THE EFFECT OF CLAY TYPE ON THE PROPERTIES OF COHESIVE SEDIMENT GRAVITY FLOWS AND THEIR DEPOSITS
THE EFFECT OF CLAY TYPE ON THE PROPERTIES OF COHESIVE SEDIMENT GRAVITY FLOWS AND THEIR DEPOSITS
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DOI：
10.2110/jsr.2017.63
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发表时间：
2017-11-01
影响因子：
2
通讯作者：
Barker, Simon
中科院分区：
文献类型：
--
作者：
Baker, Megan L.;Baas, Jaco H.;Barker, Simon
粘粒是地球上最丰富的沉积物类型之一，而水下粘粒重力流（SGF）将大量沉积物输送到海洋中，但目前对粘粒沉积物重力流（SGF）及其沉积物的了解有限。锁交换实验进行了对比SGF负载无粘性的二氧化硅粉，弱粘性高岭石，和强粘性膨润土的流动行为，头部速度，跳动距离，和存款几何形状在很宽的范围内悬浮泥沙concentrations.The三种沉积物类型共享相似的趋势，他们开发的类型的流，这些流的最大头部速度，和存款形状。随着悬沙浓度的增加，水流类型由低密度浊流→高密度浊流→泥石流→滑坡。作为增加流动密度的函数，LDTC和相对稀的HDTC的最大水头速度增加，而泥流，幻灯片，和相对密集的HDTC的最大水头速度下降。最大水头流速的增加是由悬浮泥沙的湍流支持和水流与周围流体之间的密度差驱动的。在最大头速度的减少，包括湍流的衰减颗粒之间的摩擦相互作用的二氧化硅粉流和普遍的凝聚力的高岭石和膨润土流。在体积浓度为47%、最大水头流速为0.75 m s（-1）时，石英粉的流动由粘性驱动转变为摩擦驱动;高岭石和膨润土的粘性驱动转变为粘性驱动的阈值分别为22%和0.50 m s（-1）、16%和0.37 m s（-1）。HDTC产生的沉积物呈楔形，并有块状向下流动的延伸部分，泥石流产生的沉积物呈楔形，并有部分或完全分离的外转块，滑坡产生的沉积物呈楔形，但没有延伸部分。对于泥流、滑坡和大多数HDTC，需要越来越高的浓度，以分别产生携带膨润土、高岭石和二氧化硅粉的流的类似最大水头速度和流出距离。强粘性的膨润土流能够创建一个更强的网络的颗粒债券比弱粘性的高岭石流相似的浓度。当浓度达到52%时，流场仍保持移动的，只有当浓度超过47%时，摩擦力才能抵消流场的过剩密度，减弱流场中的湍流。对实验数据的量纲分析表明，失效前悬浮体的屈服应力可以用来预测SGF的跳动距离和无量纲头部速度，与粘土类型无关。外推到自然环境表明，高密度的SGF承载弱粘性粘土达到更大的距离，从他们的起源比流，在类似的悬浮泥沙浓度进行强粘性粘土，而相当的细粒，非粘性SGF旅行最远。载有不同粘土矿物的细粒SGF的对比行为可能会延伸到深海系统中大规模沉积体结构的差异。
The present knowledge of cohesive clay-laden sediment gravity flows (SGFs) and their deposits is limited, despite clay being one of the most abundant sediment types on earth and subaqueous SGFs transporting large volumes of sediment into the ocean. Lock-exchange experiments were conducted to contrast SGFs laden with noncohesive silica flour, weakly cohesive kaolinite, and strongly cohesive bentonite in terms of flow behavior, head velocity, runout distance, and deposit geometry across a wide range of suspended-sediment concentrations.The three sediment types shared similar trends in the types of flows they developed, the maximum head velocity of these flows, and the deposit shape. As suspended-sediment concentration was increased, the flow type changed from low-density turbidity current (LDTC) via high-density turbidity current (HDTC) and mud flow to slide. As a function of increasing flow density, the maximum head velocity of LDTCs and relatively dilute HDTCs increased, whereas the maximum head velocity of the mud flows, slides, and relatively dense HDTCs decreased. The increase in maximum head velocity was driven by turbulent support of the suspended sediment and the density difference between the flow and the ambient fluid. The decrease in maximum head velocity comprised attenuation of turbulence by frictional interaction between grains in the silica-flour flows and by pervasive cohesive forces in the kaolinite and bentonite flows. The silica-flour flows changed from turbulence-driven to friction-driven at a volumetric concentration of 47% and a maximum head velocity of 0.75 m s(-1); the thresholds between turbulence-driven to cohesion-driven flow for kaolinite and bentonite were 22% and 0.50 m s(-1), and 16% and 0.37 m s(-1), respectively. The HDTCs produced deposits that were wedge-shaped with a block-shaped downflow extension, the mud flows produced wedge-shaped deposits with partly or fully detached outrunner blocks, and the slides produced wedge-shaped deposits without extension. For the mud flows, slides, and most HDTCs, an increasingly higher concentration was needed to produce similar maximum head velocities and runout distances for flows carrying bentonite, kaolinite, and silica flour, respectively. The strongly cohesive bentonite flows were able to create a stronger network of particle bonds than the weakly cohesive kaolinite flows of similar concentration. The silica-flour flows remained mobile up to an extremely high concentration of 52%, and frictional forces were able to counteract the excess density of the flows and attenuate the turbulence in these flows only at concentrations above 47%.Dimensional analysis of the experimental data shows that the yield stress of the pre-failure suspension can be used to predict the runout distance and the dimensionless head velocity of the SGFs, independent of clay type. Extrapolation to the natural environment suggests that high-density SGFs laden with weakly cohesive clay reach a greater distance from their origin than flows that carry strongly cohesive clay at a similar suspended-sediment concentration, whilst equivalent fine-grained, noncohesive SGFs travel the farthest. The contrasting behavior of fine-grained SGFs laden with different clay minerals may extend to differences in the architecture of large-scale sediment bodies in deep marine systems.