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1.
Patterns and controls of surface sediment distribution: west-central Florida inner shelf 总被引：2，自引：0，他引：2
Gregg R. Brooks Larry J. Doyle Richard A. Davis Nancy T. DeWitt Beau C. Suthard 《Marine Geology》2003,200(1-4):307-324
The west-central Florida inner shelf represents a transition between the quartz-dominated barrier-island system and the carbonate-dominated mid-outer shelf. Surface sediments exhibit a complex distribution pattern that can be attributed to multiple sediment sources and the ineffectiveness of physical processes for large-scale sediment redistribution. The west Florida shelf is the submerged extension of the Florida carbonate platform, consisting of a limestone karst surface veneered with a thin unconsolidated sediment cover. A total of 498 surface sediment samples were collected on the inner shelf and analyzed for texture and composition. Results show that sediment consists of a combination of fine quartz sand and coarse, biogenic carbonate sand and gravel, with variable but subordinate amounts of black, phosphorite-rich sand. The carbonate component consists primarily of molluskan fragments. The distribution is patchy and discontinuous with no discernible pattern, and the transition between sediment types is generally abrupt. Quartz-rich sediment dominates the inner 15 km north of the entrance into Tampa Bay, but south of the Bay is common only along the inner 3 km. Elsewhere, carbonate-rich sediment is the predominate sediment type, except where there is little sediment cover, in which cases black, phosphorite-rich sand dominates. Sediment sources are likely within, or around the periphery of the basin. Fine quartz sand is likely reworked from coastal units deposited during Pleistocene sea-level high stands. Carbonate sand and gravel is produced by marine organisms within the depositional basin. The black, phosphorite-rich sand likely originates from the bioerosion and reworking of the underlying strata that irregularly crop out within the study area. The distribution pattern contains elements of both storm- and tide-dominated siliciclastic shelves, but it is dictated primarily by the sediment source, similar to some carbonate systems. Other systems with similar sediment attributes include cool-water carbonate, sediment-starved, and mixed carbonate/siliciclastic systems. This study suggests a possible genetic link among the three systems. 相似文献
2.
A simulation of suspended sediment movement relating to tidal and wave forcing during a winter monsoon in November 1983 in the Huanghai and East China Seas continental shelf is attempted by using the model describing the cohesive/non-cohesive sediment resuspension generated by interactions between currents and waves.model simulation showed that sediment concentration was increased by resuspension at shallow depths during the strong storm conditions due to high bottom stress interacted between currents and waves. This result is in general agreement with observations in horizontal distribution of suspended sediment distribution.At three current meter mooring positions off the southern Shandong Peninsula resuspension occurred only at a depth of 22m,nearest coastal position and at deeper parts at depths of 51 and 80m wave-current interaction effects were not significant. It has shown that the present model simulation demonstrated the capability of reproduction of suspended sediment movement under wintertime extreme event reasonably well. 相似文献
3.
长江口北槽口外悬沙浓度垂线分布的数学模拟 总被引：8，自引：2，他引：6
利用垂向一维悬沙运动模型,对长江口北槽口外大、小潮悬沙浓度垂线分布进行模拟,模拟结果同“六点法”实测值拟合较好,表明影响悬沙浓度垂线分布的主要因素为悬沙垂向扩散及絮凝沉降作用。 相似文献
4.
为研究工程区海域水沙特征的时空分布、运动规律,采用不同时期的现场水文泥沙资料,对射阳港拦门沙航道工程建设前后的水流、含沙量、悬沙粒径和底质特征进行了对比分析。研究表明:射阳港一期航道工程建设后航道内潮波发生变形,涨潮流速大、历时短;落潮流速小、历时长,进入到航道内泥沙很难被带出航道,容易导致航道淤积。工程区海域整体含沙量较大,一期工程建设后导堤内涨潮含沙量明显增大,口门净输沙向口内,通过口门进入到航道的高含沙水体是航道淤积的重要沙源之一。导堤间边滩表层存在部分淤泥,且具有一定流动性,在水流及自身重力作用下,边滩淤泥可归入航道内。 相似文献
5.
