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Station 5: Soil and Rock Studies

General Information

Perhaps the first thing that came to your attention as you came into the Leinbachtal was, after the Leinbach itself, the many trees and bushes. However, have you ever considered what lies right underneath your feet? What does the soil consist of, when did it develop and what differences are there? These questions will be answered here.

 

 

 

1. Rock

1.1 Early trias

 

2. Bodentypen

2.1 Brown Earth

2.2 Para-Brown-Earth

2.3 Gley

2.4 Pseudogley

2.5 Podzol

 

 

1. Rock

1.1 Early Trias

Early trias originated between 215 and 230 million years ago, and mainly consists of quartz sandstone (red/reddish-brown colouration, at times yellow, white or violet). The typical reddish-brown colour of this stone comes from a thin membrane of iron oxide or iron hydroxide that surrounds it.

This rock is deposited in a large stretch of land in Europe, from France and Luxembourg in the west to Poland and Belarus in the east, and from Switzerland in the south to the northern border of Scandinavia.

In the time where early trias was developing, the climate fluctuated between wet-dry and dry. These desert-like conditions left desiccation cracks in clayrocks. There are very few fossils that stem from this time, but amongst these there are plant remains of ferns, horsetails or conifers, tracks and skeletal remains of vertebrates, and some freshwater animals and animal dwellings. Because of this paucity of fossils, studies concerning this rock have used the process of sedimentation as an organizing principle , sub-dividing the Bunter sandstone into three layers:

         Upper early trias with a thickness from 100 bis 190 m

          Middle early trias with a thickness from 140 bis 240 m

          Lower early trias with a thickness from 200 bis 310 m

[www.themenpark-umwelt.baden-wuerttemberg.de]

Figure Early trias: [www.data6.blog.de] 

 

Upper early trias

Towards the end of the period where early trias was created, the sea left marine deposits such as sea shells, or shells from horseshoe crabs. Soil deriving from this rock is more fertile than that derived from middle early trias.

This rock layer can be broken down into two subdivisions, plate sandstone and the red clayrock that covered it. In the lower section of the plate sandstone, there are concretions of carnelian and dolomite, which are often used as a border demarcation to differentiate layers. Middle-grained sandstone enriched with mica on layer surfaces, which gives the appearance of a plate-like surface, are mainly found in plate sandstone. In smaller quarries, this type of sandstone is still quarried as building stone or as natural stone.

The red clayrock is split into upper and lower segments by a layer of red quartzite. Red quartzite is sandstone pebbled with trace fossils. Red clayrock are reddish-brown clay and silt rocks with a waterlogged subsoil, intermediate sandstone material, and local gypsum and marlstone layers. The uppermost parts are covered with a dolomitic lime with marine-brackish fossils, a remnant of the period in which the sea covered the area.

 

Middle early trias

The middle early trias segment begins with a debris-strewn horizon, where debris is interspersed with a series of sandstone layers. The upper early trias segment is distinguished partly by its lack of debris. Middle early trias layers can be subdivided into two parts based on the presence or absence of sandy brownish flecks that weather away into holes. The upper sandstone is partially separated by thin layers of silt, and is made up of thick seams of sandstone. In many quarries up until the present day, this type of sandstone is still mined.

 

Lower early trias

Essentially the lower early trias is clay-like, sandy and colourful, with a consistent dark red colour, or very rarely, a yellowish gray tone. It is presumed that this type of sandstone developed in an estuary in shallow marine conditions. Spherical formations of sandstone mark the uppermost horizon of this segment. Towards the lowest reaches of early trias formation, where the Zechstein begins, one can find Tiger sandstone, a particularly striking stone, marked by yellow-to grayish-black flecks of manganese oxide [www.themenpark-umwelt.baden-wuerttemberg.de].
 

