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1.
水库下游河道冲淤调整是一个长期复杂的过程,对防洪、航运、生态等均会产生一定影响。为探究长江中游沙市—汉口河段演变趋势并为不利变化的防控提供参考,分析了三峡建库后悬移质分组冲淤时空变化规律：建库后,沙市—监利河段各粒径组泥沙均发生冲刷,沙市流量为10 000～25 000 m3/s时,0.125～0.250 mm粒径组泥沙冲刷量最大;以0.125 mm为粗细颗粒分界粒径,监利—螺山段呈现汛期、蓄水期“粗淤”而枯水期、消落期“冲细”现象;螺山—汉口段各粒径组泥沙均发生冲刷,且流量越大冲刷量越大。在此基础上,通过建立流量—分组输沙量关系并根据水流挟沙力公式,发现建库后沙市—监利、螺山—汉口河段冲淤受泥沙、水力因素共同作用,其中泥沙因素对沙市—监利河段影响大于螺山—汉口河段;监利—螺山河段“淤粗冲细”主要受含沙量恢复程度的影响,与上游河床冲刷补给及本河段粗、细颗粒泥沙交换有关,反映了冲刷条件下河道通过水流挟沙能力级配调整加大输沙能力。 相似文献
2.
John McManus 《Estuaries and Coasts》1998,21(4):622-634
Sedimentation in estuaries is normally viewed as a continuous process controlled by inputs of fluvial and marine materials, which migrate in response to tidal circulation. Short-term examination yields reproducible and measurable rates of sedimentation; measurement of annual cycles reveals that sediment may be eroded from a site normally subject to deposition. Likewise annual migration patterns of turbidity maximum zones permits deposition of fine sediments at different parts of the estuary according to season. Study of long-term variations in the positions of sand banks shows that advances of the tidal flat margins may occur suddenly in response to catastrophic events; events that result in mid-channel banks becoming attached to the outer margins of the tidal flat. An example is also given of a channel-margin sand bank known to have repeatedly migrated round an elliptical path, taking approximately 25 yr to regain its original position. Long-term migration of bay head beach bars driven into the Eden Estuary and moving slowly landward are shown to create areas of temporary shelter for salt marshes, which are then over-run as the bar continues toward the head of the estuary. Several examples of anthropogenic influences on estuarine sediments are noted, with major deposits of coarse gravels attributed to known shipping trade within the Tay Estuary. Finally attention is drawn to the effects of deposition of coal mine wastes on the Fife coast: the erosion and redeposition of the wastes to form coastal platforms, their removal once mining ceased (all within a period of 90 yr), and the associated mining-induced subsidence of the coastal cliffs. 相似文献
3.
A three-dimensional numerical model is used to investigate the mechanisms that contribute to the formation of the turbidity
maxima in the York River, Virginia (U.S.). The model reproduces the basic features in both salinity and total suspended sediments
(TSS) fields for three different patterns. Both the prominent estuary turbidity maximum (ETM) and the newly discovered secondary
turbidity maximum (STM) are simulated when river discharge is relatively low. At higher river inflow, the two turbidity maxima
move closer to each other. During very high river discharge event, only the prominent turbidity maximum is simulated. Diagnostic
model studies also suggest that bottom resuspension is an important source of TSS in both the ETM and the STM, and confirm
the observed association between the turbidity maxima and the stratification patterns in the York River estuary. The ETM is
usually located near the head of salt intrusion and the STM is often associated with a transition zone between upriver well
mixed and downriver more stratified water columns. Analysis of the model results from the diagnostic studies indicates that
the location of the ETM is well associated with the null point of bottom residual flow. Convergent bottom residual flow, as
well as tidal asymmetry, is the most important mechanisms that contribute to the formation of the STM. the STM often exists
in a region with landward decrease of bottom residual flow and net landward sediment flux due to tidal asymmetry. The channel
depth of this region usually decreases sharply upriver. As channel depth decreases, vertical mixing increases and hence the
water column is better mixed landward of the STM. 相似文献
4.
