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1.
冲绳海槽的晚第四纪浊流沉积 总被引：1，自引：0，他引：1
张明书 《吉林大学学报(地球科学版)》1988,(1)
冲绳海槽晚第四纪的浊流沉积发育在海底斜坡带和坡折处静水环境,属阵发性纵向浊流。物质来源于海槽中心斜坡区的滑塌沉积物、岛坡、陆坡和台湾宜兰浇滩的碎屑沉积物。受控于海底地形、滞流环境和构造岩浆活动以及伴生的浅源地震。 冲绳海槽海底表层浊流沉积物,形成在晚更新世末次冰期最盛期、末次冰期末和冰后期三个阶段,以末次冰期最盛期阵发频繁,浊积物最发育,与气候寒冷期有一定的相关性。 相似文献
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应用雷诺平均纳维尔—斯托克斯模型模拟探讨了等量突然释放型浊流在流经不同坡折渠道的流动及沉积特性,取得如下主要结论:随着底坡增加,浊流流速增长率因卷吸作用的增强而减缓;浊流深度平均速度和浓度形态相似,头部大且向尾部呈线性下降;在小坡折处产生沉积,沉积最厚处离坡折处不远且上下游平均粒径相差不大,往下游厚度呈线性减小;而在大坡折处产生侵蚀,随着坡度的增大侵蚀增加,沉积最厚处离坡折处较远且上下游平均粒径相差大,形态上呈上拱状。这些认识对于根据浊流沉积特征推测其形成环境具有一定的参考作用。 相似文献
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浊流形成条件的水动力学模拟及其在储层预测方面的作用 总被引：3，自引：0，他引：3
在对浊流形成条件地质背景研究的基础上,应用水动力学模拟原理正演模拟了由不同粒级沉积物形成的浊流的几何形态,并通过与地震资料的对比来达到储层预测的目的.采用该方法分别对莺歌海和琼东南盆地的浊流沉积进行了模拟研究,模拟结果表明:①浊流发育的最理想的坡度是1.5～3.0°;②浊流沉积一般都会形成斜坡扇和盆底扇,且单个浊积体在坡角处沉积最厚,向盆地方向逐渐减薄;③在其它参数不变的情况下,固体颗粒越大,形成的浊积体越厚,但展布范围越小;固体颗粒越小,形成的浊积体越薄,但展布范围越大.模拟结果与钻井的实际情况吻合良好. 相似文献
5.
大塘坡组锰矿石由菱锰矿内碎屑和碳泥质基质组成。菱锰矿内碎屑是浅水沉积环境中的锰质沉积物破碎而成。它们沿着盆地斜坡流入深水地区与碳、粘土和粉砂沉积在一起形成内碎屑菱锰矿。一部分矿石有递变层理,具有浊流沉积特征。 相似文献
6.
海底浊流的运动及其沉积,是目前浊流研究的热点之一。根据经过验证的基于雷诺平均纳维尔-斯托克斯方程及浮力项修正 k-ε 湍流模型的三维数值计算模型模拟了海底弯曲圆弧形峡谷内的浊流的流动和沉积,结果表明:（1）浊流在运动过程中由于对环境水体的夹带厚度不断增加,浊流厚度一般会超过峡谷深度,溢出峡谷,使浊流产生密度和动量损失;（2）浊流到达弯道部分后,由于离心力的作用会产生剥离,溢出更多的浊流至漫滩区域。浊流剥离的最大处为弯道顶点外岸下游处,其过量密度可达入流的37.5%;（3）对于模拟的横剖面为圆弧型的峡谷内的浊流来说,弯道顶点处的二次流在底部形成一个顺时针的循环圈,靠近峡谷底部从外岸指向内岸;（4）在峡谷中间及弯道顶点内岸下游处形成沉积,在弯道顶点外岸下游处形成侵蚀。这些特征对根据浊流的沉积观察推测其形成环境及油气储层的调查等方面有一定的参考意义。 相似文献
7.
