Nature and Causes of Autogenic Responses in Landscapes and Terrestrial Sedimentary Basins: A Landlab Modeling Study

Landscape and basin margin evolution are classically studied separately. Naturally, erosion and sediment transport processes act across landscapes to source the terrestrial fills of basins, resulting in a coupled source to sink system. We explore the evolution of an erosional landscape that couples to a developing half-graben basin using a Landlab numerical model and investigate the system response to steady tectonic forcing. This setup allows for separation of the self-organized response of the system ("autogenic dynamics") from the response due to the allogenic forcing. The numerical model couples hillslope creep through linear diffusion to channelized erosion, transport, and deposition via the SPACE model that transitions between detachment-limited and transport-limited behavior. Non-uniform but steady tectonic uplift acts on the footwall of a major normal fault while non-uniform and steady subsidence acts on the hanging wall throughout a 3 Myr model run. Initial results indicate that the system reaches dynamic equilibrium after ~ 1 Myr. Drainage rearrangement in both the source and sink illustrate a non-steady landscape even after dynamic equilibrium is reached. In the depositional realm, lateral channel mobility and unsteady erosion and deposition rates prevent the sediment thickness from reaching a constant steady-state, yet the basin depth tends toward a long-term dynamic equilibrium. Stratigraphic evolution shows that under steady forcing, strata preserve similar geometries indicative of intervals of erosion and deposition, with no cyclicity. Spectral analyses of deposition/erosion rates in the basin indicate a degree of stochasticity preserved in strata from autogenic processes. Sediment thickness residuals (due to system reorganization) are also dominantly scattered. We conclude that autogenic dynamics in the sinks of some terrestrial landscapes, with processes like those modeled in Landlab, may lack cyclicity and are best described as stochastic regardless of the nature of allogenic forcing. The lack of auto-cyclicity has implications for the interpretation of stratigraphy.