New high-quality multibeam and high-resolution seismic data reveal new observations on sediment transfer and distribution and margin morphometrics in the uppermost slope of Northeastern Little Bahama Bank between 20 and 300 m water depth. The echofacies/backscatter facies show an alongslope sediment distribution forming successive strips. The upper part of the uppermost slope corresponds to the alternation of several submerged coral terraces and escarpments that could be related to Late Quaternary sea-level variations. The terraces could either be related to periods of stagnating sea-level or slow-down in sea-level change and therefore increased erosion by waves, or periods of accelerated sea-level rise since the Last Glacial Maximum. Terraces could therefore be related to coral construction and drowing. The medium part corresponds to the marginal escarpment, a steep cemented area. The lower part of the uppermost slope shows a discontinuous Holocene sediment wedge with varying thickness between 0 and 35 m. It is separated from the upper part by a zone of well-cemented seafloor associated with the marginal escarpment. Passing cold fronts result in sediment export caused by density cascading. The associated sediment fall-out and convective sedimentation can generate density currents that form this wedge and eventually flow through linear structures on the upper slope. The survey reveals the presence of recently active channels that extend over the entire uppermost slope and interrupt the wedge. The channels connect shallow tidal channels to submarine valleys connected to the proximal part of canyons. They directly feed the canyons with platform-derived sediment forming low-density turbidity currents and could supply the deepest part of the system with coarse-grained sediment directly exported from the carbonate platform. 相似文献
6.
本文基于4次洪枯季同步水文观测资料,着重分析了长江口北支悬沙浓度的潮周期变化、垂向分布、纵向分布和悬沙输移及其时空差异。研究结果显示,悬沙浓度的潮周期变化过程在大中潮期以M型(双峰型)为主,下段主槽内在大潮期多出现V型,上段在枯季可出现涨潮单峰型;小潮期可出现无峰、单峰或双峰型。涨、落潮悬沙浓度峰值及均值,在枯季多涨潮大于落潮,洪季中小潮特别是小潮期易出现落潮大于涨潮;下段主槽内在大潮期易出现落潮大于涨潮。悬沙浓度的垂向分布及其变化特点,在大中潮期与悬沙的潮周期变化型式有关,其中M型存在显著的洪枯季差异。纵向上,最高悬沙浓度在枯季出现于中段灵甸港至三和港之间及附近河段,洪季则在下段三条港附近。潮周期悬沙净输移,枯季大多向陆特别是大中潮期,洪季中上段大多向海,下段大潮期多向陆、中小潮易出现向海;下段主槽内在大潮期易出现向海。 相似文献
7.
根据2014年1月及2017年2月杭州湾大、小潮水沙资料,计算了流速、含沙量、单宽潮量、单宽输沙量,进而分析了潮周期断面净潮量、净输沙量和区域冲淤分布。研究发现杭州湾涨、落潮平均流速比值整体较20世纪八九十年代增大,绝大部分区域大于1.0,涨潮流相对增强,澉浦南岸和金山北岸尤为显著。含沙量平面上分布澉浦、杭州湾南岸两个高值区(大潮大于3 kg/m3,小潮大于1.3 kg/m3)以及北岸湾口至乍浦之间的低值区(大潮小于2 kg/m3,小潮小于0.9 kg/m3),随潮汛变化显著,最大含沙量浓度通常滞后于急流时刻。各测站涨、落潮量和输沙量呈现“大涨大落”和“大进大出”的特征,造成杭州湾短时间尺度内的“大冲大淤”。大潮两涨两落金山与乍浦、乍浦与澉浦之间区域净输沙量可达几千万吨,净冲淤则在几百万吨。 相似文献
8.
A preliminary study on fingerprinting approach in marine sediment dynamics with the rare earth elements 总被引：1，自引：0，他引：1
Locating the quantitized natural sediment fingerprints is an important work for marine sediment dynamics study.The total of 146 sediment samples were collected from the Shelf of the East China Sea and five rivers,including Huanghe (Yellow),Changjiang (Yangtze),Qiantang,Ou and Min River.The sediment grain size and the contents of rare earth elements (REEs) were measured with laser particle size analyzer and ICP-MS technology.The results show that absolute REE content (ΣREE) and the concentration ratio of light REEs to heavy REEs (L/HREE) are different in the sediments among those rivers.There are higher REE contents in being less than 2 m and 2–31 μm fractions in the Changjiang Estuary surface sediments.The REE contents of bulk sediment are dominated by the corresponding values of those leading size-fractions.REE of sediment is higher close to the estuaries and declines seaward on the inner shelf of the East China Sea (ECS).The L/HREE ratio has a tendency of increase southward from 28 ? N.Hydrodynamic conditions plays a predominate role on spacial distributions of the surficial sediment’s REE parameters.In some situations,the currents tend to remove the coarser light grains from initial populations,as well as the deposit of the finer heavy mineral grains.In other situations,the currents will change the ratio of sediment constituents,such as ratio between silts and clays in the sediments.As a result,the various values of REE or L/HREE ratio in different bulk sediments are more affected by the change of size-fractions than source location.Under the long-term stable hydrodynamic environment,i.e.,the East China Sea Shelf,new sediment transport model based on the size and density gradation concept may help to understand the spatial distribution patterns of REE parameters. 相似文献
9.
