^1,2Longye Du, ^1,3Xiaoxiao Yu, ⁴Yiliang Li, ¹Xiao Wu, ¹Lin Gong, ¹Gangjian Wei, ¹Qiang Wang, ^1,5Mang Lin
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.06.019]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²University of Chinese Academy of Sciences, Beijing 100049, China
³College of Earth Science and Engineering, Shandong University of Science and Technology, Qingdao 266590, China
⁴Department of Earth and Planetary Sciences, the University of Hong Kong, Hong Kong Special Administrative Region of China
⁵Center for Advanced Planetary Science (CAPS), Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Copyright Elsevier

A primary objective of Mars sample return missions is the detection and characterization of potential biosignatures. Sulfates, among the most abundant hydrated minerals on Mars, represent promising targets for such investigation. Terrestrial studies have shown that gypsum can preserve life-associated organic matter and that its δ34S signatures provide key evidence for microbial sulfate reduction as early as ∼ 3.5 billion years ago. This study analyzes quadruple sulfur (δ34S, Δ33S, Δ36S) and triple oxygen (δ18O, Δ́17O) isotopes in gypsum from three strong evaporation basins on the Qinghai-Tibet Plateau, where sulfate deposition is extensive but surface environments are only marginally habitable due to severe limitations in water, soil development, and nutrient availability. We focus on the Qaidam Basin as a Mars analog environment and place it in context through comparison with a higher-elevation region (Shuanghu) and a magmatic rock-dominated region (Yushu). Together with isotopic mixing models, an open-system steady-state sulfur cycle model, and triple-oxygen isotope oxidation pathway calculations, our quadruple sulfur and triple oxygen isotope measurements reveal that the studied gypsum deposits preserve distinct isotopic biosignatures. In particular, the isotopic compositions of the samples reflect microbial sulfur disproportionation and cryptic sulfur cycling, both of which extend beyond widespread microbial sulfate reduction, demonstrating how sulfur can be internally recycled and energetically utilized to sustain life in Mars-analog environments. This integrated isotopic approach significantly advances our capability to decipher sulfur cycling in extreme terrestrial environments, including Mars analog systems, and provides critical methodology for interpreting potential biosignatures in returned Martian samples.

^1,2Yankun Di, ¹Magdalena H. Huyskens, ²Qing-Zhu Yin, ^1,3Yuri Amelin
Geochimica et Cosmoschimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.06.017]
¹Research School of Earth Sciences, Australian National University, Acton, ACT 2601, Australia
²Department of Earth and Planetary Sciences, University of California Davis, Davis, CA 95616, USA
³State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
Copyright Elsevier

Compared to the Earth and inner Solar System planets, calcium–aluminium-rich inclusions (CAIs) possess nucleosynthetic Sr isotope anomalies manifested as elevated ⁸⁴Sr/⁸⁶Sr after internal normalisation using ⁸⁸Sr/⁸⁶Sr. These anomalies can be generated by heterogeneous incorporation of s-, r-, or p-process nucleosynthesis components. Accurately distinguishing between the enrichment or depletion in those components is critical for correctly understanding the timing of planetary volatile depletion, as they predict very different anomalies in ⁸⁷Sr/⁸⁶Sr and lead to disparate interpretations of ⁸⁷Rb–⁸⁷Sr chronology. Here, we constrain the origin of Sr isotope anomalies in the original Mason and Taylor (1982) set of Allende CAIs by examining their nucleosynthetic Sr and Nd isotope systems. Most CAIs analysed exhibit positive μ⁸⁴Sr and negative μ^145,148,150Nd anomalies (μ-values are defined as part-per-million deviations of isotopic ratios relative to terrestrial standards) in agreement with previous studies, but we also detected significant isotope heterogeneities among them, including discovery of CAIs with Sr and Nd isotope anomalies in directions opposite to the majority. The Nd isotope heterogeneity among CAIs is predominantly consistent with variations in the abundance of the s-process component, with a minor but clearly resolved p-process deficit on μ¹⁴²Nd_corr (μ¹⁴²Nd_corr is μ¹⁴²Nd corrected for ¹⁴⁶Sm decay). The less steep μ¹⁴²Nd_corr vs. μ¹⁴⁸Nd slope defined by the CAIs compared to that predicted by stellar models supports the recent suggestion that the accessible Earth has a small radiogenic excess in μ¹⁴²Nd relative to chondrites. Correlated Sr and Nd isotope anomalies in the CAIs suggest that (1) they formed from at least two isotopically distinct reservoirs, one with and the other without p-process Sr excesses relative to Earth, (2) the majority of CAIs formed in the p-process-Sr-enriched reservoir with additional s-process excesses, and (3) variations in r-process Sr and Nd are not observed among the CAIs. The s-process-induced ⁸⁷Sr/⁸⁶Sr anomalies in CAIs (relative to the inner Solar System) predicted based on Nd isotopes are below the typical measurement precision, negating the need for nucleosynthetic correction on CAIs’ ⁸⁷Sr/⁸⁶Sr in chronological interpretations