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1.
Abstract The continental margin of northern Sinai and Israel, up to Haifa Bay, is the northeastern limb of the submarine Nile Delta Cone. It is made up predominantly of clastics from the Nile and its predecessors. The continental shelf and coastal plain of Israel are built of a series of shore-parallel ridges composed of carbonate-cemented quartz sandstone (locally named kurkar), a lithification product of windblown sands that were piled up into dunes during the Pleistocene. The drop in global sea level and regression during the last glacial period exposed the continental shelf to subaerial erosion and created a widespread regional erosional unconformity which is expressed as a prominent seismic reflector at the top of the kurkar layers. The subsequent Holocene transgression abraded much of the westernmost kurkar ridges, drowned their cores, and covered the previous lowstand deposits with marine sands, which were in turn covered by a sequence of sub-Recent clayey silts. The Mediterranean coasts of Sinai and Israel are part of the Nile littoral cell. Since the building of the Aswan dams the sand supplied to Israel's coastal system is derived mainly from erosion of the Nile Delta and from sands offshore Egypt that are stirred up by storm waves. The sands are transported by longshore and offshore currents along the coasts of northern Sinai and Israel. Their volume gradually declines northward with distance from their Nile source. The longshore transport terminates in Haifa Bay where some sand is trapped, and the test escapes to deeper water by bottom currents and through submarine canyons, thus denying Nile-derived sand supply to the 40-km-long Akko-Rosh Haniqra shelf. The sand balance along Israel's coastal zone is a product of natural processes and human intervention. Losses due to the outgoing longshore transport, seaward escape, and landward wind transport exceed the natural gains from the incoming longshore transport and the abrasion of the coastal cliffs. The deficit is aggravated by the construction of (1) seaward-projecting structures that trap sands on the upstream side and (2) offshore detached breakwaters that trap sands between themselves and the coast. The negative sand balance is manifested by the removal of sand from the seabed and the consequent exposure of archaeological remains that were hitherto protected by it. The sediments that escape seaward from the longshore transport system form a 2.5- to 4-km-wide sandy apron adjacent to the shore that extends to where the water is 30–40 m deep. The apron's slope (0.5–0.8°) is steeper than the theoretical equilibrium slope for the median grain-size diameter in this zone (0.1–0.3 mm). The beach sands and the apron's surficial sands are well sorted. Their grain size decreases with distance from shore, from 0.2–0.3 mm nearshore to 0.11–0.16 mm by the drowned ridge. The coarse-grained fraction consists of skeletal debris (commonly 5–12% carbonate matter) and wave-milled kurkar grains (locally named zifzif). In deeper water, the basal sands underlying the fine-grained sediment cover consist of 1- to 30-cm layers whose composition ranges from silty sands to various types of sands (fine, medium, coarse, and gravelly) to zifzif. For the most part, they contain large amounts of skeletal debris (20–60%) and small fragments of kurkar. Two types of kurkar rock were encountered offshore: a well-sorted, fine- to medium-grained (0.074–0.300 mm) lithified dune sand with variable amounts of carbonate cement, ranging from hard rock of low permeability to loose sand; and a porous sandstone made up predominantly of algal grains and skeletal debris (calcarenite). 相似文献
2.
Changing shoreline positions along the Sinai coast of Egypt were determined by comparing aerial photographs and historical
charts with present-day conditions. The analyses identify longshore patterns wherein erosion along a protruding stretch of
the coast gives way to accretion in an adjacent major embayment. This pattern defines two coastal subcells consisting of source/sink
couplets. There is a general correspondence between the mineral variation, grain sizes of beach sand, and the patterns of
shoreline changes. Associated with erosion/ accretion shoreline change is a selective transport of different minerals according
to their densities and grain sizes. Two heavy-mineral groups were obtained by applying Q-mode factor analysis on the heavy-mineral
data. These two groups are influenced by transport processes, including sediment provenance from different sources: eroded
Nile delta west of Sinai, relict sediments from the former Nile distributaries, and sediment supply by land valleys and from
wind-blown sand.
