EQUILIBRIUM THICKNESS OF THE HIGH-CONCENTRATION LAYER FORMED AT LOWER TURBIDITY CURRENTS

2018 ◽  
Vol 74 (5) ◽  
pp. I_811-I_816
Author(s):  
Norihiro IZUMI
Keyword(s):  
Turbidity Currents ◽  
High Concentration ◽  
Concentration Layer ◽  
Equilibrium Thickness

The Sedimentary Structures and Depositional Mechanics of Certain Ordovician Turbidites, Cloridorme Formation, Gaspé Peninsula, Quebec

1975 ◽  
Vol 12 (11) ◽  
pp. 1934-1952 ◽  
Author(s):  
Keith Skipper ◽  
Gerard V. Middleton
Keyword(s):  
Large Scale ◽  
Fine Sand ◽  
Coarse Sand ◽  
Turbidity Currents ◽  
Upstream Migration ◽  
High Concentration ◽  
Sedimentary Structures ◽  
The North ◽  
Gaspe Peninsula ◽  
Gaspé Peninsula

Turbidites, belonging to the β1, member, Cloridorme Formation, are exposed on the north shore of the Gaspé Peninsula, Quebec. Their structural attitude is such that vertical sections through turbidite beds are exposed on the wave-cut platform and their strike is approximately parallel to the paleocurrent direction, as shown by sole marks on the bases of beds.Certain thick turbidite beds, in a distal position, display a sequence of sedimentary structures which differs from the sequence defined by Bouma. Three broad divisions are recognized: a basal division consists of either limestone or quartz granule to pebble conglomerate (0–4 cm thick) or coarse sand graywacke or calcareous wacke (0–15 cm thick). Basal divisions of calcareous wacke frequently display ripple-lamination, parallel lamination, or upstream-inclined laminae. Where the upstream inclined laminae form a single set, they occur below a sinuous profile (wavelength 40–80 cm, and amplitude 2–5 cm).A second division (0–330 cm thick) consists in most places of spindle- or globular-shaped calcareous nodules scattered in an argillaceous host. In some beds, streaking and lobing of light colored, carbonate bearing material is associated with these nodules. Internal hemi-ellipsoid structures, arranged en echelon and convex towards the base of the bed, are displayed from the second division. The upper division consists of fine grained siltstone and shale.The upstream-inclined laminae in the basal division of calcareous wacke beds are interpreted as being the result of the upstream migration of antidunes. The nodules within the second division developed as 'pseudo-nodules'. The hemi-ellipsoid structures resemble damped, large scale (macroturbulent) eddies associated with the flow of dense grain dispersions.Correlation of these beds has been achieved over a distance of 12 km. Basal divisions of granule and pebble conglomerate persist over this distance and show that coarse particles may be transported by turbidity currents over long distances. The sedimentary structures of the basal divisions of several calcareous wacke beds might be interpreted as the result of either an increase in flow regime downcurrent, or of nonpreservation of structures at up-current localities.The beds were probably deposited from turbidity currents composed largely of mud and fine sand, but containing a zone of coarse grains concentrated near the bed. The basal division was deposited from this lower zone and a period of traction formed rippled, flat, or antidune bed forms. Stratification in the basal division was preserved by the rapid deposition on top of sediment that settled en masse from the subsequent high concentration body of the current. The formation of a succession of 'quick' beds led to the sedimentation of the second division. The flows responsible for the sequence of structures observed and the downcurrent persistence of the beds probably approached closely a state of 'autosuspension'.

EXPERIMENTS ON DENSITY AND TURBIDITY CURRENTS: III. DEPOSITION OF SEDIMENT

1967 ◽  
Vol 4 (3) ◽  
pp. 475-505 ◽  
Author(s):  
Gerard V. Middleton
Keyword(s):  
Settling Velocity ◽  
Size Variation ◽  
The Body ◽  
Turbidity Currents ◽  
Rapid Decline ◽  
Layer By Layer ◽  
Lateral Size ◽  
High Concentration ◽  
Low Concentration ◽  
Median Diameter

