Depositional Processes of Submarine Debris Flows in the Miocene Fan Deltas, Pohang Basin, SE Korea with Special Reference to Flow Transformation
Depositional Processes of Submarine Debris Flows in the Miocene Fan Deltas, Pohang Basin, SE Korea with Special Reference to Flow Transformation
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DOI：
10.1306/2dc40922-0e47-11d7-8643000102c1865d
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发表时间：
2000-05
影响因子：
2
通讯作者：
Y. Sohn
中科院分区：
文献类型：
--
作者：
Y. Sohn
水下泥石流经历了各种流动转变，包括表面物质的稀释和剥离，环境水渗透到流动内部，以及滑水流动前缘的分离和解体。表面转化是一个自我限制的过程，因为该过程的产物，如压倒性的悬浮沉积物云或在流动前沿的砾石装甲，抑制有效的工作过程。因此，泥石流转化的程度在很大程度上取决于泥石流是否发生滑水。对于水下泥石流，其密度弗劳德数应大于0.4，孔隙压力衰减的时间尺度应大于泥石流的持续时间。此外，泥石流应该没有一个非常渗透周围的透空砾石流头，因为高压力不能维持下面的砾石材料。详细的沉积测量和流动特性的估计，在中新世扇三角洲在韩国东南部的三个泥石流床表明，只有一个卵石泥石流与泥质（不透水）矩阵hydroplaned。另一方面，巨砾泥石流被解释为没有滑水，无论性质的矩阵。Nonhydroplaning泥石流主要受到表面改造和outrunn由表面改造的悬浮泥沙流和泥石流块后，流量进入一个基地的斜坡设置。因此，非滑水泥石流沉积物覆盖在浊流和碎屑福尔斯沉积物之上。在滑水泥石流的情况下，大块的碎片可以从流动前沿分离，反复形成一系列的小体积流，在主机泥石流的前面进行。前面的流动迅速稀释，产生大量的悬浮沉积物云，并被快速移动的宿主泥石流所超越。因此，滑水泥石流形成的存款与厚而广泛的浊流沉积物有关，浊流沉积物可能位于主泥石流存款之下或之上。与滑水泥石流相关联的浊流沉积物与非滑水泥石流相区别在于，前者包含丰富的砾石碎屑和分选不良且富含碎屑的碎屑块，这些碎屑块不能通过表面转化过程悬浮，但更可能来自滑水泥石流的分离前缘。浊流沉积物的沉积体积和粒度的差异以及相关碎屑和浊流的堆积模式提供了水下泥石流行为的线索。
ABSTRACT Subaqueous debris flows undergo various flow transformations, involving dilution and stripping of surface materials, penetration of ambient water into the flow interior, and detachment and disintegration of hydroplaning flow fronts. The surface transformation is a self-limiting process because the products of the process, such as an overriding suspended-sediment cloud or an armor of gravel at the flow front, inhibit effective working of the process. The degree of flow transformation therefore depends largely on whether a debris flow hydroplanes or not. For a subaqueous debris flow to hydroplane, its densiometric Froude number should be larger than 0.4, and the time scale of pore-pressure decay should be larger than the duration of a debris flow. In addition, a debris flow should be devoid of an extremely permeable girth of openwork gravel around the flow head because high pressures cannot be sustained underneath the gravelly material. Detailed sedimentological measurements and estimation of flow properties for three debris-flow beds in the Miocene fan deltas in SE Korea suggests that only a pebbly debris flow with a muddy (impermeable) matrix hydroplaned. On the other hand, bouldery debris flows are interpreted to have not hydroplaned irrespective of the nature of matrix. Nonhydroplaning debris flows were subject mainly to surface transformation and were outrun by surface-transformed suspended-sediment flows and debris-fall blocks after the flows entered a base-of-slope setting. Deposits of nonhydroplaning debris flows therefore overlie deposits of turbidity currents and debris falls. In the case of a hydroplaning debris flow, large chunks of debris could be detached from the flow front repetitively to form a series of small-volume flows that proceeded in front of the host debris flow. The preceding flows were promptly diluted to produce voluminous suspended-sediment clouds and were outrun by the faster-moving host debris flow. A deposit from a hydroplaning debris flow is therefore associated with thick and extensive turbiditic deposits that may either underlie or overlie the host debris-flow deposit. The turbiditic deposits associated with a hydroplaning debris flow are distinguished from those of a nonhydroplaning debris flow in that the former contain abundant gravel clasts and chunks of poorly sorted and clast-rich debris that cannot be suspended by the surface transformation process but were more likely derived from the detached fronts of a hydroplaning debris flow. These differences in sediment volume and grain size of turbiditic deposits and the stacking pattern of related debrites and turbidites provide a clue to the behavior of subaqueous debris flows.