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1.
Distribution and thickness of sedimentary facies in the coastal dune, beach and nearshore sedimentary system at Maspalomas, Canary Islands 总被引：1，自引：1，他引：0
Angela Fontán Bouzas Javier Alcántara-Carrió Isabel Montoya Montes Andrés Barranco Ojeda Silvia Albarracín Jorge Rey Díaz de Rada Jorge Rey Salgado 《Geo-Marine Letters》2013,33(2-3):117-127
Numerous studies have shown that most beaches and coastal dune systems of the world are currently eroding but very few have investigated the combined sediment budgets of subaerial and nearshore submarine systems. In the case of the dune field of the Maspalomas Natural Special Reserve (in the south of Gran Canaria), the adjacent Maspalomas and El Inglés beaches and the adjacent submarine platform, the sediment budgets have been severely affected by erosion over the past few decades. The objectives of this study were to investigate the availability of sand within the modern sedimentary system, including the coastal dunes, the beaches and the submerged shelf, but also to assess local sediment sinks. An isopach map generated on the basis of topo-bathymetric data and seismic-reflection profiles revealed that sediment thickness varies from 0–22 m in the study area. Expanses of relatively low sediment thickness were identified in the south-western sector of the coastal dune field along Maspalomas beach, and in the nearshore region to the south of this beach. These localized sediment-deficit areas earmark Maspalomas beach as the most vulnerable shore strip threatened by erosion. The shallow seismic data also revealed that the submarine platform south of Maspalomas represents a marine terrace cut into an ancient alluvial fan, thus documenting an influence of the geomorphological heritage on the present-day morphodynamics. A side-scan sonar mosaic of this nearshore platform enabled the delimitation of areas covered by rock, boulders and gravel, vegetated sand patches and a mobile sand facies, the latter including ripple and megaripple fields. The megaripple field in a valley close to the talus of the marine terrace has been identified as a major sediment sink of the Maspalomas sedimentary system. It is fed by south-westerly storm-wave events. The sediment deficit in the coastal dune field and along Maspalomas beach can therefore only be explained by a currently faster loss of sediment to an offshore sink than can be compensated by the supply of sand from outside the system. 相似文献
2.
Stratigraphic framework of sediment-starved sand ridges on a mixed siliciclastic/carbonate inner shelf; west-central Florida 总被引：1，自引：0，他引：1
J. H. Edwards S. E. Harrison S. D. Locker A. C. Hine D. C. Twichell 《Marine Geology》2003,200(1-4):195-217
Seismic reflection profiles and vibracores have revealed that an inner shelf, sand-ridge field has developed over the past few thousand years situated on an elevated, broad bedrock terrace. This terrace extends seaward of a major headland associated with the modern barrier-island coastline of west-central Florida. The overall geologic setting is a low-energy, sediment-starved, mixed siliciclastic/carbonate inner continental shelf supporting a thin sedimentary veneer. This veneer is arranged in a series of subparallel, shore-oblique, and to a minor extent, shore-parallel sand ridges. Seven major facies are present beneath the ridges, including a basal Neogene limestone gravel facies and a blue-green clay facies indicative of dominantly authigenic sedimentation. A major sequence boundary separates these older units from Holocene age, organic-rich mud facies (marsh), which grades upward into a muddy sand facies (lagoon or shallow open shelf/seagrass meadows). Cores reveal that the muddy shelf facies is either in sharp contact or grades upward into a shelly sand facies (ravinement or sudden termination of seagrass meadows). The shelly sand facies grades upward to a mixed siliciclastic/carbonate facies, which forms the sand ridges themselves. This mixed siliciclastic/carbonate facies differs from the sediment on the beach and shoreface, suggesting insignificant sediment exchange between the offshore ridges and the modern coastline. Additionally, the lack of early Holocene, pre-ridge facies in the troughs between the ridges suggests that the ridges themselves do not migrate laterally extensively. Radiocarbon dating has indicated that these sand ridges can form relatively quickly (1.3 ka) on relatively low-energy inner shelves once open-marine conditions are available, and that frequent, high-energy, storm-dominated conditions are not necessarily required. We suggest that the two inner shelf depositional models presented (open-shelf vs. migrating barrier-island) may have co-existed spatially and/or temporally to explain the distribution of facies and vertical facies contacts. 相似文献
3.
