Abstract EANA2026-238

Exploration of Jezero Crater by the Mars 2020 Perseverance mission  has identified Mg-carbonates, Fe/Mg phyllosilicates[1], hydrated silica[2], and organic-carbon-bearing mudstones[3], an assemblage consistent with aqueous alteration in fluviolacustrine environments and commonly associated with Precambrian carbonate systems with high preservation potential for microbial mat fragments, filamentous microfossils, and organic-walled microfossils[4]. Cryogenian (~720–635 Ma) stromatolites formed during intervals of dynamic environmental change, including anoxic to moderate atmospheric oxygen levels (~1–50% present atmospheric level)[5], widespread ocean redox stratification, and global-scale glaciations during (Snowball Earth). These deposits preserve records of microbial ecosystem resilience during a critical transition from largely anoxic Proterozoic oceans toward more oxygenated conditions that preceded the diversification of complex life. 

This study examines stromatolitic carbonates of the Tambien Group, northern Ethiopia, deposited during the ~700–600 Ma interval of Rodinia breakup, extreme climate variability, and biogeochemical perturbation. We characterize biosignature preservation using correlative micro- to nanoscale analyses, including optical microscopy and X-ray μCT for fabric context and 3D lamina-scale textural mapping, Raman spectroscopy for kerogen maturity and carbonaceous material spatial distribution, SEM-EDS for trace and major element mapping, NanoSIMS for in situ stable isotope analysis (δ¹³C, δ¹⁵N, δ³⁴S), STEM/EELS for ultrastructural characterization of organic-mineral interfaces, PIXE for metallome-affiliated trace element mapping, and solid-state NMR for lipid biomarker preservation assessment in carbonate-hosted kerogen. 

Raman spectroscopy of carbonaceous material through individual stromatolite columns shows systematic variation in D-band and G-band parameters with position across individual stromatolite columns and between macro-structure types. These variations track differences in structural disorder of the carbonaceous material, which we interpret in terms of local thermal history, mineral matrix effects, and/or primary heterogeneity in organic matter type or degradation state across the stromatolite fabric.

PIXE and SEM-EDS mapping additionally reveal chemical associations indicative of reducing conditions within the local environment, with evidence supporting the most significant kerogen preservation associated with microbially induced laminae showing chemical associations consistent with arsenic cycling in reducing microenvironments. Furthermore, the presence of vanadium throughout kerogenous laminae implies the alteration of precursor biological molecules, such as chlorophyll and heme porphyrin compounds from living organisms [6]. Ongoing STEM/EELS, NMR, and NanoSIMS analyses aim to further test these interpretations, targeting ultrastructural relationships between organic matter and mineral phases at the organic-mineral interface, in situ isotopic signatures (δ¹³C, δ¹⁵N, δ³⁴S) of metabolic pathways associated with the reducing microenvironments identified here, and the extent of lipid biomarker preservation within kerogen across the same lamina-scale contexts.

This project aims to address microbial survival and metabolic strategies during Cryogenian glaciations, alongside the environmental influence on biosignature preservation. Our work aims to refine biosignature criteria in carbonates and inform interpretation strategies for carbonate-bearing samples targeted in future Mars Sample Return investigations.

References

[1] Tarnas, J. D., et al. (2021). Characteristics, origins, and biosignature preservation potential of carbonate-bearing rocks within and outside of Jezero Crater. Journal of Geophysical Research: Planets, 126. https://doi.org/10.1029/2021JE006898

[2] Beck, P., et al. (2025). From hydrated silica to quartz: Potential hydrothermal precipitates found in Jezero Crater, Mars. Earth and Planetary Science Letters, 656. https://doi.org/10.1016/j.epsl.2025.119256

[3] Hurowitz, J.A., et al. (2025). Redox-driven mineral and organic associations in Jezero Crater, Mars. Nature, 645, 332–340. https://doi.org/10.1038/s41586-025-09413-0

[4] Woltz, C. R., et al. (2023). The role of clay minerals in the preservation of Precambrian organic-walled microfossils. Geobiology, 21(6), 708–724. https://doi.org/10.1111/gbi.12573

[5] Krause, A. J., et al. (2022). Extreme variability in atmospheric oxygen levels in the late Precambrian. Science Advances, 8(41). https://doi.org/10.1126/sciadv.abm8191

[6] Marshall, C. P., et al. (2017). Imaging of vanadium in microfossils: A new potential biosignature. Astrobiology, 17(11), 1069–1076. https://doi.org/10.1089/ast.2017.1709