Tempestite

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Tempestite with clearly recognizable rubble structure ( Elm limestone )
Tempestite in Silurian rocks in Estonia

A tempestite - from Latin tempestas (thunderstorm, storm, stormy time) - is a layer of sand or silt created by storm events near the coast , which is more widespread and is sharply separated from the surrounding silt . Tempestite are also known as storm sand , they are not only found in the sea, but also in lakes.

The storm sand layers go back to the fact that severe storms wash sand and silt from the coast and put them in suspension in sea water. The turbulent sediment spreads several tens of kilometers over the shelf area of the area and is redeposited according to the size. The grain size of the deposited sediment becomes finer and finer from bottom to top and with increasing distance from the coast. The characteristic layer sequence of storm deposits is called the Dott-Bourgeois sequence .

Tempestit-like sediments often show wavy or bulging layers. In some cases already solidified or partially solidified layers are detached from the subsurface by storm waves and deposited again as a confused mess (see picture). The repeated deposition of sand layers on water-saturated seabed sediments can lead to the formation of sedimentary dikes , as the pressurized water escapes upwards and creates vertical dikes filled with sediment.

Tempestites are examined by paleotempestology, for example , and offer the possibility of assessing the frequency and severity of storm events or tsunamis that have occurred in the past . The differentiation, whether a tempestit was caused by storm events or by a tsunami, is difficult and only possible with closer examination and good information .

Rock layers shaped by geological storm events can be demonstrated in numerous regions of the world by means of the characteristic storage in fine-grained sediments and the absence of the typical signs of currents involved in the deposition in turbidites .

literature

  • Dorrik AV Stow: Sedimentary rocks in the area. An illustrated guide. Spektrum Akademischer Verlag, Heidelberg 2008, ISBN 978-3-8274-2015-2 , pp. 740 .
  • Hans Füchtbauer: Sediments and sedimentary rocks . 4th edition. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart 1988, ISBN 3-510-65138-3 , pp. 740 .
  • H.-E. Reineck, IB Singh: Depositional Sedimentary Environments: With Reference to Terrigenous Clastic . 2nd Edition. Springer Verlag, Heidelberg-Berlin 1986, ISBN 0-387-10189-6 .
  • RH Dott, Jr. and J. Bourgeois: Hummocky stratification: significance of its variable bedding sequences . In: Geological Society of America (Ed.): Geological Society of America Bulletin . tape 93 , 1982, ISSN  0016-7606 , pp. 663-680 , doi : 10.1130 / 0016-7606 (1982) 93 <663: HSSOIV> 2.0.CO; 2 .

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