Normal fault control on bedrock channel incision and sediment supply: Insights from numerical modeling

The evolution of footwall drainage basins, sediment supply and hanging wall stratigraphy in rift basins is investigated using a coupled numerical model of detachment- limited stream network evolution and coarse-grained fan delta deposition. The response of bedrock channel networks to repeated footwall uplift events leads to increasing sediment supply over tens of thousands of years as the networks initiate and then expand, followed by relatively constant sediment supply as the stream networks reach their maximum spatial extent. The distinct time lag between the onset of tectonic activity and attainment of maximum sediment supply leads to stratigraphies that are initially aggradational and then progradational. Much of the variation in sediment supply is the product of the complex response and reorganization of the stream networks to faulting-related perturbations and is not directly related to specific faulting events. Increasing fault displacement drives the system toward a new steady state with a higher sediment supply but is initially expressed as a retrogradation as sediment supply lags behind increased displacement. The converse is true for a decrease in fault displacement, which is initially expressed as progradation. Continual stochastic variation in recurrence interval leads to a system that does not achieve a steady state and as a result exhibits continual variation in sediment supply. The model results emphasize the local tectonic controls on stratigraphic architectures developed within extensional basins and the complex manner in which stream network growth and response to tectonic activity can be expressed in the stratigraphic record.