Abstract
Abstract. Turbidity currents are one of the main drivers of sediment transport from the continental shelf to the deep ocean. The resulting sediment deposits can reach hundreds of kilometres into the ocean. Computer models that simulate turbidity currents and the resulting sediment deposit can help us to understand their general behaviour. However, in order to recreate real-world scenarios, the challenge is to find the turbidity current parameters that reproduce the observations of sediment deposits. This paper demonstrates a solution to the inverse sediment transportation problem: for a known sedimentary deposit, the developed model reconstructs details about the turbidity current that produced the deposit. The reconstruction is constrained here by a shallow water sediment-laden density current model, which is discretised by the finite-element method and an adaptive time-stepping scheme. The model is differentiated using the adjoint approach, and an efficient gradient-based optimisation method is applied to identify the turbidity parameters which minimise the misfit between the modelled and the observed field sediment deposits. The capabilities of this approach are demonstrated using measurements taken in the Miocene Marnoso-arenacea Formation (Italy). We find that whilst the model cannot match the deposit exactly due to limitations in the physical processes simulated, it provides valuable insights into the depositional processes and represents a significant advance in our toolset for interpreting turbidity current deposits.
Highlights
1 Introduction Turbidity currents are density currents driven by sediment particles that are suspended by turbulence in the containing fluid (Lowe, 1979)
This paper presents a shallow water sediment-laden density current model, released under the name AdjointTurbidity 1.0, that uses a novel finite-element mixed discontinuous Galerkin function space with adaptive time stepping
5 Conclusions This paper has presented a novel implementation of the shallow water equations for modelling density currents using a mixed finite-element formulation
Summary
Turbidity currents are density currents driven by sediment particles that are suspended by turbulence in the containing fluid (Lowe, 1979). This could involve the definition of a static lock-release laboratory configuration with uniform sediment depth and a single, uniform sediment grain size Such a simple configuration would at least require the definition of the initial depth of the current, the concentration of sediment in the fluid, the ratio of initial depth to length, and the parameters controlling the particle settling velocity and flow front speed. A gradient-based optimisation technique is applied to minimise the data misfit between the modelled sediment deposit and field measurements taken in the Miocene Marnoso-arenacea Formation Into account the viscous forces impeding the flow motion at the base and top of the flow This model has been applied to large-scale turbidity currents (Fukushima et al, 1985; Huang et al, 2009). The model used in this paper is based upon the single layer shallow water model of Bonnecaze et al (1993)
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