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