Attached, laminated, and lithified carbonate rocks that dominated shallow marine environments for the majority of Earth’s history preserve a record of the early Earth environment. While modern stromatolites accrete by sediment trapping and/or in-situ precipitation induced by microbial or algal activity, the processes governing the highly variable macroscopic morphology of stromatolites are not fully understood. Traditionally, the upward migration of microbes in conical stromatolites had been attributed to phototaxis; however, recent numerical modeling of modern conical microbialites indicate that conical morphology may instead be the result of nutrient limitation.
Modern-day conical stromatolites are rare and are constrained generally to sites with high temperatures and low current energy such as the hot springs of Yellowstone National Park (YNP). Past studies identify thin filamentous cyanobacteria as a key constituent in modern conical microbialites. Modern conical microbialites observed in the YNP hot springs appear morphologically similar to Archean and Proterozoic conical stromatolites and exhibit similar characteristics: slopes greater than 30 degrees, crestal thickening, and a consistent pattern of lattice spacing.
Past studies have focused on cyanobacterial diversity and activity, processes such as nutrient limitation and oxygen cycling . These studies explained lattice spacing and clumping behavior in modern-day conical microbialites and other stromatolites. The identification of nutrient limitation and oxidative stress indicates that the environment and biotic community jointly influence stromatolite morphology. Herein, we investigate the relationship between the general microbial community and distinct cone morphologies. Thus, the non-cyanobacterial community may also be a contributing factor in the formation and development of conical stromatolites.
To elucidate the role of filamentous cyanobacteria, we test whether the formation of conical structures is a consequence of an individual cyanobacterial strain, growth conditions, or a community. Our analysis focuses on the microbial interactions between the cyanobacterial and heterotrophic components within the cone-forming community under a variety of environmental conditions. We view this as a necessary, yet preliminary analysis in the deconvolution of environmental and biotic factors influencing conical stromatolite development.