CHARACTERIZATION OF THE ORGANIC CHEMISTRY WITHIN THE 1.0 GA SILICIFIED MICROBIAL MATS OF THE ANGMAAT FORMATION, BYLOT SUPERGROUP NORTHERN BAFFIN ISLAND

Peritidal early diagenetic chert deposits are common in Precambrian strata and contain exceptionally preserved microbial morphologies that have been used to identify Earth’s earliest ecosystems and provide information about the geochemistry of the ecosystem. Silica deposits have therefore been suggested as potential targets for the search for extraterrestrial microbial life. Here we investigate the extent to which exceptional morphological preservation is reflected in the preservation of molecular geochemistry of silicified microbial mats, which can provide information about both the environment of deposition and the microbial physiology and processes active at the time of silicification.

Chert within the ~1.0 Ga Angmaat Formation, Bylot Supergroup, record late Mesoproterozoic carbonate strata deposited within an intertidal to supratidal microbial flat. Microbial growth and decomposition within filamentous and coccoidal microbial mats are preserved by silica across a range of environments. Our original organic geochemical data showed the presence of various lipids, including n-alkanes, hopanes, and steranes, preserved in the chert of the Angmaat Formation that suggested thermally immature organic matter from a hypersaline environment, both of which are consistent with independent interpretations of the depositional environment. The similarity of lipid signatures amongst samples, however, convinced us that data was dominated by post-collection contamination.

Samples acquired during a 2017 field season were collected, curated, and prepared in accordance with strict contamination-control protocols. Bitumen I and bitumen II extractions from these samples revealed no indication of lipids at concentrations distinguishable from background. Our data suggest that lipids associated with silicified microorganisms may not be preserved during silicification despite exceptional microbial morphologic preservation. The lack of good lipid preservation may be a result of the silicification process itself. Silicification may have prompted the cyanobacterial trichomes to leave their sheaths and migrate to areas within the microbial mat that were not undergoing silicification. This process would have resulted in the preservation of the abandoned polysaccharide-rich, lipid-poor sheaths.