Chevron (land form)

Source: Wikipedia, the free encyclopedia.
This article is about deposits of sediment across the earth's surface. For folds in rock layers, see Chevron (geology).

A chevron is a

deposit observed on coastlines and continental interiors around the world. The term chevron was originally used independently by Maxwell and Haynes[1] and Hearty and others[2]
for large, V-shaped, sub-linear to parabolic landforms in southwestern Egypt and on islands in the eastern, windward Bahamas.

General

The Egyptian “chevrons” are active, wind-generated dunes, but the “chevrons” in the Bahamas are inactive and have been variously interpreted.

parabolic dune, and that most examples are generated by wind action.[4]

Many chevrons can be found in Australia,[5] but others are concentrated around the coastlines of the world. For instance there are chevrons in Hither Hills State Park on Long Island and in Madagascar (such as the Fenambosy Chevron), as well as in interior sites of the United States such as the Palouse region of eastern Washington State, the Great Sand Dunes National Park and Preserve, and White Sands National Park.

Formation

According to Hansen et al. 2015, powerful storms and changes in

coastlines.[9]
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.

In 2017, Abbott et al. reported that the Madagascar chevrons contain considerable quantities of early Holocene carbonate samples that resemble marine foraminifera shells, including those that are partly dolomitized and others that are infilled with mud. These findings show that the chevrons' marine carbonate tests were eroded from the continental shelf, rather than from current beaches.[8]

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.[10] Additional evidence against the mega-tsunami hypothesis is that the force of the water would not produce such regular bed forms.[3]

See also

Notes

  1. ^ Maxwell, T.A. and Haynes, C.V., Jr., 1989. Large-scale, low-amplitude bedforms (chevrons) in the Selima Sand Sheet, Egypt: Science v. 243, p. 1179-1182.
  2. S2CID 140581842
    . Retrieved 15 February 2013.
  3. ^
    doi:10.1130/G25246A.1
    . Retrieved 15 February 2013.
  4. S2CID 146434413
    .
  5. ^ Scheffers, Anja; Kelletat, Dieter (2003). "Chevron-shaped Accumulations Along the Coastlines of Australia As Potential Tsunami Evidences?" (PDF). Science of Tsunami Hazards. 21 (3): 174–188. Retrieved 15 February 2013.
  6. doi:10.5194/acpd-15-20059-2015
    .
  7. ISSN 0277-3791
    .
  8. ^
    doi:10.7916/D8F48ZDF. {{cite journal}}: Cite journal requires |journal= (help
    )
  9. ^ Gusiakov, V. Abbott, D.H., Bryant, E.A., Masse, W.B., and Breger, D., 2010. Mega tsunami of the world oceans: Chevron dune formation, micro-ejecta, and rapid climate change as the evidence of recent oceanic bolide impacts: T. Beer (ed.), Geophysical Hazards, p. 197-227; Springer Publ.
  10. Phys.Org
    . 29 April 2009. Retrieved 15 February 2013.

References

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