Long-term observations in the Weser estuary (Germany) between 1983 and 1997 provide insight into the response of the estuarine turbidity maximum (ETM) under a wide range of conditions. In this estuary the turbidity zone is closely tied to the mixing zone, and the positions of the ETM and the mixing zone vary with runoff. The intratidal suspended particulate matter (SPM) concentrations vary due to deposition during slack water periods, subsequent resubsequent and depletion of temporarily-formed and spatially-limited deposits during the following ebb or flood, and subsequent transport by tidal currents. The corresponding time history of SPM concentrations is remarkably constant over the years. Spring tide SPM concentrations can be twice the neap tide concentrations or even larger. A hysteresis in SPM levels between the falling and rising spring-neap cycle is attributed to enhanced resuspension by the stronger spring tidal currents. There is evidence that the ETM is pushed up-estuary during times of higher mean water levels due to storms. During river floods the ETM is flushed towards the outer estuary. If river floods and their decreasing parts occur during times of relatively high mean water levels, the ETM seems to be maintained in the outer estuary. If river floods and their decreasing parts occur during times of relatively low mean water levels, the ETM seems to loose inventory and may need up to half a year of non-event conditions to gain its former magnitude. During this time seasonal effects may be involved. Analyses of storm events and river floods have revealed that the conditions in the seaward boundary region play an equally important role for the SPM dynamics as those arising from the river. 相似文献
5.
A process-based numerical model is applied to investigate sediment transport dynamics and sediment budget in tide-dominated estuaries under different salt marsh erosion scenarios. Using a typical funnel-shaped estuary (Ribble Estuary, UK) as a study site, it is found that the remobilization of sediments within the estuary is increased as a result of the tidal inundation of the eroded salt marsh. The landward export of the finest sediment is also intensified. The relationship between salt marsh erosion and net landward export of sediments has been found to be non-linear—with the first 30% salt marsh erosion causing most of the predicted export. The presence of vegetation also influences the sediment budget. Results suggest that vegetation reduces the amount of sediment being transported upstream. Again, the trapping effect of salt marsh in terms of plant density is non-linear. Whilst a vegetated surface with a stem density of 64 plants/m2 decreased the net landward export of very fine sand by around 50%, a further increase in stem density from 64 to 512 plants/m2 had a relatively small effect. 相似文献
6.
A series of cruises was carried out in the estuarine turbidity maximum (ETM) region of Chesapeake Bay in 1996 to examine physical and biological variability and dynamics. A large flood event in late January shifted the salinity structure of the upper Bay towards that of a salt wedge, but most of the massive sediment load delivered by the Susquehanna River appeared to bypass the ETM zone. In contrast, suspended sediments delivered during a flood event in late October were trapped very efficiently in the ETM. The difference in sediment trapping appeared to be due to increases in particle settling speed from January to October, suggesting that the fate of sediments delivered during large events may depend on the season in which they occur. The ETM roughly tracked the limit of salt (defined as the intersection of the 1 psu isohaline with the bottom) throughout the year, but it was often separated significantly from the limit of salt with the direction of separation unrelated to the phase of the tide. This was due to a lag of ETM sediment resuspension and transport behind rapid meteorologically induced or river flow induced motion of the salt limit. Examination of detailed time series of salt, suspended sediment, and velocity collected near the limit of salt, combined with other indications, led to the conclusion that the convergence of the estuarine circulation at the limit of salt is not the primary mechanism of particle trapping in the Chesapeake Bay ETM. This convergence and its associated salinity structure contribute to strong tidal asymmetries in sediment resuspension and transport that collect and maintain a resuspendable pool of rapidly settling particles near the salt limit. Without tidal resuspension and transport, the ETM would either not exist or be greatly weakened. In spite of this repeated resuspension, sedimentation is the ultimate fate of most terrigenous material delivered to the Chesapeake Bay ETM. Sedimentation rates in the ETM channel are at least an order of magnitude greater than on the adjacent shoals, probably due to focusing mechanisms that are poorly understood. 相似文献
7.
