Benue Trough

The Benue Trough is a major geological structure underlying a large part of Nigeria and extending about 1,000 km northeast from the Bight of Benin to Lake Chad. It is part of the broader Central African Rift System.[1]

Central African Shear Zone
Central African Rift System: Benue Trough to the west in Nigeria.

Location

Benue Trough
Sketch map of Benue Trough

The trough has its southern limit at the northern boundary of the Niger Delta, where it dips down and is overlaid with Tertiary and more recent sediments. It extends in a northeasterly direction to the Chad Basin, and is about 150 km wide. The trough is arbitrarily divided into lower, middle and upper regions, and the upper region is further divided into the Gongola and Yola arms. The Anambra Basin in the west of the lower region is more recent than the rest of the trough, being formed during a later period of compression, but is considered part of the formation.[2]

Rifting and sedimentation

The Benue Trough was formed by rifting of the central West African basement, beginning at the start of the Cretaceous period.[fn 1] At first, the trough accumulated sediments deposited by rivers and lakes. During the Late Early to Middle Cretaceous, the basin subsided rapidly and was covered by the sea. Sea floor sediment accumulated, especially in the southern Abakaliki Rift, under oxygen-deficient bottom conditions.[1] In the Upper Cretaceous, the Benue Trough probably formed the main link between the Gulf of Guinea and the Tethys Ocean (predecessor of the Mediterranean Sea) via the Chad and Iullemmeden Basins.[3] Towards the end of this period the basin rose above sea level, and extensive coal forming swamps developed, particularly in the Anambra Basin.[1] The trough is estimated to contain 5,000 m of Cretaceous sediments and volcanic rocks.[4]

A common explanation of the trough's formation is that it is an aulacogen, an abandoned arm of a three-armed radial rift system. The other two arms continued to spread during the break-up of Gondwana, as South America separated from Africa.[5] The two continents seem to have started to split apart at what are now their southern tips, with the rift extending up the modern coastlines to the Benue Trough, then later split along what is now the southern coast of West Africa and the north eastern coast of South America. As the continents were wedged apart, the trough opened up. When separation was complete, the southern part of Africa swung back to some extent, with the sediments in the Benue Trough compressed and folded.[6] During the Santonian age, around 84 million years ago, the basin underwent intense compression and folding, forming over 100 anticlines and synclines. The deposits in the Benue Trough were displaced westwards at this time, causing subsidence of the Anambra Basin.[2]

Mantle plume theory

Benue Trough faults
Benue Trough and related Atlantic fracture zones

A refinement to the model involves the rise of a mantle plume, where abnormal heat leads to melting of the upper mantle, thinning and stretching the crust, followed by rifting of the weakened crust. This may have been repeated several times, with the Benue Trough deformed between rifting episodes.[7] The same plume may be responsible for the line of volcanoes in Cameroon along the Central African Shear Zone and for the volcanic island of St. Helena in the Atlantic ocean.[8]

Three periods of magmatic activity (volcanic action) have been identified, 147–106 Ma, 97–81 Ma and 68–49 Ma. The first is prominent in the north of the trough, and contemporary with magmatism in Brazil, probably occurring during a period of crustal extension before the Atlantic started to open. The second is found only in the south of the trough, and may belong to a period when the extension of the Atlantic had slowed down, ending with a period of compression. The third and last period is also found only in the south of the trough, and may be related to an isostatic response to the earlier crustal thinning.[9]

The mantle plume activity was probably limited in its effect, with most of the basins in the trough being created from a combination of extension and strike-slip faults. The faults extend into the ocean with the Chain and Charcot fault zones, and have their counterparts in northeastern Brazil.[10]

Economic importance

Nigeria is rich in coal deposits derived from terrestrial organic matter, most of which lie in the Benue Trough. These are mined in Enugu State.[11] The Enugu deposits formed in brackish marshes during the Late Campanian – early Maastrichtian ages, around 70 Ma.[2] During this time, the Anambra Basin became silted up with thick vegetation growing in low-lying marshes on a broad delta fan deposited by rivers from the interior. Later, the deep layer of vegetation became buried under coarse sands.[3] Coal is potentially a source for oil and natural gas. An exploratory well drilled in the Gongola Basin of the upper region in 2003 found no oil, although there was a narrow layer of coal between 4,710 ft and 4,770 ft.[12]

Explanatory notes

  1. ^ The Cretaceous lasted from 145.5 – 66 Ma, or million years ago.

