2DV numerical simulations of turbidites in ponded basins: Insights from depositional patterns

Abstract

A coarsening upward signature is expected for turbidites in ponded basins based on the fill-and-spill model. However, this model might be to simplistic. This study aims to identify how grain size composition and sill height affect the depositional patterns of turbidites within a 2DV ponded basin. A numerical modelling approach is adopted here and the open source software Delft3D is used to create a 2DV model of a ponded basin on a continental slope. A dataset of 15 model series was created to assess the influence of both initial composition and sill height of the ponded basin on the depositional patterns. Each series consisted of 4 or 5 surge-type turbidity current events. The presence of more cohesive material in the initial sediment composition results in larger amounts of erosion and larger currents. Two contradictory trends in grain size with decreasing sill height are observed. At the temporal and spatial scale of individual turbidites, a fining upward stacking pattern is found in the deposits. This is attributed to autogenic coarsening of the substrate. At the temporal and spatial scale of lobes or lobe complexes, the effects of flow stripping in a fill-and-spill basin are recognizable in the depositional characteristics of the turbidites. The contradiction between the two temporal and spatial scales illustrates that at a larger scale, the main autogenic process of coarsening of the substrate on the slope is counteracted by constant background sedimentation or changes in allogenic processes. These processes are put forward as controls on the recurrence interval of self-accelerating turbidity currents. Due to the displayed sensitivity of turbidity currents to changes in substrate erodibility, continued research regarding the influence of cohesive material and consolidation on turbidity current - bed interaction is recommended.