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1.
There are thousands of seeps in the deep ocean worldwide; however, many questions remain about their contributions to global biodiversity and the surrounding deep‐sea environment. In addition to being globally distributed, seeps provide several benefits to humans such as unique habitats, organisms with novel genes, and carbon regulation. The purpose of this study is to determine whether there are unique seep macrobenthic assemblages, by comparing seep and nonseep environments, different seep habitats, and seeps at different depths and locations. Infaunal community composition, diversity, and abundance were examined between seep and nonseep background environments and among three seep habitats (i.e., microbial mats, tubeworms, and soft‐bottom seeps). Abundances were higher at seep sites compared to background areas. Abundance and diversity also differed among microbial mat, tubeworm, and soft‐bottom seep habitats. Although seeps contained different macrobenthic assemblages than nonseep areas, infaunal communities were also generally unique for each seep. Variability was 75% greater within communities near seeps compared to communities in background areas. Thus, high variability in community structure characterized seep communities rather than specific taxa. The lack of similarity among seep sites supports the idea that there are no specific infauna that can be used as indicators of seepage throughout the northern Gulf of Mexico, at least at higher taxonomic levels.  相似文献   

2.
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   

3.
Methane seeps occur at depths extending to over 7000 m along the world's continental margins, but there is little information about the infaunal communities inhabiting sediments of seeps deeper than 3000 m. Biological sampling was carried out off Unimak Island (3200–3300 m) and Kodiak Island (4500 m) on the Aleutian margin, Pacific Ocean and along the Florida Escarpment (3300 m) in the Gulf of Mexico to investigate the community structure and nutrition of macrofauna at these sites. We addressed whether there are characteristic infaunal communities common to the deep‐water seeps or to the specific habitats (clam beds, pogonophoran fields, and microbial mats) studied here, and ask how these differ from background communities or from shallow‐seep settings sampled previously. We also investigated, using stable isotopic signatures, the utilization of chemosynthetically fixed and methane‐derived organic matter by macrofauna from different regions and habitats. Within seep sites, macrofaunal densities were the greatest in the Florida microbial mats (20,961 ± 11,618 ind·m−2), the lowest in the Florida pogonophoran fields (926 ± 132 ind·m−2), and intermediate in the Unimak and Kodiak seep habitats. Seep macrofaunal densities differed from those in nearby non‐seep sediments only in Florida mat habitats, where a single, abundant species of hesionid polychaete comprised 70% of the macrofauna. Annelids were the dominant taxon (>60%) at all sites and habitats except in Florida background sediments (33%) and Unimak pogonophoran fields (27%). Macrofaunal diversity (H′) was lower at the Florida than the Alaska seeps, with a trend toward reduced richness in clam bed relative to pogonophoran field or non‐seep sediments. Community composition differences between seep and non‐seep sediments were evident in each region except for the Unimak margin, but pogonophoran and clam bed macrofaunal communities did not differ from one another in Alaska. Seep δ13C and δ15N signatures were lighter for seep than non‐seep macrofauna in all regions, indicating use of chemosynthetically derived carbon. The lightest δ13C values (average of species’ means) were observed at the Florida escarpment (−42.8‰). We estimated that on average animal tissues had up to 55% methane‐derived carbon in Florida mats, 31–44% in Florida clam beds and Kodiak clam beds and pogonophoran fields, and 9–23% in Unimak seep habitats. However, some taxa such as hesionid and capitellid polychaetes exhibited tremendous intraspecific δ13C variation (>30‰) between patch types. Overall we found few characteristic communities or features common to the three deep‐water seeps (>3000 m), but common properties across habitats (mat, clam bed, pogonophorans), independent of location or water depth. In general, macrofaunal densities were lower (except at Florida microbial mats), community structure was similar, and reliance on chemosynthesis was greater than observed in shallower seeps off California and Oregon.  相似文献   