References

  1. ^ a b c "The Benue Trough". Online Nigeria. Retrieved 2011-01-29.
  2. ^ a b c Obaje Nuhu George; Nuhu George Obaje (2009). "4 - The Benue Trough". Geology and Mineral Resources of Nigeria. Springer. p. 57. ISBN 3-540-92684-4.
  3. ^ a b J. B. Wright (1985). "The Benue Trough". Geology and mineral resources of West Africa. Springer. p. 98. ISBN 0-04-556001-3.
  4. ^ CHRIS ADIGHIJE (8 November 1979). "Gravity field of Benue Trough, Nigeria". Nature. 282 (5735): 199–201. Bibcode:1979Natur.282..199A. doi:10.1038/282199a0. Retrieved 2011-01-29.
  5. ^ S. W. Petters (May 1978). "Stratigraphic Evolution of the Benue Trough and Its Implications for the Upper Cretaceous Paleogeography of West Africa". The Journal of Geology. 86 (3): 311–322. Bibcode:1978JG.....86..311P. doi:10.1086/649693. JSTOR 30061985.
  6. ^ J.B. Wright (October 1968). "South Atlantic continental drift and the Benue Trough". Tectonophysics. 6 (4): 301–310. Bibcode:1968Tectp...6..301W. doi:10.1016/0040-1951(68)90046-2. Retrieved 2011-01-29.
  7. ^ C. O. Ofoegbu (1984). "A model for the tectonic evolution of the Benue Trough of Nigeria". Geologische Rundschau. 73 (3): 1007–1018. Bibcode:1984GeoRu..73.1007O. doi:10.1007/BF01820885.
  8. ^ C. COULON; P. VIDAL; C. DUPUY; P. BAUDIN; M. POPOFF; H. MALUSKI; D. HERMITTE (1996). "The Mesozoic to Early Cenozoic Magmatism of the Benue Trough (Nigeria); Geochemical Evidence for the Involvement of the St Helena Plume". Journal of Petrology. 37 (6): 1341–1358. Bibcode:1996JPet...37.1341C. doi:10.1093/petrology/37.6.1341. Retrieved 2011-01-29.
  9. ^ H. MALUSKI; C. COULON; M. POPOFF; P. BAUDIN (1995). "40Ar/39Ar chronology, petrology and geodynamic setting of Mesozoic to early Cenozoic magmatism from the Benue Trough, Nigeria". Geological Society of London.
  10. ^ Christian M. Robert (2009). Global sedimentology of the ocean: an interplay between geodynamics and paleoenvironment. Elsevier. p. 241ff. ISBN 0-444-51817-7.
  11. ^ Aliyu Jauro. "ORGANIC GEOCHEMISTRY OF COALS FROM BENUE TROUGH, NIGERIA" (PDF). European Association of Organic Geochemists. Retrieved 2011-01-29.
  12. ^ N. G. Obaje; H. Wehner; M. B. Abubakar; M. T. Isah (April 2004). "NASARA-I WELL, GONGOLA BASIN (UPPER BENUE TROUGH, NIGERIA): SOURCE-ROCK EVALUATION". Journal of Petroleum Geology. 27 (2): 191–206. Bibcode:2004JPetG..27..191O. doi:10.1111/j.1747-5457.2004.tb00053.x.
Anambra Basin

Anambra Basin is one of the energy-rich inland sedimentary basins in Nigeria. It is a nearly triangular shaped embayment covering about 3000 km2 with a total sedimentary thickness of approximately 9 km.

Aulacogen

An aulacogen is a failed arm of a triple junction. Aulacogens are a part of plate tectonics where oceanic and continental crust is continuously being created, destroyed, and rearranged on the Earth’s surface. Specifically, aulacogens are a rift zone, where new crust is formed, that is no longer active.

Bangui magnetic anomaly

The Bangui magnetic anomaly is a local variation in the Earth's magnetic field centered at Bangui, the capital of Central African Republic. The anomaly is roughly elliptical, about 700 km × 1,000 km (430 mi × 620 mi), and covers most of the country, making it one of the "largest and most intense crustal magnetic anomalies on the African continent". The anomaly was discovered in the late 1950s, explored in the 1970s, and named in 1982. Its origin remains unclear.

Benue

Benue may refer to:

Benue River, a river in Cameroon and Nigeria

Benue State, a state in Nigeria

Benue-Plateau State, a former administrative division in Nigeria

Benue Trough, a major geological formation in Nigeria

Benue–Congo languages, a major language group in Africa

Benue State

Benue State is one of the South Eastern states in Nigeria with a population of about 4,253,641 in 2006 census. It is inhabited predominantly by the Tiv, Idoma and Igede peoples, who speak Tiv, Idoma, and Igede languages respectively. The Tivs comprise the Etulos while the Idomas comprise the Ufia's (Utonkon) to Orokam at the west border of the state. There are other ethnic groups, including the Etulo, Abakwa, Jukun, Hausa, Igbo, Igala people, Akweya and Nyifon. With its capital at Makurdi, Benue is a rich agricultural region; popularly grown crops includes; potatoes, cassava, soya bean, guinea corn, flax, yams, sesame, rice, and groundnuts, Palm Tree.