碎屑流与浊流的流体性质及沉积特征研究进展 总被引：5，自引：1，他引：4
受浊流沉积模式(即鲍马序列和浊积扇模式)的驱动和浊积岩思维定势的影响,自1970s浊流与浊积岩的概念逐渐扩大,特别是通过"高密度浊流"术语的引入,以及将水下浊流与陆上河流的错误类比,使得一部分碎屑流与底流的沉积被认为是浊积岩。随着现代观测设备的应用以及详细的岩芯观察,碎屑流(特别是砂质碎屑流)和浊流被重新认识。浊流是一种具牛顿流变性质和紊乱状态的沉积物重力流,其沉积物支撑机制是湍流。碎屑流是一种具塑性流变性质和层流状态的沉积物重力流,其沉积物支撑机制主要是基质强度和颗粒间的摩擦强度。浊流沉积具特征的正粒序韵律结构,底部为突变接触而顶部为渐变接触;碎屑流沉积一般具上、下两层韵律结构,即下部发育具平行碎屑结构的层流段,上部发育具块状层理的"刚性"筏流段。但当碎屑流被周围流体整体稀释改造且改造不彻底时,强碎屑流可变为中—弱碎屑流,相应自下而上可形成逆—正粒序的沉积韵律结构,其中发育有呈漂浮状的石英颗粒和泥质撕裂屑等碎屑颗粒,明显区别于浊流沉积单一的正粒序韵律结构特征。碎屑流沉积顶、底部均为突变接触。浊流的沉积模式为简单的具平坦盆底的坡底模式,而碎屑流则为复杂的斜坡模式。 相似文献
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珠江口盆地白云凹陷荔湾深水区为油气勘探有利区域,通过岩石学和古生物组合特征研究,认为该区珠江组下部属于典型的深水扇沉积,可划分为早期盆地扇和晚期斜坡扇两种类型,两类深水扇都以发育颗粒流、砂质碎屑流及低密度浊流等顺坡重力流沉积为主,同时夹有少量内波和等深流等深水牵引流改造沉积。砂质碎屑流为两类深水扇水道砂体的主要沉积类型,发育有逆-正粒序层理、平行层理和水平层理,粒序层内可见各种丰富的液化变形和生物逃逸构造,而水平层内发育有更多的生物钻孔和扰动现象。两类深水扇的沉积构造和古生物特征有明显差异,其中盆地扇水道砂岩中普遍含硅质小砾石,水道间泥岩中含有较多保存完好的抱球虫化石,斜坡扇水道砂岩以富含炭泥屑为典型特征,水道间泥岩含有更丰富的颗石藻和抱球虫化石,其中部分抱球虫和颗石具有遭受海底溶蚀作用的现象,指示斜坡扇相对盆地扇有更大的水体深度。平面上两类深水扇具有相似的重力流沉积的分带性,都具有自陆架坡折向盆地方向由颗粒流沉积逐渐向砂质碎屑流和近源高密度浊流、远源低密度浊流等单向演化的特点。 相似文献
9.
深水重力流沉积研究进展 总被引：1，自引：0，他引：1
深水重力流沉积研究经历了半个多世纪发展,从浊流及鲍马序列开始,到把深水砂岩普遍解释为浊流成因以及海底扇模式的建立,再到今天学者们对鲍马序列的质疑,深水重力流沉积的研究经历了认识上的螺旋式上升旋回。目前关于深水重力流沉积争议的焦点在于高密度浊流是否属于浊流的范畴,深水砂岩是否都是浊流成因。以Shanmugam为代表的学者认为,绝大多数的深水砂岩都是碎屑流成因而非浊流成因,并且提出了重力流分类新方案,同时建立了与其匹配的深水斜坡沉积模式。通过对前人成果的广泛调研,经过对比总结,认为:1根据流变学和沉积物搬运机制,重力流分为碎屑流(砂质碎屑流和泥质碎屑流)、颗粒流、浊流;2浊流的韵律结构特征为明显的正粒序且没有漂浮的碎屑颗粒,碎屑流自下而上呈逆-正粒序的两套韵律变化且发育有漂浮的碎屑颗粒;3Walker的综合扇模式与Shanmugam的斜坡沉积模式,二者是可以共存的,只是在某一地区适用性不同而已。 相似文献
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沉积物重力流的研究随着深海、深湖环境油气资源的勘探成为现阶段沉积学领域研究的重点课题之一。沉积重力流的分类与命名已不断的完善与细化,浊流与碎屑流成为沉积物重力流的研究重点,沉积学者依据其流态特征、流变学特征、流体浓度与支撑机理对两者进行区分。重力流的的研究手段从野外观察到室内水槽实验,再到区域地震识别。沉积模式从单一浊流形成的"浊积扇"到多种流体相作用的"深海扇"或"海底扇"转变。由于沉积物重力流的控制因素较多,因此在重力流的概念、分类与成因上依然存在许多争议。水槽实验的不断发展,成为沉积物重力流的研究的主要途径,但实验模拟依旧存在很多问题,需不断完善水槽实验的限定因素与控制参量。 相似文献
11.
