Department of Geological Engineering, Geomicrobiology and Biogeochemistry Laboratory, Istanbul Technical University, Istanbul, Turkey.
Laboratory of Microbiology, Wageningen University and Research, Wageningen, The Netherlands.
Geobiology. 2024 Sep-Oct;22(5):e12619. doi: 10.1111/gbi.12619.
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)SiO(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.
萨尔达湖是火星杰泽罗陨石坑古湖泊的陆相类比体，拥有活跃的、亚化石和化石水镁石微生物岩，使其成为研究微生物岩形成和后续过程的理想地点。然而，我们对这一记录的理解仍然受到以下因素的限制：对微生物岩的宏观和中观形态类型及其空间分布的了解不完整，以及对影响微生物岩形成的微生物和地球化学过程的了解不完整。在这项研究中，我们调查了萨尔达湖微生物岩的空间分布、形态类型、矿物学、地球化学和微生物多样性，并确定了该湖有六个主要微生物岩堆积区（区 I 到区 VI）。根据宏观和中观结构，新识别的微生物岩被分类。我们的研究表明，该湖含有层状叠层石、血栓石、层状血栓石、树枝状石和微生物诱导的沉积构造。在宏观尺度上，萨尔达湖微生物岩呈半球形、堆叠穹顶和侧向连接的柱状结构，而在中观尺度上，常见的有微柱、瘤块、中团块、纹层和葡萄状结构。不同微生物岩类型的宏观和中观分布与微生物群落组成和水深空间相关。深水区生长的微生物岩中蓝藻丰度较低（约 1%-4%），厚壁菌门丰度较高（28%-93%），呈陡凸状层理，产生指状微柱中观结构。相比之下，浅水区生长的微生物岩中厚壁菌门丰度较低（0%-5%），蓝藻丰度较高（11%-37%），保存完好的呈缓凸毫米级层理，产生菜花状中观结构。在深水区生长的微生物岩富硅藻层中发现了坡缕石((Mg, Al)SiO(OH))。无论微生物岩类型如何，水镁石和文石都存在于浅水区和深水区生长的微生物岩中富含胞外聚合物（EPS）的区域。总的来说，环境变化（如水深和可容空间）在宏观和中观尺度上对不同微生物岩形态的形成和空间分布起着重要作用。中观结构类型之间优势微生物相对丰度的差异表明，中观形态可能受到微生物多样性变化的影响。微生物岩形态的空间变化，以及丰富的埋藏生物量（如矿化丝）的存在，可能表明这些区域具有保存生物特征的高潜力。
