Some signals are not the same as they appear: How do erosional landscapes transform tectonic history into sediment flux records?

摘要

A change in tectonics affects erosion rates across a mountain belt, leading to a period of non-steady sediment flux delivery downstream. The nonlinear relationship between tectonics and transient sediment delivery from an erosional catchment makes extraction of paleo-tectonic signals from stratigraphy challenging. We use a numerical landscape evolution model to explore how sediment flux from an erosional watershed responds to non-steady rock uplift. We focus on the time lag between the onset of a rock uplift change and the onset of a corresponding change in the sediment flux and the magnitude of the sediment flux relative to the steady rate. We observe that (1) sediment flux does not always record changes in the rock uplift rate when the duration of a rock uplift interval is less than 25% of landscape response time, or time for a landscape to transition from one steady state to another after a perturbation; (2) sediment flux response to variable rock uplift is positively correlated with the duration of rock uplift intervals; and (3) a nonlinear response between erosion rates and tectonic perturbations can result in increasing sediment flux through time even after rock uplift rate decreases. How quickly the sediment flux signal responds to a perturbation depends on how close the landscape was to steady state before the perturbation. These results illustrate conditions under which tectonic signals have the potential to be stored in the stratigraphic record or lost in an erosional system, and the importance of network dynamics for understanding signal propagation.