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洪水型重力流是重力流沉积学的研究热点,以往研究认为洪水型重力流具有紊流支撑的流体性质,对于其流体性质转化及其沉积记录的识别不够深入。近年研究揭示重力流沉积过程中可形成多种过渡型流体,具有特殊流体转换机制和沉积特征。通过调研国内外最新文献,系统介绍了过渡型流体基本特征、沉积机制方面的研究进展,并讨论了其对洪水型重力流沉积研究的启示及地质意义。研究结果表明：在少量黏土矿物影响下,沉积物重力流流体的性质即可由紊流向层流转化,形成特殊的过渡型流体。转化过程主要取决于黏土矿物含量和类型控制的流体内聚力和流速控制的紊流应力二者之间的相互作用。过渡型流体可以产生大型流水沙纹（large current ripple）、砂质纹层—泥质纹层间互形成的低幅度沙波（low amplitude bed wave）等独特的底床类型。尽管实验研究揭示了过渡型流体可能形成的沉积底床特征,针对洪水型重力流沉积记录中过渡型流体的解释仍十分缺乏,尤其是过渡型流体转换机制及其沉积响应仍亟待深入探索。过渡型流体的沉积底形是研究洪水型重力流沉积动力机制的重要载体,可为深入理解洪水型重力流沉积过程提供新视角,同时可能具有更广泛的沉积学研究价值。 相似文献
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洪水型重力流是重力流沉积学的研究热点,以往研究认为洪水型重力流具有紊流支撑的流体性质,对于其流体性质转化及其沉积记录的识别不够深入。近年研究揭示重力流沉积过程中可形成多种过渡型流体,具有特殊流体转换机制和沉积特征。通过调研国内外最新文献,系统介绍了过渡型流体基本特征、沉积机制方面的研究进展,并讨论了其对洪水型重力流沉积研究的启示及地质意义。研究结果表明：在少量黏土矿物影响下,沉积物重力流流体的性质即可由紊流向层流转化,形成特殊的过渡型流体。转化过程主要取决于黏土矿物含量和类型控制的流体内聚力和流速控制的紊流应力二者之间的相互作用。过渡型流体可以产生大型流水沙纹(large current ripple)、砂质纹层—泥质纹层间互形成的低幅度沙波(low amplitude bed wave)等独特的底床类型。尽管实验研究揭示了过渡型流体可能形成的沉积底床特征,针对洪水型重力流沉积记录中过渡型流体的解释仍十分缺乏,尤其是过渡型流体转换机制及其沉积响应仍亟待深入探索。过渡型流体的沉积底形是研究洪水型重力流沉积动力机制的重要载体,可为深入理解洪水型重力流沉积过程提供新视角,同时可能具有更广泛的... 相似文献
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Hummocky cross-stratification-like structures in deep-sea turbidites: Upper Cretaceous Basque basins (Western Pyrenees, France) 总被引：1，自引：0，他引：1
Hummocky cross-stratification is a sedimentary structure which is widely interpreted as the sedimentary record of an oscillatory current generated by energetic storm waves remobilizing surface sediment on the continental shelf. Sedimentary structures named hummocky cross-stratification-like structures, similar to true hummocky cross-stratification, have been observed in the Turonian–Senonian Basque Flysch Basin (south-west France). The bathymetry (1000 to 1500 m) suggests that the observed sedimentary structures do not result from a hydrodynamic process similar to those acting on a continental shelf. The morphology of these three-dimensional structures shares similarities with the morphology of hummocky cross-stratification despite a smaller size. The lateral extent of these structures ranges from a few decimetres to many decimetres; they consist of convex-up domes (hummock) and concave-up swales with a non-erosive base. Four types of hummocky cross-stratification-like geometries are described; they occur in association with structures such as climbing current ripple lamination and synsedimentary deformations. In the Basque Flysch, hummocky cross-stratification-like structures are only found in the Tc interval of the Bouma sequence. Hummocky cross-stratification-like structures are sporadic in the stratigraphic series and observed only in few turbidite beds or bed packages. This observation suggests that hummocky cross-stratification-like structures are linked genetically to the turbidity current but form under a very restricted range of parameters. These structures sometimes show an up-current (upslope) migration trend (antidunes). In the described examples, they could result from standing waves forming at the upper flow interface because of Kelvin–Helmholtz instability. 相似文献
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Flows with high suspended sediment concentrations are common in many sedimentary environments, and their flow properties may show a transitional behaviour between fully turbulent and quasi‐laminar plug flows. The characteristics of these transitional flows are known to be a function of both clay concentration and type, as well as the applied fluid stress, but so far the interaction of these transitional flows with a loose sediment bed has received little attention. Information on this type of interaction is essential for the recognition and prediction of sedimentary structures formed by cohesive transitional flows in, for example, fluvial, estuarine and deep‐marine deposits. This paper investigates the behaviour of rapidly decelerated to steady flows that contain a mixture of sand, silt and clay, and explores the effect of different clay (kaolin) concentrations on the dynamics of flow over a mobile bed, and the bedforms and stratification produced. Experiments were conducted in a recirculating slurry flume capable of transporting high clay concentrations. Ultrasonic Doppler velocity profiling was used to measure the flow velocity within these concentrated suspension flows. The development of current ripples under decelerated flows of differing kaolin concentration was documented and evolution of their height, wavelength and migration rate quantified. This work confirms past work over smooth, fixed beds which showed that, as clay concentration