Late Holocene chronology,origin, and evolution of the St. Bernard Shoals,Northern Gulf of Mexico,USA
Several shore-parallel marine sand bodies lie on the Louisiana continental shelf. They are Trinity Shoal, Ship Shoal, Outer
Shoal, and the St. Bernard Shoals. These shoals mark the submerged positions of ancient shorelines associated with abandoned
deltas. Three of these shoals are single elongate deposits. The fourth shoal, the St. Bernard Shoals, consists of a group
of discrete sand bodies ranging in size from 44 to 0.05 km2, 25 km southeast of the Chandeleur Islands in 15–18 m of water. The St. Bernard Shoals are stratigraphically above the St.
Bernard delta complex, which was active 2,500–1,800 years b.p. Understanding the evolution of the St. Bernard Shoals is necessary to reconstruct the Holocene chronology of the St. Bernard
delta complex and the eastern Louisiana continental shelf. For this study, 47 vibracores and 400 km of shallow seismic reflection
data collected in 1987 across the Louisiana shelf were analyzed. In June 2008, 384 km of higher-resolution seismic reflection
data were acquired across the study area and appended to the preexisting datasets. Vibracores were integrated with seismic
profiles to identify facies and their regional distribution. Our results demonstrate that the deltaic package stratigraphically
below the St. Bernard Shoals is chronologically younger than the northern distributaries, but derived from the same trunk
distributary channel (Bayou la Loutre). The river eventually bypassed the northern distributaries, and began to deposit sediment
further onto the continental shelf. After abandonment, the overextended delta lobe was rapidly transgressed, creating a transgressive
shoreline that eventually coalesced with earlier shorelines in the region to form the Chandeleur Islands. The St. Bernard
Shoals formed by the reworking of the relict distributary deposits exposed on the inner to mid shelf during and subsequent
to shoreface ravinement. 相似文献
10.
1Introduction The sediment dynamics of intertidal flats in-volves erosion, transport, and settling processes. A-mong these, the mechanisms of sediment transportare a key question. Progress has been made in awide range of associated areas, including sedime… 相似文献
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12.
《Oceanologica Acta》1999,22(1):67-84
Diatom and coccolithophorid abundance and diatom assemblage composition found in the water column along the Portuguese margin, during upwelling and non-upwelling conditions, are compared to the distribution patterns observed in the recent sediments from the same area. The water column results indicate a one order of magnitude increase in phytoplankton biomass during upwelling conditions (summer), with diatoms being the most important contributors. Coccolithophorids, on the contrary, dominate the phytoplankton in winter (non-upwelling). The comparison of the upwelling and non-upwelling spatial distribution of these phytoplankton groups to their sedimentary record reveals the sediment record as a reflection of the upwelling situation, preserving most of its original spatial variability. The comparison between living and fossil diatom assemblages indicates that from the two genera which dominate the summer biologic assemblage, Pseudo-nitzschia and Chaetoceros, Pseudo-nitzschia is not represented in the sediments, while Chaetoceros is the dominant form of the sediment. Thalassiosira which occurs in the same abundance in both seasons, responding to both river and upwelling nutrient input, can not be a reliable indicator of any single process. However, this genus distribution in the sediments can be used as an indicator of continuous nutrient availability.Such results are of great importance for paleoceanographic reconstructions since they constitute a good indication that the sediment record, even though somewhat altered with respect to assemblage composition, does reflect the water column characteristics. 相似文献
13.
