Bedforms Created by Gravity Flows

Fedele, J. J.; Hoyal, D. C. J. D.; Barnaal, Zachary; Tulenko, Joseph P.; Awalt, Shane

doi:10.2110/sepmsp.106.12

Cited by 59 publications

(130 citation statements)

References 92 publications

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“…Alexander et al ., ; Cartigny et al ., ), although downstream migrating antidunes are known from both open‐channel flows (e.g. Kennedy, ) and gravity currents (Fedele et al ., ).…”

Section: Facies and Architecturementioning

confidence: 97%

“…Antidunes are typically associated with concave upward erosive surfaces, extensive cross‐cutting sets if they are unstable antidunes, bundles of upstream dipping laminae (if upstream migrating), laminae with low dip angles, low angle terminations against the lower set boundary, some convex bedding, and structureless parts of fills (e.g. Alexander et al ., ; Cartigny et al ., ; Fedele et al ., ). The hummock‐like bedforms in the present study share many similarities with these antidunes; however, there is an absence of structureless components, the draping of surfaces is more pronounced and more typical of HCS, the approximately parallel nature of laminae within sets is more pronounced and the number of laminae is greater.…”

Section: Facies and Architecturementioning

confidence: 97%

“…In turbidites, these bedforms have been termed ‘rounded biconvex ripples with sigmoidal laminae’, and have been associated with reflected flow facies where turbidity currents have interacted with topography (Tinterri, ; Tinterri & Muzzi Magalhaes, ; Zecchin et al ., ; Tinterri & Tagliaferri, ). A third possibility is that these are decimetre‐scale stable antidunes, since these can exhibit biconvex tops and in some cases convex‐up cross‐lamination (Alexander et al ., ; Cartigny et al ., ; Fedele et al ., ), although these bedforms may also frequently show concave laminae (Cartigny et al ., ). Typically, antidune laminae dip upstream (e.g.…”

Section: Facies and Architecturementioning

confidence: 99%

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Architecture and morphodynamics of subcritical sediment waves in an ancient channel–lobe transition zone

et al. 2018

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In modern systems, submarine channel-lobe transition zones show a welldocumented assemblage of depositional and erosional bedforms. In contrast, the stratigraphic record of channel-lobe transition zones is poorly constrained, because preservation potential is low and criteria have not been established to identify depositional bedforms in these settings. Several locations from an exhumed fine-grained base of slope system (Unit B, Laingsburg depocentre, Karoo Basin, South Africa) show exceptional preservation of sandstone beds with distinctive morphologies and internal facies distributions. The regional stratigraphic context, lack of a basal confining surface, wave-like morphology in dip section, size and facies characteristics support an interpretation of subcritical sediment waves within a channel-lobe transition zone setting. Some sediment waves show steep (10 to 25°) unevenly spaced (10 to 100 m) internal truncation surfaces that are dominantly upstream-facing, which suggests significant spatio-temporal fluctuations in flow character. Their architecture indicates that individual sediment wave beds accrete upstream, in which each swell initiates individually. Lateral switching of the flow core is invoked to explain the sporadic upstreamfacing truncation surfaces, and complex facies distributions vertically within each sediment wave. Variations in bedform character are related to the axial to marginal positions within a channel-lobe transition zone. The depositional processes documented do not correspond with known bedform development under supercritical conditions. The proposed process model departs from established mechanisms of sediment wave formation by emphasising the evidence for subcritical rather than supercritical conditions, and highlights the significance of lateral and temporal variability in flow dynamics and resulting depositional architecture.

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“…Alexander et al ., ; Cartigny et al ., ), although downstream migrating antidunes are known from both open‐channel flows (e.g. Kennedy, ) and gravity currents (Fedele et al ., ).…”

Section: Facies and Architecturementioning

confidence: 97%

Section: Facies and Architecturementioning

confidence: 97%

Section: Facies and Architecturementioning

confidence: 99%

See 1 more Smart Citation

Architecture and morphodynamics of subcritical sediment waves in an ancient channel–lobe transition zone

et al. 2018

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“…However, experiments by Fedele et al . () produced ripples from supercritical flow at relatively low Froude numbers (around one). The low‐angle convex‐up and concave‐up laminations with backsets and foresets of F1.5 are similar to the experimental strata produced (Alexander et al., ; Cartigny et al., ) by antidunes in that the bounding scour surfaces are less steep and the amplitude of the convex‐up and concave‐up laminations is smaller than in scour and fill structures.…”