rises, a distinct sequence of flow types is generated: turbulent flow, turbulence‐enhanced transitional flow, lower transitional plug flow, upper transitional plug flow and a quasi‐laminar plug flow. Each of these flow types produces an initial flat bed upon rapid flow deceleration, followed by reworking of these deposits through the development of current ripples during the subsequent steady flow in turbulent flow, turbulence‐enhanced transitional flow and lower transitional plug flow. The initial flat beds are structureless, but have diagnostic textural properties, caused by differential settling of sand, silt and cohesive mud, which forms characteristic bipartite beds that initially consist of sand overlain by silt or clay. As clay concentration in the formative flow increases, ripples first increase in mean height and wavelength under turbulence‐enhanced transitional flow and lower transitional plug‐flow regimes, which is attributed to the additional turbulence generated under these flows that subsequently causes greater lee side erosion. As clay concentration increases further from a lower transitional plug flow, ripples cease to exist under the upper transitional plug flow and quasi‐laminar plug flow conditions investigated herein. This disappearance of ripples appears due to both turbulence suppression at higher clay concentrations, as well as the increasing shear strength of the bed sediment that becomes more difficult to erode as clay concentration increases. The stratification within the ripples formed after rapid deceleration of the transitional flows reflects the availability of sediment from the bipartite bed. The exact nature of the ripple cross‐stratification in these flows is a direct function of the duration of the formative flow and the texture of the initial flat bed, and ripples do not form in cohesive flows with a Reynolds number smaller than ca 12 000. Examples are given of how the unique properties of the current ripples and plane beds, developing below decelerated transitional flows, could aid in the interpretation of depositional processes in modern and ancient sediments. This interpretation includes a new model for hybrid beds that explains their formation in terms of a combination of vertical grain‐size segregation and longitudinal flow transformation. 相似文献
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包卷层理是软沉积物变形构造的一种重要类型,其成因较为复杂。在深水沉积环境中,探讨内波、内潮汐作用与包卷层理成因之间的关系,对于丰富包卷层理形成机制和完善内波、内潮汐沉积鉴别标志均具有重要意义。鄂尔多斯盆地西缘北部内蒙古桌子山地区上奥陶统拉什仲组阻塞浊流沉积中发育的包卷层理,依据形态可分为倾向型规则包卷层理和回旋状包卷层理2类: 前者具有紧闭背形、开阔向形及背形之下发育砂核等特征,常和双向交错层理伴生; 后者属于层内扭曲变形,多限定在具有削截现象的层系内,常和复合流沉积构造及浪成波纹层理伴生。综合沉积特征、包卷层理特征、伴生沉积构造及相关研究成果可推测: 倾向型规则包卷层理主要由内潮汐形成,在液化过程中出现明显的密度倒置,因瑞利—泰勒不稳定引起变形,在流体持续剪切作用下进一步改造形成; 回旋状包卷层理主要由短周期内波形成,包括浊流反射形成的随机内波和内潮汐裂解形成的内孤立波,表现为同沉积分层液化,但一般不出现密度倒置现象,因开尔文—亥姆霍兹不稳定引起变形,流体剪切也有一定的改造作用。 相似文献
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A series of wave‐flume experiments was conducted to closely look at characteristics of geometry and migration of wave‐generated ripples, with particular reference to the effect of velocity ‘hiatuses’ during which the near‐bed flow velocity becomes much smaller than the threshold of sediment movement. Three types of wave patterns were generated: two types for simulating waves with intervening velocity hiatuses; and regular waves for comparison purposes. In the former two types, two different wavelengths of water waves were generated alternately in the course of a wave test: the wave with a longer wavelength was set large enough to mobilize the bottom sediment, whereas the wave with a shorter wavelength was set too small to mobilize the sediment. The former two types were designed to be different in sequence of convexity and concavity of wave patterns. The sequence with the convex–concave longer wave and successive convex–concave shorter wave was described as a ‘zero‐up‐crossing’ wave pattern, and the inverse sequence was described as a ‘zero‐down‐crossing’ wave pattern. The ripples developed under oscillatory flow with intervening hiatuses manifested the following characteristics in geometry and migration. (i) The morphological characteristics of ripples, namely wavelength, height and the ripple steepness, are unaffected by the intervening hiatuses of velocity. (ii) The directions of ripple migration under the zero‐up‐crossing and zero‐down‐crossing wave patterns corresponded well with the directions of the flow immediately before onset of the hiatuses. (iii) The observation of sand particle movement on the ripple surface indicated that, under the zero‐up‐crossing waves, the velocity hiatus prevents the entrained sediment cloud from being thrown onshore, and thus the sediment grains thrown onshore are fewer than those thrown offshore. As a result of the sediment movement over one wave‐cycle, the net sediment transport is directed offshore under the zero‐up‐crossing wave pattern. (iv) The velocity of ripple migration was highly correlated with acceleration skewness. Under most of the zero‐up‐crossing (zero‐down‐crossing) wave patterns, flow acceleration skewed negative (positive) and ripples migrated offshore (onshore). 相似文献
