AUTHOR=Fiorelli Lucas E. , Wunderlin Cecilia A. , Torréns Javier , Amelotti Ivana , Rothen Carolina , Sano Mathías Vazquez , Perez Loinaze Valeria S. , Vera Ezequiel I. , Cafieri Joaquín , Hechenleitner E. Martín , Grellet-Tinner Gerald 
  
TITLE=The discovery and description of an extremophile microcosmos in a Cretaceous paleogeothermal field
  
JOURNAL=Frontiers in Ecology and Evolution
  
VOLUME=Volume 13 - 2025
  
YEAR=2026
  
URL=https://www.frontiersin.org/journals/ecology-and-evolution/articles/10.3389/fevo.2025.1678418
  
DOI=10.3389/fevo.2025.1678418
  
ISSN=2296-701X
  
ABSTRACT=We report a new Fossil-Lagerstätte at the Cretaceous hydrothermal field of Sanagasta, La Rioja, northwestern Argentina, which opens a window into the paleobiology of an exceptionally preserved fossil ecosystem. Active geothermal systems harbor a diverse microbial life that thrive in high temperature, unique mineral composition and fluctuating pH. These environments are dominated by a meso- and hyperthermophilic community, including bacteria and archaea, that proliferate around the hot springs and geysers. In these environments, fossilization occurred rapidly by abiotic factors and through biomineralization—chiefly biosilicification. This process is mediated by thermophilic microorganisms, mainly cyanobacteria, allowing for the exceptional preservation of the biota. Here, we describe an ~80 million-year-old fossil extremophile biocoenosis encrusted within microbialites from the Sanagasta paleohydrothermal field. The core of the microbialites was explored using petrography, Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS) analyses in SEM. These microbialites exhibit remarkable three-dimensional preservation of microorganisms through extensive biosilicification, directly mediated by the extremophile communities. The taxonomic range of the sinterized assemblage encompasses the three domains: a noteworthy array of thermophilic ‘prokaryotes’ (chiefly bacteria and archaea), along with a rich diversity of eukaryotic ‘protists’ microorganisms (i.e., amoebozoans, myxomicetes, red algae, diatoms, and alveolates), green algae, plant remains, fungi and a variety of arthropod remains, all preserved in notable microanatomical details. The Sanagasta GeoPark contains one of the most diverse and exquisitely preserved records of microfossils known to date, illuminating a complex inland ecosystem within the first documented Cretaceous terrestrial hydrothermal environment.