Benue State is named after the Benue River and was formed from the former Benue-Plateau State in 1976, along with Igala and some part of Kwara State. In 1991 some areas of Benue state (mostly Igala area), along with areas in Kwara State, were carved out to become part of the new Kogi State. Igbo people are found in the boundary areas of Ebonyi State and Enugu State in local government areas like the Obi, Oju etc.

Samuel Ortom is the governor and Benson Abounu is the deputy governor. Both were elected under the All Progressives Congress (APC) but defected to the Peoples Democratic Party (PDP) in 2018.Benue state has three universities: Federal University of Agriculture, Makurdi, Benue State University, Makurdi, and University of Mkar, Mkar, Gboko. It has two polytechnics: Benue State Polytechnic, Ugbokolo and Fidei polytechnic, Gboko as well as the Akperan Orshi college of Agriculture Yandev. There are about four colleges of education which are Federal College of Education Agasha, College of Education Oju, College of Education Kastina Ala.

Benue State as it exists today is a surviving legacy of an administrative entity which was carved out of the protectorate of northern Nigeria at the beginning of the twentieth century. The territory was initially known as Munshi Province until 1918 when the name of its dominant geographical feature, the 'Benue River' was adopted.

Blue Nile Basin

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.

Cameroon line

The Cameroon line is a 1,600 km (990 mi) chain of volcanoes.

It includes islands in the Gulf of Guinea and mountains that extend along the border region of eastern Nigeria and western Cameroon, from Mount Cameroon on the Gulf of Guinea north and east towards Lake Chad.

The islands, which span the equator, have tropical climates and are home to many unique plant and bird species.

The mainland mountain regions are much cooler than the surrounding lowlands, and also contain unique and ecologically important environments.

The Cameroon volcanic line is geologically unusual in extending through both the ocean and the continental crust. Various hypotheses have been advanced by different geologists to explain the line.

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.

As of 2008, there was still no general agreement about how the individual shears along the lineament link up.

Chad Basin

The Chad Basin is the largest endorheic basin in Africa, centered on Lake Chad. It has no outlet to the sea and contains large areas of desert or semi-arid savanna. The drainage basin is roughly coterminous with the sedimentary basin of the same name, but extends further to the northeast and east. The basin spans seven countries, including most of Chad and a large part of Niger. The region has an ethnically diverse population of about 30 million people as of 2011, growing rapidly.

A combination of dams, increased irrigation, climate change, and reduced rainfall are causing water shortages, contributing to terrorism and the rise of Boko Haram in the region. Lake Chad continues to shrink.

Congo Basin

The Congo Basin is the sedimentary basin of the Congo River. The Congo Basin is located in Central Africa, in a region known as west equatorial Africa. The Congo Basin region is sometimes known simply as the Congo.

The basin begins in the highlands of the East African Rift system with input from the Chambeshi River, the Uele and Ubangi Rivers in the upper reaches and the Lualaba River draining wetlands in the middle reaches. Due to the young age and active uplift of the East African Rift at the headlands, the river's yearly sediment load is very large but the drainage basin occupies large areas of low relief throughout much of its area. The basin is a total of 3.7 million square kilometers and is home to some of the largest undisturbed stands of tropical rainforest on the planet, in addition to large wetlands. The basin ends where the river empties its load in the Gulf of Guinea on the Atlantic Ocean. The climate is equatorial tropical, with two rainy seasons including very high rainfalls, and high temperature year round. The basin is home to the endangered western lowland gorilla.

The basin was the watershed of the Congo River populated by pygmy peoples, and eventually Bantu peoples migrated there and founded the Kingdom of Kongo. Belgium, France, and Portugal later established colonial control over the entire region by the late 19th century. The General Act of the Berlin Conference of 1885 gave a precise definition to the "conventional basin" of the Congo, which included the entire actual basin plus some other areas. The General Act bound its signatories to neutrality within the conventional basin, but this was not respected during the First World War.

El Djouf

El Djouf (Arabic: الجوف‎) is a desert, an arid natural region of sand dunes and rock salt which covers northeastern Mauritania and part of northwestern Mali. El Djouf is a part of the Sahara Desert in the north.

A meteorite of a rare type of carbonaceous chondrite was found in el Djouf in October 1989.

Geology of Cameroon

The geology of Cameroon is almost universally Precambrian metamorphic and igneous basement rock, formed in the Archean as part of the Congo Craton and the Central African Mobile Zone and covered in laterite, recent sediments and soils. Some parts of the country have sequences of sedimentary rocks from the Paleozoic, Mesozoic and Cenozoic as well as volcanic rock produced by the 1600 kilometer Cameroon Volcanic Line, which includes the still-active Mount Cameroon. The country is notable for gold, diamonds and some onshore and offshore oil and gas.

