Periglacial layers

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Periglacial layers (also periglacial layers ) are during the Pleistocene cold periods under periglacial conditions resulting unconsolidated sediment ceilings that the slope of the relief Mountain the central widths in disguise far into the basins almost areally. They consist of several layers on top of each other, are an important starting substrate for soil formation and have a significant impact on the water balance .

Development of terms

Scientific research into periglacial slope sediments began almost simultaneously in the Federal Republic of Germany and in what was then the GDR . This resulted in various terminologies that were not easily compatible with one another: Semmel called the periglacial sediments ' cover layers ', and if there was a high skeleton content, they were also called ' rubble layers ' and subdivided them into ' Schutte ', Schilling & Wiefel subdivided them into ' consequences ', Schwanecke in ' zones ' and Kopp in ' permeability zones '. It was only at the turn of the century that the confusion of terms was standardized. On this basis, went with the, layers ' a new, nationwide unified terminology in the 4th edition of the soil mapping one. It has been slightly revised with the 5th edition (hereinafter abbreviated as KA5 ).

However, this classification is often criticized, which recently led to another terminological suggestion with ' Segments '.

Sedimentary properties of the layers

overview

All classification approaches differentiated sediments with and without an aeolian part, i. d. R. Loess . This is also followed by the KA5, which has an essentially loess-free sediment each with its base layer and top layer. The middle and main layers, on the other hand, contain loess. In addition to the classification of the locations, the KA5 also enables a location-independent approach based on sedimentological features ('facies-neutral'), which is not the subject of this article.

The identification of the locations in the terrain takes place with the help of sedimentological properties and the relative position of the layer in the profile; the typical distribution is also used as an auxiliary criterion.

The boundaries between the individual layers appear i. d. Usually sharp, so that usually striking differences in the stone content or other grain sizes are used as a criterion for drawing the boundary. As an alternative, further indicators such as changes in the storage of the components (adjusted parallel to a slope or like a roof tile, adjusted transversely, standing vertically, irregular) or the sorting can be used. In cases of doubt, laboratory tests are required, such as heavy mineral analyzes , which can prove different provenances of the sediments.

Base position

The base location (abbreviation LB , at Semmel 1968: base rubble) emerged from the rock on site or up the slope through weathering and gelifluidic displacement (local material). Fluvial interventions through periglacial flushing processes can also be involved. The LB is usually the lowest layer member in a multi-part sequence. The LB is - provided that there are suitable rocks in the vicinity - rich in skeleton , the longitudinal axes of which are parallel to the slope, and if the stones are flat, also like roof tiles. A typical feature of most LBs is their high storage density . The widespread statement that LBs are free of aeolian fractions is often wrong in this form, because mechanical flushing through the seepage water has often led to a secondary accumulation, which differs significantly from the other layers due to the distribution pattern: the silt is found regularly in the form of hoods on the larger stones and not dispersed .

Middle position

The middle layer ( LM , near Semmel 1968: Mittelschutt) contains not only local material but also a noticeable aeolian admixture. This results in a marked difference in the substrate compared to the base layer. However, if base layers emerged from rocks that in turn weather to silt, it is difficult to distinguish between them. According to KA5, the LM can have a higher loess content than the main layer above. However, this cannot be proven statistically, just like the repeatedly claimed lower skeletal content compared to all other locations. As a further criterion for identification, the KA5 specifies the spatial distribution of the LM ( see below ). The LM usually has a medium storage density.

Main location

The main layer ( LH , near Semmel 1968: deck debris, with a low stone content: deck sediment) is similar in composition to the central layer. Often a volcanic component, which originates from the Laacher See eruption of the Alleröd , is given as a distinguishing criterion. However, the tephra was not shipped to many areas, and a great deal of effort is required to prove it even in the peripheral areas of distribution. The LH is less differentiated from the central position according to sedimentological criteria than by the fact that it is usually on the surface of the earth. Important properties of the LH are its noticeably constant thickness of 50 ± 20 cm ( see below ) and the loose storage of the substrate. Adjustment parallel to the slope is rarely clearly pronounced.

Top layer

Very rarely does another sediment appear in the hanging wall of the main layer , which ideally consists exclusively of rockfall heaps , but may also have older fine material incorporated into its base, the upper layer ( LO , not mentioned in Semmel 1968).

