In order to find traces of ancient life on other rocky planets such as Mars, we must first understand how such traces may be preserved on Earth. Mid-Proterozoic and older siliciclastic sedimentary successions provide analogues for Noachian aged successions on Mars. In particular, fine-grained siliciclastic sedimentary rocks are a rich archive of early life on Earth. Phyllosilicate-rich rocks such as mudstones have proven to be effective in the preservation of organic matter and other biosignatures such as microbial structures. Recent work has suggested that phyllosilicate composition is less important than phyllosilicate abundance in determining the preservation quality of organic matter and organic fossils. However, it is currently unclear how phyllosilicate composition and abundance impact preservation on a basinal scale.

To investigate this question, we conducted an extensive investigation of organic matter, organic fossil, and microbial structure preservation quality, compared to the associated clay mineralogy in the exquisitely preserved ~1.4 Ga Greater McArthur Basin, northern Australia.

Notably, there are no clear links between organic matter, organic fossil, or microbial structure preservation quality, and the mineralogy of the associated phyllosilicates. In both settings, the preservation quality these traces is influenced by a complex web of pre- syn- and post depositional processes that interact through both time and space.

We combine these observations in a predictive tapho-facies model and use this to predict where the best-preserved examples of each feature should be within the basin.

We also map out the abundance, variety and distribution of microbial structures within these environments, and compare the results with the of distribution organic matter and organic fossil preservation quality.

Finally, new unweathered drill core material allows for a similar investigation in the 3.22 Ga Moodies Group, Barberton Greenstone Belt, South Africa. Here we report early results from these samples and compare the distribution and relative preservation quality of organic matter and microbial structures between the two units.