¹Jasmijsn Van der Graaf, ²John F. Mustard, ¹Annemiek C. Waajen, ³Frank J.A. Van Ruitenbeek, ^4,5Christopher S. Romanek, ^1,4Mónica Sánchez-Román
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117262]
¹Geobiology Lab, Earth Sciences Department, Vrije Universiteit Amsterdam, De Boelelaan 1100, 1081HV Amsterdam, the Netherlands
²Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA
³Department of Applied Earth Sciences, Faculty of Geo-Information Science and Earth Observation, University of Twente, Drienerlolaan 5, 7500 AE Enschede, the Netherlands
⁴NASA Astrobiology Institute, USA
⁵Department of Earth and Environmental Sciences, Furman University, Greenville, SC, USA
Copyright Elsevier

Microbial activity plays a crucial role in the precipitation of carbonate minerals, mediated by bacterial cells and their secreted extracellular polymeric substances (EPS). Traditional detection of such biosignatures often requires invasive chemical treatments. This study explores the potential of Fourier Transform Infrared (FTIR) spectroscopy as a non-destructive tool to identify compositional features and microbial imprints in mixed-cation carbonates, providing a new pathway for remote sensing applications and in situ mineralogical studies. Carbonate samples from natural settings and laboratory experiments, under both biotic and abiotic conditions were analyzed to reveal their distinct spectral characteristics. The minerals studied include dolomite, siderite, ankerite, (hydro)magnesite, and various carbonate hydroxides, with varying amounts of the cations Ca2+, Mg2+ and Fe2+.
Distinct FTIR spectral characteristics were observed: dolomites, in particular, exhibited consistent clustering in overtone band positions around 2300 nm and 2500 nm. While this clustering was less apparent in other carbonate types, Fe2+ content could be reliably traced through a unique near-infrared absorption feature, whose intensity correlated with Fe2+ abundance following a square root function.
Despite the overlap of biosignature and mineral spectral features, specific markers emerged in biogenic samples. These included weak absorptions near 3310 nm (indicative of alkene bonds) and enhanced OH− bands around 1400 nm and 2760 nm, possibly related to phenols, alcohols, or structural water-components often associated with microbial EPS. FTIR spectroscopy is sensitive to trace amounts of water and organic compounds, making it a promising tool for evaluating precipitation conditions and the diagenetic history of mixed-cation carbonates.

¹Sophie Benaroya, ¹Christopher D.K. Herd
Earth and Planetary Science Letters 691, 120176 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120176]
¹Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada
Copyright Elsevier

Constraining the oxygen fugacity (fO2) of the mantle of Mars is critical for understanding planetary differentiation processes and magmatic evolution. The degree to which the shergottite martian meteorites faithfully record the redox states of their mantle sources remains obscured by several factors. One of these factors is the various methods used to estimate fO2: Fe-based oxybarometers require multiple minerals to be found in chemical equilibrium, which can be challenging to obtain, while previous V-based values rely on estimated parental melt compositions. Here, we present new, mineral-specific V/Sc oxybarometers calibrated for olivine and pyroxene in shergottites using experimentally determined partition coefficients. This method obviates the need for parental melt V concentrations and allows for fO2 determination from single mineral phases, bypassing the equilibrium constraints that limit Fe-oxybarometry. We applied these calibrations to a petrologically diverse suite of geochemically depleted, intermediate, and enriched shergottites. Our results reveal that: (1) basaltic shergottites, previously estimated at fO2 ∼FMQ-1, record a significantly lower initial/magmatic fO2 of ∼FMQ-1.7; (2) the magmatic fO2 of shergottites is correlated with their geochemical enrichment; and (3) all shergottites show oxidation of a magnitude of >0.5 log units with progressive crystallization. The V/Sc oxybarometers provide a robust tool for estimating the magmatic fO2 of shergottites and tracking their redox changes throughout their petrogenetic histories.