Chevrons: Origin and relevance for the reconstruction of past wind regimes

Vimpere, Lucas; Kindler, Pascal; Castelltort, Sébastien

doi:10.1016/j.earscirev.2019.04.005

Cited by 9 publications

(9 citation statements)

References 88 publications

(157 reference statements)

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“…The term "chevron" identifies both "large U-and V-shaped ridges found in or near shorelines worldwide" [32] and structures used for river restoration. In fluvial contexts, they represent a new and suitable solution to enhance local conditions.…”

Section: Introductionmentioning

confidence: 99%

Experimental Analysis of Scour Features at Chevrons in Straight Channel

Roy

Pagliara

Palermo

2021

Water

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Eco-friendly river restoration structures are used to create localized scour pools which serve as fish nurseries and promote biodiversity. In this category, chevrons are relatively new structures designed to maintain navigability in rivers. The scour hole formed in the wake region of chevrons can either act as a disposal site for dredged material or as a resting spot for different fish species. However, only few studies are present in the literature dealing with the scour mechanism due to chevrons. Therefore, this work aims to analyze the scour features at equilibrium, under different hydraulic conditions and transversal locations in a straight channel. Tests were conducted with both isolated and multiple chevrons in series arrangement. Scour morphology types were classified and their fields of existence were established as well. A detailed dimensional analysis was conducted, allowing us to identify the main parameters governing the scour phenomenon and derive a novel equivalent densimetric Froude number. Finally, empirical equations were developed to predict the maximum scour depth and length as well as the maximum dune height.

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Section: Introductionmentioning

confidence: 99%

Experimental Analysis of Scour Features at Chevrons in Straight Channel

Roy

Pagliara

Palermo

2021

Water

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“…12; Donnelly et al, 2006;Donnelly & Sallenger, 2007;Morton et al, 2007;Williams, 2011;Mattheus & Fowler, 2015) that are several orders of magnitude smaller than 'chevrons' (table 4 in Morton et al, 2007;Jamison-Todd et al, 2020) and never display such a V-shaped morphology (Engel et al, 2015). Finally, sandy storm deposits are systematically thinning landward with slopes ranging from 1°to 5°whereas 'chevrons', like parabolic dunes, are thickening as they progress inland ( Figs 5 and 6) with the highest elevation lying near the ridge apex (Hearty et al, 1998;Hearty & Tormey, 2017;Vimpere et al, 2019). Hearty et al (1998Hearty et al ( , 2002, Hansen et al (2016Hansen et al ( , 2020, Hearty & Tormey (2017) and Tormey (1999) excluded an aeolian origin for the 'chevrons' because of the scarcity of steeply dipping foresets in these landforms.…”

Section: Morphological Criteriamentioning

confidence: 99%

“…Fenestrae have also been described from aeolianites of Holocene (Loucks & Ward, 2001;Engel et al, 2015) and Pleistocene age (Bain & Kindler, 1994;Frébourg, 2010). Finally, the morphological and sedimentological disparities between well-identified storm deposits (for example, washover lobes and conglomeratic berms) and 'chevrons' (Kindler & Strasser, 2000Engel et al, 2015;Mylroie, 2018a,b;Vimpere et al, 2019) do not agree with a wave origin for the latter. Regarding the 'megaboulders', Rovere et al (2017Rovere et al ( , 2018) used a wave model to demonstrate the needlessness of evoking 'superstorms' as an emplacement mechanism when hurricanes of historical intensity can transport boulders of such sizes.…”

Section: Introductionmentioning

confidence: 97%

“…Up to now called 'chevrons', the peculiar V-shaped and U-shaped oolitic ridges of Late Pleistocene age exposed on several Bahamian islands have drawn the attention of numerous researchers for almost two decades (Hearty et al, 1998(Hearty et al, , 2002(Hearty et al, , 2015Tormey, 1999;Kindler & Strasser, 2000Bourgeois & Weiss, 2009;Hansen et al, 2013Hansen et al, , 2020Engel et al, 2015;Tormey et al, 2016Tormey et al, , 2018Rovere et al, 2017Rovere et al, , 2018Hearty & Tormey, 2017, 2018aMylroie, 2018a,b;Vimpere et al, 2019). However, despite the numerous studies pertaining to these landforms, both their formation mechanism and their climatic significance remain uncertain and controversial.…”