CAO Chao CAI Feng LI Yan ZHENG Yongling WU Chenqiang LU Huiquan BAO Jingjing XU Yan 《《地质学报》英文版》2013,87(6):1724-1742
Based on the latest submarine topography data of the China 908 Project （China offshore marine environmental comprehensive investigation and assessment）,we analyzed the general China offshore submarine topographical characteristics and the factors influencing its development.The submarine topography off the coast of China follows the NW-SE trend of the land topography.The gradient of the submarine topography ranges from 0.2％ to 1.6％ with an average gradient of about 0.8％.The depth contours run mostly parallel to the coast,and extend out to sea in estuary areas.The submarine topography is dominated by the geological structure,which shows the typical characteristics of two uplifts and two subsidence events from north to south.The geological structure combined with the different sedimentary environments and complex hydrodynamic conditions produced topography that can be characterized by three types：sedimentary basins,compressionuplift,and transition form.In the sedimentary basin and compression-uplift regions,the topographical undulation is small,sediments are fine-grained,and the currents flow in a single direction,leading to bays with sedimentary plains and underwater accumulation slopes,which are of the same tectonic origin.Transition-type topography is characterized by strong undulations and mixed-size sediment particles,terraces and scarps inshore and shelf plains and erosion-deposition landforms offshore.This is a result of incomplete fault block development and repeated transgressions.In the deposition reformation regions （transition form type）,the topography has strong undulations,the sediments are coarse,tidal sand ridges are well-developed at terrigenoussupplied estuaries and convergence zones,and the Holocene sediments are thick,transformed by tides,river runoff,and currents. 相似文献
8.
The erosion and deposition of debris flows at Jiangjia Gully in Dongchuan section of Yunnan province, southwestern China,
was surveyed at 12 cross sections from 1999 to 2003. Deposition occurred in most sections because of the low debris-flow magnitude.
The result was an increase in their elevations except for two sections at D17 and D19, where the channel was diverted in September
1999. As the annual sediment discharge of debris flow increased, the deposited volume decreased in the upper channel and increased
in the lower channel. In each debris flow event, the erosion or deposition at the upper and the lower channel were different,
but the eroded/deposited volume and the trend of erosion or deposition were similar between the neighboring sections. The
average elevation change of all cross sections between consecutive surveys can reasonably represent the debris flow influence
on the channel. Its relationship with the total sediment discharge between two surveys follows a three-stage pattern: when
debris flow magnitude is small, deposition in the channel increases with the magnitude. When the magnitude reaches a certain
level, the deposition begins to decrease and eventually erosion takes place. In three typical cross sections which had similar
channel width, the debris flow showed a clear trend that the deposited volume decreased, while the eroded volume increased
as the discharge of debris flow sediments increased. 相似文献
9.
DAVID S. BREW 《第四纪科学杂志》1997,12(2):131-141
The history of Quaternary sedimentation in the subtidal Wash is described using high-resolution seismic profiles. The Pleistocene sequence is divided into three depositional units, comprising Anglian till overlain by possible Late Devensian subglacial scour fill and lacustrine sediments. These latter sediments may provide further evidence for a lake in the Wash impounded by ice along the Lincolnshire–Norfolk coast. The Holocene sequence is divided into six depositional units, each truncated by the one above. Estuarine sediment resting on a marine flooding surface forms the earliest unit. This sediment was partially eroded by migration of the shoreface as the marine flooding progressed landward. The following four units comprise sand and gravel banks deposited on the erosion surface. Bank deposition was followed by an episode of tidal scour caused either by increased tidal current velocities following reclamation of the Fenland or by breakdown of postulated former offshore barriers. The youngest and most extensive Holocene unit rests on the scoured surface and comprises several types of deposit. These are: large sand banks around the periphery of the subtidal area with sediment extending seawards into two NE–SW aligned troughs; low sand banks on a central ridge dividing the troughs and partially covering the sediments in the troughs; thick gravels towards the mouth of the Wash; muddy sediments forming drapes over the sand in the centre of the Wash. The data provide information on the variety of processes related to the advance and retreat of Pleistocene ice sheets in eastern England and the subsequent Holocene marine flooding of the Wash–Fenland embayment. The Holocene sequence reveals periods of widespread sedimentation separated by periods of both local and regional erosion, with possible implications for climatic and hydrodynamic change. © 1997 John Wiley & Sons, Ltd. 相似文献
10.
针对渤海湾曹妃甸海域波浪、潮流、泥沙及海床演变特点,应用波流共同作用下二维泥沙数学模型研究港区开发方案。2006年冬季和夏季大、小潮潮流泥沙验证表明,该海域潮位及15条同步垂线流速、流向、含沙量过程的计算值与实测值吻合良好,并进行了矿石码头港池前沿海域在潮流与波浪共同作用下悬沙引起的冲淤验证,计算的冲淤厚度及其分布趋势与实测值比较接近。在此基础上,研究了曹妃甸前岛后陆的港区围垦方案对水动力环境的影响问题,包括该工程引起的曹妃甸甸头以南深槽、老龙沟深槽及各港池的流速变化及底床的冲淤变形等。 相似文献
11.