Two types of morphologic features in the head of Navarinsky Canyon are attributed to mass movement of near-surface sediment.
A series of pull-aparts is located downslope of large sand waves. These pull-aparts, possibly induced by liquefaction, affect
the upper 5 to 10 m of sandy sediment (water depths 350 to 600 m) on a 1o slope. A hummocky elongate mound of muddy sand (water depths 550 to 800 m) contains chaotic internal reflectors to a subbottom
depth of 30 to 40 m and possibly is the product of a shallow slide. We speculate that Holocene seismicity is the likely triggering
mechanism. 相似文献
4.
根据１９９０年现场调查及前期观察资料，论述了海南岛新海弧形海湾不同岸段由主要动力驱动过程和海滩地貌结构组成的４种海滩地貌状态，为Ⅰ．隐蔽段消散类型，Ⅱ．脊－沟体系与低潮台地类型，Ⅲ．韵律海滩与砂坝类型，Ⅳ．开敞段消散类型。应用泥沙粒级参数概率模型分析近岸泥沙纵向运动趋势，结果表明，常波况下，沿岸泥沙存在双向运动，湾顶海滩为汇集地带，泥沙纵向运动主趋势为西南向；高能条件下，海岸北段可出现北向泥沙运动 相似文献
5.
Located in the south-eastern part of the Bay of Biscay, the Capbreton Canyon incises the continental shelf up to the 30 m isobath contour, and acts as a natural conduit for continental and shelf-derived sediments. EM1000 multibeam bathymetry shows two main features characterising the canyon — a deeply entrenched meandering channel, bordered by fluvial-like terraces constituting large sediment traps. A dataset of cores and seismic profiles together with a multibeam bathymetry map has enabled the characterisation of recent sedimentary activity in the axial channel and on the terraces. Data analysis evidenced the major role of the canyon head in recent sediment dynamics. This part of the canyon is a temporary reservoir for sediments, accumulated by coastal hydrodynamic processes. Exceptional climatic, tectonic or hydrodynamic events can mobilise the sediments and generate gravity-driven flows. Under the present-day sea-level highstand conditions, these flows are not powerful enough to bring their bedload to the deep sea, and are confined mainly to the upper part of the canyon. Turbidity currents model the axial channel pathway and are at the origin of terrace formation. Terraces in the Capbreton Canyon are not typical but rather are reduced to confined levees. Three factors control the vertical growth of a terrace: (1) the amount of overspilled sediments brought by turbidity currents, (2) hemipelagic sedimentation and (3) terrace height. The amount of sediment spilling over a terrace decreases with increased terrace elevation. Concurrently, the proportion of hemipelagic fallout depositing on a terrace increases. Terraces are considered to be fossil when the height of the terrace prevents further deposition by overspilling. The terraces studied in this paper are interpreted as having formed during the Holocene, implying that the sediment dynamics of the Capbreton Canyon is continuous through time. Highstand periods differ from lowstand periods because they show a decrease in the energy of erosive processes. Temporal variations in erosive and depositional processes in the canyon are controlled by the Adour River, which delivers large amounts of sediment to the system. 相似文献
6.