Possible confusion

All layers can be confused with each other and with colluvium . Base layers are then often difficult to separate from the other layers when they are rich in silt. Middle and main layers can only be identified with certainty if both are preserved on top of each other. If the main location is missing, for example due to soil erosion , as it often occurred under today's forest, since in the past many areas were used for arable farming, the identification of the central location is difficult because it is mainly only defined by its relative relationship to the main location. The situation becomes even more difficult when colluvia are added or replace the main layer. Since old colluvia are rarely rich in humus, they are often difficult to recognize. Nests of charcoal or a leaching of the soil that is not typical for the area as a result of previous use then serve as clues.

Genesis of the locations

Basics

The most important process in the formation of the layers, with the exception of the top layer, is gelifluction . The subsurface near the surface is slowly moved down the slope. This process does not create completely new, sharply delimited layers that concordantly overlay the existing subsurface . Rather, sediments of the gelifluction emerge from the existing substrate and mix with it more and more along the slope. Periglacial layers therefore always contain components of the person lying down .

This means that a base layer that reaches an area in the course of the slope in which a middle layer had already formed before, its facies gradually changes and from then on must be referred to as the middle layer . With exact investigations ( ground thin sections ) it can be shown that layers can contain components from older layers that have not been preserved themselves. Whether individual, older layers can be preserved depends on the depth of later gelifluction processes and on whether fresh substrate has been introduced in the meantime by other processes ( fluvial , aeolian ), which means that the older layer is no longer reached even with the same depth.

This processing and incorporation of older material can explain why alternating positions in which base layers occur not only below but also above middle layers are very rare.

Genesis of the base position

Apart from mostly minor fluvial interferences, the LB is a typical sediment of gelifluction with marked signs of regulation of the skeleton. An important feature, the high storage density, is still awaiting a conclusive explanation. FitzPatrick 1956 explains recently observed compression phenomena in Scotland through the pressure effect of the segregation ice in the permafrost body , that is, ice lenses or layers in the substrate that are formed by hygroscopic migration of the pore water towards the freezing front, which was demonstrated in laboratory experiments. This would mean that base layers were captured by permafrost after their deposition, which is consistent with ice wedges often found in them.

Genesis of the middle position

The crucial difference between the base and middle position is the aeolian part. In addition to gelifluction, which, as evidenced by the regulation of the skeleton parallel to the slope, also had an effect in the central layers, there was also accumulation by the wind. The relative temporal position of the processes to one another is unclear, i.e. whether a phase of loess accumulation occurred before the relocation, whether the loess was incorporated synsedimentarily (i.e. during the sedimentation of the location) or whether it was only applied and incorporated afterwards.

Genesis of the main position

In view of the less pronounced regulation of the skeleton, the formation of LH due to gel flux is less evident than in the lying position. However, LH were found under moors that began to grow in the late glacial, so that their cold-age position appears to be secured. Nevertheless, their storage is disturbed by later events in many places (through fallen trees, forestry, etc.).

An essential property of the LH, its very constant thickness, seems to contradict all laws of physics , since it is hardly influenced by morphometric parameters such as slope inclination , exposure or location in the slope, parameters that are considered to be essential control variables of geomorphological systems. However, results from a gelifluction measuring field ( see impregnation flow ) suggest that a phenomenon such as the main location under periglacial climate can arise when several factors come together: the shift lasts only for a short time, no fresh sediment (e.g. aeolian) is replenished and it there is no permafrost . The latter in particular is highly controversial in the literature on LH.

Genesis of the upper layer

The top layer was essentially created by falling rocks.

Spatial distribution of the locations

The locations are mostly explored through superficial digs or a 1 m long drill stick. With these exploratory methods one often just reaches the lower limit of the base position. If another substrate is found underneath, this is often interpreted as something pending . However, deeper exposures or geophysical explorations often show that base layers in particular, but also middle layers, can be much thicker or even composed of several distinguishable layers.

While main and base locations in the low mountain range occur almost extensively, the distribution of the central location is limited. Here you probably have to distinguish mountains in which a relatively constant wind direction prevailed during the cold period from other mountains, because the distribution of the middle layer depends on the loess deposit: if this was thicker than the depth of the gelifluction when the main layer was formed, a middle layer could be retained . Otherwise it was incorporated into the main location and lost its independence. Thus, one can expect a central position where the most favorable conditions for loess deposits existed, first of all the slopes in the slipstream ( leeward ) but also stronger relief unevenness on the windward side , especially dents on slopes .

