Aggradation and lateral migration shaping geometry of a tidal point bar: An example from salt marshes of the Northern Venice Lagoon (Italy)

Brivio, Lara; Ghinassi, Massimiliano; D’Alpaos, Andrea; Finotello, Alvise; Fontana, Alessandro; Roner, Marcella; Howes, Nick

doi:10.1016/j.sedgeo.2016.08.005

Cited by 46 publications

(77 citation statements)

References 77 publications

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“…Erosional surfaces flooring the beds point to repeated phases of sediment bypass and erosion; notwithstanding, the upstream‐oriented and upward‐oriented shift of inflection points within the inclined stratal surfaces is consistent with aggradation during accretion (cf. Brivio et al ., ). Moving southward, inclined stratal surfaces display a rotation in their azimuth from north‐west to south‐west, a motif consistent with a downstream‐ward shift of the channel bank.…”

Section: Study Sitesmentioning

confidence: 97%

Precambrian snapshots: Morphodynamics of Torridonian fluvial braid bars revealed by three‐dimensional photogrammetry and outcrop sedimentology

Ghinassi

Ielpi

2017

Sedimentology

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Pre‐vegetation fluvial channels have long been considered predominantly sheet‐like in geometry, owing to hydraulic sections that rapidly widened rather than incise during floods. This motif has been paralleled to that of modern dryland rivers subject to sharp discharge fluctuations during ephemeral floods. However, a number of Precambrian fluvial successions have been recently appraised as the product of deep‐channelled systems characterized by relatively stable – probably perennial – discharge regimes. One such example is the ca 1·0 Ga Applecross Formation, part of the well‐studied Torridon Group of Scotland. To contribute to this debate and to provide refined morphodynamic models for the Applecross Formation, this article presents an integration of three‐dimensional photogrammetry and outcrop sedimentology applied to key exposures at Stoer Peninsula, north‐western Scottish Highlands. Analysis of selected sandbodies reveals that high‐relief fluvial sand bars, both mid‐channel and bank‐attached, evolved within deep, braided‐channel belts. These bars grew through complex mechanisms of accretion and reactivation related to different flood stages: upstream and downstream accretion probably occurred during waning‐flood stages characterized by high hydrograph levels and abundant sediment availability; lateral accretion took place during later waning‐flood stages, and it was associated in some cases with helical recirculation and increase in bend sinuosity. Overall, the depicted morphodynamics are consistent with prolonged flood events that cannot be reconciled with sharply fluctuating discharge regimes. Critical comparisons between the internal geometry of the studied bars and modern counterparts corroborate the findings herein. Thus, this study recommends stricter comparisons between the products of modern braided channels and Precambrian fluvial rock records featuring thick and well‐developed bar forms.

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Section: Study Sitesmentioning

confidence: 97%

Precambrian snapshots: Morphodynamics of Torridonian fluvial braid bars revealed by three‐dimensional photogrammetry and outcrop sedimentology

Ghinassi

Ielpi

2017

Sedimentology

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“…Also, FA3 deposits are capped by FA2 deposits, indicating a genetic relation between these two facies associations, and only in rare cases are the upper surfaces of FA3 pedogenically altered. When these genetic associations are considered with the sedimentology and ichnology of FA2 and FA3 deposits in both PS B and PS G, the most reasonable interpretation is that deposition of these strata occurred in a tide-dominated, wave-influenced protected bay setting punctuated by relatively localized fluvio-tidal, brackish water channels (Barwis, 1977;Dalrymple et al, 2012;Davis, 2012;Hughes, 2012;Brivio et al, 2016;Gingras et al, 2016;D'Alpaos et al, 2017). Based on mapping and facies analysis, both small and large FA3 deposits appear to represent a range of channel sizes that are genetically related and formed in a tide-dominated, wave-influenced and fluvial-influenced environment that drained into the large fluvial-estuarine system that occupied the Main Fairway (Figs 16 and 17).…”

Section: Mixed Energy Deposition (Parasequences Blue and Green)mentioning

confidence: 99%

Evolution of an ancient (Lower Cretaceous) marginal‐marine system from tide‐dominated to wave‐dominated deposition, McMurray Formation