Iullemmeden Basin

The Iullemmeden Basin is a major sub-Saharan inland basin in West Africa, extending about 1000 km north to south and 800 km east to west. It covers western Niger and portions of Algeria, Mali, Benin and Nigeria. It is named after the Iullemmeden, a federation of Tuareg people who live in the central region of Niger. Its geographic range is largely coincident with the Azawagh region.The area of the Iullemmeden Basin seems to have started to subside in Permo-Triassic times, and to have experienced gradual downwarping during the Upper Cretaceous - Lower Tertiary times, while steadily filling with sediment.

Two prominent fault trends run NNE-SSW through the center of the basin, while WSW-ENE faults trends are found in the northeast of the basin near the Aïr Mountains.The sediments from Cambrian to Pleistocene times are 1,500 to 2,000 meters deep, with alternating layers formed when the basin was undersea and above sea level.

Potentially valuable minerals include uranium and copper ores and coal and salt deposits. Niger is one of the world's largest producers of uranium

Niger Delta Basin (geology)

The Niger Delta Basin, also referred to as the Niger Delta province, is an extensional rift basin located in the Niger Delta and the Gulf of Guinea on the passive continental margin near the western coast of Nigeria with suspected or proven access to Cameroon, Equatorial Guinea and São Tomé and Príncipe. This basin is very complex, and it carries high economic value as it contains a very productive petroleum system. The Niger delta basin is one of the largest subaerial basins in Africa. It has a subaerial area of about 75,000 km2, a total area of 300,000 km2, and a sediment fill of 500,000 km3. The sediment fill has a depth between 9–12 km. It is composed of several different geologic formations that indicate how this basin could have formed, as well as the regional and large scale tectonics of the area. The Niger Delta Basin is an extensional basin surrounded by many other basins in the area that all formed from similar processes. The Niger Delta Basin lies in the south westernmost part of a larger tectonic structure, the Benue Trough. The other side of the basin is bounded by the Cameroon Volcanic Line and the transform passive continental margin.

Ogaden Basin

The Ogaden Basin is an area of Ogadenia 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 miles) thick. It has geological similarities to other hydrocarbon-rich basins in the Middle East.

Taoudeni basin

The Taoudeni Basin is a major geological formation in West Africa named after the Taoudenni village in northern Mali. It covers large parts of the West African craton in Mauritania and Mali. It is of considerable interest due to its possible reserves of oil.The Taoudeni is the largest sedimentary basin in Northwest Africa, formed during the mid-late Proterozoic. It continued to subside until the mid-Paleozoic age, when Hercynian deformation and uplift occurred. It contains up to 6000 m of Late Precambrian and Paleozoic sediments. Exploratory drilling since the 1980s has found indications of petroleum in the Late Precambrian, Silurian and Late Devonian layers.

Sediments are thicker in the western half of the basin.

The government of Mali, one of the poorest countries in the world, is eager to create an oil industry. Companies that have been exploring in the area include Baraka Petroleum, Sonatrach, Eni, Total S.A., Woodside and China National Petroleum Corporation. However, the remote location and harsh environment of the Sahara Desert would make extraction expensive.

Tindouf Basin

The Tindouf Basin is a major sedimentary basin in West Africa, to the south of the little Atlas region, Morocco. It stretches from west to east about 700km and covers about 100,000 km2, mostly in Algeria but with a western extension into Morocco / Western Sahara.

In the Ordovician period (490 Ma to 445 Ma) the area was an embayment sloping down from the West African craton into the Tethys sea. It became a closed basin in the Late Carboniferous (320 Ma to 300 Ma). The basin has a steep northern edge against the Anti Atlas and more gently sloping southern edge. The basin is filled with up to 8 km of sediment from the Cambrian and Carboniferous ageas.

These marine formations are overlain by a continental Cretaceous and Pliocene Hamada cover.The basin may have potential for oil and/or gas production, but has been largely unexplored.

Trans Brazilian Lineament

The Trans Brazilian Lineament (TBL), or Transbrasiliano Lineament, is a major shear zone that developed in the Precambrian period, and that has been reactivated several times since then, mostly recently during the Mesozoic. Movement along the shear zone helps explain how the South American continent could have fitted tightly to the African continent before the breakup of Gondwana.

Triple junction

A triple junction is the point where the boundaries of three tectonic plates meet. At the triple junction each of the three boundaries will be one of 3 types - a ridge (R), trench (T) or transform fault (F) - and triple junctions can be described according to the types of plate margin that meet at them (e.g. Transform-Transform-Trench, Ridge-Ridge-Ridge, or abbreviated F-F-T, R-R-R). Of the many possible types of triple junction only a few are stable through time ('stable' in this context means that the geometrical configuration of the triple junction will not change through geologic time). The meeting of 4 or more plates is also theoretically possible but junctions will only exist instantaneously.

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