Turbidity Currents With Equilibrium Basal Driving Layers: A Mechanism for Long Runout

Luchi, R.; Balachandar, S.; Seminara, G.; Parker, Gary

doi:10.1002/2017gl075608

Cited by 39 publications

(47 citation statements)

References 38 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Given the inferred increase in viscosity from the fringe to the distal fringe of the fan, it is therefore unlikely that flow height was able to increase much along this transect. Numerical simulations constrained by field data also suggest that steadystate turbidity currents form stratified flows with a lower layer of consistent flow height containing the majority of the suspended sediment (Kneller et al, 2016;Luchi et al, 2018). A decrease in flow height could have occurred if the flows were able to spread laterally in the distal part of the system following a loss of confinement.…”

Section: Discussionmentioning

confidence: 86%

Mixed sand–mud bedforms produced by transient turbulent flows in the fringe of submarine fans: Indicators of flow transformation

Baker

Baas

2020

Sedimentology

View full text Add to dashboard Cite

The fringe of fine‐grained deep‐marine systems often exhibits complex sedimentary facies and facies associations, because the presence of clay promotes the development of transient turbulent flows with complex depositional properties. Relatively little is known about the variation of current‐induced sedimentary structures found within these facies. This study provides the first comprehensive description and interpretation of mixed sandstone–mudstone bedforms observed in the fringe of the mud‐rich submarine fan that makes up the Aberystwyth Grits Group and Borth Mudstone Formation (Wales, UK). Using textural and structural descriptions, 158 bedforms in sediment gravity flow deposits were characterized into three main types: ‘classic’ sandy current ripples, large current ripples and low‐amplitude bed‐waves. The sandy current ripples comprise clean sandstone, with average heights and lengths of 11 mm and 141 mm, respectively. The large current ripples are composed of mixed sandstone–mudstone and possess greater dimensions than the sandy current ripples, with an average height of 19 mm and an average length of 274 mm. The low‐amplitude bed‐waves are long thin bedforms composed commonly of mixed sandstone–mudstone, with an average height and length of 10 mm and 354 mm, respectively. The large current ripples and low‐amplitude bed‐waves are strikingly similar to experimental bedforms produced under decelerating mixed sand–mud flows and are interpreted to form beneath transitional flows with enhanced and attenuated near‐bed turbulence, respectively. From the fringe to the distal fringe of the fan, the dominant bedform type changed from sandy current ripples, via large current ripples, to low‐amplitude bed‐waves, suggesting that the flows changed from turbulent to increasingly turbulence‐modulated. It is proposed that the flow Reynolds number reduced, reflecting this flow transformation, from a combination of constant or decreasing flow height, flow deceleration from sediment deposition, and increasing flow viscosity due to the shear‐thinning nature of clay‐rich suspensions. Large current ripples and low‐amplitude bed‐waves are likely to be common in the fringe of other submarine fans. The presence and spatial trends in mixed sand–mud bedform types may be an important tool in interpreting fan fringe environments.

show abstract

Section: Discussionmentioning

confidence: 86%

Mixed sand–mud bedforms produced by transient turbulent flows in the fringe of submarine fans: Indicators of flow transformation

Baker

Baas

2020

Sedimentology

View full text Add to dashboard Cite

show abstract

“…Our formulation of water entrainment across the upper surface of the flow ( E w ) is extrapolated from experiments 38 , 39 . However, numerical simulations suggest entrainment in natural flows is likely to be 3–4 orders of magnitude less than predicted from experiments 40 , 41 , or so low that it would be considered negligible 34 , 42 . As an approximation we reduce our upper surface entrainment value by 3 orders of magnitude, which typically decreases the estimates of sediment concentration by approximately 0.03% vol.…”

Section: Discussionmentioning

confidence: 86%

“…We interpret the erosional trimlines to represent the thickness of the higher-concentration lower layer of the flow. The lower layer transported all the coarse-grained sediment load, which was responsible for most of the sediment concentration in the flow 5 , 8 , 17 , 34 . The sandy mud deposits from shallower than the erosional trimlines are inferred to have been deposited from the overlying dilute, fine-grained, upper-layer of the flow.…”

