Effects of topography on lofting gravity flows: Implications for the deposition of deep-water massive sands

Stevenson, C. J.; Peakall, Jeff

doi:10.1016/j.marpetgeo.2010.03.010

Cited by 27 publications

(21 citation statements)

References 87 publications

(146 reference statements)

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“…Stratification in the receiving water body can complicate the behavior of turbidity currents by splitting them into interflows and underflows (Cortes et al, 2014(Cortes et al, , 2015Wells & Nadarajah, 2009), an effect that may influence the turbidity currents in Lillooet Lake during the low river flow in 2008 (Menczel & Kostaschuk, 2013). Large topographic obstacles on the bed can cause the turbidity currents to loft upward (Stevenson & Peakall, 2010) but such obstacles are absent in our study. Density stratification within the currents themselves (Gladstone et al, 2004) can also impact current dynamics and mixing.…”

Section: Potential Influence Of Stratificationmentioning

confidence: 76%

On the Causes of Pulsing in Continuous Turbidity Currents

et al. 2018

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Velocity pulsing has previously been observed in continuous turbidity currents in lakes and reservoirs, even though the input flow is steady. Several different mechanisms have been ascribed to the generation of these fluctuations, including Rayleigh‐Taylor (RT) instabilities that are related to surface lobes along the plunge line where the river enters the receiving water body and interfacial waves such as Kelvin‐Helmholtz instabilities. However, the understanding of velocity pulsing in turbidity currents remains limited. Herein we undertake a stability analysis for inclined flows and compare it against laboratory experiments, direct numerical simulations, and field data from Lillooet Lake, Canada, and Xiaolangdi Reservoir, China, thus enabling an improved understanding of the formative mechanisms for velocity pulsing. Both RT and Kelvin‐Helmholtz instabilities are shown to be prevalent in turbidity currents depending on initial conditions and topography, with plunge line lobes and higher bulk Richardson numbers favoring RT instabilities. Other interfacial wave instabilities (Holmboe and Taylor‐Caulfield) may also be present. While this is the most detailed analysis of velocity pulsing conducted to date, the differences in spatial scales between field, direct numerical simulations, and experiments and the potential complexity of multiple processes acting in field examples indicate that further work is required. In particular, there is a need for simultaneous field measurements at multiple locations within a given system to quantify the spatiotemporal evolution of such pulsing.

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Section: Potential Influence Of Stratificationmentioning

confidence: 76%

On the Causes of Pulsing in Continuous Turbidity Currents

et al. 2018

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“…Sediment carried by the flow at the point of lofting will either be rapidly deposited or will remain in suspension within the rising plume (Pritchard and Gladstone, 2009). In laboratory flume experiments, lofted plumes rise and spread out along the water surface (Gladstone and Pritchard, 2010;Stevenson and Peakall, 2010). However, in stratified ocean basins, plumes may rise and spread along an intermediate depth of neutral buoyancy rather than the free surface, or they may be carried away to more distal regions by cross currents.…”

Section: Buoyancy Reversal In Hyperpycnal Flowsmentioning

confidence: 99%

“…This stratification could cause the upper portions of the flow, which are more dilute, to loft earlier than the base of the flow and to progressively remove fine material during the course of the flow. Furthermore, the liftoff point of the flow head is likely to migrate downstream due to the effects of lofting on the density of ambient fluid surrounding the current (Stevenson and Peakall, 2010). The combination of liftoff point migration, lofting along the upper margins of the entire flow, and the short length of the fan system (<2 km) is likely responsible for the rapid deposition and the lack of sedimentary structures within the deposits.…”

