Knickpoint retreat and landscape preservation along main fault escarpments of the Mexican Basin and Range: The case of the southern sector of the Sierra Madre Occidental (Mexico)

Estimating how landscapes adjust to tectonic activity has been a major topic in the geomorphological research of tectonically active settings. The formation and propagation of knickpoints through the fluvial network is central to these studies since such features are a mobile boundary between a landscape adjusting to a new erosive regime, controlled by the recent tectonic activity, and a relict landscape upstream, which corresponds to the pre-existing erosive regime. The latter illustrates how landscapes can prevail across timescales ranging from ca. 101 to 106 years. We analyzed the perched landscape surfaces of the southern sector of the Sierra Madre Occidental (SMO), an igneous province mainly formed during Late Oligocene to Early Miocene tectonic extension, to confirm whether those surfaces are a relict landscape. We found that knickpoints close to main fault escarpments bounding the perched surfaces do not have significant differences in their elevation, retreat distance from grabens and half-grabens and time of migration. Moreover, the knickpoint retreat distance scales with drainage area. Our data indicate that the top surfaces of the SMO correspond to a relict landscape that contrasts with the landscape below which is in transience. The relict landscape coexists with a westward migrating tectonic activity that has produced the steepening of the landscape and the migration of mobility of divides on the southwestern sector of the SMO.