Bedform-velocity matrix: The estimation of bottom current velocity from bedform observations

Geology ◽  
2009 ◽  
Vol 37 (4) ◽  
pp. 327-330 ◽  
Author(s):  
Dorrik A.V. Stow ◽  
F. Javier Hernández-Molina ◽  
Estefania Llave ◽  
Miriam Sayago-Gil ◽  
Victor Díaz del Río ◽  
...  
Keyword(s):  
Current Velocity ◽  
Bottom Current

scholarly journals NEAR-BOTTOM FLOW CHARACTERISTICS OF CURRENTS AT ARBITRARY ANGLE TO 2D RIPPLES

2011 ◽  
Vol 1 (32) ◽  
pp. 36 ◽  
Author(s):  
Ole Secher Madsen ◽  
Arlendenovega Satria Negara ◽  
Kian Yew Lim ◽  
Hin Fatt Cheong
Keyword(s):  
Current Velocity ◽  
Coastal Waters ◽  
Flow Characteristics ◽  
Velocity Profiles ◽  
Bottom Current ◽  
Arbitrary Angle ◽  
Transport Direction ◽  
Mainstream Flow ◽  
Current Flows ◽  
High Aluminum

Experimental results for near-bottom current velocity profiles for flows over artificial, definitely 2D ripples made of 1.5 cm high aluminum angle-profile spaced at 10 cm intervals are obtained for the following cases: (i) current alone perpendicular to ripples; (ii) current alone parallel to ripples; (iii) combined orthogonal wave-current flows for current parallel to ripples; and (iv) current alone at an angle of 30° to the ripple axis. The velocity profiles are analyzed by the log-profile method, and show the roughness experienced by the current to increase as the angle between ripple and current direction increases, i.e. demonstrating convincingly the reality of the concept of a direction-dependent roughness for flows over a 2D rippled bottom. Roughness experienced by the velocity component perpendicular to the ripples is, however, found to be independent of the direction of the mainstream flow relative to that of the ripples, and the different roughness experienced by the perpendicular and parallel velocity components gives rise to a turning of the current velocity vector to become increasingly aligned with the ripple crests as the bottom is approached from above. Implications of this feature, in terms of net sediment transport direction in combined wave-current flows in inner-shelf coastal waters, is discussed.

Deciphering bottom current velocity and paleoclimate signals from contourite deposits in the Gulf of Cádiz during the last 140 kyr: An inorganic geochemical approach

2014 ◽  
Vol 15 (8) ◽  
pp. 3145-3160 ◽  
Author(s):  
André Bahr ◽  
Francisco J. Jiménez-Espejo ◽  
Nada Kolasinac ◽  
Patrick Grunert ◽  
F. Javier Hernández-Molina ◽  
...  
Keyword(s):  
Current Velocity ◽  
Bottom Current ◽  
Gulf Of Cadiz ◽  
Gulf Of Cádiz ◽  
Geochemical Approach

Lenticular-bedding-like bioturbation and the onshore recognition of carbonate drifts (Oligocene, Cyprus)

2020 ◽  
Vol 90 (12) ◽  
pp. 1667-1677
Author(s):  
Jesús Reolid ◽  
Christian Betzler ◽  
Or M. Bialik ◽  
Nicolas Waldman
Keyword(s):  
Current Velocity ◽  
Early Miocene ◽  
Bottom Current ◽  
Fine Grained ◽  
Current Action ◽  
Lenticular Bedding ◽  
Diagnostic Criterion ◽  
Marly Limestone ◽  
Carbonate Deposits

