A type of soil of bright red or brown-red colour made of clay or loam, found mainly in the Mediterranean region (Southern Europe, North Africa, the Near East and partly also in the USA). The red colour is caused by the high proportion of the iron compound haematite (lustrous iron ore). It often lies directly above a water-permeable limestone layer and is therefore also called limestone red clay. It is a phenomenon in karst areas; it is assumed that undisturbed rendzines will develop into terra rossa soils in the long term. The soil formation processes already took place in the Tertiary period 15 million years ago and consisted of the leaching of the lime components while leaving behind the clay minerals found in the lime and other mineral impurities such as red iron compounds. However, more recent research suggests a much more recent history of formation, as evidence has been found of the input of red mineral dust from the Sahara and the Sahel region, which is at most 25,000 years old.
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