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Sedimentological regimes for turbidity currents: Depth‐averaged theory
Author(s) -
Halsey Thomas C.,
Kumar Amit,
Perillo Mauricio M.
Publication year - 2017
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc012635
Subject(s) - turbidity current , turbulence , geology , dimensionless quantity , sedimentary depositional environment , erosion , sediment , turbidite , sedimentation , deposition (geology) , current (fluid) , flow (mathematics) , entrainment (biomusicology) , gravity current , mechanics , geomorphology , hydrology (agriculture) , oceanography , geotechnical engineering , physics , structural basin , rhythm , acoustics , internal wave
Turbidity currents are one of the most significant means by which sediment is moved from the continents into the deep ocean; their properties are interesting both as elements of the global sediment cycle and due to their role in contributing to the formation of deep water oil and gas reservoirs. One of the simplest models of the dynamics of turbidity current flow was introduced three decades ago, and is based on depth‐averaging of the fluid mechanical equations governing the turbulent gravity‐driven flow of relatively dilute turbidity currents. We examine the sedimentological regimes of a simplified version of this model, focusing on the role of the Richardson number Ri [dimensionless inertia] and Rouse number Ro [dimensionless sedimentation velocity] in determining whether a current is net depositional or net erosional. We find that for large Rouse numbers, the currents are strongly net depositional due to the disappearance of local equilibria between erosion and deposition. At lower Rouse numbers, the Richardson number also plays a role in determining the degree of erosion versus deposition. The currents become more erosive at lower values of the product Ro × Ri, due to the effect of clear water entrainment. At higher values of this product, the turbulence becomes insufficient to maintain the sediment in suspension, as first pointed out by Knapp and Bagnold. We speculate on the potential for two‐layer solutions in this insufficiently turbulent regime, which would comprise substantial bedload flow with an overlying turbidity current.