版权声明: 2018 地球科学进展 编辑部
First author:Liu Jiangyan(1988-),female,Lingbao City, He’nan Province,Ph.D student. Research areas include reservoir sedimentology.E-mail:firstname.lastname@example.org
Tidal bore is hydraulic jump during the process of tide flooding with the tide wave moving upstream. They are widely distributed in the estuary zone with high tidal range and funnel-shaped planeform. Tidal bore deposit study is important for further understanding about paleogeomorphology, paleoenvironment, paleoclimate of areas near the estuaries, and sandbody formed by tidal bore deposit could be potential oil and gas reservoir. Researches about tidal bore have been always concentrated on hydraulic characteristics of tidal bore and its influences on estuary environment and engineering, while the study on tidal bore deposit is rarely reported. One of the most important causes is the complex hydrodynamic conditions in the estuary zone. Deposits characteristics is complicated in this zone due to comprehensive effects of river flow, waves and tides. It is hard to affirm the preservation probability of tidal bore deposits, especially in the ancient rock record. In view of this, current status and forecast about tidal-bore deposit study were expounded in this study based on comprehensive summary and discussion about typical tidal bore deposit data and reports. Criteria for recognition of tidal-bore deposits were described in detail on the aspects of sedimentary structures, grain size distribution, and facies model. One of the most critical diagnostic marks of tidal bore was a special undulating erosion surface with a series of irregular and stepped excavations on it. This surface was formed by cyclic pressure loading induced by the passage of a tidal bore. In addition, the cross-bedding inclined upstream, soft sediment deformation structures and massive sandstone on the erosion surface were also important marks of a tidal bore deposit. Problems existing in current research were discussed and some suggestions were proposed. Various methods and technology should be used to perfect tidal bore facies model, and research on diagenesis and reservoir features of sandbody formed by tidal bore should be strengthened in the future. Sandbody formed by tidal bore of different types (breaking tidal bore and undular tidal bore) should be distinguished to deepen the understanding of their various hydrodynamic conditions and reservoir scale. Tidal bore is significant geological process in estuary zone, and deposits formed by it makes great influence on the geomorphology of this area, which should be paid more attention.
Table 1 Depositional structures induced by tidal-bore that has been recognized in modern and ancient strata
|阿拉斯加Turnagain Arm 河口湾||+||+||-||-||-||++|||
涌潮发生过程中,潮头以及尾随其后的子波都会对河床产生冲刷作用,形成大量的冲刷构造。这种冲刷构造与河流中被细粒沉积物包围的水道底部冲刷面不同,具有特殊的冲刷形态,这些冲刷面上“具有一系列阶梯式、不对称、不规则的凹坑,凹坑宽度一般小于0.3 m,深度不超过0.15 m,这些凹坑波长较短、振幅相对较高,部分边缘较陡,凹坑陡面的倾向与主河道运移方向一致” [9,12](图1)。从平面位置上看,这种冲刷面基本都出现在距离河口几十公里远的河口上游区域[9,12]。在一些现代涌潮沉积的岩芯中也可观察到涌潮沉积的块状砂岩底部具有很多特殊形态的冲刷面[10,45~47]。这种明显的波状冲刷面及其特殊的冲刷形态是涌潮经过时造成的周期性压力载荷所致。Donnelly等通过水槽实验模拟从流体力学角度论述了这种冲刷面的形成机理,认为在涌潮发生过程中,越靠近河床部位,流速波动越大,在涌潮波向上游行进的过程中河床会受到频繁的流体加速和减速的影响,使得河床要经受循环性的压力载荷作用以及压力反转的影响,从而形成了这种形态特殊的波状冲刷面。值得注意的是,虽然在涌潮沉积产物中都观察到了这种特殊形态的冲刷构造,但是在不同区域其上下地层的特征却并不完全相同,这是由不同区域平面上发育的沉积类型不同导致的,在具体研究过程中应该结合某一区域的沉积特征具体分析涌潮沉积物与上下地层之间的叠置关系。但不可否认的是,这种特殊的冲刷面是涌潮沉积的重要识别标志。