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GERHARD EINSELE 《Sedimentology》1977,24(5):639-655
In growing sedimentary sequences range and velocity of vertically ascending pore water (advection) can be determined quantitatively by using a simple graphical method. During continuing deposition and maintenance of compaction equilibrium, the pore water from deeper layers cannot reach the sediment-water interface. Range and velocity of advective flow decrease from top to bottom of a sequence and depend on the thickness affected by compaction. The velocity of pore water flow as well as the transport of solutes by advective flux are proportional to the sedimentation rate. Compaction flow can also result from under-con-solidation and diagenetic reduction of pore space. At the sediment-water interface, a direct contact between the ascending pore water and the overlying water body is feasible only under special conditions (interrupted sedimentation over under-consolidated material, erosion). These results are demonstrated on geometric models of sedimentary sequences, on experimentally deposited clay, and on selected examples of the Deep Sea Drilling Project. 相似文献
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At time of the 1983 Japan Sea tsunami, waves in the form of a bore ascended many rivers. In some cases, bores had the form of one initial wave with a train of smaller waves, and in other cases, such a wave train did not appear and only a step with a flat water surface behind was observed. In the present study, it is clarified that both undular-type and nonundular-type bores can be recognized as solutions of the KdV-Burger's equation which was introduced by Johnson in 1972. Numerically obtained analytical solutions and results of laboratory experiments are compared. 相似文献
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Deep-water gravity flows are one of the most important sediment transport mechanisms on Earth. After 60 years of study,significant achievements have been made in terms of classification schemes,genetic mechanisms,and depositional models of deep-water gravity flows. The research history of deep-water gravity flows can be divided into five stages: incipience of turbidity current theory; formation of turbidity current theory; development of deep-water gravity flow theory; improvement and perfection of deep-water gravity flow theory; and comprehensive development of deep-water gravity flow theory. Currently,three primary classification schemes based on the sediment support mechanism,the rheology and transportation process,and the integration of sediment support mechanisms,rheology,sedimentary characteristics,and flow state are commonly used.Different types of deep-water gravity flow events form different types of gravity flow deposits. Sediment slump retransportation mainly forms muddy debris flows,sandy debris flows,and surge-like turbidity currents. Resuspension of deposits by storms leads to quasi-steady hyperpycnal turbidity currents(hyperpycnal flows). Sustainable sediment supplies mainly generate muddy debris flows,sandy debris flows,and hyperpycnal flows. Deep-water fans,which are commonly controlled by debris flows and hyperpycnal flows,are triggered by sustainable sediment supply; in contrast,deep-water slope sedimentary deposits consist mainly of debris flows that are triggered by the retransportation of sediment slumps and deep-water fine-grained sedimentary deposits are derived primarily from finegrained hyperpycnal flows that are triggered by the resuspension of storm deposits. Harmonization of classification schemes,transformation between different types of gravity flow deposit,and monitoring and reproduction of the sedimentary processes of deep-water gravity flows as well as a source-to-sink approach to document the evolution and deposition of deep-water gravity flows are the most important research aspects for future studies of deep-water gravity flows study in the future. 相似文献
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西秦岭造山带中三叠统复理石相研究 总被引：3，自引：4，他引：3
