¹Robin L. Haller,¹Martin R. Lee,²Mark E. Hodson
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70145]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
²Department of Environment and Geography, University of York, York, UK
Published by arrangement with John Wiley & Sons

Terrestrial weathering alters the chemical and isotopic composition, and mineralogy, of meteorites; its effects on ordinary chondrites are well-studied, but relatively little is known about the susceptibility of carbonaceous chondrites. We combined laboratory experiments, whereby Chwichiya 002 (C3-ung find), Murchison (CM2 fall) and Kolang (CM1/2 fall) were exposed to artificial rainwater for 30–180 days, with kinetic models to examine the effects of different weathering timespans and environments on mineralogy and petrologic (sub)type. Leachates derived from the Murchison and Kolang experiments were rich in S, Ca, Na, Cl, K, and Mg with less abundant Si and Fe. These results suggest that calcite and pyrrhotite, together with unknown Na-K-Cl bearing minerals, are particularly susceptible to terrestrial alteration. Chwichiya 002 was less reactive than anticipated, possibly due to earlier hot desert weathering. Models predict that primitive chondrites with amorphous material, including Chwichiya 002, oxidize within days when exposed to water, particularly in warm environments (e.g., hot deserts). Terrestrial weathering is expected to rapidly lower the petrologic (sub)type of CM3 chondrites, whereas CM2s react more slowly and their petrologic (sub)type does not change significantly.

^1,2,5Gabriel A. Pinto, ¹Vinciane Debaille, ²Jolantha Eschrig, ³Alexandre Corgne, ⁴Kevin Soto, ⁵Thierry Leduc, ⁵Sophie Decree, ²Steven Goderis
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117102]
¹Laboratoire G-Time & Brussels Laboratory of the Universe (BLU), Université Libre de Bruxelles, 1050 Brussels, Belgium
²Archaeology, Environmental Changes, and Geo-Chemistry, Vrije Universiteit Brussel, 1050 Brussels, Belgium
³Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile
⁴Departamento de Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile
⁵Institute of Natural Sciences, Geological Survey of Belgium, 1000 Brussels, Belgium
Copyright Elsevier

Evaporites are frequently reported in carbonaceous chondrites from hot and cold deserts, yet their origin remains debated between formation on the parent body or by post-fall terrestrial alteration. Here, we present a systematic characterization of Ca sulfate and Ca carbonate assemblages in four CO carbonaceous chondrites from different dense collection areas of the Atacama Desert (Los Vientos 123, El Médano 464, Calama 031, Paposo 088). We combine backscattered electron imaging, EDS, X-ray compositional mapping, Raman spectroscopy, and modal point counting to assess the distribution, mineralogy, and formation context of evaporites. Evaporites occur mainly as pore- and vein-filling phases and as replacements of Fe sulfides. Los Vientos 123 and El Médano 464 contain high abundances of Ca sulfates (~2.5 ± 0.35 vol%), Calama 031 is dominated by Ca carbonate veins (1.4 ± 0.26 vol%) with minor Ca sulfate, and Paposo 088 shows only low Ca sulfates contents (0.47 ± 0.15 vol%). These phases are systematically associated with Fe oxyhydroxides, jarosite-like phases, and strongly altered sulfides. The sulfate- and carbonate-rich assemblages in CO chondrites correlate with local soil geochemistry and microclimates. Limestone bedrock and more rain-influenced inland set different evaporite assemblages compared to coastal areas characterized by marine aerosols and salt-rich soils. Raman spectra indicate that the dominant Ca sulfate polymorph is anhydrite, lacking OH-stretching bands, consistent with precipitation from low-water activity, chloride-nitrate-rich brines and limited subsequent hydration. Disordered carbonaceous matter locally sheltered within sulfate-rich areas suggests that secondary evaporites can trap and preserve organic material, even if non-biological. Our results thus support (i) a terrestrial origin for Ca sulfates and Ca carbonates in Atacama CO chondrites; (ii) the stability of anhydrite as an indicator of extremely low water activity; and (iii) process analogues for evaporite formation in Martian settings, where anhydrite regions may be key targets to reconstruct aqueous conditions and assess organic preservation on Mars.