A temporary section in the Cuisian Bagshot Beds, which has been mapped in detail, displayed estuarine sediments with interlayered sands and muds, fine sands, channel-fill sands and intraformational (mainly mud clast) conglomerates. The facies show rapid lateral and vertical changes in grain size and bed form and a restricted suite of trace fossils including Ophiomorpha nodosa and Arenicolites sp. The sequence is shown to have been deposited in a subtidal channel where tidal, wave and fluvial processes were dominant at different times. The following points are considered to be characteristic of sedimentation in this environment: (i) correlation is difficult and facies predictability is low; (ii) there are frequent lateral facies changes from the channel to the subtidal bank environment; (iii) pene-contemporaneous erosion removes considerable amounts of sediment; (iv) load structures may be exposed, eroded, buried and reactivated; and (v) muddy layers and bioturbated horizons offer similar resistance to penecontemporaneous erosion. 相似文献
12.
在剥蚀型汇聚板块边缘,俯冲输入板块剥蚀上覆板块并将剥蚀物质带入俯冲隧道,随后,这些剥蚀物质与俯冲板块物质一同参与了俯冲带浅部与深部地幔的地球化学循环。构造地质学和地球物理研究显示中美洲俯冲带南段是典型的俯冲剥蚀型汇聚板块边缘,这为研究上覆板块俯冲剥蚀物质是否参与俯冲带物质循环过程提供了天然的实验室。由于目前仍然缺乏对该俯冲剥蚀机制的地球化学制约,综合大洋钻探计划(IODP) 344航次对中美洲俯冲带南部哥斯达黎加西部的俯冲板块和上覆板块开展了钻探工作,并获取了系统的岩芯样品。本文对IODP344航次取自上覆板块中陆坡和上陆坡的U1380和U1413站位中沉积物中的粗碎屑层位样品,开展了系统的主、微量元素与Sr-Nd-Pb-Hf同位素地球化学研究。这些沉积物粗碎屑层位组分与加勒比大火成岩省基底相似,指示它们可能来自加勒比大火成岩省基底在弧前出露的区域,可以代表上覆板块基底被俯冲剥蚀的物质组成。研究进一步探讨了晚中新世中美洲俯冲带南部大陆弧火山岩的成因,并指出上覆板块底部被剥蚀物质参与了中美洲俯冲带南部大陆弧火山岩岩浆过程,这为中美洲俯冲带南部存在俯冲剥蚀过程提供了直接的地质学证据。 相似文献
13.
Morphological response of tidal marshes,flats and channels of the Outer Yangtze River mouth to a major storm 总被引：2，自引：0，他引：2
Systematic morphological changes of the coastline of the outer Yangtze River mouth in response to storms versus calm weather
were documented by daily surveys of tidal marshes and flats between April 1999 and May 2001 and by boat surveys offshore during
this and earlier periods. The largest single event during 1999 to 2001 was Typhoon Paibaian, which eroded the unvegetated
tidal flat and lower marsh and led to accretion on the middle-to-upper marsh and in the subtidal channel. The greatest erosion
of 21 cm occurred at the border between the marsh and the unvegetated flat due to the landward retreat of the marsh edge during
the storm. Strong waves on the flats increased suspended sediment concentration by 10–20 times. On the upper marsh, where
the frequency of submergence by astronomical tides is only 3%, Typhoon Paibian led to 4 cm of accretion, accounting for 57%
of the net accretion observed over the 2-yr study. Typhoon Paibian led to 4 cm of accretion, accounting for 57% of the net
accretion observed over the 2-yr study. Typhoon Paibian and other large storms in the 1990s caused over 50 cm of accretion
along the deep axis of the river mouth outlet channel. During calm weather, when hydrodynamic energy was dominated by tides,
deposition was centered on the unvegetated flats and lower, marsh with little deposition on the high marsh and erosion in
the subtidal channel. Depositional recovery of the tidal flat from typhoon-induced erosion took only several days, whereas
recovery of the subtidal channel by erosion took several weeks. A conceptual model for the morphological responses of tidal
marshes, flats, and subtidal channels to storms and calm weather is proposed such that sediment continually moves from regions
of highest near-bed energy towards areas of lower energy. 相似文献
14.
