Auelehm

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As Auelehm a predominantly is pelitisches soft ground in the flood zone constantly flowing waters ( rivers and streams designated). By Ferdinand Schalch the name "Aulehm" was introduced 1885th With the introduction of uniform spelling in 1901, the term Auelehm became common. The terms Alluvionen and Alluvialboden are outdated . Recently the plural form floodplain has been used , especially in physical geography . By Rudolf Grahmann introduced term "Hochflutlehm" for the flood deposited on the Aueoberfläche solids is recently and especially for the Rhine Valley usefully applied to the changing deposited under cold climate temporal fine-grained sediment flow, see the Wikipedia article Hochflutlehm . Grahmann originally coined the term “Tallohm” for this sediment . With a higher psammitic proportion, the term flood sediment would be preferable for the flood clay in the sense of Grahmann. Deposits in a valley without constant flowing water, in a so-called dry valley , belong to the colluvia ( colluvium , Latin: that which was washed up). Classic areas of floodplain research are north-west Saxony (river areas Weisse Elster and Pleiße ) and the Weser area .

When the flood loam (in the Grahmann sense) is deposited , the typical alluvial loam with its vertical fissures and the mostly strong yellow-brown color is created above the mean groundwater level through diagenesis ( oxidation of the organic components, bioturbation ) . If the sedimentation speed is reduced at times, the humus substance accumulates and black-gray so-called "humus horizons" are created, raw soils of the Paternia type. When the sedimentation is inactive for a longer period, the soil type is Vega . In the area of ​​permanent groundwater, diagenetic processes are inhibited. Gray to black colors predominate and traces of stratification and organic components, transported together with the pelitic mineral substances or from local vegetation, are retained. This type of sediment, which is particularly characteristic of sedimentation in oxbow lakes , has been given a large number of names in the literature (e.g. “river silt”, or “reed” or “black floodplain”).

To form a Auelehmdecke it only comes in meandering run sections, because the "wild river", also braided river (ger .: braided river) called the high mountain regions and Arctic regions can not cover like accumulate the Hochflutlehm. In north-west Saxony, the lower terrace was accumulated during the Glacial Vistula and the river sections that meander today were also "overgrown" according to the river bed structures. The change of the river dynamics to the meandering river took place at the beginning of the Holocene. In Central Europe, alluvial clay blankets are a characteristic of warm-period rivers.

The extent of the deposition of alluvial clay depends primarily on the frequency of flooding and the degree of continentality of the climate plays a role. With an increase in continentality, it is the greater retention of winter precipitation in the mountain regions and, in summer, mostly certain weather conditions, e.g. B. the well-known large-scale weather situation Vb, which lead to large-scale floods. Local heavy rain during thermal thunderstorms can cause severe soil erosion , but the resulting flooding also has a predominantly local effect. Other important factors are high relief energy and easily erosible soil in the catchment area. Therefore, thick alluvial clay deposits are mainly associated with loess hill countries. In the hill country of western Saxony, the mighty alluvial clay coverings are structured by soils that are distributed throughout the river basins.

Cause of the clay deposits

Everyone can observe how soil material is washed away from arable land during heavy precipitation or snowmelt and how mud is deposited on floodplains by floods. There is apparently a direct causal relationship between the two processes and this is the basis for the assumption that the use of the land surface for arable farming is the cause of alluvial clay formation, that the alluvial clay is an anthropogenic sediment. In the case of the material source for the alluvial clay, however, the effect of extensive anthropogenic soil erosion is currently greatly increased compared to linear erosion . The work of Rudolf Käubler is currently being neglected . He had proven that in the Saxon old settlement area under forest cover the Kerbtal (so-called loess gorges) was the typical morphological form, i.e. not only extensive erosion was considered for the material supply. Soil erosion cannot be the sole cause because the Pleistocene also saw the formation of alluvial clay, as demonstrated by the floodplain among the travertine deposits in the Ilm Valley near Weimar . The relative rarity of Pleistocene occurrences has the simple reason that they were eroded at the beginning of the subsequent glacial period by the change in river dynamics that then occurred. Attempts to directly link the formation of alluvial clay with the history of settlement have not proven to be reliable.

The alluvial clay cover in western Saxony, which is divided by soils, plays a key role in clarifying the cause of the alluvial clay deposits. While the soils indicate phases of reduced high-tide clay deposition, the areas between the soils were formed in phases of increased high-flow clay deposition. In the case of an anthropogenic cause, the sedimentation phases would have to coincide with the settlement phases. From the beginning, archaeological finds have played a dominant role in determining the age of the alluvial clay. The first finds from 1832 and 1872 with evidence of settlement come from the Weißelstertal in Leipzig-Plagwitz. With the very precise description and the location of the find from 1872 in the area of ​​a soil embedded in the alluvial clay cover, the methodical approach for a lithostratigraphic structure was actually given. But it was not until the 1920s and 1930s that archaeological investigations returned to the layer structure, and this provided evidence of a climatic cause of the alluvial clay deposits. New findings from the White Elster / Pleisse area and in particular the detailed investigation of the ostracodal and mollusc fauna of an alluvial clay outcrop near Zeitz again suggest that the alluvial clay is not an anthropogenic sediment. Unfortunately, archeology has not yet taken up this approach to concretise the age of the soils in the alluvial clay cover.

