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How to keep sediments suspended through particle-particle interaction? Explore the magical power of particle flow!
Sediment transport is an important geological process in a variety of environments on the Earth's surface. As one of the various sediment transport mechanisms, sediment gravity flow plays an indispensable role in nature by keeping particles suspended through different sediment support mechanisms. In this article, we explore these mechanisms and gain insight into how sediment suspension is achieved through particle-particle interactions.
Sediment gravity flow is a complex and challenging subject that encompasses a wide variety of sediment transport processes.
Deposition support mechanisms
The main supporting mechanisms of sedimentation gravity flows can be divided into four types, which help particles remain suspended in the fluid. The first is granular flow, in which the interactions between particles maintain the particles in suspension and the fluid acts only as a lubricant. Collisions between particles create a diffusion pressure that helps prevent particles from settling. Although pure particle flows are relatively rare in underwater environments, interactions between particles are still crucial in high-density turbidity flows.
The second is liquefied flow, or liquefied flow, which usually occurs in non-cohesive granular materials. As particles deposited below the suspension sink, fluid is displaced upward, creating pore fluid pressure that helps suspend the upper particles. Applying external pressure, such as from an earthquake, can cause the suspended matter to start flowing, transforming the loose sand into a highly viscous suspension, similar to the phenomenon of quicksand.
The third support mechanism is a debris flow or mud flow, where particles are supported by the strength and buoyancy of the matrix. Mud and debris flows have cohesive strength, making it very difficult to predict their behavior based on the laws of physics. This makes these flows exhibit non-Newtonian fluid properties, with large particles even floating above the mud matrix.
Finally, there is turbidity flow, where particles are suspended by the fluid turbulence within the flow. The behavior of turbidity flows is largely predictable and exhibits the behavior of a Newtonian fluid, in contrast to flows with cohesive strength, such as mud and debris flows.
In underwater environments, the flow behavior of turbidity currents is strongly influenced by the flow concentration.
Results of Sedimentation
Depositions formed by these four sedimentation support mechanisms occur in nature. While pure particle flows are primarily confined to aeolian environments, underwater environments are diverse, with mud and debris flows to high- and low-density turbidity flows coexisting. These transitional flows are collectively referred to as hybrid event beds (HEBs), connecting clays, and slurry beds, all of which exhibit a transition in flow regime.
Grain flow sediments are characterized by an upward distribution of particle sizes (reverse grading), which results from the fact that during interparticle collisions, smaller particles sink between larger particles and are eventually preferentially removed. Deposit at the bottom of the flow. Liquefaction flow deposits are characterized by structures containing escaped fluid, such as disks, which are caused by rising fluid in the flow.
Debris flow deposits are characterized by a bimodal distribution of particle sizes, with larger particles or lumps floating in a fine-grained clay matrix. Because of the cohesive strength of the mud matrix, this allows larger particles to remain suspended above the sludge material and ultimately remain at the upper interface of the sediment.
The sediments of low-density turbidity currents (turbid sands) are characterized by sedimentary structures with gradually decreasing energy, commonly referred to as Bouma sequences.
Modern and ancient examples
Different types of sedimentary gravity flows, whether modern or ancient, form distinctive depositional patterns that help scientists understand the evolution of these processes and environmental changes. The preservation of organic matter in these sediments and their subsequent burial and maturation processes also suggest a close connection with the formation of oil and gas.
ImportanceSedimentary gravity flows, particularly turbidity currents, mudflows and debris flows, are believed to be the processes primarily responsible for depositing sand to the deep ocean floor. Because the anoxic environment of the deep ocean favors the preservation of organic matter, these sedimentary processes may eventually form oil and gas reservoirs. Therefore, sediments in the deep sea are not only the focus of geological research, but are also closely related to global energy resources.
These natural phenomena demonstrate the power of interaction between particles and the wonders of nature. Can they inspire us to think more deeply about nature?