The information from KA5 on the distribution of the central position contradicts this derivation, however: According to this, the maintenance of a central position is linked to an erosion-protected relief position. However, dents on slopes concentrate runoff channels and are the exact opposite of a location protected from erosion. The information provided by the KA5 on this contradicts multiple terrain experience.

Upper layers are limited to the highest areas of the low mountain range and are found in small areas at the foot of rock outcrops.

Age of the locations

In principle, periglacial layers are not chronostratigraphic units. Previous attempts to determine the age numerically, especially of older periglacial locations, have either failed or their transferability is not yet certain.

The observation that these sediments are absent on moraines from the last glacial period gives indications of a maximum age of the base layers . In a study, central layers were not found on moraines that are younger than 16,000 years. The extent to which this finding can be transferred is unknown.

The age of the main location was for a long time because of its relationship to the Laacher-See-Tephra ( see above ). T. is also superimposed, indisputable; it was dated to the Younger Dryas period. Finds from the main location under older moors contradict this, however. Either the main layer was formed or reshaped in several phases, or the age of this layer varies regionally.

The KA5 defines the upper layer as a periglacial sediment and (in contrast to the 4th edition) explicitly excludes similar, significantly later sediments. On the other hand, it does not give any clue as to how the Pleistocene age of such sediments, which obviously cannot be assigned to a periglacial process, could be determined. If this definition is strictly applied, there may be no overlay at all.

Geo-ecological significance of the periglacial layers

The material and structural composition of the near-surface subsoil differs considerably from that which would be expected solely from the weathering of the rocks in the vicinity. This has far-reaching effects on the environment in the low mountain ranges. The development of the soil is largely controlled by it. The soils would be less profound without the layers. The loess content usually has a very positive effect on the quality of the soil, as it counteracts acidification. Soils whose substrate contains a central layer are often so far decoupled from the influence of the rock below that they are exclusively characterized by lessivation . On the other hand, layers with low water permeability can lead to pseudo-gleying in flat relief . The contents of a large number of substances differ in the periglacial layers from the lying rock; this can be relevant for the environment, especially with heavy metals.

The existence of layer boundaries in the subsurface, but also the properties of the layers themselves (adjustment) lead to anisotropy . This is of great importance for the water balance of the slope and causes a deflection of the seepage water flow , which is diverted to an interflow parallel to the slope . This runoff gets into the receiving water faster because the water takes a more direct route. This presumably has an impact on the development of floods and the transport of pollutants in the environment.

Web links

literature

  • A. Kleber & B. Terhorst (Eds.): Mid-Latitude Slope Deposits (Cover Beds) . Elsevier Verlag, Developments in Sedimentology 66, Amsterdam etc. 2013, ISBN 978-0-444-53118-6 .
  • A. Semmel: Periglacial morphology . Scientific Book Society, Darmstadt 1990, ISBN 3-534-01221-6 .
  • C. Stolz (2012): Observations on the inclination of clasts in periglacial cover-beds in the Rhenish Massif (Germany) . - Journal of Geomorphology, NF 56, Supplement 4: pp. 55-76.
  • H. Liedtke (Ed.): Ice Age Research . Scientific Book Society, Darmstadt 1990, ISBN 3-534-05063-0 .
  • A. Kleber: Periglacial slope deposits and their pedogenic implications in Germany . In: Palaeogeography, Palaeoclimatology, Palaeoecology 99, 1992: pp. 361-372.
  • A. Semmel: Basics of soil geography . Teubner Study Books of Geography, Stuttgart 1993, ISBN 3-519-23408-4 .
  • J. Völkel, M. Leopold, A. Mahr & T. Raab: On the importance of cold-age slope sediments in Central European low mountain ranges and on questions of their terminology . In: Petermanns Geographische Mitteilungen 146, 2002, pp. 50–59.
  • A. Kleber: Lateral water flow in sloping sediments under forest . In: C. Lorz & D. Haase (Hrsg.): Material and water balance in catchment areas. Contributions to the EU Water Framework Directive . Springer, Berlin a. a. 2004: 7-22, ISBN 3-540-20816-X .
  • J. Völkel, H. Zepp & A. Kleber: Periglacial cover layers in low mountain ranges . In: Reports on German regional studies 76, 2002, issue 2/3.
  • A. Kleber & J. Völkel: Slope sediments and their soils . In: German working group for geomorphology (Hrsg.): The earth surface. Space for people to live and create . Journal of Geomorphology NF Suppl.-Vol. 148, 2007: pp. 20-24.
  • T. Raab, M. Leopold & J. Völkel: Character, Age, and Ecological Significance of Pleistocene Periglacial Slope Deposits in Germany . In: Physical Geography 28, 2007, pp. 451-473.
  • H. Gebhardt, R. Glaser, U. Radtke & P. ​​Reuber (Eds.): Geography . Elsevier, Spektrum, Munich 2007, ISBN 3-827-41543-8 .