Figure Spherical formation of sandstone and Tiger sandstone: [www.themenpark-umwelt.baden-wuerttemberg.de]

 

2. Types of soil

2.1Brown Earth

In temperate regions, brown earth and its sub-types are the most common and widely occurring soil type. Mainly, they do not stretch out over large contiguous areas and are recognizable by the large diversity of their parent rock. Brown earths are young, post-glacial formations (like all Central European soil) that often develop out of rankers or rendzinas (shallow soil types), and have a profile depth of 1.5 meters. The topmost soil horizon is the humic A-Horizon, below which there is the B-Horizon, which is marked by its brunification, and lastly the C-Horizon parent rock. This type of soil derives from a great diversity of loose rock and bedrock (airborne sand, loess), as well as from sandstone, granite, basalt, gneiss and stony mud. Along with the humus enrichment of the topsoil, brunification is one of the key features of brown earth. The release of iron causes the formation of brownish iron oxide and iron hydroxide; simply put, this process generates rust. A further process that also occurs in the Ah soil horizon is the regeneration of clay minerals. However, both of these processes occurring in the Ah soil horizon are not easily recognizable as they are covered by the dark-coloured humus. A third important process is decationization. Hunks of rock that have not yet been broken down in the clay-rich and typically brown Bv soil horizon provide nutrient reserves; what results is the obscuring of the boundary between the Bv horizon and the C horizon. Most of the time, humus and brown earth rich in mineral reserves emerge from basalt and till. They are lightly acidic to neutral, well-aerated and moisture-rich; these factors provide this type of earth with a high production potential. Brown earth that develops over granite or sand is, on the other hand, acidic, base-poor, and coarse. Due to their favourable hydrologic balance they are similarly mouldy. Through fertilization, conditions can be bettered so as to increase the efficacy of soil use. Despite its inconspicuous appearance, brown earth is an interesting soil type, versatile and multi-layered [www.hypersoil.uni-muenster.de] [www.bodenkunde.uni-hohenheim.de] [www.bodenwelten.de].

Figure Brown Earth: [www.hypersoil.uni-muenster.de]

 

2.2 Para-Brown-Earth

Para-brown earth types are similar to brown earth types in that they are one of the most ubiquitous soil types found in Eurasian and American temperate humid climate areas. They belong to the marl family, and develop mostly out of para-rendzinas or brown earths; these soils aid the displacement of clay through their light acidity and erosion of lime. The source rock types for this type of earth are fine-grained, mostly loose, and not too acidic, with loess and till being common substrates. The light and acidic Al soil horizon (erosion horizon), and the subsequent reddish-brown Bt soil horizon (clay enrichment horizon) are typical features of para-brown earths. The formation of the humic top soil involves the eluviation of clay content. The AI horizon and its light tone develop from the displacement of these soil particles. This displacement by means of material flow, leads to clay enrichment in the Bt soil horizon; this process is evidenced by the vaguely shiny clay film on the walls of cavities in the soil. Moreover, the clay enrichment leads to darker colouration in general. The C soil horizon is made up of the parent rock. Through acute acidification this soil type can transform into podzol-para-brown earth or podzol; the possibility for this type of transformation are higher underneath a forest. Through clay enrichment, as well as in areas that receive a great deal of precipitation, the possibility exists that waterlogging will occur, leading to the development of pseudogley-para-brown earths or pseudogleys. Para-brown earths are deep, fertile and conducive to agricultural work. These characteristics arise from the soil’s high mineral content, the high humus content, the permeable three-layered clay minerals, as well as a favourable soil structure. However this type of soil is susceptible to erosion that can be ascribed to insufficient ground cover. The use of heavy machinery on this soil can lead to reductions of the aforementioned advantages, and cause soil compression. Moreover, erosion is also common where ground cover is insufficient. [www.hypersoil.uni-muenster.de] [www.bodenkunde.uni-hohenheim.de]

Figure Para-Brown-Earth: [www.hypersoil.uni-muenster.de]

 

