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:
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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.
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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.