Upslope-Migrating Bedforms In A Proglacial Sandur Delta: Cyclic Steps From River-Derived Underflows?

Dietrich, Pierre; Ghienne, Jean‐François; Normandeau, Alexandre; Lajeunesse, Patrick

doi:10.2110/jsr.2016.4

Cited by 71 publications

(94 citation statements)

References 66 publications

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“…(C) Correlation between aspect ratio and local slope for a wide range of bedforms reviewed by Dietrich et al . () compared with those from the studied fjord‐lake deltas.…”

Section: Discussionmentioning

confidence: 99%

Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada)

et al. 2016

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High‐resolution swath bathymetry data collected in fjord‐lakes Pentecôte, Walker and Pasteur (eastern Québec, Canada) allowed imaging in great detail the deltas of four rivers in order to understand the factors controlling the formation and downslope evolution of bedforms present on their slopes. The morphometry and morphology of 199 bedforms reflect the behaviour of sediment density flows. The shape of the bedforms, mostly crescentic, and the relationships between their morphological properties indicate that they were formed by supercritical density flows and that they are cyclic steps. The crescentic shape suggests an upslope migration while the aspect ratios and increasing wavelengths with distance from the shore (and decreasing slopes) are compatible with a cyclic step origin. At the rollover point, the acceleration of the density flows on steep slopes produces tightly spaced hydraulic jumps and favours short wavelength and symmetrical bedforms. Further downslope, decreasing slopes and increasing specific discharge increase the wavelength and asymmetry of the bedforms. The wavelength and asymmetry are increased because density flows require longer distances to become supercritical again on lower slopes after each successive hydraulic jump. Bedform morphometry and morphology are used to reconstruct density flow behaviour downslope. Froude numbers are high near the rollover point and gradually decrease downslope as the slope becomes gentler. Conversely, the specific discharge and flow depth are low near the rollover point and gradually increase downslope as the flow either erodes sediments or becomes more dilute due to sediment deposition and water entrainment. The supercritical density flows are believed to be triggered mainly by hyperpycnal flows but some evidence of delta‐front slope failures is also observed. The differences in delta morphology and bedform development between the four deltas are linked to basin morphology and watershed hydrology, but also mainly to the fjord heritage of the lakes that allowed the focusing of sediment at the delta front.

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“…(C) Correlation between aspect ratio and local slope for a wide range of bedforms reviewed by Dietrich et al . () compared with those from the studied fjord‐lake deltas.…”

Section: Discussionmentioning

confidence: 99%

Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada)

et al. 2016

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“…9A, B), suggesting aggradation within increasing accommodation space in front of a retrograding shoal-water delta on a drowned glacifluvial delta plain Sohn & Son 2004;Fielding et al 2005;Winsemann et al 2009). 6I-M) were probably triggered by frequent small-volume gravitational collapses of the upper delta slope (Talling 2014;Dietrich et al 2016;Hughes Clarke 2016) during high rates of delta-front aggradation (Gobo et al 2014(Gobo et al , 2015. The seismic profile of the Porta fan and delta complex indicates that these shoal-water mouthbar deposits are genetically linked to high-angle Gilbert-type foresets that are exposed on the eastern margin of the truncated fan (Fig.…”

Section: Base-level Control On Sedimentary Facies Facies Associationmentioning

confidence: 99%

“…However, the interpretation of gravity-flow deposits has considerably changed during recent years and recently the deposition by supercritical density flows has become a major focus of research, changing previous views (Postma et al 2009;. Fielding 2006;Muto et al 2012;Lang & Winsemann 2013;Cartigny et al 2014;Dietrich et al 2016;Massari 2017;Lang et al 2017a, b). Fielding 2006;Muto et al 2012;Lang & Winsemann 2013;Cartigny et al 2014;Dietrich et al 2016;Massari 2017;Lang et al 2017a, b).…”

Section: Delta Styles and Depositional Processesmentioning

confidence: 99%

“…Related bedforms on the delta slope include deposits of antidunes, chutes-and-pools and cyclic steps, which might be partly misinterpreted as scour fills or waveinduced hummocky cross-stratification (cf. Deposits of supercritical density flows may record high-magnitude (glacial) floods (Ghienne et al 2010;Winsemann et al 2011;Girard et al 2012Girard et al , 2015Carling 2013;Ventra et al 2015) or represent delta slope failure events producing slides, slumps, debrisflows and/or turbidity currents (Talling 2014;Dietrich et al 2016;Hughes Clarke 2016). Deposits of supercritical density flows may record high-magnitude (glacial) floods (Ghienne et al 2010;Winsemann et al 2011;Girard et al 2012Girard et al , 2015Carling 2013;Ventra et al 2015) or represent delta slope failure events producing slides, slumps, debrisflows and/or turbidity currents (Talling 2014;Dietrich et al 2016;Hughes Clarke 2016).…”

