Pores in silica-rich sedimentary rocks (chert) preserve organic matter: environmental perspectives.
What is it about?
Silica-rich sedimentary rocks (chert) record past life on Earth because they host microfossils and organic molecules (OMs). A long-standing knowledge gap was how cherts preserve these OMs. This means that the spatial location of these OMs was an issue related to their preservation. Exploiting X-ray scattering interactions with rocks, our study shed light on this issue showing that differently-aged cherts are composed of nanometric quartz crystals (at least 100 nm long). Most impressively, nanometric spaces (pores) occur between those tiny crystals. We contribute by showing that these nanometric pores are filled by OMs. To this aim, the X-ray scattering properties of samples before and after their combustion permitted us to quantify the volume and size of pores holding OMs. Spatial distribution and abundance of some chemical elements and measurement of OMs helped us to delineate a full sample characterization.
Why is it important?
We contributed to understanding how the size and shape of pores evolve over time in chert and how this correlated to organic matter preservation. This issue was scarcely addressed in previous literature about this type of rock, largely suggested as a record of life in past geological time.