Sedimentary basin

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Geologic provinces of the world (USGS)
Map of the major sedimentary basins of Central and West Africa.
Chuya Basin in Russia

Sedimentary basins are regions of Earth's crust where a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock.[1][2][3] They form when long-term subsidence creates a regional depression that provides accommodation space for accumulation of sediments.[4] Over millions or tens or hundreds of millions of years the deposition of sediment, primarily gravity-driven transportation of water-borne eroded material, acts to fill the depression. As the sediments are buried, they are subject to increasing pressure and begin the processes of compaction and lithification that transform them into sedimentary rock.[5]

Sedimentary basins are created by deformation of Earth's lithosphere in diverse geological settings, usually as a result of plate tectonic activity. Mechanisms of crustal deformation that lead to subsidence and sedimentary basin formation include the thinning of underlying crust; depression of the crust by sedimentary, tectonic or volcanic loading; or changes in the thickness or density of underlying or adjacent lithosphere.[6][4][7][8] Once the process of basin formation has begun, the weight of the sediments being deposited in the basin adds a further load on the underlying crust that accentuates and amplifies basin development as a result of isostasy.[4]

The long-term preserved geologic record of a sedimentary basin is a large scale contiguous three-dimensional package of sedimentary rocks created during a particular period of geologic time, a 'stratigraphic succession', that geologists continue to refer to as a sedimentary basin even if it is no longer a bathymetric or topographic depression.[6] The Williston Basin, Molasse basin and Magallanes Basin are examples of sedimentary basins that are no longer depressions. Basins formed in different tectonic regimes vary in their preservation potential.[9] 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.[7]

Sedimentary basins are of great economic importance. Almost all the world's natural gas and petroleum and all of its coal are found in sedimentary rock. Many metal ores are found in sedimentary rocks formed in particular sedimentary environments.[10][6][2]. Sedimentary basins are also important from a purely scientific perspective because their sedimentary fill provides a record of Earth's history during the time in which the basin was actively receiving sediment.

More than six hundred sedimentary basins have been identified worldwide. They range in areal size from tens of square kilometers to well over a million, and their sedimentary fills range from one to almost twenty kilometers in thickness. [11][12] [13]


Methods of formation[edit]

Example of a sedimentary basin in a half-graben.

Sedimentary basins primarily form in active plate tectonic settings associated with convergent, divergent and transform tectonic plate boundaries, although over the lifespan of a single basin multiple tectonic processes may come into play and a single sedimentary basin's fill, sometimes referred to as a stratigraphic succession, may represent several different tectonic settings.[6]

Lithospheric stretching[edit]

Tectonic extension at divergent boundaries where continental rifting is occurring can create a nascent ocean basin leading to either an ocean or the failure of the rift zone. If the lithosphere is caused to stretch horizontally, by mechanisms such as ridge-push or trench-pull, the effect is believed to be twofold. The lower, hotter part of the lithosphere will "flow" slowly away from the main area being stretched, whilst the upper, cooler and more brittle crust will tend to fault (crack) and fracture. The combined effect of these two mechanisms is for Earth's surface in the area of extension to subside, creating a geographical depression which is then often infilled with water and/or sediments. (An analogy might be a piece of rubber, which thins in the middle when stretched.)

An example of a basin caused by lithospheric stretching is the North Sea – also an important location for significant hydrocarbon reserves. Another such feature is the Basin and Range Province which covers most of the USA state of Nevada, forming a series of horst and graben structures.

Another expression of lithospheric stretching results in the formation of ocean basins with central ridges. The Red Sea is in fact an incipient ocean, in a plate tectonic context. The mouth of the Red Sea is also a tectonic triple junction where the Indian Ocean Ridge, Red Sea Rift and East African Rift meet. This is the only place on the planet where such a triple junction in oceanic crust is exposed subaerially. This is due to a high thermal buoyancy (thermal subsidence) of the junction, and also to a local crumpled zone of seafloor crust acting as a dam against the Red Sea.

Lithospheric compression/shortening and flexure[edit]

Convergent boundaries create foreland basins through tectonic compression of oceanic and continental crust during lithospheric flexure. If a load is placed on the lithosphere, it will tend to flex in the manner of an elastic plate. The magnitude of the lithospheric flexure is a function of the imposed load and the flexural rigidity of the lithosphere, and the wavelength of flexure is a function of flexural rigidity alone. Flexural rigidity is in itself, a function of the lithospheric mineral composition, thermal regime, and effective elastic thickness. The nature of the load is varied. For instance, the Hawaiian Islands chain of volcanic edifices has sufficient mass to cause deflection in the lithosphere.

The obduction of one tectonic plate onto another also causes a load and often results in the creation of a foreland basin, such as the Po basin next to the Alps in Italy, the Molasse Basin next to the Alps in Germany, or the Ebro basin next to the Pyrenees in Spain.

