Stratigraphic and structural evolution of the Blue Nile Basin, Northwestern Ethiopian Plateau

The Blue Nile Basin, situated in the Northwestern Ethiopian Plateau, contains similar to 1400 m thick Mesozoic sedimentary section underlain by Neoproterozoic basement rocks and overlain by Early-Late Oligocene and Quaternary volcanic rocks. This study outlines the stratigaphic and structural evolution of the Blue Nile Basin based on field and remote sensing studies along the Gorge of the Nile. The Blue Nile Basin has evolved in three main phases,: (1) pre-sedimentation phase, include pre-rift peneplanation of the Neoproterozoic basement rocks, possibly during Palaeozoic time (2) sedimentation phase from Triassic to Early Cretaceous, including: (a) Triassic-Early Jurassic fluvial sedimentation (Lower Sandstone, similar to 300 m thick); (b) Early Jurassic marine transgression (glauconitic sandy mudstone, similar to 30 m thick) (c) Early-Middle Jurassic deepening of the basin (Lower Limestone, similar to 450 m thick); (d) desiccation of the basin and deposition of Early-Middle Jurassic gypsum: (e) Middle-Late Jurassic marine transgression (Upper Limestone, similar to 400 in thick) (f) Late Jurassic-Early Cretaceous basin-uplilt and marine regression (alluvial/fluvial Upper Sandstone, similar to 280 m thick); (3) the post-sedimentation phase, including Early-Late Oligocene eruption of 500-2000 m thick Lower volcanic rocks, related to the Afar Mantle Plume and emplacement of similar to 300 in thick Quaternary Upper volcanic rocks. The Mesozoic to Cenozoic units were deposited during extension attributed to Triassic-Cretaceous NE-SW-directed extension related to the Mesozoic rifting of Gondwana. The Blue Nile Basin was formed as a NW-trending rift. within which much of the Mesozoic clastic and marine sediments were deposited. This was followed by Late Miocene NW-SE-directed extension related to the Main Ethiopian Rift that formed NE-trending faults. affecting Lower volcanic rocks and the Upper part of the Mesozoic section. The region was subsequently affected by Quaternary E-W and NNE-SSW-directed extensions related to oblique opening of the Main Ethiopian Rift and development of E-trending transverse faults, as well as NE-SW-directed extension in Southern Afar (related to northeastward separation of the Arabian Plate from the African Plate) and E-W-directed extensions in western Afar (related to the stepping of the Red Sea axis into Afar). These Quaternary stress regimes resulted in the development of N-, ESE- and NW-trending extensional structures within the Blue Nile Basin. Copyripht (C) 2008 John Wiley & Sons, Ltd.