Individual evidence

  1. ↑ A. Kleber: On the transferability of the German top layer concept . In: Petermanns Geographische Mitteilungen 143, 1999: pp. 363–372.
  2. ↑ A. Semmel: On the environmental geological significance of slope sediments in German low mountain ranges . In: Journal of the German Geological Society 145, 1994, pp. 225–232.
  3. ^ A. Semmel: Young debris blankets in the Hessian low mountain ranges . In: Notes of the Hessian State Office for Soil Research 92, 1964, pp. 275–285.
  4. ^ A b c d e f A. Semmel: Studies on the course of the Young Pleistocene formation in Hesse . In: Frankfurter Geographische Hefte 45, 1968.
  5. ^ W. Schilling & H. Wiefel: Jungpleistozäne periglacial formations and their regional differentiation in some parts of Thuringia and the Harz Mountains . In: Geologie 11, 1962, pp. 428-460.
  6. ^ W. Schwanecke: For the soil systematics important results of the forest site exploration in the hill country and low mountain range of the German Democratic Republic . In: Meeting reports DAL Berlin 15, 1966, pp. 79–95.
  7. ↑ D. Kopp: Periglacial rearrangement (perstruction) zones in the north German lowlands and their soil genetic significance . In: Conference reports of the German Academy for Agriculture 102, 1970: pp. 55–81.
  8. ↑ M. Altermann: Outline of Pleistocene locations . In: Communications of the German Soil Science Society 72, 1993.
  9. ↑ a b c AG Soil: Soil-Scientific Mapping Instructions . Ed .: Federal Institute for Geosciences and Raw Materials and Geological State Offices, 4th edition, 392 pages, Hanover 1994. ISBN 3-510-95804-7 .
  10. ↑ a b c d e f g h Ad-hoc working group Soil: Soil-scientific mapping instructions . Ed .: Federal Institute for Geosciences and Raw Materials in cooperation with the State Geological Services, 5th edition, 438 pages, Hanover 2005. ISBN 3-510-95920-5 . Description of the contents of the Schweizerbart publishing house
  11. ^ J. Völkel, M. Leopold, A. Mahr & T. Raab: On the importance of cold-age slope sediments in Central European low mountain ranges and on questions of their terminology . In: Petermanns Geographische Mitteilungen 146, 2002, pp. 50–59.
  12. ↑ M. Altermann, K.-D. Jäger, D. Kopp, A. Kowalkowski, D. Kühn & W. Schwanecke: For the identification and classification of periglacial differentiations in the pedosphere . In: Waldökologie, Landschaftsforschung und Naturschutz 6, 2008, pp. 5–42. Download as PDF
  13. ↑ a b J. Völkel: Periglacial cover layers and soils in the Bavarian Forest and its peripheral areas as geogenic basis for landscape-ecological research in the area of ​​near-natural forest locations . In: Journal of Geomorphology NF Suppl.-Bd. 96, 1995, ISBN 978-3-443-21096-0 . Description of the contents of the Schweizerbart publishing house
  14. ↑ a b c d A. Kleber & A. Schellenberger: Slope hydrology triggered by cover-beds. With an example from the Frankenwald Mountains, northeastern Bavaria . In: Journal of Geomorphology NF 42, 1998, pp. 469-482.
  15. ↑ a b T. Scholten: Contribution to the comprehensive derivation of the distribution system and properties of periglacial locations in German low mountain ranges . In: Relief, Boden, Paläoklima 19, 2003, ISBN 978-3-443-09019-7 . Description of the contents of the Schweizerbart publishing house
  16. ^ H. Thiemeyer & H. Veit: Soil science and heavy mineralogical investigations on selected periglacial cover layer profiles in NE Bavaria . In: Berliner Geographische Arbeit 78, 1993, pp. 265–286.