Received: 2 June 1995 / Revision received: 29 May 1996 相似文献
3.
Gideon Almagor 《Marine Georesources & Geotechnology》2013,31(1):83-105
Abstract The continental margin of northern Sinai and Israel consists of a seaward‐inclined wedge, made up predominantly of foreset beds of mainly Nile‐derived clastics. They overlie seaward‐thickening Messinian (Upper Miocene) evaporites. Detailed bathymetric and seismic surveys reveal large areas of sea floor disturbances off northern Sinai and in several places off Israel, expressed by a complex block topography of the outer continental shelf and slope. These disturbed areas appear to be gigantic, deep‐seated, compound rotational slumps over down‐slope flowing evaporites. Many of the disturbances are above landward lobes of evaporites which fill buried Late Miocene erosion channels of the pre‐Messinian retreat of the sea. Flowage of the evaporites was presumably caused by excessive pore pressures, generated by the Pliocene‐Quaternary overload, in confined layers of the elastics interbedded within the evaporites. 相似文献
4.
Mobile sand deposits and shoreface sediment dynamics in the inner German Bight (North Sea) 总被引：1，自引：0，他引：1
This paper presents a conceptual model for the net bedload transport regime on the shoreface of the German Bight. The model is based on the spatial distribution of the surficial sediment cover (North Sea sands) which is identical to the uppermost layer in the seismic recordings. Sediment thickness was measured using very high resolution seismic profiling (chirp sonar) and vibrocoring. The three-dimensional sediment distribution was estimated using geostatistical methods (cokriging). The results demonstrate a longshore sand distribution with three distinct zones. In Zone 1 (0–10 m water depth) the sediments attain their maximum thickness of 10±2.5 m. Between 10 and 15 m water depth a relatively thin sand layer of 0.4–1.5 m is observed within Zone 2. The seaward adjacent Zone 3 (15–20 m water depth) is characterized by an averaged sand thickness of 2–3 m with local maxima of 5–6 m. Further offshore, the sand layer decreases to about 1–2 m thickness. The net bedload transport directions inferred from this sediment zonation comprise a longshore sediment bypassing in Zone 1 which results in a substantial sediment supply to the innermost part of the German Bight due to bedload convergence. Shore-normal bedload transport shifts sand to and fro across the coastal profile although the net directional transport is seawards. This results in sediment depletion between the 10 and 15 m-isobaths (Zone 2) and an adjacent sediment accumulation in deeper waters (Zone 3). 相似文献
5.
《African Journal of Marine Science》2013,35(3-4):511-524
The textural and compositional characteristics of the surficial shelf sediments north and south of the Orange River Delta are reviewed and compared. Sediments are fractionated and dispersed both north- and southwards of the Orange River mouth by wave action, longshore drift and subsurface currents. The mean grain size decreases both offshore and southwards in response to decreased wave influence at the seabed and the competence of the weak poleward undercurrent respectively. The increasing dominance of marine biogenic components in sediments south of the prodelta indicates a greater marine influence, modifying previous inferences that the Namaqualand mudbelt is primarily derived from the southward transport of Orange River sediments. A sharp distinction can be drawn between sediments of the Orange Shelf to the south and the Walvis Shelf to the north. Foraminiferarich deposits that dominate the Orange middle shelf and slope indicate that upwelling is an inner-shelf phenomenon. On the Walvis Shelf, foraminiferal sediments are confined to the slope and outer shelf. Fish debris is more common in Walvis Shelf sediments. Although phosphorite and glauconite sands often occur together in the same deposits on the Orange Shelf, the two minerals are concentrated in separate deposits on the Walvis Shelf. 相似文献
6.