2.3 Gley

Gley soil types are strongly influenced by groundwater, and are characterized by their high water content. Because of this trait, they are also referred to as hydromorphic soils. Because of their high clay content, gley soils demonstrate a high exchange capacity. When dry, deep fissures can appear, and when wet, gley soils are very difficult to work with. Because of the difficulties posed by groundwater issues, the slow warming of this type of soil, the high mobility of the nutrients released into the groundwater, and the limited opportunities for laying down roots, this type of soil is hardly suited to agricultural use. The Ah soil horizon is between 20-30 cm thick, humic and normally lime-deficient. What is referred to as the G soil horizon is rich in clay and loam, and the development of this subsoil is driven by chemical weathering. Because of oxygen deficiency in the wet groundwater area, rust-coloured iron hydroxide and manganese hydroxide are reduced to soluble bivalent iron oxide and manganese oxide. In the area just above where the groundwater level fluctuates, these iron and manganese deposits interact with the air supply, creating recognizable mottled bands. In the waterlogged subsoil horizon below, this blotchiness is replaced with green-blue-grey layers [www.hypersoil.uni-muenster.de].

Figure Gley: [www.hypersoil.uni-muenster.de]

 

2.4 Pseudogley 

Pseudogley is mainly found on top of clay-rich, finely grained and silt-rich substrates, on planes and depressions. The soil consists of two layers, the primary and secondary pseudogley. The primary pseudogley is the result of sedimentation, and is a water conducting layer with an extremely coarse texture on the AI soil horizon. The secondary pseudogley stems from para-brown earths with pronounced clay migration, and is a water-retaining and clay-deficient layer in the Bt soil horizon. In order for the two layers to develop, there must be an alternation of wet, humid and dry phases of varying durations.  The typical profile of pseudogley in the Bt soil horizon is “marbled”, with reddish-rust brown colouration interspersed with grey stripes and flecks. The system of layering is a prerequisite for the development of this type of soil. The rainwater passes through the porous Al soil horizon, and builds up over the Bt soil horizon, creating a flat standing water body. This body of water only dries out with the advent of summer temperatures, and when the plants have used up the retained water. The differences in terms of duration between the wet and dry phases is dependent on various factors, including: at what depth the water is stored, the texture of the Al soil horizon, the relief of the surface of the water-storing layer, as well as the floor surface of this layer, the amount and distribution of precipitation, and temperature and air humidity. During the wet phase, the soil life is greatly diminished due to the lack of air. Root penetration occurs mainly in the Al soil horizon, as this part is less compacted, well-aired and water permeable. Without amelioration, the qualitative improvement of the soil through drainage, liming, dewatering, and fertilization, etc., pseudogley is, at best, of little practical agricultural use [www.hypersoil.uni-muenster.de] [www.bodenkunde.uni-hohenheim.de].

Figure Pseudogley: [www.hypersoil.uni-muenster.de]

 

2.5 Podzol

The term podzol is borrowed from the Russian, and means, in short ,“ash-coloured soil”. The soil horizon that gives this soil type its name has a blanched violet-tinged light grey colouration, and is located underneath a raw-humus layer and a thin humus horizon. In the “ash-coloured” horizon, humus and iron have been washed out, but black-brown and red-brown colourations are identifiable in the underlying area. This subjacent area is often very firm and marked by black-brown and red-brown banding as it goes deeper into the subsoil. This type of soil is typical for humid and cool temperate climate areas, yet they are also the most widely distributed soil type in subpolar areas. The development of this soil type is commonly found in places where there is nutrient-deficient parent rock. Parent rock types fitting this description include sandstone, granite, airborne sand amongst others. Furthermore, the development of this soil is associated with places where there is a high level of precipitation, high levels of humidity and a low average annual temperature. The creation of podzol is strongly connected to pronounced acidification, where the strewn remains in heath and coniferous forests are not easily decomposed by microorganisms. This leads to the generation of thick humus layers, where organic acids are released. These acids bond with aluminum and iron, and convert the decomposed minerals into water-soluble substances. These substances are finally sluiced down into the subsoil where the characteristic series of soil horizons associated with podzols result, a product of the precipitation of substances through different chemical conditions. Through liming of the soil, the breaking of solid rocks, intensive humus management, and watering, there is the possibility that this type of soil can be made suitable for agricultural purposes[www.hypersoil.uni-muenster.de] [www.bodenkunde-online.de]

Figure Podsol: [www.hypersoil.uni-muenster.de]

 

 

 

 

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