Turbidity currents were formed by releasing suspensions of plastic beads (density 1.52, median diameter 0.18 mm) from a lock into a horizontal water-filled flume. Graded beds were formed; the mechanism of deposition was studied by motion photography and the size grading by 150 size analyses.Deposition of sediment took place behind the head even at a time when there was no deceleration of the head: the greater part of the thickness of the bed was deposited during a period of rapid decline in velocity of flow within the body of the current. The mechanism of deposition and the type of grading differed for beds deposited from suspensions with concentrations less than and greater than about 30% by volume. Low concentration suspensions formed 'distribution grading' in which all percentiles showed vertical grading and at least the coarser half of the distribution showed lateral size decrease away from the gate. High concentration suspensions formed 'coarse-tail grading' in which there was almost no lateral size variation and the vertical grading was shown only by the coarsest few percentiles (except at the top of the bed).In high concentration flows the bed did not accumulate layer by layer, as it did in low concentration flows, but was deposited first as an expanded 'quick' layer, which was deformed by shearing and waves produced by the entrained water flowing over the still plastic bed.In both types of graded beds the sorting coefficient (standard deviation of the logarithm of the settling velocity) decreased upward within the bed, and to a lesser extent also laterally away from the gate. The skewness reached a maximum near the center of the bed and became negative at the top.

scholarly journals The stratigraphic evolution of a submarine channel: linking seafloor dynamics to depositional products

2020 ◽  
Vol 90 (7) ◽  
pp. 673-686
Author(s):  
Stephen M. Hubbard ◽  
Zane R. Jobe ◽  
Brian W. Romans ◽  
Jacob A. Covault ◽  
Zoltan Sylvester ◽  
...  
Keyword(s):  
Turbidity Currents ◽  
High Concentration ◽  
Bounding Surface ◽  
Cross Sectional ◽  
Genetic Link ◽  
Submarine Channel ◽  
Time Space ◽  
Stratigraphic Evolution ◽  
Geomorphic Surfaces ◽  
The Relationship

ABSTRACT We investigate the relationship between the cross-sectional geomorphic expression of a submarine channel as observed on the seafloor and the stratigraphic product of long-lived erosion, bypass, and sediment deposition. Specifically, by reconstructing the time–space evolution of an individual channel fill (i.e., channel element) exposed in outcrop, we establish a genetic link between thick-bedded channel-element-axis sandstone to thinly interbedded channel-element-margin deposits. Although the bounding surface between axis sandstone and margin thin beds is sharply defined, it is composed of a series of geomorphic surface segments of various ages; as such, the composite stratigraphic surface (∼ 17 m relief) was formed from numerous incision events that repeatedly sculpted the conduit. By demonstrating the origin of the stratigraphic surface, we conclude that geomorphic surfaces with 2–7 m of erosional relief were largely responsible for the observed intra-channel-element architecture (and ultimately, the composite 17-m-thick element). The widely documented channel element axis-to-margin architecture is a product of submarine-channel thalweg dynamics, primarily recording interactions between the seafloor and the basal high-concentration layers of channelized turbidity currents.

scholarly journals A 3D Numerical Model for Turbidity Currents

2020 ◽  
Vol 15 ◽  
Keyword(s):  
Numerical Model ◽  
Two Phase Flow ◽  
Curvilinear Coordinates ◽  
Turbidity Currents ◽  
Phase Flow ◽  
High Concentration ◽  
Two Phase ◽  
Motion Equations ◽  
Vertical Coordinate ◽  
Flow Motion

A numerical model that solves two-phase flow motion equations to reproduce turbidity currents that occur in reservoirs, is proposed. Three formalizations of the two-phase flow motion equations are presented: the first one can be adopted for high concentration values; the second one is valid under the hypothesis of diluted concentrations; the third one is based on the assumption that the particles are in translational equilibrium with the fluid flow. The proposed numerical model solves the latter formalization of two-phase flow motion equations, in order to simulate turbidity currents. The motion equations are presented in an integral form in time-dependent curvilinear coordinates, with the vertical coordinate that varies in order to follow the free surface movements. The proposed numerical model is validated against experimental data and is applied to a practical engineering case study of a reservoir, in order to evaluate the possibility of the formation of turbidity currents.

scholarly journals Sediment transfer in the Rhône River Basin, Switzerland: the role of localized severe Alpine storm events on triggering turbidity currents in Lake Geneva

