Microbial Mat Taphonomy: Modern Insights into One of Earth's Earliest Ecosystems

Morphological and geochemical signatures in fossilized microbial mats inform our understanding of early life. These reflect biological processes and environmental conditions at the time of formation, as well as degradation processes that overprint these signatures. Microbial mats from Little Ambergris Cay, Turks and Caicos Islands, provide a model system for examining how these processes influence geobiological signatures recorded in rocks. The top ~1-2cm of these mats host active communities of cyanobacteria overlying and admixed with diverse communities of bacterial and eukaryotic taxa. Layers below, laid down by previous generations of mat communities, can be used to explore how the record of microbial diversity is filtered as it enters the geological record. Morphological and geochemical data indicate that large filamentous cyanobacteria are the key mat-builders and their biosignatures have the greatest preservation potential. Biosignatures of coccoidal cells, thin filamentous bacteria, diatoms, and arthropods are also present in the layers that may enter the geological record, although at lower abundances than in the surface layers. Despite differences in environmental conditions inferred from carbon and sulfur isotope patterns, many biosignatures in the deep layers are similar to those in Proterozoic microbialites. Thus, biosignatures in fossil microbial mats record information about mat surface communities with biases towards cyanobacteria and eukaryotic taxa that produce diagnostic biosignatures resistant to decay.

Speaker: Maya Gomes, Washington University, St. Louis