《Oceanologica Acta》1999,22(3):319-336
Diatom and coccolithophorid abundance and diatom assemblage composition found in the water column along the Portuguese margin, during upwelling and non-upwelling conditions, are compared to the distribution patterns observed in the recent sediments from the same area. The water column results indicate a one order of magnitude increase in phytoplankton biomass during upwelling conditions (summer), with diatoms being the most important contributors. Coccolithophorids, on the contrary, dominate the phytoplankton in winter (non-upwelling). The comparison of the upwelling and non-upwelling spatial distribution of these phytoplankton groups to their sedimentary record reveals the sediment record as a reflection of the upwelling situation, preserving most of its original spatial variability. The comparison between living and fossil diatom assemblages indicates that from the two genera which dominate the summer biological assemblage, Pseudo-nitzschia and Chaetoceros, Pseudo-nitzschia is not represented in the sediments, while Chaetoceros is the dominant form of the sediment. Thalassiosira, which occurs in the same abundance in both seasons, responding to both river and upwelling nutrient input, can not be a reliable indicator of any single process. However, this genus distribution in the sediments can be used as an indicator of continuous nutrient availability. Such results are of great importance for paleoceanographic reconstructions, since they constitute a good indication that the sediment record, even though somewhat altered with respect to assemblage composition, does reflect the water column characteristics. 相似文献
14.
Christian J. Noll Timothy M. Dellapenna Andrea Gilkinson Randall W. Davis 《Geo-Marine Letters》2009,29(1):1-16
Surficial sediment distribution within Simpson Bay is a function of antecedent bedrock and recently deposited glacial geology,
as well as active physical processes both within Simpson Bay and Prince William Sound (PWS). Simpson Bay is a turbid, outwash
fjord located in northeastern PWS, Alaska. Freshwater from heavy precipitation, and the melting of high alpine glaciers enter
the bay through bay head rivers and small shoreline creeks. The catchment has a high watershed/basin surface area ratio (∼8:1),
and easily erodible bedrock that contribute to high sediment loads. The system can be divided into three discrete basins,
each with specific morphologic and circulatory characters. Side scan sonar, swath bathymetry, and seismic profiles reveal
that bathymetric highs are areas of outcropping glacial surfaces. High backscatter coupled with surface grab samples reveal
these surfaces to be composed of coarse sediment and bedrock outcrops. Bathymetric lows are areas of low backscatter, and
grab samples reveal these areas to be ponded deposits of organic-rich estuarine muds. The data provide evidence of terminal
morainal bank systems, and glacial grounding line deposits at the mouth of the bay and rocky outcrops were identified as subsurface
extensions of aerial rocky promontories. Radioisotope analyses of short cores reveal that the bay has an average accumulation
rate of approx. 0.5 cm year−1, but that this varies in function of the watershed/basin surface area ratios of the different basins. The interaction of
tidal currents and sediment source drives sediment distribution in Simpson Bay. Hydrographic data reveal high spatial variability
in surface and bottom currents throughout the bay. Subsurface currents are tide dominated, but generally weak (5–20 cm s−1), while faster currents are found along shorelines, outcrops, and bathymetric highs. Bathymetric data reveal steep slopes
with little to no modern sediment throughout the bay, suggesting lack of deposition due to tidal currents. 相似文献
15.
M. G. Skafel 《Coastal Engineering》1995,24(3-4)
The evolution of shorelines composed of consolidated cohesive sediments is dominated by irreversible erosion. In this note, measurements, under laboratory conditions, of bottom velocities, wave heights, and breaking characteristics over an actively eroding consolidated cohesive sediment shore are reported. Erosion is enhanced under breaking conditions, and plunging breakers are markedly more erosive than spilling breakers. The turbulence at the outer edge of the breaking zone has the −5/3 power high frequency dependence indicative of the inertial subrange. 相似文献
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基于遥感反演的莱州湾悬沙分布及其沉积动力分析 总被引：5，自引：3，他引：2
选用1986-2004年不同时期的LandsatTM/ETM+影像,利用2004年黄河口附近实测数据推导的表层悬浮泥沙浓度反演模型,结合水文气象资料、多年水深数据和极端天气数模结果,研究了莱州湾西南近岸海域表层悬浮泥沙分布特征,结果表明,受黄河丰枯水期的影响,莱州湾西南部海域悬浮泥沙高浓度区主要分布于黄河口附近海域和西南沿岸,其枯水期的覆盖范围一般大于丰水期的。受潮流高流速场控制,黄河口外悬沙浓度高值区与海底泥沙堆积区对应较好,泥沙主要来源于陆源输沙和泥沙再悬浮;在西南近岸浅海区悬沙浓度高值区主要形成于泥沙的再悬浮,在近岸出现轻微冲刷。风等其他海洋动力因素,一般情况下对悬浮泥沙扩散的程度和范围具有一定的影响作用,但悬沙受潮流场影响而形成的总体扩散趋势未发生改变;极端条件下,风暴潮流使莱州湾西南部近岸浅海区的悬浮泥沙浓度显著增加。 相似文献
18.
