Bezel (geology)

from Wikipedia, the free encyclopedia

As bezel arched, relatively low are single dunes referred to her deflation area immediately in Lee surround. They resemble parabolic dunes , but do not have an active sliding slope.

etymology

The term bezel is derived from the diminutive of the French word lune , which means small moon . The plural lunettes means glasses .

description

Bezel, in English as clay dunes (sound or Lehmdünen) or lunette-dunes and in French as bourrelets referred similar in shape and in orientation relative to the prevailing wind direction to the parabolic dunes. They are not pure sand dunes, but are made up of a mixture of particles, including clay minerals , gypsum , dolomite and remains of mussel shells from salt-tolerant mollusks . The quartz sand content can sometimes be more than 50%. Because of the flocculating effect of the salts, the clay fraction is present as small spheres (pellets). The latter are often blown out into the central part of the bezel, which consists of the sand fraction. The sands are due to elevated lake levels with increased surf, whereas the clays indicate falling levels with subsequent drying out.

Lunettes are individual dunes that always emerge behind recesses in the terrain such as salt pans, playa or sabchas . Their ground plan is usually curved like glasses, but can meander or become irregular in the lee of lagoons or tidal channels. Their length depends on the extent of the upstream terrain depression. Small bezels move in the ten-meter range, but Australia's Holocene bezels can easily take lengths in the tens of kilometers. Bezel rarely exceed 15 meters high. Bezel elevations are very variable. Asymmetrical shapes can either have a steeper windward slope or a steeper leeward slope. Symmetrical shapes are usually rounded.

Origin and climate indicator

The creation process of the bezel was debated for a long time, but the work of Tricart (1954a and 1954b), Price and Kornicker (1961) and Price (1963) showed that bezels clearly represent Aeolian transport bodies. Transport agents are unidirectional winches that blow loose clay, salt and shell particles from temporarily dried-up bodies of water. In this respect, Lunette can certainly provide valuable paleoclimatic information. For the southern high plains in Texas, for example, they testify to the onset of hyperarid environmental conditions from 7000 BC. Chr. V with dune deposits in the period 4000-2500. The stratigraphy of the Australian bezel often contains charcoal and datable carbonates and thus enables a climatic reconstruction. As a result, South Australia ruled until 43,000 BC. A prolonged drought that lasted from 43,000 to 24,000 BC. Chr. Was replaced by a damp period. Between 24,000 and 16,000 BC The lake levels declined again with increasing salinity . From 15,000 BC Then began the aridity that continues to this day.

Occurrence

The occurrence of active bezels is tied to hot climates with pronounced, seasonal drought periods. They therefore occur, for example, on the edges of the Sahara (e.g. Algerian salt lakes) and on the western edge of the Gulf of Mexico . Lunettes that were in operation not so long ago are mostly found in Southeast Australia and locally in South Africa .

Occurrence in detail:

Individual evidence

  1. ↑ Nicholas Lancaster: Geomorphology of Desert Dunes . Routledge, London / New York 1995, ISBN 0-415-06093-1 ( questia.com ).
  2. ^ A b John RL Allen: Sedimentary Structures - their Character and Physical Basis (=  Developments in sedimentology . No. 30 ). Elsevier Science Publishers, Amsterdam 1984, ISBN 0-444-42232-3 .
  3. ^ Theodore M. Oberlander: Global Deserts: A Geomorphic Comparison . In: Athol D. Abrahams, Anthony J. Parsons (Eds.): Geomorphology of Desert Environments . Chapman & Hall, London 1994, ISBN 0-412-44480-1 , pp. 13-35 , doi : 10.1007 / 978-94-015-8254-4_2 .
  4. ^ W. Armstrong Price: Physicochemical and Environmental Factors in Clay Dune Genesis . In: SEPM Journal of Sedimentary Research . tape 33 , no. 3 , September 1963, p. 766-778 , doi : 10.1306 / 74D70F24-2B21-11D7-8648000102C1865D ( jsedres.sepmonline.org ).
  5. ^ JM Bowler: Clay Dunes: Their occurrence, formation and environmental significance . In: Earth Science Reviews . tape 9 , no. 4 , December 1973, pp. 315-338 , doi : 10.1016 / 0012-8252 (73) 90001-9 .
  6. ^ Vance T. Holliday: Middle Holocene drought on the southern High Plains . In: Quaternary Research . tape 31 , no. 1 , January 1989, pp. 74-82 , doi : 10.1016 / 0033-5894 (89) 90086-0 .
  7. ↑ Bowler, JM: aridity in Australia: age, origin, and expression in eolian landforms and sediments . In: Earth Science Reviews . tape 12 , no. 2 , July 1976, p. 279-310 , doi : 10.1016 / 0012-8252 (76) 90008-8 , bibcode : 1976ESRv ... 12..279B .
  8. ↑ JM Bowler: Pleistocene salinities and climatic change from lakes and lunettes in southeast eastern Australia . In: Derek John Mulvaney; Jack Golson (Ed.): Aboriginal man and environment in Australia . Australian National University Press, Canberra 1971, pp. 47-65 .
  9. ^ AT Grove: Landforms and climatic change in the Kalahari and Ngamiland . In: The Geographical Journal . tape 135 , 1969, ISSN  0016-7398 , pp. 191-212 , doi : 10.2307 / 1796824 , JSTOR : 1796824 .