Experiments with microbial mats from shallow lakes: Metabolic influence of the microorganisms in the precipitation of minerals

El proceso de formación de minerales puede observarse en lagunas continentales, donde los carbonatos, sulfatos, cloruros y silicatos precipitan en asociación con tapetes microbianos. Los modelos clásicos explican la precipitación de la mayoría de las fases por mecanismos fisicoquímicos puros sin considerar la influencia biológica. Estudios recientes consideraron la influencia biológica, sin embargo, se han enfocado en aislar los microorganismos de forma individual. En nuestro estudio proponemos una serie de experimentos para crecer tapetes microbianos completos y evaluar la precipitación mineral que ocurre en los distintos tipos de lagos, especialmente sulfatos y carbonatos. En paralelo se han colocado controles diseñados para simular la precipitación abiótica pura. Por lo tanto, las observaciones realizadas en los experimentos, incluido el desarrollo de los tapetes y los minerales precipitados, pueden usarse como una herramienta para comprender las interacciones microbio-minerales en comparación con las observaciones de campo. Los precipitados de los experimentos de tapetes se parecen a los precipitados naturales en sus texturas y paragénesis.The process of mineral formation may be observed in modern shallow lakes, where carbonates, sulfates, chlorides y silicates precipitate in association with microbial mats. Classical models explained the precipitation of most of the phases with pure physicochemical mechanisms without considering biological influence. Recent studies considered biological influence focusing to isolate microorganisms. Here, we propose an experimental design to incubate the whole microbial mats running in parallel with controls designed for pure abiotic precipitation. Thus, the observations made in the experiments, including the development of the mats y the minerals precipitated, can be used as a tool for understanding microbial-mineral interactions by comparison with field observations. Remarkably, the minerals precipitated in the laboratory resemble the natural precipitates in textures y paragenesis.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEMinisterio de Economía y Competitividad (MINECO)/FEDERCONICYTUniversidad Complutense de MadridDonación Minera Escondida Ltda.pu

Geochemistry and microbial communities in Salar de Pajonales and Salar de Gorbea, Northern Chile: Influence on the gypsum microbialites formation

Pajonales y Gorbea son dos salares andinos de Chile, compuestos mayoritariamente de yeso, y poseen lagunas de un amplio rango de salinidades, índices de saturación (IS) de yeso y pH. Hay varios estudios que han abordado la geología de los salares de forma general, pero la geoquímica, petrografía y mineralogía de estos depósitos salinos han sido poco estudiado. El objetivo es comparar la información geoquímica de las aguas de las lagunas subsaturadas y sobresaturadas de yeso de ambos salares para identificar correlaciones entre la mineralogía de las comunidades microbianas y la hidroquímica que permitan desvelar el origen del yeso. En Pajonales, el yeso precipita: en lagunas subsaturadas con pH (7,4-8,1), salinidad (1,9-4,8 %) y predominancia de α-Proteobacteria (64%) en tapices microbianos. De otra manera, en Gorbea no se reconoce una relación significativa entre la precipitación de yeso, pH (1,8 a 4,5), salinidad (0,6-15 %) y predominancia de α+γ-Proteobacteria (90%). Cabe destacar que en aguas sobresaturadas se observó que los microbialitos de yeso están colonizados por fotótrofos en Pajonales (Cianobacterias) y en Gorbea (Diatomeas). Estos resultados sugieren que las comunidades de α-Proteobacteria en aguas subsaturadas y de fotótrofos en aguas sobresaturadas pueden jugar un papel en la precipitación de yeso.Pajonales and Gorbea are two Andean salt flats in Chile, composed mainly of gypsum, and have lagoons with a wide range of salinities, gypsum saturation indices (SI), and pH. There are several studies that have addressed the geology of the salt flats in a general way, but the geochemistry, petrography and mineralogy of these salt deposits have been little studied. The objective is to compare geochemical information of the waters of the undersaturated and oversaturated gypsum lagoons of both salt flats to identify correlations between the mineralogy of the microbial communities and the hydrochemistry that allows to reveal the origin of the gypsum. In Pajonales, gypsum precipitates: in subsaturated lagoons with pH (7.4-8.1), salinity (1.9-4.8%) and a predominance of α-Proteobacteria (64%) in microbial mats. Otherwise, in Gorbea a significant relationship between gypsum precipitation, pH (1.8 to 4.5), salinity (0.6-15%) and predominance of α + γ-Proteobacteria (90%) is not recognized. It should be noted that in supersaturated waters, gypsum microbialites are colonized by phototrophs in Pajonales (Cyanobacteria) and Gorbea (diatoms). These results suggested that α-Proteobacteria communities in subsaturated waters and phototrophs in supersaturated waters may play a role in gypsum precipitation.Depto. de Mineralogía y PetrologíaFac. de Ciencias GeológicasTRUEProyecto Donaciones Minera Escondida Ltda.Beca Doctorado-ANIDpu

Surface Morphologies in a Mars-Analog Ca-Sulfate Salar, High Andes, Northern Chile

Salar de Pajonales, a Ca-sulfate salt flat in the Chilean High Andes, showcases the type of polyextreme environment recognized as one of the best terrestrial analogs for early Mars because of its aridity, high solar irradiance, salinity, and oxidation. The surface of the salar represents a natural climate-transition experiment where contemporary lagoons transition into infrequently inundated areas, salt crusts, and lastly dry exposed paleoterraces. These surface features represent different evolutionary stages in the transition from previously wetter climatic conditions to much drier conditions today. These same stages closely mirror the climate transition on Mars from a wetter early Noachian to the Noachian/Hesperian. Salar de Pajonales thus provides a unique window into what the last near-surface oases for microbial life on Mars could have been like in hypersaline environments as the climate changed and water disappeared from the surface. Here we open that climatological window by evaluating the narrative recorded in the salar surface morphology and microenvironments and extrapolating to similar paleosettings on Mars. Our observations suggest a strong inter-dependence between small and large scale features that we interpret to be controlled by extrabasinal changes in environmental conditions, such as precipitation-evaporation-balance changes and thermal cycles, and most importantly, by internal processes, such as hydration/dehydration, efflorescence/deliquescence, and recrystallization brought about by physical and chemical processes related to changes in groundwater recharge and volcanic processes. Surface structures and textures record a history of hydrological changes that impact the mineralogy and volume of Ca-sulfate layers comprising most of the salar surface. Similar surface features on Mars, interpreted as products of freeze-thaw cycles, could, instead, be products of water-driven, volume changes in salt deposits. On Mars, surface manifestations of such salt-related processes would point to potential water sources. Because hygroscopic salts have been invoked as sources of localized, transient water sufficient to support terrestrial life, such structures might be good targets for biosignature exploration on Mars