文中主要论点是:1)区内中三叠统属巨厚复理石相,它清楚地显示出以浊流为主的深水块体流沉积的各种标志性特征;2 )巨厚沉积序列的粒度和层厚自下而上呈规律性变粗变厚,构成完整的进积型沉积序列;3)除块体流沉积外,还发现深水牵引流沉积与浊积岩相伴而生,如等深积岩和内波、内潮汐沉积,由其形成的沉积构造丰富多样,如不同类型,不同规模的交错层理极为常见,它们在层面上相应形成不同特征的水流波痕;4)从有否粗粒水道沉积、垂直序列有否规律性变化、古水流特征和丰富的相类型 4个方面分析认为,属于不成熟被动边缘的海底扇。 相似文献
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Shale depositional processes: Example from the Paleozoic Barnett Shale, Fort Worth Basin, Texas, USA
A long held geologic paradigm is that mudrocks and shales are basically the product of ‘hemipelagic rain’ of silt- and/or clay-sized, detrital, biogenic and particulate organic particles onto the ocean floor over long intervals of time. However, recently published experimental and field-based studies have revealed a plethora of micro-sedimentary features that indicate these common fine-grained rocks also could have been transported and/or reworked by unidirectional currents. In this paper, we add to this growing body of knowledge by describing such features from the Paleozoic Barnett Shale in the Fort Worth Basin, Texas, U.S.A. which suggests transport and deposition was from hyperpycnal, turbidity, storm and/or contour currents, in addition to hemipelagic rain. On the basis of a variety of sedimentary textures and structures, six main sedimentary facies have been defined from four 0.3 meter intervals in a 68m (223 ft) long Barnett Shale core: massive mudstone, rhythmic mudstone, ripple and low-angle laminated mudstone, graded mudstone, clay-rich facies, and spicule-rich facies. Current-induced features of these facies include mm- to cmscale cross- and parallel-laminations, scour surfaces, clastic/biogenic particle alignment, and normal- and inverse-size grading. A spectrum of vertical facies transitions and bed types indicate deposition from waxing-waning flows rather than from steady ‘rain’ of particles to the sea floor. Detrital sponge spicule-rich facies suggests transport to the marine environment as hypopycnal or hyperpycnal flows and reversal in buoyancy by transformation from concentrated to dilute flows; alternatively the spicules could have originated by submarine slumping in front of contemporaneous shallow marine sponge reefs, and then transported basinward as turbidity current flows. The occurrence of dispersed biogenic/organic remains and inversely size graded mudstones also support a hyperpycnal and/or turbidity flow origin for a significant part of the strata. These processes and facies reported in this paper are probably present in other organic-rich shales. 相似文献
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Numerical modelling of a mid-sized gravity flow: the 1979 Nice turbidity current (dynamics, processes, sediment budget and seafloor impact) 总被引：3，自引：0，他引：3
The 1979 Nice turbidity current is modelled using a visco-plastic analysis of flow velocity because the initial flow concentrations are expected to have been very high. The complete history of the failed sediment from debris flow to turbidity current plume is therefore addressed. The turbidity current portion is considered as a steady state flow divided into a dense bottom flow and an upper plume. Model results show that a dense flow can be generated from the debris flow by the disaggregation of the initial slide. The dense flow would be strongly erosive and able to create and maintain a low-density plume at its surface. The depth of erosion of the channel floor by the dense flow is predicted to reach 6–11 m in overconsolidated sediments, with the main erosion taking place in Var Canyon and the Upper Fan Valley. The eroded volume (108 m3) provides additional material to the sediment mass of the initial failure. The dense flow appears able to inject fine sand and silt into the overlying plume during 90 km, and would disintegrate before being able to deposit sediment. The extensive sand layer along the travel path of the turbidity current may have been deposited from the tail of the trailing plume: a result of the velocity difference between the plume and the dense flow. Observations on sedimentary structures, erosion features and distribution of the sand deposit are quite in agreement with our modelling approach. For example, gravel waves can be generated when loose deposits are reworked by the supercritical dense flow. The methodology and equations presented here provide a good estimate of the geological consequences of a high-velocity gravity flow undergoing rheological transition. 相似文献
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Tsunami deposits in the geological record 总被引：2，自引：0，他引：2
