Bacterial Diversity in Calcium Carbonate Paleo Accretions ( Tosca ) in the Southern Pampas, Argentina

Abstract

Paleosoil accretions of carbonates in the Tandilia system (Southern Pampas, Argentina) dated to the lower/middle Pleistocene age are locally referred to as tosca. The characterization of this indurated layer of carbonates were analyzed via a biophysicochemical approach, including, physicochemical analysis of soils, mineral x-ray diffraction of the tosca, and microbial diversity of modern soils and tosca layers. The minerals found within tosca were calcite, albite, muscovite, quartz, orthoclase and dolomite in order of most to least abundant. The microbial metataxonomics of tosca was described for the first time. The most abundant microorganisms in tosca were g_Geobacter, g_Pseudonocardia and p_Gemmatimonadetes2 and redundancy analysis of physicochemical parameters and relative microbial abundances revealed positive correlations between Nitrospirae and calcium ions, while mineral and microbial correlations associated Gemmatimonadetes and Firmicutes with calcite and dolomite presence. Magnetospirillum, Geobacter and Bacillus were present in the tosca and the soil above, indicating possible prenucleation sites for calcite and dolomite. Core microorganism abundance was >80% throughout horizons including tosca, hence either microbial entrapment via calcium carbonate precipitation or microbial leaching occurred within this layer.