图1 葡萄牙西部卢西坦盆地晚侏罗世Lourinha组Praia de Areia Branca剖面中涌潮成因的波状冲刷构造(据参考文献修改)
Fig.1 Example of an undulating erosion surface at Praia de Areia Branca of Late Jurassic Lourinha Formation in Lusitanian Basin, Western Portugal (modified after reference )
The reversed flow directions above the erosion surface and the Taenidium barreti burrows, some burrows were truncated by the erosion surface
Fig.2 Dewatering structures triggered by tidal bore within the Tiskre Formation of different outcrops(modified after reference )
(a)Muraste outcrop section, small water-escape channels network (white arrows point to individual small channels), and autoclastic breccia (yellow arrow). (b)Ninamaa outcrop section, massive thick-bedded siltstone unit, liquefied sediment is indicated with white arrows, the stick on the picture is 1 m. (c)Homogeneous siltstone unit of Muraste outcrop, sediment on the left side of the photo retains tidal lamination (yellow arrow) while right side is largely homogenized and no original lamination is preserved
Fig.3 Core photos of WSG section show typical sedimentary structures produced by tidal bores and associated processes at the lower-middle tidal flats(modified after reference)
SD:Sand Dikes. LFS: Load-Flame Structures. ISP: Invasive Sand Patches. PS: Pipe-like Structures. CB: Convolute Bedding
(a)尖山断面粒度参数平均粒径与分选系数散点图; (b)大缺口断面粒度参数平均粒径、分选系数在尖山断面解析图上投点;TBD代表涌潮沉积; TSD代表潮成砂质沉积; TMD代表潮成泥质沉积. SD, MD分别代表砂、泥质沉积
Fig.4 The grain size parameter plot distinguishing between tidal and tidal-bore deposit in northern flat of Qiantang River in China based on mean and sorting values of the samples (modified after reference )
(a)Jianshan-section. (b)Daquekou-section. TBD:Tidal Bore Deposits. TSD:Tidal Sandy Deposits.TMD:Tidal Muddy Deposits. SD:Sandy Deposits. MD:Muddy Deposits
(1)波状起伏的底部或顶部冲刷面:与前文述及的波状冲刷面特征相似,不同的是, Fielding等模式中的冲刷面有时会被潮波不断改造成为对称或不对称的波痕。在Echo Cliff剖面观察到的很多冲刷面的波长远远小于涌潮潮头的波长,认为这里的冲刷面可能是尾随在潮头之后的“子波”冲刷作用的结果。在后期研究中可以依靠冲刷面的波长、波高、振幅等具体参数特征来判别不同冲刷构造的具体成因。
Fig.5 Facies model of tidal-bore deposit(modified after reference )
图6 美国堪萨斯州东北部晚宾夕法尼亚世Echo Cliff露头中的涌潮沉积特征(据参考文献修改)
(a)泥质砂岩透镜体东北缘近照特征,可见底部和顶部冲刷面的圆齿状特征;(b)涌潮沉积的块状泥质砂岩局部特征,可见顶底冲刷面在潮波的不断改造下已成为对称或不对称的波痕(黑色箭头),白色箭头指示的是保留下来的局部下伏地层;照片中的粉色比例尺卡片高0.3 m,黑白色比例尺长0.15 m;(c)透镜状的泥质砂岩(短箭头指示透镜体边缘,长箭头指示透镜体的长轴)切割之前沉积的植物碎屑富集的块状砂岩
Fig.6 Tidal-bore deposit of Upper Pennsylvanian Echo Cliff outcrop of northeastern Kansas, USA(modified after reference )
(a)Close-up view of the northeastern of the muddy sandstone lens and the scalloped nature of basal and top surfaces.(b)Close-up of the bore deposit, showing structureless, muddy sandstone bounded by surfaces that have been reworked into symmetrical and asymmetrical ripples (black arrows). Note the partial preservation of a lower bed in the right side of the view (white arrow). The pink clipboard is 0.3 m high, the scale bar is 0.15 m long.(c)A lens-shaped body of structureless, muddy sandstone (short arrows indicate margins, long arrow indicates axis) cutting through previously deposited plant-debris-rich, structureless sandstone
钱宁等早在20世纪60年代就对钱塘江涌潮沉积的砂体进行了研究,认为钱塘江涌潮沉积的沙坎规模巨大,主要为分选很好的粉细砂,长达130 km,厚度可达10 m以上;李从先等和李保华等也报道了全新世长江河口湾内发育分选良好的涌潮沉积砂体,多为块状层理,厚度可达20~30 m。这些砂体在经历埋藏作用之后很可能成为良好的油气储层。在今后的研究中应完善取样、多种分析化验以开展涌潮沉积砂体的微观孔隙结构特征分析,明确其成岩演化过程,深化对涌潮沉积形成的储层特征的认识。
The authors have declared that no competing interests exist.
