Growth and reworking of freshwater microbially-mediated carbonates in wind-stressed lake margins (Lago Sarmiento, Southern Patagonia) Paulo Quezada, Mauricio Calderón, Anelize Bahniuk, Carolina Henríquez, Tatiana Stepanenko, et al. Sedimentology, 2026 Understanding the biotic and abiotic influences on the deposition and diagenesis of recent microbial carbonates is crucial for addressing the environmental and ecological significance of ancient organosedimentary structures. This study investigates these factors and their expression in the microstructure of Holocene tufa thrombolites from a wind‐stressed freshwater lake (Lago Sarmiento, Chile) through 16S rRNA sequencing, petrology of modern and fossil deposits, and stable isotope geochemistry of water and carbonates. Carbonate precipitation in the littoral zone is linked to Rivulariaceae‐rich mats, whose early induration involves extracellular polymeric substances‐mediated nucleation of nanoparticles precursors to aragonite and Mg‐calcite. Only remnants of these early products are preserved in fossil deposits due to diagenetic overprinting promoted by environmental factors. A syn‐depositional constructive stage—interpreted as key for the stabilisation and growth of meter‐sized build‐ups—involves aragonite inversion to Mg‐calcite, crystal size coarsening, and Mg‐calcite cementation. A subsequent destructive stage—developed under increasing wave‐influence as the lake‐level lowered—led to spar substitution to secondary fine‐grained textures (including clotted micrite), the dissolution and/or erosion of the framework, and internal sedimentation within primary and secondary pores (primarily terrigenous grains, intraclasts and peloids), partially obliterating the filamentous microfabrics. The calcified rivulariaceans and stable isotopes suggest tufa deposition under oligotrophic and relatively cold conditions (≤12°C) throughout Holocene cold/wet to warm/dry climate transitions. The resiliency of the lacustrine system likely contributes to sustaining a low‐competition and high‐calcification setting at millennial timescales, allowing the extensive accumulation of microbially mediated freshwater carbonates—the largest in the extratropical Southern Hemisphere. The record of Lago Sarmiento provides valuable insights into early diagenetic reworking of primary microbial textures, with implications for the identification of high‐energy lacustrine systems, a setting that might be overlooked in the geologic record.
Microbial and Geochemical Diversity of Laguna Timone, an Extreme Hypersaline Crater Lake in Patagonia (52° S) Carolina Henríquez, José M. Pérez-Donoso, Nicolás Bruna, Mauricio Calderón, Leonardo Fadel Cury, et al. Microorganisms, 2025 Extreme environments, such as hypersaline habitats, hot springs, deep-sea hydrothermal vents, glaciers, and permafrost, provide diverse ecological niches for studying microbial evolution. However, knowledge of microbial communities in extreme environments at high southern latitudes remains limited, aside from Antarctica. Laguna Timone is a hypersaline crater lake located in a Pleistocene maar of the Pali Aike Volcanic Field, southern Patagonia; the lake was formed during basaltic eruptions in a periglacial setting. Here, we report the first integrative characterization of microbial communities from biofilms and microbial mats in this lake using high-throughput 16S rRNA and ITS gene sequencing, along with mineralogical and hydrochemical analyses of water, sediments, and carbonates. Bacterial communities were dominated by the genera Enterobacterales ASV1, Pseudomonas, Oscillatoria, Nodularia, and Belliella, with site-specific assemblages. Fungal communities included Laetinaevia, Ilyonectria, Thelebolus, Plectosphaerella, and Acrostalagmus, each showing distinct distribution patterns. These baseline data contribute to understanding microbial dynamics in hypersaline maar environments and support future investigations. This integrative approach highlights key microbe–mineral relationships and underscores the potential of Laguna Timone as a natural laboratory for exploring biosignature formation and microbial adaptation in chemically extreme environments, both on early Earth and potentially beyond.
Facies stacking and lateral variability of travertines from the Quaternary Vega Botijuela, Salar de Antofalla Basin, Argentina Filipe Giovanini Varejão, Guido E. Alonso, Gustavo B. Athayde, Anelize M. Bahniuk Rumbelsperger, Leonardo F. Cury Sedimentology, 2025 Travertines are non‐marine sedimentary rocks, which are typically hydrothermal in origin and characterized by high depositional rates. Despite great advances in the understanding of the geomorphological, petrological and geochemical aspects of travertines, the recognition of these rocks in the geological record is not an easy task due to the multiple parameters involved in their formation, the variable potential of preservation and the lack of a facies model with application to the geological record. This study applies classic sedimentological and stratigraphic methods, looking for vertical and lateral facies distribution at the Vega Botijuela, Salar de Antofalla, Argentina. Travertines are geomorphologically compartmentalized into proximal, intermediate and distal zones, with spring waters in the proximal zone and mixed carbonate–siliciclastic sedimentation observed towards the distal zone. The presented data corroborate previous assumptions that these systems are dominantly progradational to aggradational. Vertical facies stacking is typically coarsening‐upward, with a dominance of carbonate mudstone interbedded with grainstone, rudstone and boundstone. Distinct facies associations are observed in the Vega Botijuela and are defined here as dome, fissure ridge, gently and steeply inclined slopes, stepped slope and terminal, according to morphological criteria applied elsewhere. Biotic and abiotic travertine precipitation occurs along the geomorphological zones and is related directly to different slope gradients. Throughout the depositional history of travertines, the carbonate facies occur interbedded with siliciclastic deposits from the Salar de Antofalla, generating local facies heterogeneity in the marginal areas of the basin. This is one of the first attempts to establish vertical stacking patterns to characterize facies associations, adding important insights towards the building of a travertine facies model. In this context, these findings can be applied to recognize travertines of the geological record developed in extensional sedimentary basin margins under arid climatic conditions.