ABSTRACT The fine-grained carbonate deposits of the Oligocene to early Miocene of Cyprus are the most characteristic example of onshore outcropping carbonate drifts. These deposits were analyzed from a sedimentological and ichnological perspective, in order to determine the origin of the lenticular bedding characteristic of such deposits. The facies at the two study sections, Tsada and Petra Tou Romiou, consist of an alternation of thin, poorly cemented, intensely bioturbated marly limestone intervals and thick cemented wackestone intervals with abundant bioturbation and “lenticular bedding.” The ichnoassemblage, comprising Zoophycos, Thalassinoides, and Planolites is attributable to the Zoophycos Ichnofacies. The alternation of intervals with medium to well-preserved traces with completely biogenically homogenized facies reflects changes in substrate consistency related to changes in bottom-current velocity or to sedimentation. The presence of lenticular-bedding-like structures in the study deposits, traditionally considered diagnostic of bottom-current action in carbonate-drift outcrops, is shown to be exclusively the result of bioturbation. In the study sections, the “lenticular bedding” is the result of the coalescence of successive Zoophycos structures, which are readily preserved because they are constructed in the historical layer. It is proposed that the overlap of abundant isolated cone-shaped burrows of Zoophycos is the origin of the putative lenticular bedding recorded in the Oligocene fine-grained carbonate deposits of Cyprus, traditionally identified as drifts. Since this bedding is not related to currents in the study sections, the consideration of these carbonate deposits of Cyprus as drifts should be reevaluated. This has crucial implications for the recognition of carbonate drift outcrops elsewhere. Onshore carbonate drift outcrops wherein lenticular bedding is the main diagnostic criterion should be revisited and evaluated ichnologically.

scholarly journals Lateral variability of ichnological content in muddy contourites: Weak bottom currents affecting organisms’ behavior

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Javier Dorador ◽  
Francisco J. Rodríguez-Tovar ◽  
Anxo Mena ◽  
Guillermo Francés
Keyword(s):  
Grain Size ◽  
Current Velocity ◽  
Large Scale ◽  
Nutrient Transport ◽  
Trace Fossils ◽  
Bottom Current ◽  
Depositional Settings ◽  
Meso Scale ◽  
Iberian Margin ◽  
Hydrodynamic Energy

AbstractAlthough bioturbation is commonly recognized in contourites, only a few studies have analyzed the ichnological content of these deposits in detail. These studies have mainly focused on meso-scale bigradational sequence (a coarsening upward followed by a fining-upward sequence resulting from variations in current velocity). Here we present data from gravitational cores collected along the NW Iberian Margin showing systematic variation in ichnological content across proximal to distal depocenters within a large-scale elongated contourite drift. Data demonstrate that tracemakers’ behavior varies depending on the distance relative to the bottom current core. Trace fossils are already known to be a useful tool for studying of contouritic deposits and are even used as criterion for differentiating associated facies (e.g., turbidites, debrites), though not without controversy. We propose a mechanism by which the distance to the bottom current core exerts tangible influence on specific macro-benthic tracemaker communities in contourite deposits. This parameter itself reflects other bottom current features, such as hydrodynamic energy, grain size, nutrient transport, etc. Ichnological analysis can thus resolve cryptic features of contourite drift depositional settings.

Structure Analysis on Artificial Reefs

2018 ◽  
Vol 874 ◽  
pp. 27-34
Author(s):  
Sapto P. Kertorahardjo ◽  
Harold Vincent ◽  
Putranta H. Duta
Keyword(s):  
Current Velocity ◽  
Concrete Structure ◽  
Dynamic Pressure ◽  
Permanent Deformation ◽  
Complex Structure ◽  
Artificial Reefs ◽  
Bottom Current ◽  
Stream Velocity ◽  
Practical Consideration ◽  
Sea Bottom

Most of the artificial reefs that have been developed in the world are the concrete structure. Regarding economical and practical consideration of artificial reefs, Indonesian government - Ministry of Marine Affairs and Fisheries - has proposed a new material to make an artificial habitats including artificial reefs made from polypropylene plastics (PP). However, diminishing approximately 80% of the weight structure compare to concrete structure has created new challenges to maintain the underwater structure with similar function. Moreover, the use of less weight material for artificial reefs structure will have impact on the structure responses.The structure responses due to sea bottom current and tidal stream velocity have been evaluated at several conditions. Dynamic pressure calculation was applied gradually as external load from a simple part to whole complex structure. Stresses and strains occur at some nodes as the structure critical area, within the same time frame, displacement of its elements describe physical characteristic response. Boundary conditions was encastred the sinker- bottom structure (U1 = U2 = U3 = UR1 = UR2 = UR3 = 0). In conclusion, for input of sea bottom current velocity u = 0.2 m/s the results for maximum stress are below the material’s yield stress hence its elasticity is relatively adequate to prevent permanent deformation. The result also showed some critical part of the structure that has high value on stress should be consider as the current velocity increase. Moreover increasing input and frontal area will significantly affect the drag force which will add load on the structure.