基于大量的悬浮体现场粒度和浓度数据,借助细颗粒悬浮体作为示踪物,分析了潮流作用下南黄海辐射沙脊群海底沉积物的再悬浮和扩散特征,并探讨了沙辐射沙脊群以北泥质区的形成机制。研究结果表明：（1）在辐射沙脊群以北,近岸悬沙在离岸方向上的扩散受到限制,向南又被辐射沙脊群中心浅滩所阻挡,只能在辐射沙脊群与废黄河口之间形成沿岸分布的高浓度浑水团。（2）辐射沙脊群以北的往复潮流对海底沉积物有分选作用,倾向于把海底沉积物中的粗颗粒分选搬运至沙脊群,把细颗粒沉积物向北输送,从而在沙脊群以北形成泥质区。（3）在正常海况下,沙脊表层沉积物再悬浮作用十分微弱,沙脊上覆水体中的悬沙主要来自于临近沟槽海底沉积物的水平扩散。 相似文献
7.
Sediment-starved sand ridges on a mixed carbonate/siliciclastic inner shelf off west-central Florida
S. E. Harrison S. D. Locker A. C. Hine J. H. Edwards D. F. Naar D. C. Twichell D. J. Mallinson 《Marine Geology》2003,200(1-4):171-194
High-resolution side-scan mosaics, sediment analyses, and physical process data have revealed that the mixed carbonate/siliciclastic, inner shelf of west-central Florida supports a highly complex field of active sand ridges mantled by a hierarchy of bedforms. The sand ridges, mostly oriented obliquely to the shoreline trend, extend from 2 km to over 25 km offshore. They show many similarities to their well-known counterparts situated along the US Atlantic margin in that both increase in relief with increasing water depth, both are oriented obliquely to the coast, and both respond to modern shelf dynamics. There are significant differences in that the sand ridges on the west-central Florida shelf are smaller in all dimensions, have a relatively high carbonate content, and are separated by exposed rock surfaces. They are also shoreface-detached and are sediment-starved, thus stunting their development. Morphological details are highly distinctive and apparent in side-scan imagery due to the high acoustic contrast. The seafloor is active and not a relict system as indicated by: (1) relatively young AMS 14C dates (<1600 yr BP) from forams in the shallow subsurface (1.6 meters below seafloor), (2) apparent shifts in sharply distinctive grayscale boundaries seen in time-series side-scan mosaics, (3) maintenance of these sharp acoustic boundaries and development of small bedforms in an area of constant and extensive bioturbation, (4) sediment textural asymmetry indicative of selective transport across bedform topography, (5) morphological asymmetry of sand ridges and 2D dunes, and (6) current-meter data indicating that the critical threshold velocity for sediment transport is frequently exceeded. Although larger sand ridges are found along other portions of the west-central Florida inner shelf, these smaller sand ridges are best developed seaward of a major coastal headland, suggesting some genetic relationship. The headland may focus and accelerate the N–S reversing currents. An elevated rock terrace extending from the headland supports these ridges in a shallower water environment than the surrounding shelf, allowing them to be more easily influenced by currents and surface gravity waves. Tidal currents, storm-generated flows, and seasonally developed flows are shore-parallel and oriented obliquely to the NW–SE trending ridges, indicating that they have developed as described by the Huthnance model. Although inner shelf sand ridges have been extensively examined elsewhere, this study is the first to describe them in a low-energy, sediment-starved, dominantly mixed siliciclastic/carbonate sedimentary environment situated on a former limestone platform. 相似文献
8.
Evan B. Forde Daniel J. Stanley William B. Sawyer Karen J. Slagle 《Applied Ocean Research》1981,3(2):59-62
A sediment study suggests that Washington and Norfolk canyons off the Mid-Atlantic States are not inactive, but have served periodically since the Late Pleistocene as conduits of sediment originating on the adjacent shelf and upper slope. Large quantities of sand occur in the canyon heads as thin beds and laminae, and on the continental slope as mixtures of sand (to ), silt and clay that are extensively reworked by burrowing organisms. Sandy turbidites occur in the canyons on the rise. Basinward dispersal, from the outer shelf and uppermost slope, is recorded by heavy mineral suites and bioclastic components, primarily foraminifera of shallow marine origin, in the lower slope and upper continental rise canyon cores. The down-axis movement of material, presumably episodic, in the Holocene to recent results from offshelf spillover into canyon heads, failure on the steep walls bordering canyons on the slope, and resuspension by bottom currents. 相似文献
9.