Akimiski Strait is a wide (17–20 km), shallow, emergent (0.70 cm per century) waterway in James Bay. It is localized in a saddle of a Paleozoic reef track, which has been enhanced and molded by Pleistocene glaciers. Drumlinoid ridges form the till cores of shoals and islets of the strait. The boundary conditions of the strait change throughout the year, as it is covered by ice for six months. During spring break-up the strait remains clogged with ice at its northern approach for several weeks, and acts as a large tidal inlet. It is during this period that most of the fluvial sediments are carried to sea. Other sediments are obtained by erosion of the Pleistocene tills and Holocene subtidal clays and silts exposed in nearshore areas. Resuspension of nearshore material is achieved through the action of wind-driven, short choppy waves and ice scour. Tides are the most important process for the redistribution of sediments along the coast, both flooding onshore and flooding and ebbing into and out from the strait generating locally powerful (2 m s?1) reversing currents. Ice rafting and ice pushing are important processes in this frigid environment, particularly in upwind sides of shaols, and at/or near river mouths.Different intertidal sedimentary sequences develop as functions of sediment supply and exposure of the environments to ice, currents and waves. The eastern shores and the southern shoals of the strait develop pebble lags over till, covered by thin (5–20 cm) drapes of silty sand trapped and protected from erosion by algae. In these shores and in emerging small islands significant sedimentation (1–1.5 m thick) occurs in the marshes where the suspended load of tidal waters is trapped by vegetation. The western shores of the strait receive considerable amounts of sediment from large rivers and are affected by strong tidal longshore currents. Thick (3–4 m) and narrow tidal flats and marshes develop on the maincoast. The shoals of the northern part of the strait have characteristic sediments. Those near the western shore have thin (up to 80 cm) tidal silty sand deposits, locally heavily burrowed by Macoma balthica. Those strung across the northern approach to the strait have well-developed, thin, coarse sand dune fields, indicating a prevalent ebb flow out of the strait. 相似文献
15.
黄河三角洲东营港的泥质潮坪上发育大量的贝壳沉积。贝壳的特殊形态使其很容易被水流搬运,波浪的簸选、泥坪表面的侵蚀坑穴和植物根、堤坝等障碍物对贝壳的拦阻、与地形地貌或涨潮流的水流形态有关的流速降低都可以形成贝壳堆积。潮坪表面贝壳的沉积形态包括:与涨潮流有关的坑穴状、密集窝状、陡坎状、垄沟状、席状、带状以及潮汐水道中的混合沉积等类型;与波浪作用有关的堤坝状、堤坝遮挡沉积等类型。涨潮流流速降低的方式不同,贝壳沉积形态也会相应有较大的差别。另外,潮坪表面的细微起伏、潮坪底质类型和粘结性都会对贝壳的沉积形态造成较大影响,其中尤其是以密集窝状和陡坎状为特征。从东营港贝壳的沉积特征上看,潮坪上贝壳沉积的水动力条件与常见的砂砾滩、鲕粒滩、内碎屑滩有很大的不同,不能将介壳的富集一概归为滩坝相沉积。 相似文献
16.
17.
Compacted bentonite has been considered as a candidate buffer material in the underground repository for the disposal of high-level radioactive waste. An erosion of bentonite particles caused by a groundwater flow at the interface of a compacted bentonite and a fractured granite was studied experimentally under various geochemical conditions. The experimental results showed that bentonite particles could be eroded from a compacted bentonite buffer by a flowing groundwater depending upon the contact time, the flow rate of the groundwater, and the geochemical parameters of the groundwater such as the pH and ionic strength.
A gel formation of the bentonite was observed to be a dominant process in the erosion of bentonite particles although an intrusion of bentonite into a rock fracture also contributed to the erosion. The concentration of the eroded bentonite particles eroded by a flowing groundwater was increased with an increasing flow rate of the groundwater. It was observed from the experiments that the erosion of the bentonite particles was considerably affected by the ionic strength of a groundwater although the effect of the pH was not great within the studied pH range from 7 to 10. An erosion of the bentonite particles in a natural groundwater was also observed to be considerable and the eroded bentonite particles are expected to be stable at the given groundwater condition.
The erosion of the bentonite particles by a flowing groundwater did not significantly reduce the physical stability and thus the performance of a compacted bentonite buffer. However, it is expected that an erosion of the bentonite particles due to a groundwater flow will generate bentonite particles in a given groundwater condition, which can serve as a source of the colloids facilitating radionuclide migration through rock fractures. 相似文献
18.
