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Molecular Fossils of the Neoproterozoic-Cambrian Interval: Lipid Biomarker Geochemistry and Ancient Microbial Ecosystems


Richard Schinteie, Jochen J. Brocks


Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia

Figure 1.

 

Numerous microorganisms survive and flourish in environments that are often considered "extreme" from an anthropogenic view point. Such environments include hydrothermal vents, hydrocarbon seeps, and acid hot springs. Hypersaline environments are another type of setting where microorganisms live under salinity regimes exceeding those of seawater. In order to understand the evolution of ecosystems from such settings, Neoproterozoic and Cambrian halite-bearing evaporites were investigated for their lipid biomarker content. This time frame encompasses tremendous environmental and biotic changes (e.g., major glaciations, oxygenation of the deep ocean, evolution and radiation of microorganisms, and the first appearance of animals). While previous work identified potential halophiles in the Cambrian and Precambrian, we aim to present a more detailed investigation of biotic evolution over a significant period of geologic time.

In order to assess changes in microbial ecosystems over geologic time, it is important to focus on a variety of different environmental settings. Dissimilar environments offer different ecological niches which organisms can exploit. Such niches may respond differently to environmental changes over time.

Thus far, the results look very promising and has let to the discovery of lipid biomarkers that are over 1 billion years old. I am also trying to investigate rock samples from that period that originated in shallow water, particularly hypersaline facies. So far, most investigations concentrated on deep water facies. I have collected rock samples from drill cores (Figure 1) held at Australian drill core repositories. These rocks are from shallow water facies and contain numerous evaporate (salt-bearing) sequences. 

A major theme in any chemical work dealing with ancient life is the interpretation of molecules as original contemporaneous components of a rock sample or as more recent additions in the form of contamination. Therefore, I investigated techniques aimed at removing potential contaminants from rock samples. Thus far, the techniques have worked very well and helped me determine which biomarkers were likely derived from the Precambrian-Cambrian interval and which samples are contaminants (e.g. from the use of drilling fluids, fingerprints etc).