Lipid biomarker analyses of modern lacustrine microbialites of Laguna Negra, Catamarca Province, Argentina

BEELER, S.; GOMEZ, F.J.; BRADLEY, A.

Galveston, Texas

Congreso; Gordon Research Conference; 2016

Gordon Research Conference

Sedimentary structures formed as a result of microbial activity, termed microbialites, can provide insight into the interaction of geological and biological processes in both ancient and modern environments. Unfortunately, our ability to interpret the information preserved in these structures is clouded by a poor understanding the mechanisms responsible for their formation. Lipid biomarkers can provide insight into the organisms inhabiting microbialites, making them an intriguing tool for deciphering the biological contribution to microbialite formation. Lipid structuresprovide taxonomic information, while lipid isotopic compositions can provide information about carbon and energy metabolism. Moreover, the high recalcitrance of lipids in the environment enables their analysis in mineral structures, extant microbial mats, and fossil microbialites. To determine the relationship between biological activity and microbialite formation,a lipid biomarker study was executed on the microbialites and microbial mats found at Laguna Negra a high-alpine evaporative lake in northeastern Argentina. The carbonate structures observed at Laguna Negra exhibit a spectrum of macroscopic and microscopic morphologies each associated with visually distinct microbial mat communities. The morphological differences in these carbonate structure are hypothesized to represent differential impacts of biological activity on their formation. To elucidate these differences lipid biomarker profiles and compound specific isotope analyses were performed on carbonates representing endmember morphologies, as well as on their associated microbial mats. Fatty acid profiles of microbial mats and carbonates were similar between all types and dominated by even homologues of C14 to C24 straight chain fatty acids. Lesser abundances of unsaturated and branched C14, C16, and C18 fatty acids were also observed. The fatty acid profiles observed at Laguna Negra are consistent with those observed in other hypersaline environments indicating the potential for an environmental control on fatty acid abundances. The relative abundance of C27, C28, and C29 sterols differed between each of the carbonate endmembers and their associated microbial mats. These differences imply that changes in eukaryotic mat community structure may play a role in the morphological shifts observed at Laguna Negra. Ongoing work investigating additional biomarker classes will help to further reveal the relationship between microbial mat community function and carbonate form. These results will allow for better interpretation of microbialite structures in ancient and other modern environments.