Knickpoints as geomorphic markers of active tectonics: a case study from northeastern Sicily (southern Italy)

Unsteady base-level fall at river mouths generates knickpoints that migrate as a transient upstream through the drainage network, climbing at the same rate as long as the fluvial erosion process follows a detachment-limited stream power law. Here we demonstrate unsteady and nonuniform rock uplift using knickpoints as geomorphic markers in streams draining the eastern flank of the Peloritani Mountains (northeast Sicily), the footwall of an ~40-km-long offshore northeast-southwest-oriented normal fault where the uplift is documented by a flight of mapped and dated Pleistocene marine terraces. Using slope-area analysis on the major streams, we project the tops of prominent knickpoints down to the coast, intersecting the marine terraces, thus providing an age for that specific knickpoint and the paleo-longitudinal profile. We model the migration rate of those dated knickpoints to locally solve for the parameters in the detachment-limited stream power law, and apply the results to model the age of other knickpoints with no clear connection to marine terraces. In summary, we demonstrate that the eastern Peloritani Mountains have been nonuniformly uplifted in an along-strike elliptical pattern, consistent with the general model for the footwall of an active normal fault. A calculation of the long-term erosion rate by the volume beneath the dated paleo-longitudinal profiles reveals a tight positive nonlinear relationship with the modeled normalized channel steepness (ksn). Our analysis provides a method for using knickpoints as geomorphic markers in steep, rapidly eroding landscapes that commonly lack datable river terraces.