Paleontological Studies on Turbidite Sedimentation and Erosiona
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The postdepositional sole trails of Flysch psammites occur only in thinner beds up to a thickness particular to each species. This proves instantaneous deposition of the individual beds, as postulated by the turbidity-current theory. The majority of the sole trails are predepositional mud burrows washed out and sand cast by turbidity currents. Thus erosion of an unusual type must have preceded every turbidite sedimentation.Keywords:
Turbidity current
Sedimentation
Flysch
Deposition
Turbidity
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The postdepositional sole trails of Flysch psammites occur only in thinner beds up to a thickness particular to each species. This proves instantaneous deposition of the individual beds, as postulated by the turbidity-current theory. The majority of the sole trails are predepositional mud burrows washed out and sand cast by turbidity currents. Thus erosion of an unusual type must have preceded every turbidite sedimentation.
Turbidity current
Sedimentation
Flysch
Deposition
Turbidity
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ABSTRACT A detailed survey of the upper and middle Nova Scotian continental slope at 42°50′N and 63°30′W indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel. The range of sediment facies is diverse including hemipelagic and turbidite muds, turbidite sands and gravelly sandy muds of debris flow origin. Deformed units, interpreted as slump deposits are also observed. Several facies associations, related to discrete morphological environments, are recognized. Thick turbidite sand units with minor intervening mud beds are characteristic of the high‐relief uppermost slope and channel margin. Thinner turbidite sands, deformed slump beds and various mud facies are associated with small‐scale, hummocky mid‐slope topography. Sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents. At the lower end of the main turbidity current channel, frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe. In areas unaffected by mass movements, alternating bioturbated mud and sandy muds make up the core sequences. A local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range of settings.
Turbidity current
Continental Margin
Debris flow
Sedimentation
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SUMMARY Some results of turbidity‐current theory are applied to analyses of turbidite layers in cores from the route of a large turbidity current of sheet‐flow type. Novel features are that current velocity is estimated from the sediment sizes deposited, and the lateral spreading of the current is considered. An approximate quantitative picture of the current is obtained. It is compared with the turbidity current which caused the Grand Banks cable breaks.
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Turbidity
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Flotation is a method in which particles in liquid phase are transported to the surface by air bubbles. In this experimental study, a comparison has been made between conventional sedimentation and dissolved air flotation (DAF) systems to remove turbidity from water. Initially, optimal operational conditions for each system utilized using water artificially turbid with Kaolin. For each system, samples were taken at 20-min interval after the system reached its optimal operational conditions. Parameters, such as turbidity, alkalinity, temperature, pH, and total suspended solids, were measured. For 20, 30–50 and 90–110 NTU, turbidity average removal efficiencies in DAF system were 14.7, 11.1 and 10.9%, respectively, larger than the conventional sedimentation system. The effect of coagulant dose indicated that DAF system with lower dosage of coagulant have higher removal efficiency. On the other hand, the results showed that due to increased efficiency of DAF system, solid concentration of sludge produced in this system was more than the sedimentation system (p < 0.01). However, operation of DAF system needs accurate control devices and experienced technical staff to operate the system.
Turbidity
Sedimentation
Dissolved air flotation
Alkalinity
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Turbidity current
Debris flow
Turbidity
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SUMMARY The matrix (< 40 μ) of turbidites forms a possible clue to the density of turbidity currents and the origin of the graywacke matrix. Experiments in a circular flume provide a mechanism to study the relation between composition of suspensions at various speeds and their deposits. There is a close analogy to the lower part of turbidity currents. The lutum content of samples with median diameters greater than 400 or 500 μ is found to correspond to the suspended load of the pore water. The higher value for finer deposits can be recalculated to suspension concentration by use of the “sedimentation factor”. Hence, each turbidite carries, as it were, a sample of its depositing current. The lutum content depends not on the ratio of sand to lutum in the current, as tacitly assumed by many authors, but mainly on the ratio lutum to water, although also influenced by velocity. The average lutum density of coarser recent deep‐sea sands is 1‐2%. This indicates turbidity currents with 5‐10% lutum by weight (density 1.03–1.07). The sand must be added to ascertain the current density. In first approximation turbidity currents tend to have densities at their nose of 1.1–1.2, but higher and much lower values also occur. The maximum original lutum percentage of coarse turbidites is below 10%. Higher values are very scarce and are due to post‐depositional mixing, or we are dealing with slides. However, in fine‐grained turbidites there is more matrix up to 20% for a median of 100 p. Hence, coarse graded marine graywackes with 20 or more per cent matrix are presumably weakly metamorphic turbidites, that originally held the same modest amount of lutum as recent turbidites of the same grain size. The Trask sorting of the experimental deposits is very good, like the average of natural turbidites. Most cumulative curves of turbidite grain‐size analyses on arithmetic probability paper show a characteristic bend in fine sand or silt sizes.
Turbidity current
Flume
Turbidity
Matrix (chemical analysis)
Sedimentation
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A detailed survey of the upper and middle Nova Scotian continental slope at 42°50'N and 63°30'W indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel. The range of sediment facies is diverse including hemipelagic and turbidite muds, turbidite sands and gravelly sandy muds of debris flow origin. Deformed units, interpreted as slump deposits are also observed. Several facies associations, related to discrete morphological environments, are recognized. Thick turbidite sand units with minor intervening mud beds are characteristic of the high-relief uppermost slope and channel margin. Thinner turbidite sands, deformed slump beds and various mud facies are associated with small-scale, hummocky mid-slope topography. Sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents. At the lower end of the main turbidity current channel, frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe. In areas unaffected by mass movements, alternating bioturbated mud and sandy muds make up the core sequences. A local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range of settings.
Turbidity current
Debris flow
Continental Margin
Sedimentation
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Flysch
Turbidity current
Deposition
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