Turbidite sedimentology, biostratigraphy and paleoecology: A case study from the Oligocene Zuberec Fm. (Liptov Basin, Central Western Carpathians)
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Abstract Outcrops of a thick turbiditic succession are exposed on the northern bank of the Liptovská Mara reservoir near Liptovská Ondrašová and Ráztoky. The section consists of rhythmic, predominantly thin- to medium-bedded turbidites of the Rupelian age. Their biostratigraphy is based on the calcareous nannofossils. Facies associations of these deposits represent different components of depositional lobe deposits in the turbidity fan system, including mainly the lobe fringe and lobe distal fringe/inter-lobe facies associations and locally the medium bedded deposits of the lobe off-axis facies association. This interpretation is supported by statistical analysis. The deep-sea turbiditic deposits contain trace fossil associations, which include deep-tier fodinichnia and domichnia up to shallow-tier graphoglyptids. Paleocurrent measurements indicate that the majority of sedimentary material was transported from SW and W.Keywords:
Paleocurrent
Outcrop
Turbidity current
Lobe
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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The Orleansville earthquake in 1954 produced a turbidity current on the Algerian Mediterranean margin and adjacent South Balearic basin sea floor which broke five telephone cables. The report of this event represented a cornerstone in the evolution of turbidity current theory. The resulting turbidite has been mapped on the Balearic abyssal plain for the purpose of relating flow paths and turbidite size, and areal extent to cable break locations. This study is based on 50 gravity cores. Figure The Orleansville turbidity current actually consisted of two currents which arrived simultaneously on the basin plain via two canyon mouths separated by 30 km. The merged turbidity currents flowed 170 km out on the basin-plain floor and covered an area of 8,000 km2. The turbidite is a tongue-shaped sediment body, 50 km wide, oriented northeast-southwest. It consists of a central band of 5-cm thick sand with a fringing 2 to 3-cm thick band of coarse to fine silt. Two of the cable breaks occurred on the abyssal plain at the extreme edge of the turbidite where the sediment is only 2 cm thick. An underlying turbidite of very similar dimensions to the Orleansville turbidite is separated from it by a 10 to 15-cm pelagic sequence. The consistent spacing between these two events in icates that although the Orleansville turbidity current broke telephone cables at its extreme margins, it caused no detectable erosion on the basin-plain floor. End_of_Article - Last_Page 641------------
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ABSTRACT Experimental turbidity currents entering two‐layer density‐stratified water behave differently from similar currents flowing over the same topography into non‐stratified water. Experiments were designed as analogues for flows entering Mediterranean hypersaline pools. In both the hypersaline pools and the experiments, the water density changes abruptly across a pycnocline. Turbidity currents generated on a platform at the level of the pycnocline behaved in one of three ways as they flowed from the platform into deeper stratified water. (1) When the bulk density of the current was less than the dense water layer, the current spread at the pycnocline. The head of the current advanced rapidly when it lost contact with the bed. Grains settling out of the current fell through the dense water layer forming an extensive deposit. In nature this behaviour will lead to ‘turbidites’ with sharp but non‐erosive bases, strongly developed grading and no traction features. (2) When the bulk density of the current was greater than the dense water layer, the current continued as an underflow, plunging into the deeper water. Sedimentation lowered the bulk density of the current and the low‐density interstitial fluid caused the head to loft. Low‐density interstitial fluid convected from the body of the current, lofting particles into the water column. These particles were hydraulically sorted during upward transport and subsequent settling to the floor. The resulting turbidites had a more limited extent than the deposits of either non‐lofting underflows or interflows. By inference from the experiments, natural deposits of this type may have local (proximal) erosion and traction features at the base and strongly graded tops. (3) In some of the currents with high bulk density, the rising turbid water reached the pycnocline and spread at that level as a secondary interflow. The tail of the turbidity current, which was less dense than the head and body of the current, flowed above the pycnocline adding momentum to the secondary interflow. The thin non‐erosive graded deposit from the secondary interflow may extend beyond the deposits of the primary underflow. In all three cases (but more pronounced in cases 2 and 3) the interaction of the current with the pycnocline displaced that surface and generated a wave that was reflected back and forth from each end of the pool. The waves remobilized sediment on the ramp.
Pycnocline
Turbidity current
Stratification (seeds)
Settling
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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.
Turbidity current
Turbidity
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Turbidity current
Ripple marks
Deposition
Bedform
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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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