  17. ↑ M. Leopold: Multivariate analysis of geo-archives for the reconstruction of Iron Age land use in the vicinity of the late Latène Age Viereckschanze von Poign, district of Regensburg . In: Regensburg contributions to soil science, landscape ecology and quaternary research 2, 2003. Download as PDF
  18. ↑ A. Kleber & H. Stingl: On the river history of the Trebgasttal north of Bayreuth. A two-phase valley relocation in the Rotmain system . In: Bamberger Geographische Schriften special series 6, 2000, pp. 191–208.
  19. ^ S. Müller & H. Thiemeyer: Potentials of reconstructing the formation and transformation of slope deposits by the use of soil micromorphology . In: Geophysical Research Abstracts Vol. 12, EGU2010-2620, 2010. Abstract as PDF
  20. ↑ A. Semmel: Periglacial forms and sediments . In: H. Liedtke (Ed.): Ice Age Research . Wissenschaftliche Buchgesellschaft, Darmstadt 1990, pp. 250-260.
  21. ↑ EA FitzPatrick: An indurated soil horizon FORMED by permafrost . In: Journal of Soil Science 7, 1956, pp. 248-257.
  22. ↑ A. Pissart: Les phénomènes physiques essentiels liés au gel, les structures périglaciaires queen résultent, et leur signification climatique . In: Annales de la Societe Geologique de Belgique 93, 1970, pp. 7-49.
  23. ^ A b A. Semmel & B. Terhorst: The concept of the Pleistocene periglacial cover beds in central Europe: A review . In: Quaternary International 222, 2010, pp. 120-128.
  24. ^ A b J. Völkel & A. Mahr: New findings on the age of the periglacial cover layers in the Upper Bavarian Forest . In: Journal for Geomorphology NF 41, 1997, pp. 131-137.
  25. ↑ F. Ahnert: Introduction to Geomorphology. 3rd edition, Eugen Ulmer, Stuttgart 2003 ISBN 3-8001-2813-6 .
  26. ↑ a b A. Kleber: The age of the Central European upper layer (Hauptlage) - a synthesis deduced from analogues . In: Journal of Geomorphology NF 48, 2004, pp. 491-499.
  27. ↑ a b A. glue, R. & W. Zech Milan: Stratigraphic approach to alteration in mineral soils - the heavy metal Example . In: Soil Science Society of America Journal 62, 1998, pp. 1647-1750.
  28. ↑ J. Völkel & A. Mahr: The IRSL dating of periglacial slope sediments - results from the Bavarian Forest . In Zeitschrift für Geomorphologie NF 45, 2001, pp. 295–305.
  29. ^ D. Cover, A. Hilgers, P. Kühn & U. Radtke: The potential of optically stimulated luminescence for dating periglacial slope deposits - A case study in the Taunus area, Germany . In: Geomorphology 109, 2009, pp. 66-78.
  30. ↑ M. Kösel: The influence of relief and periglacial cover layers on soil formation in the central Rhine glacier area of ​​Upper Swabia . In: Tübinger Geoscientific Work D1, 1996.
  31. ↑ T. Raab: Würmzeit glaciation of the Bavarian Forest in the Arber area . In: Regensburg Geographical Writings 32.
  32. ^ RA Mailänder & H. Veit: Periglacial cover-beds on the Swiss Plateau: Indicators of soil, climate and landscape evolution during the Late Quaternary . In: Catena 45, 2001: pp. 251-272.
  33. ^ A. Kleber, J. Lindemann, A. Schellenberger, C. Beierkuhnlein, M. Kaupenjohann & S. Peiffer: "Slope deposits and water paths in a spring catchment, Frankenwald, Bavaria, Germany." In: "Nutrient Cycling in Agroecosystems" 50, 1998, pp. 119-126. Download as PDF  ( page no longer available , search in web archives )  Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Toter Link / www.tu-dresden.de