4.
Cold seeps on the Hikurangi Margin off New Zealand exhibit various seabed morphologies producing different intensity patterns in sidescan backscatter images. Acoustic backscatter characteristics of 25 investigated seep sites fall into four distinct types characterised by variations in backscatter intensity, distribution and inferred structural heights. The types reflect different carbonate morphologies including up to 20-m-high structures (type 1), low-relief crusts (type 2), scattered blocks (type 3) and carbonate-free sites (type 4). Each seep corresponds to a single type; intermediates were not observed. This correlates well with published data on seep fauna at each site, with the four types representing three different faunal habitats of successive stages of seep development. Backscatter signatures in sidescan sonar images of cold seeps may therefore serve as a convenient proxy for variations in faunal habitats.  相似文献   

5.
The San Clemente cold seep lies within 100–200 km of other reducing habitats in the NE Pacific, offering an opportunity to compare diversity and species overlap among reducing habitats (i.e. whale‐, kelp‐, and wood‐falls) at similar depths within a single region. Video observations from the research submersible Alvin at the San Clemente seep (1800 m depth) indicated clumps (‘thickets’) of vestimentiferans distributed as meter‐scale patches interspersed with vesicomyid clam beds and black sediments. Sediment‐core samples were collected at distances of 0 to 80–200 m along randomly oriented transects radiating outward from vestimentiferan thickets to evaluate changes in macrofaunal community structure from thickets into the background community. Macrofaunal abundance was elevated at distances of 0–1 m compared to 80–200 m (i.e. the ‘background’ community). The tube‐building frenulate worms Siboglinum spp., along with peracarid crustaceans, dominated sediments within 1 m of vestimentiferan thickets. Species diversity was depressed within 1 m of thickets but with high rates of species accumulation, suggesting that seep sites greatly increase sediment heterogeneity and facilitate colonization by non‐background macrofaunal species. Stable isotope data indicate chemosynthetic nutrition for some dominant macrofaunal species within 1 m of tubeworm thickets. The macrofaunal community near vestimentiferan thickets in San Clemente seep contains intermediate levels of species richness and diversity compared to other deep‐sea seep areas in the northeast Pacific. There was low species overlap between the San Clemente seep macrofauna and communities in reducing habitats near wood‐, whale‐, and kelp‐falls at similar depths within the region, suggesting that seeps harbor a distinct infaunal community.  相似文献   

6.
Most of the recent models which aim at explaining the origins of canyons call on mechanisms of retrogressive failure. The interpretation of high-resolution seismic reflection profiles permitted the recognition of the shelf and slope evolution of Naples Bay (eastern Tyrrhenian Sea margin) during the formation of the Dohrn canyon. Stratigraphic and structural data collected from this area suggest that the factor which triggered off the formation of the canyon was the tectonic uplift of both the outer shelf and fluvial valley mouth which took place during the eustatic fall of sea level. Received: 12 May 1999 / Revision accepted: 19 May 2000  相似文献   

7.
A geomorphological and statistical analysis of slope canyons from the northern KwaZulu-Natal continental margin is documented and compared with submarine canyons from the Atlantic margin of the USA. The northern KwaZulu-Natal margin is characterized by increasing upslope relief, concave slope-gradient profiles and features related to upslope growth of the canyon forms. Discounting slope-gradient profile, this morphology is strikingly similar to canyon systems of the New Jersey slope. Several phases of canyon incision indicate that downslope erosion is also an important factor in the evolution of the northern KwaZulu-Natal canyon systems. Despite the strong similarities between the northern KwaZulu-Natal and New Jersey slope-canyon systems, key differences are evident: (1) the concavity of the northern KwaZulu-Natal slope, contrasting with the ∼linear New Jersey slope; (2) the relative isolation of the northern KwaZulu-Natal canyons, rather than the dense clustering of the New Jersey canyons; and (3) the absence of strongly shelf-breaching canyons along the northern KwaZulu-Natal margin. In comparison with the New Jersey margin, we surmise a more youthful stage of canyon evolution, a result of either the canyons themselves being younger or the formative processes being less active. Less complicated patterns of erosion resulting from reduced sediment availability have developed in northern KwaZulu-Natal. The reduction in slope concavity on the New Jersey margin may be the result of grading of the upper slope by intensive headward erosion, a process more subdued—or less evident—on the KwaZulu-Natal margin.  相似文献   

