Morphological and Microbial Diversity of Hydromagnesite Microbialites in Lake Salda: A Mars Analog Alkaline Lake.

ABSTRACT

Lake Salda, a terrestrial analog for the paleolake in Jezero Crater on Mars, hosts active, subfossil, and fossil hydromagnesite microbialites, making it an ideal location to study microbialite formation and subsequent processes. Our understanding of this record is still limited by an incomplete knowledge of the macro- and mesoscale morphotypes of microbialites, along with their spatial distribution and correlation with microbial and geochemical processes that influence microbialite formation. In this study, we investigated the spatial distribution, morphotypes, mineralogy, geochemistry, and microbial diversity of the microbialites and identified six distinct zones (Zone I to Zone VI) with major microbialite build-ups in Lake Salda. Newly identified microbialites were classified based on the macro- and mesostructures. Our work shows that the lake contains stromatolites, thrombolites, stromatolitic thrombolites, dendrolites, and microbially induced sedimentary structures. At macroscale, Lake Salda microbialites exhibit hemispheres, stacked domes, and laterally linked columnar structures while minicolumns, knobs, mesoclots, laminae, and botryoidal structures are common at mesoscale. The macro- and mesoscale distribution of different microbialite types spatially correlates with microbial community composition and water depth. Deep-growing microbialites with a low abundance of Cyanobacteria (∼1%-4%) and high abundance of Firmicutes (28%-93%) exhibit steeply convex lamination, producing finger-like minicolumnar mesostructures. In contrast, shallow-growing microbialites with a low abundance of Firmicutes (0%-5%) and high abundance of Cyanobacteria (11%-37%) have well-preserved gently convex millimeter-scale lamination, resulting in cauliflower mesostructures. Palygorskite ((Mg, Al)2Si4O10(OH)) is identified in the diatom-rich microbial layer of the deep-growing microbialites. Regardless of the microbialite types, hydromagnesite and aragonite are present in the extracellular polymeric substance (EPS)-rich zone of the shallow and deep-growing microbialites. Overall, environmental changes (e.g., water depth and, accommodation space) play a major role in the formation and spatial distribution of different microbialite morphologies at the macro- and mesoscale. Differences in the relative abundance of dominant microorganisms between mesostructured types suggest that mesomorphology may be influenced by changes in microbial diversity. Spatial variations in the microbialite morphotypes, along with the abundant presence of entombed biomass (e.g., mineralized filaments), may indicate areas that have a high potential for the preservation of biosignatures.