Relative biotic versus abiotic contributions in rock varnish formation

Quantify the relative contributions of biotic processes (e.g., microbial Mn/Fe oxidation, EPS templating) and abiotic processes (e.g., dust leaching, photo-oxidation, silica gelation) to rock varnish formation across diverse environments, and determine how these contributions vary with climate and substrate.

Background

Multiple lines of evidence indicate both microbial activity and physico-chemical processes participate in varnish formation, but their relative importance appears to differ among sites and over time.

The review stresses that separating biotic from abiotic signals is essential for using varnish as a palaeoenvironmental archive and for astrobiological analog studies, yet current data do not resolve their relative roles.

References

However, the exact balance of biotic and abiotic contributions remains unclear, and variability in varnish composition across environments complicates universal application.

— Self-assembled versus biological pattern formation in geology (2601.00323 - Cartwright et al., 1 Jan 2026) in Subsubsection Desert or rock varnish