Our understanding of early eukaryotic diversity relies heavily on the record of organic-walled microfossils— the organic (non-mineralized) remains of microorganisms. However, changes in the conditions that preserve organic remains as fossils can greatly bias fossil diversity trends. It has been suggested that low concentrations of total organic carbon (TOC) and high concentrations of certain clay minerals (e.g., berthierineand kaolinite) are primary controls on the preservation of organic-walled microfossils. This idea stems from evidence that clay minerals can adsorb and deactivate degradative enzymes and that high levels of TOC interfere with this reaction. Here wewill explore the relationships between fossil preservation, TOC content, and clay mineralogy from shales that span late Paleoproterozoic to late Neoproterozoic time. We find that TOC concentration is the strongest predictor of microfossil preservation. Although the total clay mineral content also correlates with microfossil preservation, particular clay minerals (e.g., berthierine) only weakly correlate with preservationalquality. These results suggest that the preservation of most organic-walled microfossils does not depend on a specific clay mineral assemblage, possibly reflecting a more robust organic composition. In addition, higher total clay content might serve to curb microbial activity by isolating organic matter from degradative enzymes and/or limiting the supply of oxidants.

Bio:

Tina is a paleontologist studying the early fossil record of eukaryotes. Her interests broadly include the ecology and evolution of eukaryotes through the Proterozoic, as well as the environmental conditions that lead to their fossilization. As a postdoc in the Historical Geobiology Lab, she is investigating the effect of ocean redox chemistry on the quality of the Proterozoic fossil record and how changes in ocean redox might bias eukaryotic diversity trends.

For the Zoom information, please get in touch with Jannis Simões-Seymens 24h before the event starts (jseymens@stanford.edu)