Coupled authigenic Mg silicate and carbonate precipitation in saline lakes of the Salar de Atacama, Northern Chile

Abstract The interplay between microbial activity and mineral precipitation in extreme environments plays a critical role in shaping sedimentary textures and influencing biosignature preservation. This study explores coupled Mg silicate and carbonate precipitation in the marginal lakes of the Salar de Atacama, Northern Chile, expanding previous findings from the Salar de Llamara. Using field samples from the Aguas de Quelana and Soncor sectors, sedimentary deposits classified as sediments, unlithified microbial mats and lithified microbial buildups are each characterised by distinct microbial architectures and mineralisation processes. Detailed analyses conducted via scanning electron microscopy, energy dispersive spectroscopy (EDS) and X‐ray diffraction identified minerals and mineral associations and revealed pathways of coupled Mg silicate–carbonate precipitation. Results indicate that organic matter production is followed by precipitation of amorphous to nanocrystalline Mg silicate. Aragonite then templates on and replaces Mg silicate and infills voids. Dense microbial colonies within high‐viscosity extracellular polymeric substances (EPS) promote precipitation of welded Mg silicate (W‐MS), conferring structural stability, while loosely organised EPS networks result in porous deposits of granular sediments. W‐MS serves as a scaffolding that enhances preservation of morphological biosignatures. Overall, sedimentary product diversity reflects variations in microbial density and EPS organisation, suggesting that variations in initial microbial colony distribution and EPS determine the eventual sedimentary product. Our results also highlight the role of Mg silicate–carbonate precipitation in the formation of grainy sediments, expanding prior work on Mg silicate–carbonate coupling forming microbialites and unlithified microbial mats in the Atacama Desert. The data set presented here provides a robust analogue for interpreting ancient sedimentary systems and emphasises the significance of microbe–mineral interactions forming Mg silicate–carbonate deposits in extreme environments.