水下沙丘形态演化的数值模拟实验 总被引：1，自引：0，他引：1
水下沙丘在海洋、湖泊、河流等浅水砂质沉积区广泛分布。基于过程的数值实验方法探讨了沙丘形态演化问题,试图解释在沙丘形成过程中各因素的作用及它们之间的关系。模拟中考虑了以下的变量:水深、沉积物粒度、沉积层厚度以及台风作用。模拟结果显示,沙丘的空间分布控制了空间流场的参数k2,沙丘波高受水深、沉积物粒度以及沉积层厚度等因素的影响,沉积层厚度决定了沙丘的形态是否饱满。在台风作用中,沙丘波峰的沉积物被侵蚀,高程降低,波高渐小;台风作用后,沉积物被重新输运至波峰,沙丘高度逐渐恢复。因此,沙丘的高度取决于台风作用的时间以及2次台风作用之间的间隔。沙丘形态和尺度在台风作用前后变化较小,但沙丘演化的速度却有所提高。根据台湾浅滩和北海南部地貌系统数据的验证,模拟具有较好的效果。 相似文献
10.
水下沙丘形态演化的数值模拟实验 总被引：1，自引：0，他引：1
水下沙丘在海洋、湖泊、河流等浅水砂质沉积区广泛分布。基于过程的数值实验方法探讨了沙丘形态演化问题,试图解释在沙丘形成过程中各因素的作用及它们之间的关系。模拟中考虑了以下的变量:水深、沉积物粒度、沉积层厚度以及台风作用。模拟结果显示,沙丘的空间分布控制了空间流场的参数k2,沙丘波高受水深、沉积物粒度以及沉积层厚度等因素的影响,沉积层厚度决定了沙丘的形态是否饱满。在台风作用中,沙丘波峰的沉积物被侵蚀,高程降低,波高渐小;台风作用后,沉积物被重新输运至波峰,沙丘高度逐渐恢复。因此,沙丘的高度取决于台风作用的时间以及2次台风作用之间的间隔。沙丘形态和尺度在台风作用前后变化较小,但沙丘演化的速度却有所提高。根据台湾浅滩和北海南部地貌系统数据的验证,模拟具有较好的效果。 相似文献
11.
黄海海底地貌分区及地貌类型 总被引：6，自引：0，他引：6
本文通过多年来大量的实际调查资料,将黄海划分成北黄海海湾潮流脊与岛礁、山东半岛沿岸水下堆积岸坡及水下阶地、南黄海西部弱堆积侵蚀平原、旧黄河-古长江三角洲堆积平原、海峡等七个地貌区,它们都各具特有的地貌类型。北黄海和南黄海原为两个大型的山间盆地,尔后由于海侵、被大量沉积物充填,成为今日连成一体的黄海浅海平原。 相似文献
12.
13.
Jürgen Alheit 《Estuarine, Coastal and Shelf Science》1983,17(5):547-554
Harrington Sound, Bermuda, is a shallow subtropical lagoon with carbonate sediments. The most important fishes in this lagoon, in terms of biomass, are grunts (Haemulon aurolineatum, H. flavolineatum, H. sciurus) and a sea-bream (Diplodus bermudensis). These undertake diel feeding migrations from the shallow rocky zone towards the deeper sand and mud zones. When feeding on zoobenthos they cannot avoid swallowing carbonate sediment particles. These sediment particles pass through the alimentary canal of the fishes and are deposited again, after digestion of the food, as faeces in the shallow zones. Thus, the fishes transport the sediment in an unusual direction, from the deep to the shallow zones, in effect against the force of gravity. By recording the fish stock densities, digestion rates, and calcium carbonate content of fish stomach and guts, it was possible to estimate the amount of sediment transported by the fishes. In Harrington Sound, this amounts annually to 4530 kg calcium carbonate, 40% of which is deposited in the very shallow areas. The pH-values measured in fish stomachs seem to be acidic enough for the dissolution of carbonate sediment particles when transported by fishes. 相似文献
14.
