Changes

[[File:Webcam-toy-foto13.jpg|400px|thumbnail|right|Schematic distribution of contourite's facies. It shows a longitudinal and transverse decrease in current intensity.]]

[[File:Webcam-toy-foto13.jpg|400px|thumbnail|right|Schematic distribution of contourite's facies. It shows a longitudinal and transverse decrease in current intensity.]]

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.  

In addition of taking part in the regulation of global temperatures and the distribution of the marine fauna, countour currents generate across-slope processes, that together with along-slope processes, dominate large part of the sedimentary dynamics in deep marine environments, either within the continenetal slope or the continental rise. Along-slope processes may generate drift or contouritic features. The latter are less known than the former, which are considered erosional terraces, contourite channels, abraded surfaces, moats and furrows (Hernandez-Molina et al.,2008).  

In addition of taking part in the regulation of global temperatures and the distribution of the marine fauna, countour currents generate across-slope processes, that together with along-slope processes, dominate large part of the sedimentary dynamics in deep marine environments, either within the continenetal slope or the continental rise. Along-slope processes may generate drift or contouritic features. The latter are less known than the former, which are considered erosional terraces, contourite channels, abraded surfaces, moats and furrows (Hernandez-Molina et al.,2008).  

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.

The lithology of these deposits does not differ much with respect to pelagic sediments and hemipelagic, it's commonly a mixed nature between terrigenous, biogenic, chemogenic and volcanigenic composition. Grain sizes is commonly fine size from silt and sand but also gravel size, and are considered a good to very good selection.

The lithology of these deposits does not differ much with respect to pelagic sediments and hemipelagic, it's commonly a mixed nature between terrigenous, biogenic, chemogenic and volcanigenic composition. [[Grain size]]s are commonly fine size from silt and sand but also gravel size, and are considered a good to very good selection.

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|300px|thumbnail|left|Figure 3: 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.

The increasing use by academic institutions of high-resolution swath bathymetry and sea-floor imaging techniques, coupled correlating seismic anomalies from 3D mapping with core and well logging data reveals the depositional geometry and sedimentological characteristics of coarse-grained contourites.

The increasing use by academic institutions of high-resolution swath bathymetry and sea-floor imaging techniques, coupled correlating seismic anomalies from 3D mapping with core and well logging data reveals the depositional geometry and sedimentological characteristics of coarse-grained contourites.

Contourite deposits must present some particular characteristics. Coarse-grained sediments,preserving good petrophysical characteristics, such as porosity, permeability, and lateral and vertical transmissibility of fluids, must form part of the deposit, wich could be a great reservoir.  

Contourite deposits must present some particular characteristics. Coarse-grained sediments,preserving good petrophysical characteristics, such as porosity, permeability, and [[lateral]] and vertical transmissibility of fluids, must form part of the deposit, wich could be a great reservoir.  

Fine-grained drifts can locally and regionally develop large and thick accumulations, which have an important seal potential for trapping hydrocarbon. The depth, thickness, extent and properties of these sands are determining.  

Fine-grained drifts can locally and regionally develop large and thick accumulations, which have an important seal potential for trapping hydrocarbon. The depth, thickness, extent and properties of these sands are determining.  

== Bibliography ==

== Bibliography ==

 

* Rebesco M. and A. Camerlenghi, 2008, Contourites: Elsevier Science

* Rebesco M. and Camerlenghi A., 2008. Contourites. El SevierScience

* Stow D. A. V., C. J. Pudsey J. A. Howe J.-C. Faugères and A. R. Viana, 2002, Deep-Water Contourite Systems: Modern Drifts and Ancient Series, Seismic and Sedimentary Characteristics: Geological Society Memoir 22

* Stow D. A. V., Pudsey C. J., Howe J. A., Faugères J.-C. and Viana A. R., 2002. Deep-WaterContouriteSystems: Modern Drifts and Ancient Series, Seismic and Sedimentary Characteristics. Geological SocietyMemoir No. 22

* Zabala C., 2004, “Cuso de campo sobre Sedimentología Descriptiva”.

* Zabala C. (2004), “Cuso de campo sobre Sedimentología Descriptiva”.

* Rebesco M., A. Camerlenghi and A. J. Van Loon, 2008, “Contourite Research: A Field In Full Development, in: M. Rebesco & A. Camerlenghi, eds., Contourites: Developments in Sedmentology, 60, pp. 1-10

* Stow D.A.V., Pudsey C. J., Howe J. A., Faugeres J.-C and Viana A. R.(2002), “Deep-Water contourite Systems: modern drifts and ancient series, Seismic and sedimentary characteristics”.

* Zenk, W., 2008, Abyssal and Contour Currents, in: M. Rebesco & A. Camerlenghi, eds., Contourites: Developments in Sedmentology 60, pp. 37-57

* Rebesco1 M., Camerlenghi A. and Van Loon A.J., “Contourite Research: A Field In Full Development”

* Zenk W., “Abyssal and Contour Currents”

* Shanmugam G., “Deep-Water Bottom Currents And Their Ddeposits”

* Shanmugam G., “Deep-Water Bottom Currents And Their Ddeposits”

* Salon S., Crise A. and Van Loon A.J. “Dynamics Of The Bottom Boundary Layer”

* Salon S., Crise A. and Van Loon A.J. “Dynamics Of The Bottom Boundary Layer”

* He Y., Duan T. and Gao Z., “Sediment Entrainment”

* He Y., Duan T. and Gao Z., “Sediment Entrainment”

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

* Stow D.A.V., S. Hunter D. Wilkinson and F. J. Hernández-Molina, The Nature Of Contourite Deposition in: M. Rebesco & A. Camerlenghi, eds., Contourites: Developments in Sedmentology 60, pp. 143-156

* 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”

* Viana A. R., REBESCO M., 2007. "Economic and Palaeoceanographic Significance of Contourite Deposits"

* Viana A. R., REBESCO M., 2007. "Economic and Palaeoceanographic Significance of Contourite Deposits"