The fluvial process of the big sand bar inside the Chien Tang Chiang Esturay[J].,
Tidal bores[J]. ,
Catalog of Worldwide Tidal Bore Occurences and Characteristics[R]. Denver, CO:U.S.,
Formation of tidal bore in shallow-water flow[J]. ,
Analyses of undular hydraulic jump and undular bore[J]. ,
Research about tidal bore[J]. ,
Deformation process of tidal waves in Qiantang Estuary[J].,
The tidal bore on the North Branch of Changjiang Estuary and its effects on the estuary[J]. ,
Tide-influenced fluvial bedforms and tidal bore deposits (Late Jurassic Lourinhã Formation, Lusitanian Basin, Western Portugal)[J]. ,
In a sedimentological sense a fluvial to tidal transition zone can be defined in rivers as a zone that separates the upstream fluvial from the downstream estuarine zone. Characteristic sedimentary structures within this zone are notoriously difficult to recognize. This study demonstrates the influence of tidal modulation within the most proximal part of the fluvial-tidal transition zone (i.e. the ‘backwater zone’) of an ancient fluvial system. Criteria have been established to differentiate between purely fluvial facies and those modulated by tidal energy. The stratigraphic interval from which the data were derived is the Lourinh00 Formation (Late Jurassic) of the Lusitanian Basin, Western Portugal. An analysis of sedimentary features at four key localities has identified a temporal spectrum of tidal influence ranging from the daily modulation of fluvial flows to the effects of tidal bore passage. A combination of quantitative and qualitative data reveals systematic changes in the internal architecture of dune-scale bedforms deposited in a channel-floor setting. The key co-occurring features are: (i) increasing-decreasing organic particle concentration; (ii) increasing-decreasing bottomset thickness; (iii) increasing-decreasing foreset dip and shape (from convex to concave); and (iv) increasing-decreasing brinkpoint height. Collectively, these features are interpreted as having been produced by successive fluctuations in flow regime conditions from lower (during flood tidal retardation) to higher (during ebb tidal drawdown) current velocities. Bedforms showing these features occur in both meandering fluvial channels and straighter distributary systems. In addition, several examples of a specific type of stepped erosion surface and draping sediment have been recognized, the interpretation of which strongly suggests generation by the passage of tidal bores. If this interpretation is correct, then it represents one of the first published examples of tidal bore propagation in ancient fluvial systems. Palaeoclimatic evidence (cellular analysis of woody tissue, palaeosol character and plate reconstruction) indicates a warm, seasonal, winter wet to summer dry climate during deposition of the Lourinh00 Formation. From this evidence it is suggested that tidal modulation and tidal bore effects are more likely to develop in the ‘dry season’, when fluvial flow in the main river channels was reduced.
Characteristics of tidal bore deposit in Northern Qiantang Estuary[J]. ,
Sediment inception under breaking tidal bores[J]. ,
A tidal bore may develop in an estuary during the spring tide conditions when the tidal range exceeds 5–602m and the flood tide is confined to a narrow funnelled estuary with low freshwater levels. The tidal bore is of great importance for the geomorphology of the estuarine zone. In this study, some physical modelling was performed to investigate the sediment motion inception beneath a tidal bore on a movable gravel bed. The results show the significant impact of breaking bore propagation on the gravel bed motion. The dominant contribution to sediment transport inception is the longitudinal pressure gradient force, while the transient recirculation motion next to the bed yields to a drag force acting in the upstream direction and contributing to sediment motion.
