Download the sedimentary basins of africa.
OCHIGBO OÓFUN EUGENIA. 13/MHS02/029 GEY 309 ASSIGNMENT 2. 1.Discuss Economic importance of a typical sedimentary Environment you know 2.Write succinctly on Basins of Africa. Answers. 1. Aeolian processes, involving erosion, transportation, and deposition of sediment by the wind, occur in a variety of environments, including the coastal zone, cold and hot deserts, and agricultural fields. Common features of these environments are a sparse or nonexistent vegetation cover, a supply of fine sediment (clay, silt, and sand), and strong winds. Aeolian processes are responsible for the emission and/or mobilization of dust and the formation of areas of sand dunes. They largely depend on other geologic agents, such as rivers and waves, to supply sediment for transport. Areas of sand dunes occur in inland and coastal settings, where they often provide a distinctive environment that provides habitats for endemic and rare or threatened species. In both coastal and inland settings, dune migration and sand encroachment may impact neighbouring ecosystems and resources, as well as infrastructure. Transport of fine sediment by wind may cause dust storms, events in which visibility is reduced to less than 1 km by blowing dust. Dust storms impact air quality in their immediate vicinity as well as in areas downwind. Deposition of dust may have a significant effect on the composition and nature of soils in arid regions and beyond. Far-travelled dust from distant sources may have a significant effect on soil chemistry and nutrient status. Other economic importances include: i. ii. iii. iv. v. Regional permeability is likely to be good due to absence of shale inter-beds. Aeolian sandstones are important aquifers. Aeolian sandstones are important hydrocarbon reservoirs for oil and gas. Aeolian sandstones frequently lie within continental basin far from marine shales which could be potential source rocks. Aeolian dunes exerts control on future carbonate distribution pattern. 2. Sedimentary basins are regions of the earth of long-term subsidence creating accommodation space for infilling by sediments. The subsidence results from the thinning of underlying crust, sedimentary, volcanic, and tectonic loading, and changes in the thickness or density of adjacent lithosphere. Sedimentary basins occur in diverse geological settings usually associated with plate tectonic activity. Basins are classified structurally in various ways, with a primary classifications distinguishing among basins formed in various plate tectonic regime (divergent, convergent, transform, intraplate), the proximity of the basin to the active plate margins, and whether oceanic, continental or transitional crust underlies the basin. Basins formed in different plate tectonic regimes vary in their preservation potential. On oceanic crust, basins are likely to be subducted, while marginal continental basins may be partially preserved, and intracratonic basins have a high probability of preservation. As the sediments are buried, they are subjected to increasing pressure and begin the process of lithification. A number of basins formed in extensional settings can undergo inversion which has accounted for a number of the economically viable oil reserves on earth which were formerly basins. THE SEDIMENTARY BASINS OF AFRICA. The structural and stratigraphic character of African interior sedimentary basins is highly variable, indicating contrasting basin-forming mechanisms and subsequent subsidence histories. A stratigraphic database has been compiled for African interior depositional basins for the purpose of better understanding basin thermal and structural development. Data are recorded in the form of stratal age, lithology, thickness and elevation of top with respect to present sea level. The data are obtained from published structure contour maps, well sections, and outcrop geology and elevation. There are various degrees of data coverage of the basins, proportional to the amount of water and oil drilling activity. Consequently, there is excellent coverage of North African basins such as the Algerian basin and the Sirte basin, while there is little known about the subsurface of the Congo basin. The stratigraphic data are used to reconstruct the depositional history of the basins, while backstripping leads to the quantification of the thermo-tectonic component of basin subsidence. The nature of basement subsidence can provide constraints on lithospheric flexural rigidity. In addition, the depositional and thermo-tectonic history of each basin bears upon the mechanisms of basin formation and subsidence. Virtually all types of basins are represented in interior Africa, including thrust-loaded basins (Algerian), passive-margin rift basins (Algerian, Sirte), modern active rift basins (East African), ancient rift basins (Benue, Abu Gabra), basins caused by uplift of their margins (Congo, Chad, Illumeden) and even basins that may be related to thermal subsidence of hot-spot domes (Algerian, Sirte). The basins are as named below: Angola Basin Aoukar Blue Nile Basin Chad Basin Congo Basin Douala Basin El Djouf Foreland Karoo Basin Gabon Basin Iullemmeden Basin Kurfra Basin Murzuk 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 Tinduf