proof

  1. ^ Ferdinand Schalch: Explanations of the geological special map of the Kingdom of Saxony, Section Wurzen, sheet 13 , Leipzig 1885, 52 pages (online) .
  2. ↑ a b c Rudolf Grahmann: Could the Central German floodplains be settled in prehistoric times? In: Mannus - Journal for German Prehistory , Volume 26, Leipzig 1934, pp. 37–41
  3. ^ Rudolf Grahmann: Explanations of the special geological map of Saxony, sheet 48/39, Pegau-Predel together with Hemmendorf , 2nd edition, Leipzig 1924, pp. 1–34.
  4. ^ Hans Neumeister: Contributions to the flood problem of the Pleiße and Elster area . In: Scientific publications of the German Institute for Regional Geography NF , Volume 21/22, Leipzig 1964, pp. 65-131.
  5. ↑ Dieter Handel: The Holocene in the northwest Saxon floodplains . In: Hercynia NF , Volume 4, Leipzig 1967, pp. 152-198.
  6. ↑ Gerd Lüttig: To the structure of the Auelehms in the river area of ​​the Weser In: Eiszeitalter und Gegenwart , Volume 11, Öhringen 1960, pp. 39-50
  7. ↑ Willfried Strautz: Auelehmbildung and headings in the Weser and Leinetal with comparative timings from the basin of the Elbe . In: Contributions to the maintenance of the land , Volume 1, Stuttgart 1963, pp. 273-314.
  8. ↑ Roland Fuhrmann: The development history of post-hall glacial valley sections of the White Elster and Mulde and the stratigraphic structure of the younger Quaternary . In: Altenburger Naturwissenschaftliche Forschungen , Heft 11, Altenburg / Thüringen 1999, pp. 43–63 PDF .
  9. ^ Horst Mensching: Origin of the alluvial clay blankets in northwest Germany . In: Proceedings of the Third International Congress of Sedimentology: Groningen Wageningen, Netherlands, 5-12 July 1951 , pp. 193-210.
  10. ↑ Helmuth Nietsch: Floods, floodplain clay and prehistoric settlement - a contribution based on the Weser region . In: Geography , Volume 9, Bonn 1955, pp. 20–39 (online)
  11. ↑ Klaus-Dieter Jäger: About the age and causes of the alluvial clay deposits of Thuringian rivers . In: Prehistoric Journal , Volume 40, Berlin 1962, pp. 1-59.
  12. ↑ Rudolf Käubler: Young Historical changes of the landscape in the middle Saxon Lößgebiet . In: Scientific publications of the Deutsches Museum für Länderkunde zu Leipzig NF , Volume 5, Leipzig 1938, pp. 71–90.
  13. ↑ Rudolf Käubler: On the question of the earlier forest cover of the central Saxon old settlement area . In: Beihefte für Gekunde, Volume 2, Berlin 19949, pp. 19–37.
  14. ^ Rudolf Käubler: Contributions to old landscape research in East Central Germany . In: Petermanns Geographische Mitteilungen , Volume 96, Gotha 1952, pp. 245–249.
  15. ^ Otfried Wagenbreth, Walter Steiner, Peter Lange, Ernst Freyburg: Tasks, methods and results of a geological complex exploration in the travertine of Weimar-Ehringsdorf . In: Scientific journal of the Weimar University of Architecture and Building , Volume 16, Weimar 1969, pp. 61–84.
  16. ↑ Walter Steiner: A new profile with a palaeolithic fund horizon in the travertine of Taubach near Weimar . In: Scientific journal of the Weimar University of Architecture and Building , Volume 19, Weimar 1972, pp. 485–492.
  17. ^ Walter Steiner: The Pleistocene Travertine of Weimar - Facies model of a travertine deposit . In: Quaternary Palaeontology , Volume 5, Berlin 1984, pp. 55-210.
  18. ↑ Christian Tinapp: Geoarchaeological studies on the Holocene landscape development of the southern Leipzig lowland bay . In: Trier Geographical Studies , Issue 26, Trier 2002, pp. 1–275.
  19. ↑ Roland Fuhrmann: Climate fluctuations in the Holocene based on findings from valley sediments in Central Germany . In: Mauritiana , Volume 19, Issue 2, Altenburg / Thüringen 2005, pp. 289–304 PDF .
  20. ↑ Otto Mothes: The Elsterniederung in the so-called prehistoric time . In: Writings of the Association for the History of Leipzig , Volume 1, Leipzig 1872, pp. 217-238 (online) .
  21. ↑ Karl Braune: A new find of the bell beaker culture in the Leipziger Land . In: Mannus - Journal for German Prehistory , Volume 20, Würzburg 1928, pp. 409-415.
  22. ↑ Karl Braune: On the question of the alleged Leipzig pile dwellings . In: Mannus - Journal for German Prehistory , Volume 24, Würzburg 1932, pp. 98-109.
  23. ↑ Karl Braune, Rudolf Grahmann: Bronze Age and Slavic hearths in the Pleißenaue . In: Die Fundpflege , Volume 1, Leipzig 1933, pp. 44–45.
  24. ↑ Roland Fuhrmann: Climate fluctuations in the Holocene according to findings from river and stream deposits in northwest Saxony and neighboring areas . In: Altenburger Naturwissenschaftliche Forschungen , Heft 11, Altenburg / Thüringen 1999, pp. 3–41 PDF .
  25. ↑ Roland Fuhrmann: The ostracod and mollusc fauna of the alluvial clay profile Zeitz (Burgenland district) and their statements on the climate and land use in the younger Holocene of Central Germany . In: Mauritiana , Volume 20, Issue 2, Altenburg / Thuringia, 2008, pp. 253–281 PDF .