The Blue Nile Basin is a major geological formation in the northwestern

Ethiopian Plateau The Ethiopian Highlands is a rugged mass of mountains in Ethiopia in Northeast Africa. It forms the largest continuous area of its elevation in the continent, with little of its surface falling below , while the summits reach heights of up to . ...

formed in the

Mesozoic The Mesozoic Era ( ), also called the Age of Reptiles, the Age of Conifers, and colloquially as the Age of the Dinosaurs is the second-to-last era of Earth's geological history, lasting from about , comprising the Triassic, Jurassic and Cretaceo ...

Era during a period of

crustal extension Extensional tectonics is concerned with the structures formed by, and the tectonic processes associated with, the stretching of a planetary body's crust or lithosphere. Deformation styles The types of structure and the geometries formed depend on ...

associated with the break-up of

Gondwana Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...

, and filled with sedimentary deposits. The modern

Blue Nile The Blue Nile (; ) is a river originating at Lake Tana in Ethiopia. It travels for approximately through Ethiopia and Sudan. Along with the White Nile, it is one of the two major tributaries of the Nile and supplies about 85.6% of the water ...

river cuts across part of the

sedimentary basin Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence ...

Strata

The Blue Nile basin originated in an area of

Neoproterozoic The Neoproterozoic Era is the unit of geologic time from 1 billion to 538.8 million years ago. It is the last era of the Precambrian Supereon and the Proterozoic Eon; it is subdivided into the Tonian, Cryogenian, and Ediacaran periods. It is ...

rocks aged about 750 Ma that had become a

peneplain 390px, Sketch of a hypothetical peneplain formation after an orogeny. In geomorphology and geology, a peneplain is a low-relief plain formed by protracted erosion. This is the definition in the broadest of terms, albeit with frequency the usage ...

, possibly during the

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

era (540–250 MaMa = Million years ago). The basin was formed due to rifting during the Mesozoic era (250–66 Ma). Between the Triassic and early

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

, about 300 m of

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

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 The Indian Ocean is the third-largest of the world's five oceanic divisions, covering or ~19.8% of the water on Earth's surface. It is bounded by Asia to the north, Africa to the west and Australia to the east. To the south it is bounded by th ...

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 The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

periods the basin rose, and the 280 m upper sandstone sediments, both

alluvial Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

or fluvial, were deposited. In total, about 1.4 km of sediment was deposited over the basement rocks in this period. Later, the Afar mantle plume caused

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

eruptions in the early and late

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

(34–23 Ma), depositing

volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic r ...

s between 500 m and 2000 m thick, with further eruptions in the

Quaternary The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million years ...

depositing another 300 m of rock. These layers have been exposed where the Blue Nile river has cut through the

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

, 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.

Rifting

The NW trending rift basin originated when the basement rocks were extended between the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

and early

periods through forces related to the rifting of Gondwana. As the Blue Nile basin formed, it was filled with

clastic Clastic rocks are composed of fragments, or clasts, of pre-existing minerals and rock. A clast is a fragment of geological detritus,Essentials of Geology, 3rd Ed, Stephen Marshak, p. G-3 chunks, and smaller grains of rock broken off other rocks ...

and marine sediments. In the late

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

further rifting occurred in a NW-SE extension associated with the

Main Ethiopian rift Main may refer to: Geography * Main River (disambiguation) **Most commonly the Main (river) in Germany * Main, Iran, a village in Fars Province *"Spanish Main", the Caribbean coasts of mainland Spanish territories in the 16th and 17th centuries ...

, which formed NE-trending faults. In the

(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. Other rift basins with the same orientation formed in the region at the same time. The

Blue Nile rift The Blue Nile rift is a major geological formation in the Sudan, a rift with a NW trend that terminates on the Central African Shear Zone. It was formed through crustal extension during the break-up of Gondwana. The rift, and other rifts in the ...

Melut Basin The Melut Basin is a rift basin in South Sudan, extending into Ethiopia, where it is called the Gambella basin. Melut is situated in the Upper Nile and Jonglei, south of the capital of Sudan, Khartoum and east of the river Nile. Some parts of th ...

and

Muglad Basin The Muglad Basin is a large rift basin in Northern Africa. The basin is situated within southern Sudan and South Sudan, and it covers an area of approximately across the two nations. It contains a number of hydrocarbon accumulations of various s ...

all terminate on the line of the

Central African Shear Zone The Central African Shear Zone (CASZ) (or Shear System) is a wrench fault system extending in an ENE direction from the Gulf of Guinea through Cameroon into Sudan. The structure is not well understood. , there was still no general agreement about ...

, a major strike-slip

shear zone In geology, a shear zone is a thin zone within the Earth's crust or upper mantle that has been strongly deformed, due to the walls of rock on either side of the zone slipping past each other. In the upper crust, where rock is brittle, the shear ...

. It is now known that the Muglad and Melut connect in the southeast, and then connect to the Anza trough in

Kenya ) , national_anthem = "Ee Mungu Nguvu Yetu"() , image_map = , map_caption = , image_map2 = , capital = Nairobi , coordinates = , largest_city = Nairobi , ...

. It is possible that the Blue Nile basin may be a southeastern extension of the Blue Nile rift in the

Sudan Sudan ( or ; ar, السودان, as-Sūdān, officially the Republic of the Sudan ( ar, جمهورية السودان, link=no, Jumhūriyyat as-Sūdān), is a country in Northeast Africa. It shares borders with the Central African Republic t ...

, and may also extend southeast of the Main Ethiopian rift, connecting to the

Ogaden Basin The Ogaden Basin is an area of Huwan that may hold significant reserves of crude oil and natural gas. The basin covers an area of some 350,000 square kilometres (135,000 square miles) and is formed from sedimentary rocks up to 10,000 meters (6 mi ...

in southeast

Ethiopia Ethiopia, , om, Itiyoophiyaa, so, Itoobiya, ti, ኢትዮጵያ, Ítiyop'iya, aa, Itiyoppiya officially the Federal Democratic Republic of Ethiopia, is a landlocked country in the Horn of Africa. It shares borders with Eritrea to the ...

Explanatory notes

References

{{Major African geological formations, state=collapsed Sedimentary basins of Africa Geology of Kenya Geology of South Sudan Landforms of Kenya Landforms of South Sudan Nile basin Early Jurassic Africa Triassic Africa Oil fields of Africa Mesozoic rifts and grabens