The internal structure of deposits emplaced under upper plane bed / sheet flow transport conditions: Laboratory experiments and numerical modeling

恩里卡·维帕雷利（enrica Viparelli）， earr -1250641，南卡罗莱纳大学（University of South carolina）摘要：风暴和浊流侵位的岩石沉积物的特征是：在块状单元下面有一个较低的侵蚀边界，依次是平行层状单元和交叉层状单元。这种矿床被解释为由于能量流减弱而形成的。块状单元在宏观上是无结构的，即在沉积物中没有可见的沉积物颗粒组织。在层状单元中，不同大小的沉积物颗粒以可见的图案沉积。本研究的主要目的是调查和模拟导致块状和平行层状单元就位的水流和泥沙输送条件。实验室和野外研究表明，平行层状单元是在称为上平面床状态的泥沙输送条件下放置的。这些条件的特点是：1)一个1或2个粒径厚的移动层质，以及2)下游迁移的低振幅层质。由于平行层状单元是在上平面地层状态下沉积的，基底单元必须在更强的搬运条件下就位。本研究的中心假设是：1)这些强烈的输运条件对应于片流，这是一种以10-100个粒径厚的层状层为特征的层状层输运模式；2)片流层可以抑制平行层状的形成；3)这种抑制作用导致在持续沉积条件下放置沉积物的颗粒结构趋于均匀化。必须承认，薄片流并不是产生大量矿床的唯一机制，但在油田规模上，它的运行条件通常是可以满足的。在初步室内实验结果的基础上，提出了块状与平行层状沉积物沉积特征的实验和数值计算程序。明渠，即河流样，将进行实验室实验，以建立一个沉积在上制度平面床和板流运输条件下。这种实验设置的选择是由需要在实验室规模的板流状态下诱导沉积物沉积决定的。然而，这些实验将专门设计为模拟强烈的净沉积水下流动。数值程序的中心是开发一个模型，该模型能够再现上平面床和板流输送条件下沉积的颗粒结构。该模型将根据实验结果进行验证。实验室和数值工作的结果将提供必要的信息，以i)表征上平面床和板流运输机制的一般力学特征，以及ii)将沉积物的颗粒结构与流动和沉积物运输的特征联系起来。因此，它们有望对研究水下沉积过程、沿海和深水工程的社区产生变革性影响。一名研究生将带头进行实验和数值工作，以继续他的博士研究。他还将负责组织实验室和数值数据，并通过CDSMS和NCED资料库及时传播这些数据。将在三年内聘请四名本科生，通过本科生研究项目为研究生学习做准备，这些研究项目将由PI直接监督。

The internal structure of deposits emplaced under upper plane bed/sheet flow transport conditions: Laboratory experiments and numerical modelingEnrica Viparelli, EAR-1250641, University of South CarolinaABSTRACTRock deposits emplaced by storms and turbidity currents can be characterized by a lower erosional boundary underlying a massive unit followed in ascending order by a parallel laminated unit and a cross laminated unit. Such deposits are interpreted to be emplaced by waning energy flows. Massive units are macroscopically structureless, i.e. there is not a visible organization of sediment particles within the deposit. In the laminated units, sediment particles of different size are deposited with visible patterns.The main objective of this research is to investigate and model flow and sediment transport conditions that are responsible for the emplacement of massive and parallel laminated units. Laboratory and field studies demonstrate that parallel laminated units are emplaced under sediment transport conditions known as upper plane bed regime. These conditions are characterized by i) a moving bedload layer one or two grain diameters thick, and ii) downstream migrating low amplitude bedforms. As the parallel laminated unit is deposited under upper plane bed regime, the basal unit has to be emplaced under more intense transport conditions. The central hypotheses of the proposed research are that i) those intense transport conditions correspond to sheet flow, which is a mode of bedload transport characterized by a bedload layer 10-100s grain diameters thick, ii) the sheet flow layer can suppress the formation of parallel laminations, and iii) this suppression results in a tendency to homogenize the grain fabric of the emplaced deposit under conditions of continued deposition. It must be acknowledged that sheet flow is not the only mechanism that produces massive deposits, but the conditions for it to operate can be commonly met at field scale.Based on the results of preliminary laboratory experiments, an experimental and numerical program is proposed to characterize the deposition of massive versus parallel laminated deposits. Open channel, i.e. river-like, laboratory experiments will be performed to build a deposit under upper regime plane bed and sheet flow transport conditions. The choice of this experimental setting is dictated by the need to induce sediment deposition in the sheet flow regime at laboratory scale. However, the experiments will be specifically designed to model intense and net-depositional subaqueous flows. The numerical program is centered on the development of a model that is able to reproduce the grain fabric of the deposits emplaced under upper plane bed and sheet flow transport conditions. The model will be validated against the experimental results. The results of the laboratory and numerical work will provide the necessary information to i) characterize the mechanics of upper plane bed and sheet flow transport regimes in general, and ii) relate the grain fabric of the deposit to the characteristics of the flow and the sediment transport. They are thus expected to have a transformative impact on the communities studying subaqueous sedimentary processes, coastal and deep-water engineering. One graduate student will take the lead in the performance of the experimental and numerical work to pursue his PhD research. He will also be responsible for the organization of the laboratory and numerical data and for their timely dissemination through the CDSMS and the NCED repositories. Four undergraduate students will be hired in three years to prepare them for graduate studies via undergraduate research projects that will be directly supervised by the PI.