Insights into the sulfur cycle in the Southern Tethys upwelling belt across the Cretaceous-Paleogene boundary

Résumé fourni par la source

The Golan section of the southern Tethys upwelling belt is an organic and sulfur-rich section that records the K-Pg mass extinction interval. Geochemical and biomarker proxies indicate that the composition of the microbial and primary producer communities remained largely unchanged across the K-Pg boundary. This resilient behavior has been attributed to the long-term stratification and persistent euxinic conditions in the paleo-basin. Here, we investigate the impact of the K-Pg mass extinction event on sulfur cycling and organic matter (OM) preservation using the molecular and sulfur isotopic distribution of organic sulfur compounds (OSCs) and Fe speciation. Relationships among reactive Fe, S/Corg ratios, and sulfur isotopes of pyrite and organic sulfur indicate that excess sulfide preferentially reacted with OM, generating isotopically diverse OSCs. Redox proxies, combined with biomarkers for photic zone euxinia and hypersalinity, show that the basin remained strongly stratified and euxinic throughout the extinction interval. Most OSCs do not show significant variation in both concentration and δ 34 S values across the K-Pg boundary of the Golan section, consistent with the non‑sulfurized biomarkers, indicating a limited environmental perturbation. Nevertheless, OSCs show large isotopic variability (up to ~12‰) reflecting differences in depositional conditions and preservation pathways. Benzo- and di-benzothiophenes preserve early diagenetic δ 34 S signatures despite being affected by early thermal maturation. Furthermore, n -alkylthiolanes are 5–9‰ 34 S-enriched relative to bulk kerogen, indicating secondary and later sulfurization, whereas polycyclic terpenoid sulfides are comparatively 34 S-depleted and interpreted as early diagenetic products. These compounds also exhibit concentration and isotopic shifts (~6‰ 34 S-depletion) in the post-extinction interval, highlighting their sensitivity to paleoenvironmental perturbations. In summary, this study shows a stable sulfur cycle and OM preservation across the K-Pg interval of the Golan Section. This, in turn, supports the resilience of biogeochemical cycles in the Southern Tethys upwelling belt despite the K-Pg crisis.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.