Sedimentary basins are region-scale depressions of the Earth's crust where subsidence has occurred and a thick sequence of sediments have accumulated to form a large three-dimensional body of sedimentary rock. They form when long-term subsidence creates a regional depression that provides accommodation space for accumulation of sediments. 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.
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. 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 subsidence and thus amplifies basin development as a result of isostasy.
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. 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. Intracratonic basins, which form on highly stable continental interiors, have a high probability of preservation. In contrast, sedimentary basins formed on oceanic crust are likely to be destroyed by subduction. Continental margins formed when new ocean basins like the Atlantic are created as continents rift apart are likely to have lifespans of hundreds of millions of years, but may be only partially preserved when those ocean basins close as continents collide.
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.Boggs 1987, p.16 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.
Classification A dozen or so common types of sedimentary basins are widely recognized and several classification schemes are proposed, however no single classification scheme is recognized as the standard.
Most sedimentary basin classification schemes are based on one or more of these interrelated criteria: Plate tectonic setting – the proximity to a divergent, convergent or transform plate tectonic boundary and the type and origin of the tectonically induced forces that cause a basin to form, specifically those active at the time of active sedimentation in the basin. Nature of underlying crust – basins formed on continental crust are quite different from those formed on oceanic crust as the two types of lithosphere have very different mechanical characteristics (rheology) and different densities, which means they respond differently to isostasy. Geodynamics of basin formation – the mechanical and thermal forces that cause lithosphere to subside to form a basin. Petroleum/economic potential – basin characteristics that influence the likelihood for the basin to have an accumulations of petroleum or the manner in which it formed.
Widely recognized types Although no one basin classification scheme has been widely adopted, several common types of sedimentary basins are widely accepted and well understood as distinct types. Over its complete lifespan a single sedimentary basin can go through multiple phases and evolve from one of these types to another, such as a rift process going to completion to form a passive margin. In this case the sedimentary rocks of the rift basin phase are overlain by those rocks deposited during the passive margin phase. Hybrid basins where a single regional basin results from the processes that are characteristic of multiple of these types are also possible.
+ Widely recognized types of sedimentary basins Sedimentary basin type Associated type of plate boundary Description and formation Modern, active examples Ancient (no longer active) examples Rift basin Divergent Rift basins are elongate sedimentary basins formed in depressions created by tectonically induced thinning (stretching) of continental crust, generally bounded by normal faults that create grabens and half-grabens. Some authors recognize two subtypes: Terrestrial Rift Valleys – largely subaerial valleys that are rifts in continental crust commonly with bimodal volcanism Proto-oceanic Rift Troughs – incipient ocean basins where new oceanic crust is forming, flanked on either side by young rifted continental margins Terrestrial rift valleys Rio Grande Rift Upper Rhine Plain East African Rift
Proto-oceanic rift troughs Gulf of Suez Rift Gulf of California Newark Basin Fundy Basin Midcontinent Rift System West Antarctic Rift System Oslo Graben Reelfoot Rift Passive margin Divergent Passive margins generally have deep sedimentary basins that form along the margin of a continent after two continents have completely rifted apart to become separated by an ocean. Cooling and densification of the underlying lithosphere over tens of millions of years drives subsidence that allows thick accumulations of sediments eroded from the adjacent continent. Some authors distinguish two subtypes based on volcanism during the early phases of margin development, non-volcanic passive margins and volcanic passive margins.
Passive margins are long-lived and generally become inactive only as a result of the closing of a major ocean through continental collision resulting from plate tectonics. As a result the sedimentary record of inactive passive margins often are found as thick sedimentary sequences in mountain belts. For example the passive margins of the ancient Tethys Ocean are found in the mountain belts of the Alps and Himalayas that formed when the Tethys closed. Tethys sedimentary sequence of the Tethys Himalaya (Tibet, Nepal) Late Jurassic and Triassic sedimentary sequence of the Southern Alps (northern Italy) Paleozoic sedimentary sequence of the southern Canadian Rocky Mountains Paleozoic sedimentary rocks of the Grand Canyon Foreland Basin Convergent An elongate basin that develops adjacent and parallel to an actively growing mountain belt when the immense weight created by the growing mountains on top of continental lithosphere causes the plate to bend downward.
