Biogenic and chemogenic calcium accumulations in Mollisols developed from loess in Argentina pampas |
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| Authors: | A M Kuznetsova O S Khokhlova M L Osterrieth |
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| Institution: | 1.Biological Faculty,Moscow State University,Moscow,Russia;2.Institute of Physicochemical and Biological Problems of Soil Science,Russian Academy of Sciences,Pushchino, Moscow oblast,Russia;3.Center for Quaternary Geology of the National University of Argentina,Mar del Plata,Argentina |
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| Abstract: | The morphology of pedogenic calcium accumulations, their distribution in the soil profile, and the mechanisms of their formation
in Mollisols of Argentina pampas were studied in the southeast of the Buenos Aires province. The chemogenic collomorphic calcareous
films and tubes and the biogenic (cyanobacterial) gypsum framboidal structures (spherulites) were detected with the use of
electron microscopy. Two mechanisms of the formation of framboidal gypsum were identified: (a) the formation of crystalline
gypsum crusts around less soluble minerals (calcite) by spherical colonies of cyanobacteria and (b) the inheritance of the
spherical shape of gypsum pedofeatures from the framboidal pyrite concretions accumulated in marine deposits and subjected
to decomposition by sulfate-reducing bacteria. It is probable that the cyanobacterial gypsum accumulations are only formed
in the studied soils during the dry season and are dissolved during the wet season. |
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