Microbial mats are taxonomically and metabolically diverse microbial ecosystems, with a characteristic layering that reflects vertical gradients in light and oxygen availability. Silicified microbial mats in Proterozoic carbonate successions are generally interpreted in terms of the surficial, mat building community. However, information about biodiversity in the once-surface-layer can be lost through decay as the mats accrete. To better understand how information about surface microbial communities is impacted by processes of decay within the mat, we studied microbial mats from Little Ambergris Cay, Turks and Caicos Islands. We used molecular techniques, microscopy and geochemistry to investigate microbial mat taphonomy – how processes of degradation affect biological signatures in sedimentary rocks, including fossils, molecular fossils and isotopic records. The top < 1 cm of these mats host cyanobacteria-rich communities overlying and admixed with diverse bacterial and eukaryotic taxa. Lower layers contain abundant, often empty, sheaths of large filamentous cyanobacteria, preserving their record as key mat-builders. Morphological remains and free lipid biomarkers of several bacterial groups, as well as diatoms, arthropods, and other eukaryotes also persist in lower mat layers, although at lower abundances than in surface layers. Carbon isotope signatures of organic matter were consistent with the majority of the biomass being sourced from CO₂-limited cyanobacteria. Porewater sulfide sulfur isotope values were lower than seawater sulfate sulfur isotope values by ∼45–50‰, consistent with microbial sulfate reduction under sulfate-replete conditions. Our findings provide insight into how processes of degradation and decay bias biosignatures in the geological record of microbial mats, especially mats that formed widely during the Proterozoic (2,500–541 million years ago) Eon. Cyanobacteria were the key mat-builders, their robust and cohesive fabric retained at depth. Additionally, eukaryotic remains and eukaryotic biosignatures were preserved at depth, which suggests that microbial mats are not inherently biased against eukaryote preservation, either today or in the past.

微生物垫是生物分类学和代谢多样性的微生物生态系统，其特征层反映了光和氧气的垂直梯度。碳酸盐元古代碳酸盐岩演替过程中的硅化微生物垫通常根据表面垫构建社区来解释。但是，随着垫层的增加，曾经存在于表层的生物多样性信息可能会因腐烂而丢失。为了更好地了解垫子内的腐烂过程如何影响表面微生物群落的信息，我们研究了来自小龙涎香礁，特克斯和凯科斯群岛的微生物垫。我们使用分子技术，显微镜和地球化学来研究微生物垫的分类学-降解过程如何影响沉积岩石（包括化石）中的生物特征，分子化石和同位素记录。这些垫子的顶部<1 cm处覆盖着丰富的蓝细菌群落，并与各种细菌和真核生物类混在一起。下层含有大量的，通常是空的大型丝状蓝细菌的鞘，保留了它们作为重要垫材制造者的记录。几个细菌群以及硅藻，节肢动物和其他真核生物的形态残留物和游离脂质生物标记物也保留在较低的垫层中，尽管其丰度低于表面层。有机物的碳同位素特征与大部分源自一氧化碳的生物质一致 大型丝状蓝细菌的鞘，保留了其作为重要垫材制造者的记录。几个细菌群以及硅藻，节肢动物和其他真核生物的形态残留物和游离脂质生物标记物也保留在较低的垫层中，尽管其丰度低于表面层。有机物的碳同位素特征与大部分源自一氧化碳的生物质一致 大型丝状蓝细菌的鞘，保留了其作为重要垫材制造者的记录。几个细菌群以及硅藻，节肢动物和其他真核生物的形态残留物和游离脂质生物标记物也保留在较低的垫层中，尽管其丰度低于表面层。有机物的碳同位素特征与大部分源自一氧化碳的生物质一致_2-有限的蓝细菌。孔隙水中的硫化物硫同位素值比海水中的硫酸盐硫同位素值低约45-50‰，这与在硫酸盐充足的条件下微生物硫酸盐的还原相一致。我们的发现提供了关于微生物垫的地质记录中降解和衰变过程如何偏向生物特征的见解，特别是在元古代（2500-5.41亿年前）Eon时期广泛形成的垫。蓝细菌是关键的垫材制造商，其坚固而有凝聚力的织物保留在深处。此外，真核残留物和真核生物特征被深层保存，这表明无论今天还是过去，微生物垫都不固有地偏向于真核生物的保存。