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1.
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.
Alan William Niedoroda Donald J.P. Swift Thomas Sawyer Hopkins Chen-Mean Ma 《Marine Geology》1984,60(1-4):331-354
An open ocean shoreface typical of long, wave-dominated sandy coasts has been examined through a combination of extensive field measurements of wave and current patterns with computations of marine bedload transport and sedimentation. Sand transport on the upper shoreface is dominantly controlled by waves with only secondary transport by currents. Sand on the middle and lower shoreface, as well as the inner continental shelf is entrained by storm waves and transported by a complex pattern of bottom boundary layer currents.
Storm events have been studied and modeled for the shoreface off Tiana Beach, Long Island. The dominant effect of coastal frontal storms is to cause significant shore-parallel bedload transport with important shore-normal secondary components. These storms tend to result in net offshore transport of sand removed from the beach and surf zone systems. The bedload transport during a storm is convergent on the shoreface leading to accretion. Most accretion occurs on the upper shoreface with lesser deposits covering the middle and lower shoreface as well as the inner continental shelf. Longer-term equilibrium can be maintained by slow return of sand up the shoreface during non-storm conditions.
Annual and geologic time-scale budgets of shoreface sand transport and sedimentation yield equilibrium, net accretion or net deposition. The annual balance results from an integration of the event-scale bedload transport patterns and morphologic responses. These processes and responses have feedback mechanisms which stabilize the system over longer, but not geologic, time scales. Geologic time scale balances are controlled by relative sea level changes and relative availability of sediment supply with the event-scale shoreface and transporting processes providing the mechanism to produce the changes in long-term morphology and sedimentation patterns. In the area of study, the long-term pattern is one of net shoreface erosion, and the permanent loss of sand to the shelf floor. 相似文献
3.
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
4.
东海陆架中北部沉积物粒度特征及其沉积环境 总被引：4，自引：1，他引：3
通过对东海陆架表层沉积物粒级组成、粒度参数、14C年龄和微体古生物组合的综合分析,绘制了东海陆架的沉积物类型分布图;运用Folk等(1970)沉积物分类方法将东海表层沉积物分成砂、粉砂、粉砂质砂、砂质粉砂、砂质泥5种类型,其中粉砂质砂分布最广,砂质泥分布最少;沉积物由陆向海粒度变粗,反映沉积过程中的物源和沉积动力控制作用。根据沉积环境及成因分析,可将东海陆架沉积分为3类:分别是长江口外席状砂沉积区、现代泥质沉积区和陆架中部砂质沉积区。长江口外砂质沉积是全新世冰消期晚期潮流作用及风暴潮流共同作用的产物,是高海平面以来太平洋潮波系统作用下的潮流沙沉积,沙波地貌仍在发生变化。现代泥质沉积区包括长江前三角洲沉积、浙闽沿岸流沉积和济州岛西南泥质沉积三个区域,不同沉积区的成因机制不同。陆架中部砂质沉积是末次冰盛期之后海侵作用下发育的砂质沉积物,在海侵的不同阶段中沉积物被冲刷改造,具有不等时性特征,沉积环境与现代陆架海洋环流的动力特征不一致,现代沉积作用较弱,仅接受悬浮体细粒沉积。 相似文献
5.
A previously published wave-averaged version of Bailard's sediment transport formulation, intended for use in a numerical model of shelf sand transport, is compared against available field observations from literature. The objective was to test the performance of the transport relation over the wide range of hydrodynamical conditions that can occur at sea. A modified data analysis method was used to assess the reliability of the field observations. The modification consists of a method to cluster the data into classes to enable statistical analysis. The sediment transport formulation is part of the classification method. The method is in principle also suitable to reduce the size of data sets of non-cohesive sediment transport obtained with modern electronic equipment. The results show that the quality of the published field observations is fair, and that the wave-averaged Bailard formulation performs well for low and medium transport regimes in both currents and waves. For those conditions, it yields a slight overprediction of the transports, and a nearly uniform behaviour as a function of the conditions. The formulation underestimates transport rates for very high flow velocities in absence of waves, which is in agreement with earlier findings. The present version of Bailard's wave averaged sediment transport formulation is suitable for computing the local transport rates of fine to coarse sand on continental shelves in conditions ranging from small currents to moderate currents combined with non-breaking waves. 相似文献
6.
对南海北部陆架坡折附近取的50个表层沉积物样品,作粒度测试,计算粒度参数。粒度分析表明研究区的沉积物主要存在4种类型:含砾砂、砾质砂、砂质砾和含砾泥质砂;沉积物组分中砾石和砂占绝对优势,基本上不含黏土。综合因子分析和聚类分析的结果把研究区划分为4类沉积区:Ⅰ类沉积区属于内陆架沉积区,Ⅱ类沉积区属于陆架坡折上部沉积区,Ⅲ类沉积区属于陆架坡折下部沉积区,Ⅳ类沉积区区属于陆架边缘沉积区,每类沉积区都代表着不同的沉积环境。研究区沉积物的粒径趋势分析结果显示,陆架坡折附近的沉积物主要向内陆架和外陆架边缘或上陆坡输运,同时存在着跨陆架输运和沿陆架坡折输运现象,这与研究区实测的底流方向相一致。本研究表明,南海北部陆架坡折附近的沉积环境和沉积物输运模式比较复杂和特殊。本研究对今后陆架和陆坡区其他相关的研究具有十分重要的指导和借鉴意义。 相似文献
7.