Sediment is being transported from the Nile Delta to the Israeli coast by a wave-induced longshore current carrying mainly sand, and by the geostrophic Mediterranean Current, detected in Earth Resources and Technology Satellite (ERTS) photographs through the presence of suspended sediments. The location of these suspended sediments is consistent with computations of the maximum depth of wave stirring on the shelf. Since the construction of the Aswan Dam in 1965, sand has been more than adequately supplied by the severe erosion of the Nile Delta beaches. No changes in the longshore transport of sediment along the Israeli coast are anticipated from the Aswan Dam for a few hundred years.In memory of O. H. Oren, a pioneer in the study of the Nile flood along the Israeli coast. 相似文献
7.
岬湾相间的琼州海峡南岸在海岸动力条件作用下,岸滩发生侵蚀或堆积,特别是南岸中部的南渡江三角洲沿岸岸滩演变剧烈。该文从海岸动力地貌的角度,对琼州海峡南岸的海岸动力特征、泥沙运动以及岸滩演变进行分析。根据海峡南部三维潮流场数值模拟结果,结合经验公式初步分析潮流引起的泥沙运移速率和方向,得到岸外水域总的泥沙运移趋势为从西向东。根据波浪动力计算分析沿岸泥沙运移,探讨沙质岸滩的动态与地貌演变之间的关系,得出海峡南岸海岸地貌演变与盛行的NE和NNE向风浪有密切关系,岸滩的演变过程主要受制于这两个方向的风浪及其引起的泥沙沿岸运移。 相似文献
8.
南海北部水深８０—２５０ｍ的外大陆架和上大陆坡海底，有大片沙波地貌分布，它们主要是晚更新世末次冰期低海面时遗留下来的滨海沙波、沿岸沙丘、沙堤和沙垄，属残留沙体地貌。它们明显沿着本次冰期时形成的最低海岸线两侧分布，但在现代海底底流作用下，其两翼及沙波谷部发育有次一级的小型沙波或沙纹，它们的形态细小、排列紧密，与残留沙体地貌组成复式海底沙波。这就是流动沙波，是不稳定的地质因素，对海底工程有一定危害，但根据外大陆架实测底流数据，运用计算机数学模型方法计算，表明在细沙和中细沙大面积覆盖区，海底沙波每年均以０．１６６—０．５３４ｍ的速度向深海方向迁移，移动速度相当缓慢，其对海底工程设施不会造成直接危害。 相似文献
9.
The depositional sedimentary structures and textures of a single-barred nearshore system on the Atlantic coast of eastern Long Island, New York, were studied along seven shore-normal transects. Data along these transects consisted of textural analysis of 160 sediment samples, temporal bedform observations, and 42 can cores for the analysis of sedimentary structures.
Six sedimentary subenvironments were observed, based on distinct combinations of sediment color and texture, bedforms, physical, and biogenic sedimentary structures, and benthic infaunal communities. The shoreface environment is divided into the upper shoreface, the longshore trough, and the longshore bar. The divisions of the inner shelf environment are the shoreface-inner shelf transition, the offshore, and the coarse-grained deposit. The first five subenvironments are arranged in bands parallel to the shoreline, whereas the coarse-grained deposit occurs in patches across the inner shelf.
The location of fair-weather wave base, coinciding with a reduction in slope (3.0–0.3°) from the shoreface to the inner shelf, is characterized by the cessation of debris surge in the troughs of ripples, the formation of a “rust layer” of microorganisms over the bedform surface, and a sediment color change caused by an increase in organic detritus. The sequence of bedforms and physical sedimentary structures observed in this system fits well with existing wave-generated (oscillatory) flow regime models. These models explain the observed sequences as a response to the degree of asymmetric flow created by shoaling waves. Distribution of biogenic structures and assemblages of infaunal organisms is influenced by the distance landward or seaward of fair-weather wave base.