Recognition of tidal-bore in the rock record: Towards a facies model[J]. ,
Abstract:-傾 facies model for the deposits of tidal bores (upstream-propagating hydraulic jumps associated with the flood tide in estuarine rivers) has not yet been developed, despite the publication of data from laboratory experiments and some modern estuaries. Moreover, only one example of tidal-bore deposits has hitherto been identified in the rock record. Herein, we document evidence for tidal bores in an Upper Pennsylvanian (Virgilian, Gzhelian) incised-valley fill in northeastern Kansas, USA. Across the flanks and crest of a bank-attached bar remnant in this fill are thin (<-10聽cm) lenses of muddy, massive sandstone and massive, plant-debris-rich sandstone bounded by erosion surfaces exhibiting symmetrical wave ripples and irregular scouring. This interval is enclosed by sandstones with bidirectional cross-stratification, rhythmites, mud drapes, flaser bedding, and related sedimentary structures that together record appreciable tidal influence. The erosion surfaces bounding the massive sandstone lenses, and the massive sandstone lenses themselves, are evidence for scour and sediment suspension by upstream-propagating bores followed by deposition from suspension after their passage. Not only are these deposits the first sedimentary record of tidal bores to be documented in the Pennsylvanian of the USA, they are only the second example of such deposits to be documented in the global rock record. On the basis of our observations, we propose a provisional facies model for tidal-bore deposits that can be refined by future work.
Development of the Holocene Changjiang Delta and its influence on adjacent coastal sedimentary systems[J]. ,
1D Numerical modeling of tidal bore in the Qiantang River[J]. ,
On generation of bores in sloping and narrowing estuaries of arbitrary shape[J]. ,
Advances in global ocean tide models[J].,
2D numerical modelling of bores in the Qiantang Estuary[J]. ,
The application of numerical simulation in analysis of Qiantangjiang River: Result and discussion[J]. ,
A quasi-3D numerical model for estuarine tidal bore[J]. ,
Effects of roughness on tidal bore[J]. ,
Numerical simulation of tidal bores and hydraulic jumps[J]. ,
An implicit finite difference formulation of the nonlinear shallow water equations is developed to allow for the treatment of tidal bores and hydraulic jumps. Five different schemes are investigated involving upwind treatment of convective terms, central differences combined with dissipative interface, forward time-centering and various combinations of these techniques. The schemes are analyzed with respect to their effective amplification portraits, and they are tested on periodic bores, uniform bores and steady hydraulic jumps. In this connection the model results are verified against analytical solutions and a numerical solution obtained with a Godunov Riemann solver. Scheme 4, which combines forward time centering and dissipative interface, is found to be superior to the others and it is applicable for Courant numbers within the range 0.25 to 1.5. This scheme is applied to a case study of the tidal bore in Huangzhou Bay and Qiantang River. The model results are shown to be in very good agreement with field data.
The sediment trapping efficiency of the macro-tidal Daly Estuary, tropical Australia[J]. ,
Field studies were carried out on the water and sediment dynamics in the tropical, macro-tidal, Daly Estuary. The estuary is shallow, very-turbid, about 10002km long, and the entrance is funnel-shape. In the wet, high flow season, normal tidal ranges can be suppressed in the estuary, depending on inflow rates, and freshwater becomes dominant up to the mouth. At that time a fraction of the fine sediment load is exported offshore as a bottom-tagging nepheloid layer after the sediment falls out of suspension of the thin, near-surface, river plume. The remaining fraction and the riverine coarse sediment form a large sediment bar 1002km long, up to 602m in height and extending across the whole width of the channel near the mouth. This bar, as well as shoals in the estuary, partially pond the mid- to upper-estuary. This bar builds up from the deposition of riverine sediment during a wet season with high runoff and can raise mean water level by up to 202m in the upper estuary in the low flow season. This ponding effect takes about three successive dry years to disappear by the sediment forming the bar being redistributed all over the estuary by tidal pumping of fine and coarse sediment in the dry season, which is the low flow season. The swift reversal of the tidal currents from ebb to flood results in macro-turbulence that lasts about 2002min. Bed load transport is preferentially landward and occurs only for water currents greater than 0.602m s 611 . This high value of the threshold velocity suggests that the sand may be cemented by the mud. The Daly Estuary thus is a leaky sediment trap with an efficiency varying both seasonally and inter-annually.
