Terra fusca
The Terra fusca (from the Latin terra, land, earth ' and fuscus, brown' ), also called Kalksteinbraunlehm, is a type of soil that develops on a base of limestone or gypsum. It is a plastic, clay-rich and dense soil, the evident by the accumulation of solution residues from one caused by lime or gypsum solution rendzina.
Structure and properties
The Terra fusca has the soil horizons Ah / Tv / cC. The uppermost horizon is a mineral soil horizon ( A) having a higher organic matter content ( h), which is, however, less than 30 percent by mass. Under the A- horizon is a minimum of 10 to 30 centimeters powerful mineral subsoil horizon solution residue of carbonate rocks formed (Tv instead of conventional B- horizon). This solution residue consists of more than 65 percent by mass of clay ( Residualton ), usually with the clay minerals illite and kaolinite as the main ingredients. The bright yellowish to reddish-brown color of the T- horizon is usually the result of a relict or recent Verbraunungsprozesses (v). He also has a keen Polyedergefüge. He is acidic, so has a low pH, and goes through a transition zone from fanned hard rock in the C horizon of massive (m) of carbonate ( c ) unweathered (s ) Hard rock on ( CMCN ).
The Terra fusca belongs to the soil mapping as the Terra Rossa to the class C, the terrae calcis. In the WRB system of soil type of the Terra fusca is not specifically mentioned, here the Terra fusca belongs to the major class of cambisols.
The Terra fusca is very dense and difficult to handle due to the high clay content, especially as it often happens, alternating with stony, shallow soils. Your humus content varies. Especially with poor ventilation and cool moist climates, it may cause a severe humus accumulation. The Terra fusca has a high water capacity, whose usable by plants share is restricted by the high clay content in Tv - horizon of the soil. Due to these properties it is mainly used as woodland or pasture.
Formation
The exact cause of Terra fusca is the solution of the subjacent carbonate rocks. The soluble carbonate in calcareous rocks (limestone, dolomite), gypsum rocks ( gypsum, anhydrite) is removed by solution back the insoluble fractions, ie mostly silicates such as clay minerals remain. The often bright coloration may be the original color of the solution residue, but in most cases it goes back to a brunification, ie a release of the bound in carbonates and silicates iron, which was then oxidized. The formation of Terrae fuscae place under the present climatic conditions of Central Europe no longer takes place, so that such soils are considered soil formations dating from the Tertiary to Altpleistozäns.
The Terra fusca is in Central Europe only on old land surfaces away from active erosion, such as rivers, before. Such conditions are found for example in the Mesozoic limestones of the South German and Swiss Jura. Variously occur there in the soil formations called Bohnerz on. These are small spherical concretions of iron, whose origin is not yet fully understood. It is also unclear whether due to the formation of these concretions only to the long period of weathering or whether the tropical climate of the Tertiary Education is the main cause.