The overall relationships of this nearshore system can then be summarized as a hypothetical prograding stratigraphic sequence. The entire sequence is underlain by organic-rich, bioturbated, offshore deposits. Overlying the offshore is the planar-laminated sediments of the transition. Grading upward from the transition are the cleaner, planar-laminated, seaward slope deposits of the longshore bar. Above this, is a distinct erosional surface indicating the base of the massive to cross-laminated coarse sediments of the longshore trough. Capping the sequence are the cross- to planar-laminated, clean sands of the upper shoreface and foreshore. 相似文献
10.
G.F. Birch 《Marine Geology》1977,23(4):305-337
A combination of climatic and oceanic factors has resulted in slow sedimentation rates on the continental shelf off the west coast of South Africa since Tertiary times. This has enabled a study to be made of the residual Late Tertiary, relict Pleistocene and Holocene sediments.Sediments on the continental shelf form rough belts parallel to the coast. Most of the coarse sediment is confined to the littoral zone and Holocene mud is concentrated at the base of a rocky nearshore platform. A veneer of Quaternary quartzitic sand seawards of the Recent mud belt wedges out onto a Tertiary erosion surface on the mid shelf. Residual glauconite and phosphorite sands derived by erosion during Tertiary sea-level fluctuations cover large parts of the mid shelf in the south. Most of the slope and parts of the outer shelf in the north are draped by Recent foraminiferal and coccolithophorid debris. 相似文献
11.
The current study provides a potential method for measuring current velocities during storms.
Water hyacinth debris, carried from the Nile outlet area by the offshore current, are washed ashore along the Israeli coasts
after southwesterly winter storms. The impact of the offshore current and wind on the floating debris is such that storms
of five days duration are sufficient to transport plants from the Nile to the Carmel coast, a distance of about 400 km. The
available information indicates a high rate of transport in the southeastern Mediterranean. 相似文献
12.
Coastal shoreline protection and beach nourishment are significant issues for coastal states along the Atlantic and Gulf coasts. In some areas, there is a critical need to identify suitable sources of sand for possible use in public works projects for coastal protection. The continental shelf contains large resources of sand and gravel that could be used to support such projects. The U.S. Department of the Interior's (DOI) Minerals Management Service (MMS) provides policy direction and guidance for development of the resources located on the federal portion of the continental shelf. This article highlights the MMS's Sand Program, focusing on its cooperative resource and environmental studies with several coastal states, significant milestones and accomplishments, and anticipated activities in 1998 and beyond. Management of sand resources on the federal portion of the continental shelf has been made easier by a federal state partnership concept. Using this cooperative concept, joint projects are being conducted to investigate offshore sand resources, potential sites, extraction methods, and related environmental conditions. The MMS has procedures for negotiating sand agreements under the Outer Continental Shelf Lands Act (OCSLA) and ensuring that the resources are developed in an environ mentally sound manner. The authority to negotiate with project sponsors, an important recent change in the OCSLA, also resides with the MMS. This 1992 change in OCSLA facilitates the use of Outer Continental Shelf (OCS)resources for public projects. Further, the MMS is authorized to assess a fee based on the value of the resource and the public interest served. The MMS has worked with local sponsors and authorized the use of OCS sand for two projects. However, additional resource and environmental projects, as well as negotiated agreements, are anticipated within the near future with states and local governments along the Atlantic and Gulf coasts. 相似文献
13.
Hornblende is the least stable, and most diagnostic, mineral of the sediment blanketing the continental shelf off Georgia, U.S.A. Recent work by others has shown that the probable sources of hornblende-rich sands on the shelf are the Savannah and Altamaha Rivers, both of which originate in the southern Appalachian piedmont. Rivers with drainage basins confined to the coastal plain carry stable, low-hornblende heavy-mineral assemblages and contribute sediment to the shelf only during episodes of regression or transgression. Distribution of hornblende on the continental shelf reveals the importance of the Altamaha and Savannah Rivers, especially the Savannah, as sources of sediment. It is postulated that original point concentrations of hornblende-rich sand associated with Late Pleistocene deltas or estuaries of the Savannah River have been modified by southwest currents, possibly during winter storms. The resulting configuration is a series of northeast-trending, linear high-hornblende anomalies. The origin of the hornblende-distribution anomalies probably is identical to the origin of linear shoals that also trend northeast across the continental shelf. 相似文献
14.