Section: Facies Associationsmentioning

confidence: 99%

Variable‐discharge‐river macroforms in the Sunnyside Delta Interval of the Eocene Green River Formation, Uinta Basin, USA

Wang

Plink‐Björklund

2020

Sedimentology

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An outcrop dataset from the early Eocene Sunnyside Delta Interval of the Green River Formation in the Uinta Basin, Utah, USA, documents alluvial channel lithosomes. The abundance of Froude supercritical-flow sedimentary structures, together with an abundance of high-deposition-rate sedimentary structures, in-channel bioturbation and pedogenic modification, in-channel muds and thick soft-clast conglomerates, identify these lithosomes as deposits of variable-discharge rivers. These recognition criteria are part of an emerging facies model for variable-discharge rivers. This facies model, however, yet lacks robust recognition criteria for macro-scale or bar-scale stratal patterns of variable-discharge rivers. This study presents a dataset that corroborates some known stratal patterns and provides examples of hitherto unknown bar-scale stratal patterns of variable-discharge rivers, including: (i) low-angle downstream-accretion sets that may form as washed-out sheets in high sediment supply conditions or downstream of hydraulic jumps; (ii) high-angle upstreamaccretion sets that imply deposition from systematically upstream-migrating channel-scale hydraulic jumps (cyclic steps); (iii) concave-up, upward-flattening high-angle downstream-accretion sets that are consistent with aggradation in channel-scale hydraulic-jump scours; (iv) upstream-accretion and lateralaccretion sets that may be linked to high-magnitude flood reworking of point bars; and (v) aggradation or vertical-accretion sets of ambiguous origin. These unconventional stratal patterns are compared to the established bar strata, such as those formed by point bars and braid bars and a discussion is provided on formative conditions for the here documented unconventional strata. This work highlights a need for further studies on the effect of discharge variability on bar formation and on the link between river morphology and bar types.

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“…Thus, open‐channel flow experiments can be used as surrogates for bedload processes driven by turbidity currents. Care should be taken, however, in the extension of open‐channel flow bedform phase diagrams to the interpretation of density flow bedforms due to the presence of the density excess term at the denominator of the densimetric Froude number, which makes supercritical density currents more common than open‐channel flows (Fedele et al ., ; Koller et al ., ).…”

Section: Introductionmentioning

confidence: 99%

Emplacement of massive deposits by sheet flow

et al. 2020

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Turbidity current and coastal storm deposits are commonly characterized by a basal sandy massive (structureless) unit overlying an erosional surface and underlying a parallel or cross-laminated unit. Similar sequences have been recently identified in fluvial settings as well. Notwithstanding field, laboratory and numerical studies, the mechanisms for emplacement of these massive basal units are still under debate. It is well accepted that the sequence considered here can be deposited by waning-energy flows, and that the parallel-laminated units are deposited under transport conditions corresponding to upper plane bed at the dune-antidune transition. Thus, transport conditions that are more intense than those at the dune-antidune transition should deposit massive units. This study presents experimental, open-channel flow results showing that sandy massive units can be the result of gradual deposition from a thick bedload layer of colliding grains called sheet flow layer. When this layer forms with relatively coarse sand, the non-dimensional bed shear stress associated with skin friction, the Shields number, is larger than a threshold value approximately equal to 0Á4. For values of the Shields number smaller than 0Á4 the sheet flow layer disappeared, sediment was transported by a standard bedload layer one or two grain diameters thick, and the bed configuration was characterized by downstream migrating antidunes and washed out dunes. Parallel laminae were found in deposits emplaced with standard bedload transport demonstrating that the same dilute flow can gradually deposit the basal and the parallel-laminated unit in presence of traction at the depositional boundary. Further, the experiments suggested that two different types of upper plane bed conditions can be defined, one associated with standard bedload transport at the dune-antidune transition, and the other associated with bedload transport in sheet flow mode at the transition between upstream and downstream migrating antidunes.

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Bedforms Created by Gravity Flows

Cited by 59 publications

References 92 publications

Architecture and morphodynamics of subcritical sediment waves in an ancient channel–lobe transition zone

Architecture and morphodynamics of subcritical sediment waves in an ancient channel–lobe transition zone

Variable‐discharge‐river macroforms in the Sunnyside Delta Interval of the Eocene Green River Formation, Uinta Basin, USA

Emplacement of massive deposits by sheet flow

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