Section: Delta Styles and Depositional Processesmentioning

confidence: 99%

“…Facies association FA1.2.5 (Figs 7G, 8D, E) is dominated by climbing-ripple cross-laminated sand (facies Sr), deposited from sustained subcritical turbidity flows. These coarser-grained deposits might represent major slope failure events(Talling 2014;Dietrich et al 2016; Hughes Clarke 2016) or major meltwater discharge events(Ghienne et al 2010;Ventra et al 2015;Carvalho & Vesely 2017). This zone is characterized by flow expansion and the formation of upslope directed large vortices (cf Jopling 1965;Clemmensen & Houmark-Nielsen 1981;Winsemann et al 2007)…”

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Ice‐marginal forced regressive deltas in glacial lake basins: geomorphology, facies variability and large‐scale depositional architecture

Winsemann

Lang

Polom

et al. 2018

Boreas

130

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Brandes, C. 2018 (October): Ice-marginal forced regressive deltas in glacial lake basins: geomorphology, facies variability and large-scale depositional architecture.This study presents a synthesis of the geomorphology, facies variability and depositional architecture of ice-marginal deltas affected by rapid lake-level change. The integration of digital elevation models, outcrop, borehole, groundpenetrating radar and high-resolution shear-wave seismic data allows for a comprehensive analysis of these delta systems and provides information about the distinct types of deltaic facies and geometries generated under different lake-level trends. The exposed delta sediments record mainly the phase of maximum lake level and subsequent lake drainage. The stair-stepped profiles of the delta systems reflect the progressive basinward lobe deposition during forced regression when the lakes successively drained. Depending on the rate and magnitude of lake-level fall, fanshaped, lobate or more digitate tongue-like delta morphologies developed. Deposits of the stair-stepped transgressive delta bodies are buried, downlapped and onlapped by the younger forced regressive deposits. The delta styles comprise both Gilbert-type deltas and shoal-water deltas. The sedimentary facies of the steep Gilberttype delta foresets include a wide range of gravity-flow deposits. Delta deposits of the forced-regressive phase are commonly dominated by coarse-grained debrisflow deposits, indicating strong upslope erosion and cannibalization of older delta deposits. Deposits of supercritical turbidity currents are particularly common in sand-rich Gilbert-type deltas that formed during slow rises in lake level and during highstands. Foreset beds consist typically of laterally and vertically stacked deposits of antidunes and cyclic steps. The trigger mechanisms for these supercritical turbidity currents were both hyperpycnal meltwater flows and slope-failure events. Shoal-water deltas formed at low water depths during both low rates of lake-level rise and forced regression. Deposition occurred from tractional flows. Transgressive mouthbars form laterally extensive sand-rich delta bodies with a digitate, multi-tongue morphology. In contrast, forced regressive gravelly shoal-water deltas show a high dispersion of flow directions and form laterally overlapping delta lobes. Deformation structures in the forced-regressive ice-marginal deltas are mainly extensional features, including normal faults, small graben or half-graben structures and shear-deformation bands, which are related to gravitational delta tectonics, postglacial faulting during glacial-isostatic adjustment, and crestal collapse above salt domes. A neotectonic component cannot be ruled out in some cases. facies and the larger-scale depositional architecture. The results are compared with other marine and lacustrine delta examples from the literature, and provide information about the distinct types

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Which Triggers Produce the Most Erosive, Frequent, and Longest Runout Turbidity Currents on Deltas?

Hizzett

Clarke

Sumner

et al. 2018

Geophysical Research Letters

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Subaerial rivers and turbidity currents are the two most voluminous sediment transport processes on our planet, and it is important to understand how they are linked offshore from river mouths. Previously, it was thought that slope failures or direct plunging of river floodwater (hyperpycnal flow) dominated the triggering of turbidity currents on delta fronts. Here we reanalyze the most detailed time‐lapse monitoring yet of a submerged delta; comprising 93 surveys of the Squamish Delta in British Columbia, Canada. We show that most turbidity currents are triggered by settling of sediment from dilute surface river plumes, rather than landslides or hyperpycnal flows. Turbidity currents triggered by settling plumes occur frequently, run out as far as landslide‐triggered events, and cause the greatest changes to delta and lobe morphology. For the first time, we show that settling from surface plumes can dominate the triggering of hazardous submarine flows and offshore sediment fluxes.

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Upslope-Migrating Bedforms In A Proglacial Sandur Delta: Cyclic Steps From River-Derived Underflows?

Cited by 71 publications

References 66 publications

Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada)

Morphological expression of bedforms formed by supercritical sediment density flows on four fjord‐lake deltas of the south‐eastern Canadian Shield (Eastern Canada)

Ice‐marginal forced regressive deltas in glacial lake basins: geomorphology, facies variability and large‐scale depositional architecture

Which Triggers Produce the Most Erosive, Frequent, and Longest Runout Turbidity Currents on Deltas?

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