崎头洋附近群岛水域泥沙特征及悬沙来源分析 总被引：1，自引：0，他引：1
依据实测水文泥沙资料分析舟山群岛南部崎头洋附近海域的悬沙与底沙特征,建立该水域二维潮流数学模型,同时根据底沙及悬沙的粒径分布和潮流的运动路径对该海域的悬沙来源做进一步分析.指出崎头洋附近群岛海域的悬沙除部分来源于潮汐动力作用下的底沙起动再悬浮之外,主要是杭州湾附近灰鳖洋水域的泥沙在潮汐动力作用下经群岛西北方向水道进入群岛内部水域的,进而在潮动力作用下经由东南方向水道进入东海及象山港附近水域. 相似文献
19.
振荡流层移输沙条件下悬沙层泥沙扩散系数垂向分布特征研究 总被引：1，自引：0，他引：1
层移输沙是海岸带泥沙运动的主要形式之一,其垂向悬沙浓度分布规律的研究一直是海岸工程关心的重点。一般情况下,经典的纯扩散模型被用来描述和解释悬沙浓度的试验数据,该模型认为周期平均悬沙浓度主要由参考浓度、泥沙沉速和泥沙扩散系数确定。泥沙扩散系数可以由泥沙沉速和悬沙浓度的垂向梯度反演得到。既往研究大多直接给出泥沙扩散系数的结果,对于不同反演计算方法间结果差别的研究较少。本研究汇总了已有振荡流层移输沙试验数据,采用曲线拟合方法和直接差分方法计算了相应的泥沙扩散系数,研究表明两种方法得到的计算结果在垂向位置z 0.15 m处差异不大,随着垂向位置的升高,差分方法的计算结果略微大于拟合方法。考虑到拟合方法可以得到连续的泥沙扩散系数垂向分布,本研究推荐使用幂函数形式的曲线拟合方法求解悬移泥沙扩散系数。基于此,对比分析了层移输沙悬沙层泥沙扩散系数随泥沙粒径、振荡流周期、均方根流速和振荡流类型等物理参数的变化规律。在纯振荡流层移输沙条件下,泥沙扩散系数随泥沙粒径的增大而增大,而振荡流周期和均方根流速几乎不影响泥沙扩散系数。在振荡流和定常流共同作用下,泥沙扩散系数受振荡流周期和定常流流速的影响,泥沙扩散系数随着振荡流周期的增大或定常流流速的减小而增大。 相似文献
20.
基于2018年10月21日至11月6日莱州湾西岸连续站观测数据,本文利用集合经验模态分解、希尔伯特?黄变换和小波分析法对底层单宽输沙率的小尺度特征做分析,并针对观测期间出现的大风天气对泥沙输运的影响进行了探究。结果表明,单宽输沙率在观测时间段内具有高频、潮周期、低频以及长周期尺度变化特征,周期尺度从小到大。其中高频和潮周期分量方差贡献率及所含能量最高,对输沙率的影响最强。边际谱显示东西方向输沙率的显著周期为13.3 h,南北方向大于11 h的周期较为显著。观测期间底层净泥沙通量分别为东向305.77 kg/m、南向597.25 kg/m,余流分量贡献最大,低频和高频分量贡献最小。上强迫风场主要在风速衰减期通过湍流和波浪影响输沙速率的时频分布,使其低频变化显著增强的同时,产生1 h周期左右的高频波动。交叉小波分析显示,风速和单宽输沙率在低频波段上相干性较强,且单宽输沙率会滞后风速1/4至1/2个周期。另外,风浪会增强泥沙输运的涨落潮不对称性,进而增加潮周期分量上的泥沙净输运。 相似文献