Blue Nile Basin

Rifts in Sudan and Kenya

The Blue Nile Basin is a major geological formation in the northwestern Ethiopian Plateau formed in the Mesozoic Era during a period of crustal extension associated with the break-up of Gondwana, and filled with sedimentary deposits. The modern Blue Nile river cuts across part of the sedimentary basin.^[1]

Strata

The Blue Nile basin originated in an area of Neoproterozoic rocks aged about 750 Ma that had become a peneplain, possibly during the Paleozoic era (540–250 Ma^{[fn 1]}). The basin was formed due to rifting during the Mesozoic era (250–66 Ma). Between the Triassic and early Jurassic, about 300 m of fluvial sediments were deposited by rivers and streams. During the Jurassic (200–145 Ma) the basin was twice covered by an arm of the Indian Ocean for extended periods, creating a lower limestone sediment 450 m thick and an upper limestone sediment 400 m thick. In the late Jurassic and early Cretaceous periods the basin rose, and the 280 m upper sandstone sediments, both alluvial or fluvial, were deposited. In total, about 1.4 km of sediment was deposited over the basement rocks in this period.^[1]

Later, the Afar mantle plume caused volcanic eruptions in the early and late Oligocene (34–23 Ma), depositing volcanic rocks between 500 m and 2000 m thick, with further eruptions in the Quaternary depositing another 300 m of rock. These layers have been exposed where the Blue Nile river has cut through the strata, creating a 1,600 m gorge where the rocks of different periods can be studied. However, the architecture of the basin is not well known in other areas due to the thick upper layer of comparatively recent volcanic rock.^[1]

Rifting

The NW trending rift basin originated when the basement rocks were extended between the Triassic and early Cretaceous periods through forces related to the rifting of Gondwana. As the Blue Nile basin formed, it was filled with clastic and marine sediments. In the late Miocene further rifting occurred in a NW-SE extension associated with the Main Ethiopian rift, which formed NE-trending faults. In the Quaternary (2.5 Ma - present) the region was subject to further stresses as the Main Ethiopian rift opened obliquely, creating N, ESE and NW trending extensions within the basin.^[1]

Other rift basins with the same orientation formed in the region at the same time. The Blue Nile rift, Melut Basin and Muglad Basin all terminate on the line of the Central African Shear Zone, a major strike-slip shear zone. It is now known that the Muglad and Melut connect in the southeast, and then connect to the Anza trough in Kenya. It is possible that the Blue Nile basin may be a southeastern extension of the Blue Nile rift in the Sudan, and may also extend southeast of the Main Ethiopian rift, connecting to the Ogaden Basin in southeast Ethiopia.^[1]

Explanatory notes

↑ Ma = Million years ago

References

1 2 3 4 5 N. DS. GANI, M. G. ABDELSALAM, S. GERA and M. R. GANI (2008). "Stratigraphic and structural evolution of the Blue Nile Basin, Northwestern Ethiopian Plateau" (PDF). Geological Journal. doi:10.1002/gj.1127. Retrieved 2011-01-28.

Major African geological formations

Plates	African Plate Somali Plate Madagascar Plate Seychelles Plate

Cratons and shields	Arabian-Nubian Shield Congo Craton Kaapvaal Craton Kalahari Craton Saharan Metacraton Tanzania Craton Tuareg Shield West African Craton Zimbabwe Craton

Shear zones	Aswa Dislocation Broodkop Shear Zone Central African Shear Zone Chuan Shear Zones Foumban Shear Zone Mwembeshi Shear Zone Todi Shear Zone Western Meseta Shear Zone

Orogens	Alpide Orogen Cape Fold Belt Damara Orogen East African Orogen Eburnean Orogen Gondwanide Orogen Kuunga Orogen Mauritanide Belt Pan-African orogens Terra Australis Orogen

Rifts	Afar Triangle Anza trough Bahr el Arab rift Benue Trough Blue Nile rift East African Rift Gulf of Suez Rift Lamu Embayment Melut Basin Muglad Basin Red Sea Rift Sangha Aulacogen Atbara rift White Nile rift

Sedimentary basins	Angola Basin Aoukar Blue Nile Basin Chad Basin Congo Basin Douala Basin El Djouf Foreland Karoo Basin Gabon Basin Iullemmeden Basin Kufra Basin Murzuq Basin Niger Delta Basin Ogaden Basin Orange River basin Ouled Abdoun Basin Owambo Basin Reggane Basin Rio del Rey Basin Sirte Basin Somali Coastal Basin Taoudeni basin Tanzania Coastal Basin Tindouf Basin Turkana Basin

Mountain ranges	Aïr Mountains Atlas Mountains Aurès Mountains Bambouk Mountains Blue Mountains Cameroon line Central Pangean Mountains Chaillu Mountains Drakensberg Ethiopian Highlands East African mountains Great Escarpment Great Karas Mountains Guinée forestière Imatong Mountains Jebel Uweinat Loma Mountains Mandara Mountains Marrah Mountains Mitumba Mountains Nuba Mountains Rif Mountains Rwenzori Mountains Sankwala Mountains Serra da Leba Serra da Chela Teffedest Mountains Tibesti Mountains

This article is issued from Wikipedia - version of the 10/11/2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.