2021 ◽  
Author(s):  
François Mettra ◽  
Koen Blanckaert ◽  
Ulrich Lemmin ◽  
David Andrew Barry
Keyword(s):  
Large Scale ◽  
River Mouth ◽  
Sediment Concentration ◽  
Turbidity Currents ◽  
Storm Events ◽  
Lake Geneva ◽  
High Concentration ◽  
Low Velocity ◽  
Sediment Transfer

<p>In Lake Geneva, a deep peri-Alpine lake in Switzerland, the sublacustrine Rhône River delta presents a deep canyon, the Rhône Canyon. Previous studies and recent observations show that low-velocity underflows and high-velocity turbidity currents pass frequently in the Rhône Canyon. The former carry little sediment, are long-lasting, slow moving and typically occur in winter when the lake is destratified, whereas the latter are sediment-rich, short-lived and occasionally generate high velocities. In the present study, we revisit three different event types that can trigger turbidity currents in the Rhône Canyon: large-scale floods of the Rhône River, sublacustrine slides on the Rhône delta and short high concentration sediment transport events induced by localized severe storms in the Rhône watershed (~5500 km<sup>2</sup>). Simultaneous observations of hyperconcentrated sediment-laden floods or debris flows in small sub-catchments (as small as 4 km<sup>2</sup>), suspended sediment concentration at the Rhône river mouth, and velocity profiles in the Rhône canyon demonstrate how localized storm events trigger turbidity currents in the canyon. Evidence that these turbidity currents can continue into the deep hypolimnion of Lake Geneva is provided. Preliminary estimations of the frequency of turbidity currents relative to their type of triggering and their contribution to the total sediment load discharged into Lake Geneva are discussed.</p>

Seasonal variability in turbidity currents in Lake Ohau, New Zealand, and their influence on sedimentation

2016 ◽  
Vol 67 (11) ◽  
pp. 1725 ◽  
Author(s):  
R. Cossu ◽  
A. L. Forrest ◽  
H. A. Roop ◽  
G. B. Dunbar ◽  
M. J. Vandergoes ◽  
...  
Keyword(s):  
New Zealand ◽  
Internal Waves ◽  
Sediment Accumulation ◽  
Turbidity Currents ◽  
Physical Processes ◽  
High Concentration ◽  
Sediment Delivery ◽  
Climate Conditions ◽  
River Inflow ◽  
Rain Events

Layers of sediment that are deposited on the floor of Lake Ohau, New Zealand, offer a means to reconstruct past climate conditions in the Southern Hemisphere at subdecadal and annual resolution. A robust understanding of the modern physical processes that control the influx and dispersal of sediment in the lake is required to reconstruct climate from these sedimentary archives. In this study, water temperature and velocity measurements collected during 2012–13 were analysed to determine the primary physical processes that influence sediment transport in the lake. Sediment input from river inflow occurs throughout the year but exhibits strong seasonal variation. Large inflow events (Q>500m3s–1) that follow strong summer rainstorms trigger high-concentration turbidity currents, which are the main agents for sediment delivery and deposition. During winter, smaller turbidity currents also occur after rain events and contribute to annual sediment accumulation. In addition, large internal waves were observed during the summer and may influence sedimentation. In conclusion, several processes including river inflow, internal waves and convectively driven flows control sediment deposition and accumulation in the Lake Ohau system. We utilise these observations to establish a conceptual model to explain the observed infill stratigraphy in Lake Ohau and guide interpretation of the longer sedimentary record.

Sinking, merging and stationary plumes in a coupled chemotaxis-fluid model: a high-resolution numerical approach

2012 ◽  
Vol 694 ◽  
pp. 155-190 ◽  
Author(s):  
A. Chertock ◽  
K. Fellner ◽  
A. Kurganov ◽  
A. Lorz ◽  
P. A. Markowich
Keyword(s):  
High Resolution ◽  
Stokes Equations ◽  
Fluid Model ◽  
Numerical Approach ◽  
Navier Stokes ◽  
High Concentration ◽  
Fluid System ◽  
Concentration Layer ◽  
High Concentrations ◽  
Chemotaxis System

