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Contourites are oceanic sedimentary deposits originated by the circulation of thermohaline oceanic currents of contour, named this way because they follow bathymetric curves. These currents are caused by the global marine circulation and correspond to those of low temperature, which together warm temperature currents, conform a system of vital importance. These currents may flow upwards, downwards, around or above obstacles or irregular topographies.  

Contourites are oceanic sedimentary deposits originated by the circulation of thermohaline oceanic currents of contour, named this way because they follow bathymetric curves. These currents are caused by the global marine circulation and correspond to those of low temperature, which together warm temperature currents, conform a system of vital importance. These currents may flow upwards, downwards, around or above obstacles or irregular topographies.  

== Formation ==

== Formation ==

Bottom currents are responsible of contourites formation. They are affected by variations in temperatures, salinity, tides, waves, wind, topography and physical barriers that have to pass trough.

Bottom currents are responsible of contourites formation. They are affected by variations in temperatures, salinity, tides, waves, wind, topography and physical barriers that have to pass trough.

[[File:Thermohaline currents.png|900|thumbnail|right|Figure 1: Thermohaline currents. Shallow-water bottom currents in red; Bottom deep currents in light bue and dark blue; sea places where the currents changes dramatically its position in the water column (oranges ovals)]]

 

[[File:Thermohaline currents.png|400px|thumbnail|right|Figure 1: Thermohaline currents. Shallow-water bottom currents in red; Bottom deep currents in light blue and dark blue; sea places where the currents changes dramatically its position in the water column (oranges ovals)]]

Thermohaline currents are the most common of type of bottom current, they conform the global conveyor belt (Figure 1). Its name derives from ''thermal''= temperature and ''haline''=salinity. Its relevance is in distributing the heat all over the world, from the tropics to Polar Regions. Changes on them could cause radical climate changes.

Thermohaline currents are the most common of type of bottom current, they conform the global conveyor belt (Figure 1). Its name derives from ''thermal''= temperature and ''haline''=salinity. Its relevance is in distributing the heat all over the world, from the tropics to Polar Regions. Changes on them could cause radical climate changes.

This process of global ocean circulation is affected by several factors:

This process of global ocean circulation is affected by several factors:

[[File:Bottom currents.png|1000|thumbnail|Figure 2: Principal characteristics of bottom currents]]

[[File:Bottom currents.png|400px|thumbnail|right|Figure 2: Principal characteristics of bottom currents]]

* '''Winds''': affect surface water, generate movement direction parallel to its direction due to the effect of shear, subsequent propagation and movement through the water column. The winds that affect the flow, are the Trade winds and the West.

* '''Winds''': affect surface water, generate movement direction parallel to its direction due to the effect of shear, subsequent propagation and movement through the water column. The winds that affect the flow, are the Trade winds and the West.

* '''Coriolis Effect''': diverts the winds, which are a meridional direction. Those that go to the poles, turning east, while those who turn to Ecuador, turn west.

* '''Coriolis Effect''': diverts the winds, which are a meridional direction. Those that go to the poles, turning east, while those who turn to Ecuador, turn west.

== Contourite Facies and Features ==

== Contourite Facies and Features ==

[[File:Sedimentary structures in contourite facies models.jpg|thumbnail|right|Sedimentary structures in muddy and sandy contourite facies models.jpg]]

[[File:Sedimentary structures in contourite facies models.jpg|300px|thumbnail|right|Sedimentary structures in contourite facies models]]

Contourite deposits, also called drift, surface can range from small sizes (100km2) to giant (> 100,000 km2). A good example is the basin of Argentina that reaches cover an area 1,000,000km2. On average, its width, ranging from tens to hundreds of kilometers and its thickness from tens to 2000 meters. These can vary widely depending on factors such as sediment, stream velocity, availability of oxygen and others.

