The Chew Bahir Drilling Project - Deconvolving climatic versus tectonic forcing in the source-to-sink sediment system of extensional provinces: New insights from the Chew Bahir Basin, South Ethiopia
Final Report Abstract
Assessing the mechanisms controlling basin-wide erosion is instrumental for understanding feedbacks between surface processes and the solid earth, and to design landuse policy. Here we present 10Be-derived basin-wide denudation rates from 12 basins of the great Chew Bahir catchment in southern Ethiopia, ranging from 0.02 to 0.18 mm/yr. Chew Bahir is located at the overlapping boundary between the Kenyan and Ethiopian branches of the East African Rift. Denudation rates throughout the catchment area are strongly correlated with average basin slope while not related to either precipitation or vegetation cover. This region hosts basement uplifts controlled by normal faults flanking steep mountain fronts; the highest denudation rates occur at basins draining the >2-kmrelief Hammer Range, where tectonic uplift over the past few million years has steepened slopes promoting erosion. We conclude that rifting-related tectonic uplift has controlled denudation rates in southern Ethiopia with implications on assessing drainage-basin evolution and soil degradation hazards. Field observations and radiocarbon dating of fluvial terraces adjacent to modern rivers suggest young mediaeval ages, which imply rapid erosion rates at millennial scale associated with fluvial incision. The integration of the Chew Bahir erosion rates with previously-published rates from Kenya and the Rwenzori Mountains suggests that tectonics indeeds excerts a predominant control on erosion rates for areas with a poor vegetation cover (EVI<0.35). Areas with a denser vegetation cover (EVI>0.35) are associated with very low erosion rates (<0.08 mm/yr) suggesting that vegetation shields the bedrock precluding erosion and emphasizing the importance of soil cover and vegetation on landscape evolution.
Publications
- 2017. Short-lived increase in erosion during the African Humid Period: Evidence from the northern Kenya Rift. Earth and Planetary Science Letters, v. 459, p. 58-69
Garcin, Y., Schildgen, T.F., Torres Acosta, V., Melnick, D., Guillemoteau, J., Willenbring, J., Strecker, M.R.
(See online at https://doi.org/10.1016/j.epsl.2016.11.017) - 2019. Continental rifting at magmatic centres: structural implications from Late Quaternary Menengai Caldera, central Kenya Rift. Journal of the Geological Society of London, v. 177, p. 153-169
Riedl, S., Melnick, D., Mibei, G., Njue, L., Strecker, M.R.
(See online at https://doi.org/10.1144/jgs2019-021)
