The Niger Delta Basin, also referred to as the Niger Delta province, is an extensional rift basin located in the

Niger Delta The Niger Delta is the delta of the Niger River sitting directly on the Gulf of Guinea on the Atlantic Ocean in Nigeria. It is located within nine coastal southern Nigerian states, which include: all six states from the South South geopolitical ...

and the

Gulf of Guinea The Gulf of Guinea is the northeasternmost part of the tropical Atlantic Ocean from Cape Lopez in Gabon, north and west to Cape Palmas in Liberia. The intersection of the Equator and Prime Meridian (zero degrees latitude and longitude) is in the ...

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 A petroleum reservoir or oil and gas reservoir is a subsurface accumulation of hydrocarbons contained in porous or fractured rock formations. Such reservoirs form when kerogen (ancient plant matter) is created in surrounding rock by the presence ...

. 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 A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

that indicate how this basin could have formed, as well as the regional and large scale

tectonics Tectonics (; ) are the processes that control the structure and properties of the Earth's crust and its evolution through time. These include the processes of mountain building, the growth and behavior of the strong, old cores of continents k ...

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 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 West and Central African Rift System. Location The t ...

. The other side of the basin is bounded by the Cameroon Volcanic Line and the transform passive continental margin.

Basin formation

The Niger Delta Basin was formed by a failed rift

junction Junction may refer to: Arts and entertainment * ''Junction'' (film), a 2012 American film * Jjunction, a 2002 Indian film * Junction (album), a 1976 album by Andrew Cyrille * Junction (EP), by Basement Jaxx, 2002 * Junction (manga), or ''Hot ...

during the separation of the

South American plate The South American Plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African Plate, with which it forms the southern part of the Mid-A ...

and the

African plate The African Plate is a major tectonic plate that includes much of the continent of Africa (except for its easternmost part) and the adjacent oceanic crust to the west and south. It is bounded by the North American Plate and South American Plat ...

, as the South Atlantic began to open. Rifting in this basin started in the late

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 ...

and ended in the mid

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 ...

. As rifting continued, several faults formed many of them

thrust faults A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

. Also at this time syn-rift sands and then shales were deposited in the late Cretaceous. This indicates that the shoreline regressed during this time. Concurrently, the basin had been undergoing extension resulting in high angle normal faults and fault block rotation. At the beginning of the Paleocene there was a significant shoreline transgression. During the Paleocene, the

Akata Formation Akata Formation is part of the Tertiary Niger Delta (Akata-Agbada) petroleum system located in the Niger Delta Province, of Nigeria at the Gulf of Guinea, Atlantic Ocean. The upper Akata Formation is cited to be a primary source rock, providing ...

was deposited, followed by the Agbada Formation during the Eocene. This loading caused the underlying shale

to be squeezed into shale diapirs. Then in the Oligocene the

Benin formation Benin ( , ; french: Bénin , ff, Benen), officially the Republic of Benin (french: République du Bénin), and formerly Dahomey, is a country in West Africa. It is bordered by Togo to the west, Nigeria to the east, Burkina Faso to the north ...

was deposited, which is still being deposited today. The overall basin is divided into a few different zones due to its tectonic structure. There is an extensional zone, which lies on the continental shelf, caused by the thickened crust. Moving basinward is a transition zone, and a contraction zone, which lies in the deep sea part of the basin.

Lithology

The sediment fill in the Niger Delta basin is characterized by three major depobelts. These three cycles show that the basin experienced an overall

regression Regression or regressions may refer to: Science * Marine regression, coastal advance due to falling sea level, the opposite of marine transgression * Regression (medicine), a characteristic of diseases to express lighter symptoms or less extent ( ...

throughout time as the sediments go from deep sea mud sized grains to

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 ...

denser sand sized grains. The

lithologies The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...

of the area experience changes due to several factors. The sediment

provenance Provenance (from the French ''provenir'', 'to come from/forth') is the chronology of the ownership, custody or location of a historical object. The term was originally mostly used in relation to works of art but is now used in similar senses i ...

from the onshore highlands which feed into the

delta Delta commonly refers to: * Delta (letter) (Δ or δ), a letter of the Greek alphabet * River delta, at a river mouth * D (NATO phonetic alphabet: "Delta") * Delta Air Lines, US * Delta variant of SARS-CoV-2 that causes COVID-19 Delta may also re ...

control the mineralogy of the grains. Additionally, the impact of sea level on sediment deposition is well known; relative sea level will control the basinward extent of lithologies (see

sequence stratigraphy Sequence stratigraphy is a branch of geology, specifically a branch of stratigraphy, that attempts to discern and understand historic geology through time by subdividing and linking sedimentary deposits into unconformity bounded units on a variety ...

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 ...

activity in the area may also result in thin deposits of ash (

bentonite Bentonite () is an absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelling capacity than Ca-mon ...

). The early Cretaceous sediments are thought to be from a

tide Tides are the rise and fall of sea levels caused by the combined effects of the gravity, gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide t ...

-dominated system that were deposited on a concave shoreline, and throughout time the shoreline became

convex Convex or convexity may refer to: Science and technology * Convex lens, in optics Mathematics * Convex set, containing the whole line segment that joins points ** Convex polygon, a polygon which encloses a convex set of points ** Convex polytope ...

and it is currently a

wave In physics, mathematics, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. Waves can be periodic, in which case those quantities oscillate repeatedly about an equilibrium (res ...

-dominated system. ;Basement The oceanic basement rock is the oldest rock in the basin and is

basaltic Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90% of a ...

in composition. Also closer to the coast

Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

continental basement

crops A crop is a plant that can be grown and harvested extensively for profit or subsistence. When the plants of the same kind are cultivated at one place on a large scale, it is called a crop. Most crops are cultivated in agriculture or hydroponics ...

out onshore. ;Cretaceous There is a section of rock in this basin from the middle to late Cretaceous which is poorly understood due to its significant burial depth. It is believed to be composed of sediments from a tide-dominated coastline, and there are believed to be several layers of shales, although their distribution is unconstrained. ;Akata Formation The Akata Formation is

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

in age. It is composed of thick shales, turbidite sands, and small amounts of silt and clay. The clay content resulted in it being a

ductile Ductility is a mechanical property commonly described as a material's amenability to drawing (e.g. into wire). In materials science, ductility is defined by the degree to which a material can sustain plastic deformation under tensile stres ...

shale formation which was squeezed into shale diapirs in the basin. The Akata Formation formed during lowstands in relative sea level and

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

conditions. This formation is estimated to be up to 7,000 meters thick. ;Agbada Formation The Agbada Formation dates back to

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

in age. It is a marine facies defined by both freshwater and deep sea characteristics. This is the major

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...

and

natural gas Natural gas (also called fossil gas or simply gas) is a naturally occurring mixture of gaseous hydrocarbons consisting primarily of methane in addition to various smaller amounts of other higher alkanes. Low levels of trace gases like carbo ...

-bearing facies in the basin. The hydrocarbons in this layer formed when this layer of rock became subaerial and was covered in a

marsh A marsh is a wetland that is dominated by herbaceous rather than woody plant species.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p Marshes can often be found at ...

-type environment rich in

organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...

content. It is estimated to be 3,700 meters thick. ;Benin Formation The Benin Formation is

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 ...

and younger in age. It is composed of continental flood plain sands and alluvial deposits. It is estimated to be up to 2,000 meters thick.

Tectonic structures

The tectonic structures in the Niger Delta Basin are typical of an extensional rift system, but the added shale

diapirism A diapir (; , ) is a type of igneous intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...

due to loading makes this basin unique. The main method of deformation is gravitational collapse of the basin, although the older faulting and deformation in the basin are related to the continental breakup and rifting of the African plate and South American plates. The overall basin is divided into a few different zones due to its tectonic structure. There is an extensional zone, which lies on the continental shelf, that is caused by the thickened crust. There is a transition zone, and then there is a contraction zone, which lies in the deep sea part of the basin. ;Basin inversion Basin inversion is caused by uplift and/or compression in this basin. The compression is caused by the toe detachment of the shale diapirs. Basin inversion forms anticline structures, which serve as a great oil trap. Clay smears in the sediments seal the formations so oil does not escape out. ;Basinward dipping reflectors Basinward dipping reflectors are a common feature of extensional type rift basins. As fault blocks extend they rotate to dip towards the center of the basin. At the top of these fault blocks sub basins can form. ;Shale diapirs The shale diapirs are from the Akata Formation. This structure is formed due to the improper dehydration of the formation and the over pressuring by the overlying and denser Agbada Formation. ;High-angle normal faulting High-angle

normal fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...

ing is a feature of the extensional portion of the rifting in this basin. It is considered a growth fault and the feature lies closer towards the basins edge and transitions to the toe detachment faulting as you continue down the basin.

Oil and Gas

The Niger Delta is the twelfth largest province in the world by known oil and gas resources. The Niger Delta Basin produces around 2 million barrels of oil per day. The entire system is predicted to contain 34.5 billion barrels of oil and 94 trillion feet³ of natural gas. This area is still very heavily explored by oil companies today. It is one of the largest oil producers in the world.

Oil Pollution

In July 1979, an incident on the coastal zone of the Forcado tank 6 terminal spilled 570 thousand barrels of oil into the Forcados estuary, affecting the sea species and surrounding swamp forest. In January 1980, the Funiwa No.5 Well in Funiwa Field spilled 421 thousand barrels of oil into the ocean, damaging 836 acres of mangrove forest. In 1983, 5 000 barrels were spilled causing high mortality in crabs, fish and shrimps. Until 1999, an average of 240 thousand barrels of crude oil was spilled in the zone every year.

References

External links

The Niger Delta Petroleum System: Niger Delta Province, Nigeria, Cameroon, and Equatorial Guinea, Africa

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...

, 1999
Regional Geology and Petroleum Prospectivity
Nigeria - São Tomé and Príncipe Joint Development Zone (JDZ) {{coord missing, Nigeria Basins of Africa Gulf of Guinea Niger River Delta Geology of Cameroon Geology of Equatorial Guinea Geology of Nigeria Geology of São Tomé and Príncipe Geologic provinces Oil fields of Africa Oil fields of Nigeria Geography of Cameroon Geography of Equatorial Guinea Geography of Nigeria Geography of São Tomé and Príncipe Sedimentary basins of Africa Mesozoic rifts and grabens