Trace element concentrations (Pb, Cd, Mn, Fe, and Zn) were measured along four surface water transects across the continental shelf off Baja California, to evaluate the magnitude of heavy metal contamination in the coastal waters along the US-Mexican boundary. These initial measurements of trace elements in Mexican neritic waters revealed offshore concentration gradients, with the highest levels in coastal waters with high salinities and nutrient concentrations. There were also longshore gradients, with lower concentrations in the southern locations. Although the relative enrichment of metals detected at nearshore stations along the US-Mexican border appeared to correspond to wastewater discharges in that area, these trace metal enhancements were found to be primarily associated with physical oceanographic processes (upwelling and advection), rather than anthropogenic inputs. This was demonstrated both by metal-nutrient correlations and multivariate statistical analyses. Mass balance calculations also indicated that about 1% of Cd, 9% of Zn, and 29% of Pb were from urban discharges within the area. 相似文献
15.
Hikomaro Muraki 《Journal of Oceanography》1974,30(2):49-53
Yoshida (1967) pointed out that the coastal upwelling region may not coincide with the intense longshore wind region and shift poleward. In order to clarify this poleward shift from the existing data, the monthly mean distributions of the offshore Ekman transport and the coastal upwelling intensity are estimated along the California coast from U. S. Daily Weather Maps and from the CCOFI data in 1949, respectively. The results show that the center of the coastal upwelling region is generally shifted to the north from the position of the maximum offshore Ekman transport. The detailed discussions are given for the case of August 1949 when the shift is seen most clearly. 相似文献
16.
Abraham Golik 《Geo-Marine Letters》1993,13(3):159-164
The geographical distribution of coal particles that fell during nine years to the sea bottom from the open sea coal terminal off Hadera, Israel, shows a consistent northerly transport path, and it is inconceivable that the sand at that location would move in an opposite direction. Semicircular, current-scoured moats associated with small mounds found at the edge of the continental shelf off Ashdod and Haifa, Israel, also suggest a general northward-directed sediment transport. The northward sediment flow on the Israeli continental shelf inferred from this evidence therefore supports the model of Emery and Neev about general sand transport patterns along the Israeli coastline and continental shelf. 相似文献
17.
Two sets of moorings were deployed along a cross-shelf transect in central Santa Monica bay for four months in the winter of 1998-1999. Both sites had an array of instruments attached to tripods set on the seafloor to monitor currents over the entire water column, surface waves, near-bed temperature, water clarity and suspended sediment. A companion mooring had temperature sensors spaced approximately 10 m apart to measure temperature profiles between the surface and the seafloor. One array was deployed in 70 m of water at a site adjacent to the shelf break, just northwest of a major ocean outfall. The other was deployed on the mid shelf in 35 m of water approximately 6 km from the shelf break site. The subtidal currents in the region flowed parallel to the isobaths with fluctuating time scales around 10 days, a typical coastal-ocean pattern. However, during the falling phase of the barotropic spring tide, sets of large-amplitude, sheared cross-shore current pulses with a duration of 2-5 h were observed at the shelf break site. Currents in these pulses flowed exclusively offshore in a thin layer near the bed with amplitudes reaching 30-40 cm/s. Simultaneously, currents with amplitudes around 15-20 cm/s flowed exclusively onshore in the thicker layer between the offshore flow layer and the sea surface. The net offshore transport was about half the onshore transport. Near-surface isotherms were depressed 30-40 m. These pulses were likely internal bores generated by tidal currents. Bed stresses associated with these events exceeded 3 dynes/cm(2). These amplitudes are large enough to resuspend and transport not only fine-grained material, but also medium to coarse sands from the shelf toward the slope. Consequently, the seafloor over the shelf break was swept clear of fine sediments. The data suggest that the internal bores dissipate and are reduced in amplitude as they propagate across this relatively narrow shelf. There is evidence that they reach the 35 m site, but other coastal ocean processes obscure their distinctive characteristics. 相似文献
18.