The Middle–Late Miocene Utsira Formation of the North Sea Basin contains a fully preserved, regional marine sand deposit that records a stable paleogeographic setting of sand transport and accumulation within a deep, epeiric seaway which persisted for >8 Ma. The sediment dispersal system was defined by (1) input through a marginal prograding strandplain platform, coast-to-basin bypass, transport along a narrow strait, and accumulation in strait-mouth shoal complexes within a shelf sea; (2) a high-energy marine regime; (3) very low time-averaged rates of sediment supply and accumulation; and (4) consequent high sediment reworking ratio. Sand distribution and stratal architectures reflect regional along-strike sediment transport and local to sub-regional landward sediment transport. Plume-shaped, south-building, submarine sand shoals that formed along the recurved arc of the strandplain margin nourished the shoal system. Very low-angle sigmoid clinoforms and down-stepping, aggradational top sets are distinctive architectures of these strike-fed sand bodies. The combination of strong marine currents and slow but long-lived sand supply from the Shetland strandplain created regional, sandy shelf shoal depositional systems that individually covered 3,500 to 6,000 km2 of the basin floor. Defining attributes of the shelf shoal systems include their location within the basin axis, abundance of autochthonous sediment, and sandy marine facies composition. Diagnostic depositional architectures include the along-strike-dipping sigmoidal clinoforms, poly-directional low-angle accretionary bedding at both regional and local scales, and mounded depositional topography. Erosional features include regional hummocky, low-relief shelf deflation surfaces, broad, elongate scours and sub-circular scour pits. 相似文献
8.
Henry L. Berryhill Jr. 《Geo-Marine Letters》1981,1(2):105-110
A large buried submarine trough crosses the seaward margin of the continental shelf off the southwest coast of Louisiana.
Original length was about 90 km, and width at the shelf edge was 16 km. Maximum eroded depth may have been as much as 305
m. Seismic characteristics of the prograded fill indicate cyclically repeated sequences of retrogressive deltaic and partly
slumped sediments overlain by well-layered transgressive deposits. Slumping was increasingly prevalent toward the shelf edge.
The cyclic sequences indicate that the trough was a passageway for large volumes of sediment onto the continental slope during
several stages of lowered sea level. 相似文献
9.
海南岛西部岸外沙波的高分辨率形态特征 总被引：12，自引：1，他引：12
利用SIMRAD-EM3000多波束探测系统和DGPS定位系统,对海南岛东方岸外的沙波沙脊区进行了高精度探测,分析结果表明:从海岸到陆架底形具有明显的分带性,依次出现弱侵蚀底形段、沙波沙脊底形段和平坦底形段。沙波仅发育于沙波沙脊段,介于水深20~50 m之间,沙波形态有二维与三维两种,沙波波高多为0.7~2.5 m,波长20~70 m,沙波指数(L/H)为20~60,对称指数为1~3;沙波沙脊区沉积物的搬运方向有明显的规律性,在沙脊的西侧,沉积物主要向北搬运;在沙脊的东侧,沉积物主要向南搬运;沙波的形成和发育主要受潮流场控制,热带风暴对其有改造作用。 相似文献
10.
11.
《Marine Chemistry》1987,21(3):249-265
Total organic carbon (TOC), lignin, amino acids, sugars and amino sugars were measured in recent sediments from the continental margin off southern New England. The various organic carbon fractions decreased in concentration with increasing distance from shore. The fraction of the TOC that was accounted for by these major components also decreased with increasing distance from shore. The concentration of lignin indicated that only about 3–5% of the organic carbon in the nearshore sediment was of terrestrial origin. The various fractions were highly correlated, which was consistent with a simple linear mixing model of shelf organic matter with material from the slope and rise and indicated a significant transport of sediment from the continental shelf to the continental slope and rise. 相似文献
12.
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.
K. B. Lewis 《新西兰海洋与淡水研究杂志》2013,47(3):183-208
Sediments from the seabed off the eastern side of the North Island, New Zealand, are divided into 12 facies on the basis of grain size and mineralogy of the sand fraction. The facies are grouped into three types; modern detrital sediments, relict detrital sediments, and non‐detrital sediments. The sediments are described in terms of a modified Wentworth grain‐size scale and a modified Folk sediment classification. The modern detrital sediments range from fine sand near the shore to clayey fine silt on the lower slope. At most places they are bimodal, probably because floes and single grains are deposited together. The relict detrital sediments, which include sands and gravels, occur where deposition is slow on the inner continental shelf and near the shelf edge. Those near the shelf edge include Last Glacial sandy muds that have been winnowed and mixed with Holocene volcanic ash and glauconite. The non‐detrital sediments, which contain forarninifera, volcanic ash, and glauconite, but no detrital sand, occur on anticlinal ridges on the continental slope. In places they overlie muddier sediment deposited during the last glaciation when the sources of river‐borne detritus were nearer than at present and when mud was deposited more rapidly on the ridges than at present. 相似文献
15.