江苏沿海辐射沙脊群在国内潮成沙体中较为罕见,有关辐射沙脊形成的动力机制已有定论,但对其形成时间和物质来源说法不一。运用长时间尺度动力地貌过程数学模型复演了辐射沙脊群形成演变过程,结果表明:江苏岸外辐聚辐散的流场不依赖于局部海底地形而独立存在;不同初始地形下只要泥沙供给充足,经过150年左右潮流动力对地形不断塑造,辐射状"水道-沙脊"相间的地貌格局都能基本形成;辐射沙脊群是废黄河北归约150年后,随着废黄河水下三角洲不断被侵蚀,辐聚辐散的潮流对不同来源物质重新塑造的结果,是动力-泥沙-地形相互作用的产物。 相似文献
19.
Palaeo-heat flow values and thicknesses of eroded Permo-Carboniferous sediments in the Saar Basin were evaluated using one dimensional thermal modelling techniques. Thermal, burial and erosion histories for 16 wells were calibrated by comparing measured and calculated vitrinite reflectance using the kinetic EASY%Ro algorithm and by comparing measured and calculated temperature data. On the basis of 37 wells, coalification maps were constructed revealing a syn-kinematic coalification pattern. Thermal maturity of the sediments can only be explained by deep burial and moderate heat flows during time of maximum burial, i.e., in the Permo-Carboniferous. Calculated heat flow data range between 50 and 75 mW/m2, which implies a crustal thickness between 30 and 40 km during the time of maximum burial. These values are in accordance with the geodynamic setting of the basin. The influence of the Permo-Carboniferous volcanism on the palaeo-temperature distribution was overwhelmed by the subsequent deep burial. During Permian times, between 1800 and 3000 m of Permo-Carboniferous sediments were eroded. Different sedimentation and erosion histories are characteristic for anticlines and synclines, respectively. 相似文献
20.
Interaction of metalliferous continental brines with biogenic sulphide is the basis of some syngenetic and early diagenetic models for the formation of Cu‐(Pb‐Zn) sulphides during a depositional cycle of carbonates in restricted marine environments. A variation of these models (an ‘evaporative concentration‐lateral groundwater flow’ model) is proposed, using hydrological, geochemical and biological data from low metal, but otherwise pertinent redbed‐associated, sabkha, tidal flat and subtidal environments at Nilemah Embayment, in Hamelin Pool (Shark Bay, Western Australia). The model is constrained by: (i) the short time available for ore accumulation during a single depositional cycle; (ii) limitation of adequate rates of bacterial sulphate reduction for the formation of an ore deposit to near‐surface sediments; (iii) restriction of the most favourable ore‐forming sites to the intertidal zone and the littoral shelf; (iv) coincidence in these sites of laterally‐flowing marine/meteoric groundwater brine, and mosaics of in situ cyanobacterial mats and shallow erosional depressions containing detrital organic matter eroded from the mats. Under these conditions the metalliferous fluid would have to contain about 1000 ppm Cu and flow for 1000 years at a rate of 5 m/a through the intertidal/littoral shelf environment to produce an ore deposit. Critical features of a model that could generate this combination of very high metal concentrations and flow rates are: (i) a highly permeable unconfined aquifer system comprising alluvial fans at the base of basaltic mountain ranges and continental redbeds beneath a broad coastal plain; (ii) mobilization, concentration and transport of the metals in this aquifer to intertidal/littoral shelf sites of ore deposition; (iii) effective concentration processes in the aquifer, involving evaporation and reflux of brines in groundwater discharge areas on the coastal plain and evaporation in marine‐continental and marine sabkhas bordering the sites of deposition; (iv) rapid lateral groundwater flow of the concentrated metalliferous brines under a strong seawards‐directed hydraulic gradient; and (v) discharge of the metalliferous brines into or through topographic depressions generated by erosion and shoaling in the peritidal and littoral shelf environments. The model hydrodynamic processes and their magnitude are within the range observed in modern environments but they are most likely to be effective in coarse‐grained, topographically irregular carbonate sabkhas and tidal flats, which usually form under high‐energy conditions. Even under these conditions, the individual ore‐forming processes must combine in an optimum manner before the highly demanding metal concentrations and flow rates required for ore formation in a single marine depositional cycle can be met. 相似文献