What is a contourite drift?
Contourite drifts are the large-scale morphological expression of contourite deposition, up to 106 km2 in area and >1 km in thickness. They are a common feature in some parts of the ocean basins and are found covering large areas of the present-day seafloor beneath modern bottom current systems.
What are bottom currents?
For physical oceanographers, deep-sea bottom currents are generally defined as the flow of water masses in the cold-water sphere beneath the base of the thermocline (Zenk, 2008). Bottom currents are also affected by intermittent processes, such as giant eddies, benthic storms, flow cascading, and tsunamis.
What type of sedimentary structure do turbidites show?
graded bedding
Turbidites are the deposits of turbidity currents and commonly show graded bedding with a sequence of sedimentary structures indicative of waning flow during the passage of the turbidity current (Ye et al., 2017), and progressively declining bed shear stress during deposition of the bed (Kneller, 2003).
What are contour currents?
contour current An undercurrent, typical of the continental rise, which flows along the western boundaries of ocean basins. Contour currents are persistent, slow-moving (velocity 5–30 cm/s) flows capable of transporting mud, silt, and sand.
What do turbidity currents produce?
Turbidity currents can change the physical shape of the seafloor by eroding large areas and creating underwater canyons. These currents also deposit huge amounts of sediment wherever they flow, usually in a gradient or fan pattern, with the largest particles at the bottom and the smallest ones on top.
Where is continental rise found?
The continental rise is a low-relief zone of accumulated sediments that lies between the continental slope and the abyssal plain. It is a major part of the continental margin, covering around 10% of the ocean floor.
Are there currents under the ocean?
There are two distinct current systems in the ocean—surface circulation, which stirs a relatively thin upper layer of the sea, and deep circulation, which sweeps along the deep-sea floor. These currents move water masses through the deep ocean—taking nutrients, oxygen, and heat with them.
How are bottom currents formed?
The different bottom currents at the shelf break are also discussed. These currents are generated by surface waves, tidal forces, wind forces, thermohaline differences, and internal waves. Vertical-upwelling currents are caused either by surface waters moving away from each other or by surface waters moving offshore.
How do you identify turbidites?
Classic, low-density turbidites are characterized by graded bedding, current ripple marks, climbing ripple laminations, alternating sequences with pelagic sediments, distinct fauna changes between the turbidite and native pelagic sediments, sole markings, thick sediment sequences, regular bedding, and an absence of …
Why do turbidites fine upward?
The rocks fine upward as the flow slows, resulting in the bouma sequence. The wavy line at the base of Bouma a in Figure 7 indicates an erosional surface, and flute casts or scour marks are sometimes present.
Why is turbidity current important?
What causes turbidity?
Turbidity is the measure of relative clarity of a liquid. The higher the intensity of scattered light, the higher the turbidity. Material that causes water to be turbid include clay, silt, very tiny inorganic and organic matter, algae, dissolved colored organic compounds, and plankton and other microscopic organisms.
How is a contourite formed?
A contourite is a sedimentary deposit commonly formed on continental rise to lower slope settings, although they may occur anywhere that is below storm wave base. Countourites are produced by thermohaline -induced deepwater bottom currents and may be influenced by wind or tidal forces.
What is the difference between contourite and sedimentary deposit?
A sedimentary deposit commonly formed on continental rise to lower slope settings. A contourite is a sedimentary deposit commonly formed on continental rise to lower slope settings, although they may occur anywhere that is below storm wave base.
What is a contourite depositional system?
When a contourite depositional system develop, it includes genetically linked erosional and depositional features (sediment drifts). Most typically, contourites are composed of fine-grained, structureless, highly bioturbated mud. However, they show a wide range of grain-sizes, composition, and preserved sedimentary structures.
What are the different types of contourite accumulations?
There are five main types of contourite accumulations: giant elongate drifts, contourite sheets, channel related drifts, confined drifts and modified drift-turbidite systems. Giant elongate drifts form very large mounded elongated geometries parallel to the deepwater bottom-current flow.