Contourite deposits, also called drift, surface can range from small sizes (100km2) to giant (> 100,000 km2). A good example is the basin of Argentina that reaches cover an area 1,000,000km2. On average, its width, ranging from tens to hundreds of kilometers and its thickness from tens to 2000 meters. These can vary widely depending on factors such as sediment, stream velocity, availability of oxygen and others.

Tractive structures, product of the movement of bottom currents that form, are abundant and the most common are ripples currents and cross lamination. Some authors propose that flasser and lenticular-like structures characterized this type of deposit and different from others, as they reflect the variation in the intensity of the current, as well as the selection of grain selection (grading) and erosive scars also represent the same processes. Other common structures are horizontally or sinusoidal lamination, parallel lamination, crossbedding, pebblelags, etc. The preservation of these depends greatly on the degree of bioturbation that can reach delete left a massive structure.

Tractive structures, product of the movement of bottom currents that form, are abundant and the most common are ripples currents and cross lamination. Some authors propose that flasser and lenticular-like structures characterized this type of deposit and different from others, as they reflect the variation in the intensity of the current, as well as the selection of grain selection (grading) and erosive scars also represent the same processes. Other common structures are horizontally or sinusoidal lamination, parallel lamination, crossbedding, pebblelags, etc. The preservation of these depends greatly on the degree of bioturbation that can reach delete left a massive structure.

[[File:Drift Features.png|1000|thumbnail|left|Classification based on its morphological, sedimentological and seismic characteristics (Rebesco 2005)]]

[[File:Drift Features.png|300px|thumbnail|left|Figure 3: Classification based on its morphological, sedimentological and seismic characteristics (Rebesco 2005)]]

Biogenic structures are usually diagnostic features of contourite deposits when conditions favor the benthic life and when the speed of the current cannot erase them. The mottling is the common structure sizes ranging from millimetric to centimetric but also usually appear ichnofacies like fodichnia, pascichnia and domichnia. The factor that primarily affects their absence or abundance is the oxygenation of the ocean floor.

Biogenic structures are usually diagnostic features of contourite deposits when conditions favor the benthic life and when the speed of the current cannot erase them. The mottling is the common structure sizes ranging from millimetric to centimetric but also usually appear ichnofacies like fodichnia, pascichnia and domichnia. The factor that primarily affects their absence or abundance is the oxygenation of the ocean floor.

As for the fossil content, it depends on the parent material reworked, being common remains of planktonic animals.

As for the fossil content, it depends on the parent material reworked, being common remains of planktonic animals.

Another facies classification is proposed by Stow et al (1996). They propose that there clastic contourites (muddy, silty, sandy, gravel lag, micro-brecciated) biogenic (carbonate or siliceous) chemogenic and also the shallow water contourites.

Another facies classification is proposed by Stow et al (1996). They propose that there clastic contourites (muddy, silty, sandy, gravel lag, micro-brecciated) biogenic (carbonate or siliceous) chemogenic and also the shallow water contourites.

The depositional features can be classified into shallow (less than 300m), intermediate (between 300 and 2000 m) and deep drifts (more than 2000m). The most widely used classification (Rebesco, 2005) is based on its morphological, sedimentological and seismic characteristics shown in Figure 3.

The depositional features can be classified into shallow (less than 300m), intermediate (between 300 and 2000 m) and deep drifts (more than 2000m). The most widely used classification (Rebesco, 2005) is based on its morphological, sedimentological and seismic characteristics shown in Figure 3.

== Bibliography ==

== Bibliography ==

* Stow D.A.V., Hunter S., Wilkinson D. Hernández-Molina and F.J., “The Nature Of Contourite Deposition”

* Stow D.A.V., Hunter S., Wilkinson D. Hernández-Molina and F.J., “The Nature Of Contourite Deposition”

* Faugeres J.-C. and Stow D.A.V. “Contourite Drifts: Nature, Evolution And Controls”

* Faugeres J.-C. and Stow D.A.V. “Contourite Drifts: Nature, Evolution And Controls”