Abstract
This work aimed at understanding the lithological controls on the SW-flowing segment of the Blue Nile and its ~ 1500-m deep Nile Gorge in the NW Ethiopian Plateau. The gorge exposes a ~ 1100-m-thick Mesozoic sedimentary section overlain by ~ 400-m-thick Cenozoic flood basalt. This work found no significant controls of the river channel by local structure. A NW–SE geologic cross-section was constructed to measure the valley width, the normalized valley width, and the valley asymmetry as a function of depth at 20-m intervals. Additionally, the amount of incision through time was calculated at 1-Ma interval starting 30 Ma. The Blue Nile, during its incision on the NW Plateau, (1) maintains an increase in width of ~ 30 m per 1- m, except when it incised into the upper part of flood basalts (~ 50 m per 1-m depth), a lower part of the Mesozoic sedimentary section dominated by shale–mudstone and sandstone unit (~ 70 m per 1-m depth), and a lowermost unit of the sedimentary section dominated by sandstone unit (10 m per 1- m depth); (2) maintains a NW asymmetry except in the lowermost sandstone unit where it becomes either symmetrical or asymmetrical to the NW or SE; (3) incised for ~ 700- m through the flood basalt and the upper sedimentary section between 30 and 10 Ma, an additional ~ 200- m through the middle sedimentary section between 10 and 6 Ma, and an additional ~ 600- m through the lower sedimentary section between 6 Ma and present.
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Acknowledgments
The authors would like to thank the Addis Ababa University, Ethiopia, for logistical support. This is Oklahoma State University, Boone Pickens School of Geology contribution number 2019-110.
Funding
This work was supported by the National Science Foundation – Office of International Science and Engineering – International Research Experience for Students (NSF-OISE-IRES) program Grant Number 0927906.
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Supplementary 1
Field photograph of pre-Adigrat Sandstone (PNG 13446 kb)
Supplementary 2
Field photograph of Adigrat Sandstone (PNG 13125 kb)
Supplementary 3
Field photograph of Lower Gohatsion Formation (PNG 12649 kb)
Supplementary 4
Field photograph of Middle Gohatsion Formation (PNG 12256 kb)
Supplementary 5
Field photograph of Upper Gohatsion Formation (PNG 14679 kb)
Supplementary 6
Field photograph of Lower Antalo Limestone (PNG 11933 kb)
Supplementary 7
Field photograph of Middle Antalo Limestone (PNG 12381 kb)
Supplementary 8
Field photograph of Upper Antalo Limestone (PNG 9560 kb)
Supplementary 9
Field photograph of Lower Basalt (PNG 11336 kb)
Supplementary 10
Field photograph of Upper Basalt (PNG 11129 kb)
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Alemu, T.B., Page, J.D., Abdelsalam, M.G. et al. Stratigraphic controls on the morpho-tectonic evolution of the Nile Gorge, Ethiopia. Arab J Geosci 12, 705 (2019). https://doi.org/10.1007/s12517-019-4816-z
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DOI: https://doi.org/10.1007/s12517-019-4816-z