Thresholds of intrabed flow and other interactions of turbidity currents with soft muddy substrates 
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下载免费PDF全文 Jaco H. Baas Rafael Manica Eduardo Puhl Ana Luiza de Oliveira Borges 《Sedimentology》2016,63(7):2002-2036
Controlled laboratory experiments reveal that the lower part of turbidity currents has the ability to enter fluid mud substrates, if the bed shear stress is higher than the yield stress of the fluid mud and the density of the turbidity current is higher than the density of the substrate. Upon entering the substrate, the turbidity current either induces mixing between flow‐derived sediment and substrate sediment, or it forms a stable horizontal flow front inside the fluid mud. Such ‘intrabed’ flow is surrounded by plastically deformed mud; otherwise it resembles the front of a ‘bottom‐hugging’ turbidity current. The ‘suprabed’ portion of the turbidity current, i.e. the upper part of the flow that does not enter the substrate, is typically separated from the intrabed flow by a long horizontal layer of mud which originates from the mud that is swept over the top of the intrabed flow and then incorporated into the flow. The intrabed flow and the mixing mechanism are specific types of interaction between turbidity currents and muddy substrates that are part of a larger group of interactions, which also include bypass, deposition, erosion and soft sediment deformation. A classification scheme for these types of interactions is proposed, based on an excess bed shear stress parameter, which includes the difference in the bed shear stress imposed by the flow and the yield stress of the substrate and an excess density parameter, which relies on the density difference between the flow and the substrate. Based on this classification scheme, as well as on the sedimentological properties of the laboratory deposits, an existing facies model for intrabed turbidites is extended to the other types of interaction involving soft muddy substrates. The physical threshold of flow‐substrate mixing versus stable intrabed flow is defined using the gradient Richardson number, and this method is validated successfully with the laboratory data. The gradient Richardson number is also used to verify that stable intrabed flow is possible in natural turbidity currents, and to determine under which conditions intrabed flow is likely to be unstable. It appears that intrabed flow is likely only in natural turbidity currents with flow velocities well below ca 3·5 m s?1, although a wider range of flows is capable of entering fluid muds. Below this threshold velocity, intrabed flow is stable only at high‐density gradients and low‐velocity gradients across the upper boundary of the turbidity current. Finally, the gradient Richardson number is used as a scaling parameter to set the flow velocity limits of a natural turbidity current that formed an inferred intrabed turbidite in the deep‐marine Aberystwyth Grits Group, West Wales, United Kingdom. 相似文献
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Three series of density-current experiments were performed in a 5.76 m flume. In the first series, the flume was horizontal, and in the second and third, it was inclined with a positive slope and negative slope, respectively. Energy relations during successive stages of density-current movement were computed from observed data, which showed an appreciable frictional energy dissipation. The computed friction factors of our experimental density-flows were compared to the friction factors for pipe flows (Moody diagram), and while the calculated friction factor increases with increasing Reynold's number within the range of our experiments (Re 2 × 103?2 × 104), it is concluded that with increasing Reynold's number above about 5 × 104 the friction factor decreases. For natural turbidity currents, the Moody diagram gives a reasonable estimate of the friction factor between the current and sediment bed. The value of the friction factor for the interface between the current and overlying water was found to be about 0.2 times the friction factor for the current and flume. However, due to errors inherent in measuring the depth of the current, a value of 0.4 would be more reasonable for density-currents in our range of Reynold's number. Friction tends to decrease the value of the dimensionless coefficient in Keulegan's law of saline front and to decrease the thickness of the flow. In contrast, the presence of a slope in the direction of flow tends to compensate the effect of friction. The angle θc that provides the potential energy to exactly offset the energy losses incurred during movement by the density-currents in our experiments has a calculated value of 31′. An empirical formula φ= 0.935θ—0·57 relating friction, in terms of the hydraulic gradient φ, to the slope angle θ was obtained. Since the thickness of the current can be computed from the relationship between φ and θ, we estimated the thickness of naturally occurring density-currents in Swiss lakes. The results suggest the applicability of our experimental results to small turbidity currents in nature. Our analysis further indicates that large turbidity currents have a small φ and can be expected to flow very long distances on a flat abyssal plain. 相似文献
13.
