Soil Formation on Clay Limnoglacial Plains of North West Russia.
Natalia N. Matinian, Saint Petersburg Univ, Oranienbaum road 2, Botanicheskay 18/5 dep.17, Saint Petersburg, Russia
The main aim-to make clear of genesis of surface moistening soils on varve clays, to investigate peculiarities of profile distribution of chemical substances on the base micro morphological, chemical, mineralogical analyses. Inner zone of Valday (Wurm) glacieration can be characterized by widespread development of accumulative limnoglacial plains. These plains are composed by sedimentations of heavy granulometric composition primary by varve clays - clays having horizontal stratification (alternating layers of silt and clay). Plain relief and the varve clays peculiarities (low water, permeability and high soil particles interaction) result in soil surface excessive moistening. Areas with low moisture variations existing in soil profile(down from 20-50 cm) signify that there is no frontal soil moisture filtration. Transformation of organic and mineral substances and its migration occur against the background subsurface and surface flow. Vertical translocation of substances is usually associated with big cracks. Profile differentiation on substances distribution depends on the power of eluvial-gley processes. Genetic horizons often are differed by the degree of eluviations of substances (without accumulation in B horizon). Chemical and fermentative ferrum reduction in excessive moistening conditions stimulate its mobilization and carrying out from upper layers or soil thickness. Amorphous compounds accumulation in upper layers, development of numerous concretions and possible incorporation of ferrum ions in clay minerals crystal lattice are related to ferrum mobilization. Chemical-mineralogical changes of mineral soil base, inherited from soil rocks,show themselves in hydromica consequent transformation and formation of vermiculite and mixed laver minerals with a marked portion of smectite packets as well as partial chloritization of layered silicates. Soil acidity, associated with predominance in organic substances of surface gleyed soils low-molecular acids and humus mobile fractions, promote these changes. One of the most sensitive and stabilized indicators of surface hydromorphic soils are specific content chlorofill, magnetic susceptibility of soils and its electron paramagnetic resonance. Soils have a big nourishing substances reserve but at the same time they possesses of unfavourable agricultural physical properties. They are in need of water regime regulation by implementation.