ABSTRACT: A Numerical Model of High-Density Turbidity Current Sedimentation

Jianjun Zeng, Donald R. Lowe

Sediment deposition from high-density turbidity currents is controlled by the concentration and sorting of their suspended loads. The collapse of highly concentrated suspended sediment clouds has been studied quantitatively using a modified one-dimensional drift-flux model for multiphase systems. The model simulates sedimentation from initially homogeneous suspensions containing up to N size populations and having size distribution patterns resembling those of natural detrital sediments. Deposition begins with the formation and fall of interfaces as size populations settle with different velocities through their apparent fluids, which are mixtures of the ambient fluid and finer particles. The sediment/fluid interface rises at a rate given by the total sediment flux. The r lative movement between particles and the apparent fluid, the rise of the sediment/water interface, and the grain-size makeup of the resulting bed are computed iteratively until all interfaces merge with the sediment/water interface. Preliminary results show that high suspended sediment concentration and wide size range hinder the settling of both large and small particles and inhibit dynamic sorting. Variations in starting sediment concentration and sorting result in graded beds having a wide range of internal textures. The model provides a quantitative interpretation of the formation of graded beds during the rapid collapse of high-density turbidity currents in terms of the original suspended sediment concentration and size distribution. It represents an initial step toward a quantitat ve model predicting the downslope textural and structural variation of coarse-grained, thick-bedded turbidites.

AAPG Search and Discovery Article #91003©1990 AAPG Annual Convention, San Francisco, California, June 3-6, 1990