Contourites in the Gulf of Cadiz: a cautionary note on potentially ambiguous indicators of bottom current velocity

2013 ◽  
Vol 33 (5) ◽  
pp. 357-367 ◽  
Author(s):  
Thierry Mulder ◽  
Rim Hassan ◽  
Emmanuelle Ducassou ◽  
Sébastien Zaragosi ◽  
Eliane Gonthier ◽  
...  
Keyword(s):  
Current Velocity ◽  
Bottom Current ◽  
Gulf Of Cadiz ◽  
Cautionary Note ◽  
Gulf Of Cádiz

Bottom-current deposits in the Miocene-Pliocene Misaki Formation, Izu forearc area, Japan

Island Arc ◽  
1998 ◽  
Vol 7 (3) ◽  
pp. 315-329 ◽  
Author(s):  
I NT AE L EE ◽  
Y UJIRO O GAWA
Keyword(s):  
Bottom Current

scholarly journals Mechanism and Influencing Factors of REY Enrichment in Deep-Sea Sediments

Minerals ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 196
Author(s):  
Jiangbo Ren ◽  
Yan Liu ◽  
Fenlian Wang ◽  
Gaowen He ◽  
Xiguang Deng ◽  
...  
Keyword(s):  
Deep Sea ◽  
Research Progress ◽  
Bottom Current ◽  
Knowledge Map ◽  
P2o5 Content ◽  
Deep Sea Sediments ◽  
Potential Resource ◽  
And Migration ◽  
Adsorption Desorption ◽  
Sediment Interface

Deep-sea sediments with high contents of rare-earth elements and yttrium (REY) are expected to serve as a potential resource for REY, which have recently been proved to be mainly contributed by phosphate component. Studies have shown that the carriers of REY in deep-sea sediments include aluminosilicate, Fe-Mn oxyhydroxides, and phosphate components. The ∑REY of the phosphate component is 1–2 orders of magnitude higher than those of the other two carriers, expressed as ∑REY = 0.001 × [Al2O3] − 0.002 × [MnO] + 0.056 × [P2O5] − 32. The sediment P2O5 content of 1.5% explains 89.1% of the total variance of the sediment ∑REY content. According to global data, P has a stronger positive correlation with ∑REY compared with Mn, Fe, Al, etc.; 45.5% of samples have a P2O5 content of less than 0.25%, and ∑REY of not higher than 400 ppm. The ∑REY of the phosphate component reaches n × 104 ppm, much higher than that of marine phosphorites and lower than that of REY-phosphate minerals, which are called REY-rich phosphates in this study. The results of microscopic observation and separation by grain size indicate that the REY-rich phosphate component is mainly composed of bioapatite. When ∑REY > 2000 ppm, the average CaO/P2O5 ratio of the samples is 1.55, indicating that the phosphate composition is between carbonate fluoroapatite and hydroxyfluorapatite. According to a knowledge map of sediment elements, the phosphate component is mainly composed of P, Ca, Sr, REY, Sc, U, and Th, and its chemical composition is relatively stable. The phosphate component has a negative Ce anomaly and positive Y anomaly, and a REY pattern similar to that of marine phosphorites and seawater. After the early diagenesis process (biogeochemistry, adsorption, desorption, transformation, and migration), the REY enrichment in the phosphate component is completed near the seawater/sediment interface. In the process of REY enrichment, the precipitation and enrichment of P is critical. According to current research progress, the REY enrichment is the result of comprehensive factors, including low sedimentation rate, high ∑REY of the bottom seawater, a non-carbonate depositional environment, oxidation conditions, and certain bottom current conditions.

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