EMPLACEMENT OF FLYSCH-TYPE SAND BEDS 总被引：1，自引：0，他引：1
PH. H. KUENEN 《Sedimentology》1967,9(3):203-243
Recently several attempts have been made to explain deep-sea sands or flysch-type sandstone beds by normal currents, instead of by turbidity currents. The arguments that are offered against turbidity currents and those in favour of normal currents are inconclusive. Current measurements and calculations indicate 1 m from the bottom on abyssal plains velocities are less than 30 cm/sec. The ubiquitous structures: sole markings, graded bedding, fine-grained ripple mark between a lower and a covering set of horizontal laminae, and convolution, are shown each in turn to be inexplicable on the basis of normal traction currents and the same holds for the uniform bed thickness. On the other hand these features develop readily in a circular flume from overloaded suspension currents. These experiments show that to support a heavy charge of fine sand in a clay suspension a current must exceed 100 cm/sec, and in clear water double that amount is needed. The inadequacy of normal currents both in velocity and kind is thus established. This lends powerful support to the case for turbidity currents. Many authors claim to have found evidence for the deflection of turbidity currents or for currents flowing across the paleo-slope. Explanations offered include the Coriolis force, normal currents, multiple turbidity currents, or surge waves. Analysis shows that all are open to serious doubts. The author suggests, quite tentatively, that the deflections may be only simulated by the development of lamination and grain orientation oblique and perpendicular to the current direction. Sagging of the trough floor may also play a part by confusing the determination of paleo-slope. Another possibility is that the turbidity current deviated from its original direction by “internal slope”, by momentum, by centrifugal force, or by lack of space. Admittedly, a problem remains, for the swift deposition deduced from the climbing ripples is in contradiction with the supposed stretching of the turbidity current inferred from grading. 相似文献
14.
Deposits of depletive high-density turbidity currents: a flume analogue of bed geometry, structure and texture 总被引：1，自引：0，他引：1
Flume experiments were performed to study the flow properties and depositional characteristics of high‐density turbidity currents that were depletive and quasi‐steady to waning for periods of several tens of seconds. Such currents may serve as an analogue for rapidly expanding flows at the mouth of submarine channels. The turbidity currents carried up to 35 vol.% of fine‐grained natural sand, very fine sand‐sized glass beads or coarse silt‐sized glass beads. Data analysis focused on: (1) depositional processes related to flow expansion; (2) geometry of sediment bodies generated by the depletive flows; (3) vertical and horizontal sequences of sedimentary structures within the sediment bodies; and (4) spatial trends in grain‐size distribution within the deposits. The experimental turbidity currents formed distinct fan‐shaped sediment bodies within a wide basin. Most fans consisted of a proximal channel‐levee system connected in the downstream direction to a lobe. This basic geometry was independent of flow density, flow velocity, flow volume and sediment type, in spite of the fact that the turbidity currents of relatively high density were different from those of relatively low density in that they exhibited two‐layer flow, with a low‐density turbulent layer moving on top of a dense layer with visibly suppressed large‐scale turbulence. Yet, the geometry of individual morphological elements appeared to relate closely to initial flow conditions and grain size of suspended sediment. Notably, the fans changed from circular to elongate, and lobe and levee thickness increased with increasing grain size and flow velocity. Erosion was confined to the proximal part of the leveed channel. Erosive capacity increased with increasing flow velocity, but appeared to be constant for turbidity currents of different grain size and similar density. Structureless sediment filled the channel during the waning stages of the turbidity currents laden with fine sand. The adjacent levee sands were laminated. The massive character of the channel fills is attributed to rapid settling of suspension load and associated suppression of tractional transport. Sediment bypassing prevailed in fan channels composed of very fine sand and coarse silt, because channel floors remained fully exposed until the end of the experiments. Lobe deposits, formed by the fine sand‐laden, high‐density turbidity currents, contained massive sand in the central part grading to plane parallel‐laminated sand towards the fringes. The depletive flows produced a radial decrease in mean grain size in the lobe deposits of all fans. Vertical trends in grain size comprised inverse‐to‐normal grading in the levees and in the thickest part of the lobes, and normal grading in the channel and fringes of the fine sandy fans. The inverse grading is attributed to a process involving headward‐directed transport of relatively fine‐grained and low‐concentrated fluid at the level of the velocity maximum of the turbidity current. The normal grading is inferred to denote the waning stage of turbidity‐current transport. 相似文献
15.
