Shift level
Geomorphology refers to a terrain or relief form as a layer level or layer level landscape , which is built up from slightly inclined, almost parallel layers of rock . Their characteristics and steepness essentially depend on the weathering resistance and location of the rocks that make up them.
General
Prerequisite for the formation of layer levels (and related forms layer panel is layer comb layer rib layer and layer ramp threshold) is usually a layer package with different ablation resistant rock layers. These layers were then cut by weathering and / or erosion , resulting in the typical appearance.
The transitions between step, table, comb, rib, ramp and threshold are fluid. Other important factors are the inclination and thickness of the layers involved, as well as the type and energy of erosion and weathering. Reliefs dominated by layers are mostly heterolithic , that is, they consist of several such rock layers. Different degrees of weathering in a layer can also lead to a homolithic layer relief. In Central Europe, stratified reliefs can be found primarily in south-west Germany ( south-west German layer level country ) and in the area of southern Lower Saxony-North Hesse-Thuringia.
Layer level in the narrower sense
The terms "land level" and "layer level relief" are also common.
Description / treasure trove of shapes
Step and base builder
Ideally, at the beginning of the development of a layer stage there is usually an uplift and the associated inclination of a layer package with a more resistant rock layer on top and more flexible rock layer on the bottom by about 1-5 ° . The step is formed by erosion down to the more flexible layer below. The layer of the more erosion-resistant (“harder”) rock on top is called the step-forming element and forms the raised parts of the step (see 2.1.2). The base former is the layer of the underlying, less erosion-resistant ("softer") rock.
The degree and direction of the inclination of the strata are described using the geological terms " fall " (also "collapse" or "stratum (s) fall") and " strike ".
Step formers in Central Europe are mostly limes and sandstones , base formers mostly marl and clays .
Front and back
The transverse profile is clearly asymmetrical and is generally divided into the front and rear. The foreland of the step lies in front of the front, followed by the corresponding hinterland at the rear.
The face of a layer step in particular is called a step slope. This is divided into the step front (also "upper slope" and "upper step slope"), that is the upper, steeper slope area occupied by the step maker, and the base slope (also "lower slope" and "lower step slope"), that is the lower one (sometimes also middle), less steep slope area occupied by the base builder. The base slope can be divided into a steeper slope foot zone and less steep to flat foot surface. In the step slope you can often find a source horizon at the layer joint (i.e. layer boundary) between the step and base builder, indicating the border between the upper and lower slope.
The back, especially the layer step, is called the step surface (also “step back” and “land terrace”). It rarely coincides with the roof surface of the step builder and can carry younger rocks, which are usually cut at a very shallow angle. If necessary, the transition to the base former takes place in a next stage.
The step slope is usually designed as a front step (also "contrary step"). A front step points in the direction of the bulge of the layer package, away from the layer falling. The less common eighth stage (also known as the “conformal stage”), however, points in the direction of the layer falling. The step height depends on the thickness of the step creator.
The ridge marks the highest points of a (front) step. The eaves form the not always formed edge in the cutting of slope and surface. The area between the ridge and the eaves is called the hip. Three types of steps depend on the occurrence and location of the eaves: Ridge step (also “eaves step without hip”): ridge and eaves coincide. Eaves-hip step (also "eaves step with hip"): The ridge and eaves do not coincide, the hip between them is therefore more of a part of the step surface. Hip step: no eaves formed (the slope upwards steadily approaches zero), so the hip is more of a part of the slope.
The horizontal course of the stepped slope areas of a layer step is mostly strongly lapped and bunched due to erosion and step shifting backwards: step edge bays, step edge valleys (frontal valleys), mountain peninsulas, protrusions, terrain spurs, protrusions and witness mountains (extension mountains) occur. In contrast to the mountain peninsula, projection and spur, a protrusion is also connected to the main step in the step former, but the original step surface between the protrusion and the main step has already been eroded. A witness mountain (also "Ausliegerberg"), on the other hand, is no longer connected to the main stage in the area of the step builder, but is usually in the area of the base builder. ( Nota bene: "Auslieger" is not the same as "Ausliegerberg".) Witness mountains and Auslieger appear both with and without their own step area.
Layer level landscape
In the case of multiple coherent occurrences of strata, one speaks of a stratified landscape (also "stratified land" or "stratified land" for short). The distance between the front steps depends on the depth and thickness of the layers. Small steps can occur with thin and rapidly changing layers.
One speaks of an anticline step land when front steps of several tectonically connected units of step landscapes are opposite one another and point to the common center of the vault (e.g. south German-north French anticline step land); In the case of a syncline step land, the front steps point away from each other, in the center there is usually a trough or basin landscape (e.g. the syncline step land around the Paris basin).
Flow directions of the rivers
The flow directions of the rivers in a stratified landscape or at a stratum have been given specific names (keyword "kros"). The consequent waters flow in the direction of the fall of the layers, but already existed before the step was created. The sequential waters also flow in the direction of the fall of the strata, but only emerged after the step was created. The obsequent waters flow in the opposite direction to the contiguous and consequent waters and play an important role in the shift backward. The subsequent waters flow in stratification, tending to run parallel to the step, often as a step edge flow.
Origin / development
The origin of strata is before the Holocene (prehistoric form). In the Holocene, spring erosion , landslides and landslides only came and will . The pace of the relocation of the steps caused by the retreating erosion was around 200 meters to 60 kilometers in relation to Central Europe and the Quaternary. Details of the time of origin, development history (type of removal) and the speed of relocation are disputed.
