An Analytical Model to Predict the Sediment Flux of Each Grain-Size Class in Turbidity Current Flow; Application to Gold Channel, Tres Pasos Formation, Chile
Winda Novianti, .
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A turbidity current is the most prominent agent for transporting sediment from the continental shelf to the basin floor. However, direct monitoring of modern turbidity currents is difficult to carry out. Meanwhile, sediment flux estimation which is particularly based on different particle size is important for many applications such as the indicating whether a turbidite sandstone is suitable to be a hydrocarbon reservoir. A study by Eggenhuisen (unpublished) has led to the development of the Sediment Budget Estimator (SBE). This tool can reconstruct sediment flux from ancient turbidity current deposits. The SBE models the flow structure, consisting of velocity and suspended-sediment concentration profile, and later uses this information to reconstruct the sediment flux. However, the equation used to model the concentration profile is only an adhoc exponential equation which neglects how each grain-size class is distributed differently throughout the water column. The main achievement of this study is to replace the decay exponential equation and incorporate the Rouse Equation into a new SBE. The Rouse equation should only be applied to open channel flow but can also to be applied to submarine turbidity currents, regardless of the difference of their flow structure. The benefit of incorporating the Rouse equation is that it can model the sediment concentration for each grain-size class, and thereby, the sediment flux. This study aims to apply the new version of SBE to reconstruct the sediment flux of turbidity currents of each grain-size class throughout the Gold Channel, Tres Pasos Formation, Chile. To achieve our goal, we conduct a grain-size distribution analysis of the Gold Channel deposit. Subsequently, to reconstruct the sediment flux using the new SBE, the boundary condition for this model needs to be defined. For this, the new SBE requires (1) the grain-size distribution at 10th, 50th, and 90th percentile from a single sample at the reference level (the base of channel axis) and (2) basin configuration and characteristic of feeder channel data obtained from the literature studies of the chosen turbidity current system. The grain-size distribution of the Gold Channel indicates that it is dominated by fine-sand particles and has a coarsening trend towards medium sand in the channel margin. Contrastingly, the total sediment budget produced by the new SBE shows that the Gold Channel is 99% dominated by very-fine-sand particles, 4.99 x 107 m3. Meanwhile, fine-sand (2.42 x 106 m3) and medium-sand particles (961.3 m3) are only concentrated at the base and cannot be suspended higher in the flow.