AbstractAquatic bacteria like Bacillus subtilis are heavier than water yet they are able to swim up an oxygen gradient and concentrate in a layer below the water surface, which will undergo Rayleigh–Taylor-type instabilities for sufficiently high concentrations. In the literature, a simplified chemotaxis–fluid system has been proposed as a model for bio-convection in modestly diluted cell suspensions. It couples a convective chemotaxis system for the oxygen-consuming and oxytactic bacteria with the incompressible Navier–Stokes equations subject to a gravitational force proportional to the relative surplus of the cell density compared to the water density. In this paper, we derive a high-resolution vorticity-based hybrid finite-volume finite-difference scheme, which allows us to investigate the nonlinear dynamics of a two-dimensional chemotaxis–fluid system with boundary conditions matching an experiment of Hillesdon et al. (Bull. Math. Biol., vol. 57, 1995, pp. 299–344). We present selected numerical examples, which illustrate (i) the formation of sinking plumes, (ii) the possible merging of neighbouring plumes and (iii) the convergence towards numerically stable stationary plumes. The examples with stable stationary plumes show how the surface-directed oxytaxis continuously feeds cells into a high-concentration layer near the surface, from where the fluid flow (recurring upwards in the space between the plumes) transports the cells into the plumes, where then gravity makes the cells sink and constitutes the driving force in maintaining the fluid convection and, thus, in shaping the plumes into (numerically) stable stationary states. Our numerical method is fully capable of solving the coupled chemotaxis–fluid system and enabling a full exploration of its dynamics, which cannot be done in a linearised framework.

scholarly journals Building an 18 000-year-long paleo-earthquake record from detailed deep-sea turbidite characterisation in Poverty Bay, New Zealand

2012 ◽  
Vol 12 (6) ◽  
pp. 2077-2101 ◽  
Author(s):  
H. Pouderoux ◽  
G. Lamarche ◽  
J.-N. Proust
Keyword(s):  
New Zealand ◽  
Continental Slope ◽  
Water Depth ◽  
Source Area ◽  
Large Mass ◽  
P Wave ◽  
Turbidity Currents ◽  
Slope Failures ◽  
High Concentration ◽  
Triggering Mechanism

Abstract. Two ~20 m-long sedimentary cores collected in two neighbouring mid-slope basins of the Paritu Turbidite System in Poverty Bay, east of New Zealand, show a high concentration of turbidites (5 to 6 turbidites per meter), interlaid with hemipelagites, tephras and a few debrites. Turbidites occur as both stacked and single, and exhibit a range of facies from muddy to sandy turbidites. The age of each turbidite is estimated using the statistical approach developed in the OxCal software from an exceptionally dense set of tephrochronology and radiocarbon ages (~1 age per meter). The age, together with the facies and the petrophysical properties of the sediment (density, magnetic susceptibility and P-wave velocity), allows the correlation of turbidites across the continental slope (1400–2300 m water depth). We identify 73 synchronous turbidites, named basin events, across the two cores between 819 ± 191 and 17 729 ± 701 yr BP. Compositional, foraminiferal and geochemical signatures of the turbidites are used to characterise the source area of the sediment, the origin of the turbidity currents, and their triggering mechanism. Sixty-seven basin events are interpreted as originated from slope failures on the upper continental slope in water depth ranging from 150 to 1200 m. Their earthquake trigger is inferred from the heavily gullied morphology of the source area and the water depth at which slope failures originated. We derive an earthquake mean return time of ~230 yr, with a 90% probability range from 10 to 570 yr. The earthquake chronology indicates cycles of progressive decrease of earthquake return times from ~400 yr to ~150 yr at 0–7 kyr, 8.2–13.5 kyr, 14.7–18 kyr. The two 1.2 kyr-long intervals in between (7–8.2 kyr and 13.5–14.7 kyr) correspond to basin-wide reorganisations with anomalous turbidite deposition (finer deposits and/or non deposition) reflecting the emplacement of two large mass transport deposits much more voluminous than the "classical" earthquake-triggered turbidites. Our results show that the progressive characterisation of a turbidite record from a single sedimentary system can provide a continuous paleo-earthquake history in regions of short historical record and incomplete onland paleo-earthquake evidences. The systematic description of each turbidite enables us to infer the triggering mechanism.

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