Geometric Modeling of Submarine Channel-Levee Systems: Complex Architecture from Simple Rules

Submarine channels and valleys are often thought to have a complex history of cut-and-fill and a corresponding multi-scale hierarchy of erosional surfaces. The scales of the erosional surfaces are often linked to flow size, larger cuts being eroded by larger flows and later filled by ‘underfit' currents.

We have developed a three-dimensional model using relatively simple geometric rules, based on field observations and fundamental flow process models, that provides new insights into the formation of these channel-levee systems. In the model, channel centerlines migrate gradually except when meander cutoffs develop. Assuming that the system has a characteristic discharge, the channel cross-sectional dimensions are kept constant. A vertical channel centerpoint trajectory defines the amount of aggradation or incision during each time step and represents the long-term incision/aggradation history of the channel. Levees are modeled as thin wedges of sediment tapering away from the basic channel form that drape the underlying topography.

The model results suggest that complicated architectures and multi-scale erosional surfaces can form without repeated cut-and-fill at different scales, and that development of large valley fills does not require a switch from large erosional flows to small depositional currents. Rather, valley fills can be modeled as the result of the migration of a channel form of constant size during a single incision-aggradation cycle. Erosional surfaces larger than the basic channel form are time-transgressive and can be significantly different from the geomorphological expression of the system at any time.

Our model reproduces observations from high-resolution 3D seismic data accurately and it raises a number of questions regarding the interpretation of outcrops, particularly in terms of timing of erosion and deposition in channels.