Aeolian and fluvial sediment transport to the Atlantic Ocean offshore Mauritania were reconstructed based on grain-size distributions of the carbonate-free silt fraction of three marine sediment records of Cap Timiris Canyon to monitor the climatic evolution of present-day arid north-western Africa. During the late Pleistocene, predominantly coarse-grained particles, which are interpreted as windborne dust, characterise glacial dry climate conditions with a low sea level and extended sand seas that reach onto the exposed continental shelf off Mauritania. Subsequent particle fining and the abrupt decrease in terrigenous supply are attributed to humid climate conditions and dune stabilisation on the adjacent African continent with the onset of the Holocene humid period. Indications for an ancient drainage system, which was discharging fluvial mud offshore via Cap Timiris Canyon, are provided by the finest end member for early to mid Holocene times. However, in comparison to the Senegal and Niger River further south, the river system connecting Cap Timiris Canyon with the Mauritanian hinterland was starved during the late Holocene and is non-discharging under present-day arid climate conditions. 相似文献
16.
In recent years significant interest has emerged regarding bottom currents and sediment dispersal over continental shelves and shallow marine waters. Although many papers have been written on sediment dispersal mechanisms, they include relatively few long-term observations of bottom currents and/or sediment transport. Lack of observational data is related to the hostile nature of the environment, and the difficulty associated with placing and retrieving instruments on the floor of the continental shelf during some seasons and environmental conditions.This paper describes an instrumentation system designed for use on the floor of the continental shelf. It can remain submerged for periods of one month continuously recording water speed and direction 1 m from the sea bed, differential pressure, and bed nature by means of half-hourly photographs. Four of these systems are presently in use in arrays across the continental shelf of Washington. 相似文献
17.
Current velocity and suspended sediment concentration measurements at anchor stations in the downstream extremity of the Gironde estuary indicate that during periods of high river discharge, a significant amount of suspended sediment is transported out of the estuary onto the adjacent continental shelf. The vertical profile of the residual (non-tidal) suspended sediment flux is similar to that of the residual current velocity, with a net upstream flux near the bottom and an overlying seaward-directed transport. The overall, depth-integrated result is a net seaward transport of suspended sediment out of the estuary. It appears that this net seaward transport varies directly with tidal amplitude.Aerial photography and water sampling indicate that during high river inflow, the downstream extremity of the turbidity maximum extends onto the continental shelf at ebb tide. The tidal and coastal current patterns of the inlet and inner shelf induce a northward transport of the turbid estuarine water, and at each tidal cycle, a certain amount of suspended sediment leaves the estuary; part of this sediment is deposited in a silt and clay zone on the continental shelf. 相似文献
18.
In 1980, a large earthquake caused extensive sediment failure on the shallow continental shelf off the Klamath River in northern
California. Side-scan sonography was used to complement detailed geophysical profiling in identifying specific features and
resolving modes of failure. The features include a nearly flat failure terrace mantled with sand boils, collapse craters and
sediment flows, and bounded on the seaward side by a meandering continuous toe ridge. Seaward of the terrace lies a compression
zone delineated by small pressure ridges. Our findings indicate a temporal progression of failure from lique-faction of shallow
subsurface sand to lateral spread of intact blocks to sediment collapse and flow. 相似文献
19.
海南岛近海海域7个沉积岩芯的现代沉积速率及其分布特征 总被引：4，自引：0，他引：4
利用多道α能谱仪,对2005年8～9月在海南岛近海采集的7个沉积岩芯进行了210Pb的沉积速率测定,探讨了海南岛近海陆架上现代沉积速率的区域性分布特征,结果表明:位于港湾内的B1168站位由于沉积物供应充足,有最高的沉积速率,达2.9 cm/a;位于河口海湾附近且受沿岸流影响的B289站位,有很高的沉积速率,可达1.6 cm/a,沉积环境较稳定;位于西南海底沙脊区北缘且靠近昌化江河口的B97、B135、B10站位也有较高沉积速率,分别达到1.0、0.89和0.47 cm/a,在表层都出现了210Pb放射性活度倒置的现象,表明所处区域有较强混合作用;处于西南外陆架的C4站位受北部湾环流影响,沉积速率为0.6 cm/a;位于东部外陆架的B377站位处于上升流区,沉积速率较低,为0.21 cm/a.可见,海南岛近海陆架上的现代沉积速率存在着明显的区域分布:在物质来源丰富的沿岸流作用区和河口区附近,现代沉积速率很高;在陆架环流沉积作用区,现代沉积速率也较高;在水深较大的外陆架上,由于沉积物供应相对匮乏,沉积速率一般较低;在近岸潮流沙脊区,由于水动力很强,无法形成现代细粒沉积.同时,在陆架上,沉积速率有随着水深的增加而降低的趋势.由此可见,海南岛近海海域的沉积速率与该区的物质供应、水动力条件和海底地形等因素有密切关系. 相似文献
20.
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