Saturday, 15 July 2006

Soils on Hard Calcareous and Gypseous Rocks:Distribution, Genesis and Problems of Classification.

Sergey V. Goryachkin, Institute of Geography, Russian Academy of Sciences, Staromonetny, 29, Moscow, 119017, Russia

Calcareous rocks are widely spread in the world and especially in Europe. Hard gypsum rocks are not so extensive as limestones, however they also can be met in many countries – Poland, Spain, Germany, Romania, Ukraine, Russia, Iran, USA, Canada and others. In arid climates soils formed on calcareous and gypsum materials do not strongly differ from their “zonal” loamy analogues, as the latter ones also contain calcite and gypsum. But, as it is known, in humid climates soils on calcareous and gypsum substrates are very specific. The polish word for Ca-soils “Rędzina” and its derivatives are widely used in many national and international classification systems – Rendzic Leptosols (WRB), Rendolls (Soil Taxonomy). However, in contemporary WRB system strongly calcareous and gypseous soils are split into 3 units – Leptosols, Regosols, Cambisols. The place of soils on hard gypsum in different classification systems is problematic, for example in Polish classification they are determined as “Rędziny siarczanowe”. However, the main diagnostic feature for rendzic soils is dark granular humus horizon. It is known that neither calcite nor gypsum can accrete into granular aggregates with high content of dark humus. It means that the term “Rędzina” is used for soils developed not from pure calcite or gypsum materials but on a substrate consisting of shallow quartz-silicate layer (they often are allochthonous and rarely are autochthonous) and underlying calcareous or gypsum rock. However, besides soils with underlayed calcareous or gypseous material, the soils derived from pure superficial limestones and gypses also exist. We investigated soils on pure limestones, dolomites and hard gypses and on silicate material, underlayed by them in different parts of European Russia, Ukraine, Poland and Kazakhstan. It was confirmed that humid soils from different natural zones related to shallow limestones have many common features (Rendzic Leptosols). Soils on superficial Ca-material are very diverse depending on the size of outcrops. Large outcrops (n*10m2-100m2) are characterized by olygotrophic vegetation, deep regoliths, formed by processes of disintegration and low organic matter accumulation in upper soil horizons. When outcrops are small and they are juxtaposed to quartz-silicate soils the vegetation is luxurious, regoliths are shallow and the organic matter accumulation is well pronounced. Soils on calcareous material are characterized by mucky sticky top horizons and soils on hard gypsum – by deep litter accumulation. Unlike quartz-silicate soils very low cation exchange capacity, excessive drainage, poor structure, low humus content and low pH with geric properties (pHH2O

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