Silicified biota in high-altitude, geothermally-influenced ignimbrites at El Tatio Geyser Field, Andean Cordillera (Chile)

At El Tatio hydrothermal field, located at more than 4,200 meters above mean sea level in the Andean Cordillera (Chile), massive and poorly coherent pyroclastic, rhyolitic ignimbrites make up most of the local substrate. In these rocks, light colored amorphous silica precipitated to form different types of deposits at geyser vents and, also, during the digression of braided streams departing from hot spring pools. The rapid sinter precipitation enabled the preservation of a variety of biotic and abiotic features along beds and margins of the streams in deeply weathered ignimbrites. Biofilms and filamentous communities provided a favorable substrate for silica precipitation and, together with the adhesive properties of diatom mucilage and other mineral precipitation, also played a primary role for holding together a porous and brittle ignimbrite rock. Optical and scanning electron microscopies associated with molecular methods based on the amplification and sequencing of small subunit (SSU) rRNA genes were carried out for a comparative evaluation of the microbial diversity associated with the silicified structures. The comparative study of the microbial diversity and the taphofacies preserved at El Tatio has allowed us to define some of the interactions between colloidal silica and microbes in a hydrothermally-influenced environment that, because of the high altitude, undergoes intense ultraviolet radiation and surface oxidation processes.