Many authors recognize two subtypes of foreland basins: Peripheral foreland basins - where the topographic load of a large mountain belt being formed and thrust onto a plate, usually as a result of orogenesis due to continental collision, causes continental lithosphere to bend downward along the mountain front. Retroarc foreland basins - which form behind (landward from) an active volcanic arc associated with a convergent plate boundary Peripheral foreland basins Molasse basin Western Canadian Sedimentary Basin Himalayan foreland basin Persian Gulf Junggar Basin
Retroarc foreland basins Andean foreland basins Junggar Basin Alaska North Slope basin Western Interior Seaway Windermere Supergroup Appalachian Basin Sydney Basin Back-arc basin Convergent Back-arc basins result from stretching and thinning of crust behind volcanic arcs resulting when tensional forces created at the plate boundary pull the overriding plate toward the subducting oceanic plate in a process known as oceanic trench rollback. This only occurs when the subducting oceanic crust is older (>55 million years old), and therefore colder and denser, and being subducted at an angle greater than 30 degrees.
Sea of Japan Tyrrhenian Sea North Fiji Basin Lau Basin Pannonian Basin Rhenohercynian Zone Forearc basin Convergent A sedimentary basin formed in association with a convergent plate tectonic boundary in the gap between an active volcanic arc and the associated trench, thus above the subducting oceanic plate. The formation of a forearc basin is often created by the vertical growth of an accretionary wedge that acts as a linear dam, parallel to the volcanic arc, creating a depression in which sediments can accumulate. Mentawai Strait (aka Bengkulu-Mantawai forearc basin) Magdalena Shelf Nias Basin Strait of Georgia
Great Valley Sequence Oceanic trench Convergent Trench basins are deep linear depressions formed where a subducting oceanic plate descends into the mantle, beneath the overriding continental (Andean type) or oceanic plate (Mariana type). Trenches form in the deep ocean but, particularly where the overriding plate is continental crust they can accumulate thick sequences of sediments from eroding coastal mountains. Smaller 'trench slope basins' can form in association with a trench can form directly atop the associated accretionary prism as it grows and changes shape creating ponded basins. Middle America Trench Western edge of Vancouver Island Aleutian Trench Japan Trench Sunda Trench Peru–Chile Trench Farallon Trench Tethyan Trench Pull-apart basin Transform
Pull-apart basins is are created along major strike-slip faults where a bend in the fault geometry or the splitting of the fault into two or more faults creates tensional forces that cause crustal thinning or stretching due to extension, creating a regional depression. Frequently, the basins are rhombic, S-like or Z-like in shape. Dead Sea Los Angeles Basin Cayman Trough Salton Trough Gramscatho Basin Ridge Basin Cratonic basin (Intracratonic basin) None A broad comparatively shallow basin formed far from the edge of a continental craton as a result of prolonged, broadly distributed but slow subsidence of the continental lithosphere relative to the surrounding area. They are sometimes referred to as intracratonic sag basins. They tend to be subcircular in shape and are commonly filled with shallow water marine or terrestrial sedimentary rocks that remain flat-lying and relatively undeformed over long periods of time due to the long-lived tectonic stability of the underlying craton. The geodynamic forces that create them remain poorly understood. Barents Sea Chad Basin Michigan Basin Williston Basin Hudson Bay Basin Uinta Mountain Group Amadeus Basin Paraná Basin
Mechanics of formation Sedimentary basins form as a result of regional subsidence of the lithosphere, mostly as a result of a few geodynamic processes.
Lithospheric stretching