Abstract:

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, scanning electron microscopy, and transmittedlight 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 substances (EPSs) 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. Similar calcite micrite textures are also preserved as one lamina type in the associated oncoids. On the other hand, where EPS are absent, carbonate precipitation, related to pennate diatom blooms, is represented by euhedral aragonite needles suggesting different mechanisms and controls. Changes in the microbial communities are recorded in 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 interaction between diatoms and prokaryotic communities has on carbonate precipitation may provide some insight on the evolution of microbialite textures and fabrics, and on the change from prokaryote-dominated systems to mixed eukaryotic-prokaryotic systems.

Author affiliation: Gomez, Fernando Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

Author affiliation: Mlewski, Estela Cecilia. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

Author affiliation: Boidi, Flavia Jaquelina. Universidad Nacional de Córdoba; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina

Author affiliation: Farias, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Tucumán. Planta Piloto de Procesos Industriales Microbiológicos; Argentina. Universidad Nacional de Córdoba; Argentina

Author affiliation: Gérard, Emmanuelle. Université Paris Diderot - Paris 7; Francia

Abstract:

The La Manga Formation consists of marine carbonates and represents most of the sedimentary record of the Callovian-Oxfordian in the Neuquén Basin. Three localities in the southern Mendoza province were studied and their cyclicity was determined by means of facies analysis and their vertical arrangement. Facies of inner ramp, that were deposited in extremely shallow-water environments with intermittent subaerial exposures have been broken down into shallow subtidal, and intertidal?supratidal environments. Shallow subtidal facies are arranged into decimetre scale upward-shallowing cycles composed of marls, laminated or massive mudstones or bioclastic wackestones and intraclastic wackestone-packstones. Intertidal-supratidal centimetre-scale cycles consist of an upward-shallowing succession of restricted facies, overlaid by horizontal o crinkle microbial laminites, flat pebble conglomerates or breccias beds. The defined cycles show a shallowing upward trend in which the evidence of relative sea-level lowering is accepted. The interpretation of Fischer plots allowed the recognition of changes in accommodation space.

Author affiliation: Palma, Ricardo Manuel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina

Author affiliation: Kietzmann, Diego Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina

Author affiliation: Bressan, Graciela Susana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina

Author affiliation: Martin Chivelet, J.. Universidad Complutense de Madrid; España

Author affiliation: Lopez Gomez, J.. Universidad Complutense de Madrid; España

Author affiliation: Farias, Maria Eugenia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Tucumán. Planta Piloto de Procesos Industriales Microbiológicos (i); Argentina

Author affiliation: Iglesia Llanos, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; Argentina