Coastal cliffs at Kvalvågen, eastern Spitsbergen, expose palaeolandslide blocks and related slope failure features that record local collapse of an otherwise undisturbed succession of paralic sediments. The collapse occurred along a shallow sloping shelf at the edge of an epicontinental sea in the Early Cretaceous. The event was coincident with a rise in relative sea level along a coast that had just previously experienced a major paralic regression across a muddy marine environment. The low relief environment in which the slope failure structures formed, as well as the timing of the collapse raise questions regarding the cause of the topographic instability and the possible influence of sea level changes or tectonic activity. These outcrops have been previously interpreted as the collapse of a deltaic system triggered by local seismic activity or collapse of a shelf break in the headwall regions of submarine canyons. This paper presents new structural and stratigraphic data that refine and adjust the previous interpretations through the evaluation of a variety of possible mechanisms for collapse based on the new data. Our data suggest that active delta deposition was not occurring at Kvalvågen at the time of collapse and that the collapse was likely due to allogenic forcing. Despite the possible influence of pore fluids and rheological controls on the collapse, we find that the geometry and kinematics of landslide slip planes, synsedimentary folds, and other slope failure related features require over-steepened topography and that these are most consistent with westward-directed collapse off of a north striking escarpment with elevated topography on the east side. Fault exposures, a large contrast in palaeo-elevation, and liquifaction features support previous interpretations of a tectonic cause for the collapse and suggest that this topographic feature may have been a fault or fold scarp. This study demonstrates the importance of combining stratigraphic and sedimentological data with structural data and kinematic analysis in the interpretation of sedimentary processes. 相似文献
15.
Hamilton-type geoacoustic models were developed for Area Foxtrot, a shallow water test bed south of Long Island, for emerging active sonar systems where the surface sediment type is highly spatially variable. Reverberation levels (RL) were modeled using the finite-element parabolic equation (FEPE) propagation model to augment the generic sonar model (GSM) propagation model because the bottom loss model in GSM did not estimate transmission loss (TL) accurately in shallow water. FEPE estimates reveal that there is a greater than 15 dB difference between TL for sand and that for silt-day sediments in Area Foxtrot. The comparison between modeled RL and measured RL (from a 1991 active sonar exercise) enabled bottom scattering strength kernels to be developed for Area Foxtrot. Bottom scattering strength was found to be a function of sediment type. Hard sand sediment has a bottom scattering strength which obeys Lambert's law (sin2 &thetas;) while that of silt-clay sediment is consistent with sub-bottom volume scattering (sine). The RLs in Area Foxtrot are azimuth-dependent and are a function of TL and bottom scattering strength (and hence bottom sediment type). Sonar beams steered towards the hard sand show higher RLs than for silt-clay, and knowledge of the sediment type and its spatial variation must be known to model RL accurately. A method to determine sediment type using measured RLs and RL slopes is given 相似文献
16.
An investigation undertaken recently by the Division of Regional Geoecology and Marine Geology of the Karpinsky All-Russian
Research Geological Institute in the coastal zones of the Eastern Gulf of Finland allowed finding some specific relief forms
of both near-shore bottom topography and shoreline shape. First of all, among the most interesting objects, the sand ridges
on the surface of submarine terrace (between Repino locality and Cape Lautaranta) should be mentioned. These ridges are elongated
at an angle to the shoreline and are located beyond the limits of wave action. The other interesting morphological type is
represented by longshore sand waves up to some hundreds of meters long and some tens of meters wide near the Bol’shaya Izhora
locality. Longshore sand waves move along the southern coast of the gulf, this causing alteration of erosion and accretion
zones and leading to formation and degradation of the sand spits. Shore-face-connected ridges are believed to develop under
the action of drift currents generated during the passage of deep west cyclones. It is shown that the ridge turned toward
the current gives rise to a convergence of the cross-shore flows over the crest and provokes a shift of the maximum velocity
toward the front side of the structure. Associated changes in sediment discharges result in accumulation and growth of the
ridge. The origin of wavelike features in the shoreline contour (longshore sand waves) is due to a very oblique wave approach
caused by predominance of the west winds blowing along the axis of the gulf. Under these conditions a small perturbation of
the shoreline contour is shown to manifest a trend to increase with time. 相似文献
17.
