The Formation and Preservation of Synechococcus elongatus Cell Molds in Simulated Silica Sinter: Implications for the Identification of Microfossils

Abstract

Siliceous sinters that precipitate around modern hot spring systems are able to fossilize the indigenous microbial communities, forming molds that accurately outline the shape of the microorganisms. Over time, the biomass decays, and only silica molds or their infill may remain as evidence of the former living cells. However, little is known regarding the fidelity of such silica molds in terms of size and morphology, and the preservation of critical parameters for the identification of ancient silicified microorganisms by silica molds remains untested. Here we report experiments examining the formation of microbial molds of the cyanobacterium Synechococcus elongatus in silica gel. We demonstrate that post-depositional processes, primarily desiccation, are crucial for obtaining accurate and robust molds, and that initial desiccation acts to strengthen cell molds against further alteration. However, all silica gel treatments systematically created preservational biases (changes in size, additional structures) that may be misleading and may complicate the identification of fossil microorganisms.

Keywords:

• early diagenesis
• microfossils
• silica gel
• siliceous sinter
• silicification
• Synechococcus elongatus
• taphonomy

Acknowledgments

The authors warmly thank Dr George W. Owttrim and Dana Chamot (Department of Biological Sciences, University of Alberta) for providing the cyanobacteria fresh cultures, and De-Ann Rollings and George Braybrook (Scanning Electron Microscope Laboratory, Department of Earth and Atmospheric Sciences, University of Alberta) for their help with the SEM. F.O. was funded by the European Science Foundation ArchEnviron Exchange Grant #2723, and S.V.L. and K.O.K by the Natural Sciences and Engineering Research Council of Canada.