Paper No. 281-10
Presentation Time: 10:55 AM
INTERPLAY OF ROCK UPLIFT, EUSTASY, CLIMATE, AND KNICKPOINT MIGRATION ON THE RATE OF LANDSCAPE EVOLUTION: A CASE STUDY FROM NORTHEAST SICILY, ITALY
Unsteady base level fall at river mouths generates transient knickpoints that climb vertically upstream at the same rate as long as the fluvial erosion process follows a detachment-limited stream power law. Here, we demonstrate unsteady and non-uniform rock uplift, and the erosional response of the landscape using knickpoints as geomorphic markers in streams draining the eastern flank of the Peloritani Mountains (NE Sicily), the footwall of a ~40 km long, offshore, NE-SW oriented normal fault where the uplift is documented by a flight of mapped and dated late 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-long 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 find that the Peloritani Mountains have been non-uniformly 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 of rock removed beneath the dated paleo-long profiles reveals a tight, positive, non-linear relationship with the modeled, normalized channel steepness (ksn). Long-term erosion rates, range between 215 - 920 mm/kyr with an average ~450 mm/kyr, roughly half of published alluvial TCN-determined rates for one of our study basins underscoring the importance of the landsliding process towards the headwaters of the basins upstream of the knickpoints. In comparison, the rate of vertical incision ranges between ~390 - 1180 mm/kyr, with average value of ~690 mm/kyr, shows an apparent deceleration over time perhaps related to significant Holocene valley bottom aggradation. In summary, our analysis provides a method for using knickpoints as geomorphic markers in steep, tectonically deformed, rapidly eroding landscapes that commonly lack other geomorphic markers as well as a complimentary method to alluvial TCN erosion measurements.