Contemporary genesis of sand ridges in a tideless erosional shoreface

Guerrero, Queralt; Guillén, Jorge; Durán, Ruth; Úrgeles, Roger

doi:10.1016/j.margeo.2017.10.002

Cited by 12 publications

(13 citation statements)

References 48 publications

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“…Observations at the Sable Island and New Jersey continental shelves revealed that sand ridges become gentler and more asymmetrical with depth (Swift and Field, 1981;Goff et al, 1999;Li and King, 2007) (Figure 12). In the western Mediterranean, sand ridge asymmetry increases from~2:3 in the Ebro Delta shoreface ridges (Guerrero et al, 2018) to~1:2 in the Murcia and GoV offshore ridges (Durán et al, 2018;this work), showing a similar pattern to the NW Atlantic sand ridges. Moribund offshore sand ridges on the Murcia middle shelf are also gentler than active sand ridges on the Ebro Delta, in agreement with the transition from active nearshore to moribund offshore ridges.…”

Section: Interplay Between the Palaeotopography And Sand Ridge Formatmentioning

confidence: 71%

Sediment characteristics and internal architecture of offshore sand ridges on a tideless continental shelf (western Mediterranean)

Durán

Guillén

Ribó

et al. 2020

Earth Surf Processes Landf

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An integrated approach combining swath bathymetry, an extensive dataset of vibrocores and high-resolution seismic reflection data was used to assess the origin and evolution of offshore sand ridges on a tideless continental shelf (Gulf of Valencia, western Mediterranean). The sand ridges are located in the mid-outer shelf at 55-85m water depth, obliquely oriented to the shoreline. They are 1.5 to 7m high, with a wavelength between 600 and 1,100m and a mean height-to-wavelength ratio of 0.004. The sand ridges are composed of well-sorted medium sand and are partially covered by a mud layer, evidencing a moribund stage. They overlie an erosion surface that locally crops out at the seafloor and is interpreted as the Holocene wave-ravinement surface. In the sediment cores, this surface corresponds to an erosional lag composed of coarse sand and gravel with pebbles. Small topographic irregularities on this surface are interpreted as shoreline-associated features that may act as the precursor for ridge development. Their preservation within the sand ridges could be related to the hardness of these features. Internally, the sand ridges display high-angle dipping reflections, indicating ridge migration towards the southeast in the direction of the present-day sediment transport direction. The presence of interbedded mud layers, associated with these reflections, indicates intermittent episodes of mud deposition when active. The internal architecture of some small ridges also provides new insights into their transition from an active to moribund state, as evidenced by a change in the geometry of the internal units from progradational to aggradational, finally being overlain by onlapping finer deposits over the flanks and in the troughs. The Gulf of Valencia sand ridge field constitutes a valuable potential sand resource of 22 million m 3 of well-sorted medium and coarse sand with limited mud content, which must be preserved as a strategic sand reservoir.

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Section: Interplay Between the Palaeotopography And Sand Ridge Formatmentioning

confidence: 71%

Sediment characteristics and internal architecture of offshore sand ridges on a tideless continental shelf (western Mediterranean)

Durán

Guillén

Ribó

et al. 2020

Earth Surf Processes Landf

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“…Small-scale bedforms (1 cm high and 8-14 cm apart) appear during fair-weather conditions at ~10 m depth on the shoreface of the Ebro Delta, with further vanishing because of seabed bioturbation (Guillén et al, 2008). At the study location, a sand ridge field has been identified lying over the former Cape Tortosa river mouth in the Ebro Delta (Guerrero et al 2018). The sand ridge field extends between 5 and 15 m depth and has a maximum height and wavelength of approximately 2.5 and 400 m, respectively (Guerrero et al 2018).…”

Section: Study Areamentioning

confidence: 91%

“…At the study location, a sand ridge field has been identified lying over the former Cape Tortosa river mouth in the Ebro Delta (Guerrero et al 2018). The sand ridge field extends between 5 and 15 m depth and has a maximum height and wavelength of approximately 2.5 and 400 m, respectively (Guerrero et al 2018). The sand ridges are dynamic, with migration rates of ~10 m/y caused by SE-directed wind-induced currents.…”

Section: Study Areamentioning

confidence: 99%

“…The extrapolation of ripple migration rates to periods when provides a rough estimation of the mean ripple migration of 1.3 cm/h during the study period, which should be lower over the year because of the low-energy summer period. Moreover, the annual sand ridge migration rate was 10 m/y (Guerrero et al, 2018), representing a mean rate of 0.11 cm/h. A rough comparison between ripple/sand ridge mean size (0.015 /1.5 m) and migration rates (1.3 /0.11 cm/h) suggests, according to the relationships established by Venditti et al (2005), that the sediment transport associated with ripple migration could be one order of magnitude lower than the total transport involved in sand ridge migration.…”