本文以粤西水东湾表层沉积物样品的粒度分布为基本数据,使用对应分析方法并结合地形与波流特征,分析了海湾动力沉积环境。分析结果表明,海湾现代沉积环境可划分为4个动力沉积区。 相似文献
18.
Side-scan data from the epicentral area of the 1929 Grand Banks earthquake and cores from the resulting turbidite are used to determine a sediment budget for the event. The 1929 turbidite has a volume of about 185 cubic km, which is mostly sand. Features indicating failure on the continental slope are observed only in muddy sediment. A major source of sand in the heads of the fan valleys of the Laurentian Fan is postulated to balance the sediment budget. This sand accumulated proglacially during the Wisconsinan glaciation and probably failed through liquefaction in the 1929 earthquake. 相似文献
19.
The ecology of the family Pinnidae was studied by sampling three pinnid species from 36 sampling sites across four different microhabitats in the Gulf of Thailand. The species spatial distributions were mostly uniform, with some populations having random distributions. Species abundances differed between sandy and coral habitats according to non-metric multi-dimension scaling analyses. Although the Gulf of Thailand is a relatively small geographic area, habitats are varied enough to provide variable shell densities. Small islands are important distribution areas, and coral reefs provide both direct and indirect shelter which support high abundances, densities and increased shell size. The highest density was recorded in sand beds within coral reefs. Low density and small shell size in sand beaches might be related to high mortality in shallow water or to adaptations for survival in shallow waters. A clear correlation between sediment composition and species abundance was found in Pinna atropurpurea; abundance increased with the sand content of the sediment. For P. deltodes, abundance increased as the rock fraction of the sediment increased. These results suggest that adaptations in Pinnidae, such as shell size, shell morphology, and the exposure of the shell above the sediment-water interface, are responses for survival in different habitats. 相似文献
20.
海底浅层圈闭与浅层气地震反射特征对比 总被引：1，自引：0，他引：1
海底浅层圈闭条件是决定浅层气反射特征的重要因素,根据海底浅层圈闭条件的分析、国内外浅层气分布区反射特征与底质类型对比分析和南黄海西部地区浅部断层分析,得出结论:(1)浅层气的圈闭条件主要受海底底质类型与浅部断层控制,常见圈闭类型为岩性圈闭和断层圈闭;(2)底质类型是决定浅层气反射特征的重要因素。分析认为海底表层沉积物的泥砂含量决定了圈闭中盖层封闭能力,进而决定了浅层气聚集能力和储集量,形成不同浅层气地震反射特征;(3)某些现代三角洲地区,受潮流或河流与海洋共同作用影响,表层底质经常与整个浅层的物质组成差别较大。由于其内部一般含有较厚的细颗粒黏土质粉砂和粉砂质黏土,封闭能力较强,可封闭较多浅层气,能形成大规模的声学空白反射,但常观察到浅层气反射顶界面局部突起呈旗舰状;(4)浅部断层既可形成断层圈闭,也可充当浅层气的运移通道。断层圈闭通常较少见且难以识别,浅部断层在第四纪松散地层中更多地充当了浅层气运移的通道;(5)浅部地层存在多套含泥较多的地层且形成圈闭时,浅层气被多次圈闭,会在不同深度形成"楼层式"的多个强反射界面、声学扰动。 相似文献