A review is presented here of tsunami deposits in the geological record. It begins with a discussion of the relationships between the processes of tsunami generation and propagation and the sedimentary responses. This is followed by a consideration of the sedimentary processes associated with the passage of tsunami waves across coastlines. Attention is also given to the sedimentary processes associated with tsunami-triggered gravity backwash flows and comparisons are made with turbidity current action. We observe that despite sedimentary evidence for recent tsunamiites, geological research on ancient tsunamis has not identified stratigraphic units associated with onshore tsunami sedimentation. Equally, it is noted that nearly all published studies of sedimentary processes associated with modern tsunamis have not considered patterns of sediment transport and deposition in the offshore zone. 相似文献
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Quantifying velocity and turbulence structure in depositing sustained turbidity currents across breaks in slope 总被引：2，自引：0，他引：2
Two-dimensional experiments investigating sediment transport and turbulence structure in sustained turbidity currents that cross breaks in slope are presented as analogue illustrations for natural flows. The results suggest that in natural flows, turbulence generation at slope breaks may account for increased sand transport into basins and that the formation of a hydraulic jump may not be necessary to explain features such as the occurrence of submarine plunge pools and the deposition of coarser-grained beds in the bottomsets of Gilbert-type fan deltas. Experimental flows were generated on 0°, 3°, 6° and 9° slopes of equal length which terminated abruptly on a horizontal bed. Two-component velocities were measured on the slope, at the slope break and downstream of the slope break. Flows were depositional and non-uniform, visibly slowing and thickening with distance downstream. One-dimensional continuous wavelet transforms of velocity time series were used to produce time-period variance maps. Peaks in variance were tested against a background red-noise spectrum at the 95% level; a significant period banding occurs in the cross-wavelet transform at the slope break, attributed to increased formation of coherent flow structures (Kelvin–Helmholtz billows). Variance becomes distributed at progressively longer periods and the shape of the bed-normal-velocity spectral energy distribution changes with distance downstream. This is attributed to a shift towards larger turbulent structures caused by wake stretching. Mean velocity, Reynolds shear stress and turbulent kinetic energy profiles illustrate the mean distribution of turbulence through the currents. A turbulent kinetic energy transfer balance shows that flow non-uniformity arises through the transfer of mean streamwise slowing to mean bed-normal motion through the action of Reynolds normal stresses. Net turbulence production through the action of normal stresses is achieved on steeper slopes as turbulence dissipation due to mean bed-normal motion is limited. At the slope break, an imbalance between the production and dissipation of turbulence occurs because of the contrasting nature of the wall and free-shear boundaries at the bottom and top of the flows, respectively. A rapid reduction in mean streamwise velocity predominately affects the base of the flows and steeper proximal slope flows have to slow more at the break in slope. The increased turbulent kinetic energy, limited bed-normal motion and strong mixing imposed by steep proximal slopes means rapid slowing enhances turbulence production at the break in slope by focusing energy into coherent flow structures at a characteristic period. Thus, mean streamwise slowing is transferred into turbulence production at the slope break that causes increased transport of sediment and a decrease in deposit mass downstream of the slope break. The internal effects of flow non-uniformity therefore can be separated from the external influence of the slope break. 相似文献
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为分析风场与沉积体系之间的耦合关系,综合运用野外考察、遥感影像解译和气象数据综合分析等手段。分析结果表明：风场的变化除了受控于盛行风系以及季风的变化以外,还受到地貌、湖泊效应产生的湖陆风等因素影响。风场对青海湖沉积体系的影响体现在局部区域气候的干湿、物源的供给量、波浪和沿岸流的强弱程度等方面。局部区域气候的干湿差异性造成地表植被覆盖率有所不同,导致地表的抗风化能力有所不同。抗风化能力较弱的地带为风砂堆积提供充足的物源。盛行风向产生的波浪和沿岸流对湖泊中的砂体产生较强的搬运和改造作用。 相似文献
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海峡是不同于三角洲、陆架的一类独特沉积环境,具有特殊的沉积作用组合。海峡的形态多样,长度为几千米至数百千米,深度为几十米至上千米; 海峡由狭窄区域向两端逐渐过渡为相对开阔海区,开阔海区大多深度相比海峡更深; 海峡的狭窄区域横截面积小、流体流速最大,通常以侵蚀地貌为特征; 流体流经狭窄区域后,由于海峡横截面积增加,导致流速向两端开阔海区域锐减,并表现为沉积地貌。浅水海峡通常以潮流为最主要的沉积作用,其他的沉积物搬运方式包括单向的海流和重力流; 深水海峡则以海流和重力流为主。海峡高能区沉积以砾石滞留和发育交错层理为特征,低能区表现为泥质沉积并发育流水砂纹; 在低海平面时期,暴露的浅水海峡以河流沉积作用为主; 海平面上升过程中,河流逐渐演化为三角洲/河口湾、海湾和贯通的海峡。 相似文献