Environmental Role Of Bíominelalizations And Biogeochemistry of Iron

OSTERRIETH, M.; N. BORRELLI; M.F. ALVAREZ; M. FERNANDEZ HONAINE

Conferencia; 20th International Symposium on Enviromental Biogeochemistry; 2011

The biomineralizations present in every level of the biosphere, are the result of the metabolic function of the biota. The goal of this paper is the mineral-chemical characterization of the biomineralizations of iron, calcium and amorphous silica, in pedosedimentary sequences, located at the Buenos Aires province (36°00´ to 39°05´ S; 60°10´ to 57°00´W). Sampling was carried out in pedosedimentary sequences from different geomorphological settings, that include: eolian dunes, estuarine, paleoestuarine, salt marsh, and fluvio-eolian plain. Sampled sections were representative profiles,disturbed and undisturbed samples (micromorphology blocks) were studied by means of routine procedures. The presence of silica biomineralizations (silicophytoliths) revealed six pedological cycles in the, in the complex geomorphological units of the continental and coastal areas, with some episodes of rapid burial, from the Plio-Pleistocene to current times. Biomineralizations of ¡ron we found in the form of framboidal and polyframboidal pyrite, greigite, mackinawite and iron oxyhydroxides associated with gypsum, barite, calcite and halite, which permit us to define the redoxymorphic conditions in paleoestuary pedosedimantary sequences. The biofilms are recurrent, which is a product of the intense microbiological and multifunctional activity. The biomineralizations of calcium we found in the bioclastic and calcretized levels, associated with the processes of dissolution and re-precipitation of calcium carbonates and oxalates via biogenic action. The relationship between different types of biomineralizations, and the evolution and degradation of soils ¡n the different environments of the southeast pampean plain of the Buenos Aires province, show the qualitative characteristics and intensity of the pedogenesis, as well as paleoenvironmental characteristics.The contribution of these elements in the matrix conformation of soils, paleosoils and sediments in these environments is related to climatic changes and sea level oscillations during the Late Quaternary. In continental areas the amorphous silica-enriched matrices of the soil, contribute to increased resistance to erosion caused by the extensive and intensive agricultural activities.