8.
Cold seeps are among the most heterogeneous of all continental margin habitats. Abiotic sources of heterogeneity in these systems include local variability in fluid flow, geochemistry, and substrate type, which give rise to different sets of microbial communities, microbial symbiont-bearing foundation species, and associated heterotrophic species. Biogenic habitats created by microbial mats and the symbiotic species including vesicomyid clams, bathymodiolin mussels, and siboglinid tubeworms add an additional layer of complexity to seep habitats. These forms of habitat heterogeneity result in a variety of macrofaunal and meiofaunal communities that respond to changes in structural complexity, habitat geochemistry, nutrient sources, and interspecific interactions in different ways and at different scales. These responses are predicted by a set of theoretical metacommunity models, the most appropriate of which for seep systems appears to be the 'species sorting' concept, an extension of niche theory. This concept is demonstrated through predictable patterns of community assembly, succession, and beta-level diversity. These processes are described using a newly developed analytical technique examining the change in the slope of the species accumulation curve with the number of habitats examined. The diversity response to heterogeneity has a consistent form, but quantitatively changes at different seep sites around the world as the types of habitats present and the size-classes of fauna analyzed change. The increase in beta diversity across seep habitat types demonstrates that cold seeps and associated biogenic habitats are significant sources of heterogeneity on continental margins globally.  相似文献   

9.
Scientific study has generated a range of hypotheses about the ecological structure and function of seamounts. Interpretations of these ideas and data are vital to understanding how seamount communities will respond to anthropogenic impacts. Here, we examine how diversity and structure of seamount assemblages vary with depth and slope of the sea floor. We conducted ROV video transects on three seamounts of the Taney Seamount Chain in the Northeast Pacific Ocean. Depth and slope were both related to assemblage structure on the Taney seamounts. Depth differences were seen in alpha‐ and beta‐diversity but not density. Beta‐diversity and density but not alpha‐diversity varied with slope. Overall, slope and depth together explained 14–31% of beta‐diversity. The findings suggest that differences in beta‐diversity as related to depth gradients may differ among onshore and offshore and/or between shallow and deep summit seamounts. Specifically, we hypothesize that differences in productivity and depth gradients among seamounts may generate different patterns of beta‐diversity.  相似文献   

10.
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   

11.
Genetic connectivity and habitat characteristics were examined in two species of Acesta clams (Bivalvia: Limidae) from submarine seamounts and continental slopes along the western North America margin. Two species were identified from dive videos obtained with submarine remotely operated vehicles that surveyed a 2200‐km range between 27° and 46° N latitude. Acesta sphoni was only found at shallower habitats (545–860 m depth) in the southern part of this range, whereas Acesta mori was more abundant and widely distributed in deeper habitats (1029–1996 m). Both species occurred on seamounts and on the walls of submarine canyons and continental slopes. Segregation of these species by depth exposes them to correlated differences in water temperatures and dissolved oxygen concentrations. Ninety‐eight individuals sampled from seven seamounts and one escarpment locality were characterized with DNA‐barcodes based on 643 base pairs of mitochondrial cytochrome‐c ‐oxidase subunit I (COI). Further analysis of these sequences revealed no significant geographical subdivision across the sampled range. This lack of differentiation suggests ongoing genetic exchange between the seamount populations and those possibly distributed along the continental margins. Examination of regional bathymetric profiles suggested that an abundance of suitable habitat might exist along these margins.  相似文献   