Section: Resultsmentioning

confidence: 99%

Reconstructing the sediment concentration of a giant submarine gravity flow

et al. 2018

View full text Add to dashboard Cite

Submarine gravity flows are responsible for the largest sediment accumulations on the planet, but are notoriously difficult to measure in action. Giant flows transport 100s of km3 of sediment with run-out distances over 2000 km. Sediment concentration is a first order control on flow dynamics and deposit character. It has never been measured directly nor convincingly estimated in large submarine flows. Here we reconstruct the sediment concentration of a historic giant submarine flow, the 1929 “Grand Banks” event, using two independent approaches, each validated by estimates of flow speed from cable breaks. The calculated average bulk sediment concentration of the flow was 2.7–5.4% by volume. This is orders of magnitude higher than directly-measured smaller-volume flows in river deltas and submarine canyons. The new concentration estimate provides a test case for scaled experiments and numerical simulations, and a major step towards a quantitative understanding of these prodigious flows.

show abstract

“…Zeng & Lowe, ,). More recent CFD studies have given attention to this issue by modelling turbidity currents with a reduced vertical mixing of sediment to prevent excess thickening and dilution of the current (Heimsund et al ., ; Luchi et al ., ).…”

Section: Discussionmentioning

confidence: 99%

Response of unconfined turbidity current to deep‐water fold and thrust belt topography: Orthogonal incidence on solitary and segmented folds

Howlett

Nemec

et al. 2019

Sedimentology

View full text Add to dashboard Cite

Sea‐floor topography of deep‐water folds is widely considered to have a major impact on turbidity currents and their depositional systems, but understanding the flow response to such features was limited mainly to conceptual notions inspired by small‐scale laboratory experiments. High‐resolution three‐dimensional numerical experiments can compensate for the lack of natural‐scale flow observations. The present study combines numerical modelling of thrusts with fault‐propagation folds by Trishear3D software with computational fluid dynamics simulations of a natural‐scale unconfined turbidity current by MassFlow‐3D™ software. The study reveals the hydraulic and depositional responses of a turbidity current (ca 50 m thick) to typical topographic features that it might encounter in an orthogonal incidence on a sea‐floor deep‐water fold and thrust belt. The supercritical current (ca 10 m sec−1) decelerated and thickened due to the hydraulic jump on the fold backlimb counter‐slope, where a reverse overflow formed through current self‐reflection and a reverse underflow was issued by backward squeezing of a dense near‐bed sediment load. The reverse flows were re‐feeding sediment to the parental current, reducing its waning rate and extending its runout. The low‐efficiency current, carrying sand and silt, outran a downslope distance of >17 km with only modest deposition (<0·2 m) beyond the fold. Most of the flow volume diverted sideways along the backlimb to surround the fold and spread further downslope, with some overspill across the fold and another hydraulic jump at the forelimb toe. In the case of a segmented fold, a large part of the flow went downslope through the segment boundary. Preferential deposition (0·2 to 1·8 m) occurred on the fold backlimb and directly upslope, and on the forelimb slope in the case of a smaller fold. The spatial patterns of sand entrapment revealed by the study may serve as guidelines for assessing the influence of substrate folds on turbiditic sedimentation in a basin.

show abstract

Turbidity Currents With Equilibrium Basal Driving Layers: A Mechanism for Long Runout

Cited by 39 publications

References 38 publications

Mixed sand–mud bedforms produced by transient turbulent flows in the fringe of submarine fans: Indicators of flow transformation

Mixed sand–mud bedforms produced by transient turbulent flows in the fringe of submarine fans: Indicators of flow transformation

Reconstructing the sediment concentration of a giant submarine gravity flow

Response of unconfined turbidity current to deep‐water fold and thrust belt topography: Orthogonal incidence on solitary and segmented folds

Contact Info

Product

Resources

About