Erratic block

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As erratic block , erratikum , German Irrblock ( Latin errare ‚[around] to erren ), those stone blocks are referred to in the geosciences , which due to rare geophysical processes or human intervention are not where they would be expected. One also speaks of foreign rock (alien) .

description

In general, stones (i.e. loose rocks , loose rock ) are in situ (at the original location, for example when the wool sack was weathered ). Talus , attachment (by fluvatile shipping), sediment or rock residues are usually in the ground exists, the in situ formed or sediment from this source rock; an example of this are reading stones . It is part of the normal cycle of weatheringthat the sediment solidifies again and becomes rock. However, some stones are of irregular origin, as they were transported through less common geophysical processes.

Examples of erratic blocks in the strict sense are:

  • Boulders , which are of glaciers transported over boulders (glacial erratics) - by far the most common form
  • Drift blocks (drop stones) , rock transported by drift ice ( glaciomarine boulders on the sea floor, but also on land, e.g. transported inland with the tide)
  • Erratic debris in general (in addition to boulders, also boulders outside the regular river beds, e.g. due to extreme exceptional floods)
  • (Erratic) coral blocks, demolition material from coral reefs carried by storm and tides .
  • In caving, erratics refer to material brought into the cave from outside ( erratic sediment , rarely in the form of large blocks)
  • Wandering rocks (wind movement on ice sheets)

Erratic psephites can still appear in the rock , in conglomerate or breccia , rarely also in sandstones and comparable fine sediments. Within this (clastic) sediment they are also known as exotic clasts.

Erratics of biogenic origin (e.g. fossil stomach stones , gastrolites) are very rare, and somewhat more common are those caused by biogenic transport, e.g. with swamped root stocks .

Much more common, however, are stones carried away by humans (anthropogenic erratics) . Apart from commodities such as flint and precious stones , humans have also been transporting larger blocks of stone over long distances since the Neolithic at the latest. Therefore, in the case of an erratic of unclear origin, the first question is whether it represents a geological or archaeological fact. These useful stones go back into the natural cycle comparatively quickly (for example bank structures in the bed load torn away by floods). In addition to various building materials, ballast stones can also be found on the seabed or even on beaches . In the broadest sense, this also includes man-made “rocks” (mineral materials such as fired clays, glass, concrete, etc.).

The erratica came into the focus of geological investigations as early as the 17th century - this is where the expression Lapis Tragomontanus can be found . From the 19th century, when the glacial interpretation was secured, erratic block and boulder were increasingly interpreted as synonymous, until individual, more modern subject areas classified further irregular loads and expanded the term again.

Picture gallery

See also

  • Allochthonous (geology) - generally rocks that are no longer in the area of ​​origin
  • Tectonic scale - remnants of the subsoil planed from larger displaced rock formations, over which this rock mass has passed, and which accumulate on its front face (edge ​​scale) , or, conversely, remnants planed from its underside, which are deposited on the underground rock
  • Meteor - stone blocks from space

Web links

Commons : Glacial erratics  - collection of images

Individual evidence

  1. a b c Comp. erratic (block) , erratic cave deposit , (erratic) coral block. In: Herbert Bucksch: Dictionary Geotechnical Engineering / Dictionary GeoTechnik. Volume I: English German / Volume I: English German , Springer-Verlag, 2013, ISBN 978-366203325-8 , p. 219, column 2 ( limited preview in Google book search).
  2. Erratic block. In: Hans Murawski, Wilhelm Meyer: Geological Dictionary , 12th edition, Springer-Verlag, 2010, ISBN 978-382742244-6 , p. 43 ( limited preview in the Google book search).
  3. glaciomarin. In: Murawski, Meyer: Geological Dictionary , 2010, p. 63.
  4. Harald Zepp: Geomorphology: An Introduction. Volume 2164 of Grundriss Allgemeine Geographie Verlag UTB, 2011, ISBN 978-382523593-2 , S. ( limited preview in Google book search);
    an example is debris from the Ice Age Missoula Floods in Erratic Rock State Natural Site , Oregon.
  5. David Hopley: Encyclopedia of Modern Coral Reefs: Structure, Form and Process. Series Encyclopedia of Modern Coral Reefs , Springer Science & Business Media, 2011 ISBN 978-904812638-5 ; see Fig. 1. Reef front Wave Energy , p 887; References also p. 682 ( limited preview in Google book search).
  6. a b Roland Vinx: Rock determination in the field. 4th edition, Springer-Verlag, 2015, ISBN 978-364255418-6 , chapter clastic sedimentites, 6.3.2. Conglomerate, breccia, gravel, stones, blocks (Psephite), p. 281 col. 2 f.
  7. a b Jennifer B. Paduan, David A. Clague, Alicé S. Davis: Erratic continental rocks on volcanic seamounts off the US west coast. In: Marine Geology Vol. 246, Iss. 1 (November 28, 2007), pp. 1–8, doi : 10.1016 / j.margeo.2007.07.007 - there, for example, stomach stones from seals are mentioned, but also stones carried along by torn kelp .
  8. a b Hopley: Encyclopedia of Modern Coral Reefs. 2011, p. 108 (for details see above)
  9. And also the Geißbergerstein. Compare RF Slip: A forgotten publication on erratic blocks. In: Communications from the Natural Research Society in Bern. New series, Volume 27 (1970), pp. 6-9 ( pdf , E-Periodica, ETH Zurich).
  10. For example Lorenz Oken, Friedrich August Walchner: General natural history for all estates. Volume 1, Hoffman Verlag, 1839, Section Rock Debris and Loose Boulders. P. 673 ( Google eBook, full view ).
  11. cf. Marianne Schuller: Modernity, Losses: literary process and knowledge. Volume 29 of Nexus . Verlag Stroemfeld, 1997, ISBN 978-386109129-5 , p. 58 ( limited preview in Google book search).