2D numerical simulation of tidal bore in Qiantang River[J]. ,
Characteristic and numerical simulation of tidal bore in Qiantang River[J]. ,
在钱塘江涌潮实测资料的基础上，分析了钱塘江涌潮高度、涌潮传播速度、涌潮流速、涌潮形态及 景观、涌潮压力等涌潮特性．同时，应用基于KFVS（kinetic flux veetor splitting）格式的二维涌潮数值模型模拟了钱塘江涌潮的形成、发展和衰减的全过程，复演了“交叉潮”、“一线潮”、“回头潮”等现象．通过对计算 结果的比较分析，对涌潮特性有了进一步的认识．
Numerical simulation of a weak breaking tidal bore[J]. ,
A tidal bore is a natural and fragile phenomenon, which is of great importance for the ecology of an estuary. The bore development is closely linked with the tidal range and the river mouth shape, and its existence is sensitive to any small change in boundary conditions. Despite their ecological and cultural value, little is known on the flow field, turbulent mixing and sediment motion beneath tidal bores. Indeed, some striking features can be highlighted in two-dimensional simulations, such as large velocity fluctuations and flow recirculation structures. Using Large Eddy Simulation method, we present numerical results that show the complicated turbulent structures and their unsteadiness under a tidal bore.
A study on the hydrodynamic characteristics of the Qiantang tidal bore based on field data[J]. ,
On turbulence in bores[J]. ,
Undular bore in channels-experimental studies[J]. ,
New, detailed investigations of the formation of surge waves in open channels are presented in this paper.
Physical modelling of the flow field in all undular tidal bore[J].,
A tidal bore may form in a converging channel with a funnel shape when the tidal range exceeds 6-9 m. The advancing surge has a major impact on the estuarine ecosystem. Physical modelling of an undular bore has been conducted based upon a quasi-steady flow analogy. The experimental data highlight rapid flow redistributions between successive wave troughs and crests as well as large bottom shear stress variations. The results suggest a sediment transport process combining scour beneath wave troughs associated with upward matter dispersion between a trough and the following wave crest. The process is repeated at each trough and significant sediment transport takes place with deposition in upstream intertidal zones. The conceptual model is supported by field observations showing murky waters after the bore passage and long-lasting chaotic waves.
Experiment study on hydraulic properties of tidal bore[J]. ,
Experimental simulation and validation of the tidal bore in the flume[J]. ,
Reynolds stress and TKE production in an estuary with a tidal bore[J]. ,
The flow and elevation data have also been used to estimate the energy fluxes into and out of the estuary. Short (651h), intense energy inputs (658MW at springs) on the flood flow are largely balanced by longer, less intense seaward energy flow on the ebb. The net energy input is found to be 650.1MW at springs which is consistent with estimates of upstream dissipation. Peak dissipation in the bore itself may exceed the mean energy input but it is active only for a small fraction of the tidal cycle and its average contribution does not exceed 6512% of total dissipation.
Undular tidal bore dynamics in the Daly Estuary, Northern Australia[J]. ,
Measurements in the macro-tidal Daly Estuary show that the presence of an undular tidal bore contributed negligibly to the dissipation of tidal energy. No recirculation bubble was observed between a trough and the following wave crest in the lee waves following the undular bore. This differs to stationary undular bores in laboratory experiments at larger Froude numbers where a recirculation bubble exists. Secondary motions and the turbulence generated by the undular bore had no measurable influence on the sediment transport. This situation contrasts with the intense sediment resuspension observed in breaking tidal bores. The tidally averaged sediment budget in the Daly Estuary was controlled by the asymmetry of tidal currents. The undular bore may widen the river by breaking along the banks that it undercuts, leading to bank slippage. A patch of river-wide macro-turbulence of 3-min duration occurred about 20聽min after the passage of the bore during accelerating tidal currents.