Strike-slip deformation[edit]

In tectonic strike-slip settings, accommodation spaces occur as transpressional, transtensional or transrotational basins according to the motion of the plates along the fault zone and the local topography pull-apart basins.[7]. Deformation of the lithosphere in the plane of Earth (i.e. such that faults are vertical) occurs as a result of near horizontal maximum and minimum principal stresses. The resulting zones of subsidence are known as strike-slip or pull-apart basins. Basins formed through strike-slip action occur where a vertical fault plane curves. When the curve in the fault plane moves apart, a region of transtension results, creating a basin. Another term for a transtensional basin is a rhombochasm. A classic rhombochasm is illustrated by the Dead Sea rift, where northward movement of the Arabian Plate relative to the Anatolian Plate has caused a rhombochasm.

The opposite effect is that of transpression, where converging movement of a curved fault plane causes collision of the opposing sides of the fault. An example is the San Bernardino Mountains north of Los Angeles, which result from convergence along a curve in the San Andreas fault system. The Northridge earthquake was caused by vertical movement along local thrust and reverse faults "bunching up" against the bend in the otherwise strike-slip fault environment.

In Nigeria, the dominant type of basement rock intersected by wells drilled for hydrocarbons, limestone, or water is granite. The three sedimentary basins in Nigeria are underlain by continental crust except in the Niger Delta, where the basement rock is interpreted to be oceanic crust. Most of the wells that penetrated the basement are in the Eastern Dahomey embayment of western Nigeria. A maximum thickness of about 12,000 m of sedimentary rocks is attained in the offshore western Niger Delta, but maximum thicknesses of sedimentary rocks are about 2,000 m in the Chad basin and only 500 m in the Sokoto embayment.

Study of sedimentary basins[edit]

The specific study of sedimentary basins as entities in themselves is often referred to as sedimentary basin analysis. Study involving quantitative modelling of the dynamic geologic processes by which they evolved is called basin modelling.

In addition to this being an academic area of study, there are important economic incentives to understand the processes of sedimentary basin formation because almost all of the world's fossil fuel reserves were formed in sedimentary basins.

See also[edit]

  • Drainage basin – Area of land where precipitation collects and drains off into a common outlet
  • Endorheic basin – Closed drainage basin that allows no outflow
  • Isostasy – State of gravitational equilibrium between Earth's crust and mantle
  • Plate tectonics – Movement of Earth's lithosphere
  • Structural basin – Large-scale structural geological depression formed by tectonic warping

References[edit]

  1. ^ Selley, Richard C. (2015). Elements of petroleum geology (Third ed.). Amsterdam: Academic Press. p. 377. ISBN 978-0-12-386031-6.
  2. ^ a b Coleman, J.L., Jr.; Cahan, S.M. (2012). Preliminary catalog of the sedimentary basins of the United States: U.S. Geological Survey Open-File Report 2012–1111. p. 27.
  3. ^ Abdullayev, N.R. (30 June 2020). [10.33677/ggianas20200100040 "Analysis of sedimentary thickness, volumes and geographic extent of the world sedimentary basins"]. ANAS Transactions, Earth Sciences (1). doi:10.33677/ggianas20200100040. {{cite journal}}: Check |url= value (help)
  4. ^ a b c Allen, Philip A.; John R. Allen (2008). Basin analysis : principles and applications (2. ed., [Nachdr.] ed.). Malden, MA [u.a.]: Blackwell. ISBN 978-0-6320-5207-3.
  5. ^ Boggs, Sam, Jr. (1987). Principles of sedimentology and stratigraphy. Columbus: Merrill Pub. Co. p. 265. ISBN 0675204879.
  6. ^ a b c d Ingersoll, Raymond V. (22 December 2011). "Tectonics of Sedimentary Basins, with Revised Nomenclature". Tectonics of Sedimentary Basins: 1–43. doi:10.1002/9781444347166.ch1.
  7. ^ a b c Cathy J. Busby and Raymond V. Ingersoll, ed. (1995). Tectonics of sedimentary basins. Cambridge, Massachusetts [u.a.]: Blackwell Science. ISBN 978-0865422452.
  8. ^ Dickinson, William R. (1974). Tectonics and Sedimentation. Special Publications of the Society for Sedimentary Geology.
  9. ^ Woodcock, Nigel H. (2004). "Life span and fate of basins". Geology. 32 (8): 685. doi:10.1130/G20598.1.
  10. ^ Boggs 1987, p.16
  11. ^ Klemme, H.D. (October 1980). "PETROLEUM BASINS-CLASSIFICATIONS AND CHARACTERISTICS". Journal of Petroleum Geology. 3 (2): 187–207. doi:10.1111/j.1747-5457.1980.tb00982.x.
  12. ^ Evenick, Jonathan C. (April 2021). "Glimpses into Earth's history using a revised global sedimentary basin map". Earth-Science Reviews. 215: 103564. doi:10.1016/j.earscirev.2021.103564.
  13. ^ "Sedimentary Basins of the World". Robertson CGG.

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