Section: 2ripples and Sand Ridge Dynamicsmentioning

confidence: 99%

“…Location of tripod, sediment sample and the Buda Island meteorological station). According to Guerrero et al (2018), NW wind-induced currents are the main cause of sand ridge migration towards the SE, while waves propagated in the opposite direction may be the mechanism for reshaping these forms to more symmetrical morphologies. The development and dynamism of ripples under waves and/or currents and the feasibility of ripple migration as a potential contributor to sand ridge migration are analysed.…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of ripples superimposed on a sand ridge on a tideless shoreface

Guerrero

Guillén

2020

Estuarine, Coastal and Shelf Science

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The presence of ripples superimposed on an active sand ridge is the most usual situation under low-to moderate-energy conditions in the wave-dominated, tideless Ebro Delta coast. Four types of small-scale bedforms were identified, from the critical threshold of sediment motion to wash-out conditions: (i) small undulations with η <0.5 cm and λ ~8 cm, formed as a precursor of wave ripples when the Shields parameter was just below the theoretical critical; (ii) 2D wave ripples with η=1.2 cm and λ=7-10 cm; (iii) mixed 2D/3D current-dominated ripples with a maximum of η ~1.5 cm and λ=10-15 cm; and (iv) 3D wave-current ripples with a maximum of η ~2.2 cm and λ=7-20 cm. Ripple degradation was observed to occur when the energy of the hydrodynamic regime increased (wash-out conditions) and under lowenergy hydrodynamic conditions, when ripples progressively decayed mainly as a consequence of biological activity. The wave ripples were static, while the current-dominated ripples migrated towards the SE at a rate of ~10 cm/h. The potential role of ripple migration as an additional long-term mechanism of sediment transport is addressed. On the Ebro Delta shoreface, 3D ripple migration follows the direction of sand ridge migration towards the SE. The respective migration rates and their differences in size support the hypothesis that a subordinate part of sand ridge migration can result from the contribution of ripple migration under low to moderate regimes, suggesting that in specific environments the dynamics of small-scale bedforms can play a subordinate but not negligible role in the evolution of larger bedforms.

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Evolution of coniacian facies and environments in the Iberian basin: a longshore current controlling siliciclastic sand distribution on a carbonate platform

Gil-Gil,

Bretones,

Boix

et al. 2024

Facies

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The Coniacian carbonate sediments of the Iberian basin were deposited on a homoclinal ramp that grades upwards into a distally steepened ramp, with a major shoreline siliciclastic fringe. Twenty-three facies have been identified and grouped into three main depositional environments: outer, mid, and inner ramp. The last include barrier (shoal), lagoon, carbonate tidal-flat and shoreface sub-environments. The more prominent biogenic components show a mixture of sunlight-dependent phototrophic organisms (mainly large benthic foraminifera) and nutrient-dependent heterotrophic organisms (mainly rudists), with a remarkable rare occurrence of corals. Nutrients supplied from the emergent mainland probably promoted the development of heterozoan organisms. The vertical evolution of the ramp shows: a basal transgressive stage with facies retrogradation; a maximum flooding stage, and a regressive stage with aggradation and progradation of a distally steepened ramp. The presence and distribution of siliciclastics are problematic, since sands coming into the basin are likely to be rapidly and widely redistributed along the basin, taking into account the common storm, wave, and tidal processes preserved by the sedimentary facies. The presence of a clockwise NW-flowing longshore current is postulated to account for this distribution, which was likely induced by both dominant external currents around Iberia and wind-driven currents. These clockwise gyres facilitated the invertebrate dispersion into this enclosed basin and the local presence of upwelling. This could have been another source of episodic nutrient-rich waters from the deep ramp, which may have favored heterozoan development even in the more proximal and relatively shallower-water facies.

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Contemporary genesis of sand ridges in a tideless erosional shoreface

Cited by 12 publications

References 48 publications

Sediment characteristics and internal architecture of offshore sand ridges on a tideless continental shelf (western Mediterranean)

Sediment characteristics and internal architecture of offshore sand ridges on a tideless continental shelf (western Mediterranean)

Dynamics of ripples superimposed on a sand ridge on a tideless shoreface

Evolution of coniacian facies and environments in the Iberian basin: a longshore current controlling siliciclastic sand distribution on a carbonate platform

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