为阐明珠三坳陷西北部珠江组一段上亚段浅海陆架砂体成因机制,综合地质与地球物理数据,首先搭建了五级层序地层格架,并以此为约束,开展浅海陆架砂体识别与定量描述,剖析其时空演化规律,进而讨论其成因机制。结果表明：（1）研究区珠江组一段上亚段可划分为4个五级层序,自下向上编号为FS4、FS3、FS2与FS1;(2)研究区发育潮流沙脊与滨外沙坝两种类型陆架砂体,两者整体呈NW-SE向展布,潮流沙脊主要分布于研究区西部,滨外沙坝则集中于东部;（3）FS4、FS3与FS2 3个五级层序中,潮流沙脊与滨外沙坝均呈现较大规模与较多数量,最上部FS1五级层序中,规模与数量达到最小;（4）沉积基准面（水动力）、同沉积地貌、沉积物碎屑供给等因素共同影响了潮流沙脊与滨外沙坝的发育规模、展布特征与时空演化规律等,综合构成了珠三坳陷西北部浅海陆架砂体的成因机制。 相似文献
19.
本文设计彩沙示踪法于厦大滨海沙滩东段进行试验 ,取得了沙粒运动方向、最大运移速度、扩散范围、沿岸输沙率及粒度分异运移状态等定量数据 ,弥补了以往示踪法难以定量分析的缺陷。结果表明 :调查期间 ,厦大滨海沙滩东段沙粒运动是构成厦门岛南岸岸滩在偏东向波浪作用下形成的西南向沿岸漂沙之一个环节 :沙粒大体平行岸线向北运动 ;沙粒沿岸最大运移速度为 2 0 0m/d ;经一个潮周期 ,沙粒向两侧的最大横向扩散距离为 2 0m ,最大垂直扩散深度达 7cm ;岸滩横断面沿岸输沙率为 42 5t/d ;在该岸段沿岸漂沙中 ,粗粒沙偏向低潮带一侧 ,而细粒沙偏向高潮带。 相似文献
20.
山东半岛东部海域表层沉积物元素组成及物源指示意义 总被引：1，自引：1，他引：0
通过对山东半岛东部海域表层沉积物常量、微量元素、有机碳(TOC)以及碳酸盐(CaCO3)等指标的分析,研究了该海域表层沉积物元素组成特征及其控制因素,并对物质来源进行了探讨。结果表明,山东半岛东部海域表层沉积物元素的平均组成与上陆壳(UCC)相比Al,K,Na,Mg,Fe,Ca,Cu和Zn等元素,相对较低,而Mn,Co,Ni,Cr以及REE元素含量较高,Si和Ti与UCC的含量相当。研究区砂粒级沉积物轻重稀土分异明显,(La/Yb)N值与韩国河流的非常相近;其余粒级沉积物LREE分异较弱,标准化曲线与黄河沉积物的具有相似性。研究区沉积物的元素含量主要受控于源岩组成,存在明显的"粒级效应"。除此之外,Fe-Mn氧化物、生物碳酸盐等因素对元素组成产生一定影响。沉积物物源判别结果显示,山东半岛近岸及其东南部沉积物主要来源于黄河,该区域沉积物分布受山东半岛沿岸流及近岸潮流影响。研究区东北部为残留砂,其沉积物元素组成特征与朝鲜半岛和鸭绿江沉积物组成相近,表明研究区东北部砂质区沉积物代末次冰期低海平面时可能由朝鲜半岛或鸭绿江供应。 相似文献