Section: Introductionmentioning

confidence: 99%

“…The second hypothesis relies on the morphological resemblance between aeolian parabolic dunes and 'chevrons' (Kindler & Strasser, 2000Engel et al, 2015) and on the alignment of the latter with the present resultant drift direction of carbonate sand generated by north-easterly winds (Vimpere et al, 2019). The occurrence of rhizoliths, land snails and the omnipresence of climbing translatent stratification (CTS) within 'chevrons' and 'run-up' deposits further argues for an aeolian origin, because these fine structures are by and large considered as diagnostic of wind processes (Hunter, 1977;McKee & Ward, 1983;Fryberger & Schenk, 1988;White & Curran, 1989;Caputo, 1993;Loope & Abegg, 2001;Loucks & Ward, 2001;Frébourg et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

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Upper Pleistocene parabolic ridges (i.e. ‘chevrons’) from the Bahamas: Storm‐wave sediments or aeolian deposits? A quantitative approach

et al. 2021

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The Upper Pleistocene (Marine Isotope Stage 5e; ca 120 ka) stratigraphic record from the Bahamas comprises large, kilometre-long parabolic ridges of oolitic composition, that point landward, and have been up to now called 'chevrons'. A debate about their genesis has led previous researchers to consider two processes of deposition: (i) a catastrophic event involving giant storm-generated waves produced by specific climatic conditions at the end of Marine Isotope Stage 5e; and (ii) a more uniformitarian process which characterizes 'chevrons' as aeolian parabolic dunes because of their similar morphology. Since there are few unequivocal sedimentological criteria to discriminate aeolian from water-deposited sediments, only a quantitative, multi-method approach could provide enough evidence to produce a viable diagnosis on the genetic processes involved. Following this reasoning, the quantification of the morphological parameters of 'chevrons', a precise study of their sedimentary structures on previously and newly discovered sections, and several statistical grain-size analyses, all advocate for an aeolian origin. Moreover, when the aforementioned characteristics of 'chevrons' are compared with those of storm deposits (for example, washovers) and parabolic dunes occurring elsewhere on Earth, the dissimilarity with the former and the resemblance with the latter is evident. Amino-acid racemization dating, together with stratigraphic and petrographic investigations, constrain the age of the 'chevrons' to the late part of Marine Isotope Stage 5e. Their occurrence during this specific time interval can be explained by both strengthened easterly winds and drier climatic conditions associated with changing vegetation cover. Fixation of the arms by sparse vegetation, coupled with the loose 'chevron' nose sediment migrating farther inland, form the peculiar U-shaped morphology of these ridges.

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A Westward Shift in Tropical Cyclone Potential Intensity and Genesis Regions in the North Atlantic During the Last Interglacial

Yan

Korty

Wei

et al. 2021

Geophysical Research Letters

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Given the longstanding debate on geomorphological features (i.e., megaboulders, chevron‐shaped sand ridges, and runup deposits) observed around the Bahamas, it is unclear whether Earth experienced superstorms over the North Atlantic during the Last Interglacial (LIG). Based on multimodels from the Paleoclimate Modeling Intercomparison Project, we illustrate that the tropical North Atlantic exhibits an overall warming (∼0.9°C) during the storm season of the LIG relative to preindustrial. Potential intensity shows a zonal dipole anomaly over the main development region during the LIG, with positive anomalies in the west, offering an increased probability of extremely strong storms. Favorable conditions for storm formation shift from the eastern to the western main development region during the LIG, with enhanced large‐scale steering flows at higher latitudes (∼15 – 30°N). These results suggest a westward migration of storm activity during the LIG, with potentially more frequent and intense storms over the western North Atlantic and increased coastal erosions.

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Chevrons: Origin and relevance for the reconstruction of past wind regimes

Cited by 9 publications

References 88 publications

Experimental Analysis of Scour Features at Chevrons in Straight Channel

Experimental Analysis of Scour Features at Chevrons in Straight Channel

Upper Pleistocene parabolic ridges (i.e. ‘chevrons’) from the Bahamas: Storm‐wave sediments or aeolian deposits? A quantitative approach

A Westward Shift in Tropical Cyclone Potential Intensity and Genesis Regions in the North Atlantic During the Last Interglacial

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