Observation and dynamic characteristics of tidal bore in Qiantang River,China[J]. ,
Analysis of the affecting factors on Qiantang tidal bore[J]. ,
Coastal ecological risk assessment: Its research progress and prospect[J].,
Numerical modeling on flow and sediment in Jianshan Reach affected by strong tidal bore in the Qiantang River[J]. ,
通过建立涌潮作用下的二维泥沙 数学模型,验证了钱塘江尖山河段两种不同河势下的水文资料,并应用模拟结果分析了水沙的异同点。结果表明,两种河势下,钱塘江河口尖山河段水沙运动的共同 点是:潮波变形剧烈,是涌潮形成、发展和壮大的河段;涌潮到达时,流速及含沙量急剧增大,瞬间增幅大,且水流及含沙量均存在间断;涌潮是含沙量急速增加的 主要动力因素。水沙运动的不同点是:分汊河势下沿程各潮位站的高、低潮位均高于走南河势,但潮差略小于走南河势,涨、落潮平均流速均较走南河势强,分汊河 势存在南、北两股涌潮,最终形成交叉潮,涌潮作用下的最大含沙量为走南河势的2~3倍,单宽输沙率为走南河势的1.5~2.5倍。研究成果可为尖山河段治 理研究和有关部门管理提供技术支持。
Turbulence mixing beneath an undular bore front[J]. ,
In macrotidal estuaries, a tidal bore may form during spring tide conditions when the flood tide is confined to a narrow channel. Most field occurrences showed well-defined undulations behind the leading wave, that is, an undular bore process. Herein, detailed free-surface and turbulence measurements were performed beneath undular bore fronts using side-looking acoustic Doppler velocimetry and nonintrusive free-surface measurement devices in a laboratory channel. Undular bores were observed for Froude numbers less than 1.7, which compared favourably with past studies. Velocity measurements with a temporal resolution of 50 Hz showed a marked effect of the bore passage. Longitudinal velocities were characterised by rapid flow deceleration at all vertical elevations, while large fluctuations of transverse velocities were recorded beneath the front. Turbulent Reynolds stress data highlighted high levels in the lower flow region, including next to the bed. Maximum normal and tangential turbulent stresses were observed immediately upstream of and at wave crests.
Soft-sediment deformation produced by tides in a meizoseismic area, Turnagain Arm, Alaska[J]. ,
Turnagain Arm is a semidiurnal hypertidal estuary in southeastern Alaska with a recorded tidal range of 9 m. Contorted bedding and flow rolls preserved in tidal sediments within the estuary have previously been interpreted as resulting from the Mw 9.2 Great Alaskan earthquake of 1964. Horizons of flow rolls between undeformed beds in sediments and rock strata have been used to infer ancient earthquakes in other areas. Although many types of soft-sediment deformation structures can be formed by earthquakes, observations of sedimentation on tidal flats in the inner parts of Turnagain Arm in the summers of 2003 and 2004 show that a wide range of soft-sediment deformation structures, similar to those inferred to have been formed by earthquakes, can form in macrotidal estuaries in the absence of seismic shock. During sedimentation rate measurements in 2004, soft-sediment deformation structures were recorded that formed during one day's tide, either in response to overpressurization of tidal flats during rapid tidal drawdown or by shear stress exerted on the bed by the passage of a 1.8 m tidal bore. Structures consisted of How rolls, dish structures, flames, and small dewatering pipes in a bed 17 cm thick. In the future, if the flow rolls in Turnagain Arm were found in isolated outcrops across an area 11 km in length, in an estuary known to have been influenced by large-magnitude earthquakes, would they be interpreted as seismites? These examples show that caution is needed when using horizons of flow rolls to infer paleoseismicity in estuarine deposits because many of the mechanisms (tidal flux, tidal bores, slumping, flooding) that can cause deformation in rapidly deposited, unconsolidated silts and sands, are orders of magnitude more common than great earthquakes. ?? 2007 The Geological Society of America.
