continental slope, South China Sea. In the region, a series of 19 downslope-extending submarine canyons are developed. The canyons are kilometers apart, and separated by inter-canyon sedimentary ridges. Numerous submarine landslides, bounded by headscarps and basal glide surfaces, are identified on the seismic profiles by their distorted to chaotic reflections. Listric faults and rotational blocks in head areas and compressional folds and inverse faults at the toes of the landslides are possibly developed. Three types of submarine landslides, i.e., creeps, slumps, and landslide complexes, are recognized. These landslides are mostly distributed in the head areas and on the flanks of the canyons. As the most widespread landslides in the region, creeps are usually composed of multiple laterally-coalesced creep bodies, in which the boundaries of singular component creep bodies are difficult to delineate. In addition, a total of 77 landslides are defined, including 61 singular slumps and 16 landslide complexes that consist of two or more component landslides. Statistics show that most landslides are of a small dimension (0.53–18.09 km² in area) and a short runout distance (less than 3.5 km). Regional and local slope gradients and rheological behavior of the displaced materials might play important roles in the generation and distribution of the submarine landslides. A conceptual model for the co-evolution of the canyons and the associated landslides in the study area is presented. In the model it is assumed that the canyons are initiated from gullies created by landslides on steeper sites of the continental slope. The nascent canyons would then experience successive retrogressive landsliding events to extend upslope; at the same time canyon downcutting or incision would steepen the canyon walls to induce more landslides.  相似文献   

19.
Three mooring arrays were deployed in the Palamós Canyon axis with sediment traps, current meters and turbidimeters installed near the bottom and in intermediate waters. Frequent sharp and fast turbidity peaks along with current speed increases were recorded, particularly at 1200 m depth in spring and summer. During these events, near-bottom water turbidity increased by up to more than one order of magnitude, current velocity by two to four times and horizontal sediment fluxes by one to three orders of magnitude. When these events occurred, 9–11 days integrated downward particle fluxes collected by the near-bottom sediment trap increased by two to three times. These events were identified as sediment gravity flows triggered by trawling activities along the northern canyon wall. Sediment eroded by the trawling nets at 400–750 m depth on this wall seems to be channeled through a gully and transported downslope towards the canyon axis, where the 1200 m mooring was located. The sediment gravity flows recorded at the 1200 m site were not detected at deeper instrumented sites along the canyon axis, suggesting that they affect local areas of the canyon without traveling long distances downcanyon. These observations indicate that trawling can generate frequent sediment gravity flows and increase sediment fluxes locally in submarine canyons. Furthermore, in addition to the various natural processes currently causing sediment gravity flows and other sediment transport events, human activities such as trawling must be taken into account in modern submarine canyon sediment dynamics studies.  相似文献   

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