M. Felix 《Sedimentology》2002,49(3):397-419
A two‐dimensional numerical model is used to describe the flow structure of turbidity currents in a vertical plane. To test the accuracy of the model, it is applied to historical flows in Bute Inlet and the Grand Banks flow. The two‐dimensional spatial and temporal distributions of velocity and sediment concentration and non‐dimensionalized vertical profiles of velocity, turbulent kinetic energy and sediment concentration are discussed for several simple computational currents. The flows show a clear interaction between velocity, turbulence and sediment distribution. The results of the numerical tests show that flows with fine‐grained sediment have low vertical and high horizontal gradients of velocity and sediment concentration, show little increase in flow thickness and decelerate slowly. Steadiness and uniformity in these flows are comparable for velocity and concentration. In contrast, flows with coarse‐grained sediment have high vertical and low horizontal velocity gradients and high horizontal concentration gradients. These flows grow considerably in thickness and decelerate rapidly. Steadiness and uniformity in flows with coarse‐grained sediment are different for velocity and concentration. The results show the influence of spatial and temporal flow structure on flow duration and sediment transport. 相似文献
16.
The discharge of taconite tailings into Lake Superior at Silver Bay, Minnesota, produces turbidity current flow. The silty fine-sand tailings fraction transported to the deepest part of the lake has formed a small fan with valleys similar in gross morphology to a submarine fan. Current meters anchored 5 m above the lake floor over the wall and over the levee of a distributary valley on the fan recorded intermittent turbidity current flows during 30 weeks in 1972–73. At least twenty-five discrete periods of observation of turbidity current flow were obtained; single episodes lasted 4?328+ h. Only flows thick enough to overflow the eastern levee of the valley could be observed, and this accounts for the intermittent nature of our observations, as flow within the valleys is expected to be continuous as long as tailings are discharged. Flow velocities were higher near the valley axis where the flow is thicker. Velocities measured over the valley wall averaged 10.8 cm/s for eleven episodes; velocities measured over the levee, more than 1/2 km from the valley axis, only 3.3 cm/s. The maximum velocity during 1300 h of observation did not exceed 31 cm/s. This agrees reasonably well with velocities calculated from channel properties, as commonly done for turbidity currents on deep-sea fans. Current meters tethered above the bottom meters indicate that lake currents normally parallel the shore throughout the water column. With the onset of a turbidity current, currents higher in the water column remain unchanged but velocities near the bottom go to zero, currents then change azimuth by 90° to parallel the downslope (down-valley) direction of the fan, then increase in velocity. During a turbidity current episode, the direction of bottom flow stays relatively constant (± 20° of the down-valley trend) but the velocity oscillates (commonly with 10 cm/s amplitude), periods being of 1/2 h or less to several hours. Turbidity currents generated on Reserve Mining Company's delta are effective in carrying essentially all tailings discharged into the lake into deeper water, where they are deposited. 相似文献
17.
Modelling of turbidity currents on Navy Submarine Fan, California Continental Borderland 总被引：2，自引：1，他引：2
Several Holocene turbidites can be correlated across much of Navy Fan through more than 100 sediment core localities. The uppermost muddy turbidite unit is mapped throughout the northern half of the fan; its volume, grain-size distribution and the maximum height of deposition on the basin slopes are known. These parameters can be related to the precise channel morphology and mesotopography revealed by deep-tow surveys. Thus there is sufficient information to estimate detailed flow characteristics for this turbidity current as it moved from fan valley to distal basin plain. On the upper fan, the gradient and the increasing downstream width of the channel and only limited flow overspill suggest that the flow had a Froude number close to 1.0. The sediment associated with the channel indicates friction velocities of about 0.06 m s?1 and flow velocities of about 0.75 m s?1. Using this flow velocity and channel dimensions, sediment concentration (～2×10?3) and discharge are estimated, and from a knowledge of the total volume of sediment deposited, the flow duration is estimated to be from 2 to 9 days. It is shown that the estimates of Froude number, drag coefficient, and sediment concentration are not likely to vary by more than a factor of 2. On the mid-fan, the flow was much thicker than the height of the surface relief of the fan and it spread rapidly. The cross-flow slope, determined from the horizontal extent of turbidite sediment, is used to estimate flow velocity, which is confirmed by consideration of both sediment grain size and rate of deposition. This again allows sediment concentration and discharge to be estimated. The requirements of flow continuity, entrainment of water during flow expansion, and observed sediment deposition provide checks on all these estimates, and provide an integrated picture of the evolution of the flow. The flow characteristics of this muddy turbidity current are well constrained compared to those for more sand-rich late Pleistocene and early Holocene turbidity currents on the fan. 相似文献