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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.〔
==Basin formation==
The Niger Delta Basin was formed by a failed rift junction during separation of the South American plate and the African plate, as well as the opening of the South Atlantic. Rifting in this basin started in the late Jurassic and ended in the mid Cretaceous. As rifting continued, several faults formed, many of them thrust faults. Also at this time we have the deposition of the syn-rift sands and then shales in the late cretaceous. This shows that there was a regression in the early basin. By this time the basin has been undergoing extension by high angle normal faults and fault block rotation. Then at beginning of the Paleocene there was a large transgression.〔 Then in the Paleocene the Akata formation was deposited. In the Eocene the Agbada formation was deposited. This caused the underlying shale Akata Formation to be squeezed into shale diapirs. Then in the Oligocene the Benin formation was deposited and it 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, 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.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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