Correlation of stratigraphic architecture of sub-deltas of Changjiang River Delta[J]. ,
依据对江苏省泰兴市黄桥镇钻孔和海门市钻孔、上海长兴岛钻孔地层岩心沉积特征的研究，讨论<br />了冰后期以来长江三角洲河口地区的层序地层。研究表明，沿古河谷纵剖面各河段地层中沉积相组合关系有明<br />显区别。在古河谷下端地区，下切河谷充填层序自下而上由河流相、河口湾相、浅海相和三角洲相组成，沉积<br />相组合最完整。在古河谷上端地区，由于河口湾在海侵发生时存在着涌潮作用，因此，河漫滩泥质沉积层顶部<br />的冲刷面被确定为最大海泛面，其上覆稳定的河口砂体；浅海相和河口湾相沉积在该区域变薄直至尖灭；层序<br />顶部由中潮坪突变为高潮坪，最终形成泛滥平原。这意味着，原先确定的自西向东的长江三角洲的几个亚三角<br />洲或河口砂体沉积，并非都具有向上变粗的三角洲层序。文中报道的３个钻孔，揭露了冰后期长江三角洲完整<br />的下切河谷充填层序。河口湾顶不具备三角洲层序的地区应称为滨海平原。
Evolution and sedimentary sequence of tidal channel-flat system at bore-affected reach of the Qiantang Estuary[J]. ,
Characteristics of tidal-bore deposits and facies associations in the Qiantang Estuary, China[J]. ,
The characteristics of tidal-bore deposition in the Qiantang Estuary are studied on the basis of core strata and grain-size data, and lateral and longitudinal associations with other sedimentary facies are synthesized. A typical depositional package by tidal bores and associated flows is generally initiated with (1) an undular/planar erosion base, overlain by (2) a massive sandy bed, and (3) a sandy bed with parallel laminations or some thinly heterolithic beds. The depositional units, especially the parallel laminations, are prone to deformation into convolute bedding, flames, and boiled sand patches with water-escape structures. In the middle estuary, tidal-bore deposits (TBDs) at the main channel and the lower tidal flat transit laterally into alternative beds of TBDs andz heterolithic beds at the middle tidal flat, and then toward incomplete tidal rhythmites on the higher tidal flat. TBDs are generally coarser and less sorted than tidal sandy deposits (TSDs), and tidal muddy deposits (TMDs) have finer grains, less sorting and lower positive skewness than either TSDs or TBDs. Therefore, bivariate plotting of size parameters is a useful tool to differentiate between these three genetic sedimentary bed types. Along the axis, three facies divisions are obvious and consist of: (1) linear depositional ridges and erosion troughs at the outer estuary, (2) TBDs at the middle estuary, and (3) coarse fluvial deposits at the upper estuary. The tripartite facies model of the Qiantang Estuary is similar to other well-known tide-dominated estuarine facies models, but it is the first to stress tidal-bore deposition in the sedimentary facies using detailed discriminative textural and structural characteristics. The approaches offer the potential to better understand tidal-bore processes and their important role in sediment dispersion and facies formation within modern and ancient macrotidal to hypertidal estuaries.
Terwindt J H J. An example of soft-sediment deformations in an intertidal environment: The effect of a tidal bore[J].,
Soft-sediment deformation structures in the Cambrian (Series 2) tidal deposits (NW Estonia): Implications for identifying endogenic triggering mechanisms in ancient sedimentary record[J].,
Soft-sediment deformation structures (SSDS) are documented in several horizons within silt- and sandstones of the Cambrian Series 2 (Dominopolian Stage) Tiskre Formation, and some in the underlying argillaceous deposits of the L眉kati Formation in NW Estonia, northern part of the Baltoscandian Palaeobasin. The aim of this study was to map, describe, and analyze these deformation features, and discuss their deformation mechanism and possible triggers. Load structures (simple load casts, pillows, flame structures, and convoluted lamination) with varying shapes and sizes occur in the Tiskre Formation in sedimentary interfaces within medium-bedded peritidal rhythmites (siltstone-argillaceous material) as well as within up to 3m thick slightly seaward inclined stacked sandstone sequences. Homogenized beds, dish-and-pillar structures, and severely deformed bedding are also found within these stacked silt- and sandstone units and within a large tidal runoff channel infill. Autoclastic breccias and water-escape channels are rare and occur only in small-scale - always related to thin, horizontal tidal laminae. Profound sedimentary dykes, sand volcanoes, and thrust faults, which are often related to earthquake-triggered soft sediment deformation, were not observed within the studied intervals. Deformation horizon or horizons with large flat-topped pillows often with elongated morphologies occur at or near the boundary between the Tiskre and L眉kati formations. Deformation mechanisms identified in this study for the various deformation types are gravitationally unstable reversed density gradient (especially in case of load features that are related to profound sedimentary interfaces) and lateral shear stress due to sediment current drag (in case of deformation structures that are not related to loading at any apparent sedimentary interface). Synsedimentary liquefaction was identified as the primary driving force in most of the observed deformation horizons. Clay thixotropy may have contributed to the formation of large sandstone pillows within the Tiskre-揕眉kati boundary interval at some localities. It is discussed here that the formation of the observed SSDS is genetically related to the restless dynamics of the storm-influenced open marine tidal depositional environment. The most obvious causes of deformation were storm-wave loading, rapid-deposition and shear and slumping caused by tidal surges.