Special forms / related forms
Shift table
Layered table reliefs occur in horizontal or very flat layers of layers (dip around 0–1 °), sometimes with large plateau-like forms. The panel surface is shaped by the panel artist's roof surface. Stepped slopes can be found on all sides. Outsiders and witness mountains are called table mountains, smaller forms occur as rock towers and rock needles. With rapid fluvial deepening, canyons can form. Examples of stratified table landscapes in Central Europe are the Rheinhessisches Tafelland , the North Hessian Table Mountains and the Elbe Sandstone Mountains , in North America the Plateaux of Colorado with the Grand Canyon . Similar landscapes to stratified map landscapes can be found in large basalt and lava ceilings .
Layer comb
Ridge reliefs can occur with relatively steeply dipping layers (dipping more than about 10–12 °). In contrast to the layer steps, the ridges of the cut-out, more erosion-resistant layer (ridges) run largely in a straight line, there are no protrusions and the like. The front side is called the forehead slope. The rear side is the back slope that roofs in the direction of the fall of the layers (a surface as with layer steps is not formed). The transverse profile can also be symmetrical. In a layered ridge landscape there are clearing zones between the ridges.
Stratiform ridge landscapes occur, for example, in folded sedimentary rocks and are therefore mainly to be found in folded mountains or tectonically unstable areas. The Teutoburg Forest is a layered ridge formed from Cretan sandstone . The “ridge and valley topography” of the Appalachians is also characterized by the appearance of layered ridges.
Layer rib
Stratified ribs (landscapes) occur in vertical or very steep strata . In fold mountains, they can be sharpened to ridges.
Shift ramp and shift threshold
The layer ramp and the layer threshold are transitional forms between the layer step or crest on the one hand and the body surface on the other, with slightly steep end faces (maximum approx. 8-10 °). The cause can be a very extensive erosion or a comparatively less resistant ramp builder or threshold builder. Ramps are asymmetrical and have a ramp slope and ramp surface, thresholds are symmetrical (no significant difference in relief between the front and rear).
Significance of the Mesozoic rock layers
In Europe, layer reliefs are mostly found in the sedimentary rocks of the Mesozoic overburden .
Importance of fissure
It is not only the different erosion resistance of the rock strata that leads to the formation of strata, but also the different fissures (water permeability) of the rock. This property leads to the formation of layer sources, which play a role in the retreating erosion.
Concept of structural form
The layer level is a structural form in the geomorphological sense . This means that their formation is primarily due to geological and tectonic conditions. In contrast to this, sculptural forms (such as the fuselage surfaces similar to steps or panels ) are predominantly related to exogenous processes.
Research history
The question of whether the layer surface is an accordance or a sculptural form connects the layer level research very closely with the trunk level research. The shift level research experienced its first high phase in the middle of the 19th century. The development of layer level research began in the Anglo-American region, where the idea prevailed that the layer levels were marine abrasion platforms ( Charles Lyell ). With this thesis several important American researchers deal critically ( Andrew Ramsay , John Wesley Powell (1834-1902), Grove Karl Gilbert (1843-1918)), which again led to new theories. The first geomorphologists who dealt with the strata levels in the German-speaking area ( Georg von Neumayer , Alfred Hettner ) were still very much influenced by the Anglo-American preparatory work. In 1894 Albrecht Penck coined the concept of the layered landscape .
The cycle theory of William Morris Davis from the 1920s gave new impulses to the entire geomorphology and thus also to stratification research. However, it was criticized for not emphasizing the different rock layers sufficiently (Gradmann). Eight years after Davis' cycle model, Heinrich Schmitthenner (1887–1957) published the classical layer theory , some of which still determines the understanding of layer levels today. In the period after the Second World War, research on the levels of shifts, with a more empirical approach, increasingly expanded to include countries outside of Europe, which led to greater consideration of climatic aspects (e.g. Hans Mortensen (1894–1964), Jean Tricart (1920– 2003), Julius Büdel or Ingrid Dörrer ).
This ultimately led to a striking research dispute in the 1950s to 1970s between those who interpreted the layered surfaces as "structure-related" surfaces and those who tended more towards a sculptural form. This scholarly dispute was at the same time the culmination of the shift research. Neither of the two camps was able to fully assert itself. Since the 1980s, geomorphology has increasingly tended towards a processual understanding and is primarily “only” concerned with selected partial aspects or processes. A holistic interpretation has almost completely receded into the background.
The attempts to explain the stratified landscape always stood in the field of tension between the emphasis on exogenous (sculpture; emphasis on the fuselage) and endogenous (structure) factors.
See also
- Southwest German layer level country
- North of France layer level country
- Niagara layer level
- Grand staircase
- Large edge step
- Terrain level
literature
General
- Lexicon of Geography I, 2001, p. 108
- Lexikon der Geographie III, 2002, pp. 189–190
- Lexicon of Geosciences IV, 2001, pp. 400–403
- Harald Zepp , Geomorphologie, 2nd edition Paderborn 2003 (1st edition 2002), Chapters 12.3 and 14.3
Special
- H. Blume, Problems of the Layered Landscape, Darmstadt 1971
- H. Dongus, Structural trains in relief of the earth, in: Geographische Rundschau 9 (1975), pp. 373–378
- M. Gwinner, On the nature of the layer levels in the layer level country of Southwest Germany, Mannheimer Geographische Arbeit 1 (1977), pp. 277-293
- H. Schmitthenner, Problems of the Layered Landscape, Marburg 1956
- E. Schunke and J. Spönemann, Layer stages and layer combs in Central Europe, Göttinger Geographische Abhandlungen 60 (1972), pp. 65-92