12.
We report the northernmost and deepest known occurrence of deep-water pycnodontine oysters, based on two surveys along the French Atlantic continental margin to the La Chapelle continental slope (2006) and the Guilvinec Canyon (2008). The combined use of multibeam bathymetry, seismic profiling, CTD casts and a remotely operated vehicle (ROV) made it possible to describe the physical habitat and to assess the oceanographic control for the recently described species Neopycnodonte zibrowii. These oysters have been observed in vivo in depths from 540 to 846 m, colonizing overhanging banks or escarpments protruding from steep canyon flanks. Especially in the Bay of Biscay, such physical habitats may only be observed within canyons, where they are created by both long-term turbiditic and contouritic processes. Frequent observations of sand ripples on the seabed indicate the presence of a steady, but enhanced bottom current of about 40 cm/s. The occurrence of oysters also coincides with the interface between the Eastern North Atlantic Water and the Mediterranean Outflow Water. A combination of this water mass mixing, internal tide generation and a strong primary surface productivity may generate an enhanced nutrient flux, which is funnelled through the canyon. When the ideal environmental conditions are met, up to 100 individuals per m² may be observed. These deep-water oysters require a vertical habitat, which is often incompatible with the requirements of other sessile organisms, and are only sparsely distributed along the continental margins. The discovery of these giant oyster banks illustrates the rich biodiversity of deep-sea canyons and their underestimation as true ecosystem hotspots.  相似文献   

13.
The Pearl River Canyon system is a typical canyon system on the northern continental slope of the South China Sea, which has significant implications for hydrocarbon exploration. Through swath bathymetry in the canyon area combined with different types of seismic data, we have studied the morphotectonics and controlling factors of the canyon by analyzing its morphology and sedimentary structure, as well as the main features of the continental slope around the canyon. Results show that the Pearl River Canyon can be separated into three segments with different orientations. The upper reach is NW-oriented with a shallowly incised course, whereas the middle and lower reaches, that are located mainly in the Baiyun Sag, have a broad U-shape and have experienced consistent deposition. Seventeen deeply-cut canyons have developed in the slope north of the Baiyun Sag, playing an important role in the sedimentary processes of the middle and lower reaches of the Pearl River Canyon. These canyons display both asymmetrical V- and U-shapes along their lengths. Numerous buried channels can be identified below the modern canyons with unidirectionally migrating stacking patterns, suggesting that the canyons have experienced a cyclic evolution with several cut and fill phases of varying magnitude. These long established canyons, rather than the upper reach of the Pearl River Canyon, are the main conduits for the transport of terrigenous materials to the lower slope and abyssal basin during lowstand stage, and have contributed to the formation of vertically stacked deep-water fans in the middle reach. Canyon morphology is interpreted as a result of erosive sediment flows. The Pearl River Canyon and the 17 canyons in the slope area north of the Baiyun Sag probably have developed since the Miocene. Cenozoic tectonics, sea level change and sediment supply jointly control the morphology and sedimentary structure. The middle and lower reaches of the Pearl River Canyon developed on the paleo-terrain of the Baiyun Sag, which has been a persistently rapid depositional environment, receiving most of the materials transported via the canyons.  相似文献   

14.
基于SRTM15_Plus水深数据,利用地形表面流水分析与等高线几何分析相结合的方法对亚洲大陆边缘海底峡谷进行识别,分析峡谷的形态、分布及演化进程。共识别出海底峡谷531条,按照平面形态分为直线型、蛇曲型和树枝型三种,数量分别为239条、75条和217条。直线型峡谷主要分布在白令海盆地、千岛盆地、南海等海域;蛇曲型峡谷主要分布在孟加拉湾东部俯冲带海域;树枝型峡谷主要分布在日本海沟、伊豆小笠原海沟和南海海槽交界处,南海以及苏门答腊俯冲带海域。根据峡谷的形态与分布,结合研究区内构造背景,讨论了峡谷“直线型-蛇曲型”的形态演化进程,并依据树枝型峡谷主干谷的形态信息,推测存在“蛇曲型-树枝型”、“直线性-树枝型”的形态演化进程。  相似文献   

