Investigating sediment source to sink processes in a post-orogenic landscape
Marstellar, Tina L.
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In order to understand the life cycle of a mountain range, it is crucial to identify and quantify the processes that influence the rate of denudation, sediment flux through the landscape, and the resulting changes in relief over long time scales in tectonically-inactive regions. Geologic history and the quartz-rich lithologies make the southern Appalachian Mountains an ideal location for terrestrial cosmogenic nuclide (TCN) measurements aimed at studying erosion and denudation processes in an evolving post-orogenic landscape. We used in situ-produced TCN measurements of Beryllium-10 (10Be) to determine the denudation rate in ten catchments along the southern Appalachians. The locations selected are all within the east-draining Blue Ridge escarpment in North Carolina and Georgia. In five of the ten catchments we sampled two grain sizes, gravel and sand. In the remaining five catchments we sampled one grain size, sand. Our analysis provided erosion rates of 15 to 26 mm Ky-1 for the 0.025 to 0.050 cm sand samples and 12 to 20 mm Ky-1 for 3 to 8 cm gravel samples. We analyzed these TCN measurements in the context of several basin metrics, including slope and relief, derived from a digital elevation model (DEM). Our results provide evidence that most surficial basin metrics are not good predictors of denudation rates at a global scale, but can aid in predictions at a regional level. This finding supports the dynamic equilibrium hypothesis of landscape evolution and casts doubt on the possibility to estimate basin-wide denudation rates and watershed sediment supply at a global scale from simple metrics of basin morphology.