Weleschuk

Dashtgard

2019

Sedimentology

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Regionally extensive parasequences in the upper McMurray Formation, Grouse Paleovalley, north‐east Alberta, Canada, preserve a shift in depositional processes in a paralic environment from tide domination, with notable fluvial influence, through to wave domination. Three stacked parasequences form the upper McMurray Formation and are separated by allogenic flooding surfaces. Sediments within the three parasequences are grouped into three facies associations: wave‐dominated/storm‐dominated deltas, storm‐affected shorefaces to sheltered bay‐margin and fluvio‐tidal brackish‐water channels. The two oldest parasequences comprise dominantly tide‐dominated, wave‐influenced/fluvial‐influenced, shoreface to bay‐margin deposits bisected by penecontemporaneous brackish‐water channels. Brackish‐water channels trend approximately north‐west/south‐east, which is perpendicular to the interpreted shoreline trend; this implies that the basinward and progradational direction was towards the north‐west during deposition of the upper McMurray Formation in Grouse Paleovalley. The youngest parasequence is interpreted as amalgamated wave‐dominated/storm‐dominated delta lobes. The transition from tide‐dominated deposition in the oldest two parasequences to wave‐dominated deposition in the youngest is attributed mainly to drowning of carbonate highlands to the north and north‐west of the study area, and potentially to relative changes in accommodation space and deposition rate. The sedimentological, ichnological and regional distribution of the three facies associations within each parasequence are compared to modern and Holocene analogues that have experienced similar shifts in process dominance. Through this comparison it is possible to consider how shifts in depositional processes are expressed in the rock record. In particular, this study provides one of few ancient examples of preservation of depositional process shifts and showcases how topography impacts the character and architecture of marginal‐marine systems.

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“…Sand rich in plant debris, which underlies channel-lag deposits, was accumulated in a subtidal platform setting (cf. Brivio et al, 2016).…”

Section: Core Datamentioning

confidence: 99%

“…Salt marsh mud covering the bar thins in the direction of channel shifting, defining a geometry (cf. Brivio et al, 2016) which is not commonly observable in bends shifting laterally with a rate of several metres per year (i.e. fluvial bends).…”

Section: Bar Development Aggradation and Migration Ratesmentioning

confidence: 99%

Morphodynamic evolution and stratal architecture of translating tidal point bars: Inferences from the northern Venice Lagoon (Italy)

et al. 2017

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The widespread distribution of tidal creeks and channels that undertake meandering behaviour in modern coasts contrasts with their limited documentation in the fossil record, where point‐bar elements arising from the interaction between a mix of both fluvial and tidal currents are mainly documented. The sedimentary products of tidal channel‐bend evolution are relatively poorly known, and few studies have focused previously on specific facies models for tidal point bars present in modern settings. This study improves understanding of tidal channel meander bends through a multi‐disciplinary approach that combines analyses of historical aerial photographs, measurements of in‐channel flow velocity, high‐resolution facies analyses of sedimentary cores and three‐dimensional architectural modelling. The studied channel bend (12 to 15 m wide and 2 to 3 m deep) drains a salt marsh area located in the north‐eastern sector of the microtidal Venice Lagoon, Italy. Historical photographs show that, during the past 77 years, the bend has translated seaward ca 15 m. Results show that the channel bend formed on a non‐vegetated mud flat that was progressively colonized by vegetation. Seaward translation occurred under aggradational conditions, with an overall migration rate of 0·2 to 0·3 m year−1, and was promoted by the occurrence of cohesive, poorly erodible outer bank deposits. Ebb currents are dominant, and translation of the channel bend promotes erosion and deposition along the landward and seaward side of the bar, respectively. Tidal currents show a clear asymmetry in terms of velocity distribution, and their offset pattern provides a peculiar grain‐size distribution within the bar. During the flood stage, sand sedimentation occurs in the upper part of the bar, where the maximum flow velocity occurs. During the ebb stage, the bar experiences the secondary helical flow that accumulates sand at the toe of the bar. Lateral stacking of flood and ebb deposits has caused the formation of localized coarsening‐upward and fining‐upward sedimentary packages, respectively.

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Aggradation and lateral migration shaping geometry of a tidal point bar: An example from salt marshes of the Northern Venice Lagoon (Italy)

Cited by 46 publications

References 77 publications

Precambrian snapshots: Morphodynamics of Torridonian fluvial braid bars revealed by three‐dimensional photogrammetry and outcrop sedimentology

Precambrian snapshots: Morphodynamics of Torridonian fluvial braid bars revealed by three‐dimensional photogrammetry and outcrop sedimentology

Evolution of an ancient (Lower Cretaceous) marginal‐marine system from tide‐dominated to wave‐dominated deposition, McMurray Formation

Morphodynamic evolution and stratal architecture of translating tidal point bars: Inferences from the northern Venice Lagoon (Italy)

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