A chevron is a wedge-shaped sedimentdeposit observed on coastlines and continental interiors around the world. The term chevron was originally used independently by Maxwell and Haynes and Hearty and others for large, V-shaped, sub-linear to parabolic landforms in southwestern Egypt and on islands in the eastern, windward Bahamas.
According to Hansen et al. 2015, powerful storms and changes in sea level rise can explain chevrons, as the study elaborates: The lightly indurated ooid sand ridges are several kilometers long and appear to have originated from the action of long-period waves from a northeasterly Atlantic source. The chevron ridges contain bands of beach e, formed by air bubbles trapped in fine ooid sand inundated by water and quickly indurated. The internal sedimentary structures including the beach fenestrae and scour structures show that the chevrons were rapidly emplaced by water rather than wind. These landforms were deposited near the end of a sea level high stand, when sea level was just beginning to fall, otherwise they would have been reworked subsequently by stable or rising seas. Some chevrons contain multiple smaller ridges “nested” in a seaward direction, providing further evidence that sea level was falling fast enough to strand and preserve older chevrons as distinct landforms. Older ridges adjacent to the chevron ridges have wave runup deposits that reach heights nearly 40 m above present sea level, far above the reach of a quiescent 5e sea surface. Such elevated beach fenestrae are considered to result from runup of very large waves. These stratigraphically youngest deposits on the shore-parallel ridges are 1-5 m thick fenestrae-filled seaward-sloping tabular beds of stage 5e age that mantle older MIS 5e dune deposits. Runup beds reach more than a kilometer from the present coast, mantling the eastern flanks of stage 5e ridges. Bain and Kindler suggested the fenestrae could be raingenerated, but the fenestrae at high elevations are widespread and exclusive to the late 5e deposits. They are not commonly found in older dune ridges. Movement of these sediments, including chevrons, run-up deposits and boulders, required a potent sustained energy source. Anticipating our interpretation in terms of powerful storms driven by an unusually warm tropical ocean and strong zonal temperature gradients in the North Atlantic, we must ask whether there should not be evidence of comparable end-Eemian storms in Bermuda. Indeed, there are seaward sloping planar beds rising to about +20 m along several kilometers of the north coast of Bermuda. In an alternative view, the Holocene Impact Research Group hypothesizes that the formations could be caused by tsunamis from meteorite impacts or submarine slides which lift sediment up and carry it hundreds of miles until depositing it on coastlines. Part of the evidence they cite for this hypothesis is that the sediments contain tiny marine fossils; however, such fossils can be moved by the wind, just like sand. The impact idea is controversial not only because chevrons are similar to wind-blown landforms found far from the ocean, but also because it is unlikely that there have been enough large impacts and landslides to explain the observed chevrons. Moreover, some computer models and sediment-transport analysis do not support this theory. For example, the orientation of chevrons along the southern coast of Madagascar do not line up with what these models of mega-tsunamis have simulated. Additional evidence against the mega-tsunami hypothesis is that the force of the water would not produce such regular bed forms.