Environmental impact of undular tidal bores in tropical rivers[J].,
A tidal bore impacts significantly on the estuarine ecosystem, although little is known on the flow field, mixing and sediment motion beneath tidal bores. In the absence of detailed systematic field measurements, a quasi-steady flow analogy was applied to investigate undular tidal bores with inflow Froude numbers between 1.25 and 1.6. Experimental results indicated that rapid flow redistributions occur beneath the free-surface undulations, with significant variations in bed shear stress between wave crests and troughs. Dynamic similarity was used to predict detailed flow characteristics of undular tidal bores. The effects of periodic loading on river sediments, scour of river bed and flow mixing behind the bore are discussed. A better understanding of these processes will contribute to better management practices in tidal bore affected rivers, including the Styx and Daly rivers in tropical Australia.
Turbulence measurements in positive surges and bores[J].,
A positive surge results from a sudden change in flow that increases the flow depth. New experiments were conducted in a large channel. Most positive surge tests were conducted with a horizontal bed slope, a constant flow rate and uncontrolled flow conditions. The only dependant variable was the downstream gate opening after closure. Detailed turbulence measurements were performed with high-temporal resolution using side-looking acoustic Doppler velocimetry. Two types of positive surge were observed: undular surge for Froude numbers less than 1.7, and weak (breaking) surges above. Instantaneous velocity measurements beneath advancing surges showed a marked effect of the surge passage on the velocity field. Streamwise velocities showed rapid flow deceleration at all vertical elevations. Large fluctuations of longitudinal and transverse velocities were recorded beneath the surges, including some unsteady flow recirculation beneath a weak surge front. Turbulent stresses were deduced from high-pass filtered data. The results showed large normal and tangential Reynolds stresses beneath the surges. A comparison between undular and weak surges suggested some major difference. In weak surge flows, the data showed rapid flow separation beneath the surge front. In undular surges, maximum Reynolds stresses were observed beneath and just before each wave crest behind the leading wave.
Sedimentary textures and environments of the Hangzhou Bay[J]. ,
Sand injectites:Implications for hydrocarbon exploration and production[J]. ,
react-text: 582 Because of their potentially large volumes and excellent reservoir properties, winglike clastic intrusion complexes may represent stand-alone exploration targets. However, determining the three-dimensional (3-D) geometry of such complexes is problematic because of limited exposure in the field and insufficient seismic resolution and well coverage in the subsurface. In this study, high-quality... /react-text react-text: 583 /react-text [Show full abstract]
On the Lower Jurassic soft sediment Deformation of Southwestern Tianshan Mountains, Xinjiang, China[J]. ,
新疆西南天山乌恰地区早侏罗世软沉积物变形位于湖相砂岩中；由地震触发的软沉积物变形有三个层位，位于下侏罗统康苏组的顶部。变形主要类型为负载（load）、球 枕（ball and pillow）、滴状体（droplet）、锥形体(cusps)、液化均一层(homogeneous layer)和液化不整合(liquefied unconformity)。三个变形层位反映乌恰地区早侏罗世末曾连续发生过三次强地震；变形类型机制不同反映三次地震强度有别。乌恰下侏罗统处于中亚塔拉斯―费尔干纳巨型走滑断裂控制的拉分盆地中，断裂走滑伴随地震直接诱发软沉积物变形；古地震震级为Ms6?5~7。
The slump structures in the middle Ordovician on the Southern Margin of Ordos Basin and their seismic origin[J]. ,