Section: Deposition Of Highstand Shelf Fansmentioning

confidence: 99%

“…The recognition of highstand shelf fans may aid in the interpretation of sand bodies that would otherwise be incorrectly interpreted as deep-water or lowstand deposits. Additionally, the sorting and cleaning of sand through the process of buoyancy reversal could explain the abundance of structureless beds that are interpreted as turbidites but that lack typical Bouma-type features (Stow and Johansson, 2000;Stevenson and Peakall, 2010). In conclusion, the results of this study reveal that hyperpycnal flows are capable of depositing more significant shelf sand bodies than previously recognized, and buoyancy reversal and subsequent lofting of hyperpycnal plumes allow for the deposition of previously undescribed shelf sand bodies that are sorted through the stripping of fine-grained material in suspension at the point of liftoff.…”

Section: Deposition Of Highstand Shelf Fansmentioning

confidence: 99%

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Highstand shelf fans: The role of buoyancy reversal in the deposition of a new type of shelf sand body

Steel

Simms

Warrick

et al. 2016

Geological Society of America Bulletin

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Although sea-level highstands are typically associated with sediment-starved continental shelves, high sea level does not hinder major river floods. Turbidity currents generated by plunging of sediment-laden rivers at the fluvial-marine interface, known as hyperpycnal flows, allow for cross-shelf transport of suspended sand beyond the coastline. Hyper pycnal flows in southern California have deposited six subaqueous fans on the shelf of the northern Santa Barbara Channel in the Holocene. Using eight cores and nine grab samples, we describe the deposits, age, and stratigraphic architecture of two fans in the Santa Barbara Channel. Fan lobes have up to 3 m of relief and are composed of multiple hyperpycnite beds ~5 cm to 40 cm thick. Deposit architecture and geometry suggest the hyperpycnal flows became positively buoyant and lifted off the seabed, resulting in well-sorted, structureless, elongate sand lobes. Contrary to conventional sequence stratigraphic models, the presence of these features on the continental shelf suggests that active-margin shelves may locally develop high-quality reservoir sand bodies during sea-level highstands, and that such shelves need not be solely the site of sediment bypass. These deposits may provide a Quaternary analogue to many well-sorted sand bodies in the rock record that are interpreted as turbidites but lack typical Bouma-type features.

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“…These conditions occur in nature when fresh, sediment-laden rivers meet ocean basins or when turbidity currents initiated in warm, shallow-water environments travel into deeper and colder water (Sparks et al, 1993). Previous studies have focused on understanding two-dimensional aspects of buoyancy reversal, such as spreading rate of flow fronts (Hurzeler et al, 1995), and lift-off points (Sparks et al, 1993;Hogg et al, 1999;Sequeiros et al, 2009;Stevenson and Peakall, 2010), but few studies have explored the effects of buoyancy reversal on lateral spreading of flows and its impact on three-dimensional deposit geometry (Zavala et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

The role of buoyancy reversal in turbidite deposition and submarine fan geometry

Steel

Buttles

Simms

et al. 2017

Geology

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Although recent work has shown that changing interstitial fluid density within turbidity currents is a frequently overlooked factor affecting the texture and internal architecture of turbidites, little is known about its influence on submarine fan morphology. Here we present the results of three-dimensional flume experiments of turbidity currents that clearly demonstrate the role of low-density interstitial fluid, in combination with sediment concentration and basin gradient, on submarine fan geometry. The experiments show that turbidity currents with reversing buoyancy, and their resulting deposits, are narrower than those that remain ground hugging. Furthermore, wider deposits result from increases in sediment concentration and/or basin-floor gradient. We also propose that Taylor-Görtler vortices associated with currents traveling over a break in slope may lead to the deposition of wider lobes compared with those traveling over a constant gradient.

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Effects of topography on lofting gravity flows: Implications for the deposition of deep-water massive sands

Cited by 27 publications

References 87 publications

On the Causes of Pulsing in Continuous Turbidity Currents

On the Causes of Pulsing in Continuous Turbidity Currents

Highstand shelf fans: The role of buoyancy reversal in the deposition of a new type of shelf sand body

The role of buoyancy reversal in turbidite deposition and submarine fan geometry

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