Abstract

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.