15.
The cordgrass Spartina anglica is an introduced species that tends to invade sheltered sand and mudflats, at the upper low marsh level. In Arcachon Bay, a lagoon in South West of France, the cordgrass can also replace Zostera noltii beds. The consequence of cordgrass presence on macrobenthic fauna was estimated and compared to adjacent habitats (bare sands, Z. noltii sea grass beds) during one year. The communities of the three habitats were characterised by low species richness, low abundance and biomass (when Hydrobia ulvae, 90% of abundance, is not considered) and high seasonal stability. The infaunal assemblages were particularly homogeneous between habitats without any characteristic species.Cordgrass eradication experiments were performed and zoobenthic recolonisation was observed the following year. Modifications in benthic fauna were observed on epifauna only.These results highlight the limited structuring effect of habitat heterogeneity at high tidal levels and in soft-bottom sediments where desiccation becomes the dominant factor determining infauna community structure.  相似文献   

16.
To estimate the degree of spatial heterogeneity of benthic deep-sea communities, we carried out a multiple-scale (from m's to 200 km) investigation in the Congo-Angola margins (Equatorial West African margin, 3150–4800 m) in which we examined the metazoan meiofauna at a variety of habitats along the Congo Channel system and in the associated cold seep. We investigate the structure, density, vertical distribution patterns in the sediment and biomass of meiofaunal communities in the Gulf of Guinea and how they are controlled by hydrologic and biogeochemical processes. The meiofaunal communities in the Gulf of Guinea were shaped by heterogeneous conditions on the margin, and reflect the multiple-scale spatial variability that corresponds with the different identified habitats. The two control sites, located at >100 km away from the canyon, were inhabited by very dense and the most diverse meiobenthic communities. Similar meiobenthic communities inhabited the transition zone between the canyon and the cold seep. Sites located along the Congo Channel were obviously affected by the local high-velocity bottom currents and unstable sedimentary conditions in this active submarine system. Extremely low meiobenthic densities and very low proportions in the most surficial sediment layers provided evidence for recently highly disturbed sediments at these sites. The remote operated vehicle (ROV) Victor 6000 provided images of the cold seep, showing a patchy distribution of several types of patchy distributed megafaunal communities dominated by three key symbiotic taxa (Mytilidae, Vesicomyidae and Siboglinidae). These cold seep sediments were colonised by a unique meiobenthic community, characterised by a high small-scale (m's) patchiness, low species richness and the prominent dominance of two large-sized nematode species: Sabatieria mortenseni, which is a cosmopolitan nematode known from littoral habitats, and an undescribed Desmodora species. The high individual body weight of S. mortenseni and its dominance at the cold seep site resulted in a significantly higher nematode biomass at the seep compared to the surrounding sites. In addition, the vertical nematode profiles, with maximum proportions in subsurficial layers, points to a chemosynthesis-based meiobenthic community in this cold seep, in contrast to the phytodetritus-based communities at the control sites and at the transition zone.  相似文献   

17.
海底峡谷是陆源物质向深海运移的重要通道和深海油气资源储集的重要场所,海底峡谷在我国近海也广泛发育。通过对国外海底峡谷研究成果和方法的介绍和学习,我国海洋学家开始对冲绳海槽西坡、台湾周边海域、南海北部海域及世界上其它海域的海底峡谷进行深入的调查和研究,并取得了丰硕的成果。但与国际相比,我国海底峡谷研究还处在发现和描述的阶段,还需要进行系统的观测和深入的研究,来探讨海底峡谷的形成发育机制和控制因子,及其与我国近海演化和油气成藏的关系。  相似文献   

18.
The relative contribution of chemosynthesis in heterotrophic fauna at seeps is known to be influenced by depth and by habitat. Using stable isotopes of carbon and nitrogen, we investigated macro‐ and megafaunal nutritional patterns in Norwegian margin cold seeps by comparing food webs both among habitats within a seep site and between different sites. The very active Håkon Mosby mud volcano (HMMV) is characterized by geochemical gradients, microbial activity and faunal zonation from the centre to the periphery. The Storegga Slide (600–900 m depth) has pockmarks with patchy less active seeps, and also shows concentric zonation of habitats but at much smaller spatial scale. The dominant carbon source for macrofaunal nutrition in both areas was chemosynthetically fixed and the bulk of organic carbon was derived from sulphur‐oxidizing bacteria. In HMMV, food chains were clearly separated according to habitats, with significantly lighter δ13C signatures on microbial mats and adjacent sediment (?33.06 to ?50.62‰) than in siboglinid fields (?19.83 to ?35.03‰). Mixing model outputs revealed that the contribution of methane‐derived carbon was small in siboglinid fields (0–17%) but significant (39–61%) in the microbial mats. Moreover, the variability of macrofauna signatures within this later habitat suggests the co‐occurrence of two food chains, one based on primary production via methanotrophy and the other via sulphide oxidation. The length of the food chains also varied among habitats, with at least one more trophic level in the siboglinid fields located at the periphery of the volcano. Conversely, in Storrega pockmarks, faunal δ13C signatures did not vary among habitats but among species, although separate food chains seem to co‐occur. The small size of the seepage areas and their lower fluxes compared to HMMV allow more background species to penetrate the seep area, increasing the range of δ15N and the trophic level number. Probably due to the higher flux of photosynthetic particulate organic carbon, the overall chemosynthesis‐based carbon contribution in invertebrate nutrition was lower than that in HMMV.  相似文献   

19.
《Ocean Modelling》2002,4(3-4):221-248
Three-dimensional numerical simulations of the generation and propagation of the semidiurnal internal tide in a submarine canyon with dimensions similar to those of the Monterey Canyon are carried out using a primitive equation model. Forcing with just sea level at the offshore boundary in an initially horizontally homogeneous ocean with realistic vertical stratification, internal tides are generated at the canyon foot and rim, and along portions of the canyon floor. The results compare favorably with observations, both indicating enhancement of energy along the canyon floor propagating at an angle consistent with linear internal wave theory. Due to the earth's rotation, internal tide energy is distributed asymmetrically in the cross-canyon direction, favoring the southern side. The effect of canyon floor slope is explored, with the finding that small changes in the slope result in large changes in the amount and distribution of the internal tide energy. Canyons whose floors are subcritical with respect to the semidiurnal frequency along their entire length have very little baroclinic energy, whereas canyons that are near-critical along much of their length, such as the Monterey Canyon, develop strong internal tides that propagate shoreward. Canyons that are near-critical at their mouths but supercritical further inshore generate the most internal tidal energy overall, although little of it makes it onto the continental shelf shoreward of the canyon head. The effects of internal tides within the canyons can be seen outside the canyons as well. Water is transported from depth onto the adjacent continental shelf along the canyon rims. This tidal pumping can be responsible for alongshore internal tide propagation and tidal-period surface currents with relatively small horizontal scales of variability.  相似文献   

20.
The Golo Margin in eastern Corsica is dissected by four canyons and two gullies which fed turbidite systems. Study of the dispersal of surficial sediments and flow dynamic in the Golo system is based on Kullenberg and interface cores interpreted in relation to a previously published seismic dataset. Cores were described in detail and interpreted within a sedimentary and stratigraphic framework. During the last 42,000 years, gravity processes which occurred in the large systems with a canyon source were mainly slide-induced, differentiated turbulent surges and hyperpycnal flows. Processes occurring in the small system with a gully source are mainly hyperconcentrated and concentrated flows. Deposits from the Corsican Margin can intercalate with products of processes triggered on the Pianosa Ridge located in the eastern part of the basin. During relative sea-level lowstands or during periods of rapid or high-amplitude sea-level fall, only large canyons (South and North Golo) are supplied by carbonate-rich hyperconcentrated and concentrated flows which are channelled in incised valleys on the shelf. During periods of slow or low-amplitude sea-level fall and during sea-level rise, sediments are trapped on a shelf delta and intensely winnowed by shelf hydrodynamic processes. Sand-rich hyperconcentrated and concentrated flows occur. All the systems fed by a canyon are active simultaneously. Gullies form and are active only during periods of sea-level rise. During relative highstands of sea level (Holocene), all the system is draped by hemipelagic sediments. Relative sea-level changes and canyon location relative to river mouths have a strong influence on the nature of sediment input, and the initiation and type of gravity flows which, in turn, control morphology and geometry.  相似文献   

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