A MODEL FOR PREDICTING THE SEDIMENTOLOGICAL FEATURES OF TURBIDITE DEPOSITS.

T Mulder,J.P.M Syvitski

doi:10.5724/gcs.94.15.0023

T Mulder, J.P.M Syvitski

https://doi.org/10.5724/gcs.94.15.0023

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Publication Date: Dec 1, 1994

Citations: 20

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A numerical model useful for the prediction of the runout distance, deposit dimensions, and internal properties of turbidity current deposits is proposed. The model uses an integrated formulation of the Chezy equation and includes geotechnical properties (shear strength) of seafloor sediments. The model is applied to a historical flood of the Saguenay River (Quebec, Canada) that created a month-long turbidity current that flowed along the seafloor of the Saguenay Fjord. Model simulation of plume acceleration includes the effects of fluid drag at both the bottom and top of the plume, and grain friction within the plume is modelled as a function of volumetric concentration. Entrainment of sea water is computed to increase the volume of the plume by a factor of five. The model also includes the effects of plume pushing as a function of the rising and the falling limbs of the flood event. Sediment deposition is assessed using removal rate values published by Syvitski and Lewis (1992). Deposition of sediment depends very much on the phase of the river flood event. Measured peaks in the thickness of the turbidite deposit are simulated by the model and correspond to a progressive shift seaward in the location where deposition begins. During the initial phase of the flood event, and until the peak discharge, the turbidite is inversely graded and coarse particles (sand and core silts) represents more than 75% of the weight of the sediment deposited. During the decreasing discharge phase, initial deposition progressively shifts landward and deposition of the finer size fractions (medium silts and finer) dominate. The simulated turbidite is then well graded and matches both core lithology and deposit thickness and runout distance. Our numerical model can also be applied to large ignitive turbidity current events and their deposits, providing a useful tool in the prediction of reservoir properties of submarine fans, e.g. porosity and permeability.

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