CALCIUM CARBONATE PRECIPITATION WITHIN DIATOM-RICH MICROBIAL MATS: THE LAGUNA NEGRA HYPERSALINE LAKE, CATAMARCA (ARGENTINA)

GOMEZ, F.J.; MLEWSKI, C; BOIDI, F.J.; FARIAS, M.E.; GERARD, E.

JOURNAL OF SEDIMENTARY RESEARCH

SEPM

Año: 2018

1073-130X

Carbonate microbialites provide a window to understand microbe-mineral interactions in modern environments and in the geological record. Unraveling microbial versus physicochemical controls and biogeochemical signatures is not always straightforward. Environmental and laboratory studies have shown that microbial activity can play a central role in calcium carbonate precipitation. Most studies have focused on the effects of Bacteria and Archaea activity on carbonate precipitation processes (e.g. cyanobacteria, sulfate reducing bacteria, sulfide oxidizing bacteria and iron reducing bacteria). The influence of Eukaryotic activity, such as diatoms and other microalgae, on carbonate precipitation and microbialite formation has been the focus of less attention.This study explores carbonate mineralization in active diatom-rich microbial mats developed in a high altitude groundwater-fed hypersaline lake in the Puna region of Catamarca, Argentina. Previous work has focused on the texture, mineralogy and stable isotope chemistry of the subfossil oncoidal and laminar microbialites. Here, using 16S rDNA Bacteria diversity analysis, confocal scanning laser microscopy and scanning electron microscopy and polarized transmitted light microscopy, we explore the Bacteria and Diatom diversity in the microbial mats and the related carbonates textures and make comparisons with similar textures in the associated oncoidal microbialites. Diatom-rich subspherical aggregates, which have not been previously described in the literature, show a diverse microbial community with abundant ExoPolymeric exopolymeric Substances substances (EPS) where carbonate precipitation takes place. These aggregates are a main component of the Laguna Negra microbial mats, and show anhedral micritic calcite in the EPS matrix as the main mineral component. of the Laguna Negra microbial mats and sSimilar calcite micrite textures are also preserved as one lamina type within the associated oncoids. On the other hand, carbonate precipitation related to pennate diatom blooms, where EPS are absent, show remarkable differences in texture and mineralogy (is represented by euhedral aragonite needles), suggesting different mechanisms and controls. Changes in the microbial communities are recorded within the oncoids as different lamina types, providing a link between the currently active mats and the subfossil oncoidal structures. This is a first survey of these previously unexplored diatom-rich microbial mats developed under extreme environmental conditions in the Laguna Negra. Understanding the effect that the interactions between diatoms and prokaryotic communities has on carbonate precipitation may provide some insight on the evolution of microbialites textures and fabrics, and on the change from prokaryote dominated systems to mixed eukaryotic-prokaryotic systems.