Basin Turkana Basin The Oulad Abdoun Basin (also known as the Ouled Abdoun Basin or Khouribga Basin) is a phosphate sedimentary basin located in Morocco, near the city of Khouribga. It is the largest in Morocco, comprising 44% of Morocco's phosphate reserves, and at least 26.8 billion tons of phosphate. It is also known as an important site for vertebrate fossils, with deposits ranging from the Late Cretaceous (Cenomanian-Turonian) to the Eocene epoch (Ypresian), a period of about 25 million years. The Oulad Abdoun Basin stretches from late Cretaceous to the Eocene, and contains abundant marine vertebrate fossils, including sharks, bony fish, turtles, crocodilians, and other reptiles, as well as sea birds and a small number of terrestrial mammals. The Sirte Basin is a late Mesozoic and Cenozoic triple junction continental rift (extensional basin) along northern Africa that was initiated during the late Jurassic Period. It borders a relatively stable Paleozoic craton and cratonic sag basins along its southern margins. The province extends offshore into the Mediterranean Sea, with the northern boundary drawn at the 2,000 meter (m) bathymetric contour. It borders in the north on the Gulf of Sidra and extends south into northern Chad. Characteristics: Statistics Formation Land Area Source Rock Dominant Trap Style Rift Type System Characterised By Amount Late Mesozoic-Cenozoic ==230,000 km sq. Sirte Shale Structural Triple Junction Tethyan Rift System Desert Steepes The Chad Basin is the largest endorheic drainage basin in Africa, centered on Lake Chad. It has no outlet to the sea and contains large areas of desert or semi-arid savannah. 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 geological basin, which is smaller than the drainage basin, is a Phanerozoic sedimentary basin formed during the plate divergence that opened the South Atlantic ocean. The basin lies between the West Africa Craton and Congo Craton, and formed around the same time as the Benue Trough. It covers an area of about 2,335,000 square kilometres (902,000 sq mi). It merges into the Iullemmeden Basin to the west at the Damergou gap between the Air and Zinder massifs. The floor of the basin is made of Precambrian bedrock covered by more than 3,600 metres (11,800 ft) of sedimentary deposits. The basin may have resulted from the intersection of an "Air-Chad Trough" running NW-SE and a "Tibesti-Cameroon Trough" running NE-SW. That is, the two deepest parts are an extension of the Benue Trough that runs northeast to the margin of the basin, and another extension running from below the present lake to below the Ténéré rift structure to the east of the Air massif. The southern part of the basin is underlain by another elongated depression. This runs in an ENE direction and extends from the Yola arm of the Benue trough At times, parts of the basin were below the sea. In the North-eastern part of the Benue Trough where it enters the Chad Basin there are marine sediments from the Late Cretaceous (100.5–66 Ma). These sediments seem to be considerably thicker towards the northeast. Boreholes under Maiduguri have found marine sediments 400 metres (1,300 ft) deep, lying over continental sediments 600 metres (2,000 ft) deep. The sea seems to have retreated from the western part of the basin in the Turonian (93.5–89.3 Ma). In the Maastrichtian (72.1–66 Ma) the west was non-marine, but the southeast probably was still marine. No marine sediments have been found from the Paleocene (66–56 Ma). The eastern part of the basin, showing the Holocene "Mega Chad" lake (blue area) at its maximum size with the Chari in the south and the Benue in the south west. The modern Lake Chad is in the centre of this map, in green. For most of the Quaternary, from 2.6 million years ago to the present, the basin seems to have been a huge, well-watered plain, with many rivers and water bodies, probably rich in plant and animal life. Towards the end of this period the climate became drier. Around 20,000-40,000 years ago eolianite sand dunes began to form in the north of the basin. During the Holocene, from 11,000 years ago until recently, a giant "Lake Mega-Chad" covered an area of more than 350,000 square kilometres (140,000 sq mi) in the basin. It would have drained to the Atlantic Ocean via the Benue River. Stratigraphic records show that "Mega-Chad" varied in size as the climate changed, with a peak about 2,300 years ago. The remains of fish and molluscs from this period are found in what are now desert regions. 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 the Permo-Triassic times, and to have experienced gradual down warping 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. 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 sub-aerial basins in Africa. It has a sub-aerial 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. 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 shale 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. 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 ages. 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. THE AFRICAN PLATE SHOWING THE AGE OF EACH BASIN. WESTERN BASINS OF AFRICA. MAP OF WEST AFRICAN BASINS SHOWING THEIR AGE. MAP ON EASTERN RIFT BASIN